ATMEL ATtiny26, ATtiny26L User Manual

Features

• High-performance, Low-power AVR

• RISC Architecture

– 118 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General Purpose Working Registers – Fully Static Operation – Up to 16 MIPS Throughput at 16 MHz

• Data and Non-volatile Program Memory

– 2K Bytes of In-System Programmable Program Memory Flash

Endurance: 10,000 Write/Erase Cycles

– 128 Bytes of In-System Programmable EEPROM

Endurance: 100,000 Write/Erase Cycles – 128 Bytes Internal SRAM – Programming Lock for Flash Program and EEPROM Data Security

• Peripheral Features

– 8-bit Timer/Counter with Separate Prescaler – 8-bit High-speed Timer with Separate Prescaler

2 High Frequency PWM Outputs with Separate Output Compare Registers

Non-overlapping Inverted PWM Output Pins – Universal Serial Interface with Start Condition Detector – 10-bit ADC

11 Single Ended Channels

8 Differential ADC Channels

7 Differential ADC Channel Pairs with Programmable Gain (1x, 20x) – On-chip Analog Comparator – External Interrupt – Pin Change Interrupt on 11 Pins – Programmable Watchdog Timer with Separate On-chip Oscillator

• Special Microcontroller Features

– Low Power Idle, Noise Reduction, and Power-down Modes – Power-on Reset and Programmable Brown-out Detection – External and Internal Interrupt Sources – In-System Programmable via SPI Port – Internal Calibrated RC Oscillator

• I/O and Packages

– 20-lead PDIP/SOIC: 16 Programmable I/O Lines – 32-lead QFN/MLF: 16 programmable I/O Lines

• Operating Voltages

– 2.7V - 5.5V for ATtiny26L – 4.5V - 5.5V for ATtiny26

• Speed Grades

– 0 - 8 MHz for ATtiny26L – 0 - 16 MHz for ATtiny26

• Power Consumption at 1 MHz, 3V and 25°C for ATtiny26L

– Active 16 MHz, 5V and 25°C: Typ 15 mA – Active 1 MHz, 3V and 25°C: 0.70 mA – Idle Mode 1 MHz, 3V and 25°C: 0.18 mA – Power-down Mode: < 1 µA

8-bit Microcontroller

8-bit Microcontroller with 2K Bytes Flash

ATtiny26 ATtiny26L

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Rev. 1477F–AVR–12/04

Pin Configuration

PDIP/SOIC

(MOSI/DI/SDA/OC1A) PB0

(MISO/DO/OC1A) PB1

(SCK/SCL/OC1B) PB2

(OC1B) PB3

VCC

GND (ADC7/XTAL1) PB4 (ADC8/XTAL2) PB5

(ADC9/INT0/T0) PB6

(ADC10/RESET) PB7

1 2 3 4 5 6 7 8 9 10

20 19 18 17 16 15 14 13 12 11

MLF Top View

PB2 (SCK/SCL/OC1B)

PB1 (MISO/DO/OC1A)

PB0 (MOSI/DI/SDA/OC1A)

NCNCNC

PA0 (ADC0)

PA0 (ADC0) PA1 (ADC1) PA2 (ADC2) PA3 (AREF) GND AVCC PA4 (ADC3) PA5 (ADC4) PA6 (ADC5/AIN0) PA7 (ADC6/AIN1)

PA1 (ADC1)

(OC1B) PB3

VCC

GND

NC (ADC7/XTAL1) PB4 (ADC8/XTAL2) PB5

32313029282726

1 2 3 4 5 6 7 8

10111213141516

(ADC9/INT0/T0) PB6

(ADC6/AIN1) PA7

(ADC10/RESET) PB7

PA2 (ADC2)

PA3 (AREF)

GND

AVCC

PA4 (ADC3)

(ADC4) PA5

(ADC5/AIN0) PA6

Note: Note: The bottom pad under the QFN/MLF package should be soldered to ground.

ATtiny26(L)

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ATtiny26(L)

Description The ATtiny26(L) 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 ATtiny26(L) achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

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 conventional CISC microcontrollers. The ATtiny26(L) has a high precision ADC with up to 11 single ended channels and 8 differential channels. Seven differential channels have an optional gain of 20x. Four out of the seven differential channels, which have the optional gain, can be used at the same time. The ATtiny26(L) also has a high frequency 8-bit PWM module with two independent outputs. Two of the PWM outputs have inverted non-overlapping output pins ideal for synchronous rectification. The Universal Serial Interface of the ATtiny26(L) allows efficient software implementation of TWI (Two-wire Serial Interface) or SM-bus interface. These features allow for highly integrated battery charger and lighting ballast applications, low-end thermostats, and firedetectors, among other applications.

The ATtiny26(L) provides 2K bytes of Flash, 128 bytes EEPROM, 128 bytes SRAM, up to 16 general purpose I/O lines, 32 general purpose working registers, two 8-bit Timer/Counters, one with PWM outputs, internal and external Oscillators, internal and external interrupts, programmable Watchdog Timer, 11-channel, 10-bit Analog to Digital Converter with two differential voltage input gain stages, and four software selectable power saving modes. The Idle mode stops the CPU while allowing the Timer/Counters and interrupt system to continue functioning. The ATtiny26(L) also has a dedicated ADC Noise Reduction mode for reducing the noise in ADC conversion. In this sleep mode, only the ADC is functioning. The Power-down mode saves the register contents but freezes the oscillators, disabling all other chip functions until the next interrupt or hardware reset. The Standby mode is the same as the Power-down mode, but external oscillators are enabled. The wakeup or interrupt on pin change features enable the ATtiny26(L) to be highly responsive to external events, still featuring the lowest power consumption while in the Power-down mode.

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The device is manufactured using Atmel’s high density non-volatile memory technology. By combining an enhanced RISC 8-bit CPU with Flash on a monolithic chip, the ATtiny26(L) is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.

The ATtiny26(L) AVR is supported with a full suite of program and system development tools including: Macro assemblers, program debugger/simulators, In-circuit emulators, and evaluation kits.

Block Diagram Figure 1. The ATtiny26(L) Block Diagram

VCC

GND

AVCC

PROGRAM COUNTER

PROGRAM

FLASH

INSTRUCTION

DECODER

CONTROL

LINES

PROGRAMMING

LOGIC

STACK

POINTER

SRAM

GENERAL PURPOSE

REGISTERS

X Y Z

ALU

STATUS

ISP INTERFACE

8-BIT DATA BUS

INTERNAL

OSCILLATOR

WATCHDOG

TIMER

MCU CONTROL

MCU STATUS

TIMER/

COUNTER0

TIMER/

COUNTER1

UNIVERSAL

SERIAL

INTERFACE

INTERRUPT

UNIT

EEPROM

INTERNAL CALIBRATED OSCILLATOR

TIMING AND

CONTROL

OSCILLATORS

DATA REGISTER

PORT A

ANALOG

COMPARATOR

DATA DIR.

REG.PORT A

PORT A DRIVERS

PA0-PA7

ADC

DATA REGISTER

PORT B

PORT B DRIVERS

PB0-PB7

DATA DIR.

REG.PORT B

ATtiny26(L)

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ATtiny26(L)

Pin Descriptions

VCC Digital supply voltage pin.

GND Digital ground pin.

AVCC AVCC is the supply voltage pin for Port A and the A/D Converter (ADC). It should be

externally connected to V connected to V ADC.

Port A (PA7..PA0) Port A is an 8-bit general purpose I/O port. PA7..PA0 are all I/O pins that can provide

internal pull-ups (selected for each bit). Port A has alternate functions as analog inputs for the ADC and analog comparator and pin change interrupt as described in “Alternate Port Functions” on page 46.

Port B (PB7..PB0) Port B is an 8-bit general purpose I/O port. PB6..0 are all I/O pins that can provide inter-

nal pull-ups (selected for each bit). PB7 is an I/O pin if not used as the reset. To use pin PB7 as an I/O pin, instead of RESET pin, program (“0”) RSTDISBL Fuse. Port B has alternate functions for the ADC, clocking, timer counters, USI, SPI programming, and pin change interrupt as described in “Alternate Port Functions” on page 46.

through a low-pass filter. See page 94 for details on operating of the

, even if the ADC is not used. If the ADC is used, it should be

An External Reset is generated by a low level on the PB7/RESET longer than 50 ns will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset.

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier.

About Code Examples

This datasheet 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 documentation for more details.

pin. Reset pulses

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AVR CPU Core

Architectural Overview The fast-access Register File concept contains 32 x 8-bit general purpose working reg-

isters with a single clock cycle access time. This means that during one single clock cycle, one ALU (Arithmetic Logic Unit) operation is executed. 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 16-bit pointers for indirect memory access. These pointers are called the X-, Y-, and Z-pointers, and they can address the Register File and the Flash program memory.

Figure 2. The ATtiny26(L) AVR Enhanced RISC Architecture

8-bit Data Bus

Control

Registers

Interrupt

Unit

1024 x 16

Program

FLASH

Program

Counter

Status

and Test

Instruction

Decoder

Control Lines

Direct Addressing

Indirect Addressing

32 x 8

General

Purpose

Registers

ALU

128 x 8

SRAM

128 byte

EEPROM

Universal

Serial Interface

ISP Unit

2 x 8-bit

Timer/Counter

Watchdog

Timer

ADC

Analog

Comparator

I/O Lines

The ALU supports arithmetic and logic functions between registers or between a constant and a register. Single register operations are also executed in the ALU. Figure 2 shows the ATtiny26(L) AVR Enhanced RISC microcontroller architecture. In addition to the register operation, the conventional memory addressing modes can be used on the Register File as well. This is enabled by the fact that the Register File is assigned the 32 lowermost Data Space addresses ($00 - $1F), allowing them to be accessed as though they were ordinary memory locations.

The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, Timer/Counters, A/D Converters, 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, $20 - $5F.

ATtiny26(L)

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ATtiny26(L)

The AVR uses a Harvard architecture concept with separate memories and buses for program and data memories. The program memory is accessed with a two stage pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions to be executed in every clock cycle. The program memory is In-System programmable Flash memory.

With the relative jump and relative call instructions, the whole address space is directly accessed. All AVR instructions have a single 16-bit word format, meaning that every program memory address contains a single 16-bit instruction.

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 8-bit Stack Pointer SP is read/write accessible in the I/O space. For programs written in C, the stack size must be declared in the linker file. Refer to the C user guide for more information.

The 128 bytes data SRAM can be easily 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.

The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, Timer/Counters, and other I/O functions. The memory spaces in the AVR architecture are all linear and regular memory maps.

General Purpose Register File

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 the different interrupts have a separate Interrupt Vector in the Interrupt Vector table at the beginning of the program memory. The different interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority.

Figure 3 shows the structure of the 32 general purpose working registers in the CPU.

Figure 3. AVR CPU General Purpose Working Registers

7 0 Addr.

R0 $00

R1 $01

R2 $02

…

R13 $0D

General R14 $0E

Purpose R15 $0F

Working R16 $10

Registers R17 $11

…

R26 $1A X-register Low Byte

R27 $1B X-register High Byte

R28 $1C Y-register Low Byte

R29 $1D Y-register High Byte

R30 $1E Z-register Low Byte

R31 $1F Z-register High Byte

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All of the register operating instructions in the instruction set have direct and single cycle access to all registers. The only exceptions are the five constant arithmetic and logic instructions SBCI, SUBI, CPI, ANDI, and ORI between a constant and a register, and the LDI instruction for load immediate constant data. These instructions apply to the second half of the registers in the Register File – R16..R31. The general SBC, SUB, CP, AND, and OR, and all other operations between two registers or on a single register apply to the entire Register File.

As shown in Figure 3, 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 implemented as SRAM locations, this memory organization provides flexibility in access of the registers, as the X-, Y-, and Z-registers can be set to index any register in the file.

X-register, Y-register, and Zregister

ALU – Arithmetic Logic Unit

The registers R26..R31 have some added functions to their general purpose usage. These registers are address pointers for indirect addressing of the Data Space. The three indirect address registers X, Y, and Z are defined as:

Figure 4. X-, Y-, and Z-register

15 0

X-register 7 0 7 0

R27 ($1B) R26 ($1A)

15 0

Y-register 7 0 7 0

R29 ($1D) R28 ($1C)

15 0

Z-register 7 0 7 0

R31 ($1F) R30 ($1E)

In the different addressing modes, these address registers have functions as fixed displacement, automatic increment and decrement (see the descriptions for the different instructions).

The high-performance AVR ALU operates in direct connection with all 32 general purpose working registers. Within a single clock cycle, ALU operations between registers in the Register File are executed. The ALU operations are divided into three main categories – Arithmetic, Logical, and Bit-functions.

ATtiny26(L)

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ATtiny26(L)

Status Register – SREG The AVR Status Register – SREG – at I/O space location $3F is defined as:

Bit 76543210

$3F ($5F) 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

• Bit 7 – I: Global Interrupt Enable

The Global Interrupt Enable bit must be set (one) for the interrupts to be enabled. The individual interrupt enable control is then performed in the Interrupt Mask Registers – GIMSK and TIMSK. If the Global Interrupt Enable Register is cleared (zero), none of the interrupts are enabled independent of the GIMSK and TIMSK values. 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.

• Bit 6 – T: Bit Copy Storage

The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source and destination 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.

• Bit 5 – H: Half Carry Flag

The Half Carry Flag H indicates a Half Carry in some arithmetic operations. See the Instruction Set Description for detailed information.

• 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.

• 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.

• Bit 2 – N: Negative Flag

The Negative Flag N indicates a negative result after the different arithmetic and logic operations. See the Instruction Set Description for detailed information.

• Bit 1 – Z: Zero Flag

The Zero Flag Z indicates a zero result after the different arithmetic and logic operations. See the Instruction Set Description for detailed information.

• 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.

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Stack Pointer – SP The ATtiny26(L) Stack Pointer is implemented as an 8-bit register in the I/O space loca-

tion $3D ($5D). As the ATtiny26(L) data memory has 224 ($E0) locations, eight bits are used.

Bit 76543210

$3D ($5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SP

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 Stack Pointer points to the data SRAM stack area where the Subroutine and Interrupt Stacks are located. This Stack space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to point above $60. The Stack Pointer is decremented by one when data is pushed onto the Stack with the PUSH instruction, and it is decremented by two when an address is pushed onto the Stack with subroutine calls and interrupts. The Stack Pointer is incremented by one when data is popped from the Stack with the POP instruction, and it is incremented by two when an address is popped from the Stack with return from subroutine RET or return from interrupt RETI.

Program and Data Addressing Modes

Register Direct, Single Register Rd

The ATtiny26(L) AVR Enhanced RISC microcontroller supports powerful and efficient addressing modes for access to the Flash program memory, SRAM, Register File, and I/O Data memory. This section describes the different addressing modes supported by the AVR architecture. In the figures, OP means the operation code part of the instruction word. To simplify, not all figures show the exact location of the addressing bits.

Figure 5. Direct Single Register Addressing

The operand is contained in register d (Rd).

ATtiny26(L)

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ATtiny26(L)

Figure 6. Direct Register Addressing, Two Registers

Rd and Rr

Operands are contained in register r (Rr) and d (Rd). The result is stored in register d (Rd).

I/O Direct Figure 7. I/O Direct Addressing

Operand address is contained in 6 bits of the instruction word. n is the destination or source register address.

Data Direct Figure 8. Direct Data Addressing

OP Rr/Rd

15 0

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20 19

16 LSBs

Data Space

$0000

$00DF

A 16-bit Data Address is contained in the 16 LSBs of a two-word instruction. Rd/Rr specify the destination or source register.

Data Indirect with

Figure 9. Data Indirect with Displacement

Displacement

Y OR Z - REGISTER

OP an

Operand address is the result of the Y- or Z-register contents added to the address contained in 6 bits of the instruction word.

Data Indirect Figure 10. Data Indirect Addressing

X-, Y-, OR Z-REGISTER

Data Space

$0000

05610

$00DF

Data Space

$0000

015

Data Indirect with Predecrement

ATtiny26(L)

$00DF

Operand address is the contents of the X-, Y-, or the Z-register.

Figure 11. Data Indirect Addressing with Pre-decrement

Data Space

$0000

015

X-, Y-, OR Z-REGISTER

-1

$00DF

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ATtiny26(L)

The X-, Y-, or Z-register is decremented before the operation. Operand address is the decremented contents of the X-, Y-, or Z-register.

Data Indirect with Postincrement

Constant Addressing Using the LPM Instruction

Figure 12. Data Indirect Addressing with Post-increment

Data Space

015

X-, Y-, OR Z-REGISTER

$0000

$00DF

The X-, Y-, or Z-register is incremented after the operation. Operand address is the content of the X-, Y-, or Z-register prior to incrementing.

Figure 13. Code Memory Constant Addressing

PROGRAM MEMORY

$000

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$3FF

Constant byte address is specified by the Z-register contents. The 15 MSBs select word address (0 - 1K), the LSB selects low byte if cleared (LSB = 0) or high byte if set (LSB = 1).

Indirect Program Addressing, IJMP and ICALL

Figure 14. Indirect Program Memory Addressing

PROGRAM MEMORY

$000

$3FF

Program execution continues at address contained by the Z-register (i.e., the PC is loaded with the contents of the Z-register).

Relative Program Addressing, RJMP and RCALL

Figure 15. Relative Program Memory Addressing

PROGRAM MEMORY

$000

$3FF

Program execution continues at address PC + k + 1. The relative address k is from

-2048 to 2047.

ATtiny26(L)

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ATtiny26(L)

Memories The AVR CPU is driven by the System Clock Ø, directly generated from the external

clock crystal for the chip. No internal clock division is used.

Figure 16 shows the parallel instruction fetches and instruction executions enabled by the Harvard 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 16. The Parallel Instruction Fetches and Instruction Executions

T1 T2 T3 T4

System Clock Ø

1st Instruction Fetch

1st Instruction Execute

2nd Instruction Fetch

2nd Instruction Execute

3rd Instruction Fetch

3rd Instruction Execute

4th Instruction Fetch

Figure 17 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 destination register.

Figure 17. Single Cycle ALU Operation

T1 T2 T3 T4

System Clock Ø

Total Execution Time

ALU Operation Execute

Result Write Back

The internal data SRAM access is performed in two System Clock cycles as described in Figure 18.

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Figure 18. On-chip Data SRAM Access Cycles

T1 T2 T3 T4

System Clock Ø

In-System Programmable Flash Program Memory

Address

Prev. Address

Address

Data

Write

Data

Read

The ATtiny26(L) contains 2K bytes On-chip In-System Programmable Flash memory for program storage. Since all instructions are 16- or 32-bit words, the Flash is organized as 1K x 16. The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny26(L) Program Counter – PC – is 10 bits wide, thus addressing the 1024 program memory addresses, see “Memory Programming” on page 107 for a detailed description on Flash data downloading. See “Program and Data Addressing Modes” on page 10 for the different program memory addressing modes.

Figure 19. SRAM Organization

R0 $0000

R1 $0001

R2 $0002

... ...

R29 $001D

R30 $001E

R31 $001F

I/O Registers

$00 $0020

$01 $0021

$02 $0022

… …

$3D $005D

$3E $005E

$3F $005F

Internal SRAM

$0060

$0061

$00DE

$00DF

SRAM Data Memory Figure 19 above shows how the ATtiny26(L) SRAM Memory is organized.

The lower 224 Data Memory locations address the Register File, the I/O Memory and the internal data SRAM. The first 96 locations address the Register File and I/O Memory, and the next 128 locations address the internal data SRAM.

...

ATtiny26(L)

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ATtiny26(L)

The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register File, registers R26 to R31 feature the indirect addressing pointer registers.

The direct addressing reaches the entire data space. The Indirect with Displacement mode features a 63 address locations reach from the base address given by the Y- or Zregister.

When using register indirect addressing modes with automatic pre-decrement and postincrement, the address registers X, Y, and Z are decremented and incremented.

The 32 general purpose working registers, 64 I/O Registers and the 128 bytes of internal data SRAM in the ATtiny26(L) are all accessible through all these addressing modes.

See “Program and Data Addressing Modes” on page 10 for a detailed description of the different addressing modes.

EEPROM Data Memory The ATtiny26(L) contains 128 bytes of data EEPROM memory. It is organized as a sep-

arate data space, in which single bytes can be read and written (see “Memory Programming” on page 107). The EEPROM has an endurance of at least 100,000 write/erase cycles per location.

EEPROM Read/Write Access The EEPROM Access Registers are accessible in the I/O space.

The write access time is typically 8.3 ms. A self-timing function lets the user software detect when the next byte can be written. A special EEPROM Ready Interrupt can be set to trigger when the EEPROM is ready to accept new data.

An ongoing EEPROM write operation will complete even if a reset condition occurs.

In order to prevent unintentional EEPROM writes, a two state write procedure must be followed. Refer to the description of the EEPROM Control Register for details on this.

When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed.

EEPROM Address Register – EEAR

Bit 76543210

$1E ($3E) – EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEAR

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial Value0XXXXXXX

• Bit 7 – RES: Reserved Bits

This bit are reserved bit in the ATtiny26(L) and will always read as zero.

• Bit 6..0 – EEAR6..0: EEPROM Address

The EEPROM Address Register – EEAR – specifies the EEPROM address in the 128 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and

127. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed.

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EEPROM Data Register – EEDR

Bit 76543210

$1D ($3D) MSB LSB EEDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

• Bit 7..0 – EEDR7..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.

EEPROM Control Register – EECR

Bit 76543210

$1C ($3C) ––––EERIEEEMWEEEWEEEREEECR

Read/WriteRRRRR/WR/WR/WR/W

Initial Value00000000

• Bit 7..4 – RES: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and will always read as zero.

• Bit 3 – EERIE: EEPROM Ready Interrupt Enable

When the I-bit in SREG and EERIE are set (one), the EEPROM Ready Interrupt is enabled. When cleared (zero), the interrupt is disabled. The EEPROM Ready Interrupt generates a constant interrupt when EEWE is cleared (zero).

• Bit 2 – EEMWE: EEPROM Master Write Enable

The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written. When EEMWE is set (one), setting EEWE will write data to the EEPROM at the selected address. If EEMWE is zero, setting EEWE will have no effect. When EEMWE has been set (one) by software, hardware clears the bit to zero after four clock cycles. See the description of the EEWE bit for an EEPROM write procedure.

• Bit 1 – EEWE: EEPROM Write Enable

The EEPROM Write Enable Signal – EEWE – is the write strobe to the EEPROM. When address and data are correctly set up, the EEWE bit must be set to write the value in to the EEPROM. The EEMWE bit must be set when the logical one is written to EEWE, otherwise no EEPROM write takes place. The following procedure should be followed when writing the EEPROM (the order of steps 2 and 3 is unessential):

1. Wait until EEWE becomes zero.

2. Write new EEPROM address to EEAR (optional).

3. Write new EEPROM data to EEDR (optional).

4. Write a logical one to the EEMWE bit in EECR.

5. Within four clock cycles after setting EEMWE, write a logical one to EEWE.

Caution: An interrupt between step 4 and step 5 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 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 access time (typically 8.3 ms) has elapsed, the EEWE bit is cleared (zero) by hardware. The user software can poll this bit and wait for a zero before writing the next byte. When EEWE has been set, the CPU is halted for two cycles before the next instruction is executed.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

• Bit 0 – EERE: EEPROM Read Enable

The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the correct address is set up in the EEAR Register, the EERE bit must be set. When the EERE bit is cleared (zero) by hardware, requested data is found in the EEDR Register. The EEPROM read access takes one instruction and there is no need to poll the EERE bit. When EERE has been set, the CPU is halted for four cycles before the next instruction is executed.

The user should poll the EEWE bit before starting the read operation. If a write operation is in progress when new data or address is written to the EEPROM I/O Registers, the write operation will be interrupted, and the result is undefined.

Table 1 . EEPROM Programming Time

EEPROM Write During Powerdown Sleep Mode

Preventing EEPROM Corruption

Number of Calibrated RC

Symbol

EEPROM Write (from CPU) 8448 8.5 ms

Note: 1. Uses 1 MHz clock, independent of CKSEL-Fuse settings.

Oscillator Cycles

(1)

Typical Programming

Time

When entering Power-down sleep mode while an EEPROM write operation is active, the EEPROM write operation will continue, and will complete before the write access time has passed. However, when the write operation is completed, the crystal Oscillator continues running, and as a consequence, the device does not enter Power-down entirely. It is therefore recommended to verify that the EEPROM write operation is completed before entering Power-down.

During periods of low V

the EEPROM data can be corrupted because the supply volt-

CC,

age is too low for the CPU and the EEPROM to operate properly. These issues are the same as for board level systems using the EEPROM, and the same design solutions should be applied.

An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the EEPROM 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.

EEPROM data 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 Brown-out Reset Protection circuit can be applied.

2. Keep the AVR core in Power-down Sleep mode during periods of low V

. This will prevent the CPU from attempting to decode and execute instructions, effectively protecting the EEPROM Registers from unintentional writes.

1477F–AVR–12/04

Store constants in Flash memory if the ability to change memory contents from software is not required. Flash memory can not be updated by the CPU, and will not be subject to corruption.

I/O Memory The I/O space definition of the ATtiny26(L) is shown in Table 2

Table 2 . ATtiny26(L) I/O Space

Address Hex Name Function

$3F ($5F) SREG Status Register

$3D ($5D) SP Stack Pointer

$3B ($5B) GIMSK General Interrupt Mask Register

$3A ($5A) GIFR General Interrupt Flag Register

$39 ($59) TIMSK Timer/Counter Interrupt Mask Register

$38 ($58) TIFR Timer/Counter Interrupt Flag Register

$35 ($55) MCUCR MCU Control Register

$34 ($54) MCUSR MCU Status Register

$33 ($53) TCCR0 Timer/Counter0 Control Register

$32 ($52) TCNT0 Timer/Counter0 (8-bit)

$31 ($51) OSCCAL Oscillator Calibration Register

$30 ($50) TCCR1A Timer/Counter1 Control Register A

$2F ($4F) TCCR1B Timer/Counter1 Control Register B

$2E ($4E) TCNT1 Timer/Counter1 (8-bit)

$2D ($4D) OCR1A Timer/Counter1 Output Compare Register A

$2C ($4C) OCR1B Timer/Counter1 Output Compare Register B

(1)

$2B ($4B) OCR1C Timer/Counter1 Output Compare Register C

$29 ($29) PLLCSR PLL Control and Status Register

$21 ($41) WDTCR Watchdog Timer Control Register

$1E ($3E) EEAR EEPROM Address Register

$1D ($3D) EEDR EEPROM Data Register

$1C ($3C) EECR EEPROM Control Register

$1B ($3B) PORTA Data Register, Port A

$1A ($3A) DDRA Data Direction Register, Port A

$19 ($39) PINA Input Pins, Port A

$18 ($38) PORTB Data Register, Port B

$17 ($37) DDRB Data Direction Register, Port B

$16 ($36) PINB Input Pins, Port B

$0F ($2F) USIDR Universal Serial Interface Data Register

$0E ($2E) USISR Universal Serial Interface Status Register

$0D ($2D) USICR Universal Serial Interface Control Register

$08 ($28) ACSR Analog Comparator Control and Status Register

$07 ($27) ADMUX ADC Multiplexer Select Register

ATtiny26(L)

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ATtiny26(L)

Table 2 . ATtiny26(L) I/O Space

Address Hex Name Function

$06($26) ADCSR ADC Control and Status Register

$05($25) ADCH ADC Data Register High

$04($24) ADCL ADC Data Register Low

Note: 1. Reserved and unused locations are not shown in the table.

(1)

(Continued)

All ATtiny26(L) I/O and peripheral registers are placed in the I/O space. The I/O locations are accessed by the IN and OUT instructions transferring data between the 32 general purpose working registers and the I/O space. I/O Registers within the address range $00 - $1F 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. Refer to the instruction set chapter for more details. For compatibility with future devices, reserved bits should be written zero if accessed. Reserved I/O memory addresses should never be written.

1477F–AVR–12/04

System Clock and Clock Options

Clock Systems and their Distribution

Figure 20 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 Management and Sleep Modes” on page 36. The clock systems are detailed below.

Figure 20. Clock Distribution

Timer/Counter1

General I/O

modules

clk

I/O

ADC CPU Core RAM

clk

ADC

AVR Clock

Control Unit

Clock

Multiplexer

Source clock

clk

CPU

clk

FLASH

Reset Logic

Watchdog Timer

Watchdog clock

Watchdog

Oscillator

Flash and EEPROM

CPU Clock – clk

I/O Clock – clk

I/O

Flash Clock – clk

ADC Clock – clk

CPU

FLASH

ADC

clk

PCK

PLL

External RC

Oscillator

External clock

Crystal

Oscillator

Low-Frequency

Crystal Oscillator

Calibrated RC

Oscillator

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.

The I/O clock is used by the majority of the I/O modules, like Timer/Counters, and USI. The I/O clock is also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted.

The Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.

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.

ATtiny26(L)

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ATtiny26(L)

Internal PLL for Fast Peripheral Clock Generation – clk

PCK

The internal PLL in ATtiny26(L) generates a clock frequency that is 64x multiplied from nominally 1 MHz input. The source of the 1 MHz PLL input clock is the output of the internal RC Oscillator which is automatically divided down to 1 MHz, if needed. See the Figure 21 on page 23. When the PLL reference frequency is the nominal 1 MHz, the fast peripheral clock is 64 MHz. The fast peripheral clock, or a clock prescaled from that, can be selected as the clock source for Timer/Counter1.

The PLL is locked on the RC Oscillator and adjusting the RC Oscillator via OSCCAL Register will adjust the fast peripheral clock at the same time. However, even if the possibly divided RC Oscillator is taken to a higher frequency than 1 MHz, the fast peripheral clock frequency saturates at 70 MHz (worst case) and remains oscillating at the maximum frequency. It should be noted that the PLL in this case is not locked any more with the RC Oscillator clock.

Therefore it is recommended not to take the OSCCAL adjustments to a higher frequency than 1 MHz in order to keep the PLL in the correct operating range. The internal PLL is enabled only when the PLLE bit in the register PLLCSR is set or the PLLCK Fuse is programmed (“0”). The bit PLOCK from the register PLLCSR is set when PLL is locked.

Both internal 1 MHz RC Oscillator and PLL are switched off in Power-down and Standby sleep modes.

Figure 21. PCK Clocking System

PLLE

RC OSCILLATOR

XTAL1 XTAL2

OSCCAL

1 2 4 8 MHz

OSCILLATORS

PLLCK &

CKSEL FUSES

DIVIDE

TO 1 MHz

PLL 64x

Lock

Detector

PLOCK

PCK

DIVIDE

BY 4

1477F–AVR–12/04

Clock Sources The device has the following clock source options, selectable by Flash Fuse bits as

shown below on Table 3. The clock from the selected source is input to the AVR clock generator, and routed to the appropriate modules.The use of pins PB5 (XTAL2), and PB4 (XTAL1) as I/O pins is limited depending on clock settings, as shown below in Table 4.

Table 3 . Device Clocking Options Select

Device Clocking Option PLLCK CKSEL3..0

External Crystal/Ceramic Resonator 1 1111 - 1010

External Low-frequency Crystal 1 1001

External RC Oscillator 1 1000 - 0101

Calibrated Internal RC Oscillator 1 0100 - 0001

External Clock 1 0000

PLL Clock 0 0001

Table 4 . PB5, and PB4 Functionality vs. Device Clocking Options

Device Clocking Option PLLCK CKSEL [3:0] PB4 PB5

External Clock 1 0000 XTAL1 I/O

Internal RC Oscillator 1 0001 I/O I/O

Internal RC Oscillator 1 0010 I/O I/O

Internal RC Oscillator 1 0011 I/O I/O

Internal RC Oscillator 1 0100 I/O I/O

External RC Oscillator 1 0101 XTAL1 I/O

External RC Oscillator 1 0110 XTAL1 I/O

External RC Oscillator 1 0111 XTAL1 I/O

External RC Oscillator 1 1000 XTAL1 I/O

External Low-frequency Oscillator 1 1001 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1010 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1011 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1100 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1101 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1110 XTAL1 XTAL2

External Crystal/Resonator Oscillator 1 1111 XTAL1 XTAL2

(1)

PLL 0 0001 I/O I/O

Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.

The various choices for each clocking option is given in the following sections. When the CPU wakes up from Power-down, the selected clock source is used to time the start-up, ensuring stable oscillator operation before instruction execution starts. When the CPU starts from Reset, there is as an additional delay allowing the power to reach a stable level before commencing normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up time. The number of WDT Oscillator cycles used for

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

each time-out is shown in Table 5. The frequency of the Watchdog Oscillator is voltage dependent as shown in the Electrical Characteristics section.

Table 5 . Number of Watchdog Oscillator Cycles

Typ Time-out (VCC = 5.0V) Typ Time-out (VCC = 3.0V) Number of Cycles

4.1 ms 4.3 ms 4K (4,096)

65 ms 69 ms 64K (65,536)

Default Clock Source The deviced is shipped with CKSEL = “0001”, SUT = “10”, and PLLCK unprogrammed.

The default clock source setting is therefore the internal RC Oscillator with longest startup time. This default setting ensures that all users can make their desired clock source setting using an In-System or Parallel Programmer.

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

be configured for use as an On-chip Oscillator, as shown in Figure 22. Either a quartz crystal or a ceramic resonator may be used. The maximum frequency for resonators is 12 MHz. The CKOPT Fuse should always be unprogrammed when using this clock option. C1 and C2 should always be equal. The optimal value of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for use with crystals are given in Table 6. For ceramic resonators, the capacitor values given by the manufacturer should be used.

Figure 22. Crystal Oscillator Connections

XTAL2

XTAL1

GND

The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 6.

Table 6 . Crystal Oscillator Operating Modes

Frequency

CKSEL3..1

(1)

101

110 0.9 - 3.0 12 - 22

111

Range (MHz)

0.4 - 0.9 –

3.0 - 16 12 - 22

16 - 12 - 15

Recommended Range for Capacitors C1 and

C2 for Use with Crystals (pF)

1477F–AVR–12/04

Note: 1. This option should not be used with crystals, only with ceramic resonators.

The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table 7.

Table 7 . Start-up Times for the Crystal Oscillator Clock Selection

Start-up Time

CKSEL0 SUT1..0

0 00 258 CK

0 01 258 CK

010 1K CK

011 1K CK

100 1K CK

1 01 16K CK – Crystal Oscillator,

1 10 16K CK 4.1 ms Crystal Oscillator, fast

1 11 16K CK 65 ms Crystal Oscillator,

Notes: 1. These options should only be used when not operating close to the maximum fre-

quency of the device, and only if frequency stability at start-up is not important for the application.

2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can also be used with crystals when not operating close to the maximum frequency of the device, and if frequency stability at start-up is not important for the application.

from Power-down

(1)

(2)

Additional Delay from

Reset (VCC = 5.0V)

4.1 ms Ceramic resonator,

65 ms Ceramic resonator,

– Ceramic resonator,

4.1 ms Ceramic resonator,

65 ms Ceramic resonator,

Recommended Usage

fast rising power

slowly rising power

BOD enabled

fast rising power

slowly rising power

BOD enabled

rising power

slowly rising power

Low-frequency Crystal Oscillator

ATtiny26(L)

To use a 32.768 kHz watch crystal as the clock source for the device, the Low-frequency Crystal Oscillator must be selected by setting the PLLCK to “1” and CKSEL Fuses to “1001”. The crystal should be connected as shown in Figure 22. By programming the CKOPT Fuse, the user can enable internal capacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors. The internal capacitors have a nominal value of 36 pF.

When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in Table 8.

Table 8 . Start-up Times for the Low-frequency Crystal Oscillator Clock Selection

Start-up Time

SUT1..0

00 1K CK

01 1K CK

10 32K CK 65 ms Stable frequency at start-up

11 Reserved

Note: 1. These options should only be used if frequency stability at start-up is not important

from Power-down

(1)

for the application.

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

4.1 ms Fast rising power or BOD enabled

65 ms Slowly rising power

1477F–AVR–12/04

ATtiny26(L)

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 23

can be used. The frequency is roughly estimated by the equation f = 1/(3RC). C should be at least 22 pF. By programming the CKOPT Fuse, the user can enable an internal 36 pF capacitor between XTAL1 and GND, thereby removing the need for an external capacitor.

Figure 23. External RC Configuration

PB5 (XTAL2)

XTAL1

GND

The oscillator can operate in four different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..0 as shown in Table 9.

Table 9 . External RC Oscillator Operating Modes

CKSEL3..0 Frequency Range (MHz)

0101 0.1 - 0.9

0110 0.9 - 3.0

0111 3.0 - 8.0

1000 8.0 - 12.0

When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in Table 10.

Table 10. Start-up Times for the External RC Oscillator Clock Selection

1477F–AVR–12/04

Start-up Time

SUT1..0

00 18 CK – BOD enabled

01 18 CK 4.1 ms Fast rising power

10 18 CK 65 ms Slowly rising power

11 6 CK

Notes: 1. This option should not be used when operating close to the maximum frequency of

from Power-down

(1)

the device.

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

4.1 ms Fast rising power or BOD enabled

Calibrated Internal RC Oscillator

The calibrated internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All frequencies are nominal values at 5V and 25°C. This clock may be selected as the system clock by programming the CKSEL Fuses as shown in Table 11. If selected, it will operate with no external components. The CKOPT Fuse should always be unprogrammed when using this clock option. During Reset, hardware loads the calibration byte into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. At 5V, 25°C and 1.0 MHz Oscillator frequency selected, this calibration gives a frequency within ± 3% of the nominal frequency. Using run-time calibration methods as described in application notes available at www.atmel.com/avr it is possible to achieve ± 1% accuracy at any given V

and Temperature. 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 calibration value, see the section “Calibration Byte” on page 109.

Table 11. Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0 Nominal Frequency (MHz)

(1)

0001

0010 2.0

0011 4.0

0100 8.0

Note: 1. The device is shipped with this option selected.

1.0

When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in Table 12. PB4 (XTAL1) and PB5 (XTAL2) can be used as general I/O ports.

Oscillator Calibration Register – OSCCAL

Table 12. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

Start-up Time from

SUT1..0

00 6 CK – BOD enabled

01 6 CK 4.1 ms Fast rising power

(1)

11 Reserved

Note: 1. The device is shipped with this option selected.

Bit 76543210

$31 ($51) 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

Power-down

6 CK 65 ms Slowly rising power

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

• Bits 7..0 – CAL7..0: Oscillator Calibration Value

Writing the calibration byte to this address will trim the internal oscillator to remove process variations from the oscillator frequency. During Reset, the 1 MHz calibration value which is located in the signature row high byte (address 0x00) is automatically loaded into the OSCCAL Register. If the internal RC is used at other frequencies, the calibration value must be loaded manually. This can be done by first reading the signature row by a programmer, and then store the calibration values in the Flash or EEPROM. Then the value can be read by software and loaded into the OSCCAl Register. When OSCCAL is zero, the lowest available frequency is chosen. Writing non-zero values to this register

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

will increase the frequency of the internal oscillator. Writing $FF to the register gives the highest available frequency. The calibrated Oscillator is used to time EEPROM and Flash access. If EEPROM or Flash is written, do not calibrate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash write may fail. Note that the oscillator is intended for calibration to 1.0, 2.0, 4.0, or 8.0 MHz. Tuning to other values is not guaranteed, as indicated in Table 13.

Table 13. Internal RC Oscillator Frequency Range.

Min Frequency in Percentage of

OSCCAL Value

$00 50% 100%

$7F 75% 150%

$FF 100% 200%

Nominal Frequency

Max Frequency in Percentage of

Nominal Frequency

External Clock To drive the device from an external clock source, XTAL1 should be driven as shown in

Figure 24. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000” and PLLCK to “1”. By programming the CKOPT Fuse, the user can enable an internal 36 pF capacitor between XTAL1 and GND.

Figure 24. External Clock Drive Configuration

PB5 (XTAL2)

EXTERNAL

CLOCK

SIGNAL

XTAL1

GND

1477F–AVR–12/04

When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 14.

Table 14. Start-up Times for the External Clock Selection

Start-up Time from

SUT1..0

00 6 CK – BOD enabled

01 6 CK 4.1 ms Fast rising power

10 6 CK 65 ms Slowly rising power

11 Reserved

Power-down

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

When applying an external clock, it is required to avoid sudden changes in the applied clock frequency 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 behaviour. It is required to ensure that the MCU is kept in reset during such changes in the clock frequency.

High Frequency PLL Clock – PLL

CLK

There is an internal PLL that provides nominally 64 MHz clock rate locked to the RC Oscillator for the use of the Peripheral Timer/Counter1 and for the system clock source. When selected as a system clock source, by programming (“0”) the fuse PLLCK, it is divided by four. When this option is used, the CKSEL3..0 must be set to “0001”. This clocking option can be used only when operating between 4.5 - 5.5V to guaratee safe operation. The system clock frequency will be 16 MHz (64 MHz/4). When using this clock option, start-up times are determined by the SUT Fuses as shown in Table 15. See also “PCK Clocking System” on page 23.

Table 15. Start-up Times for the PLLCK

Start-up Time from

SUT1..0

00 1K CK – BOD enabled

01 1K CK 4.1 ms Fast rising power

10 1K CK 65 ms Slowly rising power

11 16K CK – Slowly rising power

Power-down

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

System Control and Reset

The ATtiny26(L) provides four sources of reset:

Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset

•

threshold (V

POT

• External Reset. To use the PB7/RESET pin as an External Reset, instead of I/O pin,

unprogram (“1”) the RSTDISBL Fuse. The MCU is reset when a low level is present on the

pin for more than 50 ns.

RESET

• Watchdog Reset. The MCU is reset when the Watchdog timer period expires and the

Watchdog is enabled.

• Brown-out Reset. The MCU is reset when the supply voltage V

Reset threshold (V

BOT

is below the Brown-out

During reset, all I/O Registers are then set to their initial values, and the program starts execution from address $000. The instruction placed in address $000 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. Figure 25 shows the reset logic for the ATtiny26(L). Table 16 shows the timing and electrical parameters of the reset circuitry for ATtiny26(L).

Figure 25. Reset Logic for the ATtiny26(L)

DATA BU S

MCU Status

BORF

PORF

WDRF

EXTRF

BODEN

BODLEVEL

Brown-Out

Reset Circuit

Clock

Generator

CKSEL[3:0]

Delay Counters

TIMEOUT

1477F–AVR–12/04

Table 16. Reset Characteristics

Symbol Parameter Condition Min Typ Max Units

Power-on Reset Threshold Voltage (rising)

POT

RST

BOT

BOD

HYST

Power-on Reset Threshold Voltage (falling)

(1)

RESET Pin Threshold Voltage 0.2 0.9 V

Minimum pulse width on RESET Pin

Brown-out Reset Threshold

(2)

Voltage

Minimum low voltage period for Brown-out Detection

BODLEVEL = 1 2.4 2.7 2.9

BODLEVEL = 0 3.7 4.0 4.5

BODLEVEL = 1 2 µs

BODLEVEL = 0 2 µs

Brown-out Detector hysteresis 130 mV

Notes: 1. The Power-on Reset will not work unless the supply voltage has been below V

1.4 2.3 V

1.3 2.3 V

1.5 µs

POT

(falling)

2. V

may be below nominal minimum operating voltage for some devices. For

BOT

devices where this is the case, the device is tested down to VCC = V

during the

BOT

production test. This guarantees that a Brown-out Reset will occur before V

drops to a voltage where correct operation of the microcontroller is no longer guaranteed. The test is performed using BODLEVEL=1 for ATtiny26L and BODLEVEL=0 for ATtiny26. BODLEVEL=1 is not applicable for ATtiny26.

See start-up times from reset from “System Clock and Clock Options” on page 22. When the CPU wakes up from Power-down, only the clock counting part of the start-up time is used. The Watchdog Oscillator is used for timing the real-time part of the start-up time.

Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip Detection circuit. The detec-

ATtiny26(L)

tion level is defined in Table 16 The POR is activated whenever V detection level. The POR circuit can be used to trigger the Start-up Reset, as well as detect a failure in supply voltage.

The Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the Power-on Reset threshold voltage invokes a delay counter, which determines the delay, for which the device is kept in RESET after V

period of the delay counter can be defined by the user through the CKSEL Fuses. The different selections for the delay period are presented in “System Clock and Clock Options” on page 22. The RESET signal is activated again, without any delay, when the V

decreases below detection level.

is below the

rise. The time-out

1477F–AVR–12/04

Figure 26. MCU Start-up, RESET Tied to VCC

VCC

RESET

TIME-OUT

INTERNAL

RESET

POT

RST

TOUT

ATtiny26(L)

Figure 27. MCU Start-up, RESET

VCC

RESET

TIME-OUT

INTERNAL

RESET

POT

Controlled Externally

RST

TOUT

External Reset An External Reset is generated by a low level on the RESET pin. Reset pulses longer

than 500 ns 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 period t

TOUT

Figure 28. External Reset During Operation

VCC

– on its positive edge, the delay timer starts the MCU after the Time-out

RST

has expired.

1477F–AVR–12/04

RESET

TIME-OUT

INTERNAL

RESET

RST

TOUT

Brown-out Detection ATtiny26(L) has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

level during the operation. The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is enabled (BODEN programmed), and V the trigger level, the Brown-out Reset is immediately activated. When V above the trigger level, the Brown-out Reset is deactivated after a delay. The delay is defined by the user in the same way as the delay of POR signal, in Table 29. The trigger level for the BOD can be selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed), or 4.0V (BODLEVEL programmed). The trigger level has a hysteresis of 50 mV to ensure spike free Brown-out Detection.

decreases below

increases

The BOD circuit will only detect a drop in V for longer than t

given in Table 16.

BOD

if the voltage stays below the trigger level

Figure 29. Brown-out Reset During Operation

BOT-

BOT+

RESET

TIME-OUT

TOUT

INTERNAL

RESET

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one CK cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period t

. Refer to page 78 for details on operation of the Watchdog.

TOUT

Figure 30. Watchdog Time-out

1 CK Cycle

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

MCU Status Register – MCUSR

Bit 76543210

$34 ($54) ––––WDRFBORFEXTRFPORFMCUSR

Read/Write R R R R R/W R/W R/W R/W

Initial Value0000 See Bit Description

• Bit 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

• Bit 3 – WDRF: Watchdog Reset Flag

This bit is set (one) if a Watchdog Reset occurs. The bit is reset (zero) by a Power-on Reset, or by writing a logic zero to the flag.

• Bit 2 – BORF: Brown-out Reset Flag

This bit is set (one) if a Brown-out Reset occurs. The bit is reset (zero) by a Power-on Reset, or by writing a logic zero to the flag.

• Bit 1 – EXTRF: External Reset Flag

This bit is set (one) if an External Reset occurs. The bit is reset (zero) by a Power-on Reset, or by writing a logic zero to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set (one) if a Power-on Reset occurs. The bit is reset (zero) 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 (zero) 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.

1477F–AVR–12/04

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 consumption to the application’s requirements.

To enter any of the four sleep modes, the SE bit in MCUCR must be written to logic one and a SLEEP instruction must be executed. The SM1, and SM0 bits in the MCUCR Register select which sleep mode (Idle, ADC Noise Reduction, Power Down, or Standby) will be activated by the SLEEP instruction. See Table 17 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, it 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.

Table 19 on page 38 presents the different clock systems in the ATtiny26, and their distribution. The figure is helpful in selecting an appropriate sleep mode.

MCU Control Register – MCUCR

The MCU Control Register contains control bits for general MCU functions.

Bit 76543210

$35 ($55) – PUD SE SM1 SM0 – ISC01 ISC00 MCUCR

Read/Write R R/W R/W R/W R/W R R/W R/W

Initial Value00000000

• Bits 7 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

• Bit 6 – PUD: Pull-up Disable

When this bit is set (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 “Configuring the Pin” on page 42 for more details about this feature.

• Bit 5 – SE: Sleep Enable

The SE bit must be set (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 programmers purpose, it is recommended to set the Sleep Enable SE bit just before the execution of the SLEEP instruction.

• Bits 4,3 – SM1/SM0: Sleep Mode Select Bits 1 and 0

These bits select between the four available Sleep modes, as shown in the following table.

Table 17. Sleep Modes

SM1 SM0 Sleep Mode

0 0 Idle mode

0 1 ADC Noise Reduction mode

1 0 Power-down mode

1 1 Standby mode

For details, refer to the paragraph “Sleep Modes” below.

• Bit 2 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

• Bits 1, 0 – ISC01, ISC00: 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 corresponding interrupt mask is set (one). The activity on the external INT0 pin that activates the interrupt is defined in the following table.

Table 18. Interrupt 0 Sense Control

ISC01 ISC00 Description

0 0 The low level of INT0 generates an interrupt request.

0 1 Any 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.

Note: 1. When changing the ISC10/ISC00 bits, INT0 must be disabled by clearing its Interrupt

Enable bit in the GIMSK Register. Otherwise an interrupt can occur when the bits are changed.

(1)

Idle Mode When the SM1..0 bits are written to “00”, the SLEEP instruction makes the MCU enter

Idle mode, stopping the CPU but allowing Analog Comparator, ADC, USI, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode basically halts clk

Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the Timer Overflow and USI Start and Overflow 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.

CPU

and clk

, while allowing the other clocks to run.

FLASH

ADC Noise Reduction Mode

When the SM1..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 USI start condition detection, and the Watchdog to continue operating (if enabled). This sleep mode basically halts clk

I/O

, clk

, and clk

CPU

, while allowing the

FLASH

other clocks to run.

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 form the ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an EEPROM ready interrupt, an External Level Interrupt on INT0, or a pin change interrupt can wake up the MCU from ADC Noise Reduction mode.

Power-down Mode When the SM1..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 USI start condition detection, and the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an External Level Interrupt on INT0, or a pin change interrupt can wake up the MCU. This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.

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 24.

1477F–AVR–12/04

Note that if a level triggered external interrupt or pin change interrupt is used from Power-down mode, the changed level must be held for some time to wake up the MCU. This makes the MCU less sensitive to noise.

If the wake-up condition disappears before the MCU wakes up and starts to execute, e.g., a low level on INT0 is not held long enough, the interrupt causing the wake-up will not be executed.

Standby Mode When the SM1..0 bits are “11” and an External Crystal/Resonator clock option is

selected, the SLEEP instruction forces the MCU into the Standby mode. This mode is identical to Power-down with the exception that the Oscillator is kept running. From Standby mode, the device wakes up in only six clock cycles.

Table 19. Active Clock Domains and Wake-up Sources in the different Sleep Modes.

Active Clock domains Oscillators Wake-up Sources

Sleep Mode

clk

CPU

clk

FLASH

clkIOclk

ADC

Main Clock

Source Enabled

Idle X X X X X X X X

ADC Noise Reduction X X X

Power-down X

Standby

(1)

INT0, and Pin

Change

(2)

USI Start Condition

EEPROM

Ready

ADC Other I/O

XXX

Notes: 1. Only recommended with external crystal or resonator selected as clock source.

2. Only level interrupt INT0.

ATtiny26(L)

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ATtiny26(L)

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.

Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should

be disabled before entering any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to “Analog to Digital Converter” on page 94 for details on ADC operation.

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 the 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 91 for details on how to configure the Analog Comparator.

Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned

off. If the Brown-out Detector is enabled by the BODEN Fuse, 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 consumption. Refer to “Brown-out Detection” on page 34 for details on how to configure the Brown-out Detector.

Internal Voltage Reference The Internal Voltage Reference (see Table 20) will be enabled when needed by the

Brown-out Detector, 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.

Table 20. Internal Voltage Reference

Symbol Parameter Min Typ Max Units

Bandgap reference voltage 1.15 1.18 1.40 V

Bandgap reference start-up time 40 70 µs

Bandgap reference current consumption 10 µA

Watchdog Timer If the Watchdog Timer is not needed in the application, this 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 consumption. Refer to “Watchdog Timer” on page 78 for details on how to configure the Watchdog Timer.

Port Pins When entering a sleep mode, all port pins should be configured to use minimum power.

The most important thing is then to ensure that no pins drive resistive loads. In sleep modes where the both the I/O clock (clk

) and the ADC clock (clk

I/O

) are stopped, the

ADC

input buffers of the device will 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 “Digital Input Enable and Sleep Modes” on page 45 for details on which pins are enabled. If the input buffer is enabled

1477F–AVR–12/04

and the input signal is left floating or have an analog signal level close to VCC/2, the input buffer will use excessive power.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

I/O Ports

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 changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as input). Each output buffer, except reset, has symmetrical drive characteristics with both high sink and source capability. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both V

Figure 31. I/O Pin Equivalent Schematic

and Ground as indicated in Figure 31.

Pxn

All registers and bit references in this section are written in general form. A lower case “x” represents 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 Registers and bit locations are listed in “Register Description for I/O Ports” on page 56.

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. 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 42. 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 46. Refer to the individual module sections for a full description of the alternate functions.

See Figure

"General Digital I/O" for

Logic

Details

1477F–AVR–12/04

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.

Ports as General Digital I/O

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 32 shows a functional description of one I/O-port pin, here generically called Pxn.

Figure 32. General Digital I/O

Pxn

PUD: PULLUP DISABLE SLEEP: SLEEP CONTROL clk

: I/O CLOCK

I/O

(1)

SLEEP

DDxn

CLR

RESET

PORTxn

CLR

RESET

SYNCHRONIZER

DLQ

WDx: WRITE DDRx RDx: READ DDRx WPx: WRITE PORTx RRx: READ PORTx REGISTER RPx: READ PORTx PIN

PINxn

PUD

WDx

RDx

WPx

RRx

RPx

clk

DATA B US

I/O

Note: 1. 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.

Configuring the Pin Each port pin consists of 3 Register bits: DDxn, PORTxn, and PINxn. As shown in “Reg-

ister Description for I/O Ports” on page 56, 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 a reset condition becomes active, even if no clocks are running.

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).

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 acceptable, as a high-impedant environment will not notice the

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

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.

Table 21 summarizes the control signals for the pin value.

Table 21. Port Pin Configurations

PUD

DDxn PORTxn

0 0 X Input No Tri-state (Hi-Z)

0 1 0 Input Yes

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)

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 32, the PINxn Register bit and the preceding latch constitute 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 33 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and minimum propagation delays are denoted t respectively.

(in MCUCR) I/O Pull-up Comment

Pxn will source current if ext. pulled low

pd,max

and t

pd,min

Figure 33. Synchronization when Reading an Externally Applied Pin Value

SYSTEM CLK

INSTRUCTIONS

SYNC LATCH

PINxn

r17

XXX in r17, PINx

XXX

0x00 0xFF

pd, max

pd, 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 indicated by the two arrows t

pd,max

and t

pd,min

, a single

1477F–AVR–12/04

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 indicated in Figure 34. The out instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay t

through the synchronizer is one system

clock period.

Figure 34. Synchronization when Reading a Software Assigned Pin Value

SYSTEM CLK

r16

INSTRUCTIONS

SYNC LATCH

PINxn

r17

0xFF

out PORTx, r16 nop in r17, PINx

0x00 0xFF

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

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

...

; 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

...

C Code Example

(1)

Digital Input Enable and Sleep Modes

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*/

_NOP();

/* Read port pins */

i = 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.

As shown in Figure 32, 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, Standby mode, and ADC Noise Reduction mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to V

/2.

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 46.

1477F–AVR–12/04

If a logic high level (“one”) is present on an Asynchronous External Interrupt pin configured as “Interrupt on a 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 modes, as the clamping in these sleep modes produces the requested logic change.

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, floating 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 pullup. In this case, the pullup will be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pullup or pulldown. Connecting unused pins directly to V

or GND is not recommended, since this may cause

excessive currents if the pin is accidentally configured as an output.

Alternate Port Functions Most port pins have alternate functions in addition to being general digital I/Os. Figure

35 shows how the port pin control signals from the simplified Figure 32 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.

Figure 35. Alternate Port Functions

Pxn

(1)

PUOExn

PUOVxn

DDOExn

DDOVxn

PVOExn

PVOVxn

DIEOExn

DIEOVxn

SLEEP

SYNCHRONIZER

SET

DLQ

PINxn

CLR

PUD

DDxn

CLR

RESET

PORTxn

CLR

RESET

CLR

WDx

RDx

WPx

RRx

RPx

clk

DATA B U S

I/O

ATtiny26(L)

DIxn

AIOxn

PUOExn: Pxn PULL-UP OVERRIDE ENABLE PUOVxn: Pxn PULL-UP OVERRIDE VALUE DDOExn: Pxn DATA DIRECTION OVERRIDE ENABLE DDOVxn: Pxn DATA DIRECTION OVERRIDE VALUE PVOExn: Pxn PORT VALUE OVERRIDE ENABLE PVOVxn: Pxn PORT VALUE OVERRIDE VALUE DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE SLEEP: SLEEP CONTROL

PUD: PULLUP DISABLE WDx: WRITE DDRx RDx: READ DDRx RRx: READ PORTx REGISTER WPx: WRITE PORTx RPx: READ PORTx PIN

: I/O CLOCK

clk

I/O

DIxn: DIGITAL INPUT PIN n ON PORTx AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx

Note: 1. WPx, WDx, RLx, RPx, and RDx are common to all pins within the same port. clk

SLEEP, and PUD are common to all ports. All other signals are unique for each pin.

1477F–AVR–12/04

I/O

ATtiny26(L)

Table 22 summarizes the function of the overriding signals. The pin and port indexes from Figure 35 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.

Table 22. Generic Description of Overriding Signals for Alternate Functions

Signal Name Full Name Description

PUOE Pull-up Override

Enable

PUOV Pull-up Override

Valu e

DDOE Data Direction

Override Enable

DDOV Data Direction

Override Value

PVOE Port Value

Override Enable

PVOV Port Value

Override Value

DIEOE Digital Input Enable

Override Enable

DIEOV Digital Input Enable

Override Value

DI Digital Input This is the Digital Input to alternate functions. In the

AIO Analog Input/output This is the Analog Input/Output to/from alternate

If this signal is set, the pull-up enable is controlled by the PUOV signal. If this signal is cleared, the pull-up is enabled when {DDxn, PORTxn, PUD} = 0b010.

If PUOE is set, the pull-up is enabled/disabled when PUOV is set/cleared, regardless of the setting of the DDxn, PORTxn, and PUD Register bits.

If this signal is set, the Output Driver Enable is controlled by the DDOV signal. If this signal is cleared, the Output driver is enabled by the DDxn Register bit.

If DDOE is set, the Output Driver is enabled/disabled when DDOV is set/cleared, regardless of the setting of the DDxn Register bit.

If this signal is set and the Output Driver is enabled, the port value is controlled by the PVOV signal. If PVOE is cleared, and the Output Driver is enabled, the port Value is controlled by the PORTxn Register bit.

If PVOE is set, the port value is set to PVOV, regardless of the setting of the PORTxn Register bit.

If this bit is set, the Digital Input Enable is controlled by the DIEOV signal. If this signal is cleared, the Digital Input Enable is determined by MCU-state (Normal mode, sleep modes).

If DIEOE is set, the Digital Input is enabled/disabled when DIEOV is set/cleared, regardless of the MCU state (Normal mode, sleep modes).

figure, the signal is connected to the output of the schmitt trigger but before the synchronizer. Unless the Digital Input is used as a clock source, the module with the alternate function will use its own synchronizer.

functions. The signal is connected directly to the pad, and can be used bidirectionally.

1477F–AVR–12/04

The following subsections shortly describes the alternate functions for each port, and relates the overriding signals to the alternate function. Refer to the alternate function description for further details.

MCU Control Register – MCUCR

The MCU Control Register contains control bits for general MCU functions.

Bit 76543210

$35 ($55)

Read/Write R R/W R/W R/W R/W R R/W R/W

Initial Value00000000

–PUDSE SM1 SM0 – ISC01 ISC00 MCUCR

• Bit 6 – PUD: Pull-up Disable

Alternate Functions of Port A Port A has an alternate functions as analog inputs for the ADC and Analog Comparator

and pin change interrupt as shown in Table 23. If some Port A pins are configured as outputs, it is essential that these do not switch when a conversion is in progress. This might corrupt the result of the conversion. The ADC is described in “Analog to Digital Converter” on page 94. Analog Comparator is described in “Analog Comparator” on page 91. Pin change interrupt triggers on pins PA7, PA6 and PA3 if interrupt is enabled and it is not masked by the alternate functions even if the pin is configured as an output. See details from “Pin Change Interrupt” on page 62.

Table 23. Port A Pins Alternate Functions

Port Pin Alternate Function

PA7 ADC6 (ADC input channel 6)

AIN1 (Analog Comparator negative input) PCINT1 (Pin Change Interrupt 1)

PA6 ADC5 (ADC input channel 5)

AIN0 (Analog Comparator positive input) PCINT1 (Pin Change Interrupt 1)

PA5 ADC4 (ADC input channel 4)

PA4 ADC3 (ADC input channel 3)

ATtiny26(L)

PA3 AREF (ADC external reference)

PCINT1 (Pin Change Interrupt 1)

PA2 ADC2 (ADC input channel 2)

PA1 ADC1 (ADC input channel 1)

PA0 ADC0 (ADC input channel 0)

Table 24 and Table 25 relates the alternate functions of Port A to the overriding signals shown in Figure 35 on page 46. Thera are changes on PA7, PA6, and PA3 digital inputs. PA3 output and pullup driver are also overridden.

• ADC6/AIN1 Port – A, Bit 7

AIN1: Analog Comparator Negative input and ADC6: ADC input channel 6

. 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 or analog to digital converter.

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate function do not mask the interrupt. The masking alternate function is the Analog Comparator. Digital input is enabled on pin PA7 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate function.

• ADC5/AIN0 Port – A, Bit 6

1477F–AVR–12/04

ATtiny26(L)

AIN0: Analog Comparator Positive input and ADC5: ADC input channel 5. 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 or analog to digital converter.

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate function do not mask the interrupt. The masking alternate function is the Analog Comparator. Digital input is enabled on pin PA6 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate function.

• ADC4, ADC3 Port – A, Bit 5, 4

ADC4/ADC3: ADC Input Channel 4 and 3. Configure the port pins as inputs with the internal pull-ups switched off to avoid the digital port function from interfering with the function of the analog to digital converter.

• AREF/PCINT1 Port – A, Bit 3

AREF: External Reference for ADC. Pullup and output driver are disabled on PA3 when the pin is used as an external reference or Internal Voltage Reference (2.56V) with external capacitor at the AREF pin by setting (one) the bit REFS0 in the ADC Multiplexer Selection Register (ADMUX).

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate function do not mask the interrupt. The masking alternate function is the pin usage as an analog reference for the ADC. Digital input is enabled on pin PA3 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate function.

Table 24. Overriding Signals for Alternate Functions in PA7..PA4

Signal Name

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

DIEOE PCINT1_ENABLE

DIEOV 1 1 0 0

DI PCINT1 PCINT1 – –

AIO ADC6 INPUT, AIN1 ADC5 INPUT, AIN0 ADC4 INPUT ADC3 INPUT

PA7/ADC6/ AIN1/PCINT1

ACSR[ACD]

PA6/ADC5/ AIN0/PCINT1 PA5/ADC4 PA4/ADC3

(1)

•

PCINT1_ENABLE ACSR[ACD]

(1)

•

1477F–AVR–12/04

Table 25. Overriding Signals for Alternate Functions in PA3..PA0

Signal Name PA3/AREF/PCINT1 PA2/ADC2 PA1/ADC1 PA0/ADC0

PUOE ADMUX[REFS0] 0 0 0

PUOV0 000

DDOE ADMUX[REFS0] 0 0 0

DDOV 0 0 0 0

PVOE0 000

PVOV0 000

DIEOE PCINT1_ENABLE

(2)

ADMUX[REFS0]

•

000

(1)

DIEOV1 000

DIPCINT1 –––

AIO ANALOG REFERENCE INPUT ADC2 INPUT ADC1 INPUT ADC0 INPUT

Notes: 1. Note that the PCINT1 Interrupt is only enabled if both the Global Interrupt Flag is

enabled, the PCIE1 flag in GIMSK is set and the alternate function of the pin is disabled as described in “Pin Change Interrupt” on page 62

2. Not operator is marked with “~”.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

Alternate Functions Of Port B Port B has an alternate functions for the ADC, Clocking, Timer/Counters, USI, SPI pro-

gramming and pin change interrupt. The ADC is described in “Analog to Digital Converter” on page 94, Clocking in “AVR CPU Core” on page 6, timers in “Timer/Counters” on page 64 and USI in “Universal Serial Interface – USI” on page 80. Pin change interrupt triggers on pins PB7 - PB0 if interrupt is enabled and it is not masked by the alternate functions even if the pin is configured as an output. See details from “Pin Change Interrupt” on page 62. Pin functions in programming modes are described in “Memory Programming” on page 107. The alternate functions are shown in Table 26.

Table 26. Port B Pins Alternate Functions

Port Pin Alternate Functions

PB7 ADC10 (ADC Input Channel 10)

(External Reset Input)

RESET PCINT1 (Pin Change Interrupt 1)

PB6 ADC9 (ADC Input Channel 9)

INT0 (External Interrupt 0 Input) T0 (Timer/Counter 0 External Counter Clock Input) PCINT1 (Pin Change Interrupt 1)

PB5 ADC8 (ADC Input Channel 8)

XTAL2 (Crystal Oscillator Output) PCINT1 (Pin Change Interrupt 1)

PB4 ADC7 (ADC Input Channel 7)

XTAL1 (Crystal Oscillator Input) PCINT1 (Pin Change Interrupt 1)

PB3 OC1B (Timer/Counter1 PWM Output B, Timer/Counter1Output Compare B Match

Output) PCINT0 (Pin Change Interrupt 0)

PB2 SCK (USI Clock Input/Output)

SCL (USI External Open-collector Serial Clock)

(Inverted Timer/Counter1 PWM Output B)

OC1B PCINT0 (Pin Change Interrupt 0)

1477F–AVR–12/04

PB1 DO (USI Data Output)

OC1A (Timer/Counter1 PWM Output A, Timer/Counter1 Output Compare A Match Output) PCINT0 (Pin Change Interrupt 0)

PB0 DI (USI Data Input)

SDA (USI Serial Data)

(Inverted Timer/Counter1 PWM Output A)

OC1A PCINT0 (Pin Change Interrupt 0)

The alternate pin configuration is as follows:

• ADC10/RESET

/PCINT1 – Port B, Bit 7

ADC10: ADC Input Channel 10. Configure the port pins as inputs with the internal pullups switched off to avoid the digital port function from interfering with the function of the analog to digital converter.

RESET

: External Reset input is active low and enabled by unprogramming (“1”) the RSTDISBL Fuse. Pullup is activated and output driver and digital input are deactivated when the pin is used as the RESET

pin.

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate function do not mask the interrupt. The masking alternate function is the pin usage as RESET. Digital input is enabled on pin PB7 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate function.

• ADC9/INT0/T0/PCINT1 – Port B, Bit 6

ADC9: ADC Input Channel 9. Configure the port pins as inputs with the internal pull-ups switched off to avoid the digital port function from interfering with the function of the analog to digital converter.

INT0: External Interrupt source 0: The PB6 pin can serve as an external interrupt source enabled by setting (one) the bit INT0 in the General Input Mask Register (GIMSK).

T0: Timer/Counter0 External Counter Clock input is enabled by setting (one) the bits CS02 and CS01 in the Timer/Counter0 Control Register (TCCR0).

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate functions are the external low level Interrupt source 0 (INT0) and the Timer/Counter0 External Counter clock input (T0). Digital input is enabled on pin PB6 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

• ADC8/XTAL2/PCINT1 – Port B, Bit 5

ADC8: ADC Input Channel 8. Configure the port pins as inputs with the internal pull-ups switched off to avoid the digital port function from interfering with the function of the analog to digital converter.

XTAL2: Chip Clock Oscillator pin 2. Used as clock pin for all chip clock sources except internal calibrateble RC Oscillator, external clock and PLL clock. When used as a clock pin, the pin can not be used as an I/O pin. When using internal calibratable RC Oscillator, External clock or PLL clock as Chip clock sources, PB5 serves as an ordinary I/O pin.

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate functions are the XTAL2 outputs. Digital input is enabled on pin PB5 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

• ADC7/XTAL1/PCINT1 – Port B, Bit 4

ADC7: ADC Input Channel 7. Configure the port pins as inputs with the internal pull-ups switched off to avoid the digital port function from interfering with the function of the analog to digital converter.

XTAL1: Chip Clock Oscillator pin 1. Used for all chip clock sources except internal calibrateble RC oscillator and PLL clock. When used as a clock pin, the pin can not be used as an I/O pin. When using internal calibratable RC Oscillator or PLL clock as chip clock sources, PB4 serves as an ordinary I/O pin.

PCINT1: Pin Change Interrupt 1 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate functions are the XTAL1 inputs. Digital input is enabled on pin PB4 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

• OC1B/PCINT0 – Port B, Bit 3

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

OC1B: Output Compare match output: The PB3 pin can serve as an output for the Timer/Counter1 compare match B. The PB3 pin has to be configured as an output (DDB3 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM mode.

PCINT0: Pin Change Interrupt 0 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate function is the output compare match output OC1B. Digital input is enabled on pin PB3 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

• SCK/SCL/OC1B

SCK: Clock input or output in USI Three-wire mode. When the SPI is enabled this pin is configured as an input. In the USI Three-wire mode the bit DDRB2 controls the direction of the pin, output for the Master mode and input for the Slave mode.

SCL: USI External Open-collector Serial Clock for USI Two-wire mode. The SCL pin is pulled low when PORTB2 is cleared (zero) or USI start condition is detected and DDRB2 is set (one). Pull-up is disabled in USI Two-wire mode.

OC1B

: Inverted Timer/Counter1 PWM Output B: The PB2 pin can serve as an inverted output for the Timer/Counter1 PWM mode if USI is not enabled. The PB2 pin has to be configured as an output (DDB2 set (one)) to serve this function.

/PCINT0 – Port B, Bit 2

PCINT1: Pin Change Interrupt 0 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate function are the inverted output compare match output OC1B in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

• DO/OC1A/PCINT0 – Port B, Bit 1

DO: Data Output in USI Three-wire mode. Data output (DO) overrides PORTB1 value and it is driven to the port when the data direction bit DDB1 is set (one). However the PORTB1 bit still controls the pullup, enabling pullup if direction is input and PORTB1 is set(one).

OC1A: Output Compare match output: The PB1 pin can serve as an 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 OC1B pin is also the output pin for the PWM mode timer function if not used in programming or USI.

PCINT0: Pin Change Interrupt 0 pin. Pin change interrupt is enabled on pin when global interrupt is enabled, pin change interrupt is enabled and the alternate functions do not mask the interrupt. The masking alternate functions are the output compare match output OC1A and Data Output (DO) in USI Three-wire mode. Digital input is enabled on pin PB1 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions.

and USI clocks SCK/SCL. Digital input is enabled on pin PB2 also

1477F–AVR–12/04

• DI/SDA/OC1A/PCINT0 – Port B, Bit 0

DI: Data Input in USI Three-wire mode. USI Three-wire mode does not override normal port functions., so pin must be configure as an input.

SDA: Serial Data in USI Two-wire mode. Serial data pin is bi-directional and uses opencollector output. The SDA pin is enabled by setting the pin as an output. The pin is pulled low when the PORTB0 or USI shiftRegister is zero when DDB0 is set (one). Pullup is disabled in USI Two-wire mode.

OC1A

: Inverted Timer/Counter1 PWM output A: The PB0 pin can serve as an Inverted output for the PWM mode if not used in programming or USI. The PB0 pin has to be configured as an output (DDB0 set (one)) to serve this function.

and USI data DI or SDA. Digital input is enabled on pin PB0 also in SLEEP modes, if the pin change interrupt is enabled and not masked by the alternate functions. Table 27 and Table 28 relate the alternate functions of Port B to the overriding signals shown in “Alternate Port Functions” on page 46.

Table 27. Overriding Signals for Alternate Functions in PB7..PB4

Signal Name

PUOE RSTDSBL

PB7/ADC10/RESET/ PCINT1

(1)

PB6/ADC9/INT0/TO/ PCINT1

PB5/ADC8/XTAL2/ PCINT1 PB4/ADC7/XTAL1

(5)

PB5IOENABLE

(3)

~PB4IOENABLE

(3)

PUOV 1 0 0 0

DDOE RSTDSBL

(1)

0 ~PB5IOENABLE

(3)

~PB4IOENABLE

(3)

DDOV 0 0 0 0

PVOE 0 0 0 0

PVOV 0 0 0 0

DIEOE PCINT1_ENABLE

DIEOV PCINT1_ENABLE

(5)

RSTDSBL

(1)

(2)

| RSTDSBL

(2)

•

(1)

~T0_EXT_CLOCK PCINT1_ENABLE INT0_ENABLE

1 PCINT1_ENABLE

(6)

•

(2)

(4)

PCINT1_ENABLE

~PB5IOENABLE

PB5IOENABLE

(2)

(3)

PCINT_ ENABLE ~PB4IOENABLE

(2)

(3)

EXT_CLOCK_ENABLE

(2)

•

(3)

PCINT1_ENABLE PB4IOENABLE

(2)

(3)

EXT_CLOCK_ENABLE

DI PCINT1 INT0, T0, PCINT1 PCINT1 External Clock, PCINT1

AIO ADC10, RESET INPUT ADC9 ADC8, XTAL2 XTAL1

Notes: 1. RSTDISBL Fuse (active low) is described in section “System Control and Reset” on page 31.

2. Note that the PCINT1 Interrupt is only enabled if both the Global Interrupt Flag is enabled, the PCIE1 flag in GIMSK is set and the alternate function of the pin is disabled as described in “Pin Change Interrupt” on page 62.

3. PB5IOENABLE and PB4IOENABLE are given by the PLLCK and CKSEL Fuses as described in “Clock Sources” on page

24.

4. External low level interrupt is enabled if both the Global Interrupt Flag is enabled and the INT0 flag in GIMSK is set as described in “External Interrupt” on page 62.

5. Not operator is marked with “~”.

6. The operation of the Timer/Counter0 with external clock disabled is described in “8-bit Timer/Counter0” on page 65.

7. External clock is selected by the PLLCK and CKSEL Fuses as described in “Clock Sources” on page 24.

(7)

•

ATtiny26(L)

1477F–AVR–12/04

Table 28. Overriding Signals for Alternate Functions in PB3..PB0

ATtiny26(L)

PB2/SCK/SCL/OC1B

Signal Name PB3/OC1B/PCINT0

NT0 PB1/DO/OC1A/PCINT0 PB0/DI/SDA/OC1A

PUOE 0 USI_TWO-WIRE

/PCI

(3)

0 USI_TWO-WIRE

(3)

PUOV0000

DDOE 0 USI_TWO-WIRE

DDOV 0 (USI_SCL_HOLD

PVOE OC1B_ENABLE

(1)

(8)

PORTB2) • DDB2

USI_TWO-WIRE

(3)

(4)

(3)

•

DDB2 | OC1B_ENABLE

PVOV OC1B ~(USI_TWO-WIRE •

DDB2) • OC1B

0USI_TWO-WIRE

0 (~SDA | ~PORTB0) •

DDB0

USI_THREE-WIRE

(1)

OC1A_ENABLE

USI_THREE-WIRE

(6)

| ~USI_THREE-

DO WIRE • OC1A_ENABLE

(3)

(1)

(3)

•

USI_TWO-WIRE |

_ENABLE

OC1A

~(USI_TWO-WIRE• DDB0) •

(1)

OC1A_ENABLE

(3)

• DDB0

(1)

• OC1A

DIEOE PCINT0_ENABLE

~OC1B_ENABLE

(2)

•

(1)

~(USI_TWO-WIRE | USI_THREE-WIRE |

_ENABLE) •

OC1B PCINT0_ENABLE

(2)

USI_START_I.ENABLE

~(USI_THREE-WIRE | OC1A_ENABLE) • PCINT0_ENABLE

(5)

~(USI_TWO-WIRE USI_THREE-WIRE

(2)

OC1A

_ENABLE PCINT0_ENABLE USI_START_I.ENABLE

(3)

(1)

) •

(2)

(5)

DIEOV1111

DI PCINT0 PCINT0, SCL, SCK PCINT0 PCINT0, SDA

AIO––––

Notes: 1. Enabling of the Timer/Counter1 Compare match outputs and Timer/Counter1 PWM Outputs OC1A/OC1B and OC1A/OC1B

are described in the section “8-bit Timer/Counter1” on page 67.

2. Note that the PCINT0 Interrupt is only enabled if both the Global Interrupt Flag is enabled, the PCIE0 flag in GIMSK is set and the alternate function of the pin is disabled as described in “Pin Change Interrupt” on page 62.

3. The Two-wire and Three-wire USI-modes are described in “Universal Serial Interface – USI” on page 80.

4. Shift clock (SCL) hold for USI is in described “Universal Serial Interface – USI” on page 80.

5. USI start up interrupt is enabled if both the Global Interrupt Flag is enabled and the USISIE flag in the USICR Register is set as described in “Universal Serial Interface – USI” on page 80.

6. Data Output (DO) is valid in USI Three-wire mode and the operation is described in “Universal Serial Interface – USI” on page 80.

7. Operation of the data pin SDA in USI Two-wire mode and DI in USI Three-wire mode in “Universal Serial Interface – USI” on page 80.

8. Not operator is marked with “~”.

1477F–AVR–12/04

Register Description for I/O Ports

Port A Data Register – PORTA

Port A Data Direction Register – DDRA

Port A Input Pins Address – PINA

Port B Data Register – PORTB

Port B Data Direction Register – DDRB

Bit 76543210

$1B ($3B)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

$1A ($3A) DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

$19 ($39) PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

Bit 76543210

$18 ($38) 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 Value00000000

Bit 76543210

$17 ($37) 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 Value00000000

PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA

Port B Input Pins Address – PINB

ATtiny26(L)

Bit 76543210

$16 ($36) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

1477F–AVR–12/04

ATtiny26(L)

Interrupts

Interrupt Vectors The ATtiny26(L) provides eleven interrupt sources. These interrupts and the separate

Reset Vector, each have a separate program vector in the program memory space. All the interrupts are assigned individual enable bits which must be set (one) together with the I-bit in the Status Register in order to enable the interrupt.

The lowest addresses in the program memory space are automatically defined as the Reset and Interrupt vectors. The complete list of vectors is shown in Table 29. 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 etc.

Table 29. Reset and Interrupt Vectors

Vector No Program Address Source Interrupt Definition

1 $000 RESET Hardware Pin and Watchdog Reset

2 $001 INT0 External Interrupt Request 0

3 $002 I/O Pins Pin Change Interrupt

4 $003 TIMER1, CMPA Timer/Counter1 Compare Match 1A

5 $004 TIMER1, CMPB Timer/Counter1 Compare Match 1B

6 $005 TIMER1, OVF1 Timer/Counter1 Overflow

7 $006 TIMER0, OVF0 Timer/Counter0 Overflow

8 $007 USI_STRT USI Start

9 $008 USI_OVF USI Overflow

A $009 EE_RDY EEPROM Ready

B $00A ANA_COMP Analog Comparator

C $00B ADC ADC Conversion Complete

The most typical and general program setup for the Reset and Interrupt Vector Addresses are:

Address Labels Code Comments

$000 rjmp RESET ; Reset handler

$001 rjmp EXT_INT0 ; IRQ0 handler

$002 rjmp PIN_CHANGE ; Pin change handler

$003 rjmp TIM1_CMP1A ; Timer1 compare match 1A

$004 rjmp TIM1_CMP1B ; Timer1 compare match 1B

$005 rjmp TIM1_OVF ; Timer1 overflow handler

$006 rjmp TIM0_OVF ; Timer0 overflow handler

$007 rjmp USI_STRT ; USI Start handler

$008 rjmp USI_OVF ; USI Overflow handler

$009 rjmp EE_RDY ; EEPROM Ready handler

$00A rjmp ANA_COMP ; Analog Comparator handler

$00B rjmp ADC ; ADC Conversion Handler

;

$009 RESET: ldi r16, RAMEND ; Main program start

$00A out SP, r16

1477F–AVR–12/04

$00B sei

… … … …

Interrupt Handling The ATtiny26(L) has two 8-bit Interrupt Mask Control Registers; GIMSK – General Inter-

rupt Mask Register and TIMSK – Timer/Counter Interrupt Mask Register.

When an interrupt occurs, the Global Interrupt Enable I-bit is cleared (zero) and all interrupts are disabled. The user software can set (one) the I-bit to enable nested interrupts. The I-bit is set (one) when a Return from Interrupt instruction – RETI – is executed.

When the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt handling routine, hardware clears the corresponding flag that generated the interrupt. Some of the 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 when the corresponding interrupt enable bit is cleared (zero), the interrupt flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software.

If one or more interrupt conditions occur when the Global Interrupt Enable bit is cleared (zero), the corresponding interrupt flag(s) will be set and remembered until the Global Interrupt Enable bit is set (one), and will be executed by order of priority.

Note that external level interrupt does not have a flag, and will only be remembered for as long as the interrupt condition is active.

Note that the Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt routine. This must be handled by software.

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles

minimum. After the four clock cycles the program vector address for the actual interrupt handling routine is executed. During this four clock cycle period, the Program Counter (10 bits) is pushed onto the Stack. The vector is a relative jump to the interrupt routine, and this jump takes two clock cycles. If an interrupt occurs during execution of a multicycle instruction, this instruction is completed before the interrupt is served.

A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the Program Counter (10 bits) is popped back from the Stack. When 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 – SREG – is not handled by the AVR hardware, neither for interrupts nor for subroutines. For the routines requiring a storage of the SREG, this must be performed by user software.

General Interrupt Mask Register – GIMSK

Bit 76543210

$3B ($5B) – INT0 PCIE1 PCIE0 – – – – GIMSK

Read/Write R R/W R/W R/W R R R R

Initial Value00000000

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

• Bit 6 – 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 external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU general Control Register (MCUCR) define whether the external

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

interrupt is activated on rising or falling edge, on pin change, or low level of the INT0 pin. 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 program memory address $001. See also “External Interrupt” on page 62.

• Bit 5 – PCIE1: Pin Change Interrupt Enable1

When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the interrupt pin change is enabled on analog pins PB[7:4], PA[7:6] and PA[3]. Unless the alternate function masks out the interrupt, any change on the pin mentioned before will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from program memory address $002. See also “Pin Change Interrupt” on page 62.

• Bit 4– PCIE0: Pin Change Interrupt Enable0

When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the interrupt pin change is enabled on digital pins PB[3:0]. Unless the alternate function masks out the interrupt, any change on the pin mentioned before will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from program memory address $002. See also “Pin Change Interrupt” on page 62.

• Bits 3..0 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

General Interrupt Flag Register – GIFR

Bit 76543210

$3A ($5A) – INTF0 PCIF – – – – – GIFR

Read/Write R R/W R/W R R R R R

Initial Value00000000

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

• Bit 6 – INTF0: External Interrupt Flag0

When an event on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If the I-bit in SREG and the INT0 bit in GIMSK are set (one), the MCU will jump to the Interrupt Vector at address $001. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. The flag is always cleared when INT0 is configured as level interrupt.

• Bit 5 – PCIF: Pin Change Interrupt Flag

When an event on pins PB[7:0], PA[7:6], or PA[3] triggers an interrupt request, PCIF becomes set (one). PCIE1 enables interrupt from analog pins PB[7:4], PA[7:6], and PA[3]. PCIE0 enables interrupt on digital pins PB[3:0]. Note that pin change interrupt enable bits PCIE1 and PCIE0 also mask the flag if they are not set. For example, if PCIE0 is cleared, a pin change on PB[3:0] does not set PCIF. If an alternate function is enabled on a pin, PCIF is masked from that individual pin. If the I-bit in SREG and the PCIE bit in GIMSK are set (one), the MCU will jump to the Interrupt Vector at address $002. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. See also “Pin Change Interrupt” on page 62.

• Bits 4..0 – Res: Reserved Bits

Timer/Counter Interrupt Mask Register – TIMSK

1477F–AVR–12/04

These bits are reserved bits in the ATtiny26(L) and always read as zero.

Bit 7 6 5 4 3 2 1 0

$39 ($59) – OCIE1A OCIE1B – – TOIE1 TOIE0 – TIMSK

Read/Write R R/W R/W R R R/W R/W R

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

• Bit 6 – OCIE1A: Timer/Counter1 Output Compare Interrupt Enable

When the OCIE1A bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 compare match A, interrupt is enabled. The corresponding interrupt at vector $003 is executed if a compare match A occurs. The Compare Flag in Timer/Counter1 is set (one) in the Timer/Counter Interrupt Flag Register.

• Bit 5 – OCIE1B: Timer/Counter1 Output Compare Interrupt Enable

When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 compare match B, interrupt is enabled. The corresponding interrupt at vector $004 is executed if a compare match B occurs. The Compare Flag in Timer/Counter1 is set (one) in the Timer/Counter Interrupt Flag Register.

• Bit 4..3 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

• Bit 2 – TOIE1: Timer/Counter1 Overflow Interrupt Enable

When the TOIE1 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Overflow interrupt is enabled. The corresponding interrupt (at vector $005) is executed if an overflow in Timer/Counter1 occurs. The Overflow Flag (Timer1) is set (one) in the Timer/Counter Interrupt Flag Register – TIFR.

• Bit 1 – TOIE0: Timer/Counter0 Overflow Interrupt Enable

Timer/Counter Interrupt Flag Register – TIFR

When the TOIE0 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt (at vector $006) is executed if an overflow in Timer/Counter0 occurs. The Overflow Flag (Timer0) is set (one) in the Timer/Counter Interrupt Flag Register – TIFR.

• Bit 0 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

Bit 7 6 5 4 3 2 1 0

$38 ($58) – OCF1A OCF1B – – TOV1 TOV0 – TIFR

Read/Write R R/W R/W R R R/W R/W R

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

• Bit 6 – OCF1A: Output Compare Flag 1A

The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data value in OCR1A – Output Compare Register 1A. OCF1A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1A, and OCF1A are set (one), the Timer/Counter1 A Compare Match interrupt is executed.

• Bit 5 – OCF1B: Output Compare Flag 1B

The OCF1B bit is set (one) when compare match occurs between Timer/Counter1 and the data value in OCR1B – Output Compare Register 1A. OCF1B is cleared by hard-

ATtiny26(L)

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ATtiny26(L)

ware when executing the corresponding interrupt handling vector. Alternatively, OCF1B is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1B, and OCF1B are set (one), the Timer/Counter1 B Compare Match interrupt is executed.

• Bits 4..3 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

• Bit 2 – TOV1: Timer/Counter1 Overflow Flag

The bit TOV1 is set (one) when an overflow occurs in Timer/Counter1. TOV1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV1 is cleared, after synchronization clock cycle, by writing a logical one to the flag. When the SREG I-bit, and TOIE1 (Timer/Counter1 Overflow Interrupt Enable), and TOV1 are set (one), the Timer/Counter1 Overflow interrupt is executed.

• Bit 1 – TOV0: Timer/Counter0 Overflow Flag

The bit TOV0 is set (one) 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 logical one to the flag. When the SREG I-bit, and TOIE0 (Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is executed.

• Bit 0 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny26(L) and always reads as zero.

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External Interrupt The External Interrupt is triggered by the INT0 pin. Observe that, if enabled, the interrupt

will trigger even if the INT0 pin is configured as an output. This feature provides a way of generating a software interrupt. The External Interrupt can be triggered by a falling or rising edge, a pin change, or a low level. This is set up as indicated in the specification for the MCU Control Register – MCUCR. When the External Interrupt is enabled and is configured as level triggered, the interrupt will trigger as long as the pin is held low.

The changed level is sampled twice by the Watchdog Oscillator clock, and if both these samples have the required level, the MCU will wake up. The period of the Watchdog Oscillator is 1.0 tor is voltage dependent as shown in “Electrical Characteristics” on page 126.

Pin Change Interrupt The pin change interrupt is triggered by any change on any I/O pin of Port B and pins

PA3, PA6, and PA7, if the interrupt is enabled and alternate function of the pin does not mask out the interrupt. The bit PCIE1 in GIMSK enables interrupt from pins PB[7:4], PA[7:6], and PA[3]. PCIE0 enables interrupt on digital pins PB[3:0].

The pin change interrupt is different from other interrupts in two ways. First, pin change interrupt enable bits PCIE1 and PCIE0 also mask the flag if they are not set. The normal operation on most interrupts is that the flag is always active and only the execution of the interrupt is masked by the interrupt enable.

Secondly, please note that pin change interrupt is disabled for any pin that is configured as an alternate function. For example, no pin change interrupt is generated from pins that are configured as AREF, AIN0 or AIN1, OC1A, OC1A XTAL2 in a fuse selected clock option, Timer0 clocking, or RESET 30 for alternate functions which mask the pin change interrupt and how the function is enabled. For example pin change interrupt on the PB0 is disabled when USI Two-wire mode or USI Three-wire mode or Timer/Counter1 inverted output compare is enabled.

µs (nominal) at 3.0V and 25°C. The frequency of the Watchdog Oscilla-

, OC1B, OC1B, XTAL1, or

function. See Table

If the interrupt is enabled, the interrupt will trigger even if the changing pin is configured as an output. This feature provides a way of generating a software interrupt. Also observe that the pin change interrupt will trigger even if the pin activity triggers another interrupt, for example the external interrupt. This implies that one external event might cause several interrupts.

The value of the programmed fuse is “0” and unprogrammed is “1”. Each of the lines enables the alternate function so “or” function of the lines enables the function.

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Table 30. Alternative Functions

ATtiny26(L)

Control Register[Bit Name] which

Pin Alternate Function

PA3 AREF ADMUX[REFS0] 1

PA6 Analog Comparator ACSR[ACD] 0

PA7 Analog Comparator ACSR[ACD] 0

PB0 USI Two-wire mode

USI Three-wire mode TC1 compare/PWM

PB1 USI Three-wire mode

TC1 compare/PWM

PB2 USI Two-wire mode

USI Three-wire mode TC1 compare/PWM

PB3 TC1 compare/PWM TCCR1A[COM1B1]

PB4 XTAL1, clock source FUSE[PLLCK,CKSEL]

PB5 XTAL2, clock source FUSE[PLLCK,CKSEL] 11001-11111

PB6 External interrupt

TC0 clock

PB7 RESET RSTDISBL FUSE 1

set the Alternate Function

USICR[USIWM1] USICR[USIWM1,USIWM0] TCCR1A[COM1A1,COM1A0,PWM1A]

USICR[USIWM1,USIWM0] TCCR1A[COM1A1] TCCR1A[COM1A0]

USICR[USIWM1] USICR[USIWM1,USIWM0] TCCR1A[COM1B1,COM1B0,PWM1B]

TCCR1A[COM1B0]

FUSE[PLLCK,CKSEL]

GIMSK[INT0],MCUCR[ISC01,ISC01] TCCR0[CS02,CS01]

(1)

Bit or Fuse

10101-11111

100 11

Val ue

011

1 1

011

1 1

10000

()

Notes: 1. Each line represents a bit or fuse combination which enables the function.

A fuse value of “0” is programmed, “1” is unprogrammed.

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Timer/Counters The ATtiny26(L) provides two general purpose 8-bit Timer/Counters. The

Timer/Counters have separate prescaling selection from the separate prescaler. The Timer/Counter0 clock (CK) as the clock timebase. The Timer/Counter1 has two clocking modes, a synchronous mode and an asynchronous mode. The synchronous mode uses the system clock (CK) as the clock timebase and asynchronous mode uses the fast peripheral clock (PCK) as the clock time base.

Timer/Counter0 Prescaler

Figure 36 below shows the Timer/Counter prescaler.

Figure 36. Timer/Counter0 Prescaler

PSR0

T0(PB6)

CS00 CS01 CS02

CLEAR

10-BIT T/C PRESCALER

CK/8

TIMER/COUNTER0 CLOCK SOURCE

CK/64

CK/256

CK/1024

The four prescaled selections are: CK/8, CK/64, CK/256, and CK/1024 where CK is the oscillator clock. CK, external source, and stop, can also be selected as clock sources.

ATtiny26(L)

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ATtiny26(L)

Timer/Counter1 Prescaler

Figure 37 shows the Timer/Counter1 prescaler. For Timer/Counter1 the clock selections are between PCK to PCK/16384 and stop in asynchronous mode and CK to CK/16384 and stop in synchronous. The clock options are described in Table 34 on page 72 and the Timer/Counter1 Control Register, TCCR1B. Setting the PSR1 bit in TCCR1B Register resets the prescaler. The PCKE bit in the PLLCSR Register enables the asynchronous mode.

Figure 37. Timer/Counter1 Prescaler

S A

PSR1

CS10 CS11 CS12 CS13

T1CK

14-BIT

T/C PRESCALER

T1CK

T1CK/2

T1CK/4

T1CK/8

T1CK/16

T1CK/32

T1CK/64

T1CK/128

T1CK/256

TIMER/COUNTER1 COUNT ENABLE

T1CK/512

T1CK/1024

T1CK/2048

T1CK/4096

T1CK/16384

T1CK/8192

PCKE

PCK

(64 MHz)

8-bit Timer/Counter0 Figure 38 shows the block diagram for Timer/Counter0.

The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK, or an external pin. In addition, it can be stopped as described in the specification for the Timer/Counter0 Control Register – TCCR0. The overflow status flag is found in the Timer/Counter Interrupt Flag Register – TIFR. Control signals are found in the Timer/Counter0 Control Register – TCCR0. The interrupt enable/disable settings for Timer/Counter0 are found in the Timer/Counter Interrupt Mask Register – TIMSK.

When Timer/Counter0 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To ensure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one internal CPU clock period. The external clock signal is sampled on the rising edge of the internal CPU clock.

The 8-bit Timer/Counter0 features both a high resolution and a high accuracy usage with the lower prescaling opportunities. Similarly, the high prescaling opportunities make the Timer/Counter0 useful for lower speed functions or exact timing functions with infrequent actions.

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Figure 38. Timer/Counter0 Block Diagram

Timer/Counter0 Control Register – TCCR0

Bit 76 5 4 3 210

$33 ($53) – – – – PSR0 CS02 CS01 CS00 TCCR0

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bits 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

• Bit 3 – PSR0: Prescaler Reset Timer/Counter0

When this bit is set (one), the prescaler of the Timer/Counter0 will be reset. The bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have no effect. This bit will always be read as zero.

• Bits 2, 1, 0 – CS02, CS01, CS00: Clock Select0, Bit 2, 1, and 0

The Clock Select0 bits 2, 1, and 0 define the prescaling source of Timer0.

Table 31. Clock 0 Prescale Select

CS02 CS01 CS00 Description

0 0 0 Stop, the Timer/Counter0 is stopped

001CK

010CK/8

011CK/64

100CK/256

101CK/1024

1 1 0 External Pin T0, falling edge

1 1 1 External Pin T0, rising edge

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ATtiny26(L)

The Stop condition provides a Timer Enable/Disable function. The CK down divided modes are scaled directly from the CK oscillator clock. If the external pin modes are used, the corresponding setup must be performed in the actual Data Direction Control Register (cleared to zero gives an input pin).

Timer/Counter0 – TCNT0

Bit 76543210

$32 ($52) MSB LSB TCNT0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

The Timer/Counter0 is implemented as an up-counter with read and write access. If the Timer/Counter0 is written and a clock source is present, the Timer/Counter0 continues counting in the timer clock cycle following the write operation.

8-bit Timer/Counter1 The Timer/Counter1 has two clocking modes: a synchronous mode and an asynchro-

nous mode. The synchronous mode uses the system clock (CK) as the clock timebase and asynchronous mode uses the fast peripheral clock (PCK) as the clock time base. The PCKE bit from the PLLCSR Register enables the asynchronous mode when it is set (“1”). The Timer/Counter1 general operation is described in the asynchronous mode and the operation in the synchronous mode is mentioned only if there is differences between these two modes. Figure 39 shows Timer/Counter1 synchronization register block diagram and synchronization delays in between registers. Note that all clock gating details are not shown in the figure. The Timer/Counter1 Register values go through the internal synchronization registers, which cause the input synchronization delay, before affecting the counter operation. The registers TCCR1A, TCCR1B, OCR1A, OCR1B, and OCR1C can be read back right after writing the register. The read back values are delayed for the Timer/Counter1 (TCNT1) Register and flags (OCF1A, OCF1B, and TOV1), because of the input and output synchronization.

This module features a high resolution and a high accuracy usage with the lower prescaling opportunities. Timer/Counter1 can also support two accurate, high speed, 8-bit Pulse Width Modulators using clock speeds up to 64 MHz. In this mode, Timer/Counter1 and the Output Compare Registers serve as dual stand-alone PWMs with non-overlapping non-inverted and inverted outputs. Refer to page 74 for a detailed description on this function. Similarly, the high prescaling opportunities make this unit useful for lower speed functions or exact timing functions with infrequent actions.

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Figure 39. Timer/Counter1 Synchronization Register Block Diagram

8-BIT DATABUS

PCKE

IO-registers

OCR1A

OCR1B

OCR1C

TCCR1A

TCCR1B

TCNT1

OCF1A

OCF1B

TOV1

Input syncronization registe rs

OCR1A_SI

OCR1B_SI

OCR1C_SI

TCCR1A_SI

TCCR1B_SI

TCNT1_SI

OCF1A_SI

OCF1B_SI

TOV1_SI

Timer/Counter1

TCNT1

Output syncronization registers

TCNT_SO

OCF1A_SO

OCF1B_SO

TOV1_SO

Output m ultiplexe rs

TCNT1

S A

OCF1A

S A

OCF1B

S A

TOV1

S A

PCK

SYNC MODE

ASYNC MODE

S A

1CK delay

S A

1PCK delay 1/2PCK -1CK delay 1/2PCK -1CK delay

no delay

Timer/Counter1 and the prescaler allow running the CPU from any clock source while the prescaler is operating on the fast 64 MHz PCK clock in the asynchronous mode.

Note that the system clock frequency must be lower than one half of the PCK frequency. Only when the system clock is generated from PCK dividing that by two, the ratio of the PCK/system clock can be exactly two. The synchronization mechanism of the asynchronous Timer/Counter1 needs at least two edges of the PCK when the system clock is high. If the frequency of the system clock is too high, it is a risk that data or control values are lost.

The following Figure 40 shows the block diagram for Timer/Counter1.

ATtiny26(L)

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Figure 40. Timer/Counter1 Block Diagram

T/C1 OVER-

FLOW IRQ

TOIE1

TOIE0

OCIE1A

OCIE1B

TIMER INT. MASK

TIMER/COUNTER1

(TCNT1)

T/C1 COMPARE

MATCH A IRQ

T/C1 COMPARE

MATCH B IRQ

OCF1B

OCF1A

TIMER INT. FLAG REGISTER (TIFR)

OCF1A

OCF1B

T/C CLEAR

TOV1

TOV0

OC1A

(PB0)

OC1A (PB1)

T/C CONTROL

FOC1B

FOC1A

PWM1A

COM1B0

COM1A0

COM1B1

COM1A1

T/C1 CONTROL

LOGIC

ATtiny26(L)

OC1B

(PB2)

PWM1B

OC1B (PB3)

T/C CONTROL

CS11

CS12

PSR1

CS13

CTC1

CS10

PCK

8-BIT COMPARATOR

T/C1 OUTPUT

COMPARE REGISTER

8-BIT DATA BUS

(OCR1A) (OCR1B) (OCR1C)

8-BIT COMPARATOR

T/C1 OUTPUT

COMPARE REGISTER

8-BIT COMPARATOR

T/C1 OUTPUT

COMPARE REGISTER

Three status flags (overflow and compare matches) are found in the Timer/Counter Interrupt Flag Register – TIFR. Control signals are found in the Timer/Counter Control Registers TCCR1A and TCCR1B. The interrupt enable/disable settings are found in the Timer/Counter Interrupt Mask Register – TIMSK.

The Timer/Counter1 contains three Output Compare Registers, OCR1A, OCR1B, and OCR1C, as the data source to be compared with the Timer/Counter1 contents. In normal mode the Output Compare functions are operational with all three Output Compare Registers. OCR1A determines action on the OC1A pin (PB1), and it can generate Timer1 OC1A interrupt in normal mode and in PWM mode. Likewise, OCR1B determines action on the OC1B pin (PB3) and it can generate Timer1 OC1B interrupt in normal mode and in PWM mode. OCR1C holds the Timer/Counter maximum value, i.e., the clear on compare match value. An overflow interrupt (TOV1) is generated when Timer/Counter1 counts from $FF to $00 or from OCR1C to $00. This function is the same for both normal and PWM mode. The inverted PWM outputs OC1A

and OC1B are

not connected in normal mode.

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In PWM mode, OCR1A and OCR1B provide the data values against which the Timer/Counter value is compared. Upon compare match the PWM outputs (OC1A, OC1A

, OC1B, OC1B) are generated. In PWM mode, the Timer/Counter counts up to the value specified in the Output Compare Register OCR1C and starts again from $00. This feature allows limiting the counter “full” value to a specified value, lower than $FF. Together with the many prescaler options, flexible PWM frequency selection is provided. Table 37 lists clock selection and OCR1C values to obtain PWM frequencies from 20 kHz to 250 kHz in 10 kHz steps and from 250 kHz to 500 kHz in 50 kHz steps. Higher PWM frequencies can be obtained at the expense of resolution.

Timer/Counter1 Control Register A – TCCR1A

Bit 7 6 5 4 3 2 1 0

$30 ($50)

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

COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B PWM1A PWM1B TCCR1A

• Bits 7, 6 – COM1A1, COM1A0: Comparator A Output Mode, Bits 1 and 0

The COM1A1 and COM1A0 control bits determine any output pin action following a Compare Match with Compare Register A in Timer/Counter1. Output pin actions affect pin PB1 (OC1A). Since this is an alternative function to an I/O port, the corresponding direction control bit must be set (one) in order to control an output pin. Note that OC1A

not connected in normal mode.

Table 32. Comparator A Mode Select

COM1A1 COM1A0 Description

0 0 Timer/Counter Comparator A disconnected from output pin OC1A.

0 1 Toggle the OC1A output line.

1 0 Clear the OC1A output line.

1 1 Set the OC1A output line.

In PWM mode, these bits have different functions. Refer to Table 35 on page 75 for a detailed description.

• Bits 5, 4 – COM1B1, COM1B0: Comparator B Output Mode, Bits 1 and 0

The COM1B1 and COM1B0 control bits determine any output pin action following a Compare Match with Compare Register B in Timer/Counter1. Output pin actions affect pin PB3 (OC1B). Since this is an alternative function to an I/O port, the corresponding direction control bit must be set (one) in order to control an output pin. Note that OC1B

not connected in normal mode.

Table 33. Comparator B Mode Select

COM1B1 COM1B0 Description

0 0 Timer/Counter Comparator B disconnected from output pin OC1B.

0 1 Toggle the OC1B output line.

1 0 Clear the OC1B output line.

1 1 Set the OC1B output line.

In PWM mode, these bits have different functions. Refer to Table 35 on page 75 for a detailed description.

• Bit 3 – FOC1A: Force Output Compare Match 1A

Writing a logical one to this bit forces a change in the Compare Match output pin PB1 (OC1A) according to the values already set in COM1A1 and COM1A0. If COM1A1 and COM1A0 written in the same cycle as FOC1A, the new settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1A1 and COM1A0 takes place as if a compare match had occurred, but no interrupt is generated. The FOC1A bit always reads as zero. FOC1A is not in use if PWM1A bit is set.

• Bit 2 – FOC1B: Force Output Compare Match 1B

ATtiny26(L)

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ATtiny26(L)

Writing a logical one to this bit forces a change in the Compare Match output pin PB3 (OC1B) according to the values already set in COM1B1 and COM1B0. If COM1B1 and COM1B0 written in the same cycle as FOC1B, the new settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1B1 and COM1B0 takes place as if a compare match had occurred, but no interrupt is generated. The FOC1B bit always reads as zero. FOC1B is not in use if PWM1B bit is set.

• Bit 1 – PWM1A: Pulse Width Modulator A Enable

When set (one) this bit enables PWM mode based on comparator OCR1A in Timer/Counter1 and the counter value is reset to $00 in the CPU clock cycle after a compare match with OCR1C Register value.

• Bit 0 – PWM1B: Pulse Width Modulator B Enable

When set (one) this bit enables PWM mode based on comparator OCR1B in Timer/Counter1 and the counter value is reset to $00 in the CPU clock cycle after a compare match with OCR1C Register value.

Timer/Counter1 Control Register B – TCCR1B

Bit 7 6 5 4 3 2 1 0

$2F ($4F) CTC1 PSR1 – – CS13 CS12 CS11 CS10 TCCR1B

Read/Write R/W R/W R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – CTC1: Clear Timer/Counter on Compare Match

When the CTC1 control bit is set (one), Timer/Counter1 is reset to $00 in the CPU clock cycle after a compare match with OCR1C Register value. If the control bit is cleared, Timer/Counter1 continues counting and is unaffected by a compare match.

• Bit 6 – PSR1: Prescaler Reset Timer/Counter1

When this bit is set (one), the Timer/Counter prescaler will be reset. The bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have no effect. This bit will always read as zero.

• Bit 5..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

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• Bits 3..0 – CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0

The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1.

Table 34. Timer/Counter1 Prescale Select

Description

CS13 CS12 CS11 CS10

0000Timer/Counter1 is stopped.Timer/Counter1 is stopped.

0001PCK CK

0010PCK/2 CK/2

0011PCK/4 CK/4

0100PCK/8 CK/8

0101PCK/16 CK/16

0110PCK/32 CK/32

0111PCK/64 CK/64

1000PCK/128 CK/128

1001PCK/256 CK/256

1010PCK/512 CK/512

1011PCK/1024 CK/1024

1100PCK/2048 CK/2048

1101PCK/4096 CK/4096

1110PCK/8192 CK/8192

1111PCK/16384 CK/16384

Asynchronous Mode

Description Synchronous Mode

Timer/Counter1 – TCNT1

Timer/Counter1 Output Compare RegisterA – OCR1A

The Stop condition provides a Timer Enable/Disable function.

Bit 76543210

$2E ($4E) MSB LSB TCNT1

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 8-bit register contains the value of Timer/Counter1.

Timer/Counter1 is realized as an up counter with read and write access. Due to synchronization of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one CPU clock cycle in synchronous mode and at most two CPU clock cycles for asynchronous mode.

Bit 76543210

$2D ($4D) MSB LSB OCR1A

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 is an 8-bit read/write register.

The Timer/Counter Output Compare Register A contains data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does only occur if Timer/Counter1 counts to the OCR1A value. A soft-

ATtiny26(L)

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ATtiny26(L)

ware write that sets TCNT1 and OCR1A to the same value does not generate a compare match.

A compare match will set the compare interrupt flag OCF1A after a synchronization delay following the compare event.

Timer/Counter1 Output Compare RegisterB – OCR1B

Timer/Counter1 Output Compare RegisterC – OCR1C

Bit 76543210

$2C ($4C) MSB LSB OCR1B

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 is an 8-bit read/write register.

The Timer/Counter Output Compare Register B contains data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does only occur if Timer/Counter1 counts to the OCR1B value. A software write that sets TCNT1 and OCR1B to the same value does not generate a compare match.

A compare match will set the compare interrupt flag OCF1B after a synchronization delay following the compare event.

Bit 76543210

$2B ($4B) MSB LSB OCR1C

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 C is an 8-bit read/write register.

The Timer/Counter Output Compare Register C contains data to be continuously compared with Timer/Counter1. A compare match does only occur if Timer/Counter1 counts to the OCR1C value. A software write that sets TCNT1 and OCR1C to the same value does not generate a compare match.

PLL Control and Status Register – PLLCSR

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If the CTC1 bit in TCCR1B is set, a compare match will clear TCNT1 and set an Overflow Interrupt Flag (TOV1). The flag is set after a synchronization delay following the compare event.

This register has the same function in normal mode and PWM mode.

Bit 76543210

$29 ($29) –––––PCKEPLLEPLOCKPLLCSR

Read/Write R R R R R R/W R/W R

Initial Value 0 0 0 0 0 0 0/1 0

• Bit 7..3 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and always read as zero.

• Bit 2 – PCKE: PCK Enable

The PCKE bit change the Timer/Counter1 clock source. When it is set, the asynchronous clock mode is enabled and fast 64 MHz PCK clock is used as Timer/Counter1 clock source. If this bit is cleared, the synchronous clock mode is enabled, and system clock CK is used as Timer/Counter1 clock source. This bit can be set only if PLLE bit is set. It is safe to set this bit only when the PLL is locked i.e., the PLOCK bit is 1.

• Bit 1 – PLLE: PLL Enable

When the PLLE is set, the PLL is started and if needed internal RC Oscillator is started as a PLL reference clock. If PLL is selected as a system clock source the value for this bit is always 1.

• Bit 0 – PLOCK: PLL Lock Detector

When the PLOCK bit is set, the PLL is locked to the reference clock, and it is safe to enable PCK for Timer/Counter1. After the PLL is enabled, it takes about 64 µs/100 µs (typical/worst case) for the PLL to lock.

Timer/Counter1 Initialization for Asynchronous Mode

To change Timer/Counter1 to the asynchronous mode, first enable PLL, and poll the PLOCK bit until it is set, and then set the PCKE bit.

Timer/Counter1 in PWM Mode When the PWM mode is selected, Timer/Counter1 and the Output Compare Register C

– OCR1C form a dual 8-bit, free-running and glitch-free PWM generator with outputs on the PB1(OC1A) and PB3(OC1B) pins. Also inverted, non-overlapping outputs are available on pins PB0(OC1A pairs (OC1A - OC1A

) and PB2(OC1B), respectively. The non-overlapping output

and OC1B - OC1B) are never both set at the same time. This allows driving power switches directly. The non-overlap time is one prescaled clock cycle, and the high time is one cycle shorter than the low time.

The non-overlap time is generated by delaying the rising edge, i.e., the positive edge is one prescaled and one PCK cycle delayed and the negative edge is one PCK cycle delayed in the asynchronous mode. In the synchronous mode he positive edge is one prescaled and one CK cycle delayed and the negative edge is one CK cycle delayed. The high time is also one prescaled cycle shorter in the both operation modes.

Figure 41. The Non-overlapping Output Pair

OC1x

ATtiny26(L)

non-overlap

x = A or B

When the counter value match the contents of OCR1A and OCR1B, the OC1A and OC1B outputs are set or cleared according to the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the Timer/Counter1 Control Register A – TCCR1A, as shown in Table 35 below.

Timer/Counter1 acts as an up-counter, counting from $00 up to the value specified in the Output Compare Register (OCR1C), and starting from $00 up again. A compare match with OC1C will set an Overflow Interrupt Flag (TOV1) after a synchronization delay following the compare event.

1477F–AVR–12/04

ATtiny26(L)

Table 35. Compare Mode Select in PWM Mode

COM1x1 COM1x0 Effect on Output Compare Pins

Note that in PWM mode, writing to the Output Compare Registers OCR1A or OCR1B, the data value is first transferred to a temporary location. The value is latched into OCR1A or OCR1B when the Timer/Counter reaches OCR1C. This prevents the occurrence of odd-length PWM pulses (glitches) in the event of an unsynchronized OCR1A or OCR1B. See Figure 42 for an example.

OC1x not connected. OC1x

not connected.

OC1x cleared on compare match. Set when TCNT1 = $01.

set one prescaled cycle after compare match. Cleared when

OC1x TCNT1 = $00.

OC1x cleared on compare match. Set when TCNT1 = $01.

not connected.

OC1x

OC1x set one prescaled cycle after compare match. Cleared when TCNT = $00

not connected.

OC1x

Figure 42. Effects of Unsynchronized OCR Latching

Compare Value Changes

Counter Value

Compare Value

PWM Output OC1x

Synchronized OC1x Latch

Compare Value changes

Counter Value

Compare Value

PWM Output OC1x

Unsynchronized OC1x Latch

Glitch

During the time between the write and the latch operation, a read from OCR1A or OCR1B will read the contents of the temporary location. This means that the most recently written value always will read out of OCR1A or OCR1B.

When OCR1A or OCR1B contain $00 or the top value, as specified in OCR1C Register, the output PB1(OC1A) or PB3(OC1B) is held low or high according to the settings of COM1A1/COM1A0. This is shown in Table 36.

1477F–AVR–12/04

Table 36. PWM Outputs OCR1x = $00 or OCR1C, x = A or B

COM1x1 COM1x0 OCR1x Output OC1x Output OC1x

0 1 $00 L H

0 1 OCR1C H L

1 0 $00 L Not connected

1 0 OCR1C H Not connected

1 1 $00 H Not connected

1 1 OCR1C L Not connected

In PWM mode, the Timer Overflow Flag – TOV1, is set as in normal Timer/Counter mode. Timer Overflow Interrupt1 operates exactly as in normal Timer/Counter mode, i.e., it is executed when TOV1 is set provided that Timer Overflow Interrupt and global interrupts are enabled. This also applies to the Timer Output Compare flags and interrupts.

The frequency of the PWM will be Timer Clock 1 Frequency divided by (OCR1C value + 1). See the following equation:

TCK1

PWM

----------------------------------- -=

OCR1C + 1()

Resolution shows how many bit is required to express the value in the OCR1C Register. It is calculated by following equation

Resolution

= log2(OCR1C + 1)

PWM

ATtiny26(L)

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ATtiny26(L)

Table 37. Timer/Counter1 Clock Prescale Select in the Asynchronous Mode

PWM Frequency (kHz) Clock Selection CS13..CS10 OCR1C RESOLUTION (Bits)

20 PCK/16 0101 199 7.6

30 PCK/16 0101 132 7.1

40 PCK/8 0100 199 7.6

50 PCK/8 0100 159 7.3

60 PCK/8 0100 132 7.1

70 PCK/4 0011 228 7.8

80 PCK/4 0011 199 7.6

90 PCK/4 0011 177 7.5

100 PCK/4 0011 159 7.3

110 PCK/4 0011 144 7.2

120 PCK/4 0011 132 7.1

130 PCK/2 0010 245 7.9

140 PCK/2 0010 228 7.8

150 PCK/2 0010 212 7.7

160 PCK/2 0010 199 7.6

170 PCK/2 0010 187 7.6

180 PCK/2 0010 177 7.5

190 PCK/2 0010 167 7.4

200 PCK/2 0010 159 7.3

250 PCK 0001 255 8.0

300 PCK 0001 212 7.7

350 PCK 0001 182 7.5

400 PCK 0001 159 7.3

450 PCK 0001 141 7.1

500 PCK 0001 127 7.0

1477F–AVR–12/04

Watchdog Timer The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1

MHz. This is the typical value at V other V

levels. By controlling the Watchdog Timer prescaler, the Watchdog Reset

interval can be adjusted from 16 to 2048 ms. The WDR – Watchdog Reset – instruction resets the Watchdog Timer. Eight different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog Reset, the ATtiny26(L) resets and executes from the Reset Vector. For timing details on the Watchdog Reset, refer to page 34.

To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer Control Register for details.

Figure 43. Watchdog Timer

= 5V. See characterization data for typical values at

Watchdog Timer Control Register – WDTCR

Normally 1 MHz

WATCHDOG

RESET

WDP0

WDP1

WDP2

WDE

Bit 7654 3210

$21 ($41) – – – WDCE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value000 0 0000

WATCHDOG

PRESCLALER

MCU RESET

• Bits 7..5 – Res: Reserved Bits

These bits are reserved bits in the ATtiny26(L) and will always read as zero.

• Bit 4 – WDCE: Watchdog Change Enable

This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the description of the WDE bit for a Watchdog disable procedure. In Safety Level 1 and 2, this bit must also be set when changing the prescaler bits.

• Bit 3 – WDE: Watchdog Enable

When the WDE is set (one) the Watchdog Timer is enabled, and if the WDE is cleared (zero) the Watchdog Timer function is disabled. WDE can be cleared only when the WDCE bit is set(one). To disable an enabled Watchdog Timer, the following procedure must be followed:

ATtiny26(L)

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ATtiny26(L)

1. In the same operation, write a logical one to WDCE and WDE. A logical one

must be written to WDE even though it is set to one before the disable operation starts.

2. Within the next four clock cycles, write a logical 0 to WDE. This disables the

Watchdog.

• Bits 2..0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0

The WDP2, WDP1 and WDP0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is enabled. The different prescaling values and their corresponding time-out periods are shown in Table 38.

Table 38. Watchdog Timer Prescale Select

Number of WDT

WDP2 WDP1 WDP0

0 0 0 16K (16,384) 17.1 ms 16.3 ms

0 0 1 32K (32,768) 34.3 ms 32.5 ms

0 1 0 64K (65,536) 68.5 ms 65 ms

0 1 1 128K (131,072) 0.14 s 0.13 s

1 0 0 256K (262,144) 0.27 s 0.26 s

1 0 1 512K (524,288) 0.55 s 0.52 s

1 1 0 1,024K (1,048,576) 1.1 s 1.0 s

1 1 1 2,048K (2,097,152) 2.2 s 2.1 s

Note: 1. The frequency of the Watchdog Oscillator is voltage dependent. The WDR – Watch-

dog Reset – instruction should always be executed before the Watchdog Timer is enabled. This ensures that the reset period will be in accordance with the Watchdog Timer prescale settings. If the Watchdog Timer is enabled without reset, the Watchdog Timer may not start counting from zero.

Oscillator Cycles

(1)

Typical Time-out

at VCC = 3.0V

Typical Time-out

at VCC = 5.0V

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Universal Serial Interface – USI

The Universal Serial Interface, or USI, provides the basic hardware resources needed for serial communication. Combined with a minimum of control software, the USI allows significantly higher transfer rates and uses less code space than solutions based on software only. Interrupts are included to minimize the processor load. The main features of the USI are:

•

Two-wire Synchronous Data Transfer (Master or Slave, f

• Three-wire Synchronous Data Transfer (Master, f

SCLmax

= fCK/2, Slave f

SCKmax

• Data Received Interrupt

• Wakeup from Idle Mode

• In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode

• Two-wire Start Condition Detector with Interrupt Capability

Overview A simplified block diagram of the USI is shown on Figure 44.

Figure 44. Universal Serial Interface, Block Diagram

DQ LE

Bit0

USIDR

3 2

1 0

TIM0 OVF

= fCK/16)

SCKmax

PB1

PB0

= fCK/4)

DO (Output only)

DI/SDA (Input/Open Drain)

DATA BUS

USISIF

USISIE Bit7

USIOIFUSIOIE

USIPF

USIWM1

USIDC

USISR

USICS1

USIWM0

USICR

4-bit Counter

USICLK

USICS0

USITC

3 2

1 0

[1]

Two-wire Clock

Control Unit

CLOCK

HOLD

PB2

SCK/SCL (Input/Open Drain)

The 8-bit Shift Register is directly accessible via the data bus and contains the incoming and outgoing data. The register has no buffering so the data must be read as quickly as possible to ensure that no data is lost. The most significant bit is connected to one of two output pins depending of the wire mode configuration. A transparent latch is inserted between the serial register output and output pin, which delays the change of data output to the opposite clock edge of the data input sampling. The serial input is always sampled from the Data Input (DI) pin independent of the configuration.

The 4-bit counter can be both read and written via the data bus, and can generate an overflow interrupt. Both the serial register and the counter are clocked simultaneously by the same clock source. This allows the counter to count the number of bits received or transmitted and generate an interrupt when the transfer is complete. Note that when an external clock source is selected the counter counts both clock edges. In this case the counter counts the number of edges, and not the number of bits. The clock can be selected from three different sources: the SCK pin, Timer 0 overflow, or from software.

The Two-wire clock control unit can generate an interrupt when a start condition is detected on the Two-wire bus. It can also generate wait states by holding the clock pin low after a start condition is detected, or after the counter overflows.

ATtiny26(L)

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Register Descriptions

ATtiny26(L)

USI Data Register – USIDR

Bit 7 6 5 4 3 2 1 0

$0F ($2F) MSB LSB USIDR

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 USI uses no buffering of the serial register, i.e., when accessing the Data Register (USIDR) the serial register is accessed directly. If a serial clock occurs at the same cycle the register is written, the register will contain the value written and no shift is performed. A (left) shift operation is performed depending of the USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a Timer/Counter0 overflow, or directly by software using the USICLK strobe bit. Note that even when no wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the external clock input (SCK/SCL) can still be used by the Shift Register.

The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the Data Register. The output latch is open (transparent) during the first half of a serial clock cycle when an external clock source is selected (USICS1 = 1), and constantly open when an internal clock source is used (USICS1 = 0). The output will be changed immediately when a new MSB written as long as the latch is open. The latch ensures that data input is sampled and data output is changed on opposite clock edges.

Note that the corresponding Data Direction Register (DDRB2/1) to the pin must be set to one for enabling data output from the Shift Register.

USI Status Register – USISR

Bit 76543 210

$0E ($2E)

Read/Write R/W R/W R/W R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 USISR

The Status Register contains interrupt flags, line status flags and the counter value.

Note that doing a Read-Modify-Write operation on USISR Register, i.e., using the SBI or CBI instructions, will clear pending interrupt flags. It is recommended that register contents is altered by using the OUT instruction only.

• Bit 7 – USISIF: Start Condition Interrupt Flag

When Two-wire mode is selected, the USISIF flag is set (to one) when a start condition is detected. When output disable mode or Three-wire mode is selected and (USICSx = 0b11 & USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the SCK pin sets the flag.

An interrupt will be generated when the flag is set while the USISIE bit in USICR and the Global Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one to the USISIF bit. Clearing this bit will release the start detection hold of SCL in Two-wire mode.

A start condition interrupt will wakeup the processor from all four sleep modes.

• Bit 6 – USIOIF: Counter Overflow Interrupt Flag

This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to

0). An interrupt will be generated when the flag is set while the USIOIE bit in USICR and the Global Interrupt Enable Flag are set. The flag will only be cleared if a one is written

1477F–AVR–12/04

to the USIOIF bit. Clearing this bit will release the counter overflow hold of SCL in Twowire mode.

A counter overflow interrupt will wakeup the processor from Idle sleep mode.

• Bit 5 – USIPF: Stop Condition Flag

When Two-wire mode is selected, the USIPF flag is set (one) when a stop condition is detected. The flag is cleared by writing a one to this bit. Note that this is not an interrupt flag. This signal is useful when implementing Two-wire bus master arbitration.

• Bit 4 – USIDC: Data Output Collision

This bit is logical one when bit 7 in the Shift Register differs from the physical pin value. The flag is only valid when Two-wire mode is used. This signal is useful when implementing Two-wire bus master arbitration.

• Bits 3..0 – USICNT3..0: Counter Value

These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or written by the CPU.

The 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a Timer/Counter0 overflow, or by software using USICLK or USITC strobe bits. The clock source depends of the setting of the USICS1..0 bits. For external clock operation a special feature is added that allows the clock to be generated by writing to the USITC strobe bit. This feature is enabled by write a one to the USICLK bit while setting an external clock source (USICS1 = 1).

Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input (SCK/SCL) are can still be used by the counter.

USI Control Register – USICR

Bit 7 6 5 4 3 2 1 0

$0D ($2D) USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR

Read/Write R/W R/W R/W R/W R/W R/W W W

Initial Value 0 0 0 0 0 0 0 0

The Control Register includes interrupt enable control, wire mode setting, clock select setting, and clock strobe.

• Bit 7 – USISIE: Start Condition Interrupt Enable

Setting this bit to one enables the Start Condition detector interrupt. If there is a pending interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed. Refer to the description of “Bit 7 – USISIF: Start Condition Interrupt Flag” on page 81 for further details.

• Bit 6 – USIOIE: Counter Overflow Interrupt Enable

Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed. Refer to the description of “Bit 6 – USIOIF: Counter Overflow Interrupt Flag” on page 81 for further details.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

• Bit 5..4 – USIWM1..0: Wire Mode

These bits set the type of wire mode to be used. Basically only the function of the outputs are affected by these bits. Data and clock inputs are not affected by the mode selected and will always have the same function. The counter and Shift Register can therefore be clocked externally, and data input sampled, even when outputs are disabled. The relations between USIWM1..0 and the USI operation is summarized in Table 39.

Table 39. Relations between USIWM1..0 and the USI Operation

USIWM1 USIWM0 Description

0 0 Outputs, clock hold, and start detector disabled. Port pins operates as

normal.

0 1 Three-wire mode. Uses DO, DI, and SCK pins.

The Data Output (DO) pin overrides the PORTB1 bit in the PORTB Register in this mode. However, the corresponding DDRB1 bit still controls the data direction. When the port pin is set as input (DDRB1 = 0) the pins pull-up is controlled by the PORTB1 bit.

The Data Input (DI) and Serial Clock (SCK) pins do not affect the normal port operation. When operating as master, clock pulses are software generated by toggling the PORTB2 bit while DDRB2 is set to output. The USITC bit in the USICR Register can be used for this purpose.

(1)

1 0 Two-wire mode. Uses SDA (DI) and SCL (SCK) pins

The Serial Data (SDA) and the Serial Clock (SCL) pins are bidirectional and uses open-collector output drives. The output drivers are enabled by the DDRB0/2 bit in the DDRB Register.

When the output driver is enabled for the SDA pin, the output driver will force the line SDA low if the output of the Shift Register or the PORTB0 bit in the PORTB Register is zero. Otherwise the SDA line will not be driven (i.e., it is released). When the SCL pin output driver is enabled the SCL line will be forced low if the PORTB2 bit in the PORTB Register is zero, or by the start detector. Otherwise the SCL line will not be driven.

The SCL line is held low when a start detector detects a start condition and the output is enabled. Clearing the start condition flag (USISIF) releases the line. The SDA and SCL pin inputs is not affected by enabling this mode. Pull-ups on the SDA and SCL port pin are disabled in Two-wire mode.

1 1 Two-wire mode. Uses SDA and SCL pins.

Same operation as for the Two-wire mode described above, except that the SCL line is also held low when a counter overflow occurs, and is held low until the Counter Overflow Flag (USIOIF) is cleared.

1477F–AVR–12/04

Note: 1. The DI and SCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL)

respectively to avoid confusion between the modes of operation.

• Bit 3..2 – USICS1..0: Clock Source Select

These bits set the clock source for the Shift Register and counter. The data output latch ensures that the output is changed at the opposite edge of the sampling of the data input (DI/SDA) when using external clock source (SCK/SCL). When software strobe or Timer0 overflow clock option is selected the output latch is transparent and therefore the output is changed immediately. Clearing the USICS1..0 bits enables software strobe option. When using this option, writing a one to the USICLK bit clocks both the Shift Register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no longer used as a strobe, but selects between external clocking, and software clocking by the USITC strobe bit.

Table 40 shows the relationship between the USICS1..0 and USICLK setting and clock source used for the Shift Register and the 4-bit counter.

Table 40. Relations between the USICS1..0 and USICLK Setting

Shift Register Clock

USICS1 USICS0 USICLK

0 0 0 No Clock No Clock

0 0 1 Software clock strobe

0 1 X Timer/Counter0 overflow Timer/Counter0 overflow

1 0 0 External, positive edge External, both edges

1 1 0 External, negative edge External, both edges

1 0 1 External, positive edge Software clock strobe

1 1 1 External, negative edge Software clock strobe

Source

(USICLK)

4-bit Counter Clock Source

Software clock strobe (USICLK)

(USITC)

• Bit 1 – USICLK: Clock Strobe

Writing a one to this bit location strobes the Shift Register to shift one step and the counter to increment by one provided that the USICS1..0 bits are set to zero and by doing so selects the software clock strobe option. The output will change immediately when the clock strobe is executed i.e. in the same instruction cycle. The value shifted into the Shift Register is sampled the previous instruction cycle. The bit will be read as zero.

When an external clock source is selected (USICS1 = 1), the USICLK function is changed from a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the USITC strobe bit as clock source for the 4-bit counter (see Table 40).

• Bit 0 – USITC: Toggle Clock Port Pin

Writing a one to this bit location toggles the PORTB2 (SCK/SCL) value from either from 0 to 1, or 1 to 0. The toggling is independent of the DDRB2 setting, but if the PORTB2 value is to be shown on the pin the DDRB2 must be set as output (to one). This feature allows easy clock generation when implementing master devices. The bit will be read as zero.

When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writing to the USITC strobe bit will directly clock the 4-bit counter. This allows an early detection of when the transfer is done when operating as a master device.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

Functional Descriptions

Three-wire Mode The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0

and 1, but does not have the slave select (SS) pin functionality. However, this feature can be implemented in software if necessary. Pin names used by this mode are: DI, DO, and SCK.

Figure 45. Three-wire Mode Operation, Simplified Diagram

PBx

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

SLAVE

PBy

PBz

PBx

SCK

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

PORTBz

MASTER

PBy

PBz

SCK

Figure 45 shows two USI units operating in Three-wire mode, one as master and one as slave. The two shift Registers are interconnected in such way that after eight SCK clocks, the data in each register are interchanged. The same clock also increments the USI’s 4-bit counter. The Counter Overflow (interrupt) flag, or USIOIF, can therefore be used to determine when a transfer is completed. The clock is generated by the master device software by toggling the PB2 pin via the PORTB Register or by writing a one to the USITC bit in USICR.

Figure 46. Three-wire Mode, Timing Diagram

CYCLE

SCK SCK

( Reference )

1 2 3 4 5 6 7 8

MSB

654321LSB

1477F–AVR–12/04

DCBA E

The Three-wire mode timing is shown in Figure 46. At the top of the figure is a SCK cycle reference. One bit is shifted into the USI Shift Register (USIDR) for each of these cycles. The SCK timing is shown for both external clock modes. In external clock mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (Data Register is

shifted by one) at negative edges. External clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., samples data at negative and changes the output at positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1.

Referring to the timing diagram (Figure 46.), a bus transfer involves the following steps:

1. The slave device and master device sets up its data output and, depending on

the protocol used, enables its output driver (mark A and B). The output is set up by writing the data to be transmitted to the serial Data Register. Enabling of the output is done by setting the corresponding bit in the port data direction register (DDRB2). Note that point A and B does not have any specific order, but both must be at least one half SCK cycle before point C where the data is sampled. This must be done to ensure that the data setup requirement is satisfied. The 4bit counter is reset to zero.

2. The master generates a clock pulse by software toggling the SCK line twice (C

and D). The bit value on the slave and master’s data input (DI) pin is sampled by the USI on the first edge (C), and the data output is changed on the opposite edge (D). The 4-bit counter will count both edges.

3. Step 2. is repeated eight times for a comlpete register (byte) transfer.

4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indi-

cate that the transfer is completed. The data bytes transferred must now be processed before a new transfer can be initiated. The overflow interrupt will wake up the processor if it is set to Idle mode. Depending of the protocol used the slave device can now set its output to high impedance.

SPI Master Operation Example

The following code demonstrates how to use the USI module as a SPI master:

SPITransfer:

out USIDR,r16

ldi r16,(1<<USIOIF)

out USISR,r16

ldi r16,(1<<USIWM0)+(1<<USICS1)+(1<<USICLK)+(1<<USITC)

SPITransfer_loop:

out USICR,r16

sbis USISR,USIOIF

rjmp SPITransfer_loop

in r16,USIDR

ret

The code is size optimized using only 8 instructions (+ ret). The code example assumes that the DO and SCK pins are enabled as output in the DDRB Register. The value stored in register r16 prior to the function is called is transferred to the slave device, and when the transfer is completed the data received from the slave is stored back into the r16 register.

The second and third instructions clears the USI Counter Overflow Flag and the USI counter value. The fourth and fifth instruction set Three-wire mode, positive edge Shift Register clock, count at USITC strobe, and toggle SCK (PORTB2). The loop is repeated 16 times.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

The following code demonstrates how to use the USI module as a SPI Master with maximum speed (fsck = fck/2):

SPITransfer_Fast:

out USIDR,r16

ldi r16,(1<<USIWM0)+(0<<USICS0)+(1<<USITC)

ldi r17,(1<<USIWM0)+(0<<USICS0)+(1<<USITC)+(1<<USICLK)

out USICR,r16 ; MSB

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16

out USICR,r17

out USICR,r16 ; LSB

out USICR,r17

in r16,USIDR

ret

SPI Slave Operation Example The following code demonstrates how to use the USI module as a SPI slave:

init:

ldi r16,(1<<USIWM0)+(1<<USICS1)

out USICR,r16

...

SlaveSPITransfer:

out USIDR,r16

ldi r16,(1<<USIOIF)

out USISR,r16

SlaveSPITransfer_loop:

sbis USISR,USIOIF

rjmp SlaveSPITransfer_loop

in r16,USIDR

ret

The code is size optimized using only 8 instructions (+ ret). The code example assumes that the DO is configured as output and SCK pin is configured as input in the DDRB Register. The value stored in register r16 prior to the function is called is transferred to

1477F–AVR–12/04

the master device, and when the transfer is completed the data received from the master is stored back into the r16 register.

Note that the first two instructions is for initialization only and needs only to be executed once.These instructions sets Three-wire mode and positive edge Shift Register clock. The loop is repeated until the USI Counter Overflow Flag is set.

Two-wire Mode The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew

rate limiting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.

Figure 47. Two-wire Mode Operation, Simplified Diagram

VCC

SDA

HOLD

SCL

PBy

PBz

SCL

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

SLAVE

Two-wire Clock

Control Unit

SDA

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

PORTBz

MASTER

PBy

PBz

SCL

Figure 47 shows two USI units operating in Two-wire mode, one as master and one as slave. It is only the physical layer that is shown since the system operation is highly dependent of the communication scheme used. The main differences between the master and slave operation at this level, is the serial clock generation which is always done by the master, and only the slave uses the clock control unit. Clock generation must be implemented in software, but the shift operation is done automatically by both devices. Note that only clocking on negative edge for shifting data is of practical use in this mode. The slave can insert wait states at start or end of transfer by forcing the SCL clock low. This means that the master must always check if the SCL line was actually released after it has generated a positive edge.

Since the clock also increments the counter, a counter overflow can be used to indicate that the transfer is completed. The clock is generated by the master by toggling the PB2 pin via the PORTB Register.

The data direction is not given by the physical layer. A protocol, like the one used by the TWI-bus, must be implemented to control the data flow.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

Figure 48. Two-wire Mode, Typical Timing Diagram

SDA

SCL

A B D EC F

1 - 7 8 9

ADDRESS

R/W ACK ACK

Referring to the timing diagram (Figure 48.), a bus transfer involves the following steps:

1. The a start condition is generated by the master by forcing the SDA low line while

the SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of the Shift Register, or by setting the PORTB0 bit to zero. Note that DDRB0 must be set to one for the output to be enabled. The slave device’s start detector logic (Figure 49.) detects the start condition and sets the USISIF flag. The flag can generate an interrupt if necessary.

2. In addition, the start detector will hold the SCL line low after the master has

forced an negative edge on this line (B). This allows the slave to wake up from sleep or complete its other tasks, before setting up the Shift Register to receive the address by clearing the start condition flag and reset the counter.

3. The master set the first bit to be transferred and releases the SCL line (C). The

slave samples the data and shift it into the serial register at the positive edge of the SCL clock.

4. After eight bits are transferred containing slave address and data direction (read

or write), the slave counter overflows and the SCL line is forced low (D). If the slave is not the one the master has addressed it releases the SCL line and waits for a new start condition.

5. If the slave is addressed it holds the SDA line low during the acknowledgment

cycle before holding the SCL line low again (i.e., the Counter Register must be set to 14 before releasing SCL at (D)). Depending of the R/W bit the master or slave enables its output. If the bit is set, a master read operation is in progress (i.e., the slave drives the SDA line) The slave can hold the SCL line low after the acknowledge (E).

6. Multiple bytes can now be transmitted, all in same direction, until a stop condition

is given by the master (F). Or a new start condition is given.

1 - 8 9

DATA ACK

1 - 8 9

DATA

1477F–AVR–12/04

If the slave is not able to receive more data it does not acknowledge the data byte it has last received. When the master does a read operation it must terminate the operation by force the acknowledge bit low after the last byte transmitted.

Figure 49. Start Condition Detector, Logic Diagram

USISIF

CLOCK HOLD

SDA

SCL

Write( USISIF)

CLR

Start Condition Detector The start condition detector is shown in Figure 49. The SDA line is delayed (in the range

of 50 to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is only enabled in Two-wire mode.

The start condition detector is working asynchronously and can therefore wake up the processor from the Power-down sleep mode. However, the protocol used might have restrictions on the SCL hold time. Therefore, when using this feature in this case the oscillator start-up time set by the CKSEL Fuses (see “Clock Systems and their Distribution” on page 22) must also be taken into the consideration. Refer to the description of “Bit 7 – USISIF: Start Condition Interrupt Flag” on page 81 for further details.

Alternative USI Usage When the USI unit is not used for serial communication, it can be set up to do alternative

tasks due to its flexible design.

Half-duplex Asynchronous Data Transfer

4-bit Counter The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note

12-bit Timer/Counter Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit

Edge Triggered External Interrupt

Software Interrupt The counter overflow interrupt can be used as a software interrupt triggered by a clock

By utilizing the Shift Register in Three-wire mode, it is possible to implement a more compact and higher performance UART than by software only.

that if the counter is clocked externally, both clock edges will generate an increment.

counter.

By setting the counter to maximum value (F) it can function as an additional external interrupt. The overflow flag and interrupt enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.

strobe.

ATtiny26(L)

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ATtiny26(L)

Analog Comparator The Analog Comparator compares the input values on the positive pin PA6 (AIN0) and

negative pin PA7 (AIN1). When the voltage on the positive pin PA6 (AIN0) is higher than the voltage on the negative pin PA7 (AIN1), the Analog Comparator Output, ACO is set (one). The comparator’s output can trigger a separate interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in the Figure 50.

Figure 50. Analog Comparator Block Diagram

ACBG

PA6

(AIN0)

PA7

(AIN1)

MUX

Analog Comparator Control and Status Register – ACSR

ACME

MULTIPLEXER OUTPUT

Bit 76543210

$08 ($28) ACD ACBG ACO ACI ACIE ACME ACIS1 ACIS0 ACSR

Read/Write R/W R/W R R/W R/W R/W R/W R/W

Initial Value 0 0 X 0 0 0 0 0

ADC

• Bit 7 – ACD: Analog Comparator Disable

When this bit is set(one), the power to the Analog Comparator is switched off. This bit can be set at any time to turn off the Analog Comparator. 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.

• Bit 6 – ACBG: Analog Comparator Bandgap Select

When this bit is set (one), it selects internal bandgap reference voltage (1.18V) as the positive comparator input.

• Bit 5 – ACO: Analog Comparator Output

ACO is directly connected to the comparator output.

1477F–AVR–12/04

• Bit 4 – ACI: Analog Comparator Interrupt Flag

This bit is set (one) when a comparator output event triggers the interrupt mode defined by ACI1 and ACI0. The Analog Comparator Interrupt routine is executed if the ACIE bit is set (one) and the I-bit in SREG is set (one). ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.

• Bit 3 – ACIE: Analog Comparator Interrupt Enable

When the ACIE bit is set (one) and the I-bit in the Status Register is set (one), the Analog Comparator interrupt is activated. When cleared (zero), the interrupt is disabled.

• Bit 2 – ACME: Analog Comparator Multiplexer Enable

When the ACME bit is set (one) and the ADC is switched off (ADEN in ADCSR is zero), MUX3...0 in ADMUX select the input pin to replace the negative input to the Analog Comparator, as shown in Table 42 on page 93. If ACME is cleared (zero) or ADEN is set (one), PA7(AIN1) is applied to the negative input to the Analog Comparator.

• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select

These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings are shown in Table 41.

Table 41. ACIS1/ACIS0 Settings

ACIS1 ACIS0 Interrupt Mode

0 0 Comparator Interrupt on Output Toggle

01Reserved

1 0 Comparator Interrupt on Falling Output Edge

1 1 Comparator Interrupt on Rising Output Edge

Note: 1. When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be dis-

abled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the bits are changed.

(1)

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

Table 42. Analog Comparator Input Selection

ACME ADEN MUX3...0

0 X XXXX AIN1

1 1 XXXX AIN1

1 0 0000 ADC0

1 0 0001 ADC1

1 0 0010 ADC2

1 0 0011 ADC3

1 0 0100 ADC4

1 0 0101 ADC5

1 0 0110 ADC6

1 0 0111 ADC7

1 0 1000 ADC8

1 0 1001 ADC9

1 0 1010 ADC10

1 0 1011 Undefined

1 0 1100 Undefined

(3)

Analog Comparator Negative Input

(2)

(1)

1 0 1101 Undefined

1 0 1110 Undefined

1 0 1111 Undefined

Notes: 1. MUX4 does not affect Analog Comparator input selection.

2. Pin change interrupt on PA6 and PA7 is disabled if the Analog Comparator is enabled. This happens regardless of whether AIN1 or AIN0 has been replaced as inputs to the Analog Comparator.

3. The MUX3...0 selections go into effect after one clock cycle delay.

1477F–AVR–12/04

Analog to Digital Converter

Features • 10-bit Resolution

• ±2 LSB Absolute Accuracy

• 0.5 LSB Integral Non-linearity

• Optional Offset Cancellation

• 13 - 260 µs Conversion Time

• 11 Multiplexed Single Ended Input Channels

• 8 Differential Input Channels

• 7 Differential Input Channels with Optional Gain of 20x

• Optional Left Adjustment for ADC Result Readout

• 0 - AVCC ADC Input Voltage Range

• Selectable ADC Reference Voltage

• Free Running or Single Conversion Mode

• Interrupt on ADC Conversion Complete

• Sleep Mode Noise Canceler

The ATtiny26(L) features a 10-bit successive approximation ADC. The ADC is connected to an 11-channel Analog Multiplexer which allows eight differential voltage input combinations or 11 single-ended voltage inputs constructed from seven pins from Port A and four pins from Port B. Seven of the differential inputs are equipped with a programmable gain stage, providing amplification steps of 0 dB (1x) and 26 dB (20x) on the differential input voltage before the A/D conversion. There are four groups of three differential analog input channel selections. All input channels in each group share a common negative terminal, while another ADC input can be selected as the positive input terminal. The single-ended voltage inputs refer to 0V (GND).

The ADC contains a Sample and Hold Amplifier 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 51.

The ADC has an analog supply voltage pin, AVCC. The voltage on AVCC must not differ more than ±0.3V from V page 105 on how to connect these pins.

An internal reference voltage of nominally 2.56V is provided On-chip, and this reference may be externally decoupled at the AREF pin by a capacitor.

. See the paragraph “ADC Noise Canceling Techniques” on

ATtiny26(L)

1477F–AVR–12/04

Figure 51. Analog to Digital Converter Block Schematic

ADC CONVERSION

COMPLETE IRQ

8-BIT DATA BUS

ADC MULTIPLEXER

SELECT (ADMUX)

REFS0

REFS1

ADLAR

MUX2

MUX4

MUX1

MUX3

MUX DECODER

MUX0

ADC CTRL. & STATUS

ADIF

ADFR

ADEN

ADSC

ADIE

ADIF

ADPS1

ADPS2

PRESCALER

ATtiny26(L)

15 0

ADC DATA REGISTER

(ADCH/ADCL)

ADPS0

ADC[9:0]

VCC

AREF

GND

ADC10

ADC9

ADC8

ADC7

ADC6

ADC5

ADC4

ADC3

ADC2

ADC1

ADC0

INTERNAL

2.56 V

REFERENCE

INTERNAL 1.18 V

REFERENCE

POS.

INPUT

MUX

NEG.

INPUT

MUX

CHANNEL SELECTION

GAIN SELECTION

SINGLE ENDED /

DIFFERENTIAL SELECTION

GAIN AMPLIFIER

10-BIT DAC

CONVERSION LOGIC

SAMPLE & HOLD COMPARATOR

ADC

MULTIPLEXER OUTPUT

Operation The ADC converts an analog input voltage to a 10-bit digital value through successive

approximation. The minimum value represents GND and the maximum value represents the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or and internal 2.56V reference voltage may be connected to the AREF pin by writing to the REFS bits in ADMUX. The internal voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve noise immunity.

The analog input channel and differential gain are selected by writing to the MUX bits in ADMUX. Any of the 11 ADC input pins ADC10..0, as well as GND and a fixed bandgap voltage reference of nominally 1.18V (V the ADC. A selection of ADC input pins can be selected as positive and negative inputs to the differential gain amplifier.

If differential channels are selected, the differential gain stage amplifies the voltage difference between the selected input channel pair by the selected gain factor. Note that the voltage on the positive input terminal must be higher than on the negative input ter-

1477F–AVR–12/04

), can be selected as single ended inputs to

minal, otherwise the gain stage will saturate at 0V (GND). This amplified value then becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is bypassed altogether.

The ADC can operate in two modes – Single Conversion and Free Running mode. In Single Conversion mode, each conversion will have to be initiated by the user. In Free Running mode, the ADC is constantly sampling and updating the ADC Data Register. The ADFR bit in ADCSR selects between the two available modes.

The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSR. 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.

A conversion 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 set to zero 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.

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. 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 registers 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.

Prescaling and Conversion Timing

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.

Figure 52. ADC Prescaler

ADEN

ADPS0 ADPS1 ADPS2

Reset

7-BIT ADC PRESCALER

CK/2

CK/4

ADC CLOCK SOURCE

CK/8

CK/16

CK/32

CK/64

CK/128

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

The successive approximation circuitry requires an input clock frequency between 50 kHz and 200 kHz. The ADC module contains a prescaler, which divides the system clock to an acceptable ADC clock frequency.

The ADPS bits in ADCSR are used to generate a proper ADC clock input frequency from any chip clock frequency above 100 kHz. The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit in ADCSR. The prescaler keeps running for as long as the ADEN bit is set, and is continuously reset when ADEN is low.

When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at the following rising edge of the ADC clock cycle. If differential channels are selected, the conversion will only start at every other rising edge of the ADC clock cycle after ADEN was set.

A normal conversion takes 13 ADC clock cycles. In certain situations, the ADC needs more clock cycles to initialization and minimize offset errors. Extended conversions take 25 ADC clock cycles and occur as the first conversion after the ADC is switched on (ADEN in ADCSR is set).

Special care should be taken when changing differential channels. Once a differential channel has been selected, the gain stage may take as much as 125 µs to stabilize to the new value. Thus conversions should not be started within the first 125 µs after selecting a new differential channel. Alternatively, conversions results obtained within this period should be discarded. The same settling time should be observed for the first differential conversion after changing ADC reference (by changing the REFS1:0 bits in ADMUX).

The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock cycles after the start of an extended 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. In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. Using Free Running mode and an ADC clock frequency of 200 kHz gives the lowest conversion time, 65

µs, equivalent to

15 kSPS. For a summary of conversion times, see Table 43.

Figure 53. ADC Timing Diagram, Extended Conversion (Single Conversion Mode)

Next Conversion

1 2

MSB of Result

LSB of Result

MUX and REFS Update

Cycle Number

ADC Clock

ADEN

ADSC

ADIF

ADCH

ADCL

1 2121314 15

MUX and REFS Update

Extended Conversion

16 17

Sample & Hold

18 19 20 21 22 23

Conversion

Complete

24 25

1477F–AVR–12/04

Figure 54. ADC Timing Diagram, Single Conversion

One Conversion Next Conversion

Cycle Number

ADC Clock

ADSC

ADIF

ADCH

ADCL

1 2 3 4 5 6 7 8 9 10 11 12 13

Sample & Hold

MUX and REFS Update

Conversion

Complete

Figure 55. ADC Timing Diagram, Free Running Conversion

One Conversion Next Conversion

Cycle Number

ADC Clock

ADSC

ADIF

ADCH

11 12 13

MSB of Result

LSB of Result

MUX and REFS Update

Changing Channel or Reference Selection

ADCL

Conversion

Complete

LSB of Result

Sample & Hold

MUX and REFS Update

Table 43. ADC Conversion Time

Sample & Hold (Cycles from

Condition

Start of Conversion)

Extended conversion 13.5 25 125 - 500

Normal conversions 1.5 13 65 - 260

Conversion

Time (Cycles)

Conversion

Time (µs)

The MUXn and REFS1:0 bits 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 ADCSR 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.

ATtiny26(L)

1477F–AVR–12/04

ATtiny26(L)

Special care should be taken when changing differential channels. Once a differential channel has been selected, the gain stage may take as much as 125 µs to stabilize to the new value. Thus conversions should not be started within the first 125 µs after selecting a new differential channel. Alternatively, conversion results obtained within this period should be discarded.

The same settling time should be observed for the first differential conversion after changing ADC reference (by changing the REFS1:0 bits in ADMUX).

ADC Noise Canceler Function

The ADC features a noise canceler that enables conversion during ADC Noise Reduction mode (see “Power Management and Sleep Modes” on page 36) to reduce noise induced from the CPU core and other I/O peripherals. If other I/O peripherals must be active during conversion, this mode works equivalently for Idle mode. To make use of this feature, the following procedure should be used:

1. 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. ADEN = 1 ADSC = 0 ADFR = 0 ADIE = 1

2. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted.

3. 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.

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

1024⋅

ADC

--------------------------=

REF

1477F–AVR–12/04

where V

is the voltage on the selected input pin and V

the selected voltage refer-

REF

ence (see Table 45 on page 101 and Table 46 on page 102). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one LSB.

If differential channels are used, the result is

–()GAIN 1024⋅⋅

ADC

where V

is the voltage on the positive input pin, V

POS

input pin, GAIN the selected gain factor, and V in mind that V

must be higher than V

POS

POSVNEG

---------------------------------------------------------------------------=

REF

the voltage on the negative

NEG

the selected voltage reference. Keep

REF

, otherwise, the ADC value will saturate at

NEG

0x000. Figure 56 shows the decoding of the differential input range.

Table 44 shows the resulting output codes if the differential input channel pair (ADCn ADCm) is selected with a gain of GAIN and a reference voltage of V

REF

Figure 56. Differential Measurement Range

Output Code

0x3FF

0x000

REF

/GAIN

Differential Input Voltage (Volts)

Table 44. Correlation Between Input Voltage and Output Codes

ADCn

+ V

ADCm

+ (1023/1024) V

ADCm

+ (1022/1024) V

ADCm

/GAIN 0x3FF 1023

REF

/GAIN 0x3FF 1023

REF

/GAIN 0x3FE 1022

REF

Read code Corresponding decimal value

... ... ...

ADCm

+ (1/1024) V

/GAIN 0x001 1

REF

0x000 0

Example: ADMUX = 0xEB (ADC0 - ADC1, 20x gain, 2.56V reference, left adjusted result)

Voltage on ADC0 is 400 mV, voltage on ADC1 is 300 mV. ADCR = 1024 * 20 * (400 - 300) / 2560 = 800 = 0x320

ADCL will thus read 0x00, and ADCH will read 0xC8. Writing zero to ADLAR right adjusts the result: ADCL = 0x20, ADCH = 0x03.

100

ATtiny26(L)

1477F–AVR–12/04

ATMEL ATtiny26, ATtiny26L User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

Pin Configuration

Description The ATtiny26(L) is a low-power CMOS 8-bit microcontroller based on the AVR

Block Diagram Figure 1. The ATtiny26(L) Block Diagram

Pin Descriptions

AVCC AVCC is the supply voltage pin for Port A and the A/D Converter (ADC). It should be

Port A (PA7..PA0) Port A is an 8-bit general purpose I/O port. PA7..PA0 are all I/O pins that can provide

Port B (PB7..PB0) Port B is an 8-bit general purpose I/O port. PB6..0 are all I/O pins that can provide inter-

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier.

About Code Examples

AVR CPU Core

Architectural Overview The fast-access Register File concept contains 32 x 8-bit general purpose working reg-

General Purpose Register File

Program and Data Addressing Modes

Register Direct, Single Register Rd

I/O Direct Figure 7. I/O Direct Addressing

Data Direct Figure 8. Direct Data Addressing

Figure 9. Data Indirect with Displacement

Data Indirect Figure 10. Data Indirect Addressing

Constant Addressing Using the LPM Instruction

Indirect Program Addressing, IJMP and ICALL

Relative Program Addressing, RJMP and RCALL

Memories The AVR CPU is driven by the System Clock Ø, directly generated from the external

In-System Programmable Flash Program Memory

SRAM Data Memory Figure 19 above shows how the ATtiny26(L) SRAM Memory is organized.

EEPROM Data Memory The ATtiny26(L) contains 128 bytes of data EEPROM memory. It is organized as a sep-

EEPROM Read/Write Access The EEPROM Access Registers are accessible in the I/O space.

Preventing EEPROM Corruption

I/O Memory The I/O space definition of the ATtiny26(L) is shown in Table 2

System Clock and Clock Options

Clock Systems and their Distribution

Clock Sources The device has the following clock source options, selectable by Flash Fuse bits as

Default Clock Source The deviced is shipped with CKSEL = “0001”, SUT = “10”, and PLLCK unprogrammed.

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

Low-frequency Crystal Oscillator

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 23

Calibrated Internal RC Oscillator

External Clock To drive the device from an external clock source, XTAL1 should be driven as shown in

System Control and Reset

Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip Detection circuit. The detec-

External Reset An External Reset is generated by a low level on the RESET pin. Reset pulses longer

Brown-out Detection ATtiny26(L) has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one CK cycle dura-

Power Management and Sleep Modes

Idle Mode When the SM1..0 bits are written to “00”, the SLEEP instruction makes the MCU enter

ADC Noise Reduction Mode

Power-down Mode When the SM1..0 bits are written to “10”, the SLEEP instruction makes the MCU enter

Standby Mode When the SM1..0 bits are “11” and an External Crystal/Resonator clock option is

Minimizing Power Consumption

Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should

Analog Comparator When entering Idle mode, the Analog Comparator should be disabled if not used. When

Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned

Table 20. Internal Voltage Reference

Watchdog Timer If the Watchdog Timer is not needed in the application, this module should be turned off.

Port Pins When entering a sleep mode, all port pins should be configured to use minimum power.

I/O Ports

Introduction All AVR ports have true Read-Modify-Write functionality when used as general digital

Ports as General Digital I/O

Configuring the Pin Each port pin consists of 3 Register bits: DDxn, PORTxn, and PINxn. As shown in “Reg-

Reading the Pin Value Independent of the setting of Data Direction bit DDxn, the port pin can be read through

Digital Input Enable and Sleep Modes

Unconnected Pins If some pins are unused, it is recommended to ensure that these pins have a defined

Figure 35. Alternate Port Functions

Alternate Functions of Port A Port A has an alternate functions as analog inputs for the ADC and Analog Comparator

Alternate Functions Of Port B Port B has an alternate functions for the ADC, Clocking, Timer/Counters, USI, SPI pro-

Register Description for I/O Ports

Interrupts

Interrupt Vectors The ATtiny26(L) provides eleven interrupt sources. These interrupts and the separate

Interrupt Handling The ATtiny26(L) has two 8-bit Interrupt Mask Control Registers; GIMSK – General Inter-

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles

External Interrupt The External Interrupt is triggered by the INT0 pin. Observe that, if enabled, the interrupt

Pin Change Interrupt The pin change interrupt is triggered by any change on any I/O pin of Port B and pins

Timer/Counters The ATtiny26(L) provides two general purpose 8-bit Timer/Counters. The

Timer/Counter0 Prescaler

Timer/Counter1 Prescaler