Atmel ATtiny26 User manual

1477G–AVR–03/05
Features
•High-performance, Low-power AVR®8-bit Microcontroller
•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
with 2K Bytes
Flash
ATtiny26
ATtiny26L
Rev. 1477G–AVR–03/05

2ATtiny26(L) 1477G–AVR–03/05
Pin Configuration
Note: Note: The bottom pad under the QFN/MLF package should be soldered to ground.
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
(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
PA0 (ADC0)
PA1 (ADC1)
PA2 (ADC2)
PA3 (AREF)
GND
AVCC
PA4 (ADC3)
PA5 (ADC4)
PA6 (ADC5/AIN0)
PA7 (ADC6/AIN1)
PDIP/SOIC
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
32 31 30 29 28 27 26 25
9 10 11 12 13 14 15 16
MLF Top View
NC
(OC1B) PB3
NC
VCC
GND
NC
(ADC7/XTAL1) PB4
(ADC8/XTAL2) PB5
NC
PA2 (ADC2)
PA3 (AREF)
GND
NC
NC
AVCC
PA4 (ADC3)
NC
(ADC9/INT0/T0) PB6
(ADC10/RESET) PB7
NC
(ADC6/AIN1) PA7
(ADC5/AIN0) PA6
(ADC4) PA5
NC
PB2 (SCK/SCL/OC1B) PB1 (MISO/DO/OC1A) PB0 (MOSI/DI/SDA/OC1A) NC NC NC PA0 (ADC0) PA1 (ADC1)

3
ATtiny26(L)
1477G–AVR–03/05
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 rectifica-
tion. 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 ther-
mostats, 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 hard-
ware 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.
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 effec-
tive 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.

4ATtiny26(L) 1477G–AVR–03/05
Block Diagram Figure 1. The ATtiny26(L) Block Diagram
WATCHDOG
TIMER
MCU CONTROL
REGISTER
UNIVERSAL
SERIAL
INTERFACE
TIMER/
COUNTER0
DATA DIR.
REG.PORT A
DATA REGISTER
PORT A
PROGRAMMING
LOGIC
TIMING AND
CONTROL
TIMER/
COUNTER1
MCU STATUS
REGISTER
PORT A DRIVERS
PA0-PA7
VCC
GND
+
-
ANALOG
COMPARATOR
8-BIT DATA BUS
ADC
ISP INTERFACE
INTERRUPT
UNIT
EEPROM
INTERNAL
OSCILLATOR
OSCILLATORS
CALIBRATED
OSCILLATOR
INTERNAL
DATA DIR.
REG.PORT B
DATA REGISTER
PORT B
PORT B DRIVERS
PB0-PB7
PROGRAM
COUNTER
STACK
POINTER
PROGRAM
FLASH SRAM
GENERAL
PURPOSE
REGISTERS
INSTRUCTION
REGISTER
INSTRUCTION
DECODER
STATUS
REGISTER
Z
Y
X
ALU
CONTROL
LINES
AVCC

5
ATtiny26(L)
1477G–AVR–03/05
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 VCC, even if the ADC is not used. If the ADC is used, it should be
connected to VCC through a low-pass filter. See page 94 for details on operating of the
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.
An External Reset is generated by a low level on the PB7/RESET pin. Reset pulses
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 defini-
tions in the header files and interrupt handling in C is compiler dependent. Please
confirm with the C compiler documentation for more details.

6ATtiny26(L) 1477G–AVR–03/05
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
The ALU supports arithmetic and logic functions between registers or between a con-
stant 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.
1024 x 16
Program
FLASH
Instruction
Register
Instruction
Decoder
Program
Counter
Control Lines
32 x 8
General
Purpose
Registers
ALU
Direct Addressing Indirect Addressing
Status
and Test
Control
Registers
Interrupt
Unit
2 x 8-bit
Timer/Counter
Universal
Serial Interface
Watchdog
Timer
Analog
Comparator
I/O Lines
8-bit Data Bus
ISP Unit
ADC
128 x 8
SRAM
128 byte
EEPROM

7
ATtiny26(L)
1477G–AVR–03/05
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.
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 sep-
arate 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.
General Purpose
Register File 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

8ATtiny26(L) 1477G–AVR–03/05
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 phys-
ically 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 Z-
register 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
In the different addressing modes, these address registers have functions as fixed dis-
placement, automatic increment and decrement (see the descriptions for the different
instructions).
ALU – Arithmetic Logic
Unit The high-performance AVR ALU operates in direct connection with all 32 general pur-
pose 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 catego-
ries – Arithmetic, Logical, and Bit-functions.
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)

9
ATtiny26(L)
1477G–AVR–03/05
Status Register – SREG The AVR Status Register – SREG – at I/O space location $3F is defined as:
• 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 cop-
ied 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 Comple-
ment 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 opera-
tions. 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.
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

10 ATtiny26(L) 1477G–AVR–03/05
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.
The Stack Pointer points to the data SRAM stack area where the Subroutine and Inter-
rupt 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 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.
Register Direct, Single
Register Rd Figure 5. Direct Single Register Addressing
The operand is contained in register d (Rd).
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