Features • High Performance, Low Power AVR® 8-Bit Microcontroller (cid:129) Advanced RISC Architecture – 123 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General Purpose Working Registers – Fully Static Operation (cid:129) High Endurance Non-volatile Memory Segments – 4K/8K Bytes of In-System Self-Programmable Flash Program Memory – 64/64 Bytes EEPROM 8-bit – 256/512 Bytes Internal SRAM – Write/Erase Cycles: 10,000 Flash/100,000 EEPROM Microcontroller – Data Retention: 20 years at 85°C / 100 years at 25°C – Programming Lock for Software Security with 4/8K Bytes (cid:129) Peripheral Features – One 8-bit Timer/Counter with Separate Prescaler and Compare Mode In-System – One 16-bit Timer/Counter with Prescaler, and Compare and Capture Modes Programmable – 6- or 8-channel 10-bit ADC – Master/Slave SPI Serial Interface Flash – Byte-oriented 2-wire Serial Interface (Philips I2C Compatible) – Programmable Watchdog Timer with Separate On-Chip Oscillator – On-Chip Analog Comparator – Interrupt and Wake-up on Pin Change ATtiny48/88 (cid:129) Special Microcontroller Features – debugWIRE On-Chip Debug System – In-System Programmable via SPI Port – Power-On Reset and Programmable Brown-Out Detection – Internal Calibrated Oscillator – External and Internal Interrupt Sources – Three Sleep Modes: Idle, ADC Noise Reduction and Power-Down – On-Chip Temperature Sensor (cid:129) I/O and Packages – 24 Programmable I/O Lines: (cid:129) 28-pin PDIP (cid:129) 28-pad QFN – 28 Programmable I/O Lines: (cid:129) 32-lead TQFP (cid:129) 32-pad QFN (cid:129) 32-ball UFBGA (cid:129) Operating Voltage: – 1.8 – 5.5V (cid:129) Temperature Range: – -40°C to +85°C (cid:129) Speed Grade: – 0 – 4 MHz @ 1.8 – 5.5V – 0 – 8 MHz @ 2.7 – 5.5V – 0 – 12 MHz @ 4.5 – 5.5V (cid:129) Low Power Consumption – Active Mode: 1 MHz, 1.8V: 240 µA – Power-Down Mode: 0.1 µA at 1.8V Rev. 8008H–AVR–04/11

1. Pin Configurations Figure 1-1. Pinout of ATtiny48/88 TQFP Top View D2 (INT0/PCINT18)D1 (PCINT17)D0 (PCINT16)C6 (RESET/PCINT14)C5 (ADC5/SCL/PCINT13)C4 (ADC4/SDA/PCINT12)C3 (ADC3/PCINT11)C2 (ADC2/PCINT10) (PCINT1(4P/CRIENSTE1T6)) PPCD06 12 PDIP2287 PPCC54 ((AADDCC54//SSCDAL//PPCCIINNTT1132)) PPPPPPPP (PCINT17) PD1 3 26 PC3 (ADC3/PCINT11) 3231302928272625 ((PPCCIINNTT1189//IINNTT01)) PPDD23 45 2254 PPCC21 ((AADDCC21//PPCCIINNTT190)) (PCINT19/INT1) PD3 1 24 PC1 (ADC1/PCINT9) (PCINT20/T0) PD4 6 23 PC0 (ADC0/PCINT8) (PCINT20/T0) PD4 2 23 PC0 (ADC0/PCINT8) VCC 7 22 GND (PCINT26) PA2 3 22 PA1 (ADC7/PCINT25) GND 8 21 PC7 (PCINT15) VCC 4 21 GND (PCINT6/CLKI) PB6 9 20 AVCC GND 5 20 PC7 (PCINT15) (PCINT7) PB7 10 19 PB5 (SCK/PCINT5) (PCINT27) PA3 6 19 PA0 (ADC6/PCINT24) (PCINT21/T1) PD5 11 18 PB4 (MISO/PCINT4) (PCINT6/CLKI) PB6 7 18 AVCC (PCINT22/AIN0) PD6 12 17 PB3 (MOSI/PCINT3) (PCINT7) PB7 8 17 PB5 (SCK/PCINT5) (PCINT23/AIN1) PD7 13 16 PB2 (SS/OC1B/PCINT2) (PCINT0/CLKO/ICP1) PB0 14 15 PB1 (OC1A/PCINT1) 910111213141516 D5D6D7B0B1B2B3B4 PPPPPPPP (PCINT21/T1) (PCINT22/AIN0) (PCINT23/AIN1) PCINT0/CLKO/ICP1) (PCINT1/OC1A) (PCINT2/SS/OC1B) (PCINT3/MOSI) (PCINT4/MISO) ( 32 QFN Top View 28D2 (INT0/PCINT18) QD1 (PCINT17)FND0 (PCINT16) TC6 (RESET/PCINT14)opC5 (ADC5/SCL/PCINT13) VC4 (ADC4/SDA/PCINT12)iewC3 (ADC3/PCINT11) PD2 (INT0/PCINT18)PD1 (PCINT17)PD0 (PCINT16)PC6 (RESET/PCINT14)PC5 (ADC5/SCL/PCINT13)PC4 (ADC4/SDA/PCINT12)PC3 (ADC3/PCINT11)PC2 (ADC2/PCINT10) PPPPPPP 3231302928272625 28272625242322 (PCINT19/INT1) PD3 1 24 PC1 (ADC1/PCINT9) (PCINT19/INT1) PD3 1 21 PC2 (ADC2/PCINT10) (PCINT20/T0) PD4 2 23 PC0 (ADC0/PCINT8) (PCINT20/T0) PD4 2 20 PC1 (ADC1/PCINT9) (PCINT26) PA2 3 22 PA1 (ADC7/PCINT25) VCC 3 19 PC0 (ADC0/PCINT8) VCC 4 21 GND GND 4 18 GND GND 5 20 PC7 (PCINT15) (PCINT6/CLKI) PB6 5 17 PC7 (PCI NT15) (PCINT27) PA3 6 19 PA0 (ADC6/PCINT24) (PCINT7) PB7 6 16 AVCC (PCINT6/CLKI) PB6 7 18 AVCC (PCINT21/T1) PD5 7 15 PB5 (SCK/PCINT5) (PCINT7) PB7 8 17 PB5 (SCK/PCINT5) 891011121314 910111213141516 NOTE: Bottom pad should be soldered to ground. (PCINT22/AIN0) PD6(PCINT23/AIN1) PD7(PCINT0/CLKO/ICP1) PB0(PCINT1/OC1A) PB1(PCINT2/SS/OC1B) PB2(PCINT3//MOSI) PB3(PCINT4/MISO) PB4 NOTE: Bottom pad should be soldered to ground.(PCINT21/T1) PD5(PCINT22/AIN0) PD6(PCINT23/AIN1) PD7(PCINT0/CLKO/ICP1) PB0(PCINT1/OC1A) PB1(PCINT2/SS/OC1B) PB2(PCINT3/MOSI) PB3(PCINT4/MISO) PB4 Table 1-1. 32 UFBGA Top View. See page 288. 1 2 3 4 5 6 A PD2 PD1 PC6 PC4 PC2 PC1 B PD3 PD4 PD0 PC5 PC3 PC0 C GND PA2 PA1 GND D VCC PA3 PC7 PA0 E PB6 PD6 PB0 PB2 AVCC PB5 F PB7 PD5 PD7 PB1 PB3 PB4 ATtiny48/88 2 8008H–AVR–04/11

ATtiny48/88 1.1 Pin Descriptions 1.1.1 VCC Digital supply voltage. 1.1.2 AVCC AV is the supply voltage pin for the A/D converter and a selection of I/O pins. This pin should CC be externally connected to V even if the ADC is not used. If the ADC is used, it is recom- CC mended this pin is connected to V through a low-pass filter, as described in “Analog Noise CC Canceling Techniques” on page 172. The following pins receive their supply voltage from AV : PC7, PC[5:0] and (in 32-lead pack- CC ages) PA[1:0]. All other I/O pins take their supply voltage from V . CC 1.1.3 GND Ground. 1.1.4 Port A (PA3:0) Port A is a 4-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PA[3:0] output buffers have symmetrical drive characteristics with both sink and source capabil- ity. As inputs, Port A pins that are externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running. This port is available in 32-lead TQFP, 32-pad QFN and 32-ball UFBGA packages, only. 1.1.5 Port B (PB7:0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have symmetrical drive characteristics with both sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running. Depending on the clock selection fuse settings, PB6 can be used as input to the internal clock operating circuit. The various special features of Port B are elaborated in “Alternate Functions of Port B” on page 69. 1.1.6 Port C (PC7, PC5:0) Port C is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PC7 and PC[5:0] output buffers have symmetrical drive characteristics with both sink and source capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running. 1.1.7 PC6/RESET If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical char- acteristics of PC6 differ from those of the other pins of Port C. If the RSTDISBL Fuse is unprogrammed, PC6 is used as a reset input. A low level on this pin for longer than the minimum pulse width will generate a reset, even if the clock is not running. The 3 8008H–AVR–04/11

minimum pulse length is given in Table 22-3 on page 209. Shorter pulses are not guaranteed to generate a reset. The various special features of Port C are elaborated in “Alternate Functions of Port C” on page 72. 1.1.8 Port D (PD7:0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PD[7:4] output buffers have symmetrical drive characteristics with both sink and source capabil- ities, while the PD[3:0] output buffers have high sink capabilities. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running. The various special features of Port D are elaborated in “Alternate Functions of Port D” on page 75. ATtiny48/88 4 8008H–AVR–04/11

ATtiny48/88 2. Overview The ATtiny48/88 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATtiny48/88 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power con- sumption versus processing speed. 2.1 Block Diagram Figure 2-1. Block Diagram D C N C G V Watchdog Power debugWIRE Timer Supervision POR / BOD & Watchdog Program RESET Oscillator Logic Oscillator Flash SRAM Circuits / Clock Generation CPU EEPROM 8bit T/C 0 16bit T/C 1 A/D Conv. 2 US 6 B A AT Internal D Bandgap Analog SPI TWI Comp. PORT D (8) PORT B (8) PORT C (8) PORT A (4) RESET CLKI PD[0:7] PB[0:7] PC[0:7] PA[0:3] (in TQFP and MLF) The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than con- ventional CISC microcontrollers. 5 8008H–AVR–04/11

The ATtiny48/88 provides the following features: (cid:129) 4/8K bytes of In-System Programmable Flash (cid:129) 64/64 bytes EEPROM (cid:129) 256/512 bytes SRAM (cid:129) 24 general purpose I/O lines – 28 in 32-lead TQFP, 32-pad QFN, and 32-ball UFBGA packages (cid:129) 32 general purpose working registers (cid:129) Two flexible Timer/Counters with compare modes (cid:129) Internal and external interrupts (cid:129) A byte-oriented, 2-wire serial interface (cid:129) An SPI serial port (cid:129) A 6-channel, 10-bit ADC – 8 in 32-lead TQFP, 32-pad QFN, and 32-ball UFBGA packages (cid:129) A programmable Watchdog Timer with internal oscillator (cid:129) Three software selectable power saving modes. The device includes the following modes for saving power: (cid:129) Idle mode: stops the CPU while allowing the timer/counter, ADC, analog comparator, SPI, TWI, and interrupt system to continue functioning (cid:129) ADC Noise Reduction mode: minimizes switching noise during ADC conversions by stopping the CPU and all I/O modules except the ADC (cid:129) Power-down mode: registers keep their contents and all chip functions are disabled until the next interrupt or hardware reset The device is manufactured using Atmel’s high density non-volatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed In-System through an SPI serial interface, by a conventional non-volatile memory programmer, or by an on-chip boot pro- gram running on the AVR core. The boot program can use any interface to download the application program in the Flash memory. By combining an 8-bit RISC CPU with In-System Self- Programmable Flash on a monolithic chip, the Atmel ATtiny48/88 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications. The ATtiny48/88 AVR is supported by a full suite of program and system development tools including: C compilers, macro assemblers, program debugger/simulators and evaluation kits. 2.2 Comparison Between ATtiny48 and ATtiny88 The ATtiny48 and ATtiny88 differ only in memory sizes, as summarised in Table 2-1, below. Table 2-1. Memory Size Summary Device Flash EEPROM RAM ATtiny48 4K Bytes 64 Bytes 256 Bytes ATtiny88 8K Bytes 64 Bytes 512 Bytes ATtiny48/88 6 8008H–AVR–04/11

ATtiny48/88 3. General Information 3.1 Resources A comprehensive set of development tools, application notes and datasheets are available for download at http://www.atmel.com/avr. 3.2 About Code Examples This documentation contains simple code examples that briefly show how to use various parts of the device. These code examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please confirm with the C compiler documen- tation for more details. For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. 3.3 Capacitive Touch Sensing Atmel QTouch Library provides a simple to use solution for touch sensitive interfaces on Atmel AVR microcontrollers. The QTouch Library includes support for QTouch® and QMatrix® acquisi- tion methods. Touch sensing is easily added to any application by linking the QTouch Library and using the Application Programming Interface (API) of the library to define the touch channels and sensors. The application then calls the API to retrieve channel information and determine the state of the touch sensor. The QTouch Library is free and can be downloaded from the Atmel website. For more informa- tion and details of implementation, refer to the QTouch Library User Guide – also available from the Atmel website. 3.4 Data Retention Reliability Qualification results show that the projected data retention failure rate is much less than 1 PPM over 20 years at 85°C or 100 years at 25°C. 3.5 Disclaimer Typical values contained in this datasheet are based on simulations and characterization of other AVR microcontrollers manufactured on the same process technology. 7 8008H–AVR–04/11

4. AVR CPU Core 4.1 Introduction This section discusses the AVR core architecture in general. The main function of the CPU core is to ensure correct program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and handle interrupts. 4.2 Architectural Overview Figure 4-1. Block Diagram of the AVR Architecture Data Bus 8-bit Program Status Flash Counter and Control Program Memory Interrupt 32 x 8 Unit Instruction General Register Purpose SPI Registrers Unit Instruction Watchdog Decoder Timer g g n ssin essi ALU Analog Control Lines dre ddr Comparator d A ct A ect Dire Indir I/O Module1 Data I/O Module 2 SRAM I/O Module n EEPROM I/O Lines In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with separate memories and buses for program and data. Instructions in the program memory are executed with a single level pipelining. While one instruction is being executed, the next instruc- tion is pre-fetched from the program memory. This concept enables instructions to be executed in every clock cycle. The program memory is In-System Reprogrammable Flash memory. ATtiny48/88 8 8008H–AVR–04/11

ATtiny48/88 The fast-access Register File contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ- ical ALU operation, two operands are output from the Register File, the operation is executed, and the result is stored back in the Register File – in one clock cycle. Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data Space addressing – enabling efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in Flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section. The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations can also be executed in the ALU. After an arithmetic opera- tion, the Status Register is updated to reflect information about the result of the operation. Program flow is provided by conditional and unconditional jump and call instructions, capable of directly addressing the whole address space. Most AVR instructions have a single 16-bit word format but 32-bit wide instructions also exist. The actual instruction set varies, as some devices only implement a part of the instruction set. During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack size is only limited by the total SRAM size and the usage of the SRAM. All user programs must initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through the five different addressing modes supported in the AVR architecture. The memory spaces in the AVR architecture are all linear and regular memory maps. A flexible interrupt module has its control registers in the I/O space with an additional Global Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector posi- tion. The lower the Interrupt Vector address, the higher the priority. The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis- ters, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data Space locations following those of the Register File, 0x20 – 0x5F. In addition, the ATtiny48/88 has Extended I/O space from 0x60 – 0xFF in SRAM where only the ST/STS/STD and LD/LDS/LDD instructions can be used. 4.3 ALU – Arithmetic Logic Unit The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are executed. The ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and fractional format. See external document “AVR Instruction Set” and “Instruction Set Sum- mary” on page 281 section for more information. 4.4 Status Register The Status Register contains information about the result of the most recently executed arithme- tic instruction. This information can be used for altering program flow in order to perform conditional operations. Note that the Status Register is updated after all ALU operations, as 9 8008H–AVR–04/11

specified in the Instruction Set Reference. This will in many cases remove the need for using the dedicated compare instructions, resulting in faster and more compact code. The Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt. This must be handled by software. 4.5 General Purpose Register File The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve the required performance and flexibility, the following input/output schemes are supported by the Register File: (cid:129) One 8-bit output operand and one 8-bit result input (cid:129) Two 8-bit output operands and one 8-bit result input (cid:129) Two 8-bit output operands and one 16-bit result input (cid:129) One 16-bit output operand and one 16-bit result input Figure 4-2 shows the structure of the 32 general purpose working registers in the CPU. Figure 4-2. General Purpose Working Registers 7 0 Addr. Special Function R0 0x00 R1 0x01 R2 0x02 R3 0x03 … ... R12 0x0C R13 0x0D R14 0x0E R15 0x0F R16 0x10 R17 0x11 … ... R26 0x1A X-register Low Byte R27 0x1B X-register High Byte R28 0x1C Y-register Low Byte R29 0x1D Y-register High Byte R30 0x1E Z-register Low Byte R31 0x1F Z-register High Byte Most of the instructions operating on the Register File have direct access to all registers, and most of them are single cycle instructions. ATtiny48/88 10 8008H–AVR–04/11

ATtiny48/88 As shown in Figure 4-2, each register is also assigned a data memory address, mapping them directly into the first 32 locations of the user Data Space. Although not being physically imple- mented as SRAM locations, this memory organization provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file. 4.5.1 The X-register, Y-register, and Z-register The registers R26:R31 have some added functions to their general purpose usage. These regis- ters are 16-bit address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described in Figure 4-3. Figure 4-3. The X-, Y-, and Z-registers 15 0 X-register 7 XH 0 7 XL 0 R27 R26 15 0 Y-register 7 YH 0 7 YL 0 R29 R28 15 0 Z-register 7 ZH 0 7 ZL 0 R31 R30 In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set reference for details). 4.6 Stack Pointer The stack is mainly used for storing temporary data, local variables and return addresses after interrupts and subroutine calls. The Stack Pointer registers (SPH and SPL) always point to the top of the stack. Note that the stack grows from higher memory locations to lower memory loca- tions. This means that the PUSH instructions decreases and the POP instruction increases the stack pointer value. The stack pointer points to the area of data memory where subroutine and interrupt stacks are located. This stack space must be defined by the program before any subroutine calls are exe- cuted or interrupts are enabled. The pointer is decremented by one when data is put on the stack with the PUSH instruction, and incremented by one when data is fetched with the POP instruction. It is decremented by two when the return address is put on the stack by a subroutine call or a jump to an interrupt service routine, and incremented by two when data is fetched by a return from subroutine (the RET instruction) or a return from interrupt service routine (the RETI instruction). The AVR stack pointer is typically implemented as two 8-bit registers in the I/O register file. The width of the stack pointer and the number of bits implemented is device dependent. In some 11 8008H–AVR–04/11

AVR devices all data memory can be addressed using SPL, only. In this case, the SPH register is not implemented. The stack pointer must be set to point above the I/O register areas, the minimum value being the lowest address of SRAM. See Table 5-2 on page 18. 4.7 Instruction Execution Timing This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU clock clk , directly generated from the selected clock source for the CPU chip. No internal clock division is used. Figure 4-4 shows the parallel instruction fetches and instruction executions enabled by the Har- vard architecture and the fast-access Register File concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit. Figure 4-4. The Parallel Instruction Fetches and Instruction Executions T1 T2 T3 T4 clk CPU 1st Instruction Fetch 1st Instruction Execute 2nd Instruction Fetch 2nd Instruction Execute 3rd Instruction Fetch 3rd Instruction Execute 4th Instruction Fetch Figure 4-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU operation using two register operands is executed, and the result is stored back to the destina- tion register. Figure 4-5. Single Cycle ALU Operation T1 T2 T3 T4 clk CPU Total Execution Time Register Operands Fetch ALU Operation Execute Result Write Back 4.8 Reset and Interrupt Handling The AVR provides several different interrupt sources. These interrupts and the separate Reset Vector each have a separate program vector in the program memory space. All interrupts are assigned individual enable bits which must be written logic one together with the Global Interrupt Enable bit in the Status Register in order to enable the interrupt. Depending on the Program Counter value, interrupts may be automatically disabled when Lock Bits LB2 or LB1 are pro- ATtiny48/88 12 8008H–AVR–04/11

ATtiny48/88 grammed. This feature improves software security. See the section “Lock Bits, Fuse Bits and Device Signature” on page 188 for details. The lowest addresses in the program memory space are by default defined as the Reset and Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 52. The list also determines the priority levels of the different interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request 0. Refer to “Interrupts” on page 52 for more information. When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are dis- abled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a Return from Interrupt instruction – RETI – is executed. There are basically two types of interrupts. The first type is triggered by an event that sets the Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vec- tor in order to execute the interrupt handling routine, and hardware clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the Global Interrupt Enable bit is set, and will then be executed by order of priority. The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered. When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served. Note that the Status Register is not automatically stored when entering an interrupt routine, nor restored when returning from an interrupt routine. This must be handled by software. When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the 13 8008H–AVR–04/11

CLI instruction. The following example shows how this can be used to avoid interrupts during the timed EEPROM write sequence. Assembly Code Example in r16, SREG ; store SREG value cli ; disable interrupts during timed sequence sbiEECR, EEMPE ; start EEPROM write sbiEECR, EEPE outSREG, r16 ; restore SREG value (I-bit) C Code Example char cSREG; cSREG = SREG;/* store SREG value */ /* disable interrupts during timed sequence */ _CLI(); EECR |= (1<<EEMPE); /* start EEPROM write */ EECR |= (1<<EEPE); SREG = cSREG; /* restore SREG value (I-bit) */ Note: See “About Code Examples” on page 7. When using the SEI instruction to enable interrupts, the instruction following SEI will be exe- cuted before any pending interrupts, as shown in this example. Assembly Code Example sei ; set Global Interrupt Enable sleep; enter sleep, waiting for interrupt ; note: will enter sleep before any pending interrupt(s) C Code Example __enable_interrupt(); /* set Global Interrupt Enable */ __sleep(); /* enter sleep, waiting for interrupt */ /* note: will enter sleep before any pending interrupt(s) */ Note: See “About Code Examples” on page 7. 4.8.1 Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini- mum. After four clock cycles the program vector address for the actual interrupt handling routine is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack. The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by four clock cycles. This increase comes in addition to the start-up time from the selected sleep mode. A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is incremented by two, and the I-bit in SREG is set. ATtiny48/88 14 8008H–AVR–04/11

ATtiny48/88 4.9 Register Description 4.9.1 SPH and SPL — Stack Pointer Registers Initial Value 0 0 0 0 0 0 RAMEND RAMEND Read/Write R R R R R R R/W R/W Bit 15 14 13 12 11 10 9 8 0x3E (0x5E) – – – – – – SP9 SP8 SPH 0x3D (0x5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL Bit 7 6 5 4 3 2 1 0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND (cid:129) Bits 9:0 – SP[10:0]: Stack Pointer The Stack Pointer register points to the top of the stack, which is implemented growing from higher memory locations to lower memory locations. Hence, a stack PUSH command decreases the Stack Pointer. The stack space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled. 4.9.2 SREG – Status Register Bit 7 6 5 4 3 2 1 0 0x3F (0x5F) I T H S V N Z C SREG Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – I: Global Interrupt Enable The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter- rupt enable control is then performed in separate control registers. If the Global Interrupt Enable Register is cleared, none of the interrupts are enabled independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the SEI and CLI instructions, as described in the instruction set reference. (cid:129) Bit 6 – T: Bit Copy Storage The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti- nation for the operated bit. A bit from a register in the Register File can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the BLD instruction. (cid:129) Bit 5 – H: Half Carry Flag The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful in BCD arithmetic. See the “Instruction Set Description” for detailed information. (cid:129) Bit 4 – S: Sign Bit, S = N ⊕ V The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement Overflow Flag V. See the “Instruction Set Description” for detailed information. 15 8008H–AVR–04/11

(cid:129) Bit 3 – V: Two’s Complement Overflow Flag The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the “Instruction Set Description” for detailed information. (cid:129) Bit 2 – N: Negative Flag The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. (cid:129) Bit 1 – Z: Zero Flag The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. (cid:129) Bit 0 – C: Carry Flag The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. ATtiny48/88 16 8008H–AVR–04/11

ATtiny48/88 5. Memories The AVR architecture makes a distinction between program memory and data memory, locating each memory type in a separate address space. Executable code is located in non-volatile pro- gram memory (Flash), whereas data can be placed in either volatile (SRAM) or non-volatile memory (EEPROM). See Figure 5-1, below. Figure 5-1. Memory Overview. DATA MEMORY PROGRAM MEMORY EXTENDED I/O REGISTER FILE DATA MEMORY I/O REGISTER FILE GENERAL PURPOSE REGISTER FILE FLASH SRAM EEPROM All memory spaces are linear and regular. 5.1 Program Memory (Flash) ATtiny48/88 contains 4/8K byte of on-chip, in-system reprogrammable Flash memory for pro- gram storage. Flash memories are non-volatile, i.e. they retain stored information even when not powered. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as 4096/8192 x 16 bits. The Program Counter (PC) is 11/12 bits wide, thus capable of addressing all 4096/8192 loca- tions of program memory, as illustrated in Table 5-1, below. Table 5-1. Size of Program Memory (Flash). Device Flash Size Address Range ATtiny48 4KB 0x0000 – 0x07FF ATtiny88 8KB 0x0000 – 0x0FFF Constant tables can be allocated within the entire address space of program memory. See instructions LPM (Load Program Memory), and SPM (Store Program Memory) in “Instruction Set Summary” on page 281. Flash program memory can also be programmed from an external device, as described in “External Programming” on page 191. Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim- ing” on page 12. The Flash memory has a minimum endurance of 10,000 write/erase cycles. 17 8008H–AVR–04/11

5.2 Data Memory (SRAM) and Register Files Table 5-2 shows how the data memory and register files of ATtiny48/88 are organized. These memory areas are volatile, i.e. they do not retain information when power is removed. Table 5-2. Layout of Data Memory and Register Area. Device Memory Area Size Long Address (1) Short Address (2) General purpose register file 32B 0x0000 – 0x001F n/a I/O register file 64B 0x0020 – 0x005F 0x00 – 0x3F ATtiny48 Extended I/O register file 160B 0x0060 – 0x00FF n/a Data SRAM 256B 0x0100 – 0x01FF n/a General purpose register file 32B 0x0000 – 0x001F n/a I/O register file 64B 0x0020 – 0x005F 0x00 – 0x3F ATtiny88 Extended I/O register file 160B 0x0060 – 0x00FF n/a Data SRAM 512B 0x0100 – 0x02FF n/a Note: 1. Also known as data address. This mode of addressing covers the entire data memory and reg- ister area. The address is contained in a 16-bit area of two-word instructions. 2. Also known as direct I/O address. This mode of addressing covers part of the register area, only. It is used by instructions where the address is embedded in the instruction word. The 512/768 memory locations include the general purpose register file, I/O register file, extended I/O register file, and the internal data memory. For compatibility with future devices, reserved bits should be written to zero, if accessed. Reserved I/O memory addresses should never be written. 5.2.1 General Purpose Register File The first 32 locations are reserved for the general purpose register file. These registers are described in detail in “General Purpose Register File” on page 10. 5.2.2 I/O Register File Following the general purpose register file, the next 64 locations are reserved for I/O registers. Registers in this area are used mainly for communicating with I/O and peripheral units of the device. Data can be transferred between I/O space and the general purpose register file using instructions such as IN, OUT, LD, ST, and derivatives. All I/O registers in this area can be accessed with the instructions IN and OUT. These I/O spe- cific instructions address the first location in the I/O register area as 0x00 and the last as 0x3F. The low 32 registers (address range 0x00...0x1F) are accessible by some bit-specific instruc- tions. In these registers, bits are easily set and cleared using SBI and CBI, while bit-conditional branches are readily constructed using instructions SBIC, SBIS, SBRC, and SBRS. Registers in this area may also be accessed with instructions LD/LDD/LDI/LDS and ST/STD/STS. These instructions treat the entire volatile memory as one data space and, there- fore, address I/O registers starting at 0x20. See “Instruction Set Summary” on page 281. ATtiny48/88 18 8008H–AVR–04/11

ATtiny48/88 ATtiny48/88 also contains three general purpose I/O registers that can be used for storing any information. See GPIOR0, GPIOR1 and GPIOR2 in “Register Summary” on page 277. These general purpose I/O registers are particularly useful for storing global variables and status flags, since they are accessible to bit-specific instructions such as SBI, CBI, SBIC, SBIS, SBRC, and SBRS. 5.2.3 Extended I/O Register File Following the standard I/O register file, the next 160 locations are reserved for extended I/O reg- isters. ATtiny48/88 is a complex microcontroller with more peripheral units than can be addressed with the IN and OUT instructions. Registers in the extended I/O area must be accessed using instructions LD/LDD/LDI/LDS and ST/STD/STS. See “Instruction Set Summary” on page 281. See “Register Summary” on page 277 for a list of I/O registers. 5.2.4 Data Memory (SRAM) Following the general purpose register file and the I/O register files, the remaining 256/512 loca- tions are reserved for the internal data SRAM. There are five addressing modes available: (cid:129) Direct. This mode of addressing reaches the entire data space. (cid:129) Indirect. (cid:129) Indirect with Displacement. This mode of addressing reaches 63 address locations from the base address given by the Y- or Z-register. (cid:129) Indirect with Pre-decrement. In this mode the address register is automatically decremented before access. Address pointer registers (X, Y, and Z) are located in the general purpose register file, in registers R26 to R31. See “General Purpose Register File” on page 10. (cid:129) Indirect with Post-increment. In this mode the address register is automatically incremented after access. Address pointer registers (X, Y, and Z) are located in the general purpose register file, in registers R26 to R31. See “General Purpose Register File” on page 10. All addressing modes can be used on the entire volatile memory, including the general purpose register file, the I/O register files and the data memory. Internal SRAM is accessed in two clk cycles, as illustrated in Figure 5-2, below. CPU 19 8008H–AVR–04/11

Figure 5-2. On-chip Data SRAM Access Cycles T1 T2 T3 clk CPU Address Compute Address Address valid Data e Writ WR Data d a e R RD Memory Access Instruction Next Instruction 5.3 Data Memory (EEPROM) ATtiny48/88 contains 64 bytes of non-volatile data memory. This EEPROM is organized as a separate data space, in which single bytes can be read and written. All access registers are located in the I/O space. The EEPROM memory layout is summarised in Table 5-3, below. Table 5-3. Size of Non-Volatile Data Memory (EEPROM). Device EEPROM Size Address Range ATtiny48/88 64B 0x00 – 0x3F The internal 8MHz oscillator is used to time EEPROM operations. The frequency of the oscillator must be within the requirements described in “OSCCAL – Oscillator Calibration Register” on page 34. When powered by heavily filtered supplies, the supply voltage, V , is likely to rise or fall slowly CC on power-up and power-down. Slow rise and fall times may put the device in a state where it is running at supply voltages lower than specified. To avoid problems in situations like this, see “Preventing EEPROM Corruption” on page 22. The EEPROM has a minimum endurance of 100,000 write/erase cycles. 5.3.1 Programming Methods There are two methods for EEPROM programming: (cid:129) Atomic byte programming. This is the simple mode of programming, where target locations are erased and written in a single operation. In this mode of operation the target is guaranteed to always be erased before writing but programmin times are longer. (cid:129) Split byte programming. It is possible to split the erase and write cycle in two different operations. This is useful when short access times are required, for example when supply voltage is falling. In order to take advantage of this method target locations must be erased ATtiny48/88 20 8008H–AVR–04/11

ATtiny48/88 before writing to them. This can be done at times when the system allows time-critical operations, typically at start-up and initialisation. The programming method is selected using the EEPROM Programming Mode bits (EEPM1 and EEPM0) in EEPROM Control Register (EECR). See Table 5-4 on page 26. Write and erase times are given in the same table. Since EEPROM programming takes some time the application must wait for one operation to complete before starting the next. This can be done by either polling the EEPROM Program Enable bit (EEPE) in EEPROM Control Register (EECR), or via the EEPROM Ready Interrupt. The EEPROM interrupt is controlled by the EEPROM Ready Interrupt Enable (EERIE) bit in EECR. 5.3.2 Read To read an EEPROM memory location follow the procedure below: (cid:129) Poll the EEPROM Program Enable bit (EEPE) in EEPROM Control Register (EECR) to make sure no other EEPROM operations are in process. If set, wait to clear. (cid:129) Write target address to EEPROM Address Registers (EEARH/EEARL). (cid:129) Start the read operation by setting the EEPROM Read Enable bit (EERE) in the EEPROM Control Register (EECR). During the read operation, the CPU is halted for four clock cycles before executing the next instruction. (cid:129) Read data from the EEPROM Data Register (EEDR). 5.3.3 Erase In order to prevent unintentional EEPROM writes, a specific procedure must be followed to erase memory locations. To erase an EEPROM memory location follow the procedure below: (cid:129) Poll the EEPROM Program Enable bit (EEPE) in EEPROM Control Register (EECR) to make sure no other EEPROM operations are in process. If set, wait to clear. (cid:129) Set mode of programming to erase by writing EEPROM Programming Mode bits (EEPM0 and EEPM1) in EEPROM Control Register (EECR). (cid:129) Write target address to EEPROM Address Registers (EEARH/EEARL). (cid:129) Enable erase by setting EEPROM Master Program Enable (EEMPE) in EEPROM Control Register (EECR). Within four clock cycles, start the erase operation by setting the EEPROM Program Enable bit (EEPE) in the EEPROM Control Register (EECR). During the erase operation, the CPU is halted for two clock cycles before executing the next instruction. The EEPE bit remains set until the erase operation has completed. While the device is busy pro- gramming, it is not possible to perform any other EEPROM operations. 5.3.4 Write In order to prevent unintentional EEPROM writes, a specific procedure must be followed to write to memory locations. Before writing data to EEPROM the target location must be erased. This can be done either in the same operation or as part of a split operation. Writing to an unerased EEPROM location will result in corrupted data. 21 8008H–AVR–04/11

To write an EEPROM memory location follow the procedure below: (cid:129) Poll the EEPROM Program Enable bit (EEPE) in EEPROM Control Register (EECR) to make sure no other EEPROM operations are in process. If set, wait to clear. (cid:129) Set mode of programming by writing EEPROM Programming Mode bits (EEPM0 and EEPM1) in EEPROM Control Register (EECR). Alternatively, data can be written in one operation or the write procedure can be split up in erase, only, and write, only. (cid:129) Write target address to EEPROM Address Registers (EEARH/EEARL). (cid:129) Write target data to EEPROM Data Register (EEDR). (cid:129) Enable write by setting EEPROM Master Program Enable (EEMPE) in EEPROM Control Register (EECR). Within four clock cycles, start the write operation by setting the EEPROM Program Enable bit (EEPE) in the EEPROM Control Register (EECR). During the write operation, the CPU is halted for two clock cycles before executing the next instruction. The EEPE bit remains set until the write operation has completed. While the device is busy with programming, it is not possible to do any other EEPROM operations. 5.3.5 Preventing EEPROM Corruption During periods of low V , the EEPROM data can be corrupted because the supply voltage is CC too low for the CPU and the EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design solutions should be applied. At low supply voltages data in EEPROM can be corrupted in two ways: (cid:129) The supply voltage is too low to maintain proper operation of an otherwise legitimate EEPROM program sequence. (cid:129) The supply voltage is too low for the CPU and instructions may be executed incorrectly. EEPROM data corruption is avoided by keeping the device in reset during periods of insufficient power supply voltage. This is easily done by enabling the internal Brown-Out Detector (BOD). If BOD detection levels are not sufficient for the design, an external reset circuit for low V can be CC used. Provided that supply voltage is sufficient, an EEPROM write operation will be completed even when a reset occurs. ATtiny48/88 22 8008H–AVR–04/11

ATtiny48/88 5.3.6 Program Examples The following code examples show one assembly and one C function for erase, write, or atomic write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling interrupts globally) so that no interrupts occur during execution of these functions. Assembly Code Example EEPROM_write: ; Wait for completion of previous write sbic EECR, EEPE rjmp EEPROM_write ; Set Programming mode ldi r16, (0<<EEPM1)|(0<<EEPM0) out EECR, r16 ; Set up address (r18:r17) in address registers out EEARH, r18 out EEARL, r17 ; Write data (r19) to data register out EEDR, r19 ; Write logical one to EEMPE sbi EECR, EEMPE ; Start eeprom write by setting EEPE sbi EECR, EEPE ret Note: See “About Code Examples” on page 7. C Code Example void EEPROM_write(unsigned int ucAddress, unsigned char ucData) { /* Wait for completion of previous write */ while(EECR & (1<<EEPE)) ; /* Set Programming mode */ EECR = (0<<EEPM1)|(0<<EEPM0) /* Set up address and data registers */ EEAR = ucAddress; EEDR = ucData; /* Write logical one to EEMPE */ EECR |= (1<<EEMPE); /* Start eeprom write by setting EEPE */ EECR |= (1<<EEPE); } Note: See “About Code Examples” on page 7. 23 8008H–AVR–04/11

The next code examples show assembly and C functions for reading the EEPROM. The exam- ples assume that interrupts are controlled so that no interrupts will occur during execution of these functions. Assembly Code Example EEPROM_read: ; Wait for completion of previous write sbic EECR, EEPE rjmp EEPROM_read ; Set up address (r18:r17) in address registers out EEARH, r18 out EEARL, r17 ; Start eeprom read by writing EERE sbi EECR, EERE ; Read data from data register in r16, EEDR ret Note: See “About Code Examples” on page 7. C Code Example unsigned char EEPROM_read(unsigned int ucAddress) { /* Wait for completion of previous write */ while(EECR & (1<<EEPE)) ; /* Set up address register */ EEAR = ucAddress; /* Start eeprom read by writing EERE */ EECR |= (1<<EERE); /* Return data from data register */ return EEDR; } Note: See “About Code Examples” on page 7. ATtiny48/88 24 8008H–AVR–04/11

ATtiny48/88 5.4 Register Description 5.4.1 EEARH and EEARL – EEPROM Address Register Bit 15 14 13 12 11 10 9 8 – – – – – – – – EEARH 0x21 (0x41) – – EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL 7 6 5 4 3 2 1 0 Read/Write R R R R R R R R R R R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 0 0 X X X X X X (cid:129) Bits 15:6 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 5:0 – EEAR[5:0]: EEPROM Address The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the 64/64 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 63/63. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed. 5.4.2 EEDR – EEPROM Data Register Bit 7 6 5 4 3 2 1 0 0x20 (0x40) MSB LSB EEDR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – EEDR[7:0]: EEPROM Data For the EEPROM write operation, the EEDR Register contains the data to be written to the EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address given by EEAR. 5.4.3 EECR – EEPROM Control Register Bit 7 6 5 4 3 2 1 0 0x1F (0x3F) – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR Read/Write R R R/W R/W R/W R/W R/W R/W Initial Value 0 0 X X 0 0 X 0 (cid:129) Bits 7:6 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 5:4 – EEPM[1:0]: EEPROM Programming Mode Bits EEPROM programming mode bits define the action that will be triggered when EEPE is written. Data can be programmed in a single atomic operation, where the previous value is automatically 25 8008H–AVR–04/11

erased before the new value is programmed, or Erase and Write can be split in two different operations. The programming times for the different modes are shown in Table 5-4. Table 5-4. EEPROM Programming Mode Bits and Programming Times EEPM1 EEPM0 Programming Time Operation 0 0 3.4 ms Atomic (erase and write in one operation) 0 1 1.8 ms Erase, only 1 0 1.8 ms Write, only 1 1 – Reserved When EEPE is set any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming. (cid:129) Bit 3 – EERIE: EEPROM Ready Interrupt Enable Writing this bit to one enables the EEPROM Ready Interrupt. Provided the I-bit in SREG is set, the EEPROM Ready Interrupt is triggered when non-volatile memory is ready for programming. Writing this bit to zero disables the EEPROM Ready Interrupt. (cid:129) Bit 2 – EEMPE: EEPROM Master Write Enable The EEMPE bit determines whether writing EEPE to one will have effect or not. When EEMPE is set and EEPE written within four clock cycles the EEPROM at the selected address will be programmed. Hardware clears the EEMPE bit to zero after four clock cycles. If EEMPE is zero the EEPE bit will have no effect. (cid:129) Bit 1 – EEPE: EEPROM Write Enable The EEPROM Write Enable Signal EEPE is the write strobe to the EEPROM. When address and data are correctly set up, the EEPE bit must be written to one to write the value into the EEPROM. The EEMPE bit must be written to one before a logical one is written to EEPE, other- wise no EEPROM write takes place. The following procedure should be followed when writing the EEPROM (the order of steps 3 and 4 is not essential): 1. Wait until EEPE becomes zero. 2. Wait until SELFPRGEN in SPMCSR becomes zero. 3. Write new EEPROM address to EEAR (optional). 4. Write new EEPROM data to EEDR (optional). 5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR. 6. Within four clock cycles after setting EEMPE, write a logical one to EEPE. The EEPROM can not be programmed during a CPU write to the Flash memory. The software must check that the Flash programming is completed before initiating a new EEPROM write. If the Flash is never being updated by the CPU, step 2 can be omitted. Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM is interrupting another EEPROM access, the EEAR or EEDR Register will be modified, causing the ATtiny48/88 26 8008H–AVR–04/11

ATtiny48/88 interrupted EEPROM access to fail. It is recommended to have the Global Interrupt Flag cleared during all the steps to avoid these problems. When the write access time has elapsed, the EEPE bit is cleared by hardware. The user soft- ware can poll this bit and wait for a zero before writing the next byte. When EEPE has been set, the CPU is halted for two cycles before the next instruction is executed. (cid:129) Bit 0 – EERE: EEPROM Read Enable This is the read strobe of the EEPROM. When the target address has been set up in the EEAR, the EERE bit must be written to one to trigger the EEPROM read operation. EEPROM read access takes one instruction, and the requested data is available immediately. When the EEPROM is read, the CPU is halted for four cycles before the next instruction is executed. The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it not possible to read the EEPROM, or to change the address register (EEAR). 5.4.4 GPIOR2 – General Purpose I/O Register 2 Bit 7 6 5 4 3 2 1 0 0x2B (0x4B) MSB LSB GPIOR2 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 This register may be used freely for storing any kind of data. 5.4.5 GPIOR1 – General Purpose I/O Register 1 Bit 7 6 5 4 3 2 1 0 0x2A (0x4A) MSB LSB GPIOR1 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 This register may be used freely for storing any kind of data. 5.4.6 GPIOR0 – General Purpose I/O Register 0 Bit 7 6 5 4 3 2 1 0 0x1E (0x3E) MSB LSB GPIOR0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 This register may be used freely for storing any kind of data. 27 8008H–AVR–04/11

6. Clock System Figure 6-1 presents the principal clock systems in the AVR and their distribution. All of the clocks need not be active at a given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using different sleep modes, as described in “Power Manage- ment and Sleep Modes” on page 36. The clock systems are detailed below. Figure 6-1. Clock Distribution GENERAL CPU FLASH AND TWI ADC RAM I/O MODULES CORE EEPROM clk clk clk clk clk TWIHS I/O ADC CPU FLASH CLOCK CONTROL UNIT CLOCK RESET PRESCALER LOGIC WATCHDOG SOURCE CLOCK CLOCK WATCHDOG TIMER CLOCK SWITCH EXTERNAL WATCHDOG CALIBRATED CLOCK OSCILLATOR OSCILLATOR 6.1 Clock Subsystems The clock subsystems are detailed in the sections below. 6.1.1 CPU Clock – clk CPU The CPU clock is routed to parts of the system concerned with operation of the AVR core. Examples of such modules are the General Purpose Register File, the Status Register and the data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing general operations and calculations. 6.1.2 I/O Clock – clk I/O The I/O clock is used by the majority of the I/O modules such as Timer/Counters, the Serial Peripheral Interface and the External Interrupt module. Note, that some external interrupts are detected by asynchronous logic, meaning they are recognized even if the I/O clock is halted. Also note that the start condition detection of the Two-Wire Interface module is asynchronous, meaning TWI address recognition works in all sleep modes (even when clk is halted). I/O ATtiny48/88 28 8008H–AVR–04/11

ATtiny48/88 6.1.3 Flash Clock – clk FLASH The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul- taneously with the CPU clock. 6.1.4 Analog to Digital Converter Clock – clk ADC The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion results. 6.1.5 High-Speed Two-Wire Interface Clock – clk TWIHS The TWI clock controls the operation of the Two-Wire Interface module, when operated in high- speed mode. In practice, this clock is identical to the source clock of the device. See “Bit Rate Generator Unit” on page 135. 6.2 Clock Sources The device can use any of the following sources for the system clock: (cid:129) External Clock (see page 29) (cid:129) Calibrated Internal 8MHz Oscillator (see page 30) (cid:129) Internal 128 kHz Oscillator (see page 31) The clock source is selected using CKSEL fuses. See Table 6-1. Table 6-1. Device Clocking Options CKSEL[1:0] (1) Device Clocking Option Frequency 00 External Clock 0 – 12 MHz 01 Reserved – 10 (2) Calibrated Internal 8MHz Oscillator 8.0 MHz (3) 11 Internal 128 kHz Oscillator 128 kHz Notes: 1. For all fuses “1” means unprogrammed while “0” means programmed. 2. The device is shipped with this option selected. 3. If 8 MHz frequency exceeds the specification of the device (depends on V ), the CKDIV8 fuse CC can be programmed in order to divide the internal frequency by 8. For more information on fuse bits, see “Fuse Bits” on page 189. 6.2.1 External Clock To drive the device from an external clock source, CLKI should be driven as shown in Figure 6-2 on page 30. 29 8008H–AVR–04/11

Figure 6-2. External Clock Drive Configuration EXTERNAL CLOCK CLKI SIGNAL GND When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 6-2. Table 6-2. Start-up Times for the External Clock Selection Start-up Time Additional Delay SUT[1:0] Power Conditions from Power-down from Reset (V = 5.0V) CC 00 BOD enabled 6 CK 14CK 01 Fast rising power 6 CK 14CK + 4 ms 10 Slowly rising power 6 CK 14CK + 64 ms 11 Reserved When applying an external clock, it is required to avoid sudden changes in the applied clock fre- quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable behavior. If changes of more than 2% is required, ensure that the MCU is kept in Reset during the changes. Note that the System Clock Prescaler can be used to implement run-time changes of the internal clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page 31 for details. 6.2.2 Calibrated Internal 8MHz Oscillator By default, the Internal Oscillator provides an approximate 8.0 MHz clock. Though voltage and temperature dependent, this clock can be very accurately calibrated by the user. See Table 22-1 on page 208 for more details. The device is shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 31 for more details. When selected, this oscillator operates with no external components. During reset, hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby automati- cally calibrates the oscillator. The accuracy of this calibration is shown as Factory calibration in Table 22-1 on page 208. By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on page 34, it is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is shown as User calibration in Table 22-1 on page 208. ATtiny48/88 30 8008H–AVR–04/11

ATtiny48/88 When this oscillator is used as the chip clock, the Watchdog oscillator will still be used for the Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed cali- bration value, see the section “Calibration Byte” on page 190. When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in the table below. Table 6-3. Start-up Times for the Internal Calibrated Oscillator Clock Selection Start-up Time Additional Delay SUT[1:0] Power Conditions from Power-down from Reset (V = 5.0V) CC 00 BOD enabled 6 CK 14CK (1) 01 Fast rising power 6 CK 14CK + 4 ms 10 (2) Slowly rising power 6 CK 14CK + 64 ms 11 Reserved Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to ensure programming mode can be entered. 2. The device is shipped with this option selected. 6.2.3 Internal 128 kHz Oscillator The 128 kHz internal oscillator is a low power oscillator providing a clock of 128 kHz. The fre- quency depends on supply voltage, temperature and patch variations. This clock may be selected as the system clock by programming the CKSEL Fuses to “11”. When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 6-4. Table 6-4. Start-up Times for the 128 kHz Internal Oscillator Start-up Time Additional Delay SUT[1:0] Power Conditions from Power-down from Reset 00 BOD enabled 6 CK 14CK(1) 01 Fast rising power 6 CK 14CK + 4 ms 10 Slowly rising power 6 CK 14CK + 64 ms 11 Reserved Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to ensure programming mode can be entered. 6.2.4 Default Clock Source The device is shipped with internal oscillator at 8.0 MHz and with the fuse CKDIV8 programmed, resulting in 1.0 MHz system clock. The startup time is set to maximum and time-out period enabled (CKSEL = 0b10, SUT = 0b10, CKDIV8 = 0). The default setting ensures that all users can make their desired clock source setting using any available programming interface. 6.3 System Clock Prescaler The ATtiny48/88 has a system clock prescaler, and the system clock can be divided by setting the “CLKPR – Clock Prescale Register” on page 34. This feature can be used to decrease the system clock frequency and the power consumption when the requirement for processing power 31 8008H–AVR–04/11

is low. This can be used with all clock source options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clk , clk , clk , and clk are divided by a factor I/O ADC CPU FLASH as shown in Table 6-6 on page 35. 6.3.1 Switching Prescaler Setting When switching between prescaler settings, the System Clock Prescaler ensures that no glitches occur in the clock system. It also ensures that no intermediate frequency is higher than neither the clock frequency corresponding to the previous setting, nor the clock frequency corre- sponding to the new setting. The ripple counter that implements the prescaler runs at the frequency of the undivided clock, which may be faster than the CPU's clock frequency. Hence, it is not possible to determine the state of the prescaler – even if it were readable, and the exact time it takes to switch from one clock division to the other cannot be exactly predicted. From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2 * T2 before the new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period corresponding to the new prescaler setting. To avoid unintentional changes of clock frequency, a special write procedure must befollowed to change the CLKPS bits: 1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bitsin CLKPR to zero. 2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE. Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted. 6.4 Clock Output Buffer The device can output the system clock on the CLKO pin. To enable the output, the CKOUT Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other cir- cuits on the system. The clock also will be output during reset, and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including the internal oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler is used, it is the divided system clock that is output. 6.5 Clock Startup Sequence Any clock source needs a sufficient V to start oscillating and a minimum number of oscillating CC cycles before it can be considered stable. To ensure sufficient V , the device issues an internal reset with a time-out delay (t ) after CC TOUT the device reset is released by all other reset sources. “System Control and Reset” on page 42 describes the start conditions for the internal reset. The delay (t ) is timed from the Watchdog TOUT oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits. The selectable delays are shown in Table 6-5. The frequency of the Watchdog oscillator is voltage ATtiny48/88 32 8008H–AVR–04/11

ATtiny48/88 and temperature dependent, as shown in “Watchdog Oscillator Frequency vs. VCC” on page 245 and “Watchdog Oscillator Frequency vs. Temperature” on page 246. Table 6-5. Length of Startup Sequence. CKSEL[1:0] SUT[1:0] Number of WDT Cycles Typical Time-out 00 0 0 ms 00 01 4K (4,096) 4 ms 10 11 10 8K (8,192) 64 ms 11 Reserved Reserved 01 XX Reserved Reserved The main purpose of the delay is to keep the AVR in reset until it is supplied with minimum V . CC The delay will not monitor the actual voltage and it will be required to select a delay longer than the V rise time. If this is not possible, an internal or external Brown-out Detection circuit should CC be used. A BOD circuit will ensure sufficient V before it releases the reset, and the time-out CC delay can be disabled. Disabling the time-out delay without utilizing a Brown-out Detection circuit is not recommended. The oscillator is required to oscillate for a minimum number of cycles before the clock is consid- ered stable. An internal ripple counter monitors the oscillator output clock, and keeps the internal reset active for a given number of clock cycles. The reset is then released and the device will start to execute. The start-up sequence for the clock includes both the time-out delay and the start-up time when the device starts up from reset. When starting up from Power-down mode, V is assumed to be CC at a sufficient level and only the start-up time is included. 33 8008H–AVR–04/11

6.6 Register Description 6.6.1 OSCCAL – Oscillator Calibration Register Bit 7 6 5 4 3 2 1 0 (0x66) CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value Device Specific Calibration Value The Oscillator Calibration Register is used to trim the internal oscillator to remove process varia- tions from the oscillator frequency. A pre-programmed calibration value is automatically written to this register during chip reset, giving the factory calibrated frequency as specified in Table 22- 1 on page 208. The application software can write to the OSCCAL register to change the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 22-1 on page 208. Calibra- tion outside the given range is not guaranteed. Note that this oscillator is used to time EEPROM and Flash write accesses, and the write times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail. All register bits are in use for frequency . A setting of 0x00 gives the lowest frequency and a set- ting of 0xFF gives the highest frequency. 6.6.2 CLKPR – Clock Prescale Register Bit 7 6 5 4 3 2 1 0 (0x61) CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR Read/Write R/W R R R R/W R/W R/W R/W Initial Value 0 0 0 0 See Bit Description (cid:129) Bit 7 – CLKPCE: Clock Prescaler Change Enable The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the other bits in CLKPR are simultaneously written to zero. CLKPCE is cleared by hardware four cycles after it is written or when CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the CLKPCE bit. (cid:129) Bits 6:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 3:0 – CLKPS[3:0]: Clock Prescaler Select Bits 3 - 0 These bits define the division factor between the selected clock source and the internal system clock. These bits can be written run-time to vary the clock frequency to suit the application requirements. As the divider divides the master clock input to the MCU, the speed of all synchro- nous peripherals is reduced when a division factor is used. The division factors are given in Table 6-6. The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to 0b0000. If CKDIV8 is programmed, CLKPS bits are reset to 0b0011, giving a division factor of 8 at start up. This feature should be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present operat- ing conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8 Fuse setting. The Application software must ensure that a sufficient division factor is chosen if ATtiny48/88 34 8008H–AVR–04/11

ATtiny48/88 the selected clock source has a higher frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed. Table 6-6. Clock Prescaler Select CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor 0 0 0 0 1 0 0 0 1 2 0 0 1 0 4 0 0 1 1 8 0 1 0 0 16 0 1 0 1 32 0 1 1 0 64 0 1 1 1 128 1 0 0 0 256 1 0 0 1 Reserved 1 0 1 0 Reserved 1 0 1 1 Reserved 1 1 0 0 Reserved 1 1 0 1 Reserved 1 1 1 0 Reserved 1 1 1 1 Reserved 35 8008H–AVR–04/11

7. Power Management and Sleep Modes Sleep modes enable the application to shut down unused modules in the MCU, thereby saving power. The AVR provides various sleep modes allowing the user to tailor the power consump- tion to the application’s requirements. When enabled, the Brown-out Detector (BOD) actively monitors the power supply voltage during the sleep periods. To further save power, it is possible to disable the BOD in some sleep modes. See “Software BOD Disable” on page 37 for more details. 7.1 Sleep Modes Figure 6-1 on page 28 presents the different clock systems in the ATtiny48/88, and their distribu- tion. The figure is helpful in selecting an appropriate sleep mode. Table 7-1 shows the different sleep modes, their wake up sources and the BOD disable ability. Table 7-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes Active Clock Domain Oscillator Wake-up Source bled and s Sleep Mode clkCPU clkFLASH clkIO clkADC Main Clock Source Ena INT1, INT0 Pin Change TWI AddresMatch EEPROMReady ADC WDT Other I/O Idle X X X X X X X X X ADC Noise Reduction X X X(1) X X X X Power-down X(1) X X Notes: 1. For INT1 and INT0, only level interrupt To enter any of the sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP instruction must be executed. The SM1, and SM0 bits in the SMCR Register select which sleep mode (Idle, ADC Noise Reduction, or Power-down) will be activated by the SLEEP instruction. See Table 7-2 on page 39 for a summary. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP. The contents of the Register File and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the Reset Vector. Note that if a level triggered interrupt is used for wake-up the changed level must be held for some time to wake up the MCU (and for the MCU to enter the interrupt service routine). See “External Interrupts” on page 53 for details. 7.1.1 Idle Mode When the SM[1:0] bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode, stopping the CPU but allowing the SPI, Analog Comparator, ADC, 2-wire Serial Interface, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode basically halts clk and clk , while allowing the other clocks to run. CPU FLASH ATtiny48/88 36 8008H–AVR–04/11

ATtiny48/88 Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the SPI interrupts. If wake-up from the Analog Comparator interrupt is not required, the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If the ADC is enabled, a conversion starts automatically when this mode is entered. 7.1.2 ADC Noise Reduction Mode When the SM[1:0] bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the 2- wire Serial Interface address watch and the Watchdog to continue operating (if enabled). This sleep mode basically halts clk , clk , and clk , while allowing the other clocks to run. I/O CPU FLASH This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart from the ADC Conversion Complete interrupt, only an External Reset, a Watchdog System Reset, a Watchdog Interrupt, a Brown-out Reset, a 2-wire Serial Interface address match, an EEPROM ready interrupt, an external level interrupt on INT0 or INT1 or a pin change interrupt can wake up the MCU from ADC Noise Reduction mode. 7.1.3 Power-Down Mode When the SM[1:0] bits are written to 10, the SLEEP instruction makes the MCU enter Power- down mode. In this mode, the external oscillator is stopped, while the external interrupts, the 2- wire Serial Interface address watch, and the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog System Reset, a Watchdog Interrupt, a Brown-out Reset, a 2-wire Serial Interface address match, an external level interrupt on INT0 or INT1, or a pin change interrupt can wake up the MCU. This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only. Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 53 for details. When waking up from Power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes effective. This allows the clock to restart and become stable after having been stopped. The wake-up period is defined by the same CKSEL Fuses that define the Reset Time-out period, as described in “Clock Sources” on page 29. 7.2 Software BOD Disable When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 20-4 on page 189), the BOD is actively monitoring the power supply voltage during a sleep period. To save power, it is possible for software to disable the BOD in Power-down mode. The sleep mode power consumption will then be at the same level as when BOD is globally disabled by fuses. If disabled by software, the BOD is turned off immediately after entering the sleep mode and auto- matically turned on upon wake-up. This ensures safe operation in case the V level has CC dropped during the sleep period. When the BOD has been disabled the wake-up time from sleep mode will be the same as the wake-up time from RESET. This is in order to ensure the BOD is working correctly before the MCU continues executing code. BOD disable is controlled by bit 6, BODS (BOD Sleep) in the control register MCUCR, see “MCUCR – MCU Control Register” on page 40. Writing this bit to one turns off the BOD in 37 8008H–AVR–04/11

Power-down mode, while a zero in this bit keeps BOD active. The default setting is zero, i.e. BOD active. Writing to the BODS bit is controlled by a timed sequence and an enable bit, see “MCUCR – MCU Control Register” on page 40. 7.3 Minimizing Power Consumption There are several issues to consider when trying to minimize the power consumption in an AVR controlled system. In general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as possible of the device’s functions are operating. All functions not needed should be disabled. In particular, the following modules may need special consideration when trying to achieve the lowest possible power consumption. 7.3.1 Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis- abled before entering any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to “ADC – Analog to Digital Converter” on page 164 for details on ADC operation. 7.3.2 Analog Comparator When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC Noise Reduction mode, the Analog Comparator should be disabled. In other sleep modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is set up to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep mode. Refer to “Analog Comparator” on page 161 for details on how to configure the Analog Comparator. 7.3.3 Brown-Out Detector If the Brown-out Detector is not needed by the application, this module should be turned off. If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this will contribute sig- nificantly to the total current consumption. Refer to “Brown-Out Detection” on page 44 for details on how to configure the Brown-out Detector. 7.3.4 Internal Voltage Reference The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the Analog Comparator or the ADC. If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will not be consuming power. When turned on again, the user must allow the reference to start up before the output is used. If the reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal Volt- age Reference” on page 45 for details on the start-up time. 7.3.5 Watchdog Timer If the Watchdog Timer is not needed in the application, the module should be turned off. If the Watchdog Timer is enabled, it will be enabled in all sleep modes and hence always consume power. In the deeper sleep modes, this will contribute significantly to the total current consump- tion. Refer to “Watchdog Timer” on page 46 for details on how to configure the Watchdog Timer. ATtiny48/88 38 8008H–AVR–04/11

ATtiny48/88 7.3.6 Port Pins When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then to ensure that no pins drive resistive loads. In sleep modes where both the I/O clock (clk ) and the ADC clock (clk ) are stopped, the input buffers of the device will I/O ADC be disabled. This ensures that no power is consumed by the input logic when not needed. In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 65 for details on which pins are enabled. If the input buffer is enabled and the input signal is left floating or have an analog signal level close to V /2, the input buffer will use excessive power. CC For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to V /2 on an input pin can cause significant current even in active mode. Digital CC input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and DIDR0). Refer to “DIDR1 – Digital Input Disable Register 1” on page 163 and “DIDR0 – Digital Input Disable Register 0” on page 180 for details. 7.3.7 On-chip Debug System If the On-chip debug system is enabled by the DWEN Fuse and the chip enters sleep mode, the main clock source is enabled and hence always consumes power. In the deeper sleep modes, this will contribute significantly to the total current consumption. 7.4 Register Description 7.4.1 SMCR – Sleep Mode Control Register The Sleep Mode Control Register contains control bits for power management. Bit 7 6 5 4 3 2 1 0 0x33 (0x53) – – – – – SM1 SM0 SE SMCR Read/Write R R R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:3 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 2:1 – SM[1:0]: Sleep Mode Select Bits 1 and 0 These bits select between the available sleep modes as shown in Table 7-2. Table 7-2. Sleep Mode Select SM1 SM0 Sleep Mode 0 0 Idle 0 1 ADC Noise Reduction 1 0 Power-down 1 1 Reserved (cid:129) Bit 0 – SE: Sleep Enable The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of the SLEEP instruction and to clear it immediately after waking up. 39 8008H–AVR–04/11

7.4.2 MCUCR – MCU Control Register Bit 7 6 5 4 3 2 1 0 0x35 (0x55) – BODS BODSE PUD – – – – MCUCR Read/Write R R/W R/W R/W R R R R Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7, 3:0 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 6 – BODS: BOD Sleep The BODS bit must be written to logic one in order to turn off BOD during sleep, see Table 7-2 on page 39. Writing to the BODS bit is controlled by a timed sequence and an enable bit, BODSE in MCUCR. To disable BOD in relevant sleep modes, both BODS and BODSE must first be set to one. Then, to set the BODS bit, BODS must be set to one and BODSE must be set to zero within four clock cycles. The BODS bit is active three clock cycles after it is set. A sleep instruction must be executed while BODS is active in order to turn off the BOD for the actual sleep mode. The BODS bit is automatically cleared after three clock cycles. (cid:129) Bit 5 – BODSE: BOD Sleep Enable BODSE enables setting of BODS control bit, as explained in BODS bit description. BOD disable is controlled by a timed sequence. 7.4.3 PRR – Power Reduction Register The Power Reduction Register (PRR) provides a method to stop the clock to individual peripher- als to reduce power consumption. The current state of the peripheral is frozen and the I/O registers can not be read or written. Resources used by the peripheral when stopping the clock will remain occupied, hence the peripheral should in most cases be disabled before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the same state as before shutdown. Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. In all other sleep modes, the clock is already stopped. Bit 7 6 5 4 3 2 1 0 (0x64) PRTWI – PRTIM0 – PRTIM1 PRSPI – PRADC PRR Read/Write R/W R R/W R R/W R/W R R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – PRTWI: Power Reduction TWI Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When waking up the TWI again, the TWI should be re initialized to ensure proper operation. (cid:129) Bits 6, 4, 1 – Res: Reserved These bits are reserved and will always read zero. (cid:129) Bit 5 – PRTIM0: Power Reduction Timer/Counter0 Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will continue like before the shutdown. ATtiny48/88 40 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 3 – PRTIM1: Power Reduction Timer/Counter1 Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1 is enabled, operation will continue like before the shutdown. (cid:129) Bit 2 – PRSPI: Power Reduction Serial Peripheral Interface If using debugWIRE On-chip Debug System, this bit should not be written to one. Writing a logic one to this bit shuts down the Serial Peripheral Interface by stopping the clock to the module. When waking up the SPI again, the SPI should be re initialized to ensure proper operation. (cid:129) Bit 0 – PRADC: Power Reduction ADC Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down. The analog comparator cannot be used when the ADC is shut down. 41 8008H–AVR–04/11

8. System Control and Reset 8.1 Resetting the AVR During reset, all I/O Registers are set to their initial values, and the program starts execution from the Reset Vector. The instruction placed at the Reset Vector must be an RJMP – Relative Jump – instruction to the reset handling routine. If the program never enables an interrupt source, the Interrupt Vectors are not used, and regular program code can be placed at these locations. The circuit diagram in Figure 8-1 shows the reset circuit. Table 22-3 on page 209 shows the electrical parameters of the reset circuitry. Figure 8-1. Reset Logic DATA BUS MCU Status Register (MCUSR) RFRFRFRF OOTD Power-on Reset PBEXW Circuit Brown-out BODLEVEL [2:0] Reset Circuit Pull-up Resistor SPIKE FILTER Watchdog Oscillator Clock CK Delay Counters Generator TIMEOUT CKSEL[1:0] SUT[1:0] The I/O ports of the AVR are immediately reset to their initial state when a reset source goes active. This does not require any clock source to be running. After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The dif- ferent selections for the delay period are presented in “Clock Sources” on page 29. ATtiny48/88 42 8008H–AVR–04/11

ATtiny48/88 8.2 Reset Sources The ATtiny48/88 has four sources of reset: (cid:129) Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset threshold (V ), or when the supply voltage falls rapidly. POT (cid:129) External Reset. The MCU is reset when a low level is present on the RESET pin for longer than the required pulse length. (cid:129) Watchdog System Reset. The MCU is reset when the Watchdog Timer period expires and the Watchdog System Reset mode is enabled. (cid:129) Brown-out Reset. The MCU is reset when the supply voltage V is below the Brown-out CC Reset threshold (V ) and the Brown-out Detector is enabled. BOT 8.2.1 Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level is defined in Table 22-3 on page 209. The POR is activated whenever V is below the detection CC level. The POR circuit can be used to trigger the start-up Reset, as well as to detect a failure in supply voltage. A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the Power-on Reset threshold voltage invokes the delay counter, which determines how long the device is kept in RESET after V rise. The RESET signal is activated again, without any delay, CC when V decreases below the detection level. CC Figure 8-2. MCU Start-up, RESET Tied to V CC V V POT CC V RESET RST t TIME-OUT TOUT INTERNAL RESET Figure 8-3. MCU Start-up, RESET Extended Externally V POT V CC V RESET RST t TIME-OUT TOUT INTERNAL RESET 43 8008H–AVR–04/11

8.2.2 External Reset An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum pulse width (see Table 22-3 on page 209) will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the Reset Threshold Voltage – V – on its positive edge, the delay counter starts the RST MCU after the Time-out period – t –has expired. The External Reset can be disabled by the TOUT RSTDISBL fuse, see Table 20-4 on page 189. Figure 8-4. External Reset During Operation CC 8.2.3 Brown-Out Detection ATtiny48/88 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V level dur- CC ing operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the detection level should be interpreted as V = BOT+ V + V /2 and V = V - V /2. When the BOD is enabled, and V decreases to a BOT HYST BOT- BOT HYST CC value below the trigger level (V in Figure 8-5), the Brown-out Reset is immediately activated. BOT- When V increases above the trigger level (V in Figure 8-5), the delay counter starts the CC BOT+ MCU after the Time-out period t has expired. TOUT The BOD circuit will only detect a drop in V if the voltage stays below the trigger level for lon- CC ger than t given in “System and Reset Characterizations” on page 209. BOD Figure 8-5. Brown-out Reset During Operation VCC V VBOT+ BOT- RESET TIME-OUT tTOUT INTERNAL RESET ATtiny48/88 44 8008H–AVR–04/11

ATtiny48/88 8.2.4 Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out period t . Refer to TOUT page 46 for details on operation of the Watchdog Timer. Figure 8-6. Watchdog System Reset During Operation CC CK 8.3 Internal Voltage Reference ATtiny48/88 features an internal bandgap reference. This reference is used for Brown-out Detection, and it can be used as an input to the Analog Comparator or the ADC. 8.3.1 Voltage Reference Enable Signals and Start-up Time The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in “System and Reset Characterizations” on page 209. To save power, the reference is not always turned on. The reference is on during the following situations: 1. When the BOD is enabled (by programming the BODLEVEL[2:0] Fuses). 2. When the internal reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR). 3. When the ADC is enabled. Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering Power-down mode. 45 8008H–AVR–04/11

8.4 Watchdog Timer ATtiny48/88 has an Enhanced Watchdog Timer (WDT). The WDT is a timer counting cycles of a separate on-chip 128 kHz oscillator. The WDT gives an interrupt or a system reset when the counter reaches a given time-out value. In normal operation mode, it is required that the system uses the WDR - Watchdog Timer Reset - instruction to restart the counter before the time-out value is reached. If the system doesn't restart the counter, an interrupt or system reset will be issued. Figure 8-7. Watchdog Timer 128kHz OSCILLATOR KKKKKKKKKK 2486248624 OSC/OSC/OSC/OSC/1OSC/3OSC/6OSC/12OSC/25OSC/51SC/102 O WDP0 WDP1 WATCHDOG WDP2 RESET WDP3 WDE MCU RESET WDIF INTERRUPT WDIE In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used to wake the device from sleep-modes, and also as a general system timer. One example is to limit the maximum time allowed for certain operations, giving an interrupt when the operation has run longer than expected. In System Reset mode, the WDT gives a reset when the timer expires. This is typically used to prevent system hang-up in case of runaway code. The third mode, Interrupt and System Reset mode, combines the other two modes by first giving an inter- rupt and then switch to System Reset mode. This mode will for instance allow a safe shutdown by saving critical parameters before a system reset. The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer to Sys- tem Reset mode. With the fuse programmed the System Reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure program security, altera- tions to the Watchdog set-up must follow timed sequences. The sequence for clearing WDE and changing time-out configuration is as follows: 1. In the same operation, write a logic one to the Watchdog change enable bit (WDCE) and WDE. A logic one must be written to WDE regardless of the previous value of the WDE bit. 2. Within the next four clock cycles, write the WDE and Watchdog prescaler bits (WDP) as desired, but with the WDCE bit cleared. This must be done in one operation. ATtiny48/88 46 8008H–AVR–04/11

ATtiny48/88 The following code example shows one assembly and one C function for turning off the Watch- dog Timer. The example assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during the execution of these functions. Assembly Code Example(1) WDT_off: ; Turn off global interrupt cli ; Reset Watchdog Timer wdr ; Clear WDRF in MCUSR in r16, MCUSR andi r16, (0xff & (0<<WDRF)) out MCUSR, r16 ; Write logical one to WDCE and WDE ; Keep old prescaler setting to prevent unintentional time-out lds r16, WDTCSR ori r16, (1<<WDCE) | (1<<WDE) sts WDTCSR, r16 ; Turn off WDT ldi r16, (0<<WDE) sts WDTCSR, r16 ; Turn on global interrupt sei ret C Code Example(1) void WDT_off(void) { __disable_interrupt(); __watchdog_reset(); /* Clear WDRF in MCUSR */ MCUSR &= ~(1<<WDRF); /* Write logical one to WDCE and WDE */ /* Keep old prescaler setting to prevent unintentional time-out */ WDTCSR |= (1<<WDCE) | (1<<WDE); /* Turn off WDT */ WDTCSR = 0x00; __enable_interrupt(); } Note: 1. See ”About Code Examples” on page 7. Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or Brown-out condition, the device will be reset and the Watchdog Timer will stay enabled. If the code is not set up to handle the Watchdog, this might lead to an eternal loop of time-out resets. To avoid this 47 8008H–AVR–04/11

situation, the application software should always clear the Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialization routine, even if the Watchdog is not in use. The following code example shows one assembly and one C function for changing the time-out value of the Watchdog Timer. Assembly Code Example(1) WDT_Prescaler_Change: ; Turn off global interrupt cli ; Reset Watchdog Timer wdr ; Start timed sequence lds r16, WDTCSR ori r16, (1<<WDCE) | (1<<WDE) sts WDTCSR, r16 ; -- Got four cycles to set the new values from here - ; Set new prescaler(time-out) value = 64K cycles (~0.5 s) ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0) sts WDTCSR, r16 ; -- Finished setting new values, used 2 cycles - ; Turn on global interrupt sei ret C Code Example(1) void WDT_Prescaler_Change(void) { __disable_interrupt(); __watchdog_reset(); /* Start timed sequence */ WDTCSR |= (1<<WDCE) | (1<<WDE); /* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */ WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0); __enable_interrupt(); } Note: 1. See ”About Code Examples” on page 7. Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change in the WDP bits can result in a time-out when switching to a shorter time-out period. ATtiny48/88 48 8008H–AVR–04/11

ATtiny48/88 8.5 Register Description 8.5.1 MCUSR – MCU Status Register The MCU Status Register provides information on which reset source caused an MCU reset. Bit 7 6 5 4 3 2 1 0 0x34 (0x54) – – – – WDRF BORF EXTRF PORF MCUSR Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 See Bit Description (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 3 – WDRF: Watchdog System Reset Flag This bit is set if a Watchdog System Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. (cid:129) Bit 2 – BORF: Brown-out Reset Flag This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. (cid:129) Bit 1 – EXTRF: External Reset Flag This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. (cid:129) Bit 0 – PORF: Power-on Reset Flag This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag. To make use of the Reset Flags to identify a reset condition, the user should read and then Reset the MCUSR as early as possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by examining the Reset Flags. 8.5.2 WDTCSR – Watchdog Timer Control Register Bit 7 6 5 4 3 2 1 0 (0x60) WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCSR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 X 0 0 0 (cid:129) Bit 7 – WDIF: Watchdog Interrupt Flag This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is config- ured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in SREG and WDIE are set, the Watchdog Time-out Interrupt is executed. (cid:129) Bit 6 – WDIE: Watchdog Interrupt Enable When this bit is written to one and the I-bit in the Status Register is set, the Watchdog Interrupt is enabled. If WDE is cleared in combination with this setting, the Watchdog Timer is in Interrupt Mode, and the corresponding interrupt is executed if time-out in the Watchdog Timer occurs. If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. The first time-out in the Watchdog Timer will set WDIF. Executing the corresponding interrupt vector will clear WDIE and WDIF automatically by hardware (the Watchdog goes to System Reset Mode). This is use- 49 8008H–AVR–04/11

ful for keeping the Watchdog Timer security while using the interrupt. To stay in Interrupt and System Reset Mode, WDIE must be set after each interrupt. This should however not be done within the interrupt service routine itself, as this might compromise the safety-function of the Watchdog System Reset mode. If the interrupt is not executed before the next time-out, a Sys- tem Reset will be applied. Table 8-1. Watchdog Timer Configuration WDTON WDE WDIE Mode Action on Time-out 0 0 0 Stopped None 0 0 1 Interrupt Mode Interrupt 0 1 0 System Reset Mode Reset Interrupt, then go to 0 1 1 Interrupt & System Reset Mode System Reset Mode 1 X X System Reset Mode Reset (cid:129) Bit 4 – WDCE: Watchdog Change Enable This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit, and/or change the prescaler bits, WDCE must be set. Once written to one, hardware will clear WDCE after four clock cycles. (cid:129) Bit 3 – WDE: Watchdog System Reset Enable WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is set. To clear WDE, WDRF must be cleared first. This feature ensures multiple resets during con- ditions causing failure, and a safe start-up after the failure. (cid:129) Bits 5, 2:0 – WDP[3:0]: Watchdog Timer Prescaler Bits 3, 2, 1 and 0 The WDP[3:0] bits determine the Watchdog Timer prescaling when the Watchdog Timer is run- ning. The different prescaling values and their corresponding time-out periods are shown in Table 8-2 on page 50. Table 8-2. Watchdog Timer Prescale Select Number of Typical Time-out at WDP3 WDP2 WDP1 WDP0 WDT Oscillator Cycles V = 5.0V CC 0 0 0 0 2K (2048) cycles 16 ms 0 0 0 1 4K (4096) cycles 32 ms 0 0 1 0 8K (8192) cycles 64 ms 0 0 1 1 16K (16384) cycles 0.125 s 0 1 0 0 32K (32768) cycles 0.25 s 0 1 0 1 64K (65536) cycles 0.5 s 0 1 1 0 128K (131072) cycles 1.0 s 0 1 1 1 256K (262144) cycles 2.0 s 1 0 0 0 512K (524288) cycles 4.0 s 1 0 0 1 1024K (1048576) cycles 8.0 s ATtiny48/88 50 8008H–AVR–04/11

ATtiny48/88 Table 8-2. Watchdog Timer Prescale Select (Continued) Number of Typical Time-out at WDP3 WDP2 WDP1 WDP0 WDT Oscillator Cycles V = 5.0V CC 1 0 1 0 1 0 1 1 1 1 0 0 Reserved (1) 1 1 0 1 1 1 1 0 1 1 1 1 Notes: 1. If selected, one of the valid settings below 0b1010 will be used. 51 8008H–AVR–04/11

9. Interrupts This section describes the specifics of interrupt handling in ATtiny48/88. For a general explana- tion of the AVR interrupt handling, refer to “Reset and Interrupt Handling” on page 12. 9.1 Interrupt Vectors Table 9-1. Reset and Interrupt Vectors in ATtiny48/88 Vector Program No. Address Source Interrupt Definition 1 0x000 RESET External/Power-on/Brown-out/Watchdog Reset 2 0x001 INT0 External Interrupt Request 0 3 0x002 INT1 External Interrupt Request 1 4 0x003 PCINT0 Pin Change Interrupt Request 0 5 0x004 PCINT1 Pin Change Interrupt Request 1 6 0x005 PCINT2 Pin Change Interrupt Request 2 7 0x006 PCINT3 Pin Change Interrupt Request 3 8 0x007 WDT Watchdog Time-out Interrupt 9 0x008 TIMER1_CAPT Timer/Counter1 Capture Event 10 0x009 TIMER1_COMPA Timer/Counter1 Compare Match A 11 0x00A TIMER1_COMPB Timer/Counter1 Compare Match B 12 0x00B TIMER1_OVF Timer/Counter1 Overflow 13 0x00C TIMER0_COMPA Timer/Counter0 Compare Match A 14 0x00D TIMER0_COMPB Timer/Counter0 Compare Match B 15 0x00E TIMER0_OVF Timer/Counter0 Overflow 16 0x00F SPI_STC SPI Serial Transfer Complete 17 0x010 ADC ADC Conversion Complete 18 0x011 EE_RDY EEPROM Ready 19 0x012 ANA_COMP Analog Comparator 20 0x013 TWI 2-wire Serial Interface In case the program never enables an interrupt source, the Interrupt Vectors will not be used and, consequently, regular program code can be placed at these locations. ATtiny48/88 52 8008H–AVR–04/11

ATtiny48/88 A typical and general setup for interrupt vector addresses in ATtiny48/88 is shown in the pro- gram example below. Assembly Code Example .org 0x0000 ;Set address of next statement rjmp RESET ; Address 0x0000 rjmp INT0_ISR ; Address 0x0001 rjmp INT1_ISR ; Address 0x0002 rjmp PCINT0_ISR ; Address 0x0003 rjmp PCINT1_ISR ; Address 0x0004 rjmp PCINT2_ISR ; Address 0x0005 rjmp PCINT3_ISR ; Address 0x0006 rjmp WDT_ISR ; Address 0x0007 rjmp TIM1_CAPT_ISR ; Address 0x0008 rjmp TIM1_COMPA_ISR ; Address 0x0009 rjmp TIM1_COMPB_ISR ; Address 0x000A rjmp TIM1_OVF_ISR ; Address 0x000B rjmp TIM0_COMPA_ISR ; Address 0x000C rjmp TIM0_COMPB_ISR ; Address 0x000D rjmp TIM0_OVF_ISR ; Address 0x000E rjmp SPI_STC_ISR ; Address 0x000F rjmp ADC_ISR ; Address 0x0010 rjmp EE_RDY_ISR ; Address 0x0011 rjmp ANA_COMP_ISR ; Address 0x0012 rjmp TWI_ISR ; Address 0x0013 RESET: ; Main program start <instr> ; Address 0x0038 ... Note: See “About Code Examples” on page 7. 9.2 External Interrupts The External Interrupts are triggered by the INT0 and INT1 pins or any of the PCINT[27:0] pins. Observe that, if enabled, the interrupts will trigger even if the INT0 and INT1 or PCINT[27:0] pins are configured as outputs. This feature provides a way of generating a software interrupt, as follows. (cid:129) Pin Change Interrupt PCI3 triggers if a pin in PCINT[27:24] is toggled while enabled (cid:129) Pin Change Interrupt PCI2 triggers if a pin in PCINT[23:16] is toggled while enabled (cid:129) Pin Change Interrupt PCI1 triggers if a pin in PCINT[15:8] is toggled while enabled (cid:129) Pin Change Interrupt PCI0 triggers if a pin in PCINT[7:0] is toggled while enabled The PCMSK3, PCMSK2, PCMSK1 and PCMSK0 registers control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT[27:0] are detected asynchronously. This 53 8008H–AVR–04/11

means that these interrupts can be used for waking the part also from sleep modes other than Idle mode. The INT0 and INT1 interrupts can be triggered by a falling or rising edge, or a low level. This is configured as described in “EICRA – External Interrupt Control Register A” on page 55. When INT0 or INT1 interrupts are enabled and are configured as level triggered, the interrupts will trig- ger as long as the corresponding pin is held low. Note that recognition of falling or rising edge interrupts on INT0 or INT1 requires the presence of an I/O clock, described in “I/O Clock – clkI/O” on page 28. 9.2.1 Pin Change Interrupt Timing An example of timing of a pin change interrupt is shown in Figure 9-1. Figure 9-1. Timing of pin change interrupts pin_lat pcint_in_(0) PCINT(0) D Q 0 pcint_syn pcint_setflag pin_sync PCIF LE x clk PCINT(0) in PCMSK(x) clk clk PCINT(0) pin_lat pin_sync pcint_in_(0) pcint_syn pcint_setflag PCIF 9.2.2 Low Level Interrupt Low level interrupts on INT0 and INT1 are detected asynchronously. This means that the inter- rupt sources can be used for waking the part also from sleep modes other than Idle (the I/O clock is halted in all sleep modes except Idle mode). Note that if a level triggered interrupt is used for wake-up from Power-down, the required level must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the Start-up Time, the MCU will still wake up, but no inter- ATtiny48/88 54 8008H–AVR–04/11

ATtiny48/88 rupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described in Table 6-5 on page 33. If the low level on the interrupt pin is removed before the device has woken up then program execution will not be diverted to the interrupt service routine but continue from the instruction fol- lowing the SLEEP command. 9.3 Register Description 9.3.1 EICRA – External Interrupt Control Register A The External Interrupt Control Register A contains control bits for interrupt sense control. Bit 7 6 5 4 3 2 1 0 (0x69) – – – – ISC11 ISC10 ISC01 ISC00 EICRA Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 3:2 – ISC1[1:0]: Interrupt Sense Control 1 Bit 1 and Bit 0 The External Interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the corre- sponding interrupt mask are set. The level and edges on the external INT1 pin that activate the interrupt are defined in Table 9-2. The value on the INT1 pin is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. Table 9-2. Interrupt 1 Sense Control ISC11 ISC10 Description 0 0 The low level of INT1 generates an interrupt request. 0 1 Any logical change on INT1 generates an interrupt request. 1 0 The falling edge of INT1 generates an interrupt request. 1 1 The rising edge of INT1 generates an interrupt request. (cid:129) Bits 1:0 – ISC0[1:0]: Interrupt Sense Control 0 Bit 1 and Bit 0 The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corre- sponding interrupt mask are set. The level and edges on the external INT0 pin that activate the interrupt are defined in Table 9-3. The value on the INT0 pin is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is 55 8008H–AVR–04/11

selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. Table 9-3. Interrupt 0 Sense Control ISC01 ISC00 Description 0 0 The low level of INT0 generates an interrupt request. 0 1 Any logical change on INT0 generates an interrupt request. 1 0 The falling edge of INT0 generates an interrupt request. 1 1 The rising edge of INT0 generates an interrupt request. 9.3.2 EIMSK – External Interrupt Mask Register Bit 7 6 5 4 3 2 1 0 0x1D (0x3D) – – – – – – INT1 INT0 EIMSK Read/Write R R R R R R R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:2 – Res: Reserved Bits These bits are unused in ATtiny48/88, and will always read as zero. (cid:129) Bit 1 – INT1: External Interrupt Request 1 Enable When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter- nal pin interrupt is enabled. The Interrupt Sense Control bits (ISC11 and ISC10) in the External Interrupt Control Register A (EICRA) define whether the external interrupt is activated on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an interrupt request even if INT1 is configured as an output. The corresponding interrupt of External Interrupt Request 1 is executed from the INT1 Interrupt Vector. (cid:129) Bit 0 – INT0: External Interrupt Request 0 Enable When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter- nal pin interrupt is enabled. The Interrupt Sense Control bits (ISC01 and ISC00) in the External Interrupt Control Register A (EICRA) define whether the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt Vector. 9.3.3 EIFR – External Interrupt Flag Register Bit 7 6 5 4 3 2 1 0 0x1C (0x3C) – – – – – – INTF1 INTF0 EIFR Read/Write R R R R R R R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:2 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 1 – INTF1: External Interrupt Flag 1 When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set (one). If the I-bit in SREG and the INT1 bit in EIMSK are set (one), the MCU will jump to the cor- ATtiny48/88 56 8008H–AVR–04/11

ATtiny48/88 responding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared when INT1 is configured as a level interrupt. (cid:129) Bit 0 – INTF0: External Interrupt Flag 0 When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If the I-bit in SREG and the INT0 bit in EIMSK are set (one), the MCU will jump to the cor- responding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared when INT0 is configured as a level interrupt. 9.3.4 PCICR – Pin Change Interrupt Control Register Bit 7 6 5 4 3 2 1 0 (0x68) – – – – PCIE3 PCIE2 PCIE1 PCIE0 PCICR Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 3 – PCIE3: Pin Change Interrupt Enable 3 When the PCIE3 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 3 is enabled. Any change on any enabled PCINT[27:24] pin will cause an inter- rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI3 Interrupt Vector. PCINT[27:24] pins are enabled individually by the PCMSK3 Register. (cid:129) Bit 2 – PCIE2: Pin Change Interrupt Enable 2 When the PCIE2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 2 is enabled. Any change on any enabled PCINT[23:16] pin will cause an inter- rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI2 Interrupt Vector. PCINT[23:16] pins are enabled individually by the PCMSK2 Register. (cid:129) Bit 1 – PCIE1: Pin Change Interrupt Enable 1 When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 1 is enabled. Any change on any enabled PCINT[15:8] pin will cause an inter- rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1 Interrupt Vector. PCINT[15:8] pins are enabled individually by the PCMSK1 Register. (cid:129) Bit 0 – PCIE0: Pin Change Interrupt Enable 0 When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 0 is enabled. Any change on any enabled PCINT[7:0] pin will cause an inter- rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0 Interrupt Vector. PCINT[7:0] pins are enabled individually by the PCMSK0 Register. 57 8008H–AVR–04/11

9.3.5 PCIFR – Pin Change Interrupt Flag Register Bit 7 6 5 4 3 2 1 0 0x1B (0x3B) – – – – PCIF3 PCIF2 PCIF1 PCIF0 PCIFR Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 3 – PCIF3: Pin Change Interrupt Flag 3 When a logic change on any PCINT[27:24] pin triggers an interrupt request, PCIF3 becomes set (one). If the I-bit in SREG and the PCIE3 bit in PCICR are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter- natively, the flag can be cleared by writing a logical one to it. (cid:129) Bit 2 – PCIF2: Pin Change Interrupt Flag 2 When a logic change on any PCINT[23:16] pin triggers an interrupt request, PCIF2 becomes set (one). If the I-bit in SREG and the PCIE2 bit in PCICR are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter- natively, the flag can be cleared by writing a logical one to it. (cid:129) Bit 1 – PCIF1: Pin Change Interrupt Flag 1 When a logic change on any PCINT[15:8] pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in SREG and the PCIE1 bit in PCICR are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter- natively, the flag can be cleared by writing a logical one to it. (cid:129) Bit 0 – PCIF0: Pin Change Interrupt Flag 0 When a logic change on any PCINT[7:0] pin triggers an interrupt request, PCIF0 becomes set (one). If the I-bit in SREG and the PCIE0 bit in PCICR are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter- natively, the flag can be cleared by writing a logical one to it. 9.3.6 PCMSK3 – Pin Change Mask Register 3 Bit 7 6 5 4 3 2 1 0 (0x6A) – – – – PCINT27 PCINT26 PCINT25 PCINT24 PCMSK3 Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 3:0 – PCINT[27:24]: Pin Change Enable Mask 27:24 Each PCINT[27:24] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[27:24] is set and the PCIE3 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT[27:24] is cleared, pin change interrupt on the corresponding I/O pin is disabled. ATtiny48/88 58 8008H–AVR–04/11

ATtiny48/88 9.3.7 PCMSK2 – Pin Change Mask Register 2 Bit 7 6 5 4 3 2 1 0 (0x6D) PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 PCMSK2 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – PCINT[23:16]: Pin Change Enable Mask 23:16 Each PCINT[23:16] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[23:16] is set and the PCIE2 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT[23:16] is cleared, pin change interrupt on the corresponding I/O pin is disabled. 9.3.8 PCMSK1 – Pin Change Mask Register 1 Bit 7 6 5 4 3 2 1 0 (0x6C) PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – PCINT[15:8]: Pin Change Enable Mask 15:8 Each PCINT[15:8] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[15:8] is set and the PCIE1 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT[15:8] is cleared, pin change interrupt on the corresponding I/O pin is disabled. 9.3.9 PCMSK0 – Pin Change Mask Register 0 Bit 7 6 5 4 3 2 1 0 (0x6B) PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – PCINT[7:0]: Pin Change Enable Mask 7:0 Each PCINT[7:0] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[7:0] is set and the PCIE0 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT[7:0] is cleared, pin change interrupt on the corresponding I/O pin is disabled. 59 8008H–AVR–04/11

10. I/O-Ports 10.1 Introduction All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The same applies when chang- ing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as input). The pin driver is strong enough to drive LED displays directly. All port pins have individu- ally selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both V and Ground as indicated in Figure 10-1. Refer to “Electrical Char- CC acteristics” on page 206 for a complete list of parameters. Figure 10-1. I/O Pin Equivalent Schematic R pu Pxn Logic See Figure "General Digital I/O" for Details All registers and bit references in this section are written in general form. A lower case “x” repre- sents the numbering letter for the port, and a lower case “n” represents the bit number. However, when using the register or bit defines in a program, the precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Regis- ters and bit locations are listed in “Register Description” on page 77. Three I/O memory address locations are allocated for each port, one each for the Data Register – PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins I/O location is read only, while the Data Register and the Data Direction Register are read/write. However, writing a logic one to a bit in the PINx Register, will result in a toggle in the correspond- ing bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables the pull-up function for all pins in all ports when set. Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page 61. Most port pins are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes with the port pin is described in “Alternate Port Functions” on page 65. Refer to the individual module sections for a full description of the alter- nate functions. Note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as general digital I/O. ATtiny48/88 60 8008H–AVR–04/11

ATtiny48/88 10.2 Ports as General Digital I/O The ports are bi-directional I/O ports with optional internal pull-ups. Figure 10-2 shows a func- tional description of one I/O-port pin, here generically called Pxn. Figure 10-2. General Digital I/O(1) PUD Q D DDxn QCLR WDx RESET RDx S 1 U Pxn Q D B PORTxn 0 A QCLR T A RESET D WPx WRx SLEEP RRx SYNCHRONIZER RPx D Q D Q PINxn L Q Q clk I/O WDx: WRITE DDRx PUD: PULLUP DISABLE RDx: READ DDRx SLEEP: SLEEP CONTROL WRx: WRITE PORTx clk : I/O CLOCK RRx: READ PORTx REGISTER I/O RPx: READ PORTx PIN WPx: WRITE PINx REGISTER Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk , I/O SLEEP, and PUD are common to all ports. 10.2.1 Configuring the Pin Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register Description” on page 77, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address. The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin. If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-stated when reset condition becomes active, even if no clocks are running. 61 8008H–AVR–04/11

If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero). 10.2.2 Toggling the Pin Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction can be used to toggle one single bit in a port. 10.2.3 Break-Before-Make Switching In the Break-Before-Make mode when switching the DDRxn bit from input to output an immedi- ate tri-state period lasting one system clock cycle is introduced as indicated in Figure 10-3. For example, if the system clock is 4 MHz and the DDRxn is written to make an output, the immedi- ate tri-state period of 250 ns is introduced, before the value of PORTxn is seen on the port pin. To avoid glitches it is recommended that the maximum DDRxn toggle frequency is two system clock cycles. The Break-Before-Make is a port-wise mode and it is activated by the port-wise BBMx enable bits. For details on BBMx bits, see “PORTCR – Port Control Register” on page 77. When switching the DDRxn bit from output to input there is no immediate tri-state period introduced. Figure 10-3. Break Before Make, switching between input and output SYSTEM CLK R16 0x02 R17 0x01 INSTRUCTIONS out DDRx, r16 nop out DDRx, r17 PORTx 0x55 DDRx 0x01 0x02 0x01 Px0 tri-state Px1 tri-state tri-state intermediate tri-state cycle intermediate tri-state cycle 10.2.4 Switching Between Input and Output When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn} = 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully accept- able, as a high-impedant environment will not notice the difference between a strong high driver and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all pull-ups in all ports. Switching between input with pull-up and output low generates the same problem. The user must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn} = 0b11) as an intermediate step. ATtiny48/88 62 8008H–AVR–04/11

ATtiny48/88 Table 10-1 summarizes the control signals for the pin value. Table 10-1. Port Pin Configurations PUD DDxn PORTxn (in MCUCR) (1) I/O Pull-up Comment 0 0 X Input No Tri-state (Hi-Z) 0 1 0 Input Yes Pxn will source current if ext. pulled low. 0 1 1 Input No Tri-state (Hi-Z) 1 0 X Output No Output Low (Sink) 1 1 X Output No Output High (Source) Note: 1. Or port-wise PUDx bit in PORTCR register. 10.2.5 Reading the Pin Value Independent of the setting of Data Direction bit DDxn, the port pin can be read through the PINxn Register bit. As shown in Figure 10-2, the PINxn Register bit and the preceding latch con- stitute a synchronizer. This is needed to avoid metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. Figure 10-4 shows a timing dia- gram of the synchronization when reading an externally applied pin value. The maximum and minimum propagation delays are denoted t and t respectively. pd,max pd,min Figure 10-4. Synchronization when Reading an Externally Applied Pin value SYSTEM CLK INSTRUCTIONS XXX XXX in r17, PINx SYNC LATCH PINxn r17 0x00 0xFF t pd, max tpd, min Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the clock is low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indi- cated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed between ½ and 1½ system clock period depending upon the time of assertion. When reading back a software assigned pin value, a nop instruction must be inserted as indi- cated in Figure 10-5. The out instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay tpd through the synchronizer is 1 system clock period. 63 8008H–AVR–04/11

Figure 10-5. Synchronization when Reading a Software Assigned Pin Value SYSTEM CLK r16 0xFF INSTRUCTIONS out PORTx, r16 nop in r17, PINx SYNC LATCH PINxn r17 0x00 0xFF t pd The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The resulting pin values are read back again, but as previously discussed, a nop instruction is included to be able to read back the value recently assigned to some of the pins. Assembly Code Example(1) ... ; Define pull-ups and set outputs high ; Define directions for port pins ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0) ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0) out PORTB,r16 out DDRB,r17 ; Insert nop for synchronization nop ; Read port pins in r16,PINB ... Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull- ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as strong high drivers. ATtiny48/88 64 8008H–AVR–04/11

ATtiny48/88 C Code Example unsigned char i; ... /* Define pull-ups and set outputs high */ /* Define directions for port pins */ PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0); DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0); /* Insert nop for synchronization*/ __no_operation(); /* Read port pins */ i = PINB; ... 10.2.6 Digital Input Enable and Sleep Modes As shown in Figure 10-2, the digital input signal can be clamped to ground at the input of the Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to V /2. CC SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various other alternate functions as described in “Alternate Port Functions” on page 65. If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt is not enabled, the corresponding External Interrupt Flag will be set when resuming from the above mentioned Sleep mode, as the clamping in these sleep mode produces the requested logic change. 10.2.7 Unconnected Pins If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital inputs are disabled in the deep sleep modes as described above, float- ing inputs should be avoided to reduce current consumption in all other modes where the digital inputs are enabled (Reset, Active mode and Idle mode). The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or pull-down. Connecting unused pins directly to V or GND is not recommended, since this may cause excessive currents if the pin is CC accidentally configured as an output. 10.3 Alternate Port Functions Most port pins have alternate functions in addition to being general digital I/Os. Figure 10-6 shows how the port pin control signals from the simplified Figure 10-2 can be overridden by alternate functions. The overriding signals may not be present in all port pins, but the figure serves as a generic description applicable to all port pins in the AVR microcontroller family. 65 8008H–AVR–04/11

Figure 10-6. Alternate Port Functions(1) PUOExn PUOVxn 1 PUD 0 DDOExn DDOVxn 1 0 Q D DDxn QCLR WDx PVOExn RESET RDx PVOVxn S 1 1 U Pxn B 0 Q D 0 A PORTxn PTOExn AT DIEOExn QCLR D WPx DIEOVxn RESET 1 WRx RRx 0 SLEEP SYNCHRONIZER RPx DSETQ D Q PINxn LCLRQ CLRQ clkI/O DIxn AIOxn PUOExn: Pxn PULL-UP OVERRIDE ENABLE PUD: PULLUP DISABLE PUOVxn: Pxn PULL-UP OVERRIDE VALUE WDx: WRITE DDRx DDOExn: Pxn DATA DIRECTION OVERRIDE ENABLE RDx: READ DDRx DDOVxn: Pxn DATA DIRECTION OVERRIDE VALUE RRx: READ PORTx REGISTER PVOExn: Pxn PORT VALUE OVERRIDE ENABLE WRx: WRITE PORTx PVOVxn: Pxn PORT VALUE OVERRIDE VALUE RPx: READ PORTx PIN DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE WPx: WRITE PINx DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE clk : I/O CLOCK SLEEP: SLEEP CONTROL DIxI/nO: DIGITAL INPUT PIN n ON PORTx PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk , I/O SLEEP, and PUD are common to all ports. All other signals are unique for each pin. ATtiny48/88 66 8008H–AVR–04/11

ATtiny48/88 Table 10-2 summarizes the function of the overriding signals. The pin and port indexes from Fig- ure 10-6 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function. Table 10-2. Generic Description of Overriding Signals for Alternate Functions Signal Name Full Name Description If this signal is set, the pull-up enable is controlled by the PUOV Pull-up Override PUOE signal. If this signal is cleared, the pull-up is enabled when Enable {DDxn, PORTxn, PUD} = 0b010. If PUOE is set, the pull-up is enabled/disabled when PUOV is Pull-up Override PUOV set/cleared, regardless of the setting of the DDxn, PORTxn, Value and PUD Register bits. If this signal is set, the Output Driver Enable is controlled by the Data Direction DDOE DDOV signal. If this signal is cleared, the Output driver is Override Enable enabled by the DDxn Register bit. If DDOE is set, the Output Driver is enabled/disabled when Data Direction DDOV DDOV is set/cleared, regardless of the setting of the DDxn Override Value Register bit. If this signal is set and the Output Driver is enabled, the port Port Value value is controlled by the PVOV signal. If PVOE is cleared, and PVOE Override Enable the Output Driver is enabled, the port Value is controlled by the PORTxn Register bit. Port Value If PVOE is set, the port value is set to PVOV, regardless of the PVOV Override Value setting of the PORTxn Register bit. Port Toggle PTOE If PTOE is set, the PORTxn Register bit is inverted. Override Enable Digital Input If this bit is set, the Digital Input Enable is controlled by the DIEOE Enable Override DIEOV signal. If this signal is cleared, the Digital Input Enable Enable is determined by MCU state (Normal mode, sleep mode). Digital Input If DIEOE is set, the Digital Input is enabled/disabled when DIEOV Enable Override DIEOV is set/cleared, regardless of the MCU state (Normal Value mode, sleep mode). This is the Digital Input to alternate functions. In the figure, the signal is connected to the output of the Schmitt Trigger but DI Digital Input before the synchronizer. Unless the Digital Input is used as a clock source, the module with the alternate function will use its own synchronizer. This is the Analog Input/output to/from alternate functions. The Analog AIO signal is connected directly to the pad, and can be used bi- Input/Output directionally. The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the alternate function. Refer to the alternate function description for further details. 67 8008H–AVR–04/11

10.3.1 Alternate Functions of Port A The Port A pins with alternate functions are shown in Table 10-3. Table 10-3. Port A Pins Alternate Functions Port Pin Alternate Function PA3 PCINT27 (Pin Change Interrupt 27) PA2 PCINT26 (Pin Change Interrupt 26) ADC7 (ADC Input Channel 7) PA1 PCINT25 (Pin Change Interrupt 25) ADC6 (ADC Input Channel 6) PA0 PCINT24 (Pin Change Interrupt 24) The alternate pin configuration is as follows: (cid:129) PCINT27 – Port A, Bit 3 PCINT27: Pin Change Interrupt source 27. (cid:129) PCINT26 – Port A, Bit 2 PCINT26: Pin Change Interrupt source 26. (cid:129) ADC7/PCINT25 – Port A, Bit 1 ADC7: PA1 can be used as ADC input Channel 7. PCINT25: Pin Change Interrupt source 25. (cid:129) ADC6/PCINT24 – Port A, Bit 0 ADC6: PA0 can be used as ADC input Channel 6. PCINT24: Pin Change Interrupt source 24. Table 10-4 relate the alternate functions of Port A to the overriding signals shown in Figure 10-6 on page 66. Table 10-4. Overriding Signals for Alternate Functions in PA[3:0] Signal Name PA3/PCINT27 PA2/PCINT26 PA1/ADC7/PCINT25 PA0/ADC6/PCINT24 PUOE 0 0 0 0 PUO 0 0 0 0 DDOE 0 0 0 0 DDOV 0 0 0 0 PVOE 0 0 0 0 PVOV 0 0 0 0 PCINT27 (cid:129) PCINT26 (cid:129) PCINT25 (cid:129) PCIE3 + PCINT24 (cid:129) PCIE3 + DIEOE PCIE3 PCIE3 ADC7D ADC6D DIEOV 1 1 1 1 DI PCINT27 INPUT PCINT26 INPUT PCINT25 INPUT PCINT24 INPUT AIO – – ADC7 INPUT ADC6 INPUT ATtiny48/88 68 8008H–AVR–04/11

ATtiny48/88 10.3.2 Alternate Functions of Port B The Port B pins with alternate functions are shown in Table 10-5. Table 10-5. Port B Pins Alternate Functions Port Pin Alternate Functions PB7 PCINT7 (Pin Change Interrupt 7) CLKI (External clock input) PB6 PCINT6 (Pin Change Interrupt 6) SCK (SPI Bus Master clock Input) PB5 PCINT5 (Pin Change Interrupt 5) MISO (SPI Bus Master Input/Slave Output) PB4 PCINT4 (Pin Change Interrupt 4) MOSI (SPI Bus Master Output/Slave Input) PB3 PCINT3 (Pin Change Interrupt 3) SS (SPI Bus Master Slave select) PB2 OC1B (Timer/Counter1 Output Compare Match B Output) PCINT2 (Pin Change Interrupt 2) OC1A (Timer/Counter1 Output Compare Match A Output) PB1 PCINT1 (Pin Change Interrupt 1) ICP1 (Timer/Counter1 Input Capture Input) PB0 CLKO (Divided System Clock Output) PCINT0 (Pin Change Interrupt 0) The alternate pin configuration is as follows: (cid:129) PCINT7 – Port B, Bit 7 PCINT7: Pin Change Interrupt source 7. The PB7 pin can serve as an external interrupt source. If PB7 is used as a clock pin, DDB7, PORTB7 and PINB7 will all read 0. (cid:129) CLKI/PCINT6 – Port B, Bit 6 CLKI: External clock input. When used as a clock pin, the pin can not be used as an I/O pin. PCINT6: Pin Change Interrupt source 6. The PB6 pin can serve as an external interrupt source. If PB6 is used as a clock pin, DDB6, PORTB6 and PINB6 will all read 0. (cid:129) SCK/PCINT5 – Port B, Bit 5 SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB5. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit. PCINT5: Pin Change Interrupt source 5. The PB5 pin can serve as an external interrupt source. (cid:129) MISO/PCINT4 – Port B, Bit 4 MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master, this pin is configured as an input regardless of the setting of DDB4. When the SPI is enabled as a Slave, the data direction of this pin is controlled by DDB4. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB4 bit. 69 8008H–AVR–04/11

PCINT4: Pin Change Interrupt source 4. The PB4 pin can serve as an external interrupt source. (cid:129) MOSI/PCINT3 – Port B, Bit 3 MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB3. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB3. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB3 bit. PCINT3: Pin Change Interrupt source 3. The PB3 pin can serve as an external interrupt source. (cid:129) SS/OC1B/PCINT2 – Port B, Bit 2 SS: Slave Select input. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB2. As a Slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB2. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB2 bit. OC1B, Output Compare Match output: The PB2 pin can serve as an external output for the Timer/Counter1 Compare Match B. The PB2 pin has to be configured as an output (DDB2 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM mode timer function. PCINT2: Pin Change Interrupt source 2. The PB2 pin can serve as an external interrupt source. (cid:129) OC1A/PCINT1 – Port B, Bit 1 OC1A, Output Compare Match output: The PB1 pin can serve as an external output for the Timer/Counter1 Compare Match A. The PB1 pin has to be configured as an output (DDB1 set (one)) to serve this function. The OC1A pin is also the output pin for the PWM mode timer function. PCINT1: Pin Change Interrupt source 1. The PB1 pin can serve as an external interrupt source. (cid:129) ICP1/CLKO/PCINT0 – Port B, Bit 0 ICP1, Input Capture Pin: The PB0 pin can act as an Input Capture Pin for Timer/Counter1. CLKO, Divided System Clock: The divided system clock can be output on the PB0 pin. The divided system clock will be output if the CKOUT Fuse is programmed, regardless of the PORTB0 and DDB0 settings. It will also be output during reset. PCINT0: Pin Change Interrupt source 0. The PB0 pin can serve as an external interrupt source. Table 10-6 and Table 10-7 relate the alternate functions of Port B to the overriding signals shown in Figure 10-6 on page 66. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT. ATtiny48/88 70 8008H–AVR–04/11

ATtiny48/88 Table 10-6. Overriding Signals for Alternate Functions in PB[7:4] Signal PB7/ PB6/CLKI/ PB5/SCK/ PB4/MISO/ Name PCINT7(1) PCINT6(1) PCINT5 PCINT4 PUOE 0 INTOSC SPE (cid:129) MSTR SPE (cid:129) MSTR PUOV 0 0 PORTB5 (cid:129) PUD PORTB4 (cid:129) PUD DDOE 0 INTOSC SPE (cid:129) MSTR SPE (cid:129) MSTR DDOV 0 0 0 0 PVOE 0 0 SPE (cid:129) MSTR SPE (cid:129) MSTR SPI SLAVE PVOV 0 0 SCK OUTPUT OUTPUT INTOSC + PCINT6 (cid:129) DIEOE PCINT7 (cid:129) PCIE0 PCINT5 (cid:129) PCIE0 PCINT4 (cid:129) PCIE0 PCIE0 DIEOV 1 INTOSC 1 1 PCINT5 INPUT PCINT4 INPUT DI PCINT7 INPUT PCINT6 INPUT SCK INPUT SPI MSTR INPUT AIO – Clock Input – – Notes: 1. INTOSC means that one of the internal oscillators are selected (by the CKSEL fuses), EXTCK means that external clock is selected (by the CKSEL fuses). Table 10-7. Overriding Signals for Alternate Functions in PB[3:0] Signal PB3/MOSI/ PB2/SS/OC1B/ PB1/OC1A/ PB0/ICP1/ Name PCINT3 PCINT2 PCINT1 PCINT0 PUOE SPE (cid:129) MSTR SPE (cid:129) MSTR 0 0 PUOV PORTB3 (cid:129) PUD PORTB2 (cid:129) PUD 0 0 DDOE SPE (cid:129) MSTR SPE (cid:129) MSTR 0 0 DDOV 0 0 0 0 PVOE SPE (cid:129) MSTR OC1B ENABLE OC1A ENABLE 0 PVOV SPI MSTR OUTPUT OC1B OC1A 0 DIEOE PCINT3 (cid:129) PCIE0 PCINT2 (cid:129) PCIE0 PCINT1 (cid:129) PCIE0 PCINT0 (cid:129) PCIE0 DIEOV 1 1 1 1 PCINT3 INPUT PCINT2 INPUT PCINT0 INPUT DI PCINT1 INPUT SPI SLAVE INPUT SPI SS ICP1 INPUT AIO – – – – 71 8008H–AVR–04/11

10.3.3 Alternate Functions of Port C The Port C pins with alternate functions are shown in Table 10-8. Table 10-8. Port C Pins Alternate Functions Port Pin Alternate Function PC7 PCINT15 (Pin Change Interrupt 15) RESET (Reset pin) PC6 PCINT14 (Pin Change Interrupt 14) ADC5 (ADC Input Channel 5) PC5 SCL (2-wire Serial Bus Clock Line) PCINT13 (Pin Change Interrupt 13) ADC4 (ADC Input Channel 4) PC4 SDA (2-wire Serial Bus Data Input/Output Line) PCINT12 (Pin Change Interrupt 12) ADC3 (ADC Input Channel 3) PC3 PCINT11 (Pin Change Interrupt 11) ADC2 (ADC Input Channel 2) PC2 PCINT10 (Pin Change Interrupt 10) ADC1 (ADC Input Channel 1) PC1 PCINT9 (Pin Change Interrupt 9) ADC0 (ADC Input Channel 0) PC0 PCINT8 (Pin Change Interrupt 8) The alternate pin configuration is as follows: (cid:129) PCINT15 – Port C, Bit 7 PCINT15: Pin Change Interrupt source 15. The PC7 pin can serve as an external interrupt source. (cid:129) RESET/PCINT14 – Port C, Bit 6 RESET, Reset pin: When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources. When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the pin can not be used as an I/O pin. If PC6 is used as a reset pin, DDC6, PORTC6 and PINC6 will all read 0. PCINT14: Pin Change Interrupt source 14. The PC6 pin can serve as an external interrupt source. (cid:129) SCL/ADC5/PCINT13 – Port C, Bit 5 SCL, 2-wire Serial Interface Clock: When the TWEN bit in TWCR is set (one) to enable the 2- wire Serial Interface, pin PC5 is disconnected from the port and becomes the Serial Clock I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation. PC5 can also be used as ADC input Channel 5. Note that ADC input channel 5 uses digital power. ATtiny48/88 72 8008H–AVR–04/11

ATtiny48/88 PCINT13: Pin Change Interrupt source 13. The PC5 pin can serve as an external interrupt source. (cid:129) SDA/ADC4/PCINT12 – Port C, Bit 4 SDA, 2-wire Serial Interface Data: When the TWEN bit in TWCR is set (one) to enable the 2-wire Serial Interface, pin PC4 is disconnected from the port and becomes the Serial Data I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew- rate limitation. PC4 can also be used as ADC input Channel 4. Note that ADC input channel 4 uses digital power. PCINT12: Pin Change Interrupt source 12. The PC4 pin can serve as an external interrupt source. (cid:129) ADC3/PCINT11 – Port C, Bit 3 PC3 can also be used as ADC input Channel 3. Note that ADC input channel 3 uses analog power. PCINT11: Pin Change Interrupt source 11. The PC3 pin can serve as an external interrupt source. (cid:129) ADC2/PCINT10 – Port C, Bit 2 PC2 can also be used as ADC input Channel 2. Note that ADC input channel 2 uses analog power. PCINT10: Pin Change Interrupt source 10. The PC2 pin can serve as an external interrupt source. (cid:129) ADC1/PCINT9 – Port C, Bit 1 PC1 can also be used as ADC input Channel 1. Note that ADC input channel 1 uses analog power. PCINT9: Pin Change Interrupt source 9. The PC1 pin can serve as an external interrupt source. (cid:129) ADC0/PCINT8 – Port C, Bit 0 PC0 can also be used as ADC input Channel 0. Note that ADC input channel 0 uses analog power. PCINT8: Pin Change Interrupt source 8. The PC0 pin can serve as an external interrupt source. 73 8008H–AVR–04/11

Table 10-9 and Table 10-10 relate the alternate functions of Port C to the overriding signals shown in Figure 10-6 on page 66. Table 10-9. Overriding Signals for Alternate Functions in PC[6:4](1) Signal PC6/RESET/ PC5/SCL/ADC5/ PC4/SDA/ADC4/ Name PC7/PCINT15 PCINT14 PCINT13 PCINT12 PUOE 0 RSTDISBL TWEN TWEN PUOV 0 1 PORTC5 (cid:129) PUD PORTC4 (cid:129) PUD DDOE 0 RSTDISBL TWEN TWEN DDOV 0 0 SCL_OUT SDA_OUT PVOE 0 0 TWEN TWEN PVOV 0 0 0 0 RSTDISBL + PCINT13 (cid:129) PCIE1 + PCINT12 (cid:129) PCIE1 + DIEOE PCINT15 (cid:129) PCIE1 PCINT14 (cid:129) PCIE1 ADC5D ADC4D DIEOV 1 RSTDISBL PCINT13 (cid:129) PCIE1 PCINT12 (cid:129) PCIE1 DI PCINT15 INPUT PCINT14 INPUT PCINT13 INPUT PCINT12 INPUT ADC5 INPUT / SCL ADC4 INPUT / SDA AIO - RESET INPUT INPUT INPUT Note: 1. When enabled, the 2-wire Serial Interface enables slew-rate controls on the output pins PC4 and PC5. This is not shown in the figure. In addition, spike filters are connected between the AIO outputs shown in the port figure and the digital logic of the TWI module. Table 10-10. Overriding Signals for Alternate Functions in PC[3:0] Signal PC3/ADC3/ PC2/ADC2/ PC1/ADC1/ PC0/ADC0/ Name PCINT11 PCINT10 PCINT9 PCINT8 PUOE 0 0 0 0 PUOV 0 0 0 0 DDOE 0 0 0 0 DDOV 0 0 0 0 PVOE 0 0 0 0 PVOV 0 0 0 0 PCINT11 (cid:129) PCIE1 + PCINT10 (cid:129) PCIE1 + PCINT9 (cid:129) PCIE1 + PCINT8 (cid:129) PCIE1 + DIEOE ADC3D ADC2D ADC1D ADC0D DIEOV PCINT11 (cid:129) PCIE1 PCINT10 (cid:129) PCIE1 PCINT9 (cid:129) PCIE1 PCINT8 (cid:129) PCIE1 DI PCINT11 INPUT PCINT10 INPUT PCINT9 INPUT PCINT8 INPUT AIO ADC3 INPUT ADC2 INPUT ADC1 INPUT ADC0 INPUT ATtiny48/88 74 8008H–AVR–04/11

ATtiny48/88 10.3.4 Alternate Functions of Port D The Port D pins with alternate functions are shown in Table 10-11. Table 10-11. Port D Pins Alternate Functions Port Pin Alternate Function AIN1 (Analog Comparator Negative Input) PD7 PCINT23 (Pin Change Interrupt 23) AIN0 (Analog Comparator Positive Input) PD6 PCINT22 (Pin Change Interrupt 22) T1 (Timer/Counter 1 External Counter Input) PD5 PCINT21 (Pin Change Interrupt 21) T0 (Timer/Counter 0 External Counter Input) PD4 PCINT20 (Pin Change Interrupt 20) INT1 (External Interrupt 1 Input) PD3 PCINT19 (Pin Change Interrupt 19) INT0 (External Interrupt 0 Input) PD2 PCINT18 (Pin Change Interrupt 18) PD1 PCINT17 (Pin Change Interrupt 17) PD0 PCINT16 (Pin Change Interrupt 16) The alternate pin configuration is as follows: (cid:129) AIN1/PCINT23 – Port D, Bit 7 AIN1: Analog Comparator Negative Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. PCINT23: Pin Change Interrupt source 23. The PD7 pin can serve as an external interrupt source. (cid:129) AIN0/PCINT22 – Port D, Bit 6 AIN0: Analog Comparator Positive Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. PCINT22: Pin Change Interrupt source 22. The PD6 pin can serve as an external interrupt source. (cid:129) T1/PCINT21 – Port D, Bit 5 T1: Timer/Counter1 counter source. PCINT21: Pin Change Interrupt source 21. The PD5 pin can serve as an external interrupt source. (cid:129) T0/PCINT20 – Port D, Bit 4 T0: Timer/Counter0 counter source. PCINT20: Pin Change Interrupt source 20. The PD4 pin can serve as an external interrupt source. 75 8008H–AVR–04/11

(cid:129) INT1/PCINT19 – Port D, Bit 3 INT1, External Interrupt source 1: The PD3 pin can serve as an external interrupt source. PCINT19: Pin Change Interrupt source 19. The PD3 pin can serve as an external interrupt source. (cid:129) INT0/PCINT18 – Port D, Bit 2 INT0, External Interrupt source 0: The PD2 pin can serve as an external interrupt source. PCINT18: Pin Change Interrupt source 18. The PD2 pin can serve as an external interrupt source. (cid:129) PCINT17 – Port D, Bit 1 PCINT17: Pin Change Interrupt source 17. The PD1 pin can serve as an external interrupt source. (cid:129) PCINT16 – Port D, Bit 0 PCINT16: Pin Change Interrupt source 16. The PD0 pin can serve as an external interrupt source. Table 10-12 and Table 10-13 relate the alternate functions of Port D to the overriding signals shown in Figure 10-6 on page 66. Table 10-12. Overriding Signals for Alternate Functions PD[7:4] Signal Name PD7/AIN1/PCINT23 PD6/AIN0/PCINT22 PD5/T1/PCINT21 PD4/T0/PCINT20 PUOE 0 0 0 0 PUO 0 0 0 0 DDOE 0 0 0 0 DDOV 0 0 0 0 PVOE 0 0 0 0 PVOV 0 0 0 0 DIEOE PCINT23 (cid:129) PCIE2 PCINT22 (cid:129) PCIE2 PCINT21 (cid:129) PCIE2 PCINT20 (cid:129) PCIE2 DIEOV 1 1 1 1 PCINT21 INPUT PCINT20 INPUT DI PCINT23 INPUT PCINT22 INPUT T1 INPUT T0 INPUT AIO AIN1 INPUT AIN0 INPUT – – ATtiny48/88 76 8008H–AVR–04/11

ATtiny48/88 Table 10-13. Overriding Signals for Alternate Functions in PD[3:0] Signal Name PD3/INT1/PCINT19 PD2/INT0/PCINT18 PD1/PCINT17 PD0/PCINT16 PUOE 0 0 0 0 PUO 0 0 0 0 DDOE 0 0 0 0 DDOV 0 0 0 0 PVOE 0 0 0 0 PVOV 0 0 0 0 INT1 ENABLE + INT0 ENABLE + DIEOE PCINT17 (cid:129) PCIE2 PCINT16 (cid:129) PCIE2 PCINT19 (cid:129) PCIE2 PCINT18 (cid:129) PCIE1 DIEOV 1 1 1 1 PCINT19 INPUT PCINT18 INPUT DI PCINT17 INPUT PCINT16 INPUT INT1 INPUT INT0 INPUT AIO – – – – 10.4 Register Description 10.4.1 MCUCR – MCU Control Register Bit 7 6 5 4 3 2 1 0 0x35 (0x55) – BPDS BPDSE PUD – – – – MCUCR Read/Write R R/W R/W R/W R R R R Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 4 – PUD: Pull-up Disable When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con- figuring the Pin” on page 61 for more details about this feature. 10.4.2 PORTCR – Port Control Register Bit 7 6 5 4 3 2 1 0 0x12 (0x32) BBMD BBMC BBMB BBMA PUDD PUDC PUDB PUDA PORTCR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – BBMx: Break-Before-Make Mode Enable When these bits are written to one, the port-wise Break-Before-Make mode is activated. The intermediate tri-state cycle is then inserted when writing DDRxn to make an output. For further information, see “Break-Before-Make Switching” on page 62. (cid:129) Bits 3:0 – PUDx: Port-Wise Pull-up Disable When these bits are written to one, the port-wise pull-ups in the defined I/O ports are disabled even if the DDxn and PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). The Port-Wise Pull-up Disable bits are ORed with the global Pull-up Disable bit (PUD) 77 8008H–AVR–04/11

from the MCUCR register. See “Configuring the Pin” on page 61 for more details about this feature. 10.4.3 PORTA – The Port A Data Register Bit 7 6 5 4 3 2 1 0 0x0E (0x2E) - - - - PORTA3 PORTA2 PORTA1 PORTA0 PORTA Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.4 DDRA – The Port A Data Direction Register Bit 7 6 5 4 3 2 1 0 0x0D (0x2D) - - - - DDA3 DDA2 DDA1 DDA0 DDRA Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.5 PINA – The Port A Input Pins Bit 7 6 5 4 3 2 1 0 0x0C (0x2C) - - - - PINA3 PINA2 PINA1 PINA0 PINA Read/Write R R R R R R R R Initial Value 0 0 0 0 N/A N/A N/A N/A 10.4.6 PORTB – The Port B Data Register Bit 7 6 5 4 3 2 1 0 0x05 (0x25) PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.7 DDRB – The Port B Data Direction Register Bit 7 6 5 4 3 2 1 0 0x04 (0x24) DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.8 PINB – The Port B Input Pins Bit 7 6 5 4 3 2 1 0 0x03 (0x23) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB Read/Write R R R R R R R R Initial Value N/A N/A N/A N/A N/A N/A N/A N/A 10.4.9 PORTC – The Port C Data Register Bit 7 6 5 4 3 2 1 0 0x08 (0x28) PORTC6 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.10 DDRC – The Port C Data Direction Register Bit 7 6 5 4 3 2 1 0 0x07 (0x27) DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 DDRC Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 ATtiny48/88 78 8008H–AVR–04/11

ATtiny48/88 10.4.11 PINC – The Port C Input Pins Bit 7 6 5 4 3 2 1 0 0x06 (0x26) PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC Read/Write R R R R R R R R Initial Value N/A N/A N/A N/A N/A N/A N/A N/A 10.4.12 PORTD – The Port D Data Register Bit 7 6 5 4 3 2 1 0 0x0B (0x2B) PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.13 DDRD – The Port D Data Direction Register Bit 7 6 5 4 3 2 1 0 0x0A (0x2A) DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 DDRD Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 10.4.14 PIND – The Port D Input Pins Bit 7 6 5 4 3 2 1 0 0x09 (0x29) PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND Read/Write R R R R R R R R Initial Value N/A N/A N/A N/A N/A N/A N/A N/A 79 8008H–AVR–04/11

11. 8-bit Timer/Counter0 11.1 Features (cid:129) Two Independent Output Compare Units (cid:129) Clear Timer on Compare Match (Auto Reload) (cid:129) Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B) 11.2 Overview Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output Compare Units. It allows accurate program execution timing (event management). A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 11-1. For the actual placement of I/O pins, refer to “Pinout of ATtiny48/88” on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “8-bit Timer/Counter Register Description” on page 85. The PRTIM0 bit in “PRR – Power Reduction Register” on page 40 must be written to zero to enable Timer/Counter0 module. Figure 11-1. 8-bit Timer/Counter Block Diagram Count TOVn Clear (Int.Req.) Control Logic clk Clock Select Tn Edge Tn Detector TOP ( From Prescaler ) Timer/Counter TCNTn = = OCnA (Int. Req.) OCRnA Fixed TOP S Value U B = OCnB (Int. Req.) A T A D OCRnB TCCRnA 11.2.1 Definitions Many register and bit references in this section are written in general form, where a lower case “n” replaces the Timer/Counter number (in this case 0) and a lower case “x” replaces the Output Compare Unit (in this case Compare Unit A or Compare Unit B). However, when using the regis- ATtiny48/88 80 8008H–AVR–04/11

ATtiny48/88 ter or bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing Timer/Counter0 counter value and so on. The definitions in Table 11-1 are used extensively throughout the document. Table 11-1. Definitions MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255). TOP The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0A Register. The assignment is depen- dent on the mode of operation. 11.2.2 Registers The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Inter- rupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure. The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter uses to increment its value. The Timer/Counter is inactive when no clock source is selected. The output from the Clock Select logic is referred to as the timer clock (clk ). T0 The Output Compare Registers (OCR0A and OCR0B) are compared with the Timer/Counter value at all times. The compare match event will also set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compare interrupt request. 11.3 Timer/Counter Clock Sources The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the Clock Select logic which is controlled by the Clock Select (CS0[2:0]) bits located in the Timer/Counter Control Register (TCCR0A). For details on clock sources and pres- caler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 117. 11.4 Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 11-2 shows a block diagram of the counter and its surroundings. Figure 11-2. Counter Unit Block Diagram TOVn DATA BUS (Int.Req.) Clock Select Edge count Tn clk Detector TCNTn clear Control Logic Tn ( From Prescaler ) top 81 8008H–AVR–04/11

Signal description (internal signals): count Increment or decrement TCNT0 by 1. clear Clear TCNT0 (set all bits to zero). clk Timer/Counter clock, referred to as clk in the following. Tn T0 top Signalize that TCNT0 has reached maximum value. Depending of the mode of operation used, the counter is cleared or incremented at each timer clock (clk ). clk can be generated from an external or internal clock source, selected by the T0 T0 Clock Select bits (CS0[2:0]). When no clock source is selected (CS0[2:0] = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of whether clk T0 is present or not. A CPU write overrides (has priority over) all counter clear or count operations. The counting sequence is determined by the setting of the Clear Timer on Compare Match bit (CTC0) located in the Timer/Counter Control Register (TCCR0A). For more details about advanced counting sequences, see “Modes of Operation” on page 83. The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by the CTC0 bit. TOV0 can be used for generating a CPU interrupt. 11.5 Output Compare Unit The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers (OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is exe- cuted. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location. Figure 11-3 shows a block diagram of the Output Compare unit. Figure 11-3. Output Compare Unit, Block Diagram DATA BUS OCRnx TCNTn = (8-bit Comparator ) OCFnx (Int.Req.) 11.5.1 Compare Match Blocking by TCNT0 Write All CPU write operations to the TCNT0 Register will block any compare match that occur in the next timer clock cycle, even when the timer is stopped. This feature allows OCR0x to be initial- ATtiny48/88 82 8008H–AVR–04/11

ATtiny48/88 ized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is enabled. 11.5.2 Using the Output Compare Unit Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock cycle, there are risks involved when changing TCNT0 when using the Output Compare Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT0 equals the OCR0x value, the compare match will be missed, resulting in incorrect waveform generation. 11.6 Modes of Operation The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the CTC0 bit. For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 84. 11.6.1 Normal Mode The simplest mode of operation is the Normal mode (CTC0 = 0). In this mode the counting direc- tion is always up (incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automat- ically clears the TOV0 Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new counter value can be written anytime. The Output Compare unit can be used to generate interrupts at some given time. 11.6.2 Clear Timer on Compare Match (CTC) Mode In Clear Timer on Compare or CTC mode (CTC0 = 1), the OCR0A Register is used to manipu- late the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It also sim- plifies the operation of counting external events. The timing diagram for the CTC mode is shown in Figure 11-4. The counter value (TCNT0) increases until a compare match occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared. Figure 11-4. CTC Mode, Timing Diagram OCnx Interrupt Flag Set TCNTn Period 1 2 3 4 83 8008H–AVR–04/11

An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to BOTTOM when the counter is run- ning with none or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new value written to OCR0A is lower than the current value of TCNT0, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around starting at 0x00 before the compare match can occur. As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the counter counts from MAX to 0x00. 11.7 Timer/Counter Timing Diagrams The Timer/Counter is a synchronous design and the timer clock (clk ) is therefore shown as a T0 clock enable signal in the following figures. The figures include information on when interrupt flags are set. Figure 11-5 contains timing data for basic Timer/Counter operation. The figure shows the count sequence close to the MAX value in all modes. Figure 11-5. Timer/Counter Timing Diagram, no Prescaling clk I/O clk Tn (clk /1) I/O TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1 TOVn Figure 11-6 shows the same timing data, but with the prescaler enabled. Figure 11-6. Timer/Counter Timing Diagram, with Prescaler (f /8) clk_I/O clk I/O clk Tn (clk /8) I/O TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1 TOVn Figure 11-7 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC mode. ATtiny48/88 84 8008H–AVR–04/11

ATtiny48/88 Figure 11-7. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (f /8) clk_I/O clk I/O clk Tn (clk /8) I/O TCNTn OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2 OCRnx OCRnx Value OCFnx Figure 11-8 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode where OCR0A is TOP. Figure 11-8. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres- caler (f /8) clk_I/O clk I/O clk Tn (clk /8) I/O TCNTn TOP - 1 TOP BOTTOM BOTTOM + 1 (CTC) OCRnx TOP OCFnx 11.8 8-bit Timer/Counter Register Description 11.8.1 TCCR0A – Timer/Counter Control Register A Bit 7 6 5 4 3 2 1 0 0x25 (0x45) – – – – CTC0 CS02 CS01 CS00 TCCR0A Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 3 – CTC0: Clear Timer on Compare Match Mode This bit control the counting sequence of the counter, the source for maximum (TOP) counter value, see Table 11-2. Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode (see “Modes of Operation” on page 83). 85 8008H–AVR–04/11

Table 11-2. CTC Mode Bit Description Timer/Counter Update of TOV Flag Mode CTC0 Mode of Operation TOP OCRx at Set on(1) 0 0 Normal 0xFF Immediate MAX 1 1 CTC OCRA Immediate MAX Notes: 1. MAX = 0xFF (cid:129) Bits 2:0 – CS0[2:0]: Clock Select The three Clock Select bits select the clock source to be used by the Timer/Counter. Table 11-3. Clock Select Bit Description CS02 CS01 CS00 Description 0 0 0 No clock source (Timer/Counter stopped) 0 0 1 clk (No prescaling) I/O 0 1 0 clk /8 (From prescaler) I/O 0 1 1 clk /64 (From prescaler) I/O 1 0 0 clk /256 (From prescaler) I/O 1 0 1 clk /1024 (From prescaler) I/O 1 1 0 External clock source on T0 pin. Clock on falling edge. 1 1 1 External clock source on T0 pin. Clock on rising edge. If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the pin is configured as an output. This feature allows software control of the counting. 11.8.2 TCNT0 – Timer/Counter Register Bit 7 6 5 4 3 2 1 0 0x26 (0x46) TCNT0[7:0] TCNT0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The Timer/Counter Register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running, introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers. 11.8.3 OCR0A – Output Compare Register A Bit 7 6 5 4 3 2 1 0 0x27 (0x47) OCR0A[7:0] OCR0A Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The Output Compare Register A contains an 8-bit value that is continuously compared with the counter value (TCNT0). A match can be used to generate an Output Compare interrupt. ATtiny48/88 86 8008H–AVR–04/11

ATtiny48/88 11.8.4 OCR0B – Output Compare Register B Bit 7 6 5 4 3 2 1 0 0x28 (0x48) OCR0B[7:0] OCR0B Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The Output Compare Register B contains an 8-bit value that is continuously compared with the counter value (TCNT0). A match can be used to generate an Output Compare interrupt. 11.8.5 TIMSK0 – Timer/Counter Interrupt Mask Register Bit 7 6 5 4 3 2 1 0 (0x6E) – – – – – OCIE0B OCIE0A TOIE0 TIMSK0 Read/Write R R R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:3 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter Compare Match B interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter Interrupt Flag Register – TIFR0. (cid:129) Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the Timer/Counter 0 Interrupt Flag Register – TIFR0. (cid:129) Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter 0 Inter- rupt Flag Register – TIFR0. 11.8.6 TIFR0 – Timer/Counter 0 Interrupt Flag Register Bit 7 6 5 4 3 2 1 0 0x15 (0x35) – – – – – OCF0B OCF0A TOV0 TIFR0 Read/Write R R R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:3 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 2 – OCF0B: Timer/Counter 0 Output Compare B Match Flag The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in OCR0B – Output Compare Register0 B. OCF0B is cleared by hardware when executing the cor- responding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable), and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed. 87 8008H–AVR–04/11

(cid:129) Bit 1 – OCF0A: Timer/Counter 0 Output Compare A Match Flag The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the cor- responding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable), and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed. (cid:129) Bit 0 – TOV0: Timer/Counter0 Overflow Flag The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed. See Table 11-2, “CTC Mode Bit Description” on page 86. ATtiny48/88 88 8008H–AVR–04/11

ATtiny48/88 12. 16-bit Timer/Counter1 with PWM 12.1 Features (cid:129) True 16-bit Design (i.e., Allows 16-bit PWM) (cid:129) Two independent Output Compare Units (cid:129) Double Buffered Output Compare Registers (cid:129) One Input Capture Unit (cid:129) Input Capture Noise Canceler (cid:129) Clear Timer on Compare Match (Auto Reload) (cid:129) Glitch-free, Phase Correct Pulse Width Modulator (PWM) (cid:129) Variable PWM Period (cid:129) Frequency Generator (cid:129) External Event Counter (cid:129) Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1) 12.2 Overview Most register and bit references in this section are written in general form, where a lower case “n” replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit channel. However, when using the register or bit defines in a program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on. The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave generation, and signal timing measurement. A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 12-1. Figure 12-1. 16-bit Timer/Counter Block Diagram(1) Count TOVn Clear (Int.Req.) Control Logic Direction clkTn Clock Select DeEtdegcetor Tn TOP BOTTOM ( From Prescaler ) Timer/Counter TCNTn = = 0 OCnA (Int.Req.) = GWeanveerfaotrimon OCnA OCRnA Fixed OCnB S TOP (Int.Req.) A BU = Values GWeanveerfaotrimon OCnB T A D OCRnB ( From Analog Comparator Ouput ) ICFn (Int.Req.) ICRn DeEtdegcetor CNanociseeler ICPn TCCRnA TCCRnB Note: 1. Refer to Figure 1-1 on page 2, Table 10-5 on page 69 and Table 10-11 on page 75 for Timer/Counter1 pin placement and description. 89 8008H–AVR–04/11

For actual placement of I/O pins, refer to “Pinout of ATtiny48/88” on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “Register Description” on page 110. The PRTIM1 bit in “PRR – Power Reduction Register” on page 40 must be written to zero to enable Timer/Counter1 module. 12.2.1 Registers The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture Regis- ter (ICR1) are all 16-bit registers. Special procedures must be followed when accessing the 16- bit registers. These procedures are described in the section “Accessing 16-bit Registers” on page 91. The Timer/Counter Control Registers (TCCR1A/B) are 8-bit registers and have no CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR1). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK1). TIFR1 and TIMSK1 are not shown in the figure. The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T1 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source is selected. The output from the Clock Select logic is referred to as the timer clock (clk ). T1 The double buffered Output Compare Registers (OCR1A/B) are compared with the Timer/Coun- ter value at all time. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pin (OC1A/B). See “Out- put Compare Units” on page 97.. The compare match event will also set the Compare Match Flag (OCF1A/B) which can be used to generate an Output Compare interrupt request. The Input Capture Register can capture the Timer/Counter value at a given external (edge trig- gered) event on either the Input Capture pin (ICP1) or on the Analog Comparator pins (See “Analog Comparator” on page 161.) The Input Capture unit includes a digital filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes. The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined by either the OCR1A Register, the ICR1 Register, or by a set of fixed values. When using OCR1A as TOP value in a PWM mode, the OCR1A Register can not be used for generating a PWM output. However, the TOP value will in this case be double buffered allowing the TOP value to be changed in run time. If a fixed TOP value is required, the ICR1 Register can be used as an alternative, freeing the OCR1A to be used as PWM output. 12.2.2 Definitions The following definitions are used extensively throughout the section: Table 12-1. BOTTOM The counter reaches the BOTTOM when it becomes 0x0000. MAX The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535). The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP value can be assigned to be one of the fixed values: 0x00FF, 0x01FF, TOP or 0x03FF, or to the value stored in the OCR1A or ICR1 Register. The assignment is dependent of the mode of operation. ATtiny48/88 90 8008H–AVR–04/11

ATtiny48/88 12.3 Accessing 16-bit Registers The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR CPU via the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations. Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16-bit access. The same temporary register is shared between all 16-bit registers within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a 16-bit register is written by the CPU, the high byte stored in the temporary register, and the low byte written are both copied into the 16-bit register in the same clock cycle. When the low byte of a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the tempo- rary register in the same clock cycle as the low byte is read. Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR1A/B 16- bit registers does not involve using the temporary register. To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low byte must be read before the high byte. The following code examples show how to access the 16-bit Timer Registers assuming that no interrupts updates the temporary register. The same principle can be used directly for accessing the OCR1A/B and ICR1 Registers. Note that when using “C”, the compiler handles the 16-bit access. Assembly Code Examples(1) ... ; Set TCNT1 to 0x01FF ldir17,0x01 ldir16,0xFF outTCNT1H,r17 outTCNT1L,r16 ; Read TCNT1 into r17:r16 in r16,TCNT1L in r17,TCNT1H ... C Code Examples(1) unsigned int i; ... /* Set TCNT1 to 0x01FF */ TCNT1 = 0x1FF; /* Read TCNT1 into i */ i = TCNT1; ... Note: 1. See ”About Code Examples” on page 7. For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. The assembly code example returns the TCNT1 value in the r17:r16 register pair. 91 8008H–AVR–04/11

It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or any other of the 16-bit Timer Regis- ters, then the result of the access outside the interrupt will be corrupted. Therefore, when both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during the 16-bit access. The following code examples show how to do an atomic read of the TCNT1 Register contents. Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle. Assembly Code Example(1) TIM16_ReadTCNT1: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Read TCNT1 into r17:r16 in r16,TCNT1L in r17,TCNT1H ; Restore global interrupt flag outSREG,r18 ret C Code Example(1) unsigned int TIM16_ReadTCNT1( void ) { unsigned char sreg; unsigned int i; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Read TCNT1 into i */ i = TCNT1; /* Restore global interrupt flag */ SREG = sreg; return i; } Note: 1. See ”About Code Examples” on page 7. For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. The assembly code example returns the TCNT1 value in the r17:r16 register pair. ATtiny48/88 92 8008H–AVR–04/11

ATtiny48/88 The following code examples show how to do an atomic write of the TCNT1 Register contents. Writing any of the OCR1A/B or ICR1 Registers can be done by using the same principle. Assembly Code Example(1) TIM16_WriteTCNT1: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Set TCNT1 to r17:r16 outTCNT1H,r17 outTCNT1L,r16 ; Restore global interrupt flag outSREG,r18 ret C Code Example(1) void TIM16_WriteTCNT1( unsigned int i ) { unsigned char sreg; unsigned int i; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Set TCNT1 to i */ TCNT1 = i; /* Restore global interrupt flag */ SREG = sreg; } Note: 1. See ”About Code Examples” on page 7. For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. The assembly code example requires that the r17:r16 register pair contains the value to be writ- ten to TCNT1. 12.3.1 Reusing the Temporary High Byte Register If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. However, note that the same rule of atomic operation described previously also applies in this case. 12.4 Timer/Counter Clock Sources The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the Clock Select logic which is controlled by the Clock Select (CS1[2:0]) bits 93 8008H–AVR–04/11

located in the Timer/Counter Control Register B (TCCR1B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 117. 12.5 Counter Unit The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 12-2 shows a block diagram of the counter and its surroundings. Figure 12-2. Counter Unit Block Diagram DATA BUS (8-bit) TOVn (Int.Req.) TEMP (8-bit) Clock Select Count Edge Tn TCNTnH (8-bit) TCNTnL (8-bit) Clear clk Detector Control Logic Tn Direction TCNTn (16-bit Counter) ( From Prescaler ) TOP BOTTOM Signal description (internal signals): Count Increment or decrement TCNT1 by 1. Direction Select between increment and decrement. Clear Clear TCNT1 (set all bits to zero). clk Timer/Counter clock. T1 TOP Signalize that TCNT1 has reached maximum value. BOTTOM Signalize that TCNT1 has reached minimum value (zero). The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) con- taining the upper eight bits of the counter, and Counter Low (TCNT1L) containing the lower eight bits. The TCNT1H Register can only be indirectly accessed by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU accesses the high byte temporary register (TEMP). The temporary register is updated with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with the temporary register value when TCNT1L is written. This allows the CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1 Register when the counter is counting that will give unpredictable results. The special cases are described in the sections where they are of importance. Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk ). The clk can be generated from an external or internal clock source, T1 T1 selected by the Clock Select bits (CS1[2:0]). When no clock source is selected (CS1[2:0] = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU, independent of whether clk is present or not. A CPU write overrides (has priority over) all counter clear or T1 count operations. The counting sequence is determined by the setting of the Waveform Generation mode bits (WGM1[3:0]) located in the Timer/Counter Control Registers A and B (TCCR1A and TCCR1B). There are close connections between how the counter behaves (counts) and how waveforms ATtiny48/88 94 8008H–AVR–04/11

ATtiny48/88 are generated on the Output Compare outputs OC1x. For more details about advanced counting sequences and waveform generation, see “Modes of Operation” on page 100. The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected by the WGM1[3:0] bits. TOV1 can be used for generating a CPU interrupt. 12.6 Input Capture Unit The Timer/Counter incorporates an Input Capture unit that can capture external events and give them a time-stamp indicating time of occurrence. The external signal indicating an event, or mul- tiple events, can be applied via the ICP1 pin or alternatively, via the analog-comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle, and other features of the sig- nal applied. Alternatively the time-stamps can be used for creating a log of the events. The Input Capture unit is illustrated by the block diagram shown in Figure 12-3. The elements of the block diagram that are not directly a part of the Input Capture unit are gray shaded. The small “n” in register and bit names indicates the Timer/Counter number. Figure 12-3. Input Capture Unit Block Diagram DATA BUS (8-bit) TEMP (8-bit) ICRnH (8-bit) ICRnL (8-bit) TCNTnH (8-bit) TCNTnL (8-bit) WRITE ICRn (16-bit Register) TCNTn (16-bit Counter) ACO* ACIC* ICNC ICES Analog Comparator Noise Edge ICFn (Int.Req.) Canceler Detector ICPn When a change of the logic level (an event) occurs on the Input Capture pin (ICP1), alternatively on the Analog Comparator output (ACO), and this change confirms to the setting of the edge detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter (TCNT1) is written to the Input Capture Register (ICR1). The Input Capture Flag (ICF1) is set at the same system clock as the TCNT1 value is copied into ICR1 Register. If enabled (ICIE1 = 1), the Input Capture Flag generates an Input Capture interrupt. The ICF1 Flag is automatically cleared when the interrupt is executed. Alternatively the ICF1 Flag can be cleared by software by writing a logical one to its I/O bit location. 95 8008H–AVR–04/11

Reading the 16-bit value in the Input Capture Register (ICR1) is done by first reading the low byte (ICR1L) and then the high byte (ICR1H). When the low byte is read the high byte is copied into the high byte temporary register (TEMP). When the CPU reads the ICR1H I/O location it will access the TEMP Register. The ICR1 Register can only be written when using a Waveform Generation mode that utilizes the ICR1 Register for defining the counter’s TOP value. In these cases the Waveform Genera- tion mode (WGM1[3:0]) bits must be set before the TOP value can be written to the ICR1 Register. When writing the ICR1 Register the high byte must be written to the ICR1H I/O location before the low byte is written to ICR1L. For more information on how to access the 16-bit registers refer to “Accessing 16-bit Registers” on page 91. 12.6.1 Input Capture Trigger Source The main trigger source for the Input Capture unit is the Input Capture pin (ICP1). Timer/Counter1 can alternatively use the Analog Comparator output as trigger source for the Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog Comparator Input Capture (ACIC) bit in the Analog Comparator Control and Status Register (ACSR). Be aware that changing trigger source can trigger a capture. The Input Capture Flag must therefore be cleared after the change. Both the Input Capture pin (ICP1) and the Analog Comparator output (ACO) inputs are sampled using the same technique as for the T1 pin (Figure 13-1 on page 117). The edge detector is also identical. However, when the noise canceler is enabled, additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. Note that the input of the noise canceler and edge detector is always enabled unless the Timer/Counter is set in a Wave- form Generation mode that uses ICR1 to define TOP. An Input Capture can be triggered by software by controlling the port of the ICP1 pin. 12.6.2 Noise Canceler The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored over four samples, and all four must be equal for changing the output that in turn is used by the edge detector. The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNC1) bit in Timer/Counter Control Register B (TCCR1B). When enabled the noise canceler introduces addi- tional four system clock cycles of delay from a change applied to the input, to the update of the ICR1 Register. The noise canceler uses the system clock and is therefore not affected by the prescaler. 12.6.3 Using the Input Capture Unit The main challenge when using the Input Capture unit is to assign enough processor capacity for handling the incoming events. The time between two events is critical. If the processor has not read the captured value in the ICR1 Register before the next event occurs, the ICR1 will be overwritten with a new value. In this case the result of the capture will be incorrect. When using the Input Capture interrupt, the ICR1 Register should be read as early in the inter- rupt handler routine as possible. Even though the Input Capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the maximum number of clock cycles it takes to handle any of the other interrupt requests. ATtiny48/88 96 8008H–AVR–04/11

ATtiny48/88 Using the Input Capture unit in any mode of operation when the TOP value (resolution) is actively changed during operation, is not recommended. Measurement of an external signal’s duty cycle requires that the trigger edge is changed after each capture. Changing the edge sensing must be done as early as possible after the ICR1 Register has been read. After a change of the edge, the Input Capture Flag (ICF1) must be cleared by software (writing a logical one to the I/O bit location). For measuring frequency only, the clearing of the ICF1 Flag is not required (if an interrupt handler is used). 12.7 Output Compare Units The 16-bit comparator continuously compares TCNT1 with the Output Compare Register (OCR1x). If TCNT equals OCR1x the comparator signals a match. A match will set the Output Compare Flag (OCF1x) at the next timer clock cycle. If enabled (OCIE1x = 1), the Output Com- pare Flag generates an Output Compare interrupt. The OCF1x Flag is automatically cleared when the interrupt is executed. Alternatively the OCF1x Flag can be cleared by software by writ- ing a logical one to its I/O bit location. The Waveform Generator uses the match signal to generate an output according to operating mode set by the Waveform Generation mode (WGM1[3:0]) bits and Compare Output mode (COM1x[1:0]) bits. The TOP and BOTTOM signals are used by the Waveform Generator for handling the special cases of the extreme values in some modes of operation (See “Modes of Operation” on page 100.) A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value (i.e., counter resolution). In addition to the counter resolution, the TOP value defines the period time for waveforms generated by the Waveform Generator. Figure 12-4 shows a block diagram of the Output Compare unit. The small “n” in the register and bit names indicates the device number (n = 1 for Timer/Counter 1), and the “x” indicates Output Compare unit (A/B). The elements of the block diagram that are not directly a part of the Output Compare unit are gray shaded. Figure 12-4. Output Compare Unit, Block Diagram DATA BUS (8-bit) TEMP (8-bit) OCRnxH Buf. (8-bit) OCRnxL Buf. (8-bit) TCNTnH (8-bit) TCNTnL (8-bit) OCRnx Buffer (16-bit Register) TCNTn (16-bit Counter) OCRnxH (8-bit) OCRnxL (8-bit) OCRnx (16-bit Register) = (16-bit Comparator ) OCFnx (Int.Req.) TOP Waveform Generator OCnx BOTTOM WGMn[3:0] COMnx[1:0] 97 8008H–AVR–04/11

The OCR1x Register is double buffered when using any of the twelve Pulse Width Modulation (PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR1x Com- pare Register to either TOP or BOTTOM of the counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the out- put glitch-free. The OCR1x Register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has access to the OCR1x Buffer Register, and if double buffering is dis- abled the CPU will access the OCR1x directly. The content of the OCR1x (Buffer or Compare) Register is only changed by a write operation (the Timer/Counter does not update this register automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte temporary register (TEMP). However, it is a good practice to read the low byte first as when accessing other 16-bit registers. Writing the OCR1x Registers must be done via the TEMP Reg- ister since the compare of all 16 bits is done continuously. The high byte (OCR1xH) has to be written first. When the high byte I/O location is written by the CPU, the TEMP Register will be updated by the value written. Then when the low byte (OCR1xL) is written to the lower eight bits, the high byte will be copied into the upper 8-bits of either the OCR1x buffer or OCR1x Compare Register in the same system clock cycle. For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers” on page 91. 12.7.1 Force Output Compare In non-PWM Waveform Generation modes, the match output of the comparator can be forced by writing a one to the Force Output Compare (FOC1x) bit. Forcing compare match will not set the OCF1x Flag or reload/clear the timer, but the OC1x pin will be updated as if a real compare match had occurred (the COM1[1:0] bits settings define whether the OC1x pin is set, cleared or toggled). 12.7.2 Compare Match Blocking by TCNT1 Write All CPU writes to the TCNT1 Register will block any compare match that occurs in the next timer clock cycle, even when the timer is stopped. This feature allows OCR1x to be initialized to the same value as TCNT1 without triggering an interrupt when the Timer/Counter clock is enabled. 12.7.3 Using the Output Compare Unit Since writing TCNT1 in any mode of operation will block all compare matches for one timer clock cycle, there are risks involved when changing TCNT1 when using any of the Output Compare channels, independent of whether the Timer/Counter is running or not. If the value written to TCNT1 equals the OCR1x value, the compare match will be missed, resulting in incorrect wave- form generation. Do not write the TCNT1 equal to TOP in PWM modes with variable TOP values. The compare match for the TOP will be ignored and the counter will continue to 0xFFFF. Similarly, do not write the TCNT1 value equal to BOTTOM when the counter is downcounting. The setup of the OC1x should be performed before setting the Data Direction Register for the port pin to output. The easiest way of setting the OC1x value is to use the Force Output Com- pare (FOC1x) strobe bits in Normal mode. The OC1x Register keeps its value even when changing between Waveform Generation modes. Be aware that the COM1x[1:0] bits are not double buffered together with the compare value. Changing the COM1x[1:0] bits will take effect immediately. ATtiny48/88 98 8008H–AVR–04/11

ATtiny48/88 12.8 Compare Match Output Unit The Compare Output mode (COM1x[1:0]) bits have two functions. The Waveform Generator uses the COM1x[1:0] bits for defining the Output Compare (OC1x) state at the next compare match. Secondly the COM1x[1:0] bits control the OC1x pin output source. Figure 12-5 shows a simplified schematic of the logic affected by the COM1x[1:0] bit setting. The I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers (DDR and PORT) that are affected by the COM1x[1:0] bits are shown. When referring to the OC1x state, the reference is for the internal OC1x Register, not the OC1x pin. If a system reset occur, the OC1x Register is reset to “0”. Figure 12-5. Compare Match Output Unit (non-PWM Mode), Schematic COMnx1 Waveform COMnx0 D Q Generator FOCnx 1 OCnx OCnx Pin 0 D Q S U B PORT A T A D D Q DDR clk I/O The general I/O port function is overridden by the Output Compare (OC1x) from the Waveform Generator if either of the COM1x[1:0] bits are set. However, the OC1x pin direction (input or out- put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC1x pin (DDR_OC1x) must be set as output before the OC1x value is visi- ble on the pin. The port override function is generally independent of the Waveform Generation mode, but there are some exceptions. Refer to Table 12-2, Table 12-3 and Table 12-4 for details. The design of the Output Compare pin logic allows initialization of the OC1x state before the out- put is enabled. Note that some COM1x[1:0] bit settings are reserved for certain modes of operation. See “Register Description” on page 110. The COM1x[1:0] bits have no effect on the Input Capture unit. 99 8008H–AVR–04/11

12.8.1 Compare Output Mode and Waveform Generation The Waveform Generator uses the COM1x[1:0] bits differently in normal, CTC, and PWM modes. For all modes, setting the COM1x[1:0] = 0 tells the Waveform Generator that no action on the OC1x Register is to be performed on the next compare match. For compare output actions in the non-PWM modes refer to Table 12-2 on page 110. For fast PWM mode refer to Table 12-3 on page 110, and for phase correct and phase and frequency correct PWM refer to Table 12-4 on page 111. A change of the COM1x[1:0] bits state will have effect at the first compare match after the bits are written. For non-PWM modes, the action can be forced to have immediate effect by using the FOC1x strobe bits. 12.9 Modes of Operation The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the combination of the Waveform Generation mode (WGM1[3:0]) and Compare Out- put mode (COM1x[1:0]) bits. The Compare Output mode bits do not affect the counting sequence, while the Waveform Generation mode bits do. The COM1x[1:0] bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non- PWM modes the COM1x[1:0] bits control whether the output should be set, cleared or toggle at a compare match (See “Compare Match Output Unit” on page 99.) For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 107. 12.9.1 Normal Mode The simplest mode of operation is the Normal mode (WGM1[3:0] = 0). In this mode the counting direction is always up (incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOV1) will be set in the same timer clock cycle as the TCNT1 becomes zero. The TOV1 Flag in this case behaves like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV1 Flag, the timer resolution can be increased by soft- ware. There are no special cases to consider in the Normal mode, a new counter value can be written anytime. The Input Capture unit is easy to use in Normal mode. However, observe that the maximum interval between the external events must not exceed the resolution of the counter. If the interval between events are too long, the timer overflow interrupt or the prescaler must be used to extend the resolution for the capture unit. The Output Compare units can be used to generate interrupts at some given time. Using the Output Compare to generate waveforms in Normal mode is not recommended, since this will occupy too much of the CPU time. 12.9.2 Clear Timer on Compare Match (CTC) Mode In Clear Timer on Compare or CTC mode (WGM1[3:0] = 4 or 12), the OCR1A or ICR1 Register are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT1) matches either the OCR1A (WGM1[3:0] = 4) or the ICR1 (WGM1[3:0] = 12). The OCR1A or ICR1 define the top value for the counter, hence also its res- olution. This mode allows greater control of the compare match output frequency. It also simplifies the operation of counting external events. ATtiny48/88 100 8008H–AVR–04/11

ATtiny48/88 The timing diagram for the CTC mode is shown in Figure 12-6. The counter value (TCNT1) increases until a compare match occurs with either OCR1A or ICR1, and then counter (TCNT1) is cleared. Figure 12-6. CTC Mode, Timing Diagram OCnA Interrupt Flag Set or ICFn Interrupt Flag Set (Interrupt on TOP) TCNTn OCnA (COMnA[1:0] = 1) (Toggle) Period 1 2 3 4 An interrupt can be generated at each time the counter value reaches the TOP value by either using the OCF1A or ICF1 Flag according to the register used to define the TOP value. If the interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. How- ever, changing the TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does not have the double buff- ering feature. If the new value written to OCR1A or ICR1 is lower than the current value of TCNT1, the counter will miss the compare match. The counter will then have to count to its max- imum value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode using OCR1A for defining TOP (WGM1[3:0] = 15) since the OCR1A then will be double buffered. For generating a waveform output in CTC mode, the OC1A output can be set to toggle its logical level on each compare match by setting the Compare Output mode bits to toggle mode (COM1A[1:0] = 1). The OC1A value will not be visible on the port pin unless the data direction for the pin is set to output (DDR_OC1A = 1). The waveform generated will have a maximum fre- quency of f = f /2 when OCR1A is set to zero (0x0000). The waveform frequency is OC1A clk_I/O defined by the following equation: f clk_I/O f = --------------------------------------------------- OCnA 2⋅N⋅(1+OCRnA) The N variable represents the prescaler factor (1, 8, 64, 256, or 1024). As for the Normal mode of operation, the TOV1 Flag is set in the same timer clock cycle that the counter counts from MAX to 0x0000. 12.9.3 Fast PWM Mode The fast Pulse Width Modulation or fast PWM mode (WGM1[3:0] = 5, 6, 7, 14, or 15) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is set on the compare match between TCNT1 and OCR1x, and cleared at TOP. In inverting Compare Output mode output is cleared on compare match and set at TOP. Due to the single-slope oper- 101 8008H–AVR–04/11

ation, the operating frequency of the fast PWM mode can be twice as high as the phase correct and phase and frequency correct PWM modes that use dual-slope operation. This high fre- quency makes the fast PWM mode well suited for power regulation, rectification, and DAC applications. High frequency allows physically small sized external components (coils, capaci- tors), hence reduces total system cost. The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the max- imum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can be calculated by using the following equation: log(TOP+1) R = ----------------------------------- FPWM log(2) In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM1[3:0] = 5, 6, or 7), the value in ICR1 (WGM1[3:0] = 14), or the value in OCR1A (WGM1[3:0] = 15). The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 12-7. The figure shows fast PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be set when a compare match occurs. Figure 12-7. Fast PWM Mode, Timing Diagram OCRnx/TOP Update and TOVn Interrupt Flag Set and OCnA Interrupt Flag Set or ICFn Interrupt Flag Set (Interrupt on TOP) TCNTn OCnx (COMnx[1:0] = 2) OCnx (COMnx[1:0] = 3) Period 1 2 3 4 5 6 7 8 The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. In addition the OC1A or ICF1 Flag is set at the same timer clock cycle as TOV1 is set when either OCR1A or ICR1 is used for defining the TOP value. If one of the interrupts are enabled, the interrupt han- dler routine can be used for updating the TOP and compare values. When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the Compare Registers. If the TOP value is lower than any of the Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x. Note that when using fixed TOP values the unused bits are masked to zero when any of the OCR1x Registers are written. ATtiny48/88 102 8008H–AVR–04/11

ATtiny48/88 The procedure for updating ICR1 differs from updating OCR1A when used for defining the TOP value. The ICR1 Register is not double buffered. This means that if ICR1 is changed to a low value when the counter is running with none or a low prescaler value, there is a risk that the new ICR1 value written is lower than the current value of TCNT1. The result will then be that the counter will miss the compare match at the TOP value. The counter will then have to count to the MAX value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. The OCR1A Register however, is double buffered. This feature allows the OCR1A I/O location to be written anytime. When the OCR1A I/O location is written the value written will be put into the OCR1A Buffer Register. The OCR1A Compare Register will then be updated with the value in the Buffer Register at the next timer clock cycle the TCNT1 matches TOP. The update is done at the same timer clock cycle as the TCNT1 is cleared and the TOV1 Flag is set. Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed (by changing the TOP value), using the OCR1A as TOP is clearly a better choice due to its double buffer feature. In fast PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins. Setting the COM1x[1:0] bits to two will produce a non-inverted PWM and an inverted PWM out- put can be generated by setting the COM1x[1:0] to three (see Table on page 110). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at the compare match between OCR1x and TCNT1, and clearing (or setting) the OC1x Register at the timer clock cycle the counter is cleared (changes from TOP to BOTTOM). The PWM frequency for the output can be calculated by the following equation: f clk_I/O f = ----------------------------------- OCnxPWM N⋅(1+TOP) The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). The extreme values for the OCR1x Register represents special cases when generating a PWM waveform output in the fast PWM mode. If the OCR1x is set equal to BOTTOM (0x0000) the out- put will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCR1x equal to TOP will result in a constant high or low output (depending on the polarity of the output set by the COM1x[1:0] bits.) A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set- ting OC1A to toggle its logical level on each compare match (COM1A[1:0] = 1). This applies only if OCR1A is used to define the TOP value (WGM1[3:0] = 15). The waveform generated will have a maximum frequency of f = f /2 when OCR1A is set to zero (0x0000). This feature is OC1A clk_I/O similar to the OC1A toggle in CTC mode, except the double buffer feature of the Output Com- pare unit is enabled in the fast PWM mode. 12.9.4 Phase Correct PWM Mode The phase correct Pulse Width Modulation or phase correct PWM mode (WGM1[3:0]=1, 2, 3, 10, or 11) provides a high resolution phase correct PWM waveform generation option. The phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a dual- slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is cleared on the compare match between TCNT1 and OCR1x while upcounting, and set on the compare match while downcounting. In inverting Output Compare mode, the operation is 103 8008H–AVR–04/11

inverted. The dual-slope operation has lower maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control applications. The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolu- tion in bits can be calculated by using the following equation: log(TOP+1) R = ----------------------------------- PCPWM log(2) In phase correct PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM1[3:0] = 1, 2, or 3), the value in ICR1 (WGM1[3:0] = 10), or the value in OCR1A (WGM1[3:0] = 11). The counter has then reached the TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 12-8. The figure shows phase correct PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between OCR1x and TCNT1. The OC1x Inter- rupt Flag will be set when a compare match occurs. Figure 12-8. Phase Correct PWM Mode, Timing Diagram OCRnx/TOP Update and OCnA Interrupt Flag Set or ICFn Interrupt Flag Set (Interrupt on TOP) TOVn Interrupt Flag Set (Interrupt on Bottom) TCNTn OCnx (COMnx[1:0] = 2) OCnx (COMnx[1:0] = 3) Period 1 2 3 4 The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM. When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 Flag is set accord- ingly at the same timer clock cycle as the OCR1x Registers are updated with the double buffer value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter reaches the TOP or BOTTOM value. ATtiny48/88 104 8008H–AVR–04/11

ATtiny48/88 When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the Compare Registers. If the TOP value is lower than any of the Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x. Note that when using fixed TOP values, the unused bits are masked to zero when any of the OCR1x Registers are written. As the third period shown in Figure 12-8 illustrates, changing the TOP actively while the Timer/Counter is running in the phase correct mode can result in an unsymmetrical output. The reason for this can be found in the time of update of the OCR1x Reg- ister. Since the OCR1x update occurs at TOP, the PWM period starts and ends at TOP. This implies that the length of the falling slope is determined by the previous TOP value, while the length of the rising slope is determined by the new TOP value. When these two values differ the two slopes of the period will differ in length. The difference in length gives the unsymmetrical result on the output. It is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the TOP value while the Timer/Counter is running. When using a static TOP value there are practically no differences between the two modes of operation. In phase correct PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins. Setting the COM1x[1:0] bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM1x[1:0] to three (See Table on page 111). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at the compare match between OCR1x and TCNT1 when the counter increments, and clearing (or setting) the OC1x Register at compare match between OCR1x and TCNT1 when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated by the following equation: f clk_I/O f = ---------------------------- OCnxPCPWM 2⋅N⋅TOP The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). The extreme values for the OCR1x Register represent special cases when generating a PWM waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the output will be continuously low and if set equal to TOP the output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If OCR1A is used to define the TOP value (WGM1[3:0] = 11) and COM1A[1:0] = 1, the OC1A out- put will toggle with a 50% duty cycle. 12.9.5 Phase and Frequency Correct PWM Mode The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM mode (WGM1[3:0] = 8 or 9) provides a high resolution phase and frequency correct PWM wave- form generation option. The phase and frequency correct PWM mode is, like the phase correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is cleared on the compare match between TCNT1 and OCR1x while upcounting, and set on the compare match while downcounting. In inverting Compare Output mode, the operation is inverted. The dual-slope operation gives a lower maximum operation fre- quency compared to the single-slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control applications. 105 8008H–AVR–04/11

The main difference between the phase correct, and the phase and frequency correct PWM mode is the time the OCR1x Register is updated by the OCR1x Buffer Register, (see Figure 12- 8 and Figure 12-9). The PWM resolution for the phase and frequency correct PWM mode can be defined by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can be calculated using the following equation: log(TOP+1) R = ----------------------------------- PFCPWM log(2) In phase and frequency correct PWM mode the counter is incremented until the counter value matches either the value in ICR1 (WGM1[3:0] = 8), or the value in OCR1A (WGM1[3:0] = 9). The counter has then reached the TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency correct PWM mode is shown on Figure 12-9. The figure shows phase and frequency correct PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing dia- gram shown as a histogram for illustrating the dual-slope operation. The diagram includes non- inverted and inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes repre- sent compare matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be set when a compare match occurs. Figure 12-9. Phase and Frequency Correct PWM Mode, Timing Diagram OCnA Interrupt Flag Set or ICFn Interrupt Flag Set (Interrupt on TOP) OCRnx/TOP Updateand TOVn Interrupt Flag Set (Interrupt on Bottom) TCNTn OCnx (COMnx[1:0] = 2) OCnx (COMnx[1:0 ] = 3) Period 1 2 3 4 The Timer/Counter Overflow Flag (TOV1) is set at the same timer clock cycle as the OCR1x Registers are updated with the double buffer value (at BOTTOM). When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 Flag set when TCNT1 has reached TOP. The Interrupt Flags can then be used to generate an interrupt each time the counter reaches the TOP or BOTTOM value. ATtiny48/88 106 8008H–AVR–04/11

ATtiny48/88 When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the Compare Registers. If the TOP value is lower than any of the Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x. As Figure 12-9 shows the output generated is, in contrast to the phase correct mode, symmetri- cal in all periods. Since the OCR1x Registers are updated at BOTTOM, the length of the rising and the falling slopes will always be equal. This gives symmetrical output pulses and is therefore frequency correct. Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed by changing the TOP value, using the OCR1A as TOP is clearly a better choice due to its double buffer feature. In phase and frequency correct PWM mode, the compare units allow generation of PWM wave- forms on the OC1x pins. Setting the COM1x[1:0] bits to 0b10 will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM1x[1:0] to 0b11 (See Table 12-4 on page 111). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at the compare match between OCR1x and TCNT1 when the coun- ter increments, and clearing (or setting) the OC1x Register at compare match between OCR1x and TCNT1 when the counter decrements. The PWM frequency for the output when using phase and frequency correct PWM can be calculated by the following equation: f clk_I/O f = ---------------------------- OCnxPFCPWM 2⋅N⋅TOP The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). The extreme values for the OCR1x Register represents special cases when generating a PWM waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the output will be continuously low and if set equal to TOP the output will be set to high for non- inverted PWM mode. For inverted PWM the output will have the opposite logic values. If OCR1A is used to define the TOP value and COM1A[1:0] = 1, the OC1A output will toggle with a 50% duty cycle. 12.10 Timer/Counter Timing Diagrams The Timer/Counter is a synchronous design and the timer clock (clk ) is therefore shown as a T1 clock enable signal in the following figures. The figures include information on when Interrupt Flags are set, and when the OCR1x Register is updated with the OCR1x buffer value (only for modes utilizing double buffering). Figure 12-10 shows a timing diagram for the setting of OCF1x. 107 8008H–AVR–04/11

Figure 12-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling clk I/O clk Tn (clk /1) I/O TCNTn OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2 OCRnx OCRnx Value OCFnx Figure 12-11 shows the same timing data, but with the prescaler enabled. Figure 12-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (f /8) clk_I/O clk I/O clk Tn (clk /8) I/O TCNTn OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2 OCRnx OCRnx Value OCFnx Figure 12-12 shows the count sequence close to TOP in various modes. When using phase and frequency correct PWM mode the OCR1x Register is updated at BOTTOM. The timing diagrams will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1 and so on. The same renaming applies for modes that set the TOV1 Flag at BOTTOM. ATtiny48/88 108 8008H–AVR–04/11

ATtiny48/88 Figure 12-12. Timer/Counter Timing Diagram, no Prescaling clk I/O clk Tn (clk /1) I/O TCNTn TOP - 1 TOP BOTTOM BOTTOM + 1 (CTC and FPWM) TCNTn TOP - 1 TOP TOP - 1 TOP - 2 (PC and PFC PWM) TOVn (FPWM) and ICFn (if used as TOP) OCRnx Old OCRnx Value New OCRnx Value (Update at TOP) Figure 12-13 shows the same timing data, but with the prescaler enabled. Figure 12-13. Timer/Counter Timing Diagram, with Prescaler (f /8) clk_I/O clk I/O clk Tn (clk/8) I/O TCNTn TOP - 1 TOP BOTTOM BOTTOM + 1 (CTC and FPWM) TCNTn TOP - 1 TOP TOP - 1 TOP - 2 (PC and PFC PWM) TOVn (FPWM) and ICFn (if used as TOP) OCRnx Old OCRnx Value New OCRnx Value (Update at TOP) 109 8008H–AVR–04/11

12.11 Register Description 12.11.1 TCCR1A – Timer/Counter1 Control Register A Bit 7 6 5 4 3 2 1 0 (0x80) COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 TCCR1A Read/Write R/W R/W R/W R/W R R R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:6 – COM1A[1:0]: Compare Output Mode for Channel A (cid:129) Bits 5:4 – COM1B[1:0]: Compare Output Mode for Channel B The COM1A[1:0] and COM1B[1:0] control the Output Compare pins (OC1A and OC1B respec- tively) behavior. If one or both of the COM1A[1:0] bits are written to one, the OC1A output overrides the normal port functionality of the I/O pin it is connected to. If one or both of the COM1B[1:0] bit are written to one, the OC1B output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit correspond- ing to the OC1A or OC1B pin must be set in order to enable the output driver. When the OC1A or OC1B is connected to the pin, the function of the COM1x[1:0] bits is depen- dent of the WGM1[3:0] bits setting. Table 12-2 shows the COM1x[1:0] bit functionality when the WGM1[3:0] bits are set to a Normal or a CTC mode (non-PWM). Table 12-2. Compare Output Mode, non-PWM COM1A1/COM1B1 COM1A0/COM1B0 Description 0 0 Normal port operation, OC1A/OC1B disconnected. 0 1 Toggle OC1A/OC1B on Compare Match. Clear OC1A/OC1B on Compare Match (Set output to 1 0 low level). Set OC1A/OC1B on Compare Match (Set output to 1 1 high level). Table 12-3 shows the COM1x[1:0] bit functionality when the WGM1[3:0] bits are set to the fast PWM mode. Table 12-3. Compare Output Mode, Fast PWM(1) COM1A1/COM1B1 COM1A0/COM1B0 Description 0 0 Normal port operation, OC1A/OC1B disconnected. WGM1[3:0] = 14 or 15: Toggle OC1A on Compare Match, OC1B disconnected (normal port operation). 0 1 For all other WGM1 settings, normal port operation, OC1A/OC1B disconnected. Clear OC1A/OC1B on Compare Match, set 1 0 OC1A/OC1B at TOP Set OC1A/OC1B on Compare Match, clear 1 1 OC1A/OC1B at TOP Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In this case the compare match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 101. for more details. ATtiny48/88 110 8008H–AVR–04/11

ATtiny48/88 Table 12-4 shows the COM1x[1:0] bit functionality when the WGM1[3:0] bits are set to the phase correct or the phase and frequency correct, PWM mode. Table 12-4. Compare Output Mode, Phase Correct and Phase & Frequency Correct PWM(1) COM1A1 COM1A0 COM1B1 COM1B0 Description 0 0 Normal port operation, OC1A/OC1B disconnected. WGM1[3:0] = 8, 9, 10 or 11: Toggle OC1A on Compare Match, OC1B 0 1 disconnected (normal port operation). For all other WGM1 settings, normal port operation, OC1A/OC1B disconnected. Clear OC1A/OC1B on Compare Match when up-counting. Set OC1A/OC1B 1 0 on Compare Match when downcounting. Set OC1A/OC1B on Compare Match when up-counting. Clear OC1A/OC1B 1 1 on Compare Match when downcounting. Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. See “Phase Correct PWM Mode” on page 103. for more details. (cid:129) Bits 3:2 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 1:0 – WGM1[1:0]: Waveform Generation Mode Combined with the WGM1[3:2] bits found in the TCCR1B Register, these bits control the count- ing sequence of the counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 12-5. Table 12-5. Waveform Generation Mode Bit Description WGM WGM WGM WGM Timer/Counter Update of TOV1 Flag Mode 13 12 11 10 Mode of Operation TOP OCR1x at Set on 0 0 0 0 0 Normal 0xFFFF Immediate MAX 1 0 0 0 1 PWM, Phase Correct, 8-bit 0x00FF TOP BOTTOM 2 0 0 1 0 PWM, Phase Correct, 9-bit 0x01FF TOP BOTTOM 3 0 0 1 1 PWM, Phase Correct, 10-bit 0x03FF TOP BOTTOM 4 0 1 0 0 CTC OCR1A Immediate MAX 5 0 1 0 1 Fast PWM, 8-bit 0x00FF TOP TOP 6 0 1 1 0 Fast PWM, 9-bit 0x01FF TOP TOP 7 0 1 1 1 Fast PWM, 10-bit 0x03FF TOP TOP 8 1 0 0 0 PWM, Phase & Frequency Correct ICR1 BOTTOM BOTTOM 9 1 0 0 1 PWM, Phase & Frequency Correct OCR1A BOTTOM BOTTOM 10 1 0 1 0 PWM, Phase Correct ICR1 TOP BOTTOM 11 1 0 1 1 PWM, Phase Correct OCR1A TOP BOTTOM 12 1 1 0 0 CTC ICR1 Immediate MAX 13 1 1 0 1 (Reserved) – – – 14 1 1 1 0 Fast PWM ICR1 TOP TOP 15 1 1 1 1 Fast PWM OCR1A TOP TOP 111 8008H–AVR–04/11

Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types of Pulse Width Modulation (PWM) modes. (See “Modes of Operation” on page 100.). 12.11.2 TCCR1B – Timer/Counter1 Control Register B Bit 7 6 5 4 3 2 1 0 (0x81) ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 TCCR1B Read/Write R/W R/W R R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – ICNC1: Input Capture Noise Canceler Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is activated, the input from the Input Capture pin (ICP1) is filtered. The filter function requires four successive equal valued samples of the ICP1 pin for changing its output. The Input Capture is therefore delayed by four oscillator cycles when the noise canceler is enabled. (cid:129) Bit 6 – ICES1: Input Capture Edge Select This bit selects which edge on the Input Capture pin (ICP1) that is used to trigger a capture event. When the ICES1 bit is written to zero, a falling (negative) edge is used as trigger, and when the ICES1 bit is written to one, a rising (positive) edge will trigger the capture. When a capture is triggered according to the ICES1 setting, the counter value is copied into the Input Capture Register (ICR1). The event will also set the Input Capture Flag (ICF1), and this can be used to cause an Input Capture Interrupt, if this interrupt is enabled. When the ICR1 is used as TOP value (see description of the WGM1[3:0] bits located in the TCCR1A and the TCCR1B Register), the ICP1 is disconnected and consequently the Input Cap- ture function is disabled. (cid:129) Bit 5 – Reserved Bit This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when TCCR1B is written. (cid:129) Bits 4:3 – WGM1[3:2]: Waveform Generation Mode See TCCR1A Register description. (cid:129) Bits 2:0 – CS1[2:0]: Clock Select The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure 12-10 and Figure 12-11. Table 12-6. Clock Select Bit Description CS12 CS11 CS10 Description 0 0 0 No clock source (Timer/Counter stopped). 0 0 1 clk /1 (No prescaling) I/O 0 1 0 clk /8 (From prescaler) I/O 0 1 1 clk /64 (From prescaler) I/O 1 0 0 clk /256 (From prescaler) I/O ATtiny48/88 112 8008H–AVR–04/11

ATtiny48/88 Table 12-6. Clock Select Bit Description (Continued) CS12 CS11 CS10 Description 1 0 1 clk /1024 (From prescaler) I/O 1 1 0 External clock source on T1 pin. Clock on falling edge. 1 1 1 External clock source on T1 pin. Clock on rising edge. If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the counter even if the pin is configured as an output. This feature allows software control of the counting. 12.11.3 TCCR1C – Timer/Counter1 Control Register C Bit 7 6 5 4 3 2 1 0 (0x82) FOC1A FOC1B – – – – – – TCCR1C Read/Write R/W R/W R R R R R R Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – FOC1A: Force Output Compare for Channel A (cid:129) Bit 6 – FOC1B: Force Output Compare for Channel B The FOC1A/FOC1B bits are only active when the WGM1[3:0] bits specifies a non-PWM mode. However, for ensuring compatibility with future devices, these bits must be set to zero when TCCR1A is written when operating in a PWM mode. When writing a logical one to the FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform Generation unit. The OC1A/OC1B output is changed according to its COM1x[1:0] bits setting. Note that the FOC1A/FOC1B bits are implemented as strobes. Therefore it is the value present in the COM1x[1:0] bits that determine the effect of the forced compare. A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in Clear Timer on Compare match (CTC) mode using OCR1A as TOP. The FOC1A/FOC1B bits are always read as zero. (cid:129) Bits 5:0 – Res: Reserved Bits These bits are reserved and will always read zero. 12.11.4 TCNT1H and TCNT1L – Timer/Counter1 Bit 7 6 5 4 3 2 1 0 (0x85) TCNT1[15:8] TCNT1H (0x84) TCNT1[7:0] TCNT1L Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 91. Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a com- pare match between TCNT1 and one of the OCR1x Registers. 113 8008H–AVR–04/11

Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock for all compare units. 12.11.5 OCR1AH and OCR1AL – Output Compare Register 1 A Bit 7 6 5 4 3 2 1 0 (0x89) OCR1A[15:8] OCR1AH (0x88) OCR1A[7:0] OCR1AL Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 12.11.6 OCR1BH and OCR1BL – Output Compare Register 1 B Bit 7 6 5 4 3 2 1 0 (0x8B) OCR1B[15:8] OCR1BH (0x8A) OCR1B[7:0] OCR1BL Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The Output Compare Registers contain a 16-bit value that is continuously compared with the counter value (TCNT1). A match can be used to generate an Output Compare interrupt, or to generate a waveform output on the OC1x pin. The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when the CPU writes to these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 91. 12.11.7 ICR1H and ICR1L – Input Capture Register 1 Bit 7 6 5 4 3 2 1 0 (0x87) ICR1[15:8] ICR1H (0x86) ICR1[7:0] ICR1L Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The Input Capture is updated with the counter (TCNT1) value each time an event occurs on the ICP1 pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture can be used for defining the counter TOP value. The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 91. 12.11.8 TIMSK1 – Timer/Counter1 Interrupt Mask Register Bit 7 6 5 4 3 2 1 0 (0x6F) – – ICIE1 – – OCIE1B OCIE1A TOIE1 TIMSK1 Read/Write R R R/W R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:6 – Res: Reserved Bits These bits are reserved and will always read zero. ATtiny48/88 114 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt Vector (see “Interrupts” on page 52) is executed when the ICF1 Flag, located in TIFR1, is set. (cid:129) Bits 4:3 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 2 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Output Compare B Match interrupt is enabled. The corresponding Interrupt Vector (see “Interrupts” on page 52) is executed when the OCF1B Flag, located in TIFR1, is set. (cid:129) Bit 1 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Output Compare A Match interrupt is enabled. The corresponding Interrupt Vector (see “Interrupts” on page 52) is executed when the OCF1A Flag, located in TIFR1, is set. (cid:129) Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Overflow interrupt is enabled. The corresponding Interrupt Vector (See “Watchdog Timer” on page 46.) is executed when the TOV1 Flag, located in TIFR1, is set. 12.11.9 TIFR1 – Timer/Counter1 Interrupt Flag Register Bit 7 6 5 4 3 2 1 0 0x16 (0x36) – – ICF1 – – OCF1B OCF1A TOV1 TIFR1 Read/Write R R R/W R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:6 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 5 – ICF1: Timer/Counter1, Input Capture Flag This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register (ICR1) is set by the WGM1[3:0] to be used as the TOP value, the ICF1 Flag is set when the counter reaches the TOP value. ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively, ICF1 can be cleared by writing a logic one to its bit location. (cid:129) Bits 4:3 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output Compare Register B (OCR1B). Note that a Forced Output Compare (FOC1B) strobe will not set the OCF1B Flag. 115 8008H–AVR–04/11

OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is exe- cuted. Alternatively, OCF1B can be cleared by writing a logic one to its bit location. (cid:129) Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output Compare Register A (OCR1A). Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag. OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is exe- cuted. Alternatively, OCF1A can be cleared by writing a logic one to its bit location. (cid:129) Bit 0 – TOV1: Timer/Counter1, Overflow Flag The setting of this flag is dependent of the WGM1[3:0] bits setting. In Normal and CTC modes, the TOV1 Flag is set when the timer overflows. Refer to Table 12-5 on page 111 for the TOV1 Flag behavior when using another WGM1[3:0] bit setting. TOV1 is automatically cleared when the Timer/Counter1 Overflow Interrupt Vector is executed. Alternatively, TOV1 can be cleared by writing a logic one to its bit location. ATtiny48/88 116 8008H–AVR–04/11

ATtiny48/88 13. Timer/Counter0 and Timer/Counter1 Prescalers “8-bit Timer/Counter0” on page 80 and “16-bit Timer/Counter1 with PWM” on page 89 share the same prescaler module, but the Timer/Counters can have different prescaler settings. The description below applies to both Timer/Counter1 and Timer/Counter0. 13.1 Internal Clock Source The Timer/Counter can be clocked directly by the system clock (by setting the CSn[2:0] = 1). This provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system clock frequency (f ). Alternatively, one of four taps from the prescaler can be used CLK_I/O as a clock source. The prescaled clock has a frequency of either f /8, f /64, CLK_I/O CLK_I/O f /256, or f /1024. CLK_I/O CLK_I/O 13.2 Prescaler Reset The prescaler is free running, i.e., operates independently of the Clock Select logic of the Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. Since the prescaler is not affected by the Timer/Counter’s clock select, the state of the prescaler will have implications for situations where a prescaled clock is used. One example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (CSn[2:0] = 0b010, 0b011, 0b100, or 0b101). The number of system clock cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024). It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execu- tion. However, care must be taken if the other Timer/Counter that shares the same prescaler also uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is connected to. 13.3 External Clock Source An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock (clk /clk ). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization T1 T0 logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 13-1 shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector logic. The registers are clocked at the positive edge of the internal system clock (clk ). The latch I/O is transparent in the high period of the internal system clock. The edge detector generates one clk /clk pulse for each positive (CSn[2:0] = 7) or negative T1 T0 (CSn[2:0] = 6) edge it detects. Figure 13-1. T1/T0 Pin Sampling Tn D Q D Q D Q Tn_sync (To Clock Select Logic) LE clk I/O Synchronization Edge Detector The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an edge has been applied to the T1/T0 pin to the counter is updated. 117 8008H–AVR–04/11

Enabling and disabling of the clock input must be done when T1/T0 has been stable for at least one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated. Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sampling. The external clock must be guaranteed to have less than half the sys- tem clock frequency (f < f /2) given a 50% duty cycle. Since the edge detector uses ExtClk clk_I/O sampling, the maximum frequency of an external clock it can detect is half the sampling fre- quency (Nyquist sampling theorem). However, due to variation of the system clock frequency and duty cycle caused by oscillator source tolerances, it is recommended that maximum fre- quency of an external clock source is less than f /2.5. clk_I/O An external clock source can not be prescaled. Figure 13-2. Prescaler for Timer/Counter0 and Timer/Counter1(1) clk I/O Clear PSRSYNC T0 Synchronization T1 Synchronization clk clk T1 T0 Note: 1. The synchronization logic on the input pins (T1/T0) is shown in Figure 13-1. 13.4 Register Description 13.4.1 GTCCR – General Timer/Counter Control Register Bit 7 6 5 4 3 2 1 0 0x23 (0x43) TSM – – – – – – PSRSYNC GTCCR Read/Write R/W R R R R R R R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – TSM: Timer/Counter Synchronization Mode Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the value that is written to the PSRSYNC bit is kept, hence keeping the corresponding prescaler reset signals asserted. This ensures that the corresponding Timer/Counters are halted and can be configured to the same value without the risk of one of them advancing during configuration. ATtiny48/88 118 8008H–AVR–04/11

ATtiny48/88 When the TSM bit is written to zero, the PSRSYNC bit are cleared by hardware, and the Timer/Counters start counting simultaneously. (cid:129) Bits 6:1 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 0 – PSRSYNC: Prescaler Reset When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This bit is nor- mally cleared immediately by hardware, except if the TSM bit is set. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both timers. 119 8008H–AVR–04/11

14. SPI – Serial Peripheral Interface 14.1 Features (cid:129) Full-duplex, Three-wire Synchronous Data Transfer (cid:129) Master or Slave Operation (cid:129) LSB First or MSB First Data Transfer (cid:129) Seven Programmable Bit Rates (cid:129) End of Transmission Interrupt Flag (cid:129) Write Collision Flag Protection (cid:129) Wake-up from Idle Mode (cid:129) Double Speed (CK/2) Master SPI Mode 14.2 Overview The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the ATtiny48/88 and peripheral devices or between several AVR devices. Figure 14-1. SPI Block Diagram(1) S MISO M M MOSI XTAL MSB LSB C 8 BIT SHIFT REGISTER S GI O L READ DATA BUFFER L O DIVIDER R T /2/4/8/16/32/64/128 N O C N CLOCK PI SPI CLOCK (MASTER) SELECT CLOCK S SCK LOGIC M 2X R1 R0 SS PI P P S S S R D MST SPE DOR MSTR SPI CONTROL SPE SPIF WCOL PI2X 8 SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 S SPI STATUS REGISTER SPI CONTROL REGISTER 8 8 SPI INTERRUPT INTERNAL REQUEST DATA BUS Note: 1. Refer to Figure 1-1 on page 2, and Table 10-5 on page 69 for SPI pin placement. ATtiny48/88 120 8008H–AVR–04/11

ATtiny48/88 The PRSPI bit in “PRR – Power Reduction Register” on page 40 must be written to zero to enable the SPI module. The interconnection between Master and Slave CPUs with SPI is shown in Figure 14-2. The sys- tem consists of two shift Registers, and a Master clock generator. The SPI Master initiates the communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and Slave prepare the data to be sent in their respective shift Registers, and the Master generates the required clock pulses on the SCK line to interchange data. Data is always shifted from Mas- ter to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In – Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pulling high the Slave Select, SS, line. When configured as a Master, the SPI interface has no automatic control of the SS line. This must be handled by user software before communication can start. When this is done, writing a byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of Transmission Flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, an interrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be kept in the Buffer Register for later use. When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as long as the SS pin is driven high. In this state, software may update the contents of the SPI Data Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin until the SS pin is driven low. As one byte has been completely shifted, the end of Transmission Flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an interrupt is requested. The Slave may continue to place new data to be sent into SPDR before reading the incoming data. The last incoming byte will be kept in the Buffer Register for later use. Figure 14-2. SPI Master-slave Interconnection MSB MASTER LSB MISO MISO MSB SLAVE LSB 8 BIT SHIFT REGISTER 8 BIT SHIFT REGISTER MOSI MOSI SHIFT ENABLE SPI SCK SCK CLOCK GENERATOR SS SS The system is single buffered in the transmit direction and double buffered in the receive direc- tion. This means that bytes to be transmitted cannot be written to the SPI Data Register before the entire shift cycle is completed. When receiving data, however, a received character must be read from the SPI Data Register before the next character has been completely shifted in. Oth- erwise, the first byte is lost. In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of the clock signal, the frequency of the SPI clock should never exceed f /4. osc 121 8008H–AVR–04/11

When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to Table 14-1 on page 122. For more details on automatic port overrides, refer to “Alternate Port Functions” on page 65. Table 14-1. SPI Pin Overrides(1) Pin Direction, Master SPI Direction, Slave SPI MOSI User Defined Input MISO Input User Defined SCK User Defined Input SS User Defined Input Note: 1. See “Alternate Functions of Port B” on page 69 for a detailed description of how to define the direction of the user defined SPI pins. The following code examples show how to initialize the SPI as a Master and how to perform a simple transmission. DDR_SPI in the examples must be replaced by the actual Data Direction Register controlling the SPI pins. DD_MOSI, DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin PB5, replace DD_MOSI with DDB5 and DDR_SPI with DDRB. Assembly Code Example(1) SPI_MasterInit: ; Set MOSI and SCK output, all others input ldi r17,(1<<DD_MOSI)|(1<<DD_SCK) out DDR_SPI,r17 ; Enable SPI, Master, set clock rate fck/16 ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0) out SPCR,r17 ret SPI_MasterTransmit: ; Start transmission of data (r16) out SPDR,r16 Wait_Transmit: ; Wait for transmission complete sbis SPSR,SPIF rjmp Wait_Transmit ret Note: 1. See ”About Code Examples” on page 7. ATtiny48/88 122 8008H–AVR–04/11

ATtiny48/88 C Code Example(1) void SPI_MasterInit(void) { /* Set MOSI and SCK output, all others input */ DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK); /* Enable SPI, Master, set clock rate fck/16 */ SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0); } void SPI_MasterTransmit(char cData) { /* Start transmission */ SPDR = cData; /* Wait for transmission complete */ while(!(SPSR & (1<<SPIF))) ; } Note: 1. See ”About Code Examples” on page 7. The following code examples show how to initialize the SPI as a Slave and how to perform a simple reception. Assembly Code Example(1) SPI_SlaveInit: ; Set MISO output, all others input ldi r17,(1<<DD_MISO) out DDR_SPI,r17 ; Enable SPI ldi r17,(1<<SPE) out SPCR,r17 ret SPI_SlaveReceive: ; Wait for reception complete sbis SPSR,SPIF rjmp SPI_SlaveReceive ; Read received data and return in r16,SPDR ret Note: 1. See ”About Code Examples” on page 7. 123 8008H–AVR–04/11

C Code Example(1) void SPI_SlaveInit(void) { /* Set MISO output, all others input */ DDR_SPI = (1<<DD_MISO); /* Enable SPI */ SPCR = (1<<SPE); } char SPI_SlaveReceive(void) { /* Wait for reception complete */ while(!(SPSR & (1<<SPIF))) ; /* Return Data Register */ return SPDR; } 14.3 SS Pin Functionality 14.3.1 Slave Mode When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When SS is held low, the SPI is activated, and MISO becomes an output if configured so by the user. All other pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which means that it will not receive incoming data. Note that the SPI logic will be reset once the SS pin is driven high. The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the master clock generator. When the SS pin is driven high, the SPI slave will immediately reset the send and receive logic, and drop any partially received data in the Shift Register. 14.3.2 Master Mode When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the direction of the SS pin. If SS is configured as an output, the pin is a general output pin which does not affect the SPI system. Typically, the pin will be driving the SS pin of the SPI Slave. If SS is configured as an input, it must be held high to ensure Master SPI operation. If the SS pin is driven low by peripheral circuitry when the SPI is configured as a Master with the SS pin defined as an input, the SPI system interprets this as another master selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the SPI system takes the following actions: 1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result of the SPI becoming a Slave, the MOSI and SCK pins become inputs. 2. The SPIF Flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is set, the interrupt routine will be executed. ATtiny48/88 124 8008H–AVR–04/11

ATtiny48/88 Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possi- bility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If the MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI Master mode. 14.4 Data Modes There are four combinations of SCK phase and polarity with respect to serial data, which are determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure 14-3 and Figure 14-4. Figure 14-3. SPI Transfer Format with CPHA = 0 SCK (CPOL = 0) mode 0 SCK (CPOL = 1) mode 2 SAMPLE I MOSI/MISO CHANGE 0 MOSI PIN CHANGE 0 MISO PIN SS MSB first (DORD = 0) MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB LSB first (DORD = 1) LSB Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 MSB Figure 14-4. SPI Transfer Format with CPHA = 1 SCK (CPOL = 0) mode 1 SCK (CPOL = 1) mode 3 SAMPLE I MOSI/MISO CHANGE 0 MOSI PIN CHANGE 0 MISO PIN SS MSB first (DORD = 0) MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB LSB first (DORD = 1) LSB Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 MSB 125 8008H–AVR–04/11

Data bits are shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing Table 14-3 on page 126 and Table 14-4 on page 127, as done in Table 14-2 below. Table 14-2. Setting SPI Mode using Control Bits CPOL and CPHA CPOL CPHA SPI Mode Leading Edge Trailing eDge 0 0 0 Sample (Rising) Setup (Falling) 0 1 1 Setup (Rising) Sample (Falling) 1 0 2 Sample (Falling) Setup (Rising) 1 1 3 Setup (Falling) Sample (Rising) 14.5 Register Description 14.5.1 SPCR – SPI Control Register Bit 7 6 5 4 3 2 1 0 0x2C (0x4C) SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – SPIE: SPI Interrupt Enable This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and the if the Global Interrupt Enable bit in SREG is set. (cid:129) Bit 6 – SPE: SPI Enable When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI operations. (cid:129) Bit 5 – DORD: Data Order When the DORD bit is written to one, the LSB of the data word is transmitted first. When the DORD bit is written to zero, the MSB of the data word is transmitted first. (cid:129) Bit 4 – MSTR: Master/Slave Select This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared, and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Mas- ter mode. (cid:129) Bit 3 – CPOL: Clock Polarity When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low when idle. Refer to Figure 14-3 and Figure 14-4 for an example. The CPOL functionality is sum- marized below: Table 14-3. CPOL Functionality CPOL Leading Edge Trailing Edge 0 Rising Falling 1 Falling Rising ATtiny48/88 126 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 2 – CPHA: Clock Phase The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or trailing (last) edge of SCK. Refer to Figure 14-3 and Figure 14-4 for an example. The CPOL functionality is summarized below: Table 14-4. CPHA Functionality CPHA Leading Edge Trailing Edge 0 Sample Setup 1 Setup Sample (cid:129) Bits 1:0 – SPR[1:0]: SPI Clock Rate Select 1 and 0 These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 have no effect on the Slave. The relationship between SCK and the oscillator clock frequency f is osc shown in the following table: Table 14-5. Relationship Between SCK and the Oscillator Frequency SPI2X SPR1 SPR0 SCK Frequency 0 0 0 f /4 osc 0 0 1 f /16 osc 0 1 0 f /64 osc 0 1 1 f /128 osc 1 0 0 f /2 osc 1 0 1 f /8 osc 1 1 0 f /32 osc 1 1 1 f /64 osc 14.5.2 SPSR – SPI Status Register Bit 7 6 5 4 3 2 1 0 0x2D (0x4D) SPIF WCOL – – – – – SPI2X SPSR Read/Write R R R R R R R R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – SPIF: SPI Interrupt Flag When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is in Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR). (cid:129) Bit 6 – WCOL: Write COLlision Flag The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set, and then accessing the SPI Data Register. (cid:129) Bits 5:1 – Res: Reserved Bits These bits are reserved and will always read zero. 127 8008H–AVR–04/11

(cid:129) Bit 0 – SPI2X: Double SPI Speed Bit When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI is in Master mode (see Table 14-5). This means that the minimum SCK period will be two CPU clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at f /4 osc or lower. The SPI interface on the ATtiny48/88 is also used for program memory and EEPROM down- loading or uploading. See page 200 for serial programming and verification. 14.5.3 SPDR – SPI Data Register Bit 7 6 5 4 3 2 1 0 0x2E (0x4E) MSB LSB SPDR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value X X X X X X X X Undefined The SPI Data Register is a read/write register used for data transfer between the Register File and the SPI Shift Register. Writing to the register initiates data transmission. Reading the regis- ter causes the Shift Register Receive buffer to be read. ATtiny48/88 128 8008H–AVR–04/11

ATtiny48/88 15. TWI – Two Wire Interface 15.1 Features (cid:129) Phillips I2C compatible (cid:129) SMBus compatible (with reservations) (cid:129) Simple Yet Powerful and Flexible Communication Interface, only two Bus Lines Needed (cid:129) Both Master and Slave Operation Supported (cid:129) Device can Operate as Transmitter or Receiver (cid:129) 7-bit Address Space Allows up to 128 Different Slave Addresses (cid:129) Multi-master Arbitration Support (cid:129) Data Transfer Speed Up to 400 kHz in Slave Mode (cid:129) Slew-rate Limited Output Drivers (cid:129) Noise Suppression Circuitry Rejects Spikes on Bus Lines (cid:129) Fully Programmable Slave Address with General Call Support (cid:129) Address Recognition Causes Wake-up When AVR is in Sleep Mode 15.2 Overview The Two Wire Interface (TWI) is a bi-directional, bus communication interface, which uses only two wires. The TWI is I2C compatible and, with reservations, SMBus compatible (see “Compati- bility with SMBus” on page 156). A device connected to the bus must act as a master or slave.The master initiates a data transac- tion by addressing a slave on the bus, and telling whether it wants to transmit or receive data. One bus can have several masters, and an arbitration process handles priority if two or more masters try to transmit at the same time. 15.3 Bus Definitions The Two-Wire Serial Interface (TWI) is ideally suited for typical microcontroller applications. The TWI protocol allows the systems designer to interconnect up to 128 different devices using only two bi-directional bus lines, one for clock (SCL) and one for data (SDA). The only external hard- ware needed to implement the bus is a single pull-up resistor for each of the TWI bus lines. All devices connected to the bus have individual addresses, and mechanisms for resolving bus contention are inherent in the TWI protocol. Figure 15-1. TWI Bus Interconnection V CC Device 1 Device 2 Device 3 ........ Device n R1 R2 SDA SCL 129 8008H–AVR–04/11

15.3.1 TWI Terminology The following definitions are frequently encountered in this section. Table 15-1. TWI Terminology Term Description Master The device that initiates and terminates a transmission and generates the SCL clock. Slave The device addressed by a Master. Transmitter The device placing data on the bus. Receiver The device reading data from the bus. The PRTWI bit in “PRR – Power Reduction Register” on page 40 must be written to zero to enable the 2-wire Serial Interface. 15.3.2 Electrical Interconnection As depicted in Figure 15-1, both bus lines are connected to the positive supply voltage through pull-up resistors. The bus drivers of all TWI-compliant devices are open-drain or open-collector. This implements a wired-AND function which is essential to the operation of the interface. A low level on a TWI bus line is generated when one or more TWI devices output a zero. A high level is output when all TWI devices tri-state their outputs, allowing the pull-up resistors to pull the line high. Note that all AVR devices connected to the TWI bus must be powered in order to allow any bus operation. The number of devices that can be connected to the bus is only limited by the bus capacitance limit of 400 pF and the 7-bit slave address space. A detailed specification of the electrical char- acteristics of the TWI is given in “Two-Wire Serial Interface Characteristics” on page 212. Two different sets of specifications are presented there, one relevant for bus speeds below 100 kHz, and one valid for bus speeds up to 400 kHz. 15.4 Data Transfer and Frame Format 15.4.1 Transferring Bits Each data bit transferred on the TWI bus is accompanied by a pulse on the clock line. The level of the data line must be stable when the clock line is high. The only exception to this rule is for generating start and stop conditions. Figure 15-2. Data Validity SDA SCL Data Stable Data Stable Data Change ATtiny48/88 130 8008H–AVR–04/11

ATtiny48/88 15.4.2 START and STOP Conditions The Master initiates and terminates a data transmission. The transmission is initiated when the Master issues a START condition on the bus, and it is terminated when the Master issues a STOP condition. Between a START and a STOP condition, the bus is considered busy, and no other master should try to seize control of the bus. A special case occurs when a new START condition is issued between a START and STOP condition. This is referred to as a REPEATED START condition, and is used when the Master wishes to initiate a new transfer without relin- quishing control of the bus. After a REPEATED START, the bus is considered busy until the next STOP. This is identical to the START behavior, and therefore START is used to describe both START and REPEATED START for the remainder of this datasheet, unless otherwise noted. As depicted below, START and STOP conditions are signalled by changing the level of the SDA line when the SCL line is high. Figure 15-3. START, REPEATED START and STOP conditions SDA SCL START STOP START REPEATED START STOP 15.4.3 Address Packet Format All address packets transmitted on the TWI bus are 9 bits long, consisting of 7 address bits, one READ/WRITE control bit and an acknowledge bit. If the READ/WRITE bit is set, a read opera- tion is to be performed, otherwise a write operation should be performed. When a Slave recognizes that it is being addressed, it should acknowledge by pulling SDA low in the ninth SCL (ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the Mas- ter’s request, the SDA line should be left high in the ACK clock cycle. The Master can then transmit a STOP condition, or a REPEATED START condition to initiate a new transmission. An address packet consisting of a slave address and a READ or a WRITE bit is called SLA+R or SLA+W, respectively. Figure 15-4. Address Packet Format Addr MSB Addr LSB R/W ACK SDA SCL 1 2 7 8 9 START 131 8008H–AVR–04/11

The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the designer, but the address 0000 000 is reserved for a general call. When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK cycle. A general call is used when a Master wishes to transmit the same message to several slaves in the system. When the general call address followed by a Write bit is transmitted on the bus, all slaves set up to acknowledge the general call will pull the SDA line low in the ack cycle. The following data packets will then be received by all the slaves that acknowledged the general call. Note that transmitting the general call address followed by a Read bit is meaningless, as this would cause contention if several slaves started transmitting different data. All addresses of the format 1111 xxx should be reserved for future purposes. 15.4.4 Data Packet Format All data packets transmitted on the TWI bus are nine bits long, consisting of one data byte and an acknowledge bit. During a data transfer, the Master generates the clock and the START and STOP conditions, while the Receiver is responsible for acknowledging the reception. An Acknowledge (ACK) is signalled by the Receiver pulling the SDA line low during the ninth SCL cycle. If the Receiver leaves the SDA line high, a NACK is signalled. When the Receiver has received the last byte, or for some reason cannot receive any more bytes, it should inform the Transmitter by sending a NACK after the final byte. The MSB of the data byte is transmitted first. Figure 15-5. Data Packet Format Data MSB Data LSB ACK Aggregate SDA SDA from Transmitter SDA from Receiver SCL from Master 1 2 7 8 9 STOP, REPEATED SLA+R/W Data Byte START or Next Data Byte 15.4.5 Combining Address and Data Packets into a Transmission A transmission basically consists of a START condition, a SLA+R/W, one or more data packets and a STOP condition. An empty message, consisting of a START followed by a STOP condi- tion, is illegal. Note that the Wired-ANDing of the SCL line can be used to implement handshaking between the Master and the Slave. The Slave can extend the SCL low period by pulling the SCL line low. This is useful if the clock speed set up by the Master is too fast for the Slave, or the Slave needs extra time for processing between the data transmissions. The Slave extending the SCL low period will not affect the SCL high period, which is determined by the Master. As a consequence, the Slave can reduce the TWI data transfer speed by prolonging the SCL duty cycle. Figure 15-6 shows a typical data transmission. Note that several data bytes can be transmitted between the SLA+R/W and the STOP condition, depending on the software protocol imple- mented by the application software. ATtiny48/88 132 8008H–AVR–04/11

ATtiny48/88 Figure 15-6. Typical Data Transmission Addr MSB Addr LSB R/W ACK Data MSB Data LSB ACK SDA SCL 1 2 7 8 9 1 2 7 8 9 START SLA+R/W Data Byte STOP 15.5 Multi-master Bus Systems, Arbitration and Synchronization The TWI protocol allows bus systems with several masters. Special concerns have been taken in order to ensure that transmissions will proceed as normal, even if two or more masters initiate a transmission at the same time. Two problems arise in multi-master systems: (cid:129) An algorithm must be implemented allowing only one of the masters to complete the transmission. All other masters should cease transmission when they discover that they have lost the selection process. This selection process is called arbitration. When a contending master discovers that it has lost the arbitration process, it should immediately switch to Slave mode to check whether it is being addressed by the winning master. The fact that multiple masters have started transmission at the same time should not be detectable to the slaves, i.e. the data being transferred on the bus must not be corrupted. (cid:129) Different masters may use different SCL frequencies. A scheme must be devised to synchronize the serial clocks from all masters, in order to let the transmission proceed in a lockstep fashion. This will facilitate the arbitration process. Figure 15-7. SCL Synchronization Between Multiple Masters TA TA low high SCL from Master A SCL from Master B SCL Bus Line TB TB low high Masters Start Masters Start Counting Low Period Counting High Period 133 8008H–AVR–04/11

The wired-ANDing of the bus lines is used to solve both these problems. The serial clocks from all masters will be wired-ANDed, yielding a combined clock with a high period equal to the one from the Master with the shortest high period. The low period of the combined clock is equal to the low period of the Master with the longest low period. Note that all masters listen to the SCL line, effectively starting to count their SCL high and low time-out periods when the combined SCL line goes high or low, respectively. Arbitration is carried out by all masters continuously monitoring the SDA line after outputting data. If the value read from the SDA line does not match the value the Master had output, it has lost the arbitration. Note that a Master can only lose arbitration when it outputs a high SDA value while another Master outputs a low value. The losing Master should immediately go to Slave mode, checking if it is being addressed by the winning Master. The SDA line should be left high, but losing masters are allowed to generate a clock signal until the end of the current data or address packet. Arbitration will continue until only one Master remains, and this may take many bits. If several masters are trying to address the same Slave, arbitration will continue into the data packet. Figure 15-8. Arbitration Between Two Masters START Master A Loses Arbitration, SDA SDA SDA from A Master A SDA from Master B SDA Line Synchronized SCL Line Note that arbitration is not allowed between: (cid:129) A REPEATED START condition and a data bit. (cid:129) A STOP condition and a data bit. (cid:129) A REPEATED START and a STOP condition. It is the user software’s responsibility to ensure that these illegal arbitration conditions never occur. This implies that in multi-master systems, all data transfers must use the same composi- tion of SLA+R/W and data packets. In other words: All transmissions must contain the same number of data packets, otherwise the result of the arbitration is undefined. ATtiny48/88 134 8008H–AVR–04/11

ATtiny48/88 15.6 Overview of the TWI Module The TWI module is comprised of several submodules, as shown in Figure 15-9. All registers drawn in a thick line are accessible through the AVR data bus. Figure 15-9. Overview of the TWI Module SCL SDA Slew-rate Spike Slew-rate Spike Control Filter Control Filter Bus Interface Unit Bit Rate Generator START / STOP Spike Suppression Prescaler Control Address/Data Shift Bit Rate Register Arbitration detection Ack Register (TWDR) (TWBR) Address Match Unit Control Unit t Address Register Status Register Control Register ni (TWAR) (TWSR) (TWCR) U I W State Machine and T Address Comparator Status control 15.6.1 SCL and SDA Pins These pins interface the AVR TWI with the rest of the MCU system. The output drivers contain a slew-rate limiter in order to conform to the TWI specification. The input stages contain a spike suppression unit removing spikes shorter than 50 ns. Note that the internal pull-ups in the AVR pads can be enabled by setting the PORT bits corresponding to the SCL and SDA pins, as explained in the I/O Port section. The internal pull-ups can in some systems eliminate the need for external ones. 15.6.2 Bit Rate Generator Unit When operating in a Master mode this unit controls the period of SCL. The SCL period is con- trolled by settings in the TWI Bit Rate Register (TWBR) and the Prescaler bits in the TWI Status Register (TWSR). Slave operation does not depend on bit rate or prescaler settings, but the clock frequency in the slave must be at least 16 times higher than the SCL frequency. Note that slaves may prolong the SCL low period, thereby reducing the average TWI bus clock period. 135 8008H–AVR–04/11

The TWI can be set to operate in high-speed mode, as described in “TWHSR – TWI High Speed Register” on page 160. In high-speed mode the TWI uses the system clock, whereas in normal mode it relies on a prescaled version of the same. Depending on the clock signal used, the SCL frequency is generated according to one of the following equations. In normal mode: clk f = -----------------------------------I--/-O------------------------------ SCL 16+(2×TWBR×TWPS) In high-speed mode: clk f = -------------------------------T---W----I--H---S------------------------- SCL 16+(2×TWBR×TWPS) ...where: (cid:129) clk = prescaled system clock, see Figure 6-1 on page 28 I/O (cid:129) clk = system clock, see Figure 6-1 on page 28 TWIHS (cid:129) TWBR = value of TWI Bit Rate Register, see “TWBR – TWI Bit Rate Register” on page 156 (cid:129) TWPS = value of TWI prescaler, see Table 15-7 on page 159 Note: In TWI Master mode TWBR must be 10, or higher . 15.6.3 Bus Interface Unit This unit contains the Data and Address Shift Register (TWDR), a START/STOP Controller and Arbitration detection hardware. The TWDR contains the address or data bytes to be transmitted, or the address or data bytes received. In addition to the 8-bit TWDR, the Bus Interface Unit also contains a register containing the (N)ACK bit to be transmitted or received. This (N)ACK Regis- ter is not directly accessible by the application software. However, when receiving, it can be set or cleared by manipulating the TWI Control Register (TWCR). When in Transmitter mode, the value of the received (N)ACK bit can be determined by the value in the TWSR. The START/STOP Controller is responsible for generation and detection of START, REPEATED START, and STOP conditions. The START/STOP controller is able to detect START and STOP conditions even when the AVR MCU is in one of the sleep modes, enabling the MCU to wake up if addressed by a Master. If the TWI has initiated a transmission as Master, the Arbitration Detection hardware continu- ously monitors the transmission trying to determine if arbitration is in process. If the TWI has lost an arbitration, the Control Unit is informed. Correct action can then be taken and appropriate status codes generated. 15.6.4 Address Match Unit The Address Match unit checks if received address bytes match the seven-bit address in the TWI Address Register (TWAR). If the TWI General Call Recognition Enable (TWGCE) bit in the TWAR is written to one, all incoming address bits will also be compared against the General Call address. Upon an address match, the Control Unit is informed, allowing correct action to be taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR. The Address Match unit is able to compare addresses even when the AVR MCU is in sleep ATtiny48/88 136 8008H–AVR–04/11

ATtiny48/88 mode, enabling the MCU to wake up if addressed by a Master. If another interrupt (e.g., INT0) occurs during TWI Power-down address match and wakes up the CPU, the TWI aborts opera- tion and return to it’s idle state. If this cause any problems, ensure that TWI Address Match is the only enabled interrupt when entering Power-down. 15.6.5 Control Unit The Control unit monitors the TWI bus and generates responses corresponding to settings in the TWI Control Register (TWCR). When an event requiring the attention of the application occurs on the TWI bus, the TWI Interrupt Flag (TWINT) is asserted. In the next clock cycle, the TWI Sta- tus Register (TWSR) is updated with a status code identifying the event. The TWSR only contains relevant status information when the TWI Interrupt Flag is asserted. At all other times, the TWSR contains a special status code indicating that no relevant status information is avail- able. As long as the TWINT Flag is set, the SCL line is held low. This allows the application software to complete its tasks before allowing the TWI transmission to continue. The TWINT Flag is set in the following situations: (cid:129) After the TWI has transmitted a START/REPEATED START condition. (cid:129) After the TWI has transmitted SLA+R/W. (cid:129) After the TWI has transmitted an address byte. (cid:129) After the TWI has lost arbitration. (cid:129) After the TWI has been addressed by own slave address or general call. (cid:129) After the TWI has received a data byte. (cid:129) After a STOP or REPEATED START has been received while still addressed as a Slave. (cid:129) When a bus error has occurred due to an illegal START or STOP condition. 15.7 Using the TWI The AVR TWI is byte-oriented and interrupt based. Interrupts are issued after all bus events, like reception of a byte or transmission of a START condition. Because the TWI is interrupt-based, the application software is free to carry on other operations during a TWI byte transfer. Note that the TWI Interrupt Enable (TWIE) bit in TWCR together with the Global Interrupt Enable bit in SREG allow the application to decide whether or not assertion of the TWINT Flag should gener- ate an interrupt request. If the TWIE bit is cleared, the application must poll the TWINT Flag in order to detect actions on the TWI bus. When the TWINT Flag is asserted, the TWI has finished an operation and awaits application response. In this case, the TWI Status Register (TWSR) contains a value indicating the current state of the TWI bus. The application software can then decide how the TWI should behave in the next TWI bus cycle by manipulating the TWCR and TWDR Registers. Figure 15-10 is a simple example of how the application can interface to the TWI hardware. In this example, a Master wishes to transmit a single data byte to a Slave. This description is quite abstract, a more detailed explanation follows later in this section. A simple code example imple- menting the desired behavior is also presented. 137 8008H–AVR–04/11

Figure 15-10. Interfacing the Application to the TWI in a Typical Transmission 3. Check TWSR to see if START was 5. Check TWSR to see if SLA+W was 1. Application 7. Check TWSR to see if data was sent sent. Application loads SLA+W into sent and ACK received. n writes to TWCR to and ACK received. plicatioAction transinmitiisasteion of TsWigDnRalT,s Wa innItdNo TlTo aWisd Cws Rrait,pt empnrao tkpoirn ioa sntueer ,ce o tnhtarot l AlpoTpaWldicsCa aRtipo, pnmr olaopkaridniasgt eds auctroaen ittnrhotaol t s TTigWWnDIaNlRsT ,i naistnod Aspipglnicaalsti oton sloeandds S aTpOpPro pinrtioa tTeW coCnRtr,ol p START making sure that TWINT is written to one A and TWSTA is written to zero. written to one TWI bus START SLA+W A Data A STOP Indicates e 4. TWINT set. TWIardwarAction SSTtaAt2Ru.sT T cWcoodInNedT iitn isodenict .saetenst SStaLtuAs+ cWo dsee nint,d AicCaKtes daSttaa ts6ue.s nT ctW,o AdINCeT Kin srdeeictc.aetievesd TWINT set H received 1. The first step in a TWI transmission is to transmit a START condition. This is done by writing a specific value into TWCR, instructing the TWI hardware to transmit a START condition. Which value to write is described later on. However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the START condition. 2. When the START condition has been transmitted, the TWINT Flag in TWCR is set, and TWSR is updated with a status code indicating that the START condition has success- fully been sent. 3. The application software should now examine the value of TWSR, to make sure that the START condition was successfully transmitted. If TWSR indicates otherwise, the appli- cation software might take some special action, like calling an error routine. Assuming that the status code is as expected, the application must load SLA+W into TWDR. Remember that TWDR is used both for address and data. After TWDR has been loaded with the desired SLA+W, a specific value must be written to TWCR, instructing the TWI hardware to transmit the SLA+W present in TWDR. Which value to write is described later on. However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the address packet. 4. When the address packet has been transmitted, the TWINT Flag in TWCR is set, and TWSR is updated with a status code indicating that the address packet has success- fully been sent. The status code will also reflect whether a Slave acknowledged the packet or not. 5. The application software should now examine the value of TWSR, to make sure that the address packet was successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the application software might take some spe- cial action, like calling an error routine. Assuming that the status code is as expected, the application must load a data packet into TWDR. Subsequently, a specific value must be written to TWCR, instructing the TWI hardware to transmit the data packet present in TWDR. Which value to write is described later on. However, it is important ATtiny48/88 138 8008H–AVR–04/11

ATtiny48/88 that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immedi- ately after the application has cleared TWINT, the TWI will initiate transmission of the data packet. 6. When the data packet has been transmitted, the TWINT Flag in TWCR is set, and TWSR is updated with a status code indicating that the data packet has successfully been sent. The status code will also reflect whether a Slave acknowledged the packet or not. 7. The application software should now examine the value of TWSR, to make sure that the data packet was successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the application software might take some spe- cial action, like calling an error routine. Assuming that the status code is as expected, the application must write a specific value to TWCR, instructing the TWI hardware to transmit a STOP condition. Which value to write is described later on. However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the STOP condition. Note that TWINT is NOT set after a STOP condition has been sent. Even though this example is simple, it shows the principles involved in all TWI transmissions. These can be summarized as follows: (cid:129) When the TWI has finished an operation and expects application response, the TWINT Flag is set. The SCL line is pulled low until TWINT is cleared. (cid:129) When the TWINT Flag is set, the user must update all TWI Registers with the value relevant for the next TWI bus cycle. As an example, TWDR must be loaded with the value to be transmitted in the next bus cycle. (cid:129) After all TWI Register updates and other pending application software tasks have been completed, TWCR is written. When writing TWCR, the TWINT bit should be set. Writing a one to TWINT clears the flag. The TWI will then commence executing whatever operation was specified by the TWCR setting. In the following an assembly and C implementation of the example is given. Note that the code below assumes that several definitions have been made, for example by using include-files. Assembly Code Example C Example Comments ldi r16, TWCR = (1<<TWINT)|(1<<TWSTA)| (1<<TWINT)|(1<<TWSTA)| (1<<TWEN) 1 Send START condition (1<<TWEN) out TWCR, r16 wait1: while (!(TWCR & (1<<TWINT))) Wait for TWINT Flag set. This in r16,TWCR ; 2 indicates that the START sbrs r16,TWINT condition has been transmitted rjmp wait1 139 8008H–AVR–04/11

Assembly Code Example C Example Comments in r16,TWSR if ((TWSR & 0xF8) != START) Check value of TWI Status andi r16, 0xF8 ERROR(); Register. Mask prescaler bits. If cpi r16, START status different from START go to ERROR brne ERROR 3 ldi r16, SLA_W TWDR = SLA_W; Load SLA_W into TWDR out TWDR, r16 TWCR = (1<<TWINT) | Register. Clear TWINT bit in ldi r16, (1<<TWINT) | (1<<TWEN); TWCR to start transmission of (1<<TWEN) address out TWCR, r16 wait2: while (!(TWCR & (1<<TWINT))) Wait for TWINT Flag set. This in r16,TWCR ; indicates that the SLA+W has 4 sbrs r16,TWINT been transmitted, and ACK/NACK has been received. rjmp wait2 in r16,TWSR if ((TWSR & 0xF8) != Check value of TWI Status andi r16, 0xF8 MT_SLA_ACK) Register. Mask prescaler bits. If cpi r16, MT_SLA_ACK ERROR(); status different from MT_SLA_ACK go to ERROR brne ERROR 5 ldi r16, DATA TWDR = DATA; out TWDR, r16 TWCR = (1<<TWINT) | Load DATA into TWDR Register. ldi r16, (1<<TWINT) | (1<<TWEN); Clear TWINT bit in TWCR to (1<<TWEN) start transmission of data out TWCR, r16 wait3: while (!(TWCR & (1<<TWINT))) Wait for TWINT Flag set. This in r16,TWCR ; indicates that the DATA has been 6 sbrs r16,TWINT transmitted, and ACK/NACK has been received. rjmp wait3 in r16,TWSR if ((TWSR & 0xF8) != Check value of TWI Status andi r16, 0xF8 MT_DATA_ACK) Register. Mask prescaler bits. If cpi r16, MT_DATA_ACK ERROR(); status different from MT_DATA_ACK go to ERROR brne ERROR 7 ldi r16, TWCR = (1<<TWINT)|(1<<TWEN)| (1<<TWINT)|(1<<TWEN)| (1<<TWSTO); Transmit STOP condition (1<<TWSTO) out TWCR, r16 15.8 Transmission Modes The TWI can operate in one of four major modes. These are named Master Transmitter (MT), Master Receiver (MR), Slave Transmitter (ST) and Slave Receiver (SR). Several of these modes can be used in the same application. As an example, the TWI can use MT mode to write data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other masters are present in the system, some of these might transmit data to the TWI, and then SR mode would be used. It is the application software that decides which modes are legal. ATtiny48/88 140 8008H–AVR–04/11

ATtiny48/88 The following sections describe each of these modes. Possible status codes are described along with figures detailing data transmission in each of the modes. These figures contain the following abbreviations: S: START condition Rs: REPEATED START condition R: Read bit (high level at SDA) W: Write bit (low level at SDA) A: Acknowledge bit (low level at SDA) A: Not acknowledge bit (high level at SDA) Data: 8-bit data byte P: STOP condition SLA: Slave Address In Figure 15-12 to Figure 15-18, circles are used to indicate that the TWINT Flag is set. The numbers in the circles show the status code held in TWSR, with the prescaler bits masked to zero. At these points, actions must be taken by the application to continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT Flag is cleared by software. When the TWINT Flag is set, the status code in TWSR is used to determine the appropriate soft- ware action. For each status code, the required software action and details of the following serial transfer are given in Table 15-2 to Table 15-5. Note that the prescaler bits are masked to zero in these tables. 15.8.1 Master Transmitter Mode In the Master Transmitter mode, a number of data bytes are transmitted to a Slave Receiver (see Figure 15-11). In order to enter a Master mode, a START condition must be transmitted. The format of the following address packet determines whether Master Transmitter or Master Receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R is trans- mitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or are masked to zero. Figure 15-11. Data Transfer in Master Transmitter Mode V CC Device 1 Device 2 MASTER SLAVE Device 3 ........ Device n R1 R2 TRANSMITTER RECEIVER SDA SCL 141 8008H–AVR–04/11

A START condition is sent by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 1 0 X 1 0 X TWEN must be set to enable the 2-wire Serial Interface, TWSTA must be written to one to trans- mit a START condition and TWINT must be written to one to clear the TWINT Flag. The TWI will then test the 2-wire Serial Bus and generate a START condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT Flag is set by hardware, and the status code in TWSR will be 0x08 (see Table 15-2). In order to enter MT mode, SLA+W must be transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to continue the transfer. This is accomplished by writing the follow- ing value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 0 0 X 1 0 X When SLA+W have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of status codes in TWSR are possible. Possible status codes in Master mode are 0x18, 0x20, or 0x38. The appropriate action to be taken for each of these status codes is detailed in Table 15-2. When SLA+W has been successfully transmitted, a data packet should be transmitted. This is done by writing the data byte to TWDR. TWDR must only be written when TWINT is high. If not, the access will be discarded, and the Write Collision bit (TWWC) will be set in the TWCR Regis- ter. After updating TWDR, the TWINT bit should be cleared (by writing it to one) to continue the transfer. This is accomplished by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 0 0 X 1 0 X This scheme is repeated until the last byte has been sent and the transfer is ended by generat- ing a STOP condition or a repeated START condition. A STOP condition is generated by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 0 1 X 1 0 X A REPEATED START condition is generated by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 1 0 X 1 0 X After a repeated START condition (state 0x10) the 2-wire Serial Interface can access the same Slave again, or a new Slave without transmitting a STOP condition. Repeated START enables ATtiny48/88 142 8008H–AVR–04/11

ATtiny48/88 the Master to switch between Slaves, Master Transmitter mode and Master Receiver mode with- out losing control of the bus. Table 15-2. Status codes for Master Transmitter Mode Status Code Application Software Response (TWSR) Status of the 2-wire Serial Bus To/from TWDR To TWCR Prescaler Bits and 2-wire Serial Interface are 0 Hardware STA STO TWIN TWE Next Action Taken by TWI Hardware T A 0x08 A START condition has been Load SLA+W 0 0 1 X SLA+W will be transmitted; transmitted ACK or NOT ACK will be received 0x10 A repeated START condition Load SLA+W or 0 0 1 X SLA+W will be transmitted; has been transmitted ACK or NOT ACK will be received Load SLA+R 0 0 1 X SLA+R will be transmitted; Logic will switch to Master Receiver mode 0x18 SLA+W has been transmitted; Load data byte or 0 0 1 X Data byte will be transmitted and ACK or NOT ACK will ACK has been received be received No TWDR action or 1 0 1 X Repeated START will be transmitted No TWDR action or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset No TWDR action 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset 0x20 SLA+W has been transmitted; Load data byte or 0 0 1 X Data byte will be transmitted and ACK or NOT ACK will NOT ACK has been received be received No TWDR action or 1 0 1 X Repeated START will be transmitted No TWDR action or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset No TWDR action 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset 0x28 Data byte has been transmit- Load data byte or 0 0 1 X Data byte will be transmitted and ACK or NOT ACK will ted; be received ACK has been received No TWDR action or 1 0 1 X Repeated START will be transmitted No TWDR action or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset No TWDR action 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset 0x30 Data byte has been transmit- Load data byte or 0 0 1 X Data byte will be transmitted and ACK or NOT ACK will ted; be received NOT ACK has been received No TWDR action or 1 0 1 X Repeated START will be transmitted No TWDR action or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset No TWDR action 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset 0x38 Arbitration lost in SLA+W or No TWDR action or 0 0 1 X 2-wire Serial Bus will be released and not addressed data bytes Slave mode entered No TWDR action 1 0 1 X A START condition will be transmitted when the bus becomes free 143 8008H–AVR–04/11

Figure 15-12. Formats and States in the Master Transmitter Mode MT Successfull transmission S SLA W A DATA A P to a slave receiver $08 $18 $28 Next transfer started with a RS SLA W repeated start condition $10 Not acknowledge R received after the A P slave address $20 MR Not acknowledge received after a data A P byte $30 Aadrbdirterastsio onr ldoastt ain b syltaeve A or A Otchoenrt imnuaesster A or A Otchoenrt imnuaesster $38 $38 Aadrbdirterastsioend laoss ts alanvde A Otchoenrt imnuaesster $68 $78 $B0 To corresponding states in slave mode Any number of data bytes From master to slave DATA A and their associated acknowledge bits From slave to master This number (contained in TWSR) corresponds n to a defined state of the 2-Wire Serial Bus. The prescaler bits are zero or masked to zero 15.8.2 Master Receiver Mode In the Master Receiver mode, a number of data bytes are received from a Slave Transmitter (Slave see Figure 15-13). In order to enter a Master mode, a START condition must be transmit- ted. The format of the following address packet determines whether Master Transmitter or Master Receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R is transmitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or are masked to zero. ATtiny48/88 144 8008H–AVR–04/11

ATtiny48/88 Figure 15-13. Data Transfer in Master Receiver Mode V CC Device 1 Device 2 MASTER SLAVE Device 3 ........ Device n R1 R2 RECEIVER TRANSMITTER SDA SCL A START condition is sent by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 1 0 X 1 0 X TWEN must be written to one to enable the 2-wire Serial Interface, TWSTA must be written to one to transmit a START condition and TWINT must be set to clear the TWINT Flag. The TWI will then test the 2-wire Serial Bus and generate a START condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT Flag is set by hard- ware, and the status code in TWSR will be 0x08 (See Table 15-2). In order to enter MR mode, SLA+R must be transmitted. This is done by writing SLA+R to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to continue the transfer. This is accomplished by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 0 0 X 1 0 X When SLA+R have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of status codes in TWSR are possible. Possible status codes in Master mode are 0x38, 0x40, or 0x48. The appropriate action to be taken for each of these status codes is detailed in Table 15-3. Received data can be read from the TWDR Register when the TWINT Flag is set high by hardware. This scheme is repeated until the last byte has been received. After the last byte has been received, the MR should inform the ST by sending a NACK after the last received data byte. The transfer is ended by generating a STOP condition or a repeated START condition. A STOP condition is generated by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 0 1 X 1 0 X A REPEATED START condition is generated by writing the following value to TWCR: TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 1 X 1 0 X 1 0 X 145 8008H–AVR–04/11

After a repeated START condition (state 0x10) the 2-wire Serial Interface can access the same Slave again, or a new Slave without transmitting a STOP condition. Repeated START enables the Master to switch between Slaves, Master Transmitter mode and Master Receiver mode with- out losing control over the bus. Table 15-3. Status codes for Master Receiver Mode Status Code Application Software Response (TWSR) Status of the 2-wire Serial Bus To TWCR Parree s0caler Bits aHnadrd w2a-rweire Serial Interface To/from TWDR STA STO TWIN TWE Next Action Taken by TWI Hardware T A 0x08 A START condition has been Load SLA+R 0 0 1 X SLA+R will be transmitted transmitted ACK or NOT ACK will be received 0x10 A repeated START condition Load SLA+R or 0 0 1 X SLA+R will be transmitted has been transmitted ACK or NOT ACK will be received Load SLA+W 0 0 1 X SLA+W will be transmitted Logic will switch to Master Transmitter mode 0x38 Arbitration lost in SLA+R or No TWDR action or 0 0 1 X 2-wire Serial Bus will be released and not addressed NOT ACK bit Slave mode will be entered No TWDR action 1 0 1 X A START condition will be transmitted when the bus becomes free 0x40 SLA+R has been transmitted; No TWDR action or 0 0 1 0 Data byte will be received and NOT ACK will be ACK has been received returned No TWDR action 0 0 1 1 Data byte will be received and ACK will be returned 0x48 SLA+R has been transmitted; No TWDR action or 1 0 1 X Repeated START will be transmitted NOT ACK has been received No TWDR action or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset No TWDR action 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset 0x50 Data byte has been received; Read data byte or 0 0 1 0 Data byte will be received and NOT ACK will be ACK has been returned returned Read data byte 0 0 1 1 Data byte will be received and ACK will be returned 0x58 Data byte has been received; Read data byte or 1 0 1 X Repeated START will be transmitted NOT ACK has been returned Read data byte or 0 1 1 X STOP condition will be transmitted and TWSTO Flag will be reset Read data byte 1 1 1 X STOP condition followed by a START condition will be transmitted and TWSTO Flag will be reset ATtiny48/88 146 8008H–AVR–04/11

ATtiny48/88 Figure 15-14. Formats and States in the Master Receiver Mode MR Successfull reception S SLA R A DATA A DATA A P from a slave receiver $08 $40 $50 $58 Next transfer started with a RS SLA R repeated start condition $10 Not acknowledge W received after the A P slave address $48 MT Aadrbdirterastsio onr ldoastt ain b syltaeve A or A Otchoenrt imnuaesster A Otchoenrt imnuaesster $38 $38 Aadrbdirterastsioend laoss ts alanvde A Otchoenrt imnuaesster $68 $78 $B0 Tsota cteosr riens sploanved inmgode Any number of data bytes From master to slave DATA A and their associated acknowledge bits From slave to master This number (contained in TWSR) corresponds n to a defined state of the 2-Wire Serial Bus. The prescaler bits are zero or masked to zero 15.8.3 Slave Receiver Mode In the Slave Receiver mode, a number of data bytes are received from a Master Transmitter (see Figure 15-15). All the status codes mentioned in this section assume that the prescaler bits are zero or are masked to zero. Figure 15-15. Data transfer in Slave Receiver mode V CC Device 1 Device 2 Device 3 ........ Device n R1 R2 SLAVE MASTER RECEIVER TRANSMITTER SDA SCL 147 8008H–AVR–04/11

To initiate the Slave Receiver mode, TWAR and TWCR must be initialized as follows: TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE value Device’s Own Slave Address The upper 7 bits are the address to which the 2-wire Serial Interface will respond when addressed by a Master. If the LSB is set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address. TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 0 1 0 0 0 1 0 X TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero. When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general call address if enabled) followed by the data direction bit. If the direction bit is “0” (write), the TWI will operate in SR mode, otherwise ST mode is entered. After its own slave address and the write bit have been received, the TWINT Flag is set and a valid status code can be read from TWSR. The status code is used to determine the appropriate soft- ware action. The appropriate action to be taken for each status code is detailed in Table 15-4. The Slave Receiver mode may also be entered if arbitration is lost while the TWI is in the Master mode (see states 0x68 and 0x78). If the TWEA bit is reset during a transfer, the TWI will return a “Not Acknowledge” (“1”) to SDA after the next received data byte. This can be used to indicate that the Slave is not able to receive any more bytes. While TWEA is zero, the TWI does not acknowledge its own slave address. However, the 2-wire Serial Bus is still monitored and address recognition may resume at any time by setting TWEA. This implies that the TWEA bit may be used to temporarily isolate the TWI from the 2-wire Serial Bus. In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can still acknowledge its own slave address or the general call address by using the 2-wire Serial Bus clock as a clock source. The part will then wake up from sleep and the TWI will hold the SCL clock low during the wake up and until the TWINT Flag is cleared (by writing it to one). Further data reception will be carried out as normal, with the AVR clocks run- ning as normal. Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking other data transmissions. Note that the 2-wire Serial Interface Data Register – TWDR does not reflect the last byte present on the bus when waking up from these Sleep modes. ATtiny48/88 148 8008H–AVR–04/11

ATtiny48/88 Table 15-4. Status Codes for Slave Receiver Mode Status Code Application Software Response (TWSR) Status of the 2-wire Serial Bus To TWCR Prescaler Bits and 2-wire Serial Interface Hard- To/from TWDR are 0 ware STA STO TWIN TWE Next Action Taken by TWI Hardware T A 0x60 Own SLA+W has been received; No TWDR action or X 0 1 0 Data byte will be received and NOT ACK will be ACK has been returned returned No TWDR action X 0 1 1 Data byte will be received and ACK will be returned 0x68 Arbitration lost in SLA+R/W as No TWDR action or X 0 1 0 Data byte will be received and NOT ACK will be Master; own SLA+W has been returned received; ACK has been returned No TWDR action X 0 1 1 Data byte will be received and ACK will be returned 0x70 General call address has been No TWDR action or X 0 1 0 Data byte will be received and NOT ACK will be received; ACK has been returned returned No TWDR action X 0 1 1 Data byte will be received and ACK will be returned 0x78 Arbitration lost in SLA+R/W as No TWDR action or X 0 1 0 Data byte will be received and NOT ACK will be Master; General call address has returned been received; ACK has been No TWDR action X 0 1 1 Data byte will be received and ACK will be returned returned 0x80 Previously addressed with own Read data byte or X 0 1 0 Data byte will be received and NOT ACK will be SLA+W; data has been received; returned ACK has been returned Read data byte X 0 1 1 Data byte will be received and ACK will be returned 0x88 Previously addressed with own Read data byte or 0 0 1 0 Switched to the not addressed Slave mode; SLA+W; data has been received; no recognition of own SLA or GCA NOT ACK has been returned Read data byte or 0 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1” Read data byte or 1 0 1 0 Switched to the not addressed Slave mode; no recognition of own SLA or GCA; a START condition will be transmitted when the bus becomes free Read data byte 1 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1”; a START condition will be transmitted when the bus becomes free 0x90 Previously addressed with Read data byte or X 0 1 0 Data byte will be received and NOT ACK will be general call; data has been re- returned ceived; ACK has been returned Read data byte X 0 1 1 Data byte will be received and ACK will be returned 0x98 Previously addressed with Read data byte or 0 0 1 0 Switched to the not addressed Slave mode; general call; data has been no recognition of own SLA or GCA received; NOT ACK has been Read data byte or 0 0 1 1 Switched to the not addressed Slave mode; returned own SLA will be recognized; GCA will be recognized if TWGCE = “1” Read data byte or 1 0 1 0 Switched to the not addressed Slave mode; no recognition of own SLA or GCA; a START condition will be transmitted when the bus becomes free Read data byte 1 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1”; a START condition will be transmitted when the bus becomes free 0xA0 A STOP condition or repeated No action 0 0 1 0 Switched to the not addressed Slave mode; START condition has been no recognition of own SLA or GCA received while still addressed as 0 0 1 1 Switched to the not addressed Slave mode; Slave own SLA will be recognized; GCA will be recognized if TWGCE = “1” 1 0 1 0 Switched to the not addressed Slave mode; no recognition of own SLA or GCA; a START condition will be transmitted when the bus becomes free 1 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1”; a START condition will be transmitted when the bus becomes free 149 8008H–AVR–04/11

Figure 15-16. Formats and States in the Slave Receiver Mode Reception of the own slave address and one or S SLA W A DATA A DATA A P or S more data bytes. All are acknowledged $60 $80 $80 $A0 Last data byte received is not acknowledged A P or S $88 Arbitration lost as master and addressed as slave A $68 Reception of the general call address and one or more data General Call A DATA A DATA A P or S bytes $70 $90 $90 $A0 Last data byte received is not acknowledged A P or S $98 Arbitration lost as master and addressed as slave by general call A $78 Any number of data bytes From master to slave DATA A and their associated acknowledge bits From slave to master This number (contained in TWSR) corresponds n to a defined state of the 2-Wire Serial Bus. The prescaler bits are zero or masked to zero 15.8.4 Slave Transmitter Mode In the Slave Transmitter mode, a number of data bytes are transmitted to a Master Receiver (see Figure 15-17). All the status codes mentioned in this section assume that the prescaler bits are zero or are masked to zero. Figure 15-17. Data Transfer in Slave Transmitter Mode V CC Device 1 Device 2 Device 3 ........ Device n R1 R2 SLAVE MASTER TRANSMITTER RECEIVER SDA SCL ATtiny48/88 150 8008H–AVR–04/11

ATtiny48/88 To initiate the Slave Transmitter mode, TWAR and TWCR must be initialized as follows: TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE value Device’s Own Slave Address The upper seven bits are the address to which the 2-wire Serial Interface will respond when addressed by a Master. If the LSB is set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address. TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE value 0 1 0 0 0 1 0 X TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero. When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general call address if enabled) followed by the data direction bit. If the direction bit is “1” (read), the TWI will operate in ST mode, otherwise SR mode is entered. After its own slave address and the write bit have been received, the TWINT Flag is set and a valid status code can be read from TWSR. The status code is used to determine the appropriate soft- ware action. The appropriate action to be taken for each status code is detailed in Table 15-5. The Slave Transmitter mode may also be entered if arbitration is lost while the TWI is in the Master mode (see state 0xB0). If the TWEA bit is written to zero during a transfer, the TWI will transmit the last byte of the trans- fer. State 0xC0 or state 0xC8 will be entered, depending on whether the Master Receiver transmits a NACK or ACK after the final byte. The TWI is switched to the not addressed Slave mode, and will ignore the Master if it continues the transfer. Thus the Master Receiver receives all “1” as serial data. State 0xC8 is entered if the Master demands additional data bytes (by transmitting ACK), even though the Slave has transmitted the last byte (TWEA zero and expect- ing NACK from the Master). While TWEA is zero, the TWI does not respond to its own slave address. However, the 2-wire Serial Bus is still monitored and address recognition may resume at any time by setting TWEA. This implies that the TWEA bit may be used to temporarily isolate the TWI from the 2-wire Serial Bus. In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can still acknowledge its own slave address or the general call address by using the 2-wire Serial Bus clock as a clock source. The part will then wake up from sleep and the TWI will hold the SCL clock will low during the wake up and until the TWINT Flag is cleared (by writing it to one). Further data transmission will be carried out as normal, with the AVR clocks running as normal. Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking other data transmissions. Note that the 2-wire Serial Interface Data Register – TWDR does not reflect the last byte present on the bus when waking up from these sleep modes. 151 8008H–AVR–04/11

Table 15-5. Status Codes for Slave Transmitter Mode Status Code Application Software Response (TWSR) Status of the 2-wire Serial Bus To TWCR Prescaler and 2-wire Serial Interface Hard- To/from TWDR Bits ware STA STO TWIN TWE Next Action Taken by TWI Hardware are 0 T A 0xA8 Own SLA+R has been received; Load data byte or X 0 1 0 Last data byte will be transmitted and NOT ACK should ACK has been returned be received Load data byte X 0 1 1 Data byte will be transmitted and ACK should be re- ceived 0xB0 Arbitration lost in SLA+R/W as Load data byte or X 0 1 0 Last data byte will be transmitted and NOT ACK should Master; own SLA+R has been be received received; ACK has been returned Load data byte X 0 1 1 Data byte will be transmitted and ACK should be re- ceived 0xB8 Data byte in TWDR has been Load data byte or X 0 1 0 Last data byte will be transmitted and NOT ACK should transmitted; ACK has been be received received Load data byte X 0 1 1 Data byte will be transmitted and ACK should be re- ceived 0xC0 Data byte in TWDR has been No TWDR action or 0 0 1 0 Switched to the not addressed Slave mode; transmitted; NOT ACK has been no recognition of own SLA or GCA received No TWDR action or 0 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1” No TWDR action or 1 0 1 0 Switched to the not addressed Slave mode; no recognition of own SLA or GCA; a START condition will be transmitted when the bus becomes free No TWDR action 1 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1”; a START condition will be transmitted when the bus becomes free 0xC8 Last data byte in TWDR has been No TWDR action or 0 0 1 0 Switched to the not addressed Slave mode; transmitted (TWEA = “0”); ACK no recognition of own SLA or GCA has been received No TWDR action or 0 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1” No TWDR action or 1 0 1 0 Switched to the not addressed Slave mode; no recognition of own SLA or GCA; a START condition will be transmitted when the bus becomes free No TWDR action 1 0 1 1 Switched to the not addressed Slave mode; own SLA will be recognized; GCA will be recognized if TWGCE = “1”; a START condition will be transmitted when the bus becomes free ATtiny48/88 152 8008H–AVR–04/11

ATtiny48/88 Figure 15-18. Formats and States in the Slave Transmitter Mode Reception of the own slave address and one or S SLA R A DATA A DATA A P or S more data bytes $A8 $B8 $C0 Arbitration lost as master and addressed as slave A $B0 Last data byte transmitted. Switched to not addressed A All 1's P or S slave (TWEA = '0') $C8 Any number of data bytes From master to slave DATA A and their associated acknowledge bits From slave to master This number (contained in TWSR) corresponds n to a defined state of the 2-Wire Serial Bus. The prescaler bits are zero or masked to zero 15.8.5 Miscellaneous States There are two status codes that do not correspond to a defined TWI state, see Table 15-6. Status 0xF8 indicates that no relevant information is available because the TWINT Flag is not set. This occurs between other states, and when the TWI is not involved in a serial transfer. Status 0x00 indicates that a bus error has occurred during a 2-wire Serial Bus transfer. A bus error occurs when a START or STOP condition occurs at an illegal position in the format frame. Examples of such illegal positions are during the serial transfer of an address byte, a data byte, or an acknowledge bit. When a bus error occurs, TWINT is set. To recover from a bus error, the TWSTO Flag must set and TWINT must be cleared by writing a logic one to it. This causes the TWI to enter the not addressed Slave mode and to clear the TWSTO Flag (no other bits in TWCR are affected). The SDA and SCL lines are released, and no STOP condition is transmitted. Table 15-6. Miscellaneous States Status Code Application Software Response (TWSR) Status of the 2-wire Serial Bus To TWCR Parree s0caler Bits aHnadrd w2a-rweire Serial Interface To/from TWDR STA STO TWIN TWE Next Action Taken by TWI Hardware T A 0xF8 No relevant state information No TWDR action No TWCR action Wait or proceed current transfer available; TWINT = “0” 0x00 Bus error due to an illegal No TWDR action 0 1 1 X Only the internal hardware is affected, no STOP condi- START or STOP condition tion is sent on the bus. In all cases, the bus is released and TWSTO is cleared. 153 8008H–AVR–04/11

15.8.6 Combining Several TWI Modes In some cases, several TWI modes must be combined in order to complete the desired action. Consider for example reading data from a serial EEPROM. Typically, such a transfer involves the following steps: 1. The transfer must be initiated. 2. The EEPROM must be instructed what location should be read. 3. The reading must be performed. 4. The transfer must be finished. Note that data is transmitted both from Master to Slave and vice versa. The Master must instruct the Slave what location it wants to read, requiring the use of the MT mode. Subsequently, data must be read from the Slave, implying the use of the MR mode. Thus, the transfer direction must be changed. The Master must keep control of the bus during all these steps, and the steps should be carried out as an atomical operation. If this principle is violated in a multi master sys- tem, another Master can alter the data pointer in the EEPROM between steps 2 and 3, and the Master will read the wrong data location. Such a change in transfer direction is accomplished by transmitting a REPEATED START between the transmission of the address byte and reception of the data. After a REPEATED START, the Master keeps ownership of the bus. The following figure shows the flow in this transfer. Figure 15-19. Combining Several TWI Modes to Access a Serial EEPROM Master Transmitter Master Receiver S SLA+W A ADDRESS A Rs SLA+R A DATA A P S = START Rs = REPEATED START P = STOP Transmitted from master to slave Transmitted from slave to master 15.9 Multi-master Systems and Arbitration If multiple masters are connected to the same bus, transmissions may be initiated simultane- ously by one or more of them. The TWI standard ensures that such situations are handled in such a way that one of the masters will be allowed to proceed with the transfer, and that no data will be lost in the process. An example of an arbitration situation is depicted below, where two masters are trying to transmit data to a Slave Receiver. ATtiny48/88 154 8008H–AVR–04/11

ATtiny48/88 Figure 15-20. An Arbitration Example V CC Device 1 Device 2 Device 3 MASTER MASTER SLAVE ........ Device n R1 R2 TRANSMITTER TRANSMITTER RECEIVER SDA SCL Several different scenarios may arise during arbitration, as described below: (cid:129) Two or more masters are performing identical communication with the same Slave. In this case, neither the Slave nor any of the masters will know about the bus contention. (cid:129) Two or more masters are accessing the same Slave with different data or direction bit. In this case, arbitration will occur, either in the READ/WRITE bit or in the data bits. The masters trying to output a one on SDA while another Master outputs a zero will lose the arbitration. Losing masters will switch to not addressed Slave mode or wait until the bus is free and transmit a new START condition, depending on application software action. (cid:129) Two or more masters are accessing different slaves. In this case, arbitration will occur in the SLA bits. Masters trying to output a one on SDA while another Master outputs a zero will lose the arbitration. Masters losing arbitration in SLA will switch to Slave mode to check if they are being addressed by the winning Master. If addressed, they will switch to SR or ST mode, depending on the value of the READ/WRITE bit. If they are not being addressed, they will switch to not addressed Slave mode or wait until the bus is free and transmit a new START condition, depending on application software action. This is summarized in Figure 15-21. Possible status values are given in circles. Figure 15-21. Possible Status Codes Caused by Arbitration START SLA Data STOP Arbitration lost in SLA Arbitration lost in Data Own No 38 TWI bus will be released and not addressed slave mode will be entered Address / General Call A START condition will be transmitted when the bus becomes free received Yes Write 68/78 Data byte will be received and NOT ACK will be returned Direction Data byte will be received and ACK will be returned Read Last data byte will be transmitted and NOT ACK should be received B0 Data byte will be transmitted and ACK should be received 155 8008H–AVR–04/11

15.10 Compatibility with SMBus As with any other I2C-compliant interface there are known compatibility issues the designer should be aware of before connecting a TWI device to SMBus devices. For use in SMBus envi- ronments, the following should be noted: (cid:129) All I/O pins of an AVR, including those of the two-wire interface, have protection diodes to both supply voltage and ground. See Figure 10-1 on page 60. This is in contradiction to the requirements of the SMBus specifications. As a result, supply voltage mustn’t be removed from the AVR or the protection diodes will pull the bus lines down. Power down and sleep modes is not a problem, provided supply voltages remain. (cid:129) The data hold time of the TWI is lower than specified for SMBus. (cid:129) SMBus has a low speed limit, while I2C hasn’t. As a master in an SMBus environment, the AVR must make sure bus speed does not drop below specifications, since lower bus speeds trigger timeouts in SMBus slaves. If the AVR is configured a slave there is a possibility of a bus lockup, since the TWI module doesn't identify timeouts. 15.11 Register Description 15.11.1 TWBR – TWI Bit Rate Register Bit 7 6 5 4 3 2 1 0 (0xB8) TWBR7 TWBR6 TWBR5 TWBR4 TWBR3 TWBR2 TWBR1 TWBR0 TWBR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – TWI Bit Rate Register TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency divider which generates the SCL clock frequency in the Master modes. See “Bit Rate Generator Unit” on page 135 for calculating bit rates. If the TWI operates in Master mode TWBR must be set to 10, or higher. 15.11.2 TWCR – TWI Control Register Bit 7 6 5 4 3 2 1 0 (0xBC) TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE TWCR Read/Write R/W R/W R/W R/W R R/W R R/W Initial Value 0 0 0 0 0 0 0 0 The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a Master access by applying a START condition to the bus, to generate a Receiver acknowledge, to generate a stop condition, and to control halting of the bus while the data to be written to the bus are written to the TWDR. It also indicates a write collision if data is attempted written to TWDR while the register is inaccessible. (cid:129) Bit 7 – TWINT: TWI Interrupt Flag This bit is set by hardware when the TWI has finished its current job and expects application software response. If the I-bit in SREG and TWIE in TWCR are set, the MCU will jump to the TWI Interrupt Vector. While the TWINT Flag is set, the SCL low period is stretched. The TWINT Flag must be cleared by software by writing a logic one to it. Note that this flag is not automati- cally cleared by hardware when executing the interrupt routine. Also note that clearing this flag ATtiny48/88 156 8008H–AVR–04/11

ATtiny48/88 starts the operation of the TWI, so all accesses to the TWI Address Register (TWAR), TWI Sta- tus Register (TWSR), and TWI Data Register (TWDR) must be complete before clearing this flag. (cid:129) Bit 6 – TWEA: TWI Enable Acknowledge Bit The TWEA bit controls the generation of the acknowledge pulse. If the TWEA bit is written to one, the ACK pulse is generated on the TWI bus if the following conditions are met: 1. The device’s own slave address has been received. 2. A general call has been received, while the TWGCE bit in the TWAR is set. 3. A data byte has been received in Master Receiver or Slave Receiver mode. By writing the TWEA bit to zero, the device can be virtually disconnected from the 2-wire Serial Bus temporarily. Address recognition can then be resumed by writing the TWEA bit to one again. 157 8008H–AVR–04/11

(cid:129) Bit 5 – TWSTA: TWI START Condition Bit The application writes the TWSTA bit to one when it desires to become a Master on the 2-wire Serial Bus. The TWI hardware checks if the bus is available, and generates a START condition on the bus if it is free. However, if the bus is not free, the TWI waits until a STOP condition is detected, and then generates a new START condition to claim the bus Master status. TWSTA must be cleared by software when the START condition has been transmitted. (cid:129) Bit 4 – TWSTO: TWI STOP Condition Bit Writing the TWSTO bit to one in Master mode will generate a STOP condition on the 2-wire Serial Bus. When the STOP condition is executed on the bus, the TWSTO bit is cleared auto- matically. In Slave mode, setting the TWSTO bit can be used to recover from an error condition. This will not generate a STOP condition, but the TWI returns to a well-defined unaddressed Slave mode and releases the SCL and SDA lines to a high impedance state. (cid:129) Bit 3 – TWWC: TWI Write Collision Flag The TWWC bit is set when attempting to write to the TWI Data Register – TWDR when TWINT is low. This flag is cleared by writing the TWDR Register when TWINT is high. (cid:129) Bit 2 – TWEN: TWI Enable Bit The TWEN bit enables TWI operation and activates the TWI interface. When TWEN is written to one, the TWI takes control over the I/O pins connected to the SCL and SDA pins, enabling the slew-rate limiters and spike filters. If this bit is written to zero, the TWI is switched off and all TWI transmissions are terminated, regardless of any ongoing operation. (cid:129) Bit 1 – Res: Reserved Bit This bit is reserved and will always read as zero. (cid:129) Bit 0 – TWIE: TWI Interrupt Enable When this bit is written to one, and the I-bit in SREG is set, the TWI interrupt request will be acti- vated for as long as the TWINT Flag is high. 15.11.3 TWSR – TWI Status Register Bit 7 6 5 4 3 2 1 0 (0xB9) TWS7 TWS6 TWS5 TWS4 TWS3 – TWPS1 TWPS0 TWSR Read/Write R R R R R R R/W R/W Initial Value 1 1 1 1 1 0 0 0 (cid:129) Bits 7:3 – TWS: TWI Status These 5 bits reflect the status of the TWI logic and the 2-wire Serial Bus. The different status codes are described later in this section. Note that the value read from TWSR contains both the 5-bit status value and the 2-bit prescaler value. The application designer should mask the pres- caler bits to zero when checking the Status bits. This makes status checking independent of prescaler setting. This approach is used in this datasheet, unless otherwise noted. (cid:129) Bit 2 – Res: Reserved Bit This bit is reserved and will always read as zero. ATtiny48/88 158 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bits 1:0 – TWPS: TWI Prescaler Bits These bits can be read and written, and control the bit rate prescaler. Table 15-7. TWI Bit Rate Prescaler TWPS1 TWPS0 Prescaler Value 0 0 1 0 1 4 1 0 16 1 1 64 To calculate bit rates, see “Bit Rate Generator Unit” on page 135. The value of TWPS1:0 is used in the equation. 15.11.4 TWDR – TWI Data Register Bit 7 6 5 4 3 2 1 0 (0xBB) TWD7 TWD6 TWD5 TWD4 TWD3 TWD2 TWD1 TWD0 TWDR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 1 1 1 1 1 1 1 1 In Transmit mode, TWDR contains the next byte to be transmitted. In Receive mode, the TWDR contains the last byte received. It is writable while the TWI is not in the process of shifting a byte. This occurs when the TWI Interrupt Flag (TWINT) is set by hardware. Note that the Data Regis- ter cannot be initialized by the user before the first interrupt occurs. The data in TWDR remains stable as long as TWINT is set. While data is shifted out, data on the bus is simultaneously shifted in. TWDR always contains the last byte present on the bus, except after a wake up from a sleep mode by the TWI interrupt. In this case, the contents of TWDR is undefined. In the case of a lost bus arbitration, no data is lost in the transition from Master to Slave. Handling of the ACK bit is controlled automatically by the TWI logic, the CPU cannot access the ACK bit directly. (cid:129) Bits 7:0 – TWD: TWI Data Register These eight bits constitute the next data byte to be transmitted, or the latest data byte received on the 2-wire Serial Bus. 15.11.5 TWAR – TWI (Slave) Address Register Bit 7 6 5 4 3 2 1 0 (0xBA) TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE TWAR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 1 1 1 1 1 1 1 0 The TWAR should be loaded with the 7-bit Slave address (in the seven most significant bits of TWAR) to which the TWI will respond when programmed as a Slave Transmitter or Receiver, and not needed in the Master modes. In multi master systems, TWAR must be set in masters which can be addressed as Slaves by other Masters. The LSB of TWAR is used to enable recognition of the general call address (0x00). There is an associated address comparator that looks for the slave address (or general call address if enabled) in the received serial address. If a match is found, an interrupt request is generated. (cid:129) Bits 7:1 – TWA: TWI (Slave) Address Register These seven bits constitute the slave address of the TWI unit. 159 8008H–AVR–04/11

(cid:129) Bit 0 – TWGCE: TWI General Call Recognition Enable Bit If set, this bit enables the recognition of a General Call given over the 2-wire Serial Bus. 15.11.6 TWAMR – TWI (Slave) Address Mask Register Bit 7 6 5 4 3 2 1 0 (0xBD) TWAM[6:0] – TWAMR Read/Write R/W R/W R/W R/W R/W R/W R/W R Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:1 – TWAM: TWI Address Mask The TWAMR can be loaded with a 7-bit Salve Address mask. Each of the bits in TWAMR can mask (disable) the corresponding address bits in the TWI Address Register (TWAR). If the mask bit is set to one then the address match logic ignores the compare between the incoming address bit and the corresponding bit in TWAR. Figure 15-22 shown the address match logic in detail. Figure 15-22. TWI Address Match Logic, Block Diagram TWAR0 Address Address Match Bit 0 TWAMR0 Address Bit Comparator 0 Address Bit Comparator 6..1 (cid:129) Bit 0 – Res: Reserved Bit This bit is reserved and will always read zero. 15.11.7 TWHSR – TWI High Speed Register Bit 7 6 5 4 3 2 1 0 (0xBE) – – – – – – – TWHS TWHSR Read/Write R R R R R R R R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:1 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 0 – TWHS: TWI High Speed Enable TWI High Speed mode is enabled by writing this bit to one. In this mode the undivided system clock is selected as TWI clock. See Figure 6-1 on page 28. The TWI High Speed mode requires that the high-speed clock, clk , is exactly two times TWIHS higher than the I/O clock frequency, clk . This means the user must make sure the I/O clock I/O frequency clk is scaled down by a factor of 2. For example, if the internal 8 MHz oscillator has I/O been selected as source clock, the user must set the prescaler to scale the system clock (and, hence, the I/O clock) down to 4 MHz. For more information about clock systems, see “Clock System” on page 28. ATtiny48/88 160 8008H–AVR–04/11

ATtiny48/88 16. Analog Comparator The Analog Comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin AIN1, the Analog Comparator output, ACO, is set. The comparator’s output can be set to trigger the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on com- parator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 16-1. The ADC Power Reduction bit, PRADC, must be disabled in order to use the ADC input multi- plexer. This is done by clearing the PRADC bit in the Power Reduction Register, PRR. See “PRR – Power Reduction Register” on page 40 for more details. Figure 16-1. Analog Comparator Block Diagram(2) BANDGAP REFERENCE ACBG ACME ADEN ADC MULTIPLEXER OUTPUT(1) Notes: 1. See Table 16-1 on page 161. 2. Refer to Figure 1-1 on page 2 and Table 10-11 on page 75 for Analog Comparator pin placement. 16.1 Analog Comparator Multiplexed Input It is possible to select any of the ADC[7:0] pins to replace the negative input to the Analog Com- parator. The ADC multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX[2:0] in ADMUX select the input pin to replace the negative input to the Analog Comparator, as shown in Table 16-1. If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the Analog Comparator. Table 16-1. Analog Comparator Multiplexed Input ACME ADEN MUX[2:0] Analog Comparator Negative Input 0 x xxx AIN1 1 1 xxx AIN1 1 0 000 ADC0 1 0 001 ADC1 161 8008H–AVR–04/11

Table 16-1. Analog Comparator Multiplexed Input (Continued) ACME ADEN MUX[2:0] Analog Comparator Negative Input 1 0 010 ADC2 1 0 011 ADC3 1 0 100 ADC4 1 0 101 ADC5 1 0 110 ADC6 1 0 111 ADC7 16.2 Register Description 16.2.1 ADCSRB – ADC Control and Status Register B Bit 7 6 5 4 3 2 1 0 (0x7B) – ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB Read/Write R R/W R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 6 – ACME: Analog Comparator Multiplexer Enable When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed description of this bit, see “Analog Comparator Multiplexed Input” on page 161. 16.2.2 ACSR – Analog Comparator Control and Status Register Bit 7 6 5 4 3 2 1 0 0x30 (0x50) ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR Read/Write R/W R/W R R/W R/W R/W R/W R/W Initial Value 0 0 N/A 0 0 0 0 0 (cid:129) Bit 7 – ACD: Analog Comparator Disable When this bit is written logic one, the power to the Analog Comparator is switched off. This bit can be set at any time to turn off the Analog Comparator. This will reduce power consumption in Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is changed. (cid:129) Bit 6 – ACBG: Analog Comparator Bandgap Select When this bit is set, a fixed internal bandgap reference voltage replaces the positive input to the Analog Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog Comparator. See “Internal Voltage Reference” on page 45. (cid:129) Bit 5 – ACO: Analog Comparator Output The output of the Analog Comparator is synchronized and then directly connected to ACO. The synchronization introduces a delay of 1 – 2 clock cycles. ATtiny48/88 162 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 4 – ACI: Analog Comparator Interrupt Flag This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding inter- rupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag. (cid:129) Bit 3 – ACIE: Analog Comparator Interrupt Enable When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Com- parator interrupt is activated. When written logic zero, the interrupt is disabled. (cid:129) Bit 2 – ACIC: Analog Comparator Input Capture Enable When written logic one, this bit enables the input capture function in Timer/Counter1 to be trig- gered by the Analog Comparator. The comparator output is in this case directly connected to the input capture front-end logic, making the comparator utilize the noise canceler and edge select features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection between the Analog Comparator and the input capture function exists. To make the comparator trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask Register (TIMSK1) must be set. (cid:129) Bits 1:0 – ACIS[1:0]: Analog Comparator Interrupt Mode Select These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings are shown in Table 16-2. Table 16-2. ACIS1/ACIS0 Settings ACIS1 ACIS0 Interrupt Mode 0 0 Comparator Interrupt on Output Toggle. 0 1 Reserved 1 0 Comparator Interrupt on Falling Output Edge. 1 1 Comparator Interrupt on Rising Output Edge. When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the bits are changed. 16.2.3 DIDR1 – Digital Input Disable Register 1 Bit 7 6 5 4 3 2 1 0 (0x7F) – – – – – – AIN1D AIN0D DIDR1 Read/Write R R R R R R R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:2 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bits 1:0 – AIN1D, AIN0D: AIN[1:0] Digital Input Disable When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corre- sponding PIN Register bit will always read as zero when this bit is set. When an analog signal is applied to the AIN1/0 pin and the digital input from this pin is not needed, this bit should be writ- ten logic one to reduce power consumption in the digital input buffer. 163 8008H–AVR–04/11

17. ADC – Analog to Digital Converter 17.1 Features (cid:129) 10-bit Resolution (cid:129) 1 LSB Integral Non-linearity (cid:129) ± 2 LSB Absolute Accuracy (cid:129) 14 µs Conversion Time (cid:129) 15 kSPS at Maximum Resolution (cid:129) Six Multiplexed Single Ended Input Channels – Two Additional Input Channels in 32-lead/pad/ball TQFP, QFN, and UFBGA Packages (cid:129) Temperature Sensor Input Channel (cid:129) Optional Left Adjustment for ADC Result Readout (cid:129) 0 – V ADC Input Voltage Range CC (cid:129) Selectable 1.1V ADC Reference Voltage (cid:129) Free Running or Single Conversion Mode (cid:129) Interrupt on ADC Conversion Complete (cid:129) Sleep Mode Noise Canceler 17.2 Overview ATtiny48/88 features a 10-bit, successive approximation Analog-to-Digital Converter (ADC). The ADC is wired to a nine-channel analog multiplexer, which allows the ADC to measure the volt- age at six (or eight, in 32-lead/pad/ball packages) single-ended input pins and from one internal, single-ended voltage channel coming from the internal temperature sensor. Single-ended volt- age inputs are referred to 0V (GND). The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a constant level during conversion. A block diagram of the ADC is shown in Figure 17-1 on page 165. There is a separate analog supply voltage pin for the ADC, AV . The voltage difference CC between supply voltage pins V and AV may not exceed 0.3V. See section “ADC Noise Can- CC CC celer” on page 171 on how to connect the analog suplly voltage pin. Internal reference voltage of nominally 1.1V is provided on-chip. Alternatively, V can be used CC as reference voltage. ATtiny48/88 164 8008H–AVR–04/11

ATtiny48/88 Figure 17-1. Analog to Digital Converter Block Schematic Operation ADC CONVERSION COMPLETE IRQ 8-BIT DATA BUS ADIF ADIE 15 0 ADC MULTIPLEXER ADC CTRL. & STATUS ADC DATA REGISTER SELECT (ADMUX) REGISTER (ADCSRA) (ADCH/ADCL) REFS0 ADLAR MUX3 MUX2 MUX1 MUX0 ADEN ADSC ADFR ADIF ADPS2 ADPS1 ADPS0 C[9:0] D A MUX DECODER PRESCALER N O CTI E EL CONVERSION LOGIC S AVCC EL N N A H C INTERNAL 1.1V REFERENCE SAMPLE & HOLD COMPARATOR 10-BIT DAC - + GND BANDGAP REFERENCE TEMPERATURE SENSOR ADC7 INPUT ADC MULTIPLEXER ADC6 MUX OUTPUT ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 17.3 Operation In order to be able to use the ADC the Power Reduction bit, PRADC, in the Power Reduction Register must be disabled. This is done by clearing the PRADC bit. See “PRR – Power Reduc- tion Register” on page 40 for more details. The ADC converts an analog input voltage to a 10-bit digital value through successive approxi- mation. The minimum value represents GND and the maximum value represents the reference voltage. The ADC voltage reference may be selected by writing the REFS0 bit in the ADMUX register. Alternatives are the V supply pin and the internal 1.1V voltage reference. CC 165 8008H–AVR–04/11

The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the ADC input pins, as well as GND and a fixed bandgap voltage reference, can be selected as single ended inputs to the ADC. The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage reference and input channel selections will not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is recommended to switch off the ADC before entering power saving sleep modes. The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and ADCL. By default, the result is presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in ADMUX. If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH, only. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the Data Registers belongs to the same conversion. Once ADCL is read, ADC access to Data Reg- isters is blocked. This means that if ADCL has been read, and a conversion completes before ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the ADCH and ADCL Registers is re-enabled. The ADC has its own interrupt which can be triggered when a conversion completes. When ADC access to the Data Registers is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost. 17.4 Starting a Conversion Make sure the ADC is powered by clearing the ADC Power Reduction bit, PRADC, in the Power Reduction Register, PRR (see “PRR – Power Reduction Register” on page 40). A single conver- sion is started by writing a logical one to the ADC Start Conversion bit, ADSC. This bit stays high as long as the conversion is in progress and will be cleared by hardware when the conversion is completed. If a different data channel is selected while a conversion is in progress, the ADC will finish the current conversion before performing the channel change. Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB (See description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting con- versions at fixed intervals. If the trigger signal still is set when the conversion completes, a new conversion will not be started. If another positive edge occurs on the trigger signal during con- version, the edge will be ignored. Note that an Interrupt Flag will be set even if the specific interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus be triggered without causing an interrupt. However, the Interrupt Flag must be cleared in order to trigger a new conversion at the next interrupt event. ATtiny48/88 166 8008H–AVR–04/11

ATtiny48/88 Figure 17-2. ADC Auto Trigger Logic ADTS[2:0] PRESCALER START CLK ADC ADIF ADATE SOURCE 1 . CONVERSION . LOGIC . . EDGE DETECTOR SOURCE n ADSC Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon as the ongoing conversion has finished. The ADC then operates in Free Running mode, con- stantly sampling and updating the ADC Data Register. The first conversion must be started by writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not. If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion, independently of how the conversion was started. 17.5 Prescaling and Conversion Timing By default, the successive approximation circuitry requires an input clock frequency between 50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate. It is not recommended to use a higher input clock frequency than 1MHz. Figure 17-3. ADC Prescaler ADEN Reset START 7-BIT ADC PRESCALER CK 8 6 2 4 2 2 4 8 1 3 6 1 K/ K/ K/ K/ K/ K/ K/ C C C C C C C ADPS0 ADPS1 ADPS2 ADC CLOCK SOURCE 167 8008H–AVR–04/11

The ADC module contains a prescaler, as illustrated in Figure 17-3 on page 167, which gener- ates an acceptable ADC clock frequency from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA. The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously reset when ADEN is low. When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising edge of the ADC clock cycle. A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry, as shown in Figure 17-4 below. Figure 17-4. ADC Timing Diagram, First Conversion (Single Conversion Mode) Next First Conversion Conversion Cycle Number 1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3 ADC Clock ADEN ADSC ADIF ADCH Sign and MSB of Result ADCL LSB of Result MUX and REFS Conversion MUX and REFS Update Sample & Hold Complete Update The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver- sion and 13.5 ADC clock cycles after the start of an first conversion. When a conversion is complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new conversion will be initiated on the first rising ADC clock edge. Figure 17-5. ADC Timing Diagram, Single Conversion One Conversion Next Conversion Cycle Number 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 ADC Clock ADSC ADIF ADCH Sign and MSB of Result ADCL LSB of Result Sample & Hold Conversion MUX and REFS MUX and REFS Complete Update Update ATtiny48/88 168 8008H–AVR–04/11

ATtiny48/88 When Auto Triggering is used, the prescaler is reset when the trigger event occurs, as shown in Figure 17-6. This assures a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold takes place two ADC clock cycles after the rising edge on the trigger source signal. Three additional CPU clock cycles are used for synchronization logic. Figure 17-6. ADC Timing Diagram, Auto Triggered Conversion One Conversion Next Conversion Cycle Number 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 ADC Clock Trigger Source ADATE ADIF ADCH Sign and MSB of Result ADCL LSB of Result Sample & Conversion Prescaler Prescaler Hold Complete Reset Reset MUX and REFS Update In Free Running mode, a new conversion will be started immediately after the conversion com- pletes, while ADSC remains high. See Figure 17-7. Figure 17-7. ADC Timing Diagram, Free Running Conversion One Conversion Next Conversion 12 13 14 1 2 3 4 Cycle Number ADC Clock ADSC ADIF ADCH Sign and MSB of Result ADCL LSB of Result Sample & Hold Conversion Complete MUX and REFS Update 169 8008H–AVR–04/11

For a summary of conversion times, see Table 17-1. Table 17-1. ADC Conversion Time Sample & Hold Conversion Time Condition (Cycles from Start of Conversion) (Cycles) First conversion 13.5 25 Normal conversions, single ended 1.5 13 Auto Triggered conversions 2 13.5 Free Running conversions 2.5 14 17.6 Changing Channel or Reference Selection Bits MUXn and REFS0 in the ADMUX Register are single buffered through a temporary register to which the CPU has random access. This ensures that the channels and reference selection only takes place at a safe point during the conversion. The channel and reference selection is continuously updated until a conversion is started. Once the conversion starts, the channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in ADC- SRA is set). Note that the conversion starts on the following rising ADC clock edge after ADSC is written. The user is thus advised not to write new channel or reference selection values to ADMUX until one ADC clock cycle after ADSC is written. If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken when updating the ADMUX Register, in order to control which conversion will be affected by the new settings. If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX Register is changed in this period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX can be safely updated in the following ways: (cid:129) When ADATE or ADEN is cleared. (cid:129) During conversion, minimum one ADC clock cycle after the trigger event. (cid:129) After a conversion, before the Interrupt Flag used as trigger source is cleared. When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion. 17.6.1 ADC Input Channels When changing channel selections, the user should observe the following guidelines to ensure that the correct channel is selected: In Single Conversion mode, always select the channel before starting the conversion. The chan- nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the conversion to complete before changing the channel selection. In Free Running mode, always select the channel before starting the first conversion. The chan- nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the first conversion to complete, and then change the channel ATtiny48/88 170 8008H–AVR–04/11

ATtiny48/88 selection. Since the next conversion has already started automatically, the next result will reflect the previous channel selection. Subsequent conversions will reflect the new channel selection. 17.6.2 ADC Voltage Reference The ADC reference voltage (V ) indicates the conversion range for the ADC. Single ended REF channels that exceed V will result in codes close to 0x3FF. V can be selected as either REF REF AV , or internal 1.1V reference. The internal 1.1V reference is generated from the internal CC bandgap reference (V ) through an internal amplifier. BG The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is advised to discard this result. 17.7 ADC Noise Canceler The ADC features a noise canceler that enables conversion during sleep mode. This reduces noise induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the following procedure should be used: (cid:129) Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be selected and the ADC conversion complete interrupt must be enabled. (cid:129) Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted. (cid:129) If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt request will be generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep command is executed. Note that the ADC will not automatically be turned off when entering other sleep modes than Idle mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter- ing such sleep modes to avoid excessive power consumption. 17.8 Analog Input Circuitry The analog input circuitry for single ended channels is illustrated in Figure 17-8 An analog source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard- less of whether that channel is selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined resistance in the input path). The ADC is optimized for analog signals with an output impedance of approximately 10kΩ or less. If such a source is used, the sampling time will be negligible. If a source with higher imped- ance is used, the sampling time will depend on how long time the source needs to charge the S/H capacitor, which can vary widely. The user is recommended to only use low impedance sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor. In order to avoid distortion from unpredictable signal convolution, signal components higher than the Nyquist frequency (f /2) should not be present. The user is advised to remove high fre- ADC quency components with a low-pass filter before applying the signals as inputs to the ADC. 171 8008H–AVR–04/11

Figure 17-8. Analog Input Circuitry I IH ADCn 1..100 kOhm C = 14 pF S/H I IL V /2 CC Note: The capacitor in the figure depicts the total capacitance, including the sample/hold capacitor and any stray or parasitic capacitance inside the device. The value given is worst case. 17.9 Analog Noise Canceling Techniques Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. When conversion accuracy is critical, the noise level can be reduced by applying the following techniques: (cid:129) Keep analog signal paths as short as possible. (cid:129) Make sure analog tracks run over the analog ground plane. (cid:129) Keep analog tracks well away from high-speed switching digital tracks. (cid:129) If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress. (cid:129) The analog supply voltage pin (AV ) should be connected to the digital supply voltage pin CC (V ) via an LC network as shown in Figure 17-9. CC Figure 17-9. ADC Power Connections L) A) C D C5/S C4/S C3) C2) ane D D D D Pl PD0 PC6 PC5 (A PC4 (A PC3 (A PC2 (A Ground g o al n A PC1 (ADC1) PC0 (ADC0) VCC PA1 (ADC7) GND F n PC7 00 1 H m PA0 (ADC6) 0 1 AVCC PB5 ATtiny48/88 172 8008H–AVR–04/11

ATtiny48/88 Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as described in Section 17.7 on page 171. This is especially the case when system clock frequency is above 1 MHz, or when the ADC is used for reading the internal temperature sensor, as described in Section 17.12 on page 175. A good system design with properly placed, external bypass capacitors does reduce the need for using ADC Noise Reduction Mode 17.10 ADC Accuracy Definitions An n-bit single-ended ADC converts a voltage linearly between GND and V in 2n steps REF (LSBs). The lowest code is read as 0, and the highest code is read as 2n-1. Several parameters describe the deviation from the ideal behavior: (cid:129) Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 LSB). Ideal value: 0 LSB. Figure 17-10. Offset Error Output Code Ideal ADC Actual ADC Offset Error V Input Voltage REF 173 8008H–AVR–04/11

(cid:129) Gain error: After adjusting for offset, the gain error is found as the deviation of the last transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum). Ideal value: 0 LSB Figure 17-11. Gain Error Output Code Gain Error Ideal ADC Actual ADC V Input Voltage REF (cid:129) Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0 LSB. Figure 17-12. Integral Non-linearity (INL) Output Code IN L Ideal ADC Actual ADC V Input Voltage REF ATtiny48/88 174 8008H–AVR–04/11

ATtiny48/88 (cid:129) Differential Non-linearity (DNL): The maximum deviation of the actual code width (the interval between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB. Figure 17-13. Differential Non-linearity (DNL) Output Code 0x3FF 1 LSB DNL 0x000 0 V Input Voltage REF (cid:129) Quantization Error: Due to the quantization of the input voltage into a finite number of codes, a range of input voltages (1 LSB wide) will code to the same value. Always ±0.5 LSB. (cid:129) Absolute accuracy: The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for any code. This is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. Ideal value: ±0.5 LSB. 17.11 ADC Conversion Result After the conversion is complete (ADIF is high), the conversion result can be found in the ADC Result Registers (ADCL, ADCH). For single ended conversion, the result is V ⋅1024 ADC = ----I--N-------------------- V REF where V is the voltage on the selected input pin and V the selected voltage reference (see IN REF Table 17-3 on page 176 and Table 17-4 on page 177). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one LSB. 17.12 Temperature Measurement The temperature measurement is based on an on-chip temperature sensor that is coupled to a single-ended ADC8 channel. Selecting the ADC8 channel by writing the MUX[3:0] bits in 175 8008H–AVR–04/11

ADMUX register to “1000” enables the temperature sensor. The internal 1.1V voltage reference must also be selected for the ADC voltage reference source in the temperature sensor measure- ment. When the temperature sensor is enabled, the ADC converter can be used in single conversion mode to measure the voltage over the temperature sensor. The measured voltage has a linear relationship to the temperature as described in Table 17-2 The sensitivity is approximately 1 LSB / °C and the accuracy depends on the method of user cal- ibration. Typically, the measurement accuracy after a single temperature calibration is ±10°C, assuming calibration at room temperature. Better accuracies are achieved by using two temperature points for calibration. Table 17-2. Temperature vs. Sensor Output Voltage (Typical Case) Temperature -40°C +25°C +85°C ADC 230 LSB 300 LSB 370 LSB The values described in Table 17-2 are typical values. However, due to process variation the temperature sensor output voltage varies from one chip to another. To be capable of achieving more accurate results the temperature measurement can be calibrated in the application soft- ware. The sofware calibration can be done using the formula: T = k * [(ADCH << 8) | ADCL] + T OS where ADCH and ADCL are the ADC data registers, k is the fixed slope coefficient and T is the OS temperature sensor offset. Typically, k is very close to 1.0 and in single-point calibration the coefficient may be omitted. Where higher accuracy is required the slope coefficient should be evaluated based on measurements at two temperatures. 17.13 Register Description 17.13.1 ADMUX – ADC Multiplexer Selection Register Bit 7 6 5 4 3 2 1 0 (0x7C) – REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 ADMUX Read/Write R R/W R/W R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7, 4 – Res: Reserved Bits These bits are reserved and will always read zero. (cid:129) Bit 6 – REFS0: Reference Selection Bit This bit select the voltage reference for the ADC, as shown in Table 17-3. If this bit is changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set). Table 17-3. Voltage Reference Selections for ADC REFS0 Voltage Reference Selection 0 Internal 1.1V Voltage Reference 1 AV Reference CC ATtiny48/88 176 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 5 – ADLAR: ADC Left Adjust Result The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register. Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver- sions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data Register” on page 179. (cid:129) Bits 3:0 – MUX[3:0]: Analog Channel Selection Bits The value of these bits selects which analog inputs are connected to the ADC. Selecting the sin- gle-ended channel ADC8 enables the temperature measurement. See Table 17-4 for details. If these bits are changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set). Table 17-4. Input Channel Selections MUX[3:0] Single Ended Input 0000 ADC0 0001 ADC1 0010 ADC2 0011 ADC3 0100 ADC4 0101 ADC5 0110 ADC6 0111 ADC7 1000 ADC8 (1) 1001 (reserved) 1010 (reserved) 1011 (reserved) 1100 (reserved) 1101 (reserved) 1110 1.1V (V ) (2) BG 1111 0V (GND) Note: 1. See “Temperature Measurement” on page 175. 2. After switching to internal voltage reference the ADC requires a settling time of 1ms before measurements are stable. Conversions starting before this may not be reliable. The ADC must be enabled during the settling time. 177 8008H–AVR–04/11

17.13.2 ADCSRA – ADC Control and Status Register A Bit 7 6 5 4 3 2 1 0 (0x7A) ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSRA Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – ADEN: ADC Enable Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is in progress, will terminate this conversion. (cid:129) Bit 6 – ADSC: ADC Start Conversion In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode, write this bit to one to start the first conversion. The first conversion after ADSC has been written after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initializa- tion of the ADC. ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing zero to this bit has no effect. (cid:129) Bit 5 – ADATE: ADC Auto Trigger Enable When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a con- version on a positive edge of the selected trigger signal. The trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB. (cid:129) Bit 4 – ADIF: ADC Interrupt Flag This bit is set when an ADC conversion completes and the Data Registers are updated. The ADC Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is cleared by hardware when executing the corresponding interrupt handling vector. Alter- natively, ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify- Write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions are used. (cid:129) Bit 3 – ADIE: ADC Interrupt Enable When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete Inter- rupt is activated. (cid:129) Bits 2:0 – ADPS[2:0]: ADC Prescaler Select Bits These bits determine the division factor between the system clock frequency and the input clock to the ADC. Table 17-5. ADC Prescaler Selections ADPS2 ADPS1 ADPS0 Division Factor 0 0 0 2 0 0 1 2 0 1 0 4 0 1 1 8 1 0 0 16 ATtiny48/88 178 8008H–AVR–04/11

ATtiny48/88 Table 17-5. ADC Prescaler Selections (Continued) ADPS2 ADPS1 ADPS0 Division Factor 1 0 1 32 1 1 0 64 1 1 1 128 17.13.3 ADCL and ADCH – The ADC Data Register 17.13.3.1 ADLAR = 0 Bit 15 14 13 12 11 10 9 8 (0x79) – – – – – – ADC9 ADC8 ADCH (0x78) ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL 7 6 5 4 3 2 1 0 Read/Write R R R R R R R R R R R R R R R R Initial Value 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17.13.3.2 ADLAR = 1 Bit 15 14 13 12 11 10 9 8 (0x79) ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH (0x78) ADC1 ADC0 – – – – – – ADCL 7 6 5 4 3 2 1 0 Read/Write R R R R R R R R R R R R R R R R Initial Value 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 (cid:129) ADC[9:0]: ADC Conversion Result These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on page 175. When an ADC conversion is complete, the result is found in these two registers. When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH. The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted. 17.13.4 ADCSRB – ADC Control and Status Register B Bit 7 6 5 4 3 2 1 0 (0x7B) – ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB Read/Write R R/W R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7, 5:3 – Res: Reserved Bits These bits are reserved for future use. To ensure compatibility with future devices, these bits must be written to zero when ADCSRB is written. 179 8008H–AVR–04/11

(cid:129) Bits 2:0 – ADTS[2:0]: ADC Auto Trigger Source If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion. If ADATE is cleared, the ADTS[2:0] settings will have no effect. A conver- sion will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive edge on the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set. Table 17-6. ADC Auto Trigger Source Selections ADTS2 ADTS1 ADTS0 Trigger Source 0 0 0 Free Running mode 0 0 1 Analog Comparator 0 1 0 External Interrupt Request 0 0 1 1 Timer/Counter0 Compare Match A 1 0 0 Timer/Counter0 Overflow 1 0 1 Timer/Counter1 Compare Match B 1 1 0 Timer/Counter1 Overflow 1 1 1 Timer/Counter1 Capture Event 17.13.5 DIDR0 – Digital Input Disable Register 0 Bit 7 6 5 4 3 2 1 0 (0x7E) ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bits 7:0 – ADC7D:ADC0D: ADC[7:0] Digital Input Disable When this bit is written logic one, the digital input buffer on the corresponding ADC pin is dis- abled. The corresponding PIN Register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC[7:0] pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer. ATtiny48/88 180 8008H–AVR–04/11

ATtiny48/88 18. debugWIRE On-Chip Debug System 18.1 Features (cid:129) Complete Program Flow Control (cid:129) Emulates All On-Chip Functions, Both Digital and Analog, except RESET Pin (cid:129) Real-time Operation (cid:129) Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs) (cid:129) Unlimited Number of Program Break Points (Using Software Break Points) (cid:129) Non-intrusive Operation (cid:129) Electrical Characteristics Identical to Real Device (cid:129) Automatic Configuration System (cid:129) High-Speed Operation (cid:129) Programming of Non-volatile Memories 18.2 Overview The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the program flow, execute AVR instructions in the CPU and to program the different non-volatile memories. 18.3 Physical Interface When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed, the debugWIRE system within the target device is activated. The RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the commu- nication gateway between target and emulator. Figure 18-1. The debugWIRE Setup 1.8 - 5.5V VCC dW dW(RESET) GND Figure 18-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system clock is not affected by debugWIRE and will always be the clock source selected by the CKSEL Fuses. 181 8008H–AVR–04/11

When designing a system where debugWIRE will be used, the following observations must be made for correct operation: (cid:129) Pull-up resistors on the dW/(RESET) line must not be smaller than 10kΩ. The pull-up resistor is not required for debugWIRE functionality. (cid:129) Connecting the RESET pin directly to V will not work. CC (cid:129) Capacitors connected to the RESET pin must be disconnected when using debugWire. (cid:129) All external reset sources must be disconnected. 18.4 Software Break Points debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruc- tion replaced by the BREAK instruction will be stored. When program execution is continued, the stored instruction will be executed before continuing from the Program memory. A break can be inserted manually by putting the BREAK instruction in the program. The Flash must be re-programmed each time a Break Point is changed. This is automatically handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore reduce the Flash Data retention. Devices used for debugging purposes should not be shipped to end customers. 18.5 Limitations of debugWIRE The debugWIRE communication pin (dW) is physically located on the same pin as External Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is enabled. The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e., when the program in the CPU is running. When the CPU is stopped, care must be taken while accessing some of the I/O Registers via the debugger (AVR Studio). The debugWIRE interface is asynchronous, which means that the debugger needs to synchro- nize to the system clock. If the system clock is changed by software (e.g. by writing CLKPS bits) communication via debugWIRE may fail. Also, clock frequencies below 100 kHz may cause communication problems. A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should be disabled when debugWire is not used. 18.6 Register Description 18.6.1 DWDR – debugWire Data Register Bit 7 6 5 4 3 2 1 0 0x31 (0x51) DWDR[7:0] DWDR Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 The DWDR Register provides a communication channel from the running program in the MCU to the debugger. This register is only accessible by the debugWIRE and can therefore not be used as a general purpose register in the normal operations. ATtiny48/88 182 8008H–AVR–04/11

ATtiny48/88 19. Self-Programming the Flash The device provides a Self-Programming mechanism for downloading and uploading program code by the MCU itself. The Self-Programming can use any available data interface and associ- ated protocol to read code and write (program) that code into the Program memory. The SPM instruction is disabled by default but it can be enabled by programming the SELFPRGEN fuse (to “0”). The Program memory is updated in a page by page fashion. Before programming a page with the data stored in the temporary page buffer, the page must be erased. The temporary page buf- fer is filled one word at a time using SPM and the buffer can be filled either before the Page Erase command or between a Page Erase and a Page Write operation: Alternative 1, fill the buffer before a Page Erase: (cid:129) Fill temporary page buffer (cid:129) Perform a Page Erase (cid:129) Perform a Page Write Alternative 2, fill the buffer after Page Erase: (cid:129) Perform a Page Erase (cid:129) Fill temporary page buffer (cid:129) Perform a Page Write If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page buffer) before the erase, and then be re-written. Alternative 1 provides an effective Read-Modify-Write feature which allows the user software to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not pos- sible to read the old data while loading since the page is already erased. The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in both the Page Erase and Page Write operation is addressing the same page. 19.0.1 Performing Page Erase by SPM To execute Page Erase, set up the address in the Z-pointer, write “00000011” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will be ignored during this operation. The CPU is halted during the Page Erase operation. 19.0.2 Filling the Temporary Buffer (Page Loading) To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write “00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The content of PCWORD in the Z-register is used to address the data in the temporary buffer. The temporary buffer will auto-erase after a Page Write operation or by writing the CTPB bit in SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than one time to each address without erasing the temporary buffer. If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be lost. 183 8008H–AVR–04/11

19.0.3 Performing a Page Write To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to zero during this operation. The CPU is halted during the Page Write operation. 19.1 Addressing the Flash During Self-Programming The Z-pointer is used to address the SPM commands. Bit 15 14 13 12 11 10 9 8 ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8 ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0 7 6 5 4 3 2 1 0 Since the Flash is organized in pages (see “Memory Parametrics” on page 191), the Program Counter can be treated as having two different sections. One section, consisting of the least sig- nificant bits, is addressing the words within a page, while the most significant bits are addressing the pages. This is shown in Figure 19-1. Note that the Page Erase and Page Write operations are addressed independently. Therefore it is of major importance that the software addresses the same page in both the Page Erase and Page Write operation. The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used. Figure 19-1. Addressing the Flash During SPM(1) BIT 15 ZPCMSB ZPAGEMSB 1 0 Z - REGISTER 0 PCMSB PAGEMSB PROGRAM PCPAGE PCWORD COUNTER PAGE ADDRESS WORD ADDRESS WITHIN THE FLASH WITHIN A PAGE PROGRAM MEMORY PAGE PCWORD[PAGEMSB:0]: PAGE INSTRUCTION WORD 00 01 02 PAGEEND Note: 1. The different variables used in Figure 19-1 are listed in Table 21-1 on page 191. ATtiny48/88 184 8008H–AVR–04/11

ATtiny48/88 19.1.1 EEPROM Write Prevents Writing to SPMCSR Note that an EEPROM write operation will block all software programming to Flash. Reading the Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies that the bit is cleared before writing to the SPMCSR Register. 19.1.2 Reading the Fuse and Lock Bits from Software It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the Z-pointer with 0x0001 and set the RFLB and SELFPRGEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the RFLB and SELFPRGEN bits are set in SPMCSR, the value of the Lock bits will be loaded in the destination register. The RFLB and SELFPRGEN bits will auto-clear upon completion of reading the Lock bits or if no LPM instruc- tion is executed within three CPU cycles or no SPM instruction is executed within four CPU cycles. When RFLB and SELFPRGEN are cleared, LPM will work as described in the Instruction set Manual. Bit 7 6 5 4 3 2 1 0 Rd – – – – – – LB2 LB1 The algorithm for reading the Fuse Low byte is similar to the one described above for reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the RFLB and SELFPRGEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the RFLB and SELFPRGEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will be loaded in the destination register as shown below.See Table 20-5 on page 190 for a detailed description and mapping of the Fuse Low byte. Bit 7 6 5 4 3 2 1 0 Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0 Similarly, when reading the Fuse High byte (FHB), load 0x0003 in the Z-pointer. When an LPM instruction is executed within three cycles after the RFLB and SELFPRGEN bits are set in the SPMCSR, the value of the Fuse High byte will be loaded in the destination register as shown below. See Table 20-4 on page 189 for detailed description and mapping of the Fuse High byte. Bit 7 6 5 4 3 2 1 0 Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0 Fuse Extended byte can be read by loading the Z-pointer with 0x0002. When an LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse Extended Byte (FEB) will be loaded in the destination register as shown below. See Table 20-3 on page 189 for detailed description and mapping of the Fuse Extended byte. Bit 7 6 5 4 3 2 1 0 Rd FEB7 FEB6 FEB5 FEB4 FEB3 FEB2 FEB1 FEB0 Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are unprogrammed, will be read as one. 185 8008H–AVR–04/11

19.1.3 Preventing Flash Corruption During periods of low V , the Flash program can be corrupted because the supply voltage is CC too low for the CPU and the Flash to operate properly. These issues are the same as for board level systems using the Flash, and the same design solutions should be applied. A Flash program corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions is too low. Flash corruption can easily be avoided by following these design recommendations (one is sufficient): 1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the internal Brown-out Detector (BOD) if the operating voltage matches the detection level. If not, an external low V reset protection circuit CC can be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient. 2. Keep the AVR core in Power-down sleep mode during periods of low V . This will pre- CC vent the CPU from attempting to decode and execute instructions, effectively protecting the SPMCSR Register and thus the Flash from unintentional writes. 19.1.4 Programming Time for Flash when Using SPM The calibrated oscillator is used to time Flash accesses. Table 19-1 shows the typical program- ming time for Flash accesses from the CPU. Table 19-1. SPM Programming Time Symbol Min Programming Time Max Programming Time Flash write (Page Erase, Page Write, and 3.7 ms 4.5 ms write Lock bits by SPM) 19.2 Register Description 19.2.1 SPMCSR – Store Program Memory Control and Status Register The Store Program Memory Control and Status Register contains the control bits needed to con- trol the Program memory operations. Bit 7 6 5 4 3 2 1 0 0x37 (0x57) – RWWSB – CTPB RFLB PGWRT PGERS SELFPRGEN SPMCSR Read/Write R R R R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0 (cid:129) Bit 7 – Res: Reserved Bit This bit is reserved and will always read zero. (cid:129) Bit 6 – RWWSB: Read-While-Write Section Busy This bit is for compatibility with devices supporting Read-While-Write. It will always read as zero in ATtiny48/88. ATtiny48/88 186 8008H–AVR–04/11

ATtiny48/88 (cid:129) Bit 5 – Res: Reserved Bit This bit is reserved and will always read zero. (cid:129) Bit 4 – CTPB: Clear Temporary Page Buffer If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be cleared and the data will be lost. (cid:129) Bit 3 – RFLB: Read Fuse and Lock Bits An LPM instruction within three cycles after RFLB and SELFPRGEN are set in the SPMCSR Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the destination register. See “Reading the Fuse and Lock Bits from Software” on page 185 for details. (cid:129) Bit 2 – PGWRT: Page Write If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four clock cycles executes Page Write, with the data stored in the temporary buffer. The page address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire Page Write operation. (cid:129) Bit 1 – PGERS: Page Erase If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four clock cycles executes Page Erase. The page address is taken from the high part of the Z- pointer. The data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase, or if no SPM instruction is executed within four clock cycles. The CPU is halted dur- ing the entire Page Write operation. (cid:129) Bit 0 – SELFPRGEN: Self Programming Enable This bit enables the SPM instruction for the next four clock cycles. If written to one together with either CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction will have a special meaning, see description above. If only SELFPRGEN is written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of the Z-pointer is ignored. The SELFPRGEN bit will auto-clear upon completion of an SPM instruction, or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write, the SELFPRGEN bit remains high until the operation is completed. Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower five bits will have no effect. 187 8008H–AVR–04/11

20. Lock Bits, Fuse Bits and Device Signature 20.1 Lock Bits ATtiny48/88 provide the program and data memory lock bits listed in Table 20-1. Table 20-1. Lock Bit Byte Lock Bit Byte Bit No Description Default Value (1) 7 – 1 (unprogrammed) 6 – 1 (unprogrammed) 5 – 1 (unprogrammed) 4 – 1 (unprogrammed) 3 – 1 (unprogrammed) 2 – 1 (unprogrammed) LB2 1 Lock bit 1 (unprogrammed) LB1 0 Lock bit 1 (unprogrammed) Notes: 1. “1” means unprogrammed, “0” means programmed. Lock bits can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 20-2. Table 20-2. Lock Bit Protection Modes(1)(2) Memory Lock Bits Protection Type LB Mode LB2 LB1 1 1 1 No memory lock features enabled. Further programming of Flash and EEPROM is disabled in 2 1 0 parallel and serial programming mode. Fuse bits are locked in both serial and parallel programming mode (1) Further reading and programming of Flash and EEPROM is 3 0 0 disabled in parallel and serial programming mode. Fuse bits are locked in both serial and parallel programming mode (1) Notes: 1. Program the Fuse bits before programming the LB1 and LB2. 2. “1” means unprogrammed, “0” means programmed Lock bits can be erased to “1” with the Chip Erase command, only. The ATtiny48/88 has no separate Boot Loader section. The SPM instruction is enabled for the whole Flash if the SELFPRGEN fuse is programmed (“0”), otherwise it is disabled. ATtiny48/88 188 8008H–AVR–04/11

ATtiny48/88 20.2 Fuse Bits The ATtiny48/88 has three Fuse bytes. Table 20-3 – Table 20-5 describe briefly the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses are read as logical zero, “0”, if they are programmed. Table 20-3. Fuse Extended Byte Fuse Extended Byte Bit No Description Default Value – 7 – 1 – 6 – 1 – 5 – 1 – 4 – 1 – 3 – 1 – 2 – 1 – 1 – 1 SELFPRGEN (1) 0 Self Programming Enable 1 (unprogrammed) Notes: 1. Enables SPM instruction. See “Self-Programming the Flash” on page 183. Table 20-4. Fuse High Byte Fuse High Byte Bit No Description Default Value RSTDISBL(1) (2) 7 External Reset Disable 1 (unprogrammed) DWEN(2) 6 debugWIRE Enable 1 (unprogrammed) Enable Serial Program and Data 0 (programmed) SPIEN(3) 5 Downloading (SPI programming enabled) WDTON(4) 4 Watchdog Timer Always On 1 (unprogrammed) EEPROM memory preserved 1 (unprogrammed) EESAVE 3 through chip erase (EEPROM not preserved) BODLEVEL2(5) 2 Brown-out Detector trigger level 1 (unprogrammed) BODLEVEL1(5) 1 Brown-out Detector trigger level 1 (unprogrammed) BODLEVEL0(5) 0 Brown-out Detector trigger level 1 (unprogrammed) Notes: 1. See “Alternate Functions of Port C” on page 72 for description of RSTDISBL Fuse. 2. Programming this fuse bit will change the functionality of the RESET pin and render further programming via the serial interface impossible. The fuse bit can be unprogrammed using the parallel programming algorithm (see page 191). 3. The SPIEN Fuse is not accessible in serial programming mode. 4. See “WDTCSR – Watchdog Timer Control Register” on page 49 for details. 5. See Table 22-4 on page 210 for BODLEVEL Fuse decoding. 189 8008H–AVR–04/11

Table 20-5. Fuse Low Byte Fuse Low Byte Bit No Description Default Value CKDIV8(4) 7 Divide clock by 8 0 (programmed) CKOUT(3) 6 Clock output 1 (unprogrammed) SUT1 5 Select start-up time 1 (unprogrammed)(1) SUT0 4 Select start-up time 0 (programmed)(1) - 3 - 1 (unprogrammed)(2) - 2 - 1 (unprogrammed)(2) CKSEL1 1 Select Clock source 1 (unprogrammed)(2) CKSEL0 0 Select Clock source 0 (programmed)(2) Note: 1. The default value of SUT[1:0] results in maximum start-up time for the default clock source. See Table 6-3 on page 31 for details. 2. The default setting of CKSEL[1:0] results in internal oscillator @ 8 MHz. See Table 6-1 on page 29 for details. 3. The CKOUT Fuse allows the system clock to be output on PORTB0. See “Clock Output Buffer” on page 32 for details. 4. See “System Clock Prescaler” on page 31 for details. The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits. 20.2.1 Latching of Fuses The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect until the part leaves Programming mode. This does not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on Power-up in Normal mode. 20.3 Signature Bytes All Atmel microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial and parallel mode, also when the device is locked. The three bytes reside in a separate address space. For the ATtiny48/88 the signature bytes are given in Table 20-6. Table 20-6. Device ID Signature Bytes Address Part 0x000 0x001 0x002 ATtiny48 0x1E 0x92 0x09 ATtiny88 0x1E 0x93 0x11 20.4 Calibration Byte The ATtiny48/88 has a byte calibration value for the internal oscillator. This byte resides in the high byte of address 0x000 in the signature address space. During reset, this byte is automati- cally written into the OSCCAL Register to ensure correct frequency of the calibrated oscillator. ATtiny48/88 190 8008H–AVR–04/11

ATtiny48/88 21. External Programming This section describes how to program and verify Flash memory, EEPROM, lock bits, and fuse bits in ATtiny48/88. 21.1 Memory Parametrics Flash memory parametrics are summarised in Table 21-1, below. Table 21-1. Flash Parametrics No. of Device Flash Size Page Size PCWORD Pages PCPAGE PCMSB 2K words ATtiny48 32 words PC[4:0] 64 PC[10:5] 10 (4K bytes) 4K words ATtiny88 32 words PC[4:0] 128 PC[11:5] 11 (8K bytes) EEPROM parametrics are summarised in Table 21-2, below. Table 21-2. EEPROM Parametrics EEPROM Page No. of Device Size Size PCWORD Pages PCPAGE EEAMSB ATtiny48 64 bytes 4 bytes EEA[1:0] 16 EEA[5:2] 5 ATtiny88 64 bytes 4 bytes EEA[1:0] 16 EEA[5:2] 5 21.2 Parallel Programming Parallel programming signals and connections are illustrated in Figure 21-1, below. Figure 21-1. Parallel Programming Signals +4.5 - 5.5V RDY/BSY PD1 VCC OE PD2 +4.5 - 5.5V WR PD3 AVCC BS1 PD4 XA0 PD5 PC[1:0]:PB[5:0] DATA XA1 PD6 PAGEL PD7 +12 V RESET BS2 PC2 CLKI GND 191 8008H–AVR–04/11

Signals are described in Table 21-3, below. Pins not listed in the table are referenced by pin names. Table 21-3. Pin Name Mapping Signal Name in Programming Mode Pin Name I/O Function 0: Device is busy programming, 1: Device is RDY/BSY PD1 O ready for new command OE PD2 I Output Enable (Active low) WR PD3 I Write Pulse (Active low) Byte Select 1 (“0” selects Low byte, “1” selects BS1 PD4 I High byte) XA0 PD5 I XTAL Action Bit 0 XA1 PD6 I XTAL Action Bit 1 Program memory and EEPROM Data Page PAGEL PD7 I Load Byte Select 2 (“0” selects Low byte, “1” selects BS2 PC2 I 2’nd High byte) DATA {PC[1:0]: PB[5:0]} I/O Bi-directional Data bus (Output when OE is low) Note: V - 0.3V < AV < V + 0.3V, however, AV should always be within 4.5 – 5.5V CC CC CC CC Pulses are assumed to be at least 250 ns, unless otherwise noted. Table 21-4. Pin Values Used to Enter Programming Mode Pin Symbol Value PAGEL Prog_enable[3] 0 XA1 Prog_enable[2] 0 XA0 Prog_enable[1] 0 BS1 Prog_enable[0] 0 The XA1/XA0 pins determine the action executed when the CLKI pin is given a positive pulse. The bit coding is shown in Table 21-5. Table 21-5. XA1 and XA0 Coding XA1 XA0 Action when CLKI is Pulsed 0 0 Load Flash or EEPROM Address (High or low address byte determined by BS1). 0 1 Load Data (High or Low data byte for Flash determined by BS1). 1 0 Load Command 1 1 No Action, Idle ATtiny48/88 192 8008H–AVR–04/11

ATtiny48/88 When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 21-6. Table 21-6. Command Byte Bit Coding Command Byte Command Executed 1000 0000 Chip Erase 0100 0000 Write Fuse bits 0010 0000 Write Lock bits 0001 0000 Write Flash 0001 0001 Write EEPROM 0000 1000 Read Signature Bytes and Calibration byte 0000 0100 Read Fuse and Lock bits 0000 0010 Read Flash 0000 0011 Read EEPROM 21.2.1 Enter Programming Mode The following algorithm puts the device in Parallel (High-voltage) Programming mode: 1. Set Prog_enable pins listed in Table 21-4 on page 192 to “0000”, RESET pin to 0V and V to 0V. CC 2. Apply 4.5 – 5.5V between V and GND. Ensure that V reaches at least 1.8V within CC CC the next 20 µs. 3. Wait 20 – 60 µs, and apply 11.5 – 12.5V to RESET. 4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been applied to ensure the Prog_enable Signature has been latched. 5. Wait at least 300 µs before giving any parallel programming commands. 6. Exit Programming mode by power the device down or by bringing RESET pin to 0V. If the rise time of the V is unable to fulfill the requirements listed above, the following alterna- CC tive algorithm can be used. 1. Set Prog_enable pins listed in Table 21-4 on page 192 to “0000”, RESET pin to 0V and V to 0V. CC 2. Apply 4.5 – 5.5V between V and GND. CC 3. Monitor V , and as soon as V reaches 0.9 – 1.1V, apply 11.5 – 12.5V to RESET. CC CC 4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been applied to ensure the Prog_enable Signature has been latched. 5. Wait until V actually reaches 4.5 -5.5V before giving any parallel programming CC commands. 6. Exit Programming mode by power the device down or by bringing RESET pin to 0V. 21.2.2 Considerations for Efficient Programming The loaded command and address are retained in the device during programming. For efficient programming, the following should be considered. 193 8008H–AVR–04/11

(cid:129) The command needs only be loaded once when writing or reading multiple memory locations. (cid:129) Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE Fuse is programmed) and Flash after a Chip Erase. (cid:129) Address high byte needs only be loaded before programming or reading a new 256 word window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes reading. 21.2.3 Chip Erase A Chip Erase must be performed before the Flash and/or EEPROM are reprogrammed. The Chip Erase command will erase all Flash and EEPROM plus lock bits. If the EESAVE fuse is programmed, the EEPROM is not erased. Lock bits are not reset until the program memory has been completely erased. Fuse bits are not changed. The Chip Erase command is loaded as follows: 1. Set XA1, XA0 to “10”. This enables command loading 2. Set BS1 to “0” 3. Set DATA to “1000 0000”. This is the command for Chip Erase 4. Give CLKI a positive pulse. This loads the command 5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low 6. Wait until RDY/BSY goes high before loading a new command 21.2.4 Programming the Flash The Flash is organized in pages, see Table 21-1 on page 191. When programming the Flash, the program data is latched into a page buffer. This allows one page of program data to be pro- grammed simultaneously. The following procedure describes how to program the entire Flash memory: A. Load Command “Write Flash” 1. Set XA1, XA0 to “10”. This enables command loading. 2. Set BS1 to “0”. 3. Set DATA to “0001 0000”. This is the command for Write Flash. 4. Give CLKI a positive pulse. This loads the command. B. Load Address Low byte 1. Set XA1, XA0 to “00”. This enables address loading. 2. Set BS1 to “0”. This selects low address. 3. Set DATA = Address low byte (0x00 – 0xFF). 4. Give CLKI a positive pulse. This loads the address low byte. C. Load Data Low Byte 1. Set XA1, XA0 to “01”. This enables data loading. 2. Set DATA = Data low byte (0x00 – 0xFF). ATtiny48/88 194 8008H–AVR–04/11

ATtiny48/88 3. Give CLKI a positive pulse. This loads the data byte. D. Load Data High Byte 1. Set BS1 to “1”. This selects high data byte. 2. Set XA1, XA0 to “01”. This enables data loading. 3. Set DATA = Data high byte (0x00 – 0xFF). 4. Give CLKI a positive pulse. This loads the data byte. E. Latch Data 1. Set BS1 to “1”. This selects high data byte. 2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 21-3 for signal waveforms) F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded. While the lower bits in the address are mapped to words within the page, the higher bits address the pages within the FLASH. This is illustrated in Figure 21-2 on page 196. Note that if less than eight bits are required to address words in the page (pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a Page Write. G. Load Address High byte 1. Set XA1, XA0 to “00”. This enables address loading. 2. Set BS1 to “1”. This selects high address. 3. Set DATA = Address high byte (0x00 – 0xFF). 4. Give CLKI a positive pulse. This loads the address high byte. H. Program Page 1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY goes low. 2. Wait until RDY/BSY goes high (See Figure 21-3 for signal waveforms). I. Repeat B through H until the entire Flash is programmed or until all data has been programmed. J. End Page Programming 1. 1. Set XA1, XA0 to “10”. This enables command loading. 2. Set DATA to “0000 0000”. This is the command for No Operation. 3. Give CLKI a positive pulse. This loads the command, and the internal write signals are reset. 195 8008H–AVR–04/11

Flash page addressing is illustrated in Figure 21-2, below. Symbols used are described in Table 21-1 on page 191. Figure 21-2. Addressing the Flash Which is Organized in Pages PCMSB PAGEMSB PROGRAM PCPAGE PCWORD COUNTER PAGE ADDRESS WORD ADDRESS WITHIN THE FLASH WITHIN A PAGE PROGRAM MEMORY PAGE PCWORD[PAGEMSB:0]: PAGE INSTRUCTION WORD 00 01 02 PAGEEND Flash programming waveforms are illustrated in Figure 21-3, where XX means “don’t care” and letters refer to the programming steps described earlier. Figure 21-3. Programming the Flash Waveforms F A B C D E B C D E G H DATA 0x10 ADDR. LOW DATA LOW DATA HIGH XX ADDR. LOW DATA LOW DATA HIGH XX ADDR. HIGH XX XA1 XA0 BS1 CLKI WR RDY/BSY RESET +12V OE PAGEL BS2 21.2.5 Programming the EEPROM The EEPROM is organized in pages, see Table 21-2 on page 191. When programming the EEPROM, the program data is latched into a page buffer. This allows one page of data to be ATtiny48/88 196 8008H–AVR–04/11

ATtiny48/88 programmed simultaneously. The programming algorithm for the EEPROM data memory is as follows (refer to “Programming the Flash” on page 194 for details on Command, Address and Data loading): (cid:129) A: Load command “0001 0001” (cid:129) G: Load address high byte (0x00 – 0xFF) (cid:129) B: Load address low byte (0x00 – 0xFF) (cid:129) C: Load data (0x00 – 0xFF) (cid:129) E: Latch data (give PAGEL a positive pulse) (cid:129) K: Repeat steps B, C, and E until the entire buffer is filled (cid:129) L: Program EEPROM page: – Set BS1 to “0” – Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY goes low – Wait until to RDY/BSY goes high before programming the next page (See Figure 21- 4 for signal waveforms) EEPROM programming waveforms are illustrated in Figure 21-4, where XX means “don’t care” and letters refer to the programming steps described above. Figure 21-4. Programming the EEPROM Waveforms K A G B C E B C E L DATA 0x11 ADDR. HIGH ADDR. LOW DATA XX ADDR. LOW DATA XX XA1 XA0 BS1 CLKI WR RDY/BSY RESET +12V OE PAGEL BS2 21.2.6 Reading the Flash The algorithm for reading the Flash memory is as follows (see “Programming the Flash” on page 194 for details on command and address loading): (cid:129) A: Load command “0000 0010” (cid:129) G: Load address high byte (0x00 – 0xFF) (cid:129) B: Load address low byte (0x00 – 0xFF) (cid:129) Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA 197 8008H–AVR–04/11

(cid:129) Set BS1 to “1”. The Flash word high byte can now be read at DATA (cid:129) Set OE to “1” 21.2.7 Reading the EEPROM The algorithm for reading the EEPROM memory is as follows (see “Programming the Flash” on page 194 for details on command and address loading): (cid:129) A: Load command “0000 0011” (cid:129) G: Load address high byte (0x00 – 0xFF) (cid:129) B: Load address low byte (0x00 – 0xFF) (cid:129) Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA (cid:129) Set OE to “1” 21.2.8 Programming Low Fuse Bits The algorithm for programming the low fuse bits is as follows (see “Programming the Flash” on page 194 for details on command and data loading): (cid:129) A: Load command “0100 0000” (cid:129) C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit (cid:129) Give WR a negative pulse and wait for RDY/BSY to go high 21.2.9 Programming High Fuse Bits The algorithm for programming the high fuse bits is as follows (see “Programming the Flash” on page 194 for details on command and data loading): (cid:129) A: Load command “0100 0000” (cid:129) C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit (cid:129) Set BS1 to “1” and BS2 to “0”. This selects high data byte (cid:129) Give WR a negative pulse and wait for RDY/BSY to go high (cid:129) Set BS1 to “0”. This selects low data byte 21.2.10 Programming Extended Fuse Bits The algorithm for programming the extended fuse bits is as follows (see “Programming the Flash” on page 194 for details on command and data loading): (cid:129) A: Load command “0100 0000” (cid:129) C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit (cid:129) Set BS1 to “0” and BS2 to “1”. This selects extended data byte (cid:129) Give WR a negative pulse and wait for RDY/BSY to go high (cid:129) Set BS2 to “0”. This selects low data byte EEPROM programming waveforms are illustrated in Figure 21-5, where XX means “don’t care” and letters refer to the programming steps described above. ATtiny48/88 198 8008H–AVR–04/11

ATtiny48/88 Figure 21-5. Programming the FUSES Waveforms Write Fuse Low byte Write Fuse high byte Write Extended Fuse byte A C A C A C DATA 0x40 DATA XX 0x40 DATA XX 0x40 DATA XX XA1 XA0 BS1 BS2 CLKI WR RDY/BSY RESET +12V OE PAGEL 21.2.11 Programming the Lock Bits The algorithm for programming the lock bits is as follows (see “Programming the Flash” on page 194 for details on command and data loading): (cid:129) A: Load command “0010 0000” (cid:129) C: Load data low byte. Bit n = “0” programs the Lock bit. If LB1 and LB2 have been programmed, it is not possible to program the Lock Bits by any External Programming mode (cid:129) Give WR a negative pulse and wait for RDY/BSY to go high Lock bits can only be cleared by executing Chip Erase. 21.2.12 Reading Fuse and Lock Bits The algorithm for reading fuse and lock bits is as follows (see “Programming the Flash” on page 194 for details on command loading): (cid:129) A: Load command “0000 0100” (cid:129) Set OE to “0”, BS2 to “0” and BS1 to “0”. Low fuse bits can now be read at DATA (“0” means programmed) (cid:129) Set OE to “0”, BS2 to “1” and BS1 to “1”. High fuse bits can now be read at DATA (“0” means programmed) (cid:129) Set OE to “0”, BS2 to “1”, and BS1 to “0”. Extended fuse bits can now be read at DATA (“0” means programmed) (cid:129) Set OE to “0”, BS2 to “0” and BS1 to “1”. Lock bits can now be read at DATA (“0” means programmed) (cid:129) Set OE to “1” Fuse and lock bit mapping is illustrated in Figure 21-6, below. 199 8008H–AVR–04/11

Figure 21-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read Fuse Low Byte 0 0 Extended Fuse Byte 1 DATA BS2 Lock Bits 0 1 BS1 Fuse High Byte 1 BS2 21.2.13 Reading Signature Bytes The algorithm for reading the signature bytes is as follows (see “Programming the Flash” on page 194 for details on command and address loading): 1. A: Load command “0000 1000” 2. B: Load address low byte (0x00 – 0x02) 3. Set OE to “0”, and BS1 to “0”. The selected signature byte can now be read at DATA. 4. Set OE to “1”. 21.2.14 Reading the Calibration Byte The algorithm for reading the calibration byte is as follows (see “Programming the Flash” on page 194 for details on command and address loading): 1. A: Load command “0000 1000”. 2. B: Load address low byte, 0x00. 3. Set OE to “0”, and BS1 to “1”. The calibration byte can now be read at DATA. 4. Set OE to “1”. 21.3 Serial Programming Flash and EEPROM memory arrays can both be programmed using the serial SPI bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (out- put). After RESET is set low, the Programming Enable instruction needs to be executed before program/erase operations can be executed. Serial programming signals and connections are illustrated in Figure 21-7, below. The pin map- ping is listed in Table 21-7 on page 202. ATtiny48/88 200 8008H–AVR–04/11

ATtiny48/88 Figure 21-7. Serial Programming and Verify(1) +1.8 - 5.5V VCC +1.8 - 5.5V(2) MOSI AVCC MISO SCK CLKI RESET GND Notes: 1. If the device is clocked by the internal oscillator, it is no need to connect a clock source to the CLKI pin. 2. V - 0.3V < AV < V + 0.3V, however, AV should always be within 1.8 – 5.5V CC CC CC CC When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase instruction. The Chip Erase operation turns the content of every memory location in both the Program and EEPROM arrays into 0xFF. Depending on CKSEL fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK) input are defined as follows: (cid:129) Minimum low period of serial clock: – When f < 12MHz: > 2 CPU clock cycles ck – When f >= 12MHz: 3 CPU clock cycles ck (cid:129) Minimum high period of serial clock: – When f < 12MHz: > 2 CPU clock cycles ck – When f >= 12MHz: 3 CPU clock cycles ck 201 8008H–AVR–04/11

21.3.1 Pin Mapping The pin mapping is listed in Table 21-7. Table 21-7. Pin Mapping Serial Programming Symbol Pins I/O Description MOSI PB3 I Serial Data in MISO PB4 O Serial Data out SCK PB5 I Serial Clock 21.3.2 Programming Algorithm When writing serial data to the ATtiny48/88, data is clocked on the rising edge of SCK. When reading data from the ATtiny48/88, data is clocked on the falling edge of SCK. See Figure 22-9 on page 217 and Figure 22-10 on page 217 for timing details. To program and verify the ATtiny48/88 in the serial programming mode, the following sequence is recommended (See Serial Programming Instruction set in Table 21-8 on page 203): 1. Power-up sequence: apply power between V and GND while RESET and SCK are CC set to “0”. – In some systems, the programmer can not guarantee that SCK is held low during power-up. In this case, RESET must be given a positive pulse after SCK has been set to '0'. The duration of the pulse must be at least t plus two CPU clock cycles. RST See Table 22-3 on page 209 for definition of minimum pulse width on RESET pin, t RST 2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI. 3. The serial programming instructions will not work if the communication is out of syn- chronization. When in sync. the second byte (0x53), will echo back when issuing the third byte of the Programming Enable instruction. – Whether the echo is correct or not, all four bytes of the instruction must be transmitted. – If the 0x53 did not echo back, give RESET a positive pulse and issue a new Programming Enable command. 4. The Flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 6 LSB of the address and data together with the Load Program Memory Page instruction. – To ensure correct loading of the page, the data low byte must be loaded before data high byte is applied for a given address. – The Program Memory Page is stored by loading the Write Program Memory Page instruction with the 7 MSB of the address. – If polling (RDY/BSY) is not used, the user must wait at least t before issuing WD_FLASH the next page (See Table 21-9). Accessing the serial programming interface before the Flash write operation completes can result in incorrect programming. 5. The EEPROM can be programmed one byte or one page at a time. – A: The EEPROM array is programmed one byte at a time by supplying the address and data together with the appropriate Write instruction. An EEPROM memory location is first automatically erased before new data is written. If polling (RDY/BSY) is not used, the user must wait at least t before issuing the next byte (See WD_EEPROM ATtiny48/88 202 8008H–AVR–04/11

ATtiny48/88 Table 21-9). In a chip erased device, no 0xFFs in the data file(s) need to be programmed. – B: The EEPROM array is programmed one page at a time. The Memory page is loaded one byte at a time by supplying the 6 LSB of the address and data together with the Load EEPROM Memory Page instruction. The EEPROM Memory Page is stored by loading the Write EEPROM Memory Page Instruction with the 7 MSB of the address. When using EEPROM page access only byte locations loaded with the Load EEPROM Memory Page instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used must wait at least t WD_EEPROM before issuing the next byte (See Table 21-9). In a chip erased device, no 0xFF in the data file(s) need to be programmed. 6. Any memory location can be verified by using the Read instruction which returns the content at the selected address at serial output MISO. 7. At the end of the programming session, RESET can be set high to commence normal operation. 8. Power-off sequence (if needed): Set RESET to “1”. Turn V power off. CC 21.3.3 Programming Instruction set Table 21-8 on page 203 and Figure 21-8 on page 204 describes the Instruction set. Table 21-8. Serial Programming Instruction Set (Hexadecimal values) Instruction Format Instruction/Operation Byte 1 Byte 2 Byte 3 Byte4 Programming Enable $AC $53 $00 $00 Chip Erase (Program Memory/EEPROM) $AC $80 $00 $00 Poll RDY/BSY $F0 $00 $00 data byte out Load Instructions Load Extended Address byte(1) $4D $00 Extended adr $00 Load Program Memory Page, High byte $48 $00 adr LSB high data byte in Load Program Memory Page, Low byte $40 $00 adr LSB low data byte in Load EEPROM Memory Page (page access) $C1 $00 0000 000aa data byte in Read Instructions Read Program Memory, High byte $28 adr MSB adr LSB high data byte out Read Program Memory, Low byte $20 adr MSB adr LSB low data byte out Read EEPROM Memory $A0 0000 00aa aaaa aaaa data byte out Read Lock bits $58 $00 $00 data byte out Read Signature Byte $30 $00 0000 000aa data byte out Read Fuse bits $50 $00 $00 data byte out Read Fuse High bits $58 $08 $00 data byte out Read Fuse Extended Bits $50 $08 $00 data byte out Read Calibration Byte $38 $00 $00 data byte out Write Instructions 203 8008H–AVR–04/11

Table 21-8. Serial Programming Instruction Set (Hexadecimal values) (Continued) Instruction Format Instruction/Operation Byte 1 Byte 2 Byte 3 Byte4 Write Program Memory Page $4C adr MSB adr LSB $00 Write EEPROM Memory $C0 0000 00aa aaaa aaaa data byte in Write EEPROM Memory Page (page access) $C2 0000 00aa aaaa aa00 $00 Write Lock bits $AC $E0 $00 data byte in Write Fuse bits $AC $A0 $00 data byte in Write Fuse High bits $AC $A8 $00 data byte in Write Fuse Extended Bits $AC $A4 $00 data byte in Notes: 1. Not all instructions are applicable for all parts. 2. a = address. 3. Bits are programmed ‘0’, unprogrammed ‘1’. 4. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (‘1’) . 5. Refer to the correspondig section for Fuse and Lock bits, Calibration and Signature bytes and Page size. 6. See htt://www.atmel.com/avr for Application Notes regarding programming and programmers. If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until this bit returns ‘0’ before the next instruction is carried out. Within the same page, the low data byte must be loaded prior to the high data byte. After data is loaded to the page buffer, program the EEPROM page, see Figure 21-8 on page 204. Figure 21-8. Serial Programming Instruction example Serial Programming Instruction Load Program Memory Page (High/Low Byte)/ Write Program Memory Page/ Load EEPROM Memory Page (page access) Write EEPROM Memory Page Byte 1 Byte 2 Byte 3 Byte 4 Byte 1 Byte 2 Byte 3 Byte 4 AAdr MMSSB Adr LSB Adr MSB AAdrr LLSBB Bit 15 B 0 Bit 15 B 0 Page Buffer Page Offset Page 0 Page 1 Page 2 Page Number Page N-1 Program Memory/ EEPROM Memory ATtiny48/88 204 8008H–AVR–04/11

ATtiny48/88 21.4 Programming Time for Flash and EEPROM Flash and EEPROM wait times are listed in Table 21-9. Table 21-9. Typical Wait Delay Before Writing the Next Flash or EEPROM Location Symbol Minimum Wait Delay t 4.5 ms WD_FLASH t 3.6 ms WD_EEPROM t 9.0 ms WD_ERASE 205 8008H–AVR–04/11

22. Electrical Characteristics 22.1 Absolute Maximum Ratings* Operating Temperature..................................-55°C to +125°C *NOTICE: Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent dam- Storage Temperature.....................................-65°C to +150°C age to the device. This is a stress rating only and functional operation of the device at these or Voltage on any Pin except RESET other conditions beyond those indicated in the with respect to Ground...............................-0.5V to V +0.5V operational sections of this specification is not CC implied. Exposure to absolute maximum rating Voltage on RESET with respect to Ground......-0.5V to +13.0V conditions for extended periods may affect device reliability. Maximum Operating Voltage............................................6.0V DC Current per I/O Pin...............................................40.0 mA DC Current V and GND Pins................................200.0 mA CC 22.2 DC Characteristics T = -40°C to +85°C, V = 1.8V to 5.5V (unless otherwise noted) A CC Symbol Parameter Condition Min Typ (1) Max Units Input Low Voltage, VCC = 1.8V – 2.4V -0.5 0.2VCC(2) V Except RESET pin V = 2.4V – 5.5V -0.5 0.3V (2) V V CC CC IL Input Low Voltage, V = 1.8V – 5.5V -0.5 0.2V (2) V RESET pin as reset (3) CC CC Input High Voltage, VCC = 1.8V – 2.4V 0.7VCC(4) VCC + 0.5 V Except RESET pin V = 2.4V – 5.5V 0.6V (4) V + 0.5 V V CC CC CC IH Input High Voltage, V = 1.8V – 5.5V 0.9V (4) V + 0.5 V RESET pin as reset (3) CC CC CC I = 10 mA, V = 5V 0.7 V Output Low Voltage (5), OL CC Except High Sink I/O pins I = 5 mA, V = 3V 0.5 V OL CC and RESET pin as I/O (6) I = 2 mA, V = 1.8V 0.4 V OL CC I = 20 mA, V = 5V 0.7 V OL CC Output Low Voltage V I = 10 mA, V = 3V 0.5 V OL High Sink I/O pins (7) OL CC I = 4 mA, V = 1.8V 0.4 V OL CC I = 2 mA, V = 5V 0.7 V OL CC Output Low Voltage (3) I = 1 mA, V = 3V 0.5 V RESET pin as I/O (6) OL CC I = 0.4 mA, V = 1.8V 0.4 V OL CC I = -10 mA, V = 5V 4.3 V Output High Voltage (8), OH CC Except High Sink I/O pins I = -5 mA, V = 3V 2.5 V OH CC and RESET pin as I/O (6) I = -2 mA, V = 1.8V 1.4 V OH CC V OH I = -10 mA, V = 5V 4.3 V OH CC Output HighVoltage I = -5 mA, V = 3V 2.5 V High Sink I/O pins (7) OH CC I = -2 mA, V = 1.8V 1.4 V OH CC ATtiny48/88 206 8008H–AVR–04/11

ATtiny48/88 T = -40°C to +85°C, V = 1.8V to 5.5V (unless otherwise noted) (Continued) A CC Symbol Parameter Condition Min Typ (1) Max Units Input Leakage V = 5.5V, pin low I CC < 0.05 1 (9) µA LIL Current I/O Pin (absolute value) Input Leakage V = 5.5V, pin high I CC < 0.05 1 (9) µA LIH Current I/O Pin (absolute value) Pull-up Resistor, I/O Pin V = 5.5V, input low 20 50 kΩ CC R PU Pull-up Resistor, Reset Pin V = 5.5V, input low 30 60 kΩ CC f = 1MHz, V = 2V 0.2 0.4 mA CC Supply Current, f = 4MHz, V = 3V 1.4 2.5 mA Active Mode (10) CC f = 8MHz, V = 5V 4.5 8 mA CC f = 1MHz, V = 2V 0.03 0.1 mA CC ICC Supply Current, f = 4MHz, V = 3V 0.25 0.6 mA Idle Mode CC f = 8MHz, V = 5V 1 2 mA CC Supply Current, WDT enabled, VCC = 3V 4 10 µA Power-down Mode (11) WDT disabled, V = 3V < 0.2 2 µA CC Notes: 1. Typical values at 25°C. 2. “Max” means the highest value where the pin is guaranteed to be read as low. 3. These parameters are not tested in production. 4. “Min” means the lowest value where the pin is guaranteed to be read as high. 5. Although each I/O port can sink more than the test conditions (10 mA at V = 5V, 5 mA at V = 3V, 2 mA at V = 1.8V) CC CC CC under steady state conditions (non-transient), the following must be observed: (cid:129) The sum of all I , for ports A0, A3, B0 – B7, C7, D5 – D7 should not exceed 100 mA. OL (cid:129) The sum of all I , for ports A1 – A2, C0 – C6, D0 – D4 should not exceed 100 mA. OL If I exceeds the test condition, V may exceed the related specification. Pins are not guaranteed to sink current greater OL OL than the listed test condition. 6. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence, has a weak drive strength as compared to regular I/O pins. See Figure 23-34, Figure 23-35, Figure 23-36, Figure 23-37, Fig- ure 23-38 and Figure 23-39 (starting on page 236). 7. High Sink I/O pins are PD0, PD1, PD2 and PD3. 8. Although each I/O port can source more than the test conditions (10 mA at V = 5V, 5mA at V = 3V, 2 mA at V = 1.8V) CC CC CC under steady state conditions (non-transient), the following must be observed: (cid:129) The sum of all I , for ports A2 – A3, B0 – B7, C6, D0 – D7 should not exceed 100 mA. OH (cid:129) The sum of all I , for ports A0 – A1, C0 – C5, C7 should not exceed 100 mA. OH If II exceeds the test condition, V may exceed the related specification. Pins are not guaranteed to source current OH OH greater than the listed test condition. 9. These are test limits, which account for leakage currents of the test environment. Actual device leakage currents are lower. 10.Values are with external clock using methods described in “Minimizing Power Consumption” on page 38. Power reduction is enabled (PRR = 0xFF) and there is no I/O drive. 11.Measured with Brown-Out Detection (BOD) disabled. 207 8008H–AVR–04/11

22.3 Speed The maximum operating frequency of the device is dependent on supply voltage, V . The rela- CC tionship between supply voltage and maximum operating frequency is piecewise linear, as shown in Figure 22-1, the Maximum Frequency vs. V curve is linear between 1.8V < V < CC CC 4.5V. Figure 22-1. Maximum Operating Frequency vs. Supply Voltage 12 MHz 8 MHz 4 MHz 1.8V 2.7V 4.5V 5.5V 22.4 Clock Characterizations 22.4.1 Calibrated Internal Oscillator Accuracy It is possible to manually calibrate the internal oscillator to be more accurate than default factory calibration. Please note that the oscillator frequency depends on temperature and voltage. Volt- age and temperature characteristics can be found in Figure 23-55 on page 246, Figure 23-56 on page 247, Figure 23-112 and Figure 23-113 on page 275. Table 22-1. Calibration Accuracy of Internal Oscillator Calibration Accuracy at given Method Target Frequency V Temperature Voltage & Temperature(1) CC Factory Calibration 8.0 MHz 3V 25°C ±10% Fixed frequency within: Fixed voltage within: Fixed temperature within: ±1% User Calibration 7.3 – 8.1 MHz 1.8V – 5.5V -40°C to +85°C Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage). ATtiny48/88 208 8008H–AVR–04/11

ATtiny48/88 22.4.2 External Clock Drive Figure 22-2. External Clock Drive Waveforms V IH1 V IL1 Table 22-2. External Clock Drive V = 1.8-5.5V V = 2.7-5.5V V = 4.5-5.5V CC CC CC Symbol Parameter Min. Max. Min. Max. Min. Max. Units Oscillator 1/t 0 2 0 6 0 12 MHz CLCL Frequency t Clock Period 250 166 83 ns CLCL t High Time 120 80 40 ns CHCX t Low Time 120 80 40 ns CLCX t Rise Time 2.0 1.6 0.5 µs CLCH t Fall Time 2.0 1.6 0.5 µs CHCL Change in period Δt from one clock 2 2 2 % CLCL cycle to the next Note: All DC Characteristics contained in this datasheet are based on simulation and characterization of other AVR microcontrollers manufactured in the same process technology. 22.5 System and Reset Characterizations Table 22-3. Reset, Brown-out, and Internal Voltage Characteristics (1) Symbol Parameter Condition Min Typ Max Units Power-on Reset Threshold T = -40 to +85°C 1.5 V Voltage (rising) A V POT Power-on Reset Threshold T = -40 to +85°C 1.2 V Voltage (falling)(2) A RESET Pin Threshold V 0.2V 0.9V V RST Voltage CC CC V = 1.8V 2000 Minimum pulse width on CC t V = 3V 700 ns RST RESET Pin CC V = 5V 400 CC 209 8008H–AVR–04/11

Table 22-3. Reset, Brown-out, and Internal Voltage Characteristics (1) (Continued) Symbol Parameter Condition Min Typ Max Units Brown-out Detector V 50 mV HYST Hysteresis Min Pulse Width on t 2 µs BOD Brown-out Reset Internal bandgap reference V = 5V V CC 1.0 1.1 1.2 V BG voltage T =25°C A Internal bandgap reference V = 5V t CC 40 70 µs BG start-up time T =25°C A Internal bandgap reference V = 5V I CC 15 µA BG current consumption T =25°C A Note: 1. Values are guidelines, only 2. The Power-on Reset will not work unless the supply voltage has been below V (falling) POT Table 22-4. V vs. BODLEVEL Fuse Coding(1) BOT BODLEVEL[2:0] Fuses Min Typ Max Units 111 BOD Disabled 110 1.7 1.8 2.0 101 2.5 2.7 2.9 V 100 4.1 4.3 4.5 0XX Reserved Note: 1. V may be below nominal minimum operating voltage for some devices. For devices where BOT this is the case, the device is tested down to V = V during the production test. This guar- CC BOT antees that a Brown-out Reset will occur before V drops to a voltage where correct CC operation of the microcontroller is no longer guaranteed. 22.6 Analog Comparator Characteristics Table 22-5. Analog Comparator Characteristics, T = -40°C to +85°C A Symbol Parameter Condition Min Typ Max Units V Input Offset Voltage V = 5V, V = V / 2 < 10 40 mV AIO CC IN CC I Input Leakage Current V = 5V, V = V / 2 -50 50 nA LAC CC IN CC Analog Propagation Delay VCC = 2.7V 750 (from saturation to slight overdrive) V = 4.0V 500 CC t ns APD Analog Propagation Delay VCC = 2.7V 100 (large step change) V = 4.0V 75 CC t Digital Propagation Delay V = 1.8V - 5.5V 1 2 CLK DPD CC Note: All parameters are based on simulation results and are not tested in production ATtiny48/88 210 8008H–AVR–04/11

ATtiny48/88 22.7 ADC Characteristics Table 22-6. ADC Characteristics , Single Ended Channels. -40°C to +85°C Symbol Parameter Condition Min Typ Max Units Resolution 10 Bits V = 4V, V = 4V, REF CC 2 LSB ADC clock = 200 kHz V = 4V, V = 4V, REF CC 3 LSB ADC clock = 1 MHz Absolute accuracy (Including V = 4V, V = 4V, INL, DNL, quantization error, REF CC gain and offset error) ADC clock = 200 kHz 1.5 LSB Noise Reduction Mode V = 4V, V = 4V, REF CC ADC clock = 1 MHz 2.5 LSB Noise Reduction Mode V = 4V, V = 4V, Integral Non-Linearity (INL) REF CC 1 LSB ADC clock = 200 kHz Differential Non-Linearity V = 4V, V = 4V, REF CC 0.5 LSB (DNL) ADC clock = 200 kHz V = 4V, V = 4V, Gain Error REF CC 2.5 LSB ADC clock = 200 kHz V = 4V, V = 4V, Offset Error REF CC 1.5 LSB ADC clock = 200 kHz Conversion Time Free Running Conversion 13 260 µs Clock Frequency 50 1000 kHz AV Analog Supply Voltage (1) V - 0.3 V + 0.3 V CC CC CC V Reference Voltage V AV V REF INT CC V Input Voltage GND V V IN REF Input Bandwidth 38.5 kHz V Internal Voltage Reference 1.0 1.1 1.2 V INT R Reference Input Resistance 32 kΩ REF R Analog Input Resistance 100 MΩ AIN Note: 1. AV absolute min/max: 1.8V/5.5V CC 211 8008H–AVR–04/11

22.8 Two-Wire Serial Interface Characteristics The following data is based on simulations and characterisations. Parameters listed in Table 22-7 are not tested in produc- tion. Symbols refer to Figure 22-3. Table 22-7. Two-Wire Serial Interface Characteristics Symbol Parameter Condition Min Max Unit V Input Low voltage -0.5 0.3 V V IL CC V Input High voltage 0.7 V V + 0.5 V IH CC CC V (cid:0) 2.7V 0.05 V V CC CC V Hysteresis of Schmitt-trigger inputs – HYS V < 2.7V 0 CC V Output Low voltage 3mA sink current 0 0.4 V OL t Spikes suppressed by input filter 0 50 ns SP f SCL clock frequency (1) f > max(16f , 250kHz) 0 400 kHz SCL CK SCL t Hold time (repeated) START Condition 0.6 – µs HD:STA t Low period of SCL clock 1.3 – µs LOW t High period of SCL clock 0.6 – µs HIGH t Set-up time for repeated START condition 0.6 – µs SU:STA t Data hold time 0 0.9 µs HD:DAT t Data setup time 100 – ns SU:DAT t Setup time for STOP condition 0.6 – µs SU:STO t Bus free time between STOP and START condition 1.3 – µs BUF Notes: 1. f = CPU clock frequency. CK Figure 22-3. Two-Wire Serial Bus Timing tof tHIGH tr t t LOW LOW SCL tSU;STA tHD;STA tHD;DAT tSU;DAT t SU;STO SDA t BUF ATtiny48/88 212 8008H–AVR–04/11

ATtiny48/88 22.9 SPI Characteristics See Figure 22-4 and Figure 22-5 for details. Table 22-8. SPI Timing Parameters Description Mode Min Typ Max 1 SCK period Master See Table 14-5 2 SCK high/low Master 50% duty cycle 3 Rise/Fall time Master 3.6 4 Setup Master 10 5 Hold Master 10 6 Out to SCK Master 0.5 (cid:129) t sck 7 SCK to out Master 10 8 SCK to out high Master 10 9 SS low to out Slave 15 ns 10 SCK period Slave 4 (cid:129) t ck 11 SCK high/low(1) Slave 2 (cid:129) t ck 12 Rise/Fall time Slave 1600 13 Setup Slave 10 14 Hold Slave t ck 15 SCK to out Slave 15 16 SCK to SS high Slave 20 17 SS high to tri-state Slave 10 18 SS low to SCK Slave 20 Note: 1. In SPI Programming mode the minimum SCK high/low period is: - 2 t for f < 12 MHz CLCL CK - 3 t for f > 12 MHz CLCL CK 2. All DC Characteristics contained in this datasheet are based on simulation and characteriza- tion of other AVR microcontrollers manufactured in the same process technology. 213 8008H–AVR–04/11

Figure 22-4. SPI Interface Timing Requirements (Master Mode) SS 6 1 SCK (CPOL = 0) 2 2 SCK (CPOL = 1) 4 5 3 MISO MSB ... LSB (Data Input) 7 8 MOSI MSB ... LSB (Data Output) Figure 22-5. SPI Interface Timing Requirements (Slave Mode) SS 10 16 9 SCK (CPOL = 0) 11 11 SCK (CPOL = 1) 13 14 12 MOSI MSB ... LSB (Data Input) 15 17 MISO MSB ... LSB X (Data Output) ATtiny48/88 214 8008H–AVR–04/11

ATtiny48/88 22.10 Parallel Programming Characteristics Figure 22-6. Parallel Programming Timing, Including some General Timing Requirements t XLWL t CLKI XHXL t t DVXH XLDX Data & Contol (DATA, XA0/1, BS1, BS2) t t t BVPH PLBX BVWL t WLBX PAGEL t PHPL t WLWH WR t PLWL WLRL RDY/BSY t WLRH Figure 22-7. Parallel Programming Timing, Loading Sequence with Timing Requirements(1) LOAD ADDRESS LOAD DATA LOAD DATA LOAD DATA LOAD ADDRESS (LOW BYTE) (LOW BYTE) (HIGH BYTE) (LOW BYTE) t tXLXH XLPH tPLXH CLKI BS1 PAGEL z DATA ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte) XA0 XA1 Note: 1. The timing requirements shown in Figure 22-6 (i.e., t , t , and t ) also apply to loading operation. DVXH XHXL XLDX 215 8008H–AVR–04/11

Figure 22-8. Parallel Programming Timing, Reading Sequence (within the Same Page) with Timing Requirements(1) LOAD ADDRESS READ DATA READ DATA LOAD ADDRESS (LOW BYTE) (LOW BYTE) (HIGH BYTE) (LOW BYTE) t XLOL CLKI t BVDV BS1 t OLDV OE t OHDZ DATA ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte) XA0 XA1 Note: 1. The timing requirements shown in Figure 22-6 (i.e., t , t , and t ) also apply to reading operation. DVXH XHXL XLDX Table 22-9. Parallel Programming Characteristics, T = 25°C, V = 5V A CC Symbol Parameter Min Typ Max Units V Programming Enable Voltage 11.5 12.5 V PP I Programming Enable Current 250 µA PP t Data and Control Valid before CLKI High 67 ns DVXH t CLKI Low to CLKI High 200 ns XLXH t CLKI Pulse Width High 150 ns XHXL t Data and Control Hold after CLKI Low 67 ns XLDX t CLKI Low to WR Low 0 ns XLWL t CLKI Low to PAGEL high 0 ns XLPH t PAGEL low to CLKI high 150 ns PLXH t BS1 Valid before PAGEL High 67 ns BVPH t PAGEL Pulse Width High 150 ns PHPL t BS1 Hold after PAGEL Low 67 ns PLBX t BS2/1 Hold after WR Low 67 ns WLBX t PAGEL Low to WR Low 67 ns PLWL t BS1 Valid to WR Low 67 ns BVWL t WR Pulse Width Low 150 ns WLWH t WR Low to RDY/BSY Low 0 1 µs WLRL ATtiny48/88 216 8008H–AVR–04/11

ATtiny48/88 Table 22-9. Parallel Programming Characteristics, T = 25°C, V = 5V (Continued) A CC Symbol Parameter Min Typ Max Units t WR Low to RDY/BSY High(1) 3.7 4.5 ms WLRH t WR Low to RDY/BSY High for Chip Erase(2) 7.5 9 ms WLRH_CE t CLKI Low to OE Low 0 ns XLOL t BS1 Valid to DATA valid 0 250 ns BVDV t OE Low to DATA Valid 250 ns OLDV t OE High to DATA Tri-stated 250 ns OHDZ Notes: 1. t is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits WLRH commands. 2. t is valid for the Chip Erase command. WLRH_CE 22.11 Serial Programming Characteristics Figure 22-9. Serial Programming Timing MOSI t t t OVSH SHOX SLSH SCK t SHSL MISO t SLIV Figure 22-10. Serial Programming Waveforms SERIAL DATA INPUT MSB LSB (MOSI) SERIAL DATA OUTPUT MSB LSB (MISO) SERIAL CLOCK INPUT (SCK) SAMPLE 217 8008H–AVR–04/11

Table 22-10. Serial Programming Characteristics, T = -40°C to +85°C, V = 1.8 – 5.5V A CC (Unless Otherwise Noted) Symbol Parameter Min Typ Max Units 1/t Oscillator Frequency (V = 2.7V – 5.5V) 0 6 MHz CLCL CC t Oscillator Period (V = 2.7V – 5.5V) 166 ns CLCL CC 1/t Oscillator Frequency (V = 4.5V – 5.5V) 0 12 MHz CLCL CC t Oscillator Period (V = 4.5V – 5.5V) 83 ns CLCL CC t SCK Pulse Width High 2 t ns SHSL CLCL* t SCK Pulse Width Low 2 t ns SLSH CLCL* t MOSI Setup to SCK High t ns OVSH CLCL t MOSI Hold after SCK High 2 t ns SHOX CLCL ATtiny48/88 218 8008H–AVR–04/11

ATtiny48/88 23. Typical Characteristics The data contained in this section is largely based on simulations and characterization of similar devices in the same process and design methods. Thus, the data should be treated as indica- tions of how the part will behave. The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock source. The power consumption in Power-down mode is independent of clock selection. The current consumption is a function of several factors such as: operating voltage, operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient tempera- ture. The dominating factors are operating voltage and frequency. The current drawn from capacitive loaded pins may be estimated (for one pin) as C *V *f L CC where C = load capacitance, V = operating voltage and f = average switching frequency of L CC I/O pin. The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at frequencies higher than the ordering code indicates. The difference between current consumption in Power-down mode with Watchdog Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential cur- rent drawn by the Watchdog Timer. 23.1 ATtiny48 23.1.1 Current Consumption in Active Mode Figure 23-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz) ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY 0.1 - 1.0 MHz 1 5.5 V 0.9 0.8 5.0 V 0.7 4.5 V 0.6 4.0 V A) m 0.5 (C 3.3 V C I 0.4 2.7 V 0.3 0.2 1.8 V 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency (MHz) 219 8008H–AVR–04/11

Figure 23-2. Active Supply Current vs. Frequency (1 - 12 MHz) ACTIVE SUPPLY CURRENT vs. FREQUENCY 1 - 12 MHz 8 5.5 V 7 5.0 V 6 4.5 V 5 4.0 V A) m 4 (C C I 3 3.3 V 2 2.7 V 1 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) Figure 23-3. Active Supply Current vs. V (Internal oscillator, 8 MHz) CC ACTIVE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 8 MHz 7 6 85 °C 25 °C 5 -40 °C A) 4 m (C C 3 I 2 1 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC ATtiny48/88 220 8008H–AVR–04/11

ATtiny48/88 Figure 23-4. Active Supply Current vs. V (Internal Oscillator, 1 MHz) CC ACTIVE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 1 MHz 1.2 85 °C 25 °C 1 -40 °C 0.8 A) m 0.6 (C C I 0.4 0.2 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 VCC (V) Figure 23-5. Active Supply Current vs. V (Internal Oscillator, 128 kHz) CC ACTIVE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 128 KHz 0.15 -40 °C 25 °C 85 °C 0.1 A) m (C C I 0.05 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 221 8008H–AVR–04/11

23.1.2 Current Consumption in Idle Mode Figure 23-6. Idle Supply Current vs. low Frequency (0.1 - 1.0 MHz) IDLE SUPPLY CURRENT vs. LOW FREQUENCY 0.1 - 1.0 MHz 0.16 5.5 V 0.14 5.0 V 0.12 4.5 V 0.1 4.0 V mA) 0.08 3.3 V I (CC 0.06 2.7 V 0.04 1.8 V 0.02 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency (MHz) Figure 23-7. Idle Supply Current vs. Frequency (1 - 12 MHz) IDLE SUPPLY CURRENT vs. FREQUENCY 1 -12 MHz 2 5.5 V 5.0 V 1.5 4.5 V 4.0 V A) 1 m (C C I 3.3 V 0.5 2.7 V 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) ATtiny48/88 222 8008H–AVR–04/11

ATtiny48/88 Figure 23-8. Idle Supply Current vs. V (Internal Oscillator, 8 MHz) CC IDLE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 8 MHz 1.4 85 °C 25 °C 1.2 -40 °C 1 0.8 A) m (C 0.6 C I 0.4 0.2 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC Figure 23-9. Idle Supply Current vs. V (Internal Oscilllator, 1 MHz) CC IDLE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 1 MHz 0.3 85 °C 25 °C -40 °C 0.2 A) m (C C I 0.1 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 223 8008H–AVR–04/11

Figure 23-10. Idle Supply Current vs. V (Internal Oscillator, 128 kHz) CC IDLE SUPPLY CURRENT vs. V CC INTERNAL RC OSCILLATOR, 128 KHz 0.025 -40 °C 25 °C 85 °C 0.02 0.015 A) m (C 0.01 C I 0.005 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 23.1.3 Current Consumption in Power-down Mode Figure 23-11. Power-down Supply Current vs. V (Watchdog Timer Disabled) CC POWER-DOWN SUPPLY CURRENT vs. V CC WATCHDOG TIMER DISABLED 0.7 0.6 0.5 85 °C 0.4 A) u (C IC 0.3 0.2 25 °C 0.1 -40 °C 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC ATtiny48/88 224 8008H–AVR–04/11

ATtiny48/88 Figure 23-12. Power-down Supply Current vs. V (Watchdog Timer Enabled) CC POWER-DOWN SUPPLY CURRENT vs. V CC WATCHDOG TIMER ENABLED 9 8 7 6 uA) 5 -40 °C (CC 4 I 25 °C 3 85 °C 2 1 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 23.1.4 Current Consumption in Reset Figure 23-13. Reset Supply Current vs. Low Frequency (0.1 - 1.0 MHz) RESET SUPPLY CURRENT vs. LOW FREQUENCY 0.1 - 1.0 MHz 0.16 0.14 5.5 V 0.12 5.0 V 0.1 4.5 V A) m 0.08 4.0 V (C C I 3.3 V 0.06 2.7 V 0.04 1.8 V 0.02 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency (MHz) 225 8008H–AVR–04/11

Figure 23-14. Reset Supply Current vs. Frequency (1 - 12 MHz) RESET SUPPLY CURRENT vs. FREQUENCY 1 - 12 MHz 1.6 5.5 V 1.4 5.0 V 1.2 4.5 V 1 A) 4.0 V m 0.8 (C C I 0.6 3.3 V 0.4 2.7 V 0.2 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) 23.1.5 Current Consumption in Peripheral Units Figure 23-15. Brownout Detector Current vs. V CC BROWNOUT DETECTOR CURRENT vs. V CC 25 85 °C 25 °C -40 °C 20 15 A) u (C C I 10 5 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC ATtiny48/88 226 8008H–AVR–04/11

ATtiny48/88 Figure 23-16. ADC Current vs. V (AREF = AV ) CC CC ADC CURRENT vs. V CC AREF = AV CC 350 85 °C 300 25 °C -40 °C 250 200 A) u (C IC 150 100 50 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC Figure 23-17. Analog Comparator Current vs. V CC ANALOG COMPARATOR CURRENT vs. V CC 90 85 °C 80 25 °C -40 °C 70 60 A) 50 u (CC 40 I 30 20 10 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 227 8008H–AVR–04/11

Figure 23-18. Programming Current vs. V CC PROGRAMMING CURRENT vs. V CC 9 8 -40 °C 7 6 25 °C A) 5 m (CC 4 85 °C I 3 2 1 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 23.1.6 Pull-up Resistors Figure 23-19. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 1.8V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE V = 1.8V CC 60 50 40 A) (uOP 30 I 20 -40 °C 10 25 °C 85 °C 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 V (V) OP ATtiny48/88 228 8008H–AVR–04/11

ATtiny48/88 Figure 23-20. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 2.7V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE V = 2.7 CC 80 70 60 50 A) (uOP 40 I 30 20 25 °C 10 -40 °C 85 °C 0 0 0.5 1 1.5 2 2.5 3 V (V) OP Figure 23-21. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 5V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE V = 5V CC 160 140 120 100 A) (uOP 80 I 60 40 -40 °C 20 25 °C 85 °C 0 0 1 2 3 4 5 6 V (V) OP 229 8008H–AVR–04/11

Figure 23-22. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 1.8V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE V = 1.8V CC 40 35 30 25 A) u ( 20 RESET I 15 10 -40 °C 5 25 °C 85 °C 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 V (V) RESET Figure 23-23. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 2.7V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE V = 2.7V CC 60 50 40 A) u ( 30 RESET I 20 10 -40 °C 25 °C 85 °C 0 0 0.5 1 1.5 2 2.5 3 V (V) RESET ATtiny48/88 230 8008H–AVR–04/11

ATtiny48/88 Figure 23-24. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 5V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE V = 5V CC 120 100 80 A) u ( 60 RESET I 40 -40 °C 20 25 °C 85 °C 0 0 1 2 3 4 5 6 V (V) RESET 23.1.7 Output Driver Strength Figure 23-25. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC HIGH SINK I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 1.8V CC 1 0.9 0.8 85 °C 0.7 0.6 V) 25 °C (OL 0.5 V 0.4 -40 °C 0.3 0.2 0.1 0 0 1 2 3 4 5 6 7 8 9 10 I (mA) OL 231 8008H–AVR–04/11

Figure 23-26. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 3V) OL CC HIGH SINK I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 3V CC 0.8 0.7 85 °C 0.6 25 °C 0.5 V) -40 °C (OL 0.4 V 0.3 0.2 0.1 0 0 5 10 15 20 25 I (mA) OL Figure 23-27. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 5V) OL CC HIGH SINK I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 5V CC 0.6 0.5 85 °C 0.4 25 °C V) -40 °C (OL 0.3 V 0.2 0.1 0 0 5 10 15 20 25 I (mA) OL ATtiny48/88 232 8008H–AVR–04/11

ATtiny48/88 Figure 23-28. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 1.8V CC 1 0.8 85 °C 0.6 25 °C V) (OL V 0.4 -40 °C 0.2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 I (mA) OL Figure 23-29. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 3V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 3V CC 1.2 85 °C 1 25 °C 0.8 V) -40 °C (OL 0.6 V 0.4 0.2 0 0 2 4 6 8 10 12 14 I (mA) OL 233 8008H–AVR–04/11

Figure 23-30. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 5V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 5V CC 1 85 °C 0,8 25 °C 0,6 -40 °C V) (OL V 0,4 0,2 0 0 5 10 15 20 25 I (mA) OL Figure 23-31. V : Standard I/O Pin Output Voltage vs. Source Current (V = 1.8V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 1.8V CC 2 1.8 1.6 1.4 1.2 V) (H 1 O V 0.8 0.6 85 °C -40 °C 0.4 0.2 0 25 °C 0 1 2 3 4 5 6 I (mA) OH ATtiny48/88 234 8008H–AVR–04/11

ATtiny48/88 Figure 23-32. V : Standard I/O Pin Output Voltage vs. Source Current (V = 3V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 3V CC 3.1 2.9 2.7 2.5 V) (H 2.3 O V 2.1 1.9 -40 °C 85 °C 25 °C 1.7 1.5 0 5 10 15 20 25 I (mA) OH Figure 23-33. V : Standard I/O Pin Output Voltage vs. Source Current (V = 5V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 5V CC 5.2 5 4.8 V) (H 4.6 O V 4.4 -40 °C 4.2 25 °C 85 °C 4 0 5 10 15 20 25 I (mA) OH 235 8008H–AVR–04/11

Figure 23-34. V : Reset Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 1.8V CC 0.3 85 °C 25 °C 0.2 -40 °C V) (OL V 0.1 0 0 0.1 0.2 0.3 0.4 0.5 I (mA) OL Figure 23-35. V : Reset Pin Output Voltage vs. Sink Current (V = 3V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 3V CC 1.5 85 °C 1 25 °C V) (OL V -40 °C 0.5 0 0 0.5 1 1.5 2 2.5 3 I (mA) OL ATtiny48/88 236 8008H–AVR–04/11

ATtiny48/88 Figure 23-36. V : Reset Pin Output Voltage vs. Sink Current (V = 5V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT V = 5V CC 6 5 85 °C 4 V) (OL 3 V 25 °C 2 -40 °C 1 0 0 2 4 6 8 10 12 I (mA) OL Figure 23-37. V : Reset Pin Output Voltage vs. Source Current (V = 1.8V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 1.8V CC 1.5 1 V) (H O V 0.5 -40 °C 85 °C 25 °C 0 0 0.5 1 1.5 2 2.5 I (mA) OH 237 8008H–AVR–04/11

Figure 23-38. V : Reset Pin Output Voltage vs. Source Current (V = 3V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 3V CC 3 2.5 2 V) (H 1.5 O V -40 °C 1 25 °C 85 °C 0.5 0 0 0.5 1 1.5 2 2.5 I (mA) OH Figure 23-39. V : Reset Pin Output Voltage vs. Source Current (V = 5V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT V = 5V CC 4.5 4 3.5 3 -40 °C 25 °C (V)H 2.5 85 °C VO 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 I (mA) OH ATtiny48/88 238 8008H–AVR–04/11

ATtiny48/88 23.1.8 Input Threshold and Hysteresis Figure 23-40. V : I/O Pin Input Threshold Voltage vs. V (IO Pin Read as ‘1’) IH CC I/O PIN INPUT THRESHOLD VOLTAGE vs. V CC VIH, IO PIN READ AS '1' 3.5 85 °C 3 25 °C -40 °C 2.5 d (V) 2 ol h s e 1.5 hr T 1 0.5 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC Figure 23-41. V : I/O Pin Input Threshold Voltage vs. V (IO Pin Read as ‘0’) IL CC I/O PIN INPUT THRESHOLD VOLTAGE vs. V CC VIL, IO PIN READ AS '0' 2.5 85 °C 25 °C -40 °C 2 V) 1.5 d ( ol h s e hr 1 T 0.5 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 239 8008H–AVR–04/11

Figure 23-42. V -V : I/O Pin Input Hysteresis vs. V IH IL CC I/O PIN INPUT HYSTERESIS vs. V CC 0.6 -40 °C 25 °C V) 0.4 s ( 85 °C si e er st y H ut np 0.2 I 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC Figure 23-43. V : Input Threshold Voltage vs. V (Reset Pin as I/O, Read as ‘1’) IH CC RESET PIN AS I/O THRESHOLD VOLTAGE vs. V CC VIH, RESET READ AS '1' 3,5 3 -40 °C 25 °C 85 °C 2,5 V) 2 d ( ol h es hr1,5 T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) ATtiny48/88 240 8008H–AVR–04/11

ATtiny48/88 Figure 23-44. V : Input Threshold Voltage vs. V (Reset Pin as I/O, Read as ‘0’) IL CC RESET PIN AS I/O THRESHOLD VOLTAGE vs. V CC VIL, RESET READ AS '0' 2,5 85 °C 25 °C -40 °C 2 1,5 V) d ( ol h es hr T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-45. V -V : Input Hysteresis vs. V (Reset Pin as I/O) IH IL CC RESET PIN AS IO, INPUT HYSTERESIS vs. V CC VIL, IO PIN READ AS "0" 0,8 -40 °C 0,7 0,6 25 °C V)0,5 esis ( 85 °C Hyster0,4 ut p n0,3 I 0,2 0,1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 241 8008H–AVR–04/11

23.1.9 BOD, Bandgap and Reset Figure 23-46. BOD Threshold vs. Temperature (BOD Level is 4.3V) BOD THRESHOLDS vs. TEMPERATURE BOD LEVEL IS 4.3V 4.34 4.33 Rising V CC 4.32 4.31 4.3 V) d ( 4.29 ol sh 4.28 e hr T 4.27 4.26 Falling V CC 4.25 4.24 4.23 -60 -40 -20 0 20 40 60 80 100 Temperature (C) Figure 23-47. BOD Threshold vs. Temperature (BOD Level is 2.7V) BOD THRESHOLDS vs. TEMPERATURE BOD LEVEL IS 2.7V 2.76 2.75 Rising V CC 2.74 2.73 V) 2.72 d ( ol 2.71 h s e hr 2.7 T 2.69 2.68 Falling V CC 2.67 2.66 -60 -40 -20 0 20 40 60 80 100 Temperature (C) ATtiny48/88 242 8008H–AVR–04/11

ATtiny48/88 Figure 23-48. BOD Threshold vs. Temperature (BOD Level is 1.8V) BOD THRESHOLDS vs. TEMPERATURE BOD LEVEL IS 1.8V 1,825 1,82 Rising V CC 1,815 1,81 V) 1,805 d ( ol 1,8 h s e hr 1,795 T 1,79 Falling V CC 1,785 1,78 1,775 -60 -40 -20 0 20 40 60 80 100 Temperature (C) Figure 23-49. V : Reset Input Threshold Voltage vs. V (IO Pin Read as ‘1’) IH CC RESET INPUT THRESHOLD VOLTAGE vs. V CC VIH, IO PIN READ AS '1' 2.5 2 -40 °C V) 1.5 d ( ol 25 °C h s e hr 1 T 85 °C 0.5 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 243 8008H–AVR–04/11

Figure 23-50. V : Reset Input Threshold Voltage vs. V (IO Pin Read as ‘0’) IL CC RESET INPUT THRESHOLD VOLTAGE vs. V CC VIL, IO PIN READ AS '0' 2.5 85 °C 25 °C 2 -40 °C V) 1.5 d ( ol h s e hr 1 T 0.5 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC Figure 23-51. V -V : Reset Pin Input Hysteresis vs. V IH IL CC RESET PIN INPUT HYSTERESIS vs. V CC 0.6 0.5 -40 °C V) 0.4 s ( si 25 °C e er 0.3 st y H ut np 0.2 I 85 °C 0.1 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC ATtiny48/88 244 8008H–AVR–04/11

ATtiny48/88 Figure 23-52. Minimum Reset Pulse Width vs. V CC MINIMUM RESET PULSE WIDTH vs. V CC 2500 2000 s) 1500 n h ( dt wi e uls 1000 P 500 85 °C 25 °C -40 °C 0 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 23.1.10 Internal Oscillator Speed Figure 23-53. Watchdog Oscillator Frequency vs. V CC WATCHDOG OSCILLATOR FREQUENCY vs. V CC 114 113 112 111 -40 °C 110 z) (HC 109 25 °C R F 108 107 106 105 85 °C 104 1.5 2 2.5 3 3.5 4 4.5 5 5.5 V (V) CC 245 8008H–AVR–04/11

Figure 23-54. Watchdog Oscillator Frequency vs. Temperature WATCHDOG OSCILLATOR FREQUENCY vs. TEMPERATURE 113 112 111 110 z) 109 H k (RC 108 1.8 V F 2.7 V 107 3.3 V 106 4.0 V 105 5.5 V 104 -60 -40 -20 0 20 40 60 80 100 Temperature Figure 23-55. Calibrated 8 MHz Oscillator Frequency vs. V CC CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. V CC 8.6 8.5 85 °C 25 °C 8.4 -40 °C 8.3 z) 8.2 H M (C 8.1 R F 8 7.9 7.8 7.7 1.5 1.9 2.3 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 V (V) CC ATtiny48/88 246 8008H–AVR–04/11

ATtiny48/88 Figure 23-56. Calibrated 8 MHz Oscillator Frequency vs. Temperature CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE 8.7 8.6 5.5 V 8.5 8.4 8.3 z) H M 8.2 (C R F 8.1 3.0 V 8 7.9 7.8 7.7 -60 -40 -20 0 20 40 60 80 100 Temperature Figure 23-57. Calibrated 8 MHz Oscillator Frequency vs. OSCCAL Value CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE 14 85 °C 12 25 °C -40 °C 10 z) 8 H M (RC 6 F 4 2 0 0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 OSCCAL (X1) 247 8008H–AVR–04/11

23.2 ATtiny88 23.2.1 Current Consumption in Active Mode Figure 23-58. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz) ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY (ATtiny88) 0.1 - 1.0 MHz 1 0,9 5.5 V 0,8 5.0 V 0,7 4.5 V 0,6 A) 4.0 V m 0,5 I (CC 3.3 V 0,4 0,3 2.7 V 0,2 1.8 V 0,1 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Frequency (MHz) Figure 23-59. Active Supply Current vs. Frequency (1 - 12 MHz) ACTIVE SUPPLY CURRENT vs. FREQUENCY (ATtiny88) 1 - 12 MHz 8 7 5.5 V 6 5.0 V 5 4.5 V A) m 4 I (CC 4.0 V 3 3.3 V 2 2.7 V 1 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) ATtiny48/88 248 8008H–AVR–04/11

ATtiny48/88 Figure 23-60. Active Supply Current vs. V (Internal oscillator, 8 MHz) CC ACTIVE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 8 MHz 6 5 -40 °C 25 °C 85 °C 4 A) m 3 I (CC 2 1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-61. Active Supply Current vs. V (Internal Oscillator, 1 MHz) CC ACTIVE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 1 MHz 1,2 -40 °C 25 °C 1 85 °C 0,8 A) m 0,6 I (CC 0,4 0,2 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 249 8008H–AVR–04/11

Figure 23-62. Active Supply Current vs. V (Internal Oscillator, 128 kHz) CC ACTIVE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 128 KHz 0,15 -40 °C 25 °C 85 °C 0,1 A) m I (CC 0,05 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 23.2.2 Current Consumption in Idle Mode Figure 23-63. Idle Supply Current vs. low Frequency (0.1 - 1.0 MHz) IDLE SUPPLY CURRENT vs. LOW FREQUENCY (ATtiny88) 0.1 - 1.0 MHz 0,16 0,14 5.5 V 0,12 5.0 V 0,1 4.5 V 4.0 V 0,08 A) m I (CC 0,06 3.3 V 2.7 V 0,04 1.8 V 0,02 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Frequency (MHz) ATtiny48/88 250 8008H–AVR–04/11

ATtiny48/88 Figure 23-64. Idle Supply Current vs. Frequency (1 - 12 MHz) IDLE SUPPLY CURRENT vs. FREQUENCY (ATtiny88) 1 - 12 MHz 2 1,8 1,6 5.5 V 1,4 5.0 V 1,2 4.5 V 1 mA) 4.0 V I (CC 0,8 0,6 3.3 V 0,4 2.7 V 0,2 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) Figure 23-65. Idle Supply Current vs. V (Internal Oscillator, 8 MHz) CC IDLE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 8 MHz 1,4 85 °C 25 °C 1,2 -40 °C 1 0,8 A) m I (CC 0,6 0,4 0,2 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 251 8008H–AVR–04/11

Figure 23-66. Idle Supply Current vs. V (Internal Oscilllator, 1 MHz) CC IDLE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 1 MHz 0,3 85 °C 25 °C -40 °C 0,2 A) m I (CC 0,1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-67. Idle Supply Current vs. V (Internal Oscillator, 128 kHz) CC IDLE SUPPLY CURRENT vs. V (ATtiny88) CC INTERNAL RC OSCILLATOR, 128 KHz 0,025 -40 °C 25 °C 85 °C 0,02 0,015 A) m I (CC 0,01 0,005 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) ATtiny48/88 252 8008H–AVR–04/11

ATtiny48/88 23.2.3 Current Consumption in Power-down Mode Figure 23-68. Power-down Supply Current vs. V (Watchdog Timer Disabled) CC POWER-DOWN SUPPLY CURRENT vs. V (ATtiny88) CC WATCHDOG TIMER DISABLED 0,8 85 °C 0,7 0,6 0,5 A) I (uCC 0,4 0,3 0,2 25 °C -40 °C 0,1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-69. Power-down Supply Current vs. V (Watchdog Timer Enabled) CC POWER-DOWN SUPPLY CURRENT vs. V (ATtiny88) CC WATCHDOG TIMER ENABLED 9 8 -40 °C 25 °C 7 85 °C 6 5 A) u I (CC 4 3 2 1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 253 8008H–AVR–04/11

23.2.4 Current Consumption in Reset Figure 23-70. Reset Supply Current vs. Low Frequency (0.1 - 1.0 MHz) RESET SUPPLY CURRENT vs. LOW FREQUENCY (ATtiny88) EXCLUDING CURRENT THROUGH THE RESET PULLUP 0,16 0,14 0,12 5.5 V 0,1 5.0 V A) 4.5 V m 0,08 I (CC 4.0 V 0,06 3.3 V 2.7 V 0,04 1.8 V 0,02 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Frequency (MHz) Figure 23-71. Reset Supply Current vs. Frequency (1 - 12 MHz) RESET SUPPLY CURRENT vs. FREQUENCY (ATtiny88) EXCLUDING CURRENT THROUGH THE RESET PULLUP 1,6 1,4 5.5 V 1,2 5.0 V 1 4.5 V A) m 0,8 I (CC 4.0 V 0,6 3.3 V 0,4 2.7 V 0,2 1.8 V 0 0 2 4 6 8 10 12 Frequency (MHz) ATtiny48/88 254 8008H–AVR–04/11

ATtiny48/88 23.2.5 Current Consumption in Peripheral Units Figure 23-72. Brownout Detector Current vs. V CC BROWNOUT DETECTOR CURRENT vs. V (ATtiny88) CC 30 25 85 °C 25 °C -40 °C 20 A) I (uCC 15 10 5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-73. ADC Current vs. V (AREF = AV ) CC CC ACTIVE SUPPLY CURRENT WITH ADC AT 50KHz vs. V (ATtiny88) CC 400 85 °C 350 25 °C -40 °C 300 250 A) I (uCC 200 150 100 50 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 255 8008H–AVR–04/11

Figure 23-74. Analog Comparator Current vs. V CC ANALOG COMPARATOR CURRENT vs. V (ATtiny88) CC 110 100 85 °C 90 80 25 °C -40 °C 70 60 A) u I (CC 50 40 30 20 10 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-75. Programming Current vs. V CC PROGRAMMING CURRENT vs. V (ATtiny88) CC 20 -40 °C 18 16 25 °C 14 12 85 °C mA) 10 I (CC 8 6 4 2 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) ATtiny48/88 256 8008H–AVR–04/11

ATtiny48/88 23.2.6 Pull-up Resistors Figure 23-76. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 1.8V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE (ATtiny88) VCC = 1.8V 50 40 30 A) u (OP I 20 10 -40 °C 25 °C 85 °C 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 VOP (V) Figure 23-77. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 2.7V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE (ATtiny88) VCC = 2.7V 80 70 60 50 A) u 40 (OP I 30 20 10 25 °C -40 °C 85 °C 0 0 0,5 1 1,5 2 2,5 3 VOP (V) 257 8008H–AVR–04/11

Figure 23-78. I/O Pin Pull-up Resistor Current vs. Input Voltage (V = 5V) CC I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE (ATtiny88) VCC = 5V 160 140 120 100 A) u 80 (OP I 60 40 20 -40 °C 25 °C 85 °C 0 0 1 2 3 4 5 6 VOP (V) Figure 23-79. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 1.8V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE (ATtiny88) VCC = 1.8V 40 35 30 25 A) u I (RESET 20 15 10 5 25 °C -40 °C 85 °C 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 VRESET (V) ATtiny48/88 258 8008H–AVR–04/11

ATtiny48/88 Figure 23-80. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 2.7V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE (ATtiny88) VCC = 2.7V 60 50 40 A) u I (RESET 30 20 10 25 °C -40 °C 85 °C 0 0 0,5 1 1,5 2 2,5 3 VRESET (V) Figure 23-81. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V = 5V) CC RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE (ATtiny88) VCC = 5V 120 100 80 A) u I (RESET 60 40 20 25 °C -40 °C 85 °C 0 0 1 2 3 4 5 6 VRESET (V) 259 8008H–AVR–04/11

23.2.7 Output Driver Strength Figure 23-82. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC HIGH SINK I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 1.8V 1 0,9 0,8 0,7 85 °C 0,6 V) 25 °C (OL 0,5 V 0,4 -40 °C 0,3 0,2 0,1 0 0 1 2 3 4 5 6 7 8 9 10 IOL (mA) Figure 23-83. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 3V) OL CC HIGH SINK I/O OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 3V 0,8 0,7 85 °C 0,6 25 °C 0,5 V) -40 °C (OL 0,4 V 0,3 0,2 0,1 0 0 2 4 6 8 10 12 14 16 18 20 IOL (mA) ATtiny48/88 260 8008H–AVR–04/11

ATtiny48/88 Figure 23-84. V : High Sink I/O Pin Output Voltage vs. Sink Current (V = 5V) OL CC HIGH SINK I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 5V 0,6 0,5 85 °C 0,4 25 °C V) -40 °C (OL 0,3 V 0,2 0,1 0 0 2 4 6 8 10 12 14 16 18 20 IOL (mA) Figure 23-85. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 1.8V 1 0,8 85 °C 0,6 V) (OL 25 °C V 0,4 -40 °C 0,2 0 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 IOL (mA) 261 8008H–AVR–04/11

Figure 23-86. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 3V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 3V 1,2 85 °C 1 0,8 25 °C V) -40 °C (OL 0,6 V 0,4 0,2 0 0 2 4 6 8 10 12 14 IOL (mA) Figure 23-87. V : Standard I/O Pin Output Voltage vs. Sink Current (V = 5V) OL CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 5V 1 85 °C 0,8 25 °C -40 °C 0,6 V) (OL V 0,4 0,2 0 0 5 10 15 20 IOL (mA) ATtiny48/88 262 8008H–AVR–04/11

ATtiny48/88 Figure 23-88. V : Standard I/O Pin Output Voltage vs. Source Current (V = 1.8V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 1.8V 2 1,8 1,6 1,4 -40 °C 1,2 V) 25 °C (OH 1 V 0,8 85 °C 0,6 0,4 0,2 0 0 1 2 3 4 5 6 IOH (mA) Figure 23-89. V : Standard I/O Pin Output Voltage vs. Source Current (V = 3V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 3V 3,1 2,9 2,7 2,5 V) (OH 2,3 V 2,1 -40 °C 1,9 25 °C 1,7 85 °C 1,5 0 5 10 15 20 25 IOH (mA) 263 8008H–AVR–04/11

Figure 23-90. V : Standard I/O Pin Output Voltage vs. Source Current (V = 5V) OH CC STANDARD I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 5V 5,2 5 4,8 V) (OH 4,6 V 4,4 -40 °C 4,2 25 °C 85 °C 4 0 5 10 15 20 25 IOH (mA) Figure 23-91. V : Reset Pin Output Voltage vs. Sink Current (V = 1.8V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 1.8V 0,3 85 °C 25 °C 0,2 -40 °C V) V (OL 0,1 0 0 0,1 0,2 0,3 0,4 0,5 IOL (mA) ATtiny48/88 264 8008H–AVR–04/11

ATtiny48/88 Figure 23-92. V : Reset Pin Output Voltage vs. Sink Current (V = 3V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 3V 1,5 85 °C 1 25 °C V) V (OL -40 °C 0,5 0 0 0,5 1 1,5 2 2,5 3 IOL (mA) Figure 23-93. V : Reset Pin Output Voltage vs. Sink Current (V = 5V) OL CC RESET I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT (ATtiny88) VCC = 5V 7 85 °C 6 5 V) 4 V (OL 3 25 °C 2 -40 °C 1 0 0 2 4 6 8 10 12 IOL (mA) 265 8008H–AVR–04/11

Figure 23-94. V : Reset Pin Output Voltage vs. Source Current (V = 1.8V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 1.8V 1,5 1 V) V (OH 0,5 -40 °C 25 °C 85 °C 0 0 0,5 1 1,5 2 2,5 IOH (mA) Figure 23-95. V : Reset Pin Output Voltage vs. Source Current (V = 3V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 3V 3 2,5 2 V) V (OH 1,5 -40 °C 1 25 °C 85 °C 0,5 0 0 0,5 1 1,5 2 2,5 IOH (mA) ATtiny48/88 266 8008H–AVR–04/11

ATtiny48/88 Figure 23-96. V : Reset Pin Output Voltage vs. Source Current (V = 5V) OH CC RESET I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT (ATtiny88) VCC = 5V 4,5 4 3,5 3 -40 °C 25 °C V (V)OH 2,5 85 °C 2 1,5 1 0,5 0 0 0,5 1 1,5 2 2,5 IOH (mA) 23.2.8 Input Threshold and Hysteresis Figure 23-97. V : I/O Pin Input Threshold Voltage vs. V (IO Pin Read as ‘1’) IH CC I/O PIN INPUT THRESHOLD VOLTAGE vs. V (ATtiny88) CC VIH, IO PIN READ AS '1' 3,5 3 85 °C 25 °C -40 °C 2,5 V) 2 d ( ol h es hr 1,5 T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 267 8008H–AVR–04/11

Figure 23-98. V : I/O Pin Input Threshold Voltage vs. V (IO Pin Read as ‘0’) IL CC I/O PIN INPUT THRESHOLD VOLTAGE vs. V (ATtiny88) CC VIL, IO PIN READ AS '0' 2,5 85 °C 25 °C -40 °C 2 1,5 V) d ( ol h es hr T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-99. V -V : I/O Pin Input Hysteresis vs. V IH IL CC I/O PIN INPUT HYSTERESIS vs. V (ATtiny88) CC 0,6 -40 °C 25 °C 0,4 V) esis ( 85 °C er Hyst ut p n I 0,2 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) ATtiny48/88 268 8008H–AVR–04/11

ATtiny48/88 Figure 23-100.V : Input Threshold Voltage vs. V (Reset Pin as I/O, Read as ‘1’) IH CC RESET PIN AS I/O THRESHOLD VOLTAGE vs. V (ATtiny88) CC VIH, RESET READ AS '1' 3,5 3 -40 °C 25 °C 85 °C 2,5 V) 2 d ( ol h es hr 1,5 T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-101.V : Input Threshold Voltage vs. V (Reset Pin as I/O, Read as ‘0’) IL CC RESET PIN AS I/O THRESHOLD VOLTAGE vs. VCC (ATtiny88) VIL, RESET READ AS '0' 2,5 85 °C 25 °C 2 -40 °C 1,5 V) d ( ol h es hr T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 269 8008H–AVR–04/11

Figure 23-102.V -V : Input Hysteresis vs. V (Reset Pin as I/O) IH IL CC RESET PIN AS IO, INPUT HYSTERESIS vs. V (ATtiny88) CC VIL, IO PIN READ AS "0" 0,8 -40 °C 0,7 0,6 25 °C V) 0,5 esis ( 85 °C Hyster 0,4 ut p n 0,3 I 0,2 0,1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 23.2.9 BOD, Bandgap and Reset Figure 23-103.BOD Threshold vs. Temperature (BOD Level is 4.3V) BOD THRESHOLDS vs. TEMPERATURE (ATtiny88) BODLEVEL = 4.3V 4,4 4,38 4,36 4,34 4,32 V) hold ( 4,3 RisingVCC es hr T 4,28 4,26 4,24 FallingV CC 4,22 4,2 -40 -20 0 20 40 60 80 100 Temperature (C) ATtiny48/88 270 8008H–AVR–04/11

ATtiny48/88 Figure 23-104.BOD Threshold vs. Temperature (BOD Level is 2.7V) BOD THRESHOLDS vs. TEMPERATURE (ATtiny88) BODLEVEL = 2.7V 2,78 2,76 2,74 RisingVCC V) d ( hol 2,72 es hr T 2,7 2,68 FallingV CC 2,66 -40 -20 0 20 40 60 80 100 Temperature (C) Figure 23-105.BOD Threshold vs. Temperature (BOD Level is 1.8V) BOD THRESHOLDS vs. TEMPERATURE (ATtiny88) BODLEVEL = 1.8V 1,83 1,825 1,82 1,815 RisingVCC 1,81 V) d ( 1,805 ol h es 1,8 hr T 1,795 1,79 1,785 FallingV CC 1,78 1,775 -40 -20 0 20 40 60 80 100 Temperature (C) 271 8008H–AVR–04/11

Figure 23-106.V : Reset Input Threshold Voltage vs. V (IO Pin Read as ‘1’) IH CC RESET INPUT THRESHOLD VOLTAGE vs. V (ATtiny88) CC VIH, IO PIN READ AS '1' 2,5 2 1,5 V) old ( -40 °C h es 25 °C hr T 1 85 °C 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-107.V : Reset Input Threshold Voltage vs. V (IO Pin Read as ‘0’) IL CC RESET INPUT THRESHOLD VOLTAGE vs. V (ATtiny88) CC VIL, IO PIN READ AS '0' 2,5 85 °C 25 °C -40 °C 2 1,5 V) d ( ol h es hr T 1 0,5 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) ATtiny48/88 272 8008H–AVR–04/11

ATtiny48/88 Figure 23-108.V -V : Reset Pin Input Hysteresis vs. V IH IL CC RESET PIN INPUT HYSTERESIS vs. V (ATtiny88) CC 0,6 -40 °C 0,5 0,4 V) 25 °C esis ( Hyster 0,3 ut p In 85 °C 0,2 0,1 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-109.Minimum Reset Pulse Width vs. V CC MINIMUM RESET PULSE WIDTH vs. V (ATtiny88) CC 2500 2000 ns) 1500 h ( dt wi e uls P 1000 500 85 °C 25 °C -40 °C 0 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) 273 8008H–AVR–04/11

23.2.10 Internal Oscillator Speed Figure 23-110.Watchdog Oscillator Frequency vs. V CC WATCHDOG OSCILLATOR FREQUENCY vs. OPERATING VOLTAGE (ATtiny88) 126 124 122 -40 °C 120 25 °C 118 Hz) 116 F (RC 114 85 °C 112 110 108 106 104 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-111.Watchdog Oscillator Frequency vs. Temperature WATCHDOG OSCILLATOR FREQUENCY vs. TEMPERATURE (ATtiny88) 124 122 120 118 116 1.8 V Hz) 2.7 V F (kRC 114 43..03 VV 112 5.5 V 110 108 106 104 -40 -20 0 20 40 60 80 100 Temperature ATtiny48/88 274 8008H–AVR–04/11

ATtiny48/88 Figure 23-112.Calibrated 8 MHz Oscillator Frequency vs. V CC CALIBRATED 8.0MHz RC OSCILLATOR FREQUENCY vs. V (ATtiny88) CC 8,6 8,5 8,4 -40 °C 8,3 Hz) 8,2 25 °C M F (RC 8,1 8 85 °C 7,9 7,8 7,7 1,5 2 2,5 3 3,5 4 4,5 5 5,5 VCC (V) Figure 23-113.Calibrated 8 MHz Oscillator Frequency vs. Temperature CALIBRATED 8.0MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE (ATtiny88) 8,7 8,6 8,5 8,4 8,3 Hz) M 8,2 F (RC 8,1 8 5.5 V 7,9 3.0 V 7,8 7,7 -40 -20 0 20 40 60 80 100 Temperature 275 8008H–AVR–04/11

Figure 23-114.Calibrated 8 MHz Oscillator Frequency vs. OSCCAL Value CALIBRATED 8.0MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE (ATtiny88) (Vcc=3V) 16 -40 °C 14 25 °C 85 °C 12 10 Hz) M 8 F (RC 6 4 2 0 0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 OSCCAL (X1) ATtiny48/88 276 8008H–AVR–04/11

ATtiny48/88 24. Register Summary Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page (0xFF) Reserved – – – – – – – – (0xFE) Reserved – – – – – – – – (0xFD) Reserved – – – – – – – – (0xFC) Reserved – – – – – – – – (0xFB) Reserved – – – – – – – – (0xFA) Reserved – – – – – – – – (0xF9) Reserved – – – – – – – – (0xF8) Reserved – – – – – – – – (0xF7) Reserved – – – – – – – – (0xF6) Reserved – – – – – – – – (0xF5) Reserved – – – – – – – – (0xF4) Reserved – – – – – – – – (0xF3) Reserved – – – – – – – – (0xF2) Reserved – – – – – – – – (0xF1) Reserved – – – – – – – – (0xF0) Reserved – – – – – – – – (0xEF) Reserved – – – – – – – – (0xEE) Reserved – – – – – – – – (0xED) Reserved – – – – – – – – (0xEC) Reserved – – – – – – – – (0xEB) Reserved – – – – – – – – (0xEA) Reserved – – – – – – – – (0xE9) Reserved – – – – – – – – (0xE8) Reserved – – – – – – – – (0xE7) Reserved – – – – – – – – (0xE6) Reserved – – – – – – – – (0xE5) Reserved – – – – – – – – (0xE4) Reserved – – – – – – – – (0xE3) Reserved – – – – – – – – (0xE2) Reserved – – – – – – – – (0xE1) Reserved – – – – – – – – (0xE0) Reserved – – – – – – – – (0xDF) Reserved – – – – – – – – (0xDE) Reserved – – – – – – – – (0xDD) Reserved – – – – – – – – (0xDC) Reserved – – – – – – – – (0xDB) Reserved – – – – – – – – (0xDA) Reserved – – – – – – – – (0xD9) Reserved – – – – – – – – (0xD8) Reserved – – – – – – – – (0xD7) Reserved – – – – – – – – (0xD6) Reserved – – – – – – – – (0xD5) Reserved – – – – – – – – (0xD4) Reserved – – – – – – – – (0xD3) Reserved – – – – – – – – (0xD2) Reserved – – – – – – – – (0xD1) Reserved – – – – – – – – (0xD0) Reserved – – – – – – – – (0xCF) Reserved – – – – – – – – (0xCE) Reserved – – – – – – – – (0xCD) Reserved – – – – – – – – (0xCC) Reserved – – – – – – – – (0xCB) Reserved – – – – – – – – (0xCA) Reserved – – – – – – – – (0xC9) Reserved – – – – – – – – (0xC8) Reserved – – – – – – – – (0xC7) Reserved – – – – – – – – (0xC6) Reserved – – – – – – – – (0xC5) Reserved – – – – – – – – (0xC4) Reserved – – – – – – – – (0xC3) Reserved – – – – – – – – (0xC2) Reserved – – – – – – – – (0xC1) Reserved – – – – – – – – (0xC0) Reserved – – – – – – – – (0xBF) Reserved – – – – – – – – 277 8008H–AVR–04/11

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page (0xBE) TWHSR – – – – – – – TWHS 160 (0xBD) TWAMR TWAM6 TWAM5 TWAM4 TWAM3 TWAM2 TWAM1 TWAM0 – 160 (0xBC) TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE 156 (0xBB) TWDR 2-wire Serial Interface Data Register 159 (0xBA) TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE 159 (0xB9) TWSR TWS7 TWS6 TWS5 TWS4 TWS3 – TWPS1 TWPS0 158 (0xB8) TWBR 2-wire Serial Interface Bit Rate Register 156 (0xB7) Reserved – – – – – – – – (0xB6) Reserved – – – – – – – – (0xB5) Reserved – – – – – – – – (0xB4) Reserved – – – – – – – – (0xB3) Reserved – – – – – – – – (0xB2) Reserved – – – – – – – – (0xB1) Reserved – – – – – – – – (0xB0) Reserved – – – – – – – – (0xAF) Reserved – – – – – – – – (0xAE) Reserved – – – – – – – – (0xAD) Reserved – – – – – – – – (0xAC) Reserved – – – – – – – – (0xAB) Reserved – – – – – – – – (0xAA) Reserved – – – – – – – – (0xA9) Reserved – – – – – – – – (0xA8) Reserved – – – – – – – – (0xA7) Reserved – – – – – – – – (0xA6) Reserved – – – – – – – – (0xA5) Reserved – – – – – – – – (0xA4) Reserved – – – – – – – – (0xA3) Reserved – – – – – – – – (0xA2) Reserved – – – – – – – – (0xA1) Reserved – – – – – – – – (0xA0) Reserved – – – – – – – – (0x9F) Reserved – – – – – – – – (0x9E) Reserved – – – – – – – – (0x9D) Reserved – – – – – – – – (0x9C) Reserved – – – – – – – – (0x9B) Reserved – – – – – – – – (0x9A) Reserved – – – – – – – – (0x99) Reserved – – – – – – – – (0x98) Reserved – – – – – – – – (0x97) Reserved – – – – – – – – (0x96) Reserved – – – – – – – – (0x95) Reserved – – – – – – – – (0x94) Reserved – – – – – – – – (0x93) Reserved – – – – – – – – (0x92) Reserved – – – – – – – – (0x91) Reserved – – – – – – – – (0x90) Reserved – – – – – – – – (0x8F) Reserved – – – – – – – – (0x8E) Reserved – – – – – – – – (0x8D) Reserved – – – – – – – – (0x8C) Reserved – – – – – – – – – (0x8B) OCR1BH Timer/Counter1 Output Compare Register B High Byte 114 – (0x8A) OCR1BL Timer/Counter1 Output Compare Register B Low Byte 114 – (0x89) OCR1AH Timer/Counter1 Output Compare Register A High Byte 114 – (0x88) OCR1AL Timer/Counter1 Output Compare Register A Low Byte 114 – (0x87) ICR1H Timer/Counter1 Input Capture Register High Byte 114 – (0x86) ICR1L Timer/Counter1 Input Capture Register Low Byte 114 – (0x85) TCNT1H Timer/Counter1 Counter Register High Byte 113 – (0x84) TCNT1L Timer/Counter1 Counter Register Low Byte 113 (0x83) Reserved – – – – – – – – (0x82) TCCR1C FOC1A FOC1B – – – – – – 113 (0x81) TCCR1B ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 112 (0x80) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 110 (0x7F) DIDR1 – – – – – – AIN1D AIN0D 163 (0x7E) DIDR0 ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D 180 (0x7D) Reserved – – – – – – – – ATtiny48/88 278 8008H–AVR–04/11

ATtiny48/88 Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page (0x7C) ADMUX – REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 176 (0x7B) ADCSRB – ACME – – – ADTS2 ADTS1 ADTS0 162, 179 (0x7A) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 178 (0x79) ADCH ADC Data Register High byte 179 (0x78) ADCL ADC Data Register Low byte 179 (0x77) Reserved – – – – – – – – (0x76) Reserved – – – – – – – – (0x75) Reserved – – – – – – – – (0x74) Reserved – – – – – – – – (0x73) Reserved – – – – – – – – (0x72) Reserved – – – – – – – – (0x71) Reserved – – – – – – – – (0x70) Reserved – – – – – – – – (0x6F) TIMSK1 – – ICIE1 – – OCIE1B OCIE1A TOIE1 114 (0x6E) TIMSK0 – – – – – OCIE0B OCIE0A TOIE0 87 (0x6D) PCMSK2 PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 59 (0x6C) PCMSK1 PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 59 (0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 59 (0x6A) PCMSK3 – – - - PCINT27 PCINT26 PCINT25 PCINT24 59 (0x69) EICRA – – – – ISC11 ISC10 ISC01 ISC00 55 (0x68) PCICR – – – – PCIE3 PCIE2 PCIE1 PCIE0 57 (0x67) Reserved – – – – – – – – (0x66) OSCCAL Oscillator Calibration Register 34 (0x65) Reserved – – – – – – – – (0x64) PRR PRTWI – PRTIM0 – PRTIM1 PRSPI – PRADC 40 (0x63) Reserved – – – – – – – – (0x62) Reserved – – – – – – – – (0x61) CLKPR CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 34 (0x60) WDTCSR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 49 0x3F (0x5F) SREG I T H S V N Z C 9 0x3E (0x5E) SPH – – – – – – SP9 SP8 11 0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 11 0x3C (0x5C) Reserved – – – – – – – – 0x3B (0x5B) Reserved – – – – – – – – 0x3A (0x5A) Reserved – – – – – – – – 0x39 (0x59) Reserved – – – – – – – – 0x38 (0x58) Reserved – – – – – – – – 0x37 (0x57) SPMCSR – RWWSB – CTPB RFLB PGWRT PGERS SELFPRGEN 186 0x36 (0x56) Reserved – – – – – 0x35 (0x55) MCUCR – BODS BODSE PUD – – – – 40, 77 0x34 (0x54) MCUSR – – – – WDRF BORF EXTRF PORF 49 0x33 (0x53) SMCR – – – – – SM1 SM0 SE 39 0x32 (0x52) Reserved – – – – – – – – 0x31 (0x51) DWDR debugWire Data Register 182 0x30 (0x50) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 162 0x2F (0x4F) Reserved – – – – – – – – 0x2E (0x4E) SPDR SPI Data Register 128 0x2D (0x4D) SPSR SPIF WCOL – – – – – SPI2X 127 0x2C (0x4C) SPCR SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 126 0x2B (0x4B) GPIOR2 General Purpose I/O Register 2 27 0x2A (0x4A) GPIOR1 General Purpose I/O Register 1 27 0x29 (0x49) Reserved – – – – – – – – 0x28 (0x48) OCR0B Timer/Counter0 Output Compare Register B 87 0x27 (0x47) OCR0A Timer/Counter0 Output Compare Register A 86 0x26 (0x46) TCNT0 Timer/Counter0 (8-bit) 86 0x25 (0x45) TCCR0A – – – – CTC0 CS02 CS01 CS00 85 0x24 (0x44) Reserved – – – – – – – – 0x23 (0x43) GTCCR TSM – – – – – – PSRSYNC 118 0x22 (0x42) Reserved – – – – – – – – 0x21 (0x41) EEARL EEPROM Address Register Low Byte 25 0x20 (0x40) EEDR EEPROM Data Register 25 0x1F (0x3F) EECR – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE 25 0x1E (0x3E) GPIOR0 General Purpose I/O Register 0 27 0x1D (0x3D) EIMSK – – – – – – INT1 INT0 56 0x1C (0x3C) EIFR – – – – – – INTF1 INTF0 56 0x1B (0x3B) PCIFR – – – – PCIF3 PCIF2 PCIF1 PCIF0 58 279 8008H–AVR–04/11

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page 0x1A (0x3A) Reserved – – – – – – – – 0x19 (0x39) Reserved – – – – – – – – 0x18 (0x38) Reserved – – – – – – – – 0x17 (0x37) Reserved – – – – – – – – 0x16 (0x36) TIFR1 – – ICF1 – – OCF1B OCF1A TOV1 115 0x15 (0x35) TIFR0 – – – – – OCF0B OCF0A TOV0 87 0x14 (0x34) Reserved – – – – – – – – 0x13 (0x33) Reserved – – – – – – – – 0x12 (0x32) PORTCR BBMD BBMC BBMB BBMA PUDD PUDC PUDB PUDA 77 0x11 (0x31) Reserved – – – – – – – – 0x10 (0x30) Reserved – – – – – – – – 0x0F (0x2F) Reserved – – – – – – – – 0x0E (0x2E) PORTA – – – – PORTA3 PORTA2 PORTA1 PORTA0 78 0x0D (0x2D) DDRA – – – – DDA3 DDA2 DDA1 DDA0 78 0x0C (0x2C) PINA – – – – PINA3 PINA2 PINA1 PINA0 78 0x0B (0x2B) PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 79 0x0A (0x2A) DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 79 0x09 (0x29) PIND PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 79 0x08 (0x28) PORTC PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 78 0x07 (0x27) DDRC DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 78 0x06 (0x26) PINC PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 79 0x05 (0x25) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 78 0x04 (0x24) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 78 0x03 (0x23) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 78 0x02 (0x22) Reserved – – – – – – – – 0x01 (0x21) Reserved – – – – – – – – 0x00 (0x20) Reserved – – – – – – – – Note: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written. 2. I/O Registers within the address range 0x00 – 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. 3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only. 4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 – 0x3F must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The ATtiny48/88 is a com- plex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 – 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used. ATtiny48/88 280 8008H–AVR–04/11

ATtiny48/88 25. Instruction Set Summary Mnemonics Operands Description Operation Flags #Clocks ARITHMETIC AND LOGIC INSTRUCTIONS ADD Rd, Rr Add two Registers Rd ← Rd + Rr Z,C,N,V,H 1 ADC Rd, Rr Add with Carry two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1 ADIW Rdl,K Add Immediate to Word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2 SUB Rd, Rr Subtract two Registers Rd ← Rd - Rr Z,C,N,V,H 1 SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1 SBC Rd, Rr Subtract with Carry two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1 SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1 SBIW Rdl,K Subtract Immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z,C,N,V,S 2 AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1 ANDI Rd, K Logical AND Register and Constant Rd ← Rd • K Z,N,V 1 OR Rd, Rr Logical OR Registers Rd ← Rd v Rr Z,N,V 1 ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1 EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕ Rr Z,N,V 1 COM Rd One’s Complement Rd ← 0xFF − Rd Z,C,N,V 1 NEG Rd Two’s Complement Rd ← 0x00 − Rd Z,C,N,V,H 1 SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1 CBR Rd,K Clear Bit(s) in Register Rd ← Rd • (0xFF - K) Z,N,V 1 INC Rd Increment Rd ← Rd + 1 Z,N,V 1 DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1 TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V 1 CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V 1 SER Rd Set Register Rd ← 0xFF None 1 BRANCH INSTRUCTIONS RJMP k Relative Jump PC ← PC + k + 1 None 2 IJMP Indirect Jump to (Z) PC ← Z None 2 RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3 ICALL Indirect Call to (Z) PC ← Z None 3 RET Subroutine Return PC ← STACK None 4 RETI Interrupt Return PC ← STACK I 4 CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3 CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1 CPC Rd,Rr Compare with Carry Rd − Rr − C Z, N,V,C,H 1 CPI Rd,K Compare Register with Immediate Rd − K Z, N,V,C,H 1 SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3 SBRS Rr, b Skip if Bit in Register is Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3 SBIC P, b Skip if Bit in I/O Register Cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3 SBIS P, b Skip if Bit in I/O Register is Set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3 BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2 BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC←PC+k + 1 None 1/2 BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1/2 BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1/2 BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1/2 BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1/2 BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2 BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2 BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1/2 BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1/2 BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2 BRLT k Branch if Less Than Zero, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2 BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2 BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2 BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1/2 BRTC k Branch if T Flag Cleared if (T = 0) then PC ← PC + k + 1 None 1/2 BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1/2 BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1/2 BRIE k Branch if Interrupt Enabled if ( I = 1) then PC ← PC + k + 1 None 1/2 BRID k Branch if Interrupt Disabled if ( I = 0) then PC ← PC + k + 1 None 1/2 BIT AND BIT-TEST INSTRUCTIONS SBI P,b Set Bit in I/O Register I/O(P,b) ← 1 None 2 CBI P,b Clear Bit in I/O Register I/O(P,b) ← 0 None 2 LSL Rd Logical Shift Left Rd(n+1) ← Rd(n), Rd(0) ← 0 Z,C,N,V 1 LSR Rd Logical Shift Right Rd(n) ← Rd(n+1), Rd(7) ← 0 Z,C,N,V 1 ROL Rd Rotate Left Through Carry Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7) Z,C,N,V 1 ROR Rd Rotate Right Through Carry Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0) Z,C,N,V 1 281 8008H–AVR–04/11

Mnemonics Operands Description Operation Flags #Clocks ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1 SWAP Rd Swap Nibbles Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0) None 1 BSET s Flag Set SREG(s) ← 1 SREG(s) 1 BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1 BST Rr, b Bit Store from Register to T T ← Rr(b) T 1 BLD Rd, b Bit load from T to Register Rd(b) ← T None 1 SEC Set Carry C ← 1 C 1 CLC Clear Carry C ← 0 C 1 SEN Set Negative Flag N ← 1 N 1 CLN Clear Negative Flag N ← 0 N 1 SEZ Set Zero Flag Z ← 1 Z 1 CLZ Clear Zero Flag Z ← 0 Z 1 SEI Global Interrupt Enable I ← 1 I 1 CLI Global Interrupt Disable I ← 0 I 1 SES Set Signed Test Flag S ← 1 S 1 CLS Clear Signed Test Flag S ← 0 S 1 SEV Set Twos Complement Overflow. V ← 1 V 1 CLV Clear Twos Complement Overflow V ← 0 V 1 SET Set T in SREG T ← 1 T 1 CLT Clear T in SREG T ← 0 T 1 SEH Set Half Carry Flag in SREG H ← 1 H 1 CLH Clear Half Carry Flag in SREG H ← 0 H 1 DATA TRANSFER INSTRUCTIONS MOV Rd, Rr Move Between Registers Rd ← Rr None 1 MOVW Rd, Rr Copy Register Word Rd+1:Rd ← Rr+1:Rr None 1 LDI Rd, K Load Immediate Rd ← K None 1 LD Rd, X Load Indirect Rd ← (X) None 2 LD Rd, X+ Load Indirect and Post-Inc. Rd ← (X), X ← X + 1 None 2 LD Rd, - X Load Indirect and Pre-Dec. X ← X - 1, Rd ← (X) None 2 LD Rd, Y Load Indirect Rd ← (Y) None 2 LD Rd, Y+ Load Indirect and Post-Inc. Rd ← (Y), Y ← Y + 1 None 2 LD Rd, - Y Load Indirect and Pre-Dec. Y ← Y - 1, Rd ← (Y) None 2 LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2 LD Rd, Z Load Indirect Rd ← (Z) None 2 LD Rd, Z+ Load Indirect and Post-Inc. Rd ← (Z), Z ← Z+1 None 2 LD Rd, -Z Load Indirect and Pre-Dec. Z ← Z - 1, Rd ← (Z) None 2 LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2 LDS Rd, k Load Direct from SRAM Rd ← (k) None 2 ST X, Rr Store Indirect (X) ← Rr None 2 ST X+, Rr Store Indirect and Post-Inc. (X) ← Rr, X ← X + 1 None 2 ST - X, Rr Store Indirect and Pre-Dec. X ← X - 1, (X) ← Rr None 2 ST Y, Rr Store Indirect (Y) ← Rr None 2 ST Y+, Rr Store Indirect and Post-Inc. (Y) ← Rr, Y ← Y + 1 None 2 ST - Y, Rr Store Indirect and Pre-Dec. Y ← Y - 1, (Y) ← Rr None 2 STD Y+q,Rr Store Indirect with Displacement (Y + q) ← Rr None 2 ST Z, Rr Store Indirect (Z) ← Rr None 2 ST Z+, Rr Store Indirect and Post-Inc. (Z) ← Rr, Z ← Z + 1 None 2 ST -Z, Rr Store Indirect and Pre-Dec. Z ← Z - 1, (Z) ← Rr None 2 STD Z+q,Rr Store Indirect with Displacement (Z + q) ← Rr None 2 STS k, Rr Store Direct to SRAM (k) ← Rr None 2 LPM Load Program Memory R0 ← (Z) None 3 LPM Rd, Z Load Program Memory Rd ← (Z) None 3 LPM Rd, Z+ Load Program Memory and Post-Inc Rd ← (Z), Z ← Z+1 None 3 SPM Store Program Memory (Z) ← R1:R0 None - IN Rd, P In Port Rd ← P None 1 OUT P, Rr Out Port P ← Rr None 1 PUSH Rr Push Register on Stack STACK ← Rr None 2 POP Rd Pop Register from Stack Rd ← STACK None 2 MCU CONTROL INSTRUCTIONS NOP No Operation None 1 SLEEP Sleep (see specific descr. for Sleep function) None 1 WDR Watchdog Reset (see specific descr. for WDR/timer) None 1 BREAK Break For On-chip Debug Only None N/A ATtiny48/88 282 8008H–AVR–04/11

ATtiny48/88 26. Ordering Information 26.1 ATtiny48 Speed (MHz) Power Supply Ordering Code(1) Package(2) Operational Range ATtiny48-MMU 28M1 ATtiny48-MMUR 28M1 ATtiny48-MMH 28M1 ATtiny48-MMHR 28M1 ATtiny48-PU 28P3 Industrial 12 1.8 – 5.5V ATtiny48-AU 32A (-40°C to +85°C)(3) ATtiny48-AUR 32A ATtiny48-CCU 32CC1 ATtiny48-CCUR 32CC1 ATtiny48-MU 32M1-A ATtiny48-MUR 32M1-A Notes: 1. Code indicators: – H: NiPdAu lead finish – U: matte tin – R: tape & reel 2. All packages are Pb-free, halide-free and fully green and they comply with the European directive for Restriction of Hazard- ous Substances (RoHS). 3. These devices can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering informa- tion and minimum quantities. Package Type 28M1 28-pad, 4 x 4 x 1.0 body, Lead Pitch 0.45 mm, Quad Flat No-Lead (QFN) 28P3 28-lead, 0.300” Wide, Plastic Dual Inline Package (PDIP) 32A 32-lead, Thin (1.0 mm) Plastic Quad Flat Package (TQFP) 32CC1 32-ball (6 x 6 Array), 0.50 mm Pitch, 4 x 4 x 0.6 mm, Ultra Thin, Fine-Pitch Ball Grid Array Package (UFBGA) 32M1-A 32-pad, 5 x 5 x 1.0 body, Lead Pitch 0.50 mm, Quad Flat No-Lead (QFN) 283 8008H–AVR–04/11

26.2 ATtiny88 Speed (MHz) Power Supply Ordering Code(1) Package(2) Operational Range ATtiny88-MMU 28M1 ATtiny88-MMUR 28M1 ATtiny88-MMH 28M1 ATtiny88-MMHR 28M1 ATtiny88-PU 28P3 Industrial 12 1.8 – 5.5V ATtiny88-AU 32A (-40°C to +85°C)(3) ATtiny88-AUR 32A ATtiny88-CCU 32CC1 ATtiny88-CCUR 32CC1 ATtiny88-MU 32M1-A ATtiny88-MUR 32M1-A Notes: 1. Code indicators: – H: NiPdAu lead finish – U: matte tin – R: tape & reel 2. All packages are Pb-free, halide-free and fully green and they comply with the European directive for Restriction of Hazard- ous Substances (RoHS). 3. These devices can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering informa- tion and minimum quantities. Package Type 28M1 28-pad, 4 x 4 x 1.0 body, Lead Pitch 0.45 mm, Quad Flat No-Lead (QFN) 28P3 28-lead, 0.300” Wide, Plastic Dual Inline Package (PDIP) 32A 32-lead, Thin (1.0 mm) Plastic Quad Flat Package (TQFP) 32CC1 32-ball (6 x 6 Array), 0.50 mm Pitch, 4 x 4 x 0.6 mm, Ultra Thin, Fine-Pitch Ball Grid Array Package (UFBGA) 32M1-A 32-pad, 5 x 5 x 1.0 body, Lead Pitch 0.50 mm, Quad Flat No-Lead (QFN) ATtiny48/88 284 8008H–AVR–04/11

ATtiny48/88 27. Packaging Information 27.1 28M1 D C 1 2 Pin 1 ID 3 E SIDE VIEW A1 TOP VIEW A y K D2 0.45 COMMON DIMENSIONS 1 (Unit of Measure = mm) 2 R 0.20 SYMBOL MIN NOM MAX NOTE 3 A 0.80 0.90 1.00 E2 A1 0.00 0.02 0.05 b 0.17 0.22 0.27 b C 0.20 REF D 3.95 4.00 4.05 D2 2.35 2.40 2.45 L E 3.95 4.00 4.05 e E2 2.35 2.40 2.45 0.4 Ref e 0.45 (4x) BOTTOM VIEW L 0.35 0.40 0.45 y 0.00 – 0.08 Note: The terminal #1 ID is a Laser-marked Feature. K 0.20 – – 10/24/08 TITLE GPC DRAWING NO. REV. Package Drawing Contact: 28M1, 28-pad, 4 x 4 x 1.0 mm Body, Lead Pitch 0.45 mm, packagedrawings@atmel.com 2.4 x 2.4 mm Exposed Pad, Thermally Enhanced ZBV 28M1 B Plastic Very Thin Quad Flat No Lead Package (VQFN) 285 8008H–AVR–04/11

27.2 28P3 D PIN 1 E1 A SEATING PLANE A1 L B2 B (4 PLACES) B1 e E COMMON DIMENSIONS 0º ~ 15º REF (Unit of Measure = mm) C SYMBOL MIN NOM MAX NOTE eB A – – 4.5724 A1 0.508 – – D 34.544 – 34.798 Note 1 E 7.620 – 8.255 E1 7.112 – 7.493 Note 1 B 0.381 – 0.533 B1 1.143 – 1.397 Note: 1.Dimensions D and E1 do not include mold Flash or Protrusion. Mold Flash or Protrusion shall not exceed 0.25 mm (0.010"). B2 0.762 – 1.143 L 3.175 – 3.429 C 0.203 – 0.356 eB – – 10.160 e 2.540 TYP 09/28/01 TITLE DRAWING NO. REV. 2325 Orchard Parkway 28P3, 28-lead (0.300"/7.62 mm Wide) Plastic Dual R San Jose, CA 95131 Inline Package (PDIP) 28P3 B ATtiny48/88 286 8008H–AVR–04/11

ATtiny48/88 27.3 32A PIN 1 IDENTIFIER PIN 1 B e E1 E D1 D C 0°~7° A1 A2 A L COMMON DIMENSIONS (Unit of Measure = mm) SYMBOL MIN NOM MAX NOTE A – – 1.20 A1 0.05 – 0.15 A2 0.95 1.00 1.05 D 8.75 9.00 9.25 D1 6.90 7.00 7.10 Note 2 E 8.75 9.00 9.25 Notes: E1 6.90 7.00 7.10 Note 2 1. This package conforms to JEDEC reference MS-026, Variation ABA. 2. Dimensions D1 and E1 do not include mold protrusion. Allowable B 0.30 – 0.45 protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum C 0.09 – 0.20 plastic body size dimensions including mold mismatch. 3. Lead coplanarity is 0.10 mm maximum. L 0.45 – 0.75 e 0.80 TYP 2010-10-20 TITLE DRAWING NO. REV. 2325 Orchard Parkway 32A, 32-lead, 7 x 7 mm Body Size, 1.0 mm Body Thickness, San Jose, CA 95131 32A C R 0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP) 287 8008H–AVR–04/11

27.4 32CC1 1 2 3 4 5 6 0.08 A B Pin#1 ID C SIDE VIEW D D E F b1 A1 E A TOP VIEW A2 E1 e 32-Øb 1 2 3 4 5 6 F COMMON DIMENSIONS E (Unit of Measure = mm) D SYMBOL MIN NOM MAX NOTE D1 C A – – 0.60 B A1 0.12 – – e A A2 0.38 REF b 0.25 0.30 0.35 1 b1 0.25 – – 2 A1 BALL CORNER D 3.90 4.00 4.10 BOTTOM VIEW D1 2.50 BSC E 3.90 4.00 4.10 E1 2.50 BSC Note1 : Dimension “b” is measured at the maximum ball dia. in a plane parallel e 0.50 BSC to the seating plane. Note2 : Dimension “b1” is the solderable surface defined by the opening of the solder resist layer. 07/06/10 TITLE GPC DRAWING NO. REV. Package Drawing Contact: 32CC1, 32-ball (6 x 6 Array), 4 x 4 x 0.6 mm packagedrawings@atmel.com package, ball pitch 0.50 mm, Ultra Thin, CAG 32CC1 B Fine-Pitch Ball Grid Array (UFBGA) ATtiny48/88 288 8008H–AVR–04/11

ATtiny48/88 27.5 32M1-A D D1 1 0 2 3 Pin 1 ID E1 E SIDE VIEW TOP VIEW A3 A2 A1 A K 0.08C COMMON DIMENSIONS P (Unit of Measure = mm) D2 SYMBOL MIN NOM MAX NOTE A 0.80 0.90 1.00 1 A1 – 0.02 0.05 P Pin #1 Notch 2 A2 – 0.65 1.00 (0.20 R) 3 A3 0.20 REF E2 b 0.18 0.23 0.30 K D 4.9 0 5.00 5.10 D1 4.7 0 4.75 4.80 D2 2.95 3.10 3.25 E 4.90 5.00 5.10 b e L E1 4.70 4.75 4.80 BOTTOM VIEW E2 2.95 3.10 3.25 e 0.50 BSC L 0.30 0.40 0.50 P – – 0.60 0 – – 12o Note: JEDEC Standard MO-220, Fig. 2 (Anvil Singulation), VHHD-2. K 0.20 – – 5/25/06 TITLE DRAWING NO. REV. 2325 Orchard Parkway 32M1-A, 32-pad, 5 x 5 x 1.0 mm Body, Lead Pitch 0.50 mm, San Jose, CA 95131 32M1-A E R 3.10 mm Exposed Pad, Micro Lead Frame Package (MLF) 289 8008H–AVR–04/11

28. Errata 28.1 ATtiny48 28.1.1 Rev. C No known errata. 28.1.2 Rev. B Not sampled. 28.1.3 Rev. A Not sampled. ATtiny48/88 290 8008H–AVR–04/11

ATtiny48/88 28.2 ATtiny88 28.2.1 Rev. C No known errata. 28.2.2 Rev. B No known errata. 28.2.3 Rev. A Not sampled. 291 8008H–AVR–04/11

29. Datasheet Revision History 29.1 Rev. 8008H - 04/11 1. Updated: – “Ordering Information” on page 283, added tape & reel code -MMUR 29.2 Rev. 8008G - 04/11 1. Updated: – “Block Diagram” on page 5 – “Memories” on page 17 – “Clock System” on page 28 – “Lock Bits, Fuse Bits and Device Signature” on page 188 – “External Programming” on page 191 – “Speed” on page 208 – “Two-Wire Serial Interface Characteristics” on page 212 2. Added: – “Capacitive Touch Sensing” on page 7 – “Register Description” on page 15 – “Overview” on page 129 – “Compatibility with SMBus” on page 156 3. Changed document status from “Preliminary” to “Final”. 29.3 Rev. 8008F - 06/10 1. Updated notes 1 and 10 in table in Section 22.2 “DC Characteristics” on page 206. 2. Updated package drawing in Section 27.4 “32CC1” on page 288. 3. Updated bit syntax throughout the datasheet, e.g. from CS02:0 to CS0[2:0]. 29.4 Rev. 8008E - 05/10 1. Section 24. “Register Summary” on page 277, added SPH at address 0x3E. 2. Section 27.1 “28M1” on page 285 updated with correct package drawing. 29.5 Rev. 8008D - 03/10 1. Separated Typical Characteristic plots, added Section 23.2 “ATtiny88” on page 248. 2. Updated: – Section 1.1 “Pin Descriptions” on page 3, Port D, adjusted texts ‘sink and source’ and ‘high sink’. – Table 6-3 on page 28 adjusted, to fix TBD. – Section 6.2.3 “Internal 128 kHz Oscillator” on page 31 adjusted, to fix TBD. – Section 8.4 “Watchdog Timer” on page 46, updated. – Section 22.2 “DC Characteristics” on page 206, updated TBD in notes 5 and 8. 3. Added: ATtiny48/88 292 8008H–AVR–04/11

ATtiny48/88 – UFBGA package (32CC1) in, “Features” on page 1, “Pin Configurations” on page 2, Section 26. “Ordering Information” on page 283, and Section 27. “Packaging Information” on page 285 – Addresses in all Register Desc. tables, with cross-references to Register Summary – Tape and reel in Section 26. “Ordering Information” on page 283 29.6 Rev. 8008C - 03/09 1. Updated sections: – “Features” on page 1 – “Reset and Interrupt Handling” on page 12 – “EECR – EEPROM Control Register” on page 25 – “Features” on page 129 – “Bit Rate Generator Unit” on page 135 – “TWBR – TWI Bit Rate Register” on page 156 – “TWHSR – TWI High Speed Register” on page 160 – “Analog Comparator” on page 161 – “Overview” on page 164 – “Operation” on page 165 – “Starting a Conversion” on page 166 – “Programming the Lock Bits” on page 199 – “Absolute Maximum Ratings*” on page 206 – “DC Characteristics” on page 206 – “Speed” on page 208 – “Register Summary” on page 277 2. Added sections – “High-Speed Two-Wire Interface Clock – clkTWIHS” on page 29 – “Analog Comparator Characteristics” on page 210 3. Updated Figure 6-1 on page 28. 4. Updated order codes on page 283 and page 284 to reflect changes in leadframe composition. 29.7 Rev. 8008B - 06/08 1. Updated introduction of “I/O-Ports” on page 60. 2. Updated “DC Characteristics” on page 206. 3. Added “Typical Characteristics” on page 219. 29.8 Rev. 8008A - 06/08 1. Initial revision. 293 8008H–AVR–04/11

ATtiny48/88 294 8008H–AVR–04/11

ATtiny48/88 Table of Contents Features.....................................................................................................1 1 Pin Configurations ...................................................................................2 1.1 Pin Descriptions .................................................................................................3 2 Overview ...................................................................................................5 2.1 Block Diagram ...................................................................................................5 2.2 Comparison Between ATtiny48 and ATtiny88 ...................................................6 3 General Information .................................................................................7 3.1 Resources .........................................................................................................7 3.2 About Code Examples .......................................................................................7 3.3 Capacitive Touch Sensing .................................................................................7 3.4 Data Retention ...................................................................................................7 3.5 Disclaimer ..........................................................................................................7 4 AVR CPU Core ..........................................................................................8 4.1 Introduction ........................................................................................................8 4.2 Architectural Overview .......................................................................................8 4.3 ALU – Arithmetic Logic Unit ...............................................................................9 4.4 Status Register ..................................................................................................9 4.5 General Purpose Register File ........................................................................10 4.6 Stack Pointer ...................................................................................................11 4.7 Instruction Execution Timing ...........................................................................12 4.8 Reset and Interrupt Handling ...........................................................................12 4.9 Register Description ........................................................................................15 5 Memories ................................................................................................17 5.1 Program Memory (Flash) .................................................................................17 5.2 Data Memory (SRAM) and Register Files .......................................................18 5.3 Data Memory (EEPROM) ................................................................................20 5.4 Register Description ........................................................................................25 6 Clock System .........................................................................................28 6.1 Clock Subsystems ...........................................................................................28 6.2 Clock Sources .................................................................................................29 6.3 System Clock Prescaler ..................................................................................31 6.4 Clock Output Buffer .........................................................................................32 i 8008H–AVR–04/11

6.5 Clock Startup Sequence ..................................................................................32 6.6 Register Description ........................................................................................34 7 Power Management and Sleep Modes .................................................36 7.1 Sleep Modes ....................................................................................................36 7.2 Software BOD Disable .....................................................................................37 7.3 Minimizing Power Consumption ......................................................................38 7.4 Register Description ........................................................................................39 8 System Control and Reset ....................................................................42 8.1 Resetting the AVR ...........................................................................................42 8.2 Reset Sources .................................................................................................43 8.3 Internal Voltage Reference ..............................................................................45 8.4 Watchdog Timer ..............................................................................................46 8.5 Register Description ........................................................................................49 9 Interrupts ................................................................................................52 9.1 Interrupt Vectors ..............................................................................................52 9.2 External Interrupts ...........................................................................................53 9.3 Register Description ........................................................................................55 10 I/O-Ports ..................................................................................................60 10.1 Introduction ......................................................................................................60 10.2 Ports as General Digital I/O .............................................................................61 10.3 Alternate Port Functions ..................................................................................65 10.4 Register Description ........................................................................................77 11 8-bit Timer/Counter0 ..............................................................................80 11.1 Features ..........................................................................................................80 11.2 Overview ..........................................................................................................80 11.3 Timer/Counter Clock Sources .........................................................................81 11.4 Counter Unit ....................................................................................................81 11.5 Output Compare Unit .......................................................................................82 11.6 Modes of Operation .........................................................................................83 11.7 Timer/Counter Timing Diagrams .....................................................................84 11.8 8-bit Timer/Counter Register Description ........................................................85 12 16-bit Timer/Counter1 with PWM ..........................................................89 12.1 Features ..........................................................................................................89 12.2 Overview ..........................................................................................................89 ATtiny48/88 ii 8008H–AVR–04/11

ATtiny48/88 12.3 Accessing 16-bit Registers ..............................................................................91 12.4 Timer/Counter Clock Sources .........................................................................93 12.5 Counter Unit ....................................................................................................94 12.6 Input Capture Unit ...........................................................................................95 12.7 Output Compare Units .....................................................................................97 12.8 Compare Match Output Unit ............................................................................99 12.9 Modes of Operation .......................................................................................100 12.10 Timer/Counter Timing Diagrams ...................................................................107 12.11 Register Description ......................................................................................110 13 Timer/Counter0 and Timer/Counter1 Prescalers ..............................117 13.1 Internal Clock Source ....................................................................................117 13.2 Prescaler Reset .............................................................................................117 13.3 External Clock Source ...................................................................................117 13.4 Register Description ......................................................................................118 14 SPI – Serial Peripheral Interface .........................................................120 14.1 Features ........................................................................................................120 14.2 Overview ........................................................................................................120 14.3 SS Pin Functionality ......................................................................................124 14.4 Data Modes ...................................................................................................125 14.5 Register Description ......................................................................................126 15 TWI – Two Wire Interface ....................................................................129 15.1 Features ........................................................................................................129 15.2 Overview ........................................................................................................129 15.3 Bus Definitions ...............................................................................................129 15.4 Data Transfer and Frame Format ..................................................................130 15.5 Multi-master Bus Systems, Arbitration and Synchronization .........................133 15.6 Overview of the TWI Module .........................................................................135 15.7 Using the TWI ................................................................................................137 15.8 Transmission Modes .....................................................................................140 15.9 Multi-master Systems and Arbitration ............................................................154 15.10 Compatibility with SMBus ..............................................................................156 15.11 Register Description ......................................................................................156 16 Analog Comparator .............................................................................161 16.1 Analog Comparator Multiplexed Input ...........................................................161 16.2 Register Description ......................................................................................162 iii 8008H–AVR–04/11

17 ADC – Analog to Digital Converter .....................................................164 17.1 Features ........................................................................................................164 17.2 Overview ........................................................................................................164 17.3 Operation .......................................................................................................165 17.4 Starting a Conversion ....................................................................................166 17.5 Prescaling and Conversion Timing ................................................................167 17.6 Changing Channel or Reference Selection ...................................................170 17.7 ADC Noise Canceler .....................................................................................171 17.8 Analog Input Circuitry ....................................................................................171 17.9 Analog Noise Canceling Techniques .............................................................172 17.10 ADC Accuracy Definitions .............................................................................173 17.11 ADC Conversion Result .................................................................................175 17.12 Temperature Measurement ...........................................................................175 17.13 Register Description ......................................................................................176 18 debugWIRE On-Chip Debug System ..................................................181 18.1 Features ........................................................................................................181 18.2 Overview ........................................................................................................181 18.3 Physical Interface ..........................................................................................181 18.4 Software Break Points ...................................................................................182 18.5 Limitations of debugWIRE .............................................................................182 18.6 Register Description ......................................................................................182 19 Self-Programming the Flash ...............................................................183 19.1 Addressing the Flash During Self-Programming ...........................................184 19.2 Register Description ......................................................................................186 20 Lock Bits, Fuse Bits and Device Signature .......................................188 20.1 Lock Bits ........................................................................................................188 20.2 Fuse Bits ........................................................................................................189 20.3 Signature Bytes .............................................................................................190 20.4 Calibration Byte .............................................................................................190 21 External Programming ........................................................................191 21.1 Memory Parametrics .....................................................................................191 21.2 Parallel Programming ....................................................................................191 21.3 Serial Programming .......................................................................................200 21.4 Programming Time for Flash and EEPROM .................................................205 ATtiny48/88 iv 8008H–AVR–04/11

ATtiny48/88 22 Electrical Characteristics ....................................................................206 22.1 Absolute Maximum Ratings* .........................................................................206 22.2 DC Characteristics .........................................................................................206 22.3 Speed ............................................................................................................208 22.4 Clock Characterizations .................................................................................208 22.5 System and Reset Characterizations ............................................................209 22.6 Analog Comparator Characteristics ...............................................................210 22.7 ADC Characteristics ......................................................................................211 22.8 Two-Wire Serial Interface Characteristics .....................................................212 22.9 SPI Characteristics ........................................................................................213 22.10 Parallel Programming Characteristics ...........................................................215 22.11 Serial Programming Characteristics ..............................................................217 23 Typical Characteristics ........................................................................219 23.1 ATtiny48 ........................................................................................................219 23.2 ATtiny88 ........................................................................................................248 24 Register Summary ...............................................................................277 25 Instruction Set Summary ....................................................................281 26 Ordering Information ...........................................................................283 26.1 ATtiny48 ........................................................................................................283 26.2 ATtiny88 ........................................................................................................284 27 Packaging Information ........................................................................285 27.1 28M1 ..............................................................................................................285 27.2 28P3 ..............................................................................................................286 27.3 32A ................................................................................................................287 27.4 32CC1 ...........................................................................................................288 27.5 32M1-A ..........................................................................................................289 28 Errata .....................................................................................................290 28.1 ATtiny48 ........................................................................................................290 28.2 ATtiny88 ........................................................................................................291 29 Datasheet Revision History ................................................................292 29.1 Rev. 8008H - 04/11 .......................................................................................292 29.2 Rev. 8008G - 04/11 .......................................................................................292 29.3 Rev. 8008F - 06/10 ........................................................................................292 29.4 Rev. 8008E - 05/10 ........................................................................................292 v 8008H–AVR–04/11

29.5 Rev. 8008D - 03/10 .......................................................................................292 29.6 Rev. 8008C - 03/09 .......................................................................................293 29.7 Rev. 8008B - 06/08 ........................................................................................293 29.8 Rev. 8008A - 06/08 ........................................................................................293 Table of Contents.......................................................................................i ATtiny48/88 vi 8008H–AVR–04/11

ATtiny48/88 vii 8008H–AVR–04/11

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