ATMEL ATTINY26 8-bit microcontroller with 2k bytes flash Datasheet

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
1477I–AVR–10/06
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
PA0 (ADC0)
PA1 (ADC1)
PA2 (ADC2)
PA3 (AREF)
GND
AVCC
PA4 (ADC3)
PA5 (ADC4)
PA6 (ADC5/AIN0)
PA7 (ADC6/AIN1)
32
31
30
29
28
27
26
25
PB2 (SCK/SCL/OC1B)
PB1 (MISO/DO/OC1A)
PB0 (MOSI/DI/SDA/OC1A)
NC
NC
NC
PA0 (ADC0)
PA1 (ADC1)
MLF Top View
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
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
9
10
11
12
13
14
15
16
NC
(OC1B) PB3
NC
VCC
GND
NC
(ADC7/XTAL1) PB4
(ADC8/XTAL2) PB5
Note:
2
The bottom pad under the QFN/MLF package should be soldered to ground.
ATtiny26(L)
1477I–AVR–10/06
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.
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.
3
1477I–AVR–10/06
Block Diagram
Figure 1. The ATtiny26(L) Block Diagram
VCC
8-BIT DATA BUS
INTERNAL
OSCILLATOR
INTERNAL
CALIBRATED
OSCILLATOR
TIMING AND
CONTROL
GND
PROGRAM
COUNTER
STACK
POINTER
WATCHDOG
TIMER
PROGRAM
FLASH
SRAM
MCU CONTROL
REGISTER
AVCC
INSTRUCTION
REGISTER
MCU STATUS
REGISTER
GENERAL
PURPOSE
REGISTERS
TIMER/
COUNTER0
X
Y
Z
INSTRUCTION
DECODER
TIMER/
COUNTER1
CONTROL
LINES
ALU
UNIVERSAL
SERIAL
INTERFACE
STATUS
REGISTER
INTERRUPT
UNIT
ANALOG
COMPARATOR
+
-
PROGRAMMING
LOGIC
DATA REGISTER
PORT A
DATA DIR.
REG.PORT A
PORT A DRIVERS
PA0-PA7
4
EEPROM
ISP INTERFACE
ADC
OSCILLATORS
DATA REGISTER
PORT B
DATA DIR.
REG.PORT B
PORT B DRIVERS
PB0-PB7
ATtiny26(L)
1477I–AVR–10/06
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 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 96 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 48.
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 internal 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 48.
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.
5
1477I–AVR–10/06
Resources
6
A comprehensive set of development tools, application notes and datasheets are available for download on http://www.atmel.com/avr.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
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.
7
1477I–AVR–10/06
AVR CPU Core
Architectural Overview
The fast-access Register File concept contains 32 x 8-bit general purpose working registers 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
1024 x 16
Program
FLASH
Program
Counter
Status
and Test
32 x 8
General
Purpose
Registers
Instruction
Register
Interrupt
Unit
Universal
Serial Interface
Control Lines
Indirect Addressing
Instruction
Decoder
Direct Addressing
ISP Unit
2 x 8-bit
Timer/Counter
ALU
Watchdog
Timer
128 x 8
SRAM
128 byte
EEPROM
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.
8
ATtiny26(L)
1477I–AVR–10/06
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.
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.
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
9
1477I–AVR–10/06
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
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
X-register
7
0
0
R27 ($1B)
7
15
Y-register
7
0
0
R29 ($1D)
7
7
R31 ($1F)
0
R28 ($1C)
15
Z-register
0
R26 ($1A)
0
0
7
0
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).
ALU – Arithmetic Logic
Unit
10
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)
1477I–AVR–10/06
ATtiny26(L)
Status Register – SREG
The AVR Status Register – SREG – at I/O space location $3F is defined as:
Bit
7
6
5
4
3
2
1
0
$3F ($5F)
I
T
H
S
V
N
Z
C
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
SREG
• 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.
11
1477I–AVR–10/06
Stack Pointer – SP
The ATtiny26(L) Stack Pointer is implemented as an 8-bit register in the I/O space location $3D ($5D). As the ATtiny26(L) data memory has 224 ($E0) locations, eight bits are
used.
Bit
7
6
5
4
3
2
1
0
$3D ($5D)
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
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
SP
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
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).
12
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Register Direct, Two Registers
Rd and Rr
Figure 6. Direct Register Addressing, Two Registers
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
Data Space
20 19
31
OP
16
$0000
Rr/Rd
16 LSBs
15
0
$00DF
13
1477I–AVR–10/06
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
Displacement
Figure 9. Data Indirect with Displacement
Data Space
$0000
15
0
Y OR Z - REGISTER
15
10
OP
6 5
n
0
a
$00DF
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
Data Space
$0000
15
0
X-, Y-, OR Z-REGISTER
$00DF
Operand address is the contents of the X-, Y-, or the Z-register.
Data Indirect with Predecrement
Figure 11. Data Indirect Addressing with Pre-decrement
Data Space
$0000
15
0
X-, Y-, OR Z-REGISTER
-1
$00DF
14
ATtiny26(L)
1477I–AVR–10/06
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
Figure 12. Data Indirect Addressing with Post-increment
Data Space
$0000
15
0
X-, Y-, OR Z-REGISTER
1
$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.
Constant Addressing Using
the LPM Instruction
Figure 13. Code Memory Constant Addressing
PROGRAM MEMORY
$000
$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).
15
1477I–AVR–10/06
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
+1
$3FF
Program execution continues at address PC + k + 1. The relative address k is from
-2048 to 2047.
16
ATtiny26(L)
1477I–AVR–10/06
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
Register Operands Fetch
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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1477I–AVR–10/06
Figure 18. On-chip Data SRAM Access Cycles
T1
T2
T3
T4
System Clock Ø
Address
Prev. Address
Address
Write
Data
WR
Read
Data
RD
In-System Programmable 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
Flash Program Memory
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 109 for a detailed description
on Flash data downloading. See “Program and Data Addressing Modes” on page 12 for
the different program memory addressing modes.
Figure 19. SRAM Organization
Register File
Data Address Space
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.
18
ATtiny26(L)
1477I–AVR–10/06
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 12 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 separate data space, in which single bytes can be read and written (see “Memory
Programming” on page 109). 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
7
6
5
4
3
2
1
0
$1E ($3E)
–
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
X
X
X
X
X
X
X
EEAR
• 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.
19
1477I–AVR–10/06
EEPROM Data Register –
EEDR
Bit
7
6
5
4
3
2
1
0
$1D ($3D)
MSB
LSB
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
EEDR
• 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
7
6
5
4
3
2
1
0
$1C ($3C)
–
–
–
–
EERIE
EEMWE
EEWE
EERE
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EECR
• 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.
20
ATtiny26(L)
1477I–AVR–10/06
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
Symbol
EEPROM Write (from CPU)
Note:
Number of Calibrated RC
Oscillator Cycles(1)
Typical Programming
Time
8448
8.5 ms
1. Uses 1 MHz clock, independent of CKSEL-Fuse settings.
EEPROM Write During Powerdown Sleep Mode
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.
Preventing EEPROM
Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage 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 VCC. This
will prevent the CPU from attempting to decode and execute instructions, effectively protecting the EEPROM Registers from unintentional writes.
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.
21
1477I–AVR–10/06
I/O Memory
The I/O space definition of the ATtiny26(L) is shown in Table 2
Table 2. ATtiny26(L) I/O Space(1)
22
Address Hex
Name
Function
$3F ($5F)
SREG
Status Register
$3D ($5D)
SP
$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
$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
Stack Pointer
ADC Multiplexer Select Register
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Table 2. ATtiny26(L) I/O Space(1) (Continued)
Address Hex
Name
$06($26)
ADCSR
$05($25)
ADCH
ADC Data Register High
$04($24)
ADCL
ADC Data Register Low
Note:
Function
ADC Control and Status Register
1. Reserved and unused locations are not shown in the table.
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.
23
1477I–AVR–10/06
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 38. The clock systems
are detailed below.
Figure 20. Clock Distribution
Timer/Counter1
General I/O
modules
ADC
CPU Core
Flash and
EEPROM
RAM
clkADC
clkI/O
AVR Clock
Control Unit
clkCPU
clkFLASH
Reset Logic
Source clock
Watchdog clock
Clock
Multiplexer
clkPCK
Watchdog Timer
Watchdog
Oscillator
clkPLL
PLL
External RC
Oscillator
External clock
Crystal
Oscillator
Low-Frequency
Crystal Oscillator
Calibrated RC
Oscillator
CPU Clock – clkCPU
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.
I/O Clock – clkI/O
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.
Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually
active simultaneously with the CPU clock.
ADC Clock – clkADC
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.
24
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Internal PLL for Fast
Peripheral Clock Generation –
clkPCK
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 25. 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
PLLCK &
CKSEL
FUSES
OSCCAL
PLOCK
Lock
Detector
1
RC OSCILLATOR 2
4
8 MHz
DIVIDE
TO 1 MHz
PCK
PLL
64x
DIVIDE
BY 4
CK
XTAL1
XTAL2
OSCILLATORS
25
1477I–AVR–10/06
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(1)
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
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
26
ATtiny26(L)
1477I–AVR–10/06
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
C2
XTAL2
C1
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
CKSEL3..1
Frequency
Range (MHz)
Recommended Range for Capacitors C1 and
C2 for Use with Crystals (pF)
101(1)
0.4 - 0.9
–
110
0.9 - 3.0
12 - 22
3.0 - 16
12 - 22
16 -
12 - 15
111
Note:
1. This option should not be used with crystals, only with ceramic resonators.
27
1477I–AVR–10/06
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
CKSEL0
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (VCC = 5.0V)
0
00
258 CK(1)
4.1 ms
Ceramic resonator,
fast rising power
0
01
258 CK(1)
65 ms
Ceramic resonator,
slowly rising power
0
10
1K CK(2)
–
Ceramic resonator,
BOD enabled
0
11
1K CK(2)
4.1 ms
Ceramic resonator,
fast rising power
1
00
1K CK(2)
65 ms
Ceramic resonator,
slowly rising power
1
01
16K CK
–
1
10
16K CK
4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
65 ms
Crystal Oscillator,
slowly rising power
Notes:
Low-frequency Crystal
Oscillator
Recommended
Usage
Crystal Oscillator,
BOD enabled
1. These options should only be used when not operating close to the maximum frequency 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.
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
SUT1..0
Additional Delay from
Reset (VCC = 5.0V)
Recommended Usage
(1)
4.1 ms
Fast rising power or BOD enabled
01
(1)
1K CK
65 ms
Slowly rising power
10
32K CK
65 ms
Stable frequency at start-up
00
11
Note:
28
Start-up Time
from Power-down
1K CK
Reserved
1. These options should only be used if frequency stability at start-up is not important
for the application.
ATtiny26(L)
1477I–AVR–10/06
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
VCC
PB5 (XTAL2)
R
XTAL1
C
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
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
18 CK
–
01
18 CK
4.1 ms
Fast rising power
10
18 CK
65 ms
Slowly rising power
11
(1)
4.1 ms
Fast rising power or BOD enabled
Notes:
6 CK
Recommended Usage
BOD enabled
1. This option should not be used when operating close to the maximum frequency of
the device.
29
1477I–AVR–10/06
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 VCC 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 111.
Table 11. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
Nominal Frequency (MHz)
(1)
1.0
0001
Note:
0010
2.0
0011
4.0
0100
8.0
1. The device is shipped with this option selected.
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.
Table 12. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0
Start-up Time from
Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
–
01
6 CK
4.1 ms
Fast rising power
6 CK
65 ms
Slowly rising power
(1)
10
11
Note:
Oscillator Calibration Register
– OSCCAL
Recommended Usage
BOD enabled
Reserved
1. The device is shipped with this option selected.
Bit
$31 ($51)
Read/Write
Initial Value
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
OSCCAL
Device Specific Calibration Value
• 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
30
ATtiny26(L)
1477I–AVR–10/06
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.
External Clock
OSCCAL Value
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
$00
50%
100%
$7F
75%
150%
$FF
100%
200%
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
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
SUT1..0
Start-up Time from
Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
–
01
6 CK
4.1 ms
Fast rising power
10
6 CK
65 ms
Slowly rising power
11
Recommended Usage
BOD enabled
Reserved
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.
31
1477I–AVR–10/06
High Frequency PLL
Clock – PLLCLK
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 25.
Table 15. Start-up Times for the PLLCK
32
SUT1..0
Start-up Time from
Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
1K CK
–
01
1K CK
4.1 ms
Fast rising power
10
1K CK
65 ms
Slowly rising power
11
16K CK
–
Slowly rising power
Recommended Usage
BOD enabled
ATtiny26(L)
1477I–AVR–10/06
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 (VPOT).
• 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
RESET pin for more than 500 ns.
• 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 VCC is below the Brown-out
Reset threshold (VBOT).
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 BUS
PORF
BORF
EXTRF
WDRF
MCU Status
Register (MCUSR)
BODEN
BODLEVEL
Brown-Out
Reset Circuit
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
33
1477I–AVR–10/06
Table 16. Reset Characteristics
Symbol
VPOT
Parameter
Condition
Min
Typ
Max
Units
Power-on Reset Threshold
Voltage (rising)
1.4
2.3
V
Power-on Reset Threshold
Voltage (falling)(1)
1.3
2.3
V
0.9
VCC
1.5
µs
VRST
RESET Pin Threshold Voltage
tRST
Minimum pulse width on
RESET Pin
Brown-out Reset Threshold
Voltage(2)
BODLEVEL = 1
2.4
2.7
2.9
VBOT
BODLEVEL = 0
3.7
4.0
4.5
Minimum low voltage period for
Brown-out Detection
BODLEVEL = 1
2
µs
tBOD
BODLEVEL = 0
2
µs
VHYST
Brown-out Detector hysteresis
130
mV
Notes:
0.2
V
1. The Power-on Reset will not work unless the supply voltage has been below VPOT
(falling)
2. VBOT may be below nominal minimum operating voltage for some devices. For
devices where this is the case, the device is tested down to VCC = VBOT during the
production test. This guarantees that a Brown-out Reset will occur before VCC 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 24.
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 detection level is defined in Table 16 The POR is activated whenever V CC is below the
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 CC rise. The time-out
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 24. The RESET signal is activated again, without any delay, when the
VCC decreases below detection level.
34
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 26. MCU Start-up, RESET Tied to VCC
VCC
RESET
VPOT
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
Figure 27. MCU Start-up, RESET Controlled Externally
VCC
VPOT
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
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 – VRST – on its positive edge, the delay timer starts the MCU after the Time-out
period tTOUT has expired.
Figure 28. External Reset During Operation
VCC
RESET
VRST
t TOUT
TIME-OUT
INTERNAL
RESET
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1477I–AVR–10/06
Brown-out Detection
ATtiny26(L) has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC
level during the operation. The BOD circuit can be enabled/disabled by the fuse
BODEN. When the BOD is enabled (BODEN programmed), and VCC decreases below
the trigger level, the Brown-out Reset is immediately activated. When VCC increases
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.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level
for longer than tBOD given in Table 16.
Figure 29. Brown-out Reset During Operation
VCC
VBOT-
VBOT+
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out period
tTOUT. Refer to page 80 for details on operation of the Watchdog.
Figure 30. Watchdog Time-out
1 CK Cycle
36
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
MCU Status Register –
MCUSR
Bit
7
6
5
4
3
2
1
0
$34 ($54)
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
MCUSR
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.
37
1477I–AVR–10/06
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 40 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
7
6
5
4
3
2
1
0
$35 ($55)
–
PUD
SE
SM1
SM0
–
ISC01
ISC00
Read/Write
R
R/W
R/W
R/W
R/W
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• 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 44 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.
38
ATtiny26(L)
1477I–AVR–10/06
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(1)
ISC01
ISC00
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:
Idle Mode
Description
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.
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 clkCPU and clkFLASH, while allowing the other clocks to run.
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.
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 clkI/O, clkCPU, and clkFLASH, while allowing the
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 26.
39
1477I–AVR–10/06
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
Sleep Mode
clkCPU
clkFLASH
Idle
ADC Noise
Reduction
Oscillators
clkIO
clkADC
Main Clock
Source Enabled
INT0, and Pin
Change
USI Start
Condition
EEPROM
Ready
ADC
Other I/O
X
X
X
X
X
X
X
X
X
X
X(2)
X
X
X
(2)
X
X
X(2)
X
Power-down
Standby(1)
Notes:
40
Wake-up Sources
X
1. Only recommended with external crystal or resonator selected as clock source.
2. Only level interrupt INT0.
ATtiny26(L)
1477I–AVR–10/06
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 96 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 93 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 36 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
VBG
Bandgap reference voltage
1.15
1.18
1.40
V
tBG
Bandgap reference start-up time
40
70
µs
IBG
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 80 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 (clkI/O) and the ADC clock (clkADC) are stopped, the
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 47 for details on which pins are enabled. If the input buffer is enabled
41
1477I–AVR–10/06
and the input signal is left floating or have an analog signal level close to VCC/2, the
input buffer will use excessive power.
42
ATtiny26(L)
1477I–AVR–10/06
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 VCC and Ground as indicated in Figure 31.
Figure 31. I/O Pin Equivalent Schematic
Rpu
Logic
Pxn
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case
“x” 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 58.
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 44. 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 48. Refer to the individual module sections for a
full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use
of the other pins in the port as general digital I/O.
43
1477I–AVR–10/06
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(1)
PUD
Q
D
DDxn
Q CLR
RESET
WDx
Q
Pxn
D
PORTxn
Q CLR
WPx
DATA BUS
RDx
RESET
RRx
SLEEP
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD:
SLEEP:
clkI/O:
Note:
Configuring the Pin
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
WDx:
RDx:
WPx:
RRx:
RPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
1. WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
Each port pin consists of 3 Register bits: DDxn, PORTxn, and PINxn. As shown in “Register Description for I/O Ports” on page 58, 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
44
ATtiny26(L)
1477I–AVR–10/06
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
Reading the Pin Value
DDxn
PORTxn
PUD
(in MCUCR)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled
low
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output Low (Sink)
1
1
X
Output
No
Output High (Source)
Comment
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 tpd,max and tpd,min
respectively.
Figure 33. Synchronization when Reading an Externally Applied Pin Value
SYSTEM CLK
INSTRUCTIONS
XXX
XXX
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd, max
t 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 tpd,max and tpd,min, a single
45
1477I–AVR–10/06
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 tpd through the synchronizer is one system
clock period.
Figure 34. Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
0xFF
out PORTx, r16
nop
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd
46
ATtiny26(L)
1477I–AVR–10/06
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(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi
r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out
PORTB,r16
out
DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINB;
...
Note:
Digital Input Enable and Sleep
Modes
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 VCC/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 48.
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.
47
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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 VCC 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(1)
PUOExn
PUOVxn
1
PUD
0
DDOExn
DDOVxn
1
Q D
DDxn
0
Q CLR
WDx
PVOExn
RESET
1
Pxn
Q
0
D
PORTxn
Q CLR
DIEOExn
WPx
DATA BUS
RDx
PVOVxn
RESET
DIEOVxn
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
D
RPx
Q
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
Note:
48
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP CONTROL
PUD:
WDx:
RDx:
RRx:
WPx:
RPx:
clkI/O:
DIxn:
AIOxn:
PULLUP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
1. WPx, WDx, RLx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.
ATtiny26(L)
1477I–AVR–10/06
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
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.
PUOV
Pull-up Override
Value
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.
DDOE
Data Direction
Override Enable
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.
DDOV
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled
when DDOV is set/cleared, regardless of the setting of
the DDxn Register bit.
PVOE
Port Value
Override Enable
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.
PVOV
Port Value
Override Value
If PVOE is set, the port value is set to PVOV,
regardless of the setting of the PORTxn Register bit.
DIEOE
Digital Input Enable
Override Enable
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).
DIEOV
Digital Input Enable
Override Value
If DIEOE is set, the Digital Input is enabled/disabled
when DIEOV is set/cleared, regardless of the MCU
state (Normal mode, sleep modes).
DI
Digital Input
This is the Digital Input to alternate functions. In the
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.
AIO
Analog Input/output
This is the Analog Input/Output to/from alternate
functions. The signal is connected directly to the pad,
and can be used bidirectionally.
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.
49
1477I–AVR–10/06
MCU Control Register –
MCUCR
The MCU Control Register contains control bits for general MCU functions.
Bit
7
6
5
4
3
2
1
0
$35 ($55)
–
PUD
SE
SM1
SM0
–
ISC01
ISC00
Read/Write
R
R/W
R/W
R/W
R/W
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• 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 44 for more details about this feature.
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 96. Analog Comparator is described in “Analog Comparator” on
page 93. 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 64.
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)
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 48. 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
50
ATtiny26(L)
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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
PA7/ADC6/
AIN1/PCINT1
PA6/ADC5/
AIN0/PCINT1
PA5/ADC4
PA4/ADC3
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
PCINT1_ENABLE •
ACSR[ACD]
0
0
0
(1)
•
(1)
DIEOE
PCINT1_ENABLE
ACSR[ACD]
DIEOV
1
1
0
0
DI
PCINT1
PCINT1
–
–
AIO
ADC6 INPUT, AIN1
ADC5 INPUT, AIN0
ADC4 INPUT
ADC3 INPUT
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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
PUOV
0
0
0
0
DDOE
ADMUX[REFS0]
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
DIEOE
PCINT1_ENABLE(1) •
~(2)ADMUX[REFS0]
0
0
0
DIEOV
1
0
0
0
DI
PCINT1
–
–
–
AIO
ANALOG REFERENCE INPUT
ADC2 INPUT
ADC1 INPUT
ADC0 INPUT
Notes:
52
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 64
2. Not operator is marked with “~”.
ATtiny26(L)
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ATtiny26(L)
Alternate Functions Of Port B
Port B has an alternate functions for the ADC, Clocking, Timer/Counters, USI, SPI programming and pin change interrupt. The ADC is described in “Analog to Digital
Converter” on page 96, Clocking in “AVR CPU Core” on page 8, timers in
“Timer/Counters” on page 66 and USI in “Universal Serial Interface – USI” on page 82.
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 64. Pin functions in programming modes are
described in “Memory Programming” on page 109. 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)
RESET (External Reset Input)
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)
OC1B (Inverted Timer/Counter1 PWM Output B)
PCINT0 (Pin Change Interrupt 0)
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)
OC1A (Inverted Timer/Counter1 PWM Output A)
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.
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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
54
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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/PCINT0 – Port B, Bit 2
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.
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 and USI clocks SCK/SCL. Digital input is enabled on pin PB2 also
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.
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• 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.
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 inverted output compare
match output OC1A 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 48.
Table 27. Overriding Signals for Alternate Functions in PB7..PB4
Signal
Name
PB7/ADC10/RESET/
PCINT1
PB5/ADC8/XTAL2/
PCINT1
RSTDSBL
0
~ PB5IOENABLE
~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(2) | RSTDSBL(1)
~T0_EXT_CLOCK (6) •
PCINT1_ENABLE(2) |
INT0_ENABLE(4)
PCINT1_ENABLE(2) |
~PB5IOENABLE(3)
PCINT_ ENABLE (2) |
~PB4IOENABLE(3) |
EXT_CLOCK_ENABLE(7)
DIEOV
PCINT1_ENABLE(2) •
~(5)RSTDSBL(1)
1
PCINT1_ENABLE(2) •
PB5IOENABLE(3)
PCINT1_ENABLE(2)•
PB4IOENABLE(3) |
EXT_CLOCK_ENABLE
DI
PCINT1
INT0, T0, PCINT1
PCINT1
External Clock, PCINT1
AIO
ADC10, RESET INPUT
ADC9
ADC8, XTAL2
XTAL1
56
(5)
(3)
PB4/ADC7/XTAL1
PUOE
Notes:
(1)
PB6/ADC9/INT0/TO/
PCINT1
1. RSTDISBL Fuse (active low) is described in section “System Control and Reset” on page 33.
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 64.
3. PB5IOENABLE and PB4IOENABLE are given by the PLLCK and CKSEL Fuses as described in “Clock Sources” on page
26.
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 64.
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 67.
7. External clock is selected by the PLLCK and CKSEL Fuses as described in “Clock Sources” on page 26.
ATtiny26(L)
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ATtiny26(L)
Table 28. Overriding Signals for Alternate Functions in PB3..PB0
Signal Name
PB3/OC1B/PCINT0
PB2/SCK/SCL/OC1B/PCI
NT0
PB1/DO/OC1A/PCINT0
PB0/DI/SDA/OC1A
PUOE
0
USI_TWO-WIRE(3)
0
USI_TWO-WIRE(3)
PUOV
0
0
0
0
0
USI_TWO-WIRE(3)
(3)
DDOE
0
USI_TWO-WIRE
DDOV
0
(USI_SCL_HOLD(4) |
~(8)PORTB2) • DDB2
0
(~SDA | ~PORTB0) •
DDB0
PVOE
OC1B_ENABLE(1)
USI_TWO-WIRE(3) •
DDB2 | OC1B_ENABLE(1)
USI_THREE-WIRE(3) |
OC1A_ENABLE(1)
USI_TWO-WIRE(3)• DDB0
|
OC1A_ENABLE(1)
PVOV
OC1B
~(USI_TWO-WIRE •
DDB2) • OC1B
USI_THREE-WIRE(3) •
DO(6) | ~USI_THREEWIRE • OC1A_ENABLE(1)
• OC1A
~(USI_TWO-WIRE•
DDB0) •
OC1A_ENABLE(1) • OC1A
DIEOE
PCINT0_ENABLE(2) •
~OC1B_ENABLE(1)
~(USI_TWO-WIRE |
USI_THREE-WIRE |
OC1B_ENABLE) •
PCINT0_ENABLE(2) |
USI_START_I.ENABLE(5)
~(USI_THREE-WIRE |
OC1A_ENABLE) •
PCINT0_ENABLE(2)
~(USI_TWO-WIRE(3) |
USI_THREE-WIRE(3) |
OC1A_ENABLE(1)) •
PCINT0_ENABLE(2) |
USI_START_I.ENABLE(5)
DIEOV
1
1
1
1
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 69.
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 64.
3. The Two-wire and Three-wire USI-modes are described in “Universal Serial Interface – USI” on page 82.
4. Shift clock (SCL) hold for USI is in described “Universal Serial Interface – USI” on page 82.
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 82.
6. Data Output (DO) is valid in USI Three-wire mode and the operation is described in “Universal Serial Interface – USI” on
page 82.
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 82.
8. Not operator is marked with “~”.
57
1477I–AVR–10/06
Register Description for
I/O Ports
Port A Data Register – PORTA
Bit
Port A Data Direction Register
– DDRA
Port A Input Pins Address –
PINA
7
6
5
4
3
2
1
0
$1B ($3B)
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
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
6
5
4
3
2
1
0
$1A ($3A)
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
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
6
5
4
3
2
1
0
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$19 ($39)
PORTA
DDRA
PINA
Port B Data Register – PORTB
Bit
7
6
5
4
3
2
1
0
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
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
$18 ($38)
Port B Data Direction Register
– DDRB
Bit
7
6
5
4
3
2
1
0
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
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
$17 ($37)
Port B Input Pins Address –
PINB
Bit
7
6
5
4
3
2
1
0
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$16 ($36)
58
PORTB
DDRB
PINB
ATtiny26(L)
1477I–AVR–10/06
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
ldi
r16, RAMEND
; Main program start
out
SP, r16
;
$009
$00A
RESET:
59
1477I–AVR–10/06
$00B
…
Interrupt Handling
sei
…
…
…
The ATtiny26(L) has two 8-bit Interrupt Mask Control Registers; GIMSK – General Interrupt 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
7
6
5
4
3
2
1
$3B ($5B)
–
INT0
PCIE1
PCIE0
–
–
–
0
–
Read/Write
R
R/W
R/W
R/W
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIMSK
• 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
60
ATtiny26(L)
1477I–AVR–10/06
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 64.
• 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 64.
• 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 64.
• 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
7
6
5
4
3
2
1
0
$3A ($5A)
–
INTF0
PCIF
–
–
–
–
–
Read/Write
R
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIFR
• 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 64.
• Bits 4..0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny26(L) and always read as zero.
Timer/Counter Interrupt Mask
Register – TIMSK
Bit
7
6
5
4
3
2
1
0
$39 ($59)
–
OCIE1A
OCIE1B
–
–
TOIE1
TOIE0
–
TIMSK
61
1477I–AVR–10/06
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
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.
Timer/Counter Interrupt Flag
Register – TIFR
Bit
7
6
5
4
3
2
1
0
$38 ($58)
–
OCF1A
OCF1B
–
–
TOV1
TOV0
–
Read/Write
R
R/W
R/W
R
R
R/W
R/W
R
Initial Value
0
0
0
0
0
0
0
0
TIFR
• 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-
62
ATtiny26(L)
1477I–AVR–10/06
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.
63
1477I–AVR–10/06
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 µs (nominal) at 3.0V and 25°C. The frequency of the Watchdog Oscillator is voltage dependent as shown in “Electrical Characteristics” on page 128.
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, OC1B, OC1B, XTAL1, or
XTAL2 in a fuse selected clock option, Timer0 clocking, or RESET function. See Table
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.
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.
64
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Table 30. Alternative Functions
Pin
Alternate Function
Control Register[Bit Name] which
set the Alternate Function(1)
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
USICR[USIWM1]
USICR[USIWM1,USIWM0]
TCCR1A[COM1A1,COM1A0,PWM1A]
1
01
011
PB1
USI Three-wire mode
TC1 compare/PWM
USICR[USIWM1,USIWM0]
TCCR1A[COM1A1]
TCCR1A[COM1A0]
01
1
1
PB2
USI Two-wire mode
USI Three-wire mode
TC1 compare/PWM
USICR[USIWM1]
USICR[USIWM1,USIWM0]
TCCR1A[COM1B1,COM1B0,PWM1B]
1
01
011
PB3
TC1 compare/PWM
TCCR1A[COM1B1]
TCCR1A[COM1B0]
PB4
XTAL1, clock source
FUSE[PLLCK,CKSEL]
FUSE[PLLCK,CKSEL]
10000
10101-11111
PB5
XTAL2, clock source
FUSE[PLLCK,CKSEL]
11001-11111
PB6
External interrupt
TC0 clock
GIMSK[INT0],MCUCR[ISC01,ISC01]
TCCR0[CS02,CS01]
100
11
PB7
RESET
RSTDISBL FUSE
1
Notes:
Bit or Fuse
Value()
1
1
1. Each line represents a bit or fuse combination which enables the function.
A fuse value of “0” is programmed, “1” is unprogrammed.
65
1477I–AVR–10/06
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
CK/1024
CK/256
CK/64
10-BIT T/C PRESCALER
CLEAR
CK/8
CK
T0(PB6)
0
CS00
CS01
CS02
TIMER/COUNTER0 CLOCK SOURCE
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.
66
ATtiny26(L)
1477I–AVR–10/06
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 74 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
PSR1
T1CK
T1CK/16384
T1CK/8192
T1CK/4096
T1CK/2048
T1CK/1024
T1CK/512
T1CK/256
T1CK/128
T1CK/64
T1CK/32
T1CK/16
0
T1CK/8
14-BIT
T/C PRESCALER
T1CK/4
S
A
T1CK/2
CK
PCK
(64 MHz)
T1CK
PCKE
CS10
CS11
CS12
CS13
TIMER/COUNTER1 COUNT ENABLE
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.
67
1477I–AVR–10/06
Figure 38. Timer/Counter0 Block Diagram
Timer/Counter0 Control
Register – TCCR0
Bit
7
6
5
4
3
2
1
0
$33 ($53)
–
–
–
–
PSR0
CS02
CS01
CS00
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0
• 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
68
CS02
CS01
CS00
Description
0
0
0
Stop, the Timer/Counter0 is stopped
0
0
1
CK
0
1
0
CK/8
0
1
1
CK/64
1
0
0
CK/256
1
0
1
CK/1024
1
1
0
External Pin T0, falling edge
1
1
1
External Pin T0, rising edge
ATtiny26(L)
1477I–AVR–10/06
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
7
6
5
4
3
2
1
0
$32 ($52)
MSB
LSB
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
TCNT0
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 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.
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 76 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
IO-registers
Input syncronization Timer/Counter1
registers
OCR1A
OCR1A_SI
OCR1B
OCR1B_SI
OCR1C
OCR1C_SI
TCCR1A
TCCR1A_SI
TCCR1B
TCCR1B_SI
Output
syncronization
registers
Output
multiplexers
TCNT1
TCNT_SO
S
A
OCF1A
OCF1A_SO
S
A
OCF1B
OCF1B_SO
S
A
TOV1
TOV1_SO
S
A
TCNT1
TCNT1
TCNT1_SI
OCF1A
OCF1A_SI
OCF1B
OCF1B_SI
TOV1
TOV1_SI
PCKE
CK
S
A
S
A
PCK
SYNC
MODE
ASYNC
MODE
1CK delay
1/2PCK -1CK delay
1PCK delay
no 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.
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ATtiny26(L)
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ATtiny26(L)
Figure 40. Timer/Counter1 Block Diagram
CS10
CS11
CS12
CS13
CTC1
T/C CONTROL
REGISTER 1 (TCCR1B)
PSR1
PWM1B
FOC1B
PWM1A
FOC1A
COM1B0
COM1A0
COM1A1
TOV1
T/C CONTROL
REGISTER 1 (TCCR1A)
COM1B1
TOV1
OC1B
(PB3)
OC1B
(PB2)
TOV0
OCF1B
OCF1A
OC1A
(PB1)
OC1A
(PB0)
TIMER INT. FLAG
REGISTER (TIFR)
OCF1A
TIMER INT. MASK
REGISTER (TIMSK)
OCF1B
TOIE1
TOIE0
OCIE1A
OCIE1B
T/C1 OVER- T/C1 COMPARE T/C1 COMPARE
FLOW IRQ MATCH A IRQ MATCH B IRQ
TIMER/COUNTER1
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
T/C1 CONTROL
LOGIC
8-BIT COMPARATOR
8-BIT COMPARATOR
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
(OCR1A)
T/C1 OUTPUT
COMPARE REGISTER
(OCR1B)
T/C1 OUTPUT
COMPARE REGISTER
(OCR1C)
CK
PCK
8-BIT DATA BUS
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.
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.
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Timer/Counter1 Control
Register A – TCCR1A
Bit
7
6
5
4
3
2
1
0
COM1A1
COM1A0
COM1B1
COM1B0
FOC1A
FOC1B
PWM1A
PWM1B
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
$30 ($50)
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 is
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 77 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 is
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 77 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
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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
CTC1
PSR1
–
–
CS13
CS12
CS11
CS10
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
$2F ($4F)
TCCR1B
• 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
Asynchronous Mode
Description
Synchronous Mode
0
Timer/Counter1 is stopped.
Timer/Counter1 is stopped.
0
1
PCK
CK
0
1
0
PCK/2
CK/2
0
0
1
1
PCK/4
CK/4
0
1
0
0
PCK/8
CK/8
0
1
0
1
PCK/16
CK/16
0
1
1
0
PCK/32
CK/32
0
1
1
1
PCK/64
CK/64
1
0
0
0
PCK/128
CK/128
1
0
0
1
PCK/256
CK/256
1
0
1
0
PCK/512
CK/512
1
0
1
1
PCK/1024
CK/1024
1
1
0
0
PCK/2048
CK/2048
1
1
0
1
PCK/4096
CK/4096
1
1
1
0
PCK/8192
CK/8192
1
1
1
1
PCK/16384
CK/16384
CS13
CS12
CS11
CS10
0
0
0
0
0
0
The Stop condition provides a Timer Enable/Disable function.
Timer/Counter1 – TCNT1
Bit
7
6
5
4
3
2
1
0
$2E ($4E)
MSB
LSB
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
TCNT1
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.
Timer/Counter1 Output
Compare RegisterA – OCR1A
Bit
7
6
5
4
3
2
1
0
$2D ($4D)
MSB
LSB
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
OCR1A
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-
74
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
Bit
7
6
5
4
3
2
1
0
$2C ($4C)
MSB
LSB
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
OCR1B
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.
Timer/Counter1 Output
Compare RegisterC – OCR1C
Bit
7
6
5
4
3
2
1
0
$2B ($4B)
MSB
LSB
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
OCR1C
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.
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.
PLL Control and Status
Register – PLLCSR
Bit
7
6
5
4
3
2
1
0
$29 ($29)
–
–
–
–
–
PCKE
PLLE
PLOCK
Read/Write
R
R
R
R
R
R/W
R/W
R
Initial Value
0
0
0
0
0
0
0/1
0
PLLCSR
• 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
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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) and PB2(OC1B), respectively. The non-overlapping output
pairs (OC1A - OC1A 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
OC1x
t 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.
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ATtiny26(L)
Table 35. Compare Mode Select in PWM Mode
COM1x1
COM1x0
Effect on Output Compare Pins
0
0
OC1x not connected.
OC1x not connected.
0
1
OC1x cleared on compare match. Set when TCNT1 = $01.
OC1x set one prescaled cycle after compare match. Cleared when
TCNT1 = $00.
1
0
OC1x cleared on compare match. Set when TCNT1 = $01.
OC1x not connected.
1
1
OC1x set one prescaled cycle after compare match. Cleared when
TCNT = $00
OC1x not connected.
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.
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.
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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:
f TCK1
f PWM = ----------------------------------( OCR1C + 1 )
Resolution shows how many bit is required to express the value in the OCR1C Register.
It is calculated by following equation
ResolutionPWM = log2(OCR1C + 1)
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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
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Watchdog Timer
The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1
MHz. This is the typical value at VCC = 5V. See characterization data for typical values at
other VCC 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 36.
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
WATCHDOG
PRESCLALER
Normally 1 MHz
WATCHDOG
RESET
WDP0
WDP1
WDP2
WDE
MCU RESET
Watchdog Timer Control
Register – WDTCR
Bit
7
6
5
4
3
2
1
0
$21 ($41)
–
–
–
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
WDTCR
• 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:
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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(1)
WDP2
WDP1
WDP0
Number of WDT
Oscillator Cycles
Typical Time-out
at VCC = 3.0V
Typical Time-out
at VCC = 5.0V
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 – Watchdog 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.
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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, fSCLmax = fCK/16)
• Three-wire Synchronous Data Transfer (Master, fSCKmax = fCK/2, Slave fSCKmax = fCK/4)
• 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
USIPF
1
0
4-bit Counter
USIDC
USIOIF
USISIF
DO
(Output only)
PB0
DI/SDA
(Input/Open Drain)
3
2
USIDR
DATA BUS
PB1
Bit0
Bit7
D Q
LE
TIM0 OVF
3
2
0
PB2
1
1
0
SCK/SCL
(Input/Open Drain)
CLOCK
HOLD
[1]
Two-wire Clock
Control Unit
USISR
USITC
USICLK
USICS0
USICS1
USIWM0
USIWM1
USISIE
USIOIE
2
USICR
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.
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ATtiny26(L)
Register Descriptions
USI Data Register – USIDR
Bit
7
6
5
4
3
2
1
0
$0F ($2F)
MSB
LSB
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
USIDR
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
7
6
5
4
3
2
1
0
$0E ($2E)
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
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
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
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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
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
USICR
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 83 for further details.
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.
• 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 83 for further details.
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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.
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.
Table 39. Relations between USIWM1..0 and the USI Operation
USIWM1
USIWM0
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
0
Two-wire mode. Uses SDA (DI) and SCL (SCK) pins(1).
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.
Note:
Description
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.
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• 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
Source
4-bit Counter Clock
Source
0
No Clock
No Clock
0
1
Software clock strobe
(USICLK)
Software clock strobe
(USICLK)
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
(USITC)
1
1
1
External, negative edge
Software clock strobe
(USITC)
USICS1
USICS0
USICLK
0
0
0
• 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.
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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
DO
PBx
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
PBy
Bit0
SCK
PBz
SLAVE
DO
PBx
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
PBy
Bit0
SCK
PBz
PORTBz
MASTER
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
( Reference )
1
2
3
4
5
6
7
8
SCK
SCK
DO
MSB
DI
MSB
A
B
C
D
6
5
4
3
2
1
LSB
6
5
4
3
2
1
LSB
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
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1477I–AVR–10/06
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 indicate 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.
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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
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1477I–AVR–10/06
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
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
PBy
Bit0
PBz
SDA
SCL
HOLD
SCL
Two-wire Clock
Control Unit
SLAVE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
PBy
Bit0
PBz
SDA
SCL
PORTBz
MASTER
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.
90
ATtiny26(L)
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ATtiny26(L)
Figure 48. Two-wire Mode, Typical Timing Diagram
SDA
SCL
S
A
B
1-7
8
9
1-8
9
1-8
9
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
C
D
E
P
F
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.
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
D Q
D Q
CLR
CLR
SDA
CLOCK
HOLD
SCL
Write( USISIF)
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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.
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.
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 24) must also be taken into the consideration. Refer to the description of
“Bit 7 – USISIF: Start Condition Interrupt Flag” on page 83 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
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.
4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note
that if the counter is clocked externally, both clock edges will generate an increment.
12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
Edge Triggered External
Interrupt
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.
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock
strobe.
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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)
MUX
PA7
(AIN1)
MUX
ACME
ADC
MULTIPLEXER OUTPUT
Analog Comparator Control
and Status Register – ACSR
Bit
7
6
5
4
3
2
1
0
$08 ($28)
ACD
ACBG
ACO
ACI
ACIE
ACME
ACIS1
ACIS0
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
ACSR
• 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.
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• 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 95. 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(1)
ACIS1
ACIS0
0
0
Comparator Interrupt on Output Toggle
0
1
Reserved
1
0
Comparator Interrupt on Falling Output Edge
1
1
Comparator Interrupt on Rising Output Edge
Note:
94
Interrupt Mode
1. When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt
can occur when the bits are changed.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Table 42. Analog Comparator Input Selection(1)
ACME
ADEN
MUX3...0(3)
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(2)
1
0
0111
ADC7(2)
1
0
1000
ADC8
1
0
1001
ADC9
1
0
1010
ADC10
1
0
1011
Undefined
1
0
1100
Undefined
1
0
1101
Undefined
1
0
1110
Undefined
1
0
1111
Undefined
Notes:
Analog Comparator Negative Input
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.
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1477I–AVR–10/06
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 VCC. See the paragraph “ADC Noise Canceling Techniques” on
page 107 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.
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ATtiny26(L)
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ATtiny26(L)
Figure 51. Analog to Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
15
ADC[9:0]
ADPS0
ADPS1
ADPS2
ADIF
ADFR
ADEN
ADSC
0
ADC DATA REGISTER
(ADCH/ADCL)
ADC CTRL. & STATUS
REGISTER (ADCSR)
MUX0
MUX2
MUX1
MUX4
MUX3
ADLAR
REFS0
REFS1
ADC MULTIPLEXER
SELECT (ADMUX)
ADIE
ADIF
8-BIT DATA BUS
PRESCALER
VCC
GAIN SELECTION
CHANNEL SELECTION
MUX DECODER
CONVERSION LOGIC
AREF
SAMPLE & HOLD
COMPARATOR
INTERNAL
2.56 V
REFERENCE
10-BIT DAC
+
GND
INTERNAL 1.18 V
REFERENCE
ADC10
ADC9
ADC8
ADC7
SINGLE ENDED /
DIFFERENTIAL SELECTION
ADC6
ADC5
POS.
INPUT
MUX
ADC
MULTIPLEXER OUTPUT
ADC4
ADC3
+
GAIN
AMPLIFIER
ADC2
ADC1
ADC0
NEG.
INPUT
MUX
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 (VBG), can be selected as single ended inputs to
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-
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1477I–AVR–10/06
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.
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.
Prescaling and
Conversion Timing
Figure 52. ADC Prescaler
ADEN
Reset
7-BIT ADC PRESCALER
CK/64
CK/128
CK/32
CK/8
CK/16
CK/4
CK/2
CK
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
98
ATtiny26(L)
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ATtiny26(L)
The successive approximation circuitry requires an input clock frequency between
50 kHz and 200 kHz. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can be as high as 1000 kHz to get a higher sample rate.
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
Extended Conversion
Cycle Number
1
2
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
2
3
ADC Clock
ADEN
ADSC
ADIF
ADCH
MSB of Result
ADCL
LSB of Result
MUX and REFS
Update
Sample & Hold
Conversion
Complete
MUX and REFS
Update
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1477I–AVR–10/06
Figure 54. ADC Timing Diagram, Single Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
Next Conversion
9
10
11
12
13
1
2
3
ADC Clock
ADSC
ADIF
ADCH
MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
MUX and REFS
Update
MUX and REFS
Update
Figure 55. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
11
12
Next Conversion
13
1
2
3
4
ADC Clock
ADSC
ADIF
ADCH
MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
MUX and REFS
Update
Table 43. ADC Conversion Time
Sample & Hold (Cycles from
Start of Conversion)
Conversion
Time (Cycles)
Conversion
Time (µs)
Extended conversion
13.5
25
125 - 500
Normal conversions
1.5
13
65 - 260
Condition
Changing Channel or
Reference Selection
100
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)
1477I–AVR–10/06
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 38) 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
V IN ⋅ 1024
ADC = -------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 45 on page 103 and Table 46 on page 104). 0x000 represents analog
ground, and 0x3FF represents the selected reference voltage minus one LSB.
If differential channels are used, the result is
( V POS – V NEG ) ⋅ GAIN ⋅ 1024
ADC = --------------------------------------------------------------------------V REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative
input pin, GAIN the selected gain factor, and VREF the selected voltage reference. Keep
in mind that VPOS must be higher than VNEG, otherwise, the ADC value will saturate at
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 VREF.
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1477I–AVR–10/06
Figure 56. Differential Measurement Range
Output Code
0x3FF
0x000
0
VREF/GAIN
Differential Input
Voltage (Volts)
Table 44. Correlation Between Input Voltage and Output Codes
VADCn
Read code
Corresponding decimal value
VADCm + VREF /GAIN
0x3FF
1023
VADCm + (1023/1024) VREF /GAIN
0x3FF
1023
VADCm + (1022/1024) VREF /GAIN
0x3FE
1022
...
...
...
VADCm + (1/1024) VREF /GAIN
0x001
1
VADCm
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.
102
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
ADC Multiplexer Selection
Register – ADMUX
Bit
7
6
5
4
3
2
1
0
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
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
$07 ($27)
ADMUX
• Bit 7, 6 – REFS1, REFS0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 45. If these bits
are changed during a conversion, the change will not go in effect until this conversion is
complete (ADIF in ADCSR is set). The user should disregard the first conversion result
after changing these bits to obtain maximum accuracy. If differential channels are used,
using AVCC or an external AREF higher than (AVCC - 0.2V) is not recommended, as
this will affect ADC accuracy. The internal voltage reference may not be used if an
external reference voltage is being applied to the AREF pin.
Table 45. Voltage Reference Selections for ADC
•
REFS1
REFS0
Voltage Reference Selection
0
0
AVCC
0
1
AREF (PA3), Internal Vref turned off.
1
0
Internal Voltage Reference (2.56 V), AREF pin (PA3) not connected.
1
1
Internal Voltage Reference (2.56 V) with external capacitor at AREF pin
(PA3).
Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data
Register. If ADLAR is cleared, the result is right adjusted. If ADLAR is set, the result is
left adjusted. Changing the ADLAR bit will affect the ADC Data Register immediately,
regardless of any ongoing conversions. For a complete description of this bit, see “ADC
Data Register – ADCL and ADCH” on page 106.
• Bits 4..0 – MUX4..MUX0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. These bits also select the gain for the differential channels. See Table 46 for
details. If these bits are changed during a conversion, the change will not go in effect
until this conversion is complete (ADIF in ADCSR is set).
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1477I–AVR–10/06
Table 46. Input Channel and Gain Selections
MUX4..0
Single Ended
Input
00000
ADC0
00001
ADC1
00010
ADC2
00011
ADC3
00100
ADC4
00101
ADC5
00110
ADC6
00111
ADC7
01000
ADC8
01001
ADC9
01010
ADC10
Positive Differential
Input
Negative Differential
Input
Gain
N/A
01011
ADC0
ADC1
20x
01100
ADC0
ADC1
1x
ADC1
ADC1
20x
01110
ADC2
ADC1
20x
01111
ADC2
ADC1
1x
10000
ADC2
ADC3
1x
ADC3
ADC3
20x
10010
ADC4
ADC3
20x
10011
ADC4
ADC3
1x
10100
ADC4
ADC5
20x
10101
ADC4
ADC5
1x
ADC5
ADC5
20x
10111
ADC6
ADC5
20x
11000
ADC6
ADC5
1x
11001
ADC8
ADC9
20x
11010
ADC8
ADC9
1x
ADC9
ADC9
20x
11100
ADC10
ADC9
20x
11101
ADC10
ADC9
1x
(1)
01101
N/A
(1)
10001
N/A
10110(1)
(1)
11011
N/A
11110
1.18V (VBG)
11111
0V (GND)
Note:
104
N/A
N/A
1. For offset measurements only. See “Offset Compensation Schemes” on page 107.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
ADC Control and Status
Register – ADCSR
Bit
7
6
5
4
3
2
1
0
ADEN
ADSC
ADFR
ADIF
ADIE
ADPS2
ADPS1
ADPS0
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
$06 ($26)
ADCSR
• Bit 7 – ADEN: ADC Enable
Writing a logical “1” to this bit enables the ADC. By clearing this bit to zero, the ADC is
turned off. Turning the ADC off while a conversion is in progress, will terminate this
conversion.
• Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, a logical “1” must be written to this bit to start each conversion. In Free Running mode, a logical “1” must be written to this bit to start the first
conversion. The first time ADSC has been written after the ADC has been enabled, or if
ADSC is written at the same time as the ADC is enabled, a dummy conversion will precede the initiated conversion. This dummy conversion performs initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is
complete, it returns to zero. When a dummy conversion precedes a real conversion,
ADSC will stay high until the real conversion completes. Writing a 0 to this bit has no
effect.
• Bit 5 – ADFR: ADC Free Running Select
When this bit is set (one) the ADC operates in Free Running mode. In this mode, the
ADC samples and updates the Data Registers continuously. Clearing this bit (zero) will
terminate Free Running mode.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set (one) when an ADC conversion completes and the data registers are
updated. The ADC Conversion Complete Interrupt is executed if the ADIE bit and the Ibit in SREG are set (one). ADIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical one to the
flag. Beware that if doing a read-modify-write on ADCSR, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is set (one) and the I-bit in SREG is set (one), the ADC Conversion Complete Interrupt is activated.
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1477I–AVR–10/06
• Bits 2..0 – ADPS2..0: ADC Prescaler Select Bits
These bits determine the division factor between the CK frequency and the input clock
to the ADC.
Table 47. ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
ADC Data Register – ADCL
and ADCH
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
$05 ($25)
–
–
–
–
–
–
ADC9
ADC8
ADCH
$04 ($24)
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Read/Write
Initial Value
ADLAR = 1
Bit
15
14
13
12
11
10
9
8
$05 ($25)
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
$04 ($24)
ADC1
ADC0
–
–
–
–
–
–
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Read/Write
Initial Value
When an ADC conversion is complete, the result is found in these two registers. The
ADLAR bit in ADMUX affect the way the result is read from the registers. If ADLAR is
set, the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted. 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.
• ADC9..0: ADC Conversion Result
These bits represent the result from the conversion. For differential channels, this is the
absolute value after gain adjustment, as indicated in Table 46 on page 104. For single
ended channels, $000 represents analog ground, and $3FF represents the selected reference voltage minus one LSB.
106
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Scanning Multiple
Channels
Since change of analog channel always is delayed until a conversion is finished, the
Free Running mode can be used to scan multiple channels without interrupting the converter. Typically, the ADC Conversion Complete interrupt will be used to perform the
channel shift. However, the user should take the following fact into consideration:
The interrupt triggers once the result is ready to be read. In Free Running mode, the
next conversioin will start immediately when the interrupt triggers. If ADMUX is
changed after the interrupt triggers, the next conversion has already started, and the
old setting is used.
ADC Noise Canceling
Techniques
Digital circuitry inside and outside the ATtiny26(L) generates EMI which might affect the
accuracy of analog measurements. If conversion accuracy is critical, the noise level can
be reduced by applying the following techniques:
1. The analog part of the ATtiny26(L) and all analog components in the application
should have a separate analog ground plane on the PCB. This ground plane is
connected to the digital ground plane via a single point on the PCB.
2. Keep analog signal paths as short as possible. Make sure analog tracks run over
the analog ground plane, and keep them well away from high-speed switching
digital tracks.
3. The AVCC pin on the ATtiny26(L) should be connected to the digital VCC supply
voltage via an LC network as shown in Figure 57.
4. Use the ADC noise canceler function to reduce induced noise from the CPU.
5. If some pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress in that port.
Offset Compensation
Schemes
The gain stage has a built-in offset cancellation circuitry that nulls the offset of differential measurements as much as possible. The remaining offset in the analog path can be
measured directly by selecting the same channel for both differential inputs. This offset
residue can be then subtracted in software from the measurement results. Using this
kind of software based offset correction, offset on any channel can be reduced below
one LSB.
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1
20
PA0 (ADC0)
(MISO/DO/OC1A) PB1
2
19
PA1 (ADC1)
(SCK/SCL/OC1B) PB2
3
18
PA2 (ADC2)
(OC1B) PB3
4
17
PA3 (AREF)
5
16
VCC
108
ATtiny26/L
10μΗ
(MOSI/DI/SDA/OC1A) PB0
Analog Ground Plane
Figure 57. ADC Power Connections
GND
AVCC
6
15
(ADC7/XTAL1) PB4
7
14
PA4 (ADC3)
(ADC8/XTAL2) PB5
8
13
PA5 (ADC4)
(ADC9/INT0/T0) PB6
9
12
PA6 (ADC5/AIN0)
(ADC10/RESET) PB7
10
11
PA7 (ADC6/AIN1)
100nF
GND
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Memory
Programming
Program and Data
Memory Lock Bits
The ATtiny26 provides two Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 49. The Lock bits can
only be erased to “1” with the Chip Erase command.
Table 48. Lock Bit Byte(1)
Lock Bit Byte
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
4
–
1 (unprogrammed)
3
–
1 (unprogrammed)
2
–
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
Note:
Bit No
1. “1” means unprogrammed, “0” means programmed
Table 49. Lock Bit Protection Modes
Memory Lock Bits
LB Mode
LB2(2)
LB1(2)
1
1
1
No memory lock features enabled.
0
Further programming of the Flash and EEPROM is
disabled in parallel and serial programming mode. The
Fuse bits are locked in both serial and parallel
programming mode.(1)
0
Further programming and verification of the Flash and
EEPROM is disabled in parallel and serial programming
mode. The Fuse bits are locked in both serial and parallel
programming mode.(1)
2
3
Notes:
1
0
Protection Type
1. Program the Fuse bits before programming the Lock bits.
2. “1” means unprogrammed, “0” means programmed
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Fuse Bits
The ATtiny26 has two Fuse bytes. Table 50 and Table 51 describe briefly the functionality of all the fuses and how they are mapped into the fuse bytes. Note that the fuses are
read as logical zero, “0”, if they are programmed.
Table 50. Fuse High Byte
Fuse High Byte
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
RSTDISBL(2)
4
Select if PB7 is I/O pin or
RESET pin
1 (unprogrammed, PB7 is
RESET pin)
SPIEN(1)
3
Enable Serial Program
and Data Downloading
0 (programmed, SPI prog.
enabled)
EESAVE
2
EEPROM memory is
preserved through the Chip
Erase
1 (unprogrammed, EEPROM not
preserved)
BODLEVEL
1
Brown out detector trigger
level
1 (unprogrammed)
BODEN
0
Notes:
Bit No
Brown out detector enable
1 (unprogrammed, BOD
disabled)
1. The SPIEN Fuse is not accessible in serial programming mode.
2. When programming the RSTDISBL Fuse, Parallel Programming has to be used to
change fuses or perform further programming.
Table 51. Fuse Low Byte
Fuse Low Byte
Bit No
Description
Default Value
PLLCK
7
Use PLL for internal clock
1 (unprogrammed)
CKOPT(3)
6
Oscillator options
1 (unprogrammed)
SUT1
5
Select start-up time
1 (unprogrammed)(1)
SUT0
4
Select start-up time
0 (programmed)(1)
CKSEL3
3
Select Clock source
0 (programmed)(2)
CKSEL2
2
Select Clock source
0 (programmed)(2)
CKSEL1
1
Select Clock source
0 (programmed)(2)
CKSEL0
0
Select Clock source
1 (unprogrammed)(2)
Notes:
1. The default value of SUT1..0 results in maximum start-up time. See Table 12 on page
30 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator at 1 MHz. See
Table 3 on page 26 for details.
3. The CKOPT Fuse functionality depends on the setting of the CKSEL bits. See “System Clock and Clock Options” on page 24 for details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are
locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the
Lock bits.
110
ATtiny26(L)
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ATtiny26(L)
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of
the fuse values will have no effect until the part leaves programming mode. This does
not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses
are also latched on Power-up in normal mode.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device.
This code can be read in both serial and parallel mode, also when the device is locked.
The three bytes reside in a separate address space.
For the ATtiny26 the signature bytes are:
1. $000: $1E (indicates manufactured by Atmel).
2. $001: $91 (indicates 2KB Flash memory).
3. $002: $09 (indicates ATtiny26 device when $001 is $91).
Calibration Byte
The ATtiny26 stores four different calibration values for the internal RC Oscillator. These
bytes resides in the signature row high byte of the addresses 0x0000, 0x0001, 0x0002,
and 0x0003 for 1, 2, 4, and 8 MHz respectively. During Reset, the 1 MHz value is automatically loaded into the OSCCAL Register. If other frequencies are used, the
calibration value has to be loaded manually, see “Oscillator Calibration Register – OSCCAL” on page 30 for details.
Page Size
Table 52. No. of Words in a Page and no. of Pages in the Flash
Flash Size
1K words (2K bytes)
Page Size
PCWORD
No. of Pages
PCPAGE
PCMSB
16 words
PC[3:0]
64
PC[9:4]
9
Table 53. No. of Words in a Page and no. of Pages in the EEPROM
EEPROM Size
Page Size
PCWORD
No. of Pages
PCPAGE
EEAMSB
128 bytes
4 bytes
EEA[1:0]
32
EEA[7:0]
7
Parallel Programming
Parameters, Pin
Mapping, and
Commands
This section describes how to parallel program and verify Flash Program memory,
EEPROM Data memory, Memory Lock bits, and Fuse bits in the ATtiny26. Pulses are
assumed to be at least 250 ns unless otherwise noted.
Signal Names
In this section, some pins of the ATtiny26 are referenced by signal names describing
their functionality during parallel programming, see Figure 58 and Table 54. Pins not
described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in Table 56.
When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 57.
111
1477I–AVR–10/06
Figure 58. Parallel Programming
+5V
WR
PB0
XA0
PB1
XA1/BS2
PB2
PAGEL/BS1
PB3
OE
PB5
RDY/BSY
PB6
VCC
+5V
AVCC
+12 V
PA7: PA0
DATA
RESET
XTAL1/PB4
GND
Table 54. Pin Name Mapping
Signal Name in
Programming Mode
WR
XA0
Pin Name
I/O
PB0
I
Write Pulse (Active low)
PB1
I
XTAL Action Bit 0
PB2
I
XTAL Action Bit 1 multiplexed with Byte Select 2
(“0” selects low byte, “1” selects 2’nd high byte)
PB3
I
Program Memory and EEPROM data Page Load
multiplexed with Byte Select 1 (“0” selects low
byte, “1” selects high byte).
PB5
I
Output Enable (Active low)
PB6
O
0: Device is busy programming, 1: Device is ready
for new command
PA7:0
I/O
Bidirectional Data bus (Output when OE is low)
(1)
XA1/BS2
PAGEL/BS1(1)
OE
RDY/BSY
DATA
Note:
Function
1. The pin is used for two different control signals. In the description below, normally
only one of the signals is referred. E.g., “give BS1 a positive pulse” equals “give
PAGEL/BS1 a positive pulse”.
Table 55. Pin Values used to Enter Programming Mode
Pin
112
Symbol
Value
PAGEL/BS1
Prog_enable[3]
0
XA1/BS2
Prog_enable[2]
0
XA0
Prog_enable[1]
0
WR
Prog_enable[0]
0
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Table 56. XA1 and XA0 Coding(1)
XA1
XA0
0
0
Load Flash or EEPROM Address (High or low address byte determined by
BS1).
0
1
Load Data (High or Low data byte for Flash determined by BS1).
1
0
Load Command
1
1
No Action, Idle
Note:
Action when XTAL1 is Pulsed
1. [XA1, XA0] = 0b11 is “No Action, Idle”. As long as XTAL1 is not pulsed, the Command, Address, and Data Registers remain unchanged. Therefore, there are no
problems using BS2 as described below even though BS2 is multiplexed with XA1.
BS2 is only asserted when reading the fuses (OE is low) and XTAL1 is not pulsed.
Table 57. Command Byte Bit Coding
Command Byte
Command Executed
1000 0000
Chip Erase
0100 0000
Write Fuse Bits
0010 0000
Write Lock Bits
0001 0000
Write Flash
0001 0001
Write EEPROM
0000 1000
Read Signature Bytes and Calibration Byte
0000 0100
Read Fuse and Lock Bits
0000 0010
Read Flash
0000 0011
Read EEPROM
113
1477I–AVR–10/06
Parallel Programming
Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
Step 2-7 must be completed within 64ms.
1. Set Prog_enable pins listed in Table 55 on page 112, RESET and Vcc to 0V.
2. Apply 4.5 - 5.5V between Vcc/AVcc and GND.
3. Wait at least 60us.
4. Apply between 4.5V - 5.5V (Same as on Vcc/AVcc) to RESET pin.
5. Wait at least 20us.
6. Apply between 11.5V - 12.5V to RESET pin.
7. Wait at least 10us.
8. Program fuses to internal clock mode, 8 MHz, with 64ms delay. (CKSEL[3..0] =
0100, SUT[1..0] = 10). If Lock bits are programmed, a Chip Erase command
must be executed before changing the fuses.
9. Exit Programming mode by power the device down or by bringing RESET pin to
0V.
10. Repeat step 1 to 7 too re-enter programming mode.
Considerations for Efficient
Programming
114
The loaded command and address are retained in the device during programming. For
efficient programming, the following should be considered.
•
The command needs only be loaded once when writing or reading multiple memory
locations.
•
Skip writing the data value $FF, that is the contents of the entire EEPROM (unless
the EESAVE Fuse is programmed) and Flash after a Chip Erase.
•
Address high byte needs only be loaded before programming or reading a new 256word window in Flash or 256-byte EEPROM. This consideration also applies to
Signature bytes reading.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Chip Erase
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock
bits are not reset until the program memory has been completely erased. The Fuse bits
are not changed. A Chip Erase must be performed before the Flash and/or EEPROM
are reprogrammed.
Note:
1. The EEPROM memory is preserved during Chip Erase if the EESAVE Fuse is
programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
Programming the Flash
The Flash is organized in pages, see Table 52 on page 111. When programming the
Flash, the program data is latched into a page buffer. This allows one page of program
data to be programmed simultaneously. The following procedure describes how to program the entire Flash memory:
A. Load Command "Write Flash"
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte ($00 - $FF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte ($00 - $FF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte ($00 - $FF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Repeat B through D until the entire buffer is filled or until all data within the page is
loaded.
While the lower bits in the address are mapped to words within the page, the higher bits
address the pages within the FLASH. This is illustrated in Figure 59 on page 116. Note
that if less than 8 bits are required to address words in the page (pagesize < 256), the
most significant bit(s) in the address low byte are used to address the page when performing a page write.
115
1477I–AVR–10/06
F. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte ($00 - $03).
4. Give XTAL1 a positive pulse. This loads the address high byte.
G. Program Page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the entire page of data.
RDY/BSYgoes low.
3. Wait until RDY/BSY goes high. (See Figure 60 for signal waveforms.)
H. Repeat B through G until the entire Flash is programmed or until all data has been
programmed.
I. End Page Programming
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.
Figure 59. Addressing the Flash which is Organized in Pages(1)
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
116
1. PCPAGE and PCWORD are listed in Table 52 on page 111.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 60. Programming the Flash Waveforms(1)
E
DATA
A
B
$10
ADDR. LOW
C
D
B
C
DATA LOW DATA HIGH ADDR. LOW DATA LOW
D
F
DATA HIGH ADDR. HIGH
G
XX
XA1/BS2
XA0
PAGEL/BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
Note:
Programming the EEPROM
1. “XX” is don’t care. The letters refer to the programming description above.
The EEPROM is organized in pages, see Table 53 on page 111. When programming
the EEPROM, the program data is latched into a page buffer. This allows one page of
data to be programmed simultaneously. The programming algorithm for the EEPROM
data memory is as follows (refer to “Programming the Flash” on page 115 for details on
Command, Address and Data loading):
1. A: Load Command “0001 0001”.
2. B: Load Address Low Byte ($00 - $FF).
3. C: Load Data ($00 - $FF).
J: Repeat 2 and 3 until the entire buffer is filled
K: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page.
RDY/BSY goes low.
3. Wait until to RDY/BSY goes high before programming the next page.
(See Figure 61 for signal waveforms.)
117
1477I–AVR–10/06
Figure 61. Programming the EEPROM Waveforms
J
DATA
A
B
C
B
C
$11
ADDR. LOW
DATA
ADDR. LOW
DATA
K
XX
XA1/BS2
XA0
PAGEL/BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the
Flash” on page 115 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. F: Load Address High Byte ($00 - $03).
3. B: Load Address Low Byte ($00 - $FF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS1 to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the
Flash” on page 115 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. B: Load Address Low Byte ($00 - $FF).
3. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at
DATA.
4. Set OE to “1”.
Programming the Fuse Low
Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming
the Flash” on page 115 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 and BS2 to “0”.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
118
ATtiny26(L)
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ATtiny26(L)
Programming the Fuse High
Bits
The algorithm for programming the Fuse high bits is as follows (refer to “Programming
the Flash” on page 115 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
Figure 62. Programming the Fuse Waveforms
Write Fuse Low Byte
DATA
A
C
$40
DATA
XX
Write Fuse High Byte
A
C
$40
DATA
XX
XA1/BS2
XA0
PAGEL/BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” on page 115 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
Reading the Fuse and Lock
Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming
the Flash” on page 115 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0”, and BS1 to “0”. The status of the Fuse Low bits can
now be read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1”, and BS1 to “1”. The status of the Fuse High bits can
now be read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “0”, and BS1 to “1”. The status of the Lock bits can now be
read at DATA (“0” means programmed).
5. Set OE to “1”.
119
1477I–AVR–10/06
Figure 63. Mapping Between BS1, BS2 and the Fuse- and Lock-bits During Read
0
Fuse Low Byte
DATA
0
Lock Bits
1
BS1
Fuse High Byte
1
BS2
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to Programming the
Flash for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte ($00 - $02).
3. Set OE to “0” and BS1 to “0”. The selected Signature byte can now be read at
DATA.
4. Set OE to “1”.
Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to Programming the
Flash for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte.
3. Set OE to “0” and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Parallel Programming
Characteristics
Figure 64. Parallel Programming Timing, Including some General Timing
Requirements
tXLWL
tXHXL
XTAL1
tDVXH
Data & Contol
(DATA, XA0, XA1/BS2
PAGEL/BS1)
tXLDX
t BVWL
tWLWH
tWLBX
WR
WLRL
RDY/BSY
tWLRH
120
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 65. Parallel Programming Timing, Loading Sequence with Timing
Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA
(LOW BYTE)
LOAD DATA
(HIGH BYTE)
t XLXH
t XLXH
LOAD ADDRESS
(LOW BYTE)
t XLXH
XTAL1
PAGEL/BS1
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1/BS2
Note:
1. The timing requirements shown in Figure 64 (i.e., tDVXH, tXHXL, and tXLDX) also apply
to loading operation.
Figure 66. Parallel Programming Timing, Reading Sequence (Within the Same Page)
with Timing Requirements()
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
tXLOL
XTAL1
tBHDV
PAGEL/BS1
tOLDV
OE
DATA
tOHDZ
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1/BS2
Note:
1. The timing requirements shown in Figure 64 (i.e. tDVXH, tXHXL, and tXLDX) also apply
to reading operation.
121
1477I–AVR–10/06
Table 58. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol
Parameter
Min
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXLXH
XTAL1 Low to XTAL1 High
200
ns
tXHXL
XTAL1 Pulse Width High
150
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
0
ns
tWLBX
BS2/1 Hold after WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tWLWH
WR Pulse Width Low
150
ns
tWLRL
WR Low to RDY/BSY Low
(1)
WR Low to RDY/BSY High
tWLRH
Max
Units
12.5
V
250
μA
0
1
μs
3.7
4.5
ms
7.5
9
ms
tWLRH_CE
WR Low to RDY/BSY High for Chip Erase
tXLOL
XTAL1 Low to OE Low
0
tBVDV
BS1 Valid to DATA valid
0
tOLDV
tOHDZ
Notes:
122
(2)
Typ
ns
250
ns
OE Low to DATA Valid
250
ns
OE High to DATA Tri-stated
250
ns
1.
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock
bits commands.
2. tWLRH_CE is valid for the Chip Erase command.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Serial Downloading
Serial Programming Pin
Mapping
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI
bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI
(input) and MISO (output). After RESET is set low, the Programming Enable instruction
needs to be executed first before program/erase operations can be executed. NOTE, in
Table 59 on page 123, the pin mapping for SPI programming is listed. Not all parts use
the SPI pins dedicated for the internal SPI interface. Note that throughout the description about Serial downloading, MOSI and MISO are used to describe the serial data in
and serial data out respectively.
Table 59. Pin Mapping Serial Programming
Symbol
Pins
I/O
Description
MOSI
PB0
I
Serial data in
MISO
PB1
O
Serial data out
SCK
PB2
I
Serial clock
Figure 67. Serial Programming and Verify(1)
2.7 - 5.5V
VCC
2.7 - 5.5V(2)
MOSI
PB0
MISO
PB1
SCK
PB2
AVCC
XTAL1
RESET
GND
Notes:
1. If the device is clocked by the internal oscillator, there is no need to connect a clock
source to the XTAL1 pin.
2. VCC -0.3V < AVCC < VCC +0.3V, however, AVCC should always be within 2.7 - 5.5V.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the serial mode ONLY) and there is no need to first execute the
Chip Erase instruction. The Chip Erase operation turns the content of every memory
location in both the Program and EEPROM arrays into $FF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high
periods for the serial clock (SCK) input are defined as follows:
Low: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck ≥ 12 MHz
High: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck ≥ 12 MHz
123
1477I–AVR–10/06
SPI Serial Programming
Algorithm
When writing serial data to the ATtiny26, data is clocked on the rising edge of SCK.
When reading data from the ATtiny26, data is clocked on the falling edge of SCK. See
Figure 68, Figure 69, and Table 69 for timing details.
To program and verify the ATtiny26 in the serial programming mode, the following
sequence is recommended (See four byte instruction formats in Table 61):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In
some systems, the programmer can not guarantee that SCK is held low during
Power-up. In this case, RESET must be given a positive pulse of at least two
CPU clock cycles duration after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of
synchronization. When in synchronize the second byte ($53), will echo back
when issuing the third byte of the Programming Enable instruction. Whether the
echo is correct or not, all 4 bytes of the instruction must be transmitted. If the $53
did not echo back, give RESET a positive pulse and issue a new Programming
Enable command.
4. The Flash is programmed one page at a time. The page size is found in Table 52
on page 111. The memory page is loaded one byte at a time by supplying the 4
LSB of the address and data together with the Load Program Memory Page
instruction. To ensure correct loading of the page, the data low byte must be
loaded before data high byte is applied for given address. The Program Memory
Page is stored by loading the Write Program Memory Page instruction with the 6
MSB of the address. If polling is not used, the user must wait at least tWD_FLASH
before issuing the next page. (See Table 60). Accessing the serial programming
interface before the Flash write operation completes can result in incorrect
programming.
5. The EEPROM array is programmed one byte at a time by supplying the address
and data together with the appropriate Write instruction. An EEPROM memory
location is first automatically erased before new data is written. If polling is not
used, the user must wait at least tWD_EEPROM before issuing the next byte. (See
Table 60). In a chip erased device, no $FFs in the data file(s) need to be
programmed.
6. Any memory location can be verified by using the Read instruction which returns
the content at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence
normal operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
124
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Data Polling Flash
When a page is being programmed into the Flash, reading an address location within
the page being programmed will give the value $FF. At the time the device is ready for a
new page, the programmed value will read correctly. This is used to determine when the
next page can be written. Note that the entire page is written simultaneously and any
address within the page can be used for polling. Data polling of the Flash will not work
for the value $FF, so when programming this value, the user will have to wait for at least
tWD_FLASH before programming the next page. As a chip-erased device contains $FF in
all locations, programming of addresses that are meant to contain $FF, can be skipped.
See Table 60 for tWD_FLASH value.
Data Polling EEPROM
When a new byte has been written and is being programmed into EEPROM, reading the
address location being programmed will give the value $FF. At the time the device is
ready for a new byte, the programmed value will read correctly. This is used to determine when the next byte can be written. This will not work for the value $FF, but the user
should have the following in mind: As a chip-erased device contains $FF in all locations,
programming of addresses that are meant to contain $FF, can be skipped. This does
not apply if the EEPROM is re-programmed without chip-erasing the device. In this
case, data polling cannot be used for the value $FF, and the user will have to wait at
least tWD_EEPROM before programming the next byte. See Table 60 for tWD_EEPROM value.
Table 60. Minimum Wait Delay before Writing the Next Flash or EEPROM Location
Symbol
Minimum Wait Delay
tWD_FLASH
4.5 ms
tWD_EEPROM
9.0 ms
tWD_ERASE
9.0 ms
tWD_FUSE
4.5 ms
Figure 68. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
125
1477I–AVR–10/06
Table 61. Serial Programming Instruction Set
Instruction
Instruction Format
Operation
Byte 1
Byte 2
Byte 3
Byte4
Programming Enable
1010 1100
0101 0011
xxxx xxxx
xxxx xxxx
Enable Serial Programming after
RESET goes low.
Chip Erase
1010 1100
100x xxxx
xxxx xxxx
xxxx xxxx
Chip Erase EEPROM and Flash.
Read Program Memory
0010 H000
xxxx xxaa
bbbb bbbb
oooo oooo
Read H (high or low) data o from
Program memory at word address a:b.
Load Program Memory Page
0100 H000
xxxx xxxx
xxxx bbbb
iiii iiii
Write H (high or low) data i to Program
Memory page at word address b. Data
low byte must be loaded before data
high byte is applied within the same
address.
Write Program Memory Page
0100 1100
xxxx xxaa
bbbb xxxx
xxxx xxxx
Write Program Memory Page at
address a:b.
Read EEPROM Memory
1010 0000
xxxx xxxx
xbbb bbbb
oooo oooo
Read data o from EEPROM memory at
address b.
Write EEPROM Memory
1100 0000
xxxx xxxx
xbbb bbbb
iiii iiii
Write data i to EEPROM memory at
address b.
Read Lock Bits
0101 1000
0000 0000
xxxx xxxx
xxxx xxoo
Read Lock bits. “0” = programmed, “1”
= unprogrammed. See Table 48 on
page 109 for details.
Write Lock Bits
1010 1100
111x xxxx
xxxx xxxx
1111 11ii
Write Lock bits. Set bits = “0” to
program Lock bits. See Table 48 on
page 109 for details.
Read Signature Byte
0011 0000
xxxx xxxx
xxxx xxbb
oooo oooo
Read Signature Byte o at address b.
Write Fuse Bits
1010 1100
1010 0000
xxxx xxxx
iiii iiii
Set bits = “0” to program, “1” to
unprogram. See Table 51 on page
110 for details.
Write Fuse High Bits
1010 1100
1010 1000
xxxx xxxx
xxxi iiii
Set bits = “0” to program, “1” to
unprogram. See Table 50 on page
110 for details.
Read Fuse Bits
0101 0000
0000 0000
xxxx xxxx
oooo oooo
Read Fuse bits. “0” = programmed, “1”
= unprogrammed. See Table 51 on
page 110 for details.
Read Fuse High Bits
0101 1000
0000 1000
xxxx xxxx
xxxo oooo
Read Fuse high bits.
“0” = programmed,
“1” = unprogrammed. See Table 50
on page 110 for details.
Read Calibration Byte
0011 1000
xxxx xxxx
0000 00bb
oooo oooo
Read Calibration Byte o.
Note:
126
a = address high bits
b = address low bits
H = 0 – Low byte, 1 – High Byte
o = data out
i = data in
x = don’t care
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Serial Programming
Characteristics
Figure 69. Serial Programming Timing
MOSI
tSLSH
t SHOX
t OVSH
SCK
t SHSL
MISO
t SLIV
Table 62. Serial Programming Characteristics, TA = -40°C to 85°C, VCC = 2.7V - 5.5V
(Unless Otherwise Noted)(1)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (VCC = 2.7 - 5.5 V)
1/tCLCL
Typ
0
Oscillator Period (VCC = 2.7 - 5.5 V)
tCLCL
tCLCL
Min
Max
Units
8
MHz
125
Oscillator Frequency (VCC = 4.5 - 5.5 V)
ns
0
Oscillator Period (VCC = 4.5 - 5.5 V)
16
62.5
(1)
MHz
ns
tSHSL
SCK Pulse Width High
2 tCLCL
ns
tSLSH
SCK Pulse Width Low
2 tCLCL(1)
ns
tOVSH
MOSI Setup to SCK High
tCLCL
ns
tSHOX
MOSI Hold after SCK High
2 tCLCL
ns
tSLIV
SCK Low to MISO Valid
Note:
20
ns
1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
127
1477I–AVR–10/06
Electrical Characteristics
Absolute Maximum Ratings*
Operating Temperature.................................. -55°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on Any Pin except RESET
with Respect to Ground .............................-0.5V to VCC + 0.5V
Voltage on RESET with Respect to Ground ....-0.5V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins ................................ 200.0 mA
DC Characteristics
TA = -40°C to 85°C, VCC = 2.7V to 5.5V (unless otherwise noted)
Symbol
Parameter
Condition
Min.
VIL
Input Low Voltage
Except XTAL1 pin and
RESET pins
VIH
Input High Voltage
VIL1
Typ.(1)
Max.
Units
-0.5
0.2VCC
V
Except XTAL1 and
RESET pins
0.6VCC(3)
VCC +0.5
V
Input Low Voltage
XTAL1 pin, External
Clock Selected
-0.5
0.1VCC
V
VIH1
Input High Voltage
XTAL1 pin, External
Clock Selected
0.8VCC(3)
VCC +0.5
V
VIL2
Input Low Voltage
RESET pin
-0.5
0.2VCC
V
0.9VCC(3)
VCC +0.5
V
VIH2
Input High Voltage
RESET pin
VIL3
Input Low Voltage
RESET pin as I/O
-0.5
0.2VCC
V
RESET pin as I/O
0.6VCC(3)
VCC +0.5
V
0.7
0.5
V
V
VIH3
Input High Voltage
(4)
IOL = 20 mA, VCC = 5V
IOL = 10 mA, VCC = 3V
VOL
Output Low Voltage
(Ports A, B)
VOH
Output High Voltage(5)
(Ports A, B)
IOH = -20 mA, VCC = 5V
IOH = -10 mA, VCC = 3V
IIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value)
1
µA
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value)
1
µA
RRST
Reset Pull-up Resistor
20
100
kΩ
Rpu
I/O Pin Pull-up Resistor
20
100
kΩ
128
ATtiny26(L)
4.2
2.3
V
V
1477I–AVR–10/06
ATtiny26(L)
TA = -40°C to 85°C, VCC = 2.7V to 5.5V (unless otherwise noted) (Continued)
Symbol
Parameter
Power Supply Current
ICC
Power-down mode(6)
Condition
Typ.(1)
Max.
Units
Active 1 MHz, VCC = 3V
(ATtiny26L)
0.70
Active 4 MHz, VCC = 3V
(ATtiny26L)
2.5
6
mA
Active 8 MHz, VCC = 5V
(ATtiny26)
8
15
mA
mA
Idle 1 MHz, VCC = 3V
(ATtiny26L)
0.18
Idle 4 MHz, VCC = 3V
(ATtiny26L)
0.75
2
mA
Idle 8 MHz, VCC = 5V
(ATtiny26)
3.5
7
mA
WDT enabled, VCC = 3V
7.5
15
µA
WDT disabled, VCC = 3V
0.3
3
µA
<10
40
mV
50
nA
VACIO
Analog Comparator
Input Offset Voltage
VCC = 5V
Vin = VCC/2
IACLK
Analog Comparator
Input Leakage Current
VCC = 5V
Vin = VCC/2
tACID
Analog Comparator
Propagation Delay
VCC = 2.7V
VCC = 4.0V
Notes:
Min.
-50
750
500
mA
ns
1.
2.
3.
4.
Typical value at 25°C
“Max” means the highest value where the pin is guaranteed to be read as low
“Min” means the lowest value where the pin is guaranteed to be read as high
Although each I/O port can sink more than the test conditions (20mA at Vcc = 5V, 10 mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for port A0 - A7, should not exceed 300 mA.
3] The sum of all IOL, for ports B0 - B7 should not exceed 300 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
5. Although each I/O port can source more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 400 mA.
2] The sum of all IOH, for port A0 - A7, should not exceed 300 mA.
3] The sum of all IOH, for ports B0 - B7 should not exceed 300 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
6. Minimum VCC for Power-down is 2.5V
129
1477I–AVR–10/06
External Clock Drive
Waveforms
Figure 70. External Clock Drive Waveforms
V IH1
V IL1
External Clock Drive
Table 63. External Clock Drive
VCC = 2.7 - 5.5V
VCC = 4.5 - 5.5V
Symbol
Parameter
1/tCLCL
Oscillator Frequency
tCLCL
Clock Period
125
62.5
ns
tCHCX
High Time
50
25
ns
tCLCX
Low Time
50
25
ns
tCLCH
Rise Time
1.6
0.5
μs
tCHCL
Fall Time
1.6
0.5
μs
ΔtCLCL
Change in period from one clock
cycle to the next
2
2
Min
Max
Min
Max
Units
0
8
0
16
MHz
Table 64. External RC Oscillator, Typical Frequencies
Notes:
130
R [kΩ](1)
C [pF]
f(2)
33
22
650 kHz
10
22
2.0 MHz
1. R should be in the range 3 kΩ - 100 kΩ, and C should be at least 20 pF. The C values
given in the table includes pin capacitance. This will vary with package type.
2. The frequency will vary with package type and board layout.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
ADC Characteristics
Table 65. ADC Characteristics, Single Ended Channels, TA = -40°C to 85°C
Symbol
Parameter
Condition
Resolution
Single Ended Conversion
10
Bits
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
1
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 1 MHz
2
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
Noise Reduction mode
1
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 1 MHz
Noise Reduction mode
2
LSB
Integral Non-Linearity (INL)
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
0.5
LSB
Differential Non-Linearity (DNL)
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
0.5
LSB
Gain Error
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
0.75
LSB
Offset error
Single Ended Conversion
VREF = 4V, VCC = 4V
ADC clock = 200 kHz
0.5
LSB
Absolute Accuracy
(Including INL, DNL, Quantization Error, Gain
and Offset Error)
Clock Frequency
50
Conversion Time
13
AVCC
Analog Supply Voltage
VREF
Reference Voltage
VIN
Min
Input Voltage
ADC Conversion Output
Typ
Max
Units
1000
kHz
260
µs
(2)
(1)
VCC - 0.3
VCC + 0.3
V
2.0
AVCC
V
GND
VREF
V
0
1023
LSB
Input Bandwidth
38.5
VINT
Internal Voltage Reference
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
Note:
2.4
2.7
kHz
2.9
V
1. Minimum for AVCC is 2.7V.
2. Maximum for AVCC is 5.5V
131
1477I–AVR–10/06
Table 66. ADC Characteristics, Differential Channels, TA = -40°C to 85°C
Symbol
Parameter
Condition
Min
Typ
Max
Units
Gain = 1x
10
Bits
Gain = 20x
10
Bits
Resolution
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
24
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
27
LSB
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
1.5
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
2
LSB
Gain = 1x
2
%
Gain = 20x
2.5
%
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
4
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
6
LSB
Absolute Accuracy
Integral Non-Linearity (INL)
(Accuracy after Calibration for Offset and
Gain Error)
Gain Error
Offset Error
Clock Frequency
50
Conversion Time
26
65
µs
VCC + 0.3
V
2.0
AVCC - 0.5
V
GND
VCC
V
Input Differential Voltage
0
VREF/Gain
V
ADC Conversion Output
0
1023
LSB
Analog Supply Voltage
VREF
Reference Voltage
VDIFF
kHz
(2)
AVCC
VIN
200
Input Voltage
(1)
VCC - 0.3
Input Bandwidth
4
VINT
Internal Voltage Reference
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
Notes:
132
2.4
2.7
kHz
2.9
V
1. Minimum for AVCC is 2.7V.
2. Maximum for AVCC is 5.5V.
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
ATtiny26 Typical
Characteristics
The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins
configured as inputs and with internal pull-ups enabled. A sine wave generator with railto-rail output is used as clock source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage,
operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and
ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as
CL*VCC*f where CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog
Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.
Active Supply Current
Figure 71. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
1.6
1.4
5.5V
1.2
5.0V
4.5V
4.0V
3.3V
3.0V
2.7V
ICC (mA)
1
0.8
0.6
0.4
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
133
1477I–AVR–10/06
Figure 72. Active Supply Current vs. Frequency (1 - 20 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
25
5.5V
20
5.0V
ICC (mA)
4.5V
15
4.0V
10
3.3V
5
3.0V
2.7V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 73. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
14
-40°C
25°C
85°C
12
ICC (mA)
10
8
6
4
2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
134
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 74. Active Supply Current vs. VCC (Internal RC Oscillator, 4 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 4 MHz
8
85°C
25°C
-40°C
7
6
ICC (mA)
5
4
3
2
1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 75. Active Supply Current vs. VCC (Internal RC Oscillator, 2 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 2 MHz
4
3.5
85°C
25°C
3
-40°C
ICC (mA)
2.5
2
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
135
1477I–AVR–10/06
Figure 76. Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 1 MHz
1.8
25°C
85°C
-40°C
1.6
1.4
ICC (mA)
1.2
1
0.8
0.6
0.4
0.2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 77. Active Supply Current vs. VCC (PLL Oscillator)
ACTIVE SUPPLY CURRENT vs. VCC
PLL OSCILLATOR
25
-40°C
25°C
85°C
ICC (mA)
20
15
10
5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
136
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 78. Active Supply Current vs. VCC (32 kHz External Oscillator)
ACTIVE SUPPLY CURRENT vs. VCC
32kHz EXTERNAL OSCILLATOR
70
25°C
60
ICC (uA)
50
40
30
20
10
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Idle Supply Current
Figure 79. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
0.6
5.5V
0.5
5.0V
ICC (mA)
0.4
4.5V
4.0V
0.3
3.3V
3.0V
2.7V
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
137
1477I–AVR–10/06
Figure 80. Idle Supply Current vs. Frequency (1 - 20 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
12
5.5V
10
5.0V
ICC (mA)
8
4.5V
6
4.0V
4
3.3V
2
3.0V
2.7V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 81. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
7
-40°C
25°C
85°C
6
ICC (mA)
5
4
3
2
1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
138
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 82. Idle Supply Current vs. VCC (Internal RC Oscillator, 4 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 4 MHz
3.5
-40°C
25°C
85°C
3
ICC (mA)
2.5
2
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 83. Idle Supply Current vs. VCC (Internal RC Oscillator, 2 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 2 MHz
1.6
25°C
1.4
85°C
-40°C
1.2
ICC (mA)
1
0.8
0.6
0.4
0.2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
139
1477I–AVR–10/06
Figure 84. Idle Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 1 MHz
25°C
85°C
-40°C
0.8
0.7
0.6
ICC (mA)
0.5
0.4
0.3
0.2
0.1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 85. Idle Supply Current vs. VCC (PLL Oscillator)
IDLE SUPPLY CURRENT vs. VCC
PLL OSCILLATOR
10
25°C
85°C
ICC (mA)
8
-40°C
6
4
2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
140
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 86. Idle Supply Current vs. VCC (32 kHz External Oscillator)
IDLE SUPPLY CURRENT vs. VCC
32kHz EXTERNAL OSCILLATOR
30
25°C
25
ICC (uA)
20
15
10
5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Power-down Supply Current
Figure 87. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER DISABLED
1.8
85°C
1.6
1.4
-40°C
ICC (uA)
1.2
25°C
1
0.8
0.6
0.4
0.2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
141
1477I–AVR–10/06
Figure 88. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER ENABLED
20
85°C
25°C
-40°C
18
16
14
ICC (uA)
12
10
8
6
4
2
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Standby Supply Current
Figure 89. Standby Supply Current vs. VCC (455 kHz Resonator, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. V CC
455 kHz RESONATOR, WATCHDOG TIMER DISABLED
70
60
ICC (uA)
50
40
30
20
10
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
142
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 90. Standby Supply Current vs. V CC (1 MHz Resonator, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. V CC
1 MHz RESONATOR, WATCHDOG TIMER DISABLED
60
50
ICC (uA)
40
30
20
10
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 91. Standby Supply Current vs. V CC (2 MHz Resonator, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. V CC
2 MHz RESONATOR, WATCHDOG TIMER DISABLED
80
70
60
ICC (uA)
50
40
30
20
10
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
143
1477I–AVR–10/06
Figure 92. Standby Supply Current vs. VCC (2 MHz XTAL, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V CC
2 MHz XTAL, WATCHDOG TIMER DISABLED
90
80
70
ICC (uA)
60
50
40
30
20
10
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 93. Standby Supply Current vs. V CC (4 MHz Resonator, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. V CC
4 MHz RESONATOR, WATCHDOG TIMER DISABLED
120
100
ICC (uA)
80
60
40
20
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
144
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 94. Standby Supply Current vs. VCC (4 MHz XTAL, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V CC
4 MHz XTAL, WATCHDOG TIMER DISABLED
120
100
ICC (uA)
80
60
40
20
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 95. Standby Supply Current vs. V CC (6 MHz Resonator, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. V CC
6 MHz RESONATOR, WATCHDOG TIMER DISABLED
160
140
120
ICC (uA)
100
80
60
40
20
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
145
1477I–AVR–10/06
Figure 96. Standby Supply Current vs. VCC (6 MHz XTAL, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V CC
6 MHz XTAL, WATCHDOG TIMER DISABLED
180
160
140
ICC (uA)
120
100
80
60
40
20
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Pin Pull-up
Figure 97. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5V
160
85°C
140
25°C
120
-40°C
IOP (uA)
100
80
60
40
20
0
0
1
2
3
4
5
6
VOP (V)
146
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 98. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7V
80
85°C
25°C
70
60
-40°C
IOP (uA)
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VOP (V)
Figure 99. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 5V
120
-40°C
25°C
100
85°C
IRESET (uA)
80
60
40
20
0
VRESET (V)
147
1477I–AVR–10/06
Figure 100. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 2.7V
60
-40°C
25°C
50
85°C
IRESET (uA)
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VRESET (V)
Pin Driver Strength
Figure 101. I/O Pin Source Current vs. Output Voltage (VCC = 5V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
90
80
-40°C
70
25°C
IOH (mA)
60
85°C
50
40
30
20
10
0
0
1
2
3
4
VOH (V)
148
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 102. I/O Pin Source Current vs. Output Voltage (VCC = 2.7V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
30
-40°C
25
25°C
85°C
IOH (mA)
20
15
10
5
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
Figure 103. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
90
-40°C
IOL (mA)
80
70
25°C
60
85°C
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
VOL (V)
149
1477I–AVR–10/06
Figure 104. I/O Pin Sink Current vs. Output Voltage (VCC = 2.7V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
35
-40°C
30
25°C
25
IOL (mA)
85°C
20
15
10
5
0
0
0.5
1
1.5
2
2.5
VOL (V)
Figure 105. Reset Pin as I/O – Source Current vs. Output Voltage (VCC = 5V)
RESET PIN AS I/O - SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
1.4
-40°C
1.2
25°C
Current (mA)
1
85°C
0.8
0.6
0.4
0.2
0
0
1
2
3
VOH (V)
150
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 106. Reset Pin as I/O – Source Current vs. Output Voltage (VCC = 2.7V)
RESET PIN AS I/O - SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
2.5
-40°C
2
Current (mA)
25°C
1.5
85°C
1
0.5
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
Figure 107. Reset Pin as I/O –Sink Current vs. Output Voltage (VCC = 5V)
RESET PIN AS I/O - SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
14
-40°C
Current (mA)
12
10
25°C
8
85°C
6
4
2
0
0
0.5
1
1.5
2
2.5
VOL (V)
151
1477I–AVR–10/06
Figure 108. Reset Pin as I/O – Sink Current vs. Output Voltage (VCC = 2.7V)
RESET PIN AS I/O - SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
4.5
-40°C
4
3.5
25°C
Current (mA)
3
85°C
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
VOL (V)
Pin Thresholds and
Hysteresis
Figure 109. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as “1”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
2.5
-40°C
85°C
25°C
Threshold (V)
2
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
152
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 110. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as “0”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIL, IO PIN READ AS '0'
2
-40°C
25°C
85°C
Threshold (V)
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 111. I/O Pin Input Hysteresis vs. VCC
I/O PIN INPUT HYSTERESIS vs. VCC
0.7
0.6
85°C
25°C
Threshold (V)
0.5
-40°C
0.4
0.3
0.2
0.1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
153
1477I–AVR–10/06
Figure 112. Reset Pin as I/O – Input Threshold Voltage vs. VCC
(VIH, Reset Pin Read as “1”)
RESET PIN AS I/O - INPUT THRESHOLD VOLTAGE vs. VCC
VIH, RESET PIN READ AS '1'
2.5
-40°C
85°C
25°C
Threshold (V)
2
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 113. Reset Pin as I/O – Input Threshold Voltage vs. VCC
(VIL, Reset Pin Read as “0”)
RESET PIN AS I/O - INPUT THRESHOLD VOLTAGE vs. VCC
VIL, RESET PIN READ AS '0'
2.5
Threshold (V)
2
-40°C
25°C
85°C
1.5
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
154
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 114. Reset Pin as I/O – Pin Hysteresis vs. VCC
RESET PIN AS I/O - PIN HYSTERESIS vs. VCC
0.7
0.6
85°C
-40°C
Threshold (V)
0.5
25°C
0.4
0.3
0.2
0.1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 115. Reset Input Threshold Voltage vs. VCC (VIH, Reset Pin Read as “1”)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIH, RESET PIN READ AS '1'
2.5
Threshold (V)
2
1.5
-40°C
25°C
85°C
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
155
1477I–AVR–10/06
Figure 116. Reset Input Threshold Voltage vs. VCC (VIL, Reset Pin Read as “0”)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIL, RESET PIN READ AS '0'
2.5
Threshold (V)
2
1.5
85°C
25°C
-40°C
1
0.5
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 117. Reset Input Pin Hysteresis vs. VCC
RESET INPUT PIN HYSTERESIS vs. VCC
0.5
-40°C
0.45
0.4
Threshold (V)
0.35
0.3
0.25
25°C
0.2
0.15
0.1
85°C
0.05
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
156
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
BOD Thresholds and Analog
Comparator Offset
Figure 118. BOD Thresholds vs. Temperature (BOD Level is 4.0V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 4.0V
4.3
4.2
Threshold (V)
Rising VCC
4.1
4
Falling VCC
3.9
3.8
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
90
100
Temperature (C)
Figure 119. BOD Thresholds vs. Temperature (BOD Level is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 2.7V
3.1
Threshold (V)
3
Rising VCC
2.9
2.8
Falling VCC
2.7
2.6
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
Temperature (C)
157
1477I–AVR–10/06
Figure 120. Bandgap Voltage vs. VCC
BANDGAP vs. VCC
1.236
1.234
-40°C
85°C
25°C
Bandgap Voltage (V)
1.232
1.23
1.228
1.226
1.224
1.222
1.22
1.218
1.216
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Figure 121. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC= 5.0V)
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
Vcc = 5V
0.009
Comparator Offset Voltage (V)
0.008
0.007
0.006
0.005
-40°C
0.004
25°C
0.003
85°C
0.002
0.001
0
0
1
2
3
4
Common Mode Voltage (V)
158
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 122. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC= 2.7V)
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
Vcc = 2.7V
0.009
Comparator Offset Voltage (V)
0.008
0.007
0.006
0.005
0.004
-40°C
25°C
85°C
0.003
0.002
0.001
0
0
0.5
1
1.5
2
2.5
3
Common Mode Voltage (V)
Internal Oscillator Speed
Figure 123. Watchdog Oscillator Frequency vs. VCC
WATCHDOG OSCILLATOR FREQUENCY vs. VCC
1.4
1.35
-40°C
25°C
85°C
FRC (MHz)
1.3
1.25
1.2
1.15
1.1
1.05
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
159
1477I–AVR–10/06
Figure 124. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
8.9
FRC (MHz)
8.4
7.9
5.0V
7.4
3.5V
6.9
2.7V
6.4
-60
-40
-20
0
20
40
60
80
100
Ta (˚C)
Figure 125. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. VCC
FRC (MHz)
9
8.5
-40°C
8
25°C
85°C
7.5
7
6.5
6
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
160
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 126. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
17.5
15.5
FRC (MHz)
13.5
11.5
9.5
7.5
5.5
3.5
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL VALUE
Figure 127. Calibrated 4 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
4.3
4.2
4.1
FRC (MHz)
4
3.9
5.0V
3.8
3.5V
3.7
2.7V
3.6
3.5
3.4
-60
-40
-20
0
20
40
60
80
100
Ta (˚C)
161
1477I–AVR–10/06
Figure 128. Calibrated 4 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. VCC
4.4
4.3
4.2
-40°C
FRC (MHz)
4.1
25°C
4
85°C
3.9
3.8
3.7
3.6
3.5
3.4
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 129. Calibrated 4 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
9.6
8.6
FRC (MHz)
7.6
6.6
5.6
4.6
3.6
2.6
1.6
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL VALUE
162
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 130. Calibrated 2 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 2MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
2.15
2.1
2.05
FRC (MHz)
2
1.95
5.0V
1.9
3.5V
1.85
2.7V
1.8
1.75
-60
-40
-20
0
20
40
60
80
100
Ta (˚C)
Figure 131. Calibrated 2 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 2MHz RC OSCILLATOR FREQUENCY vs. VCC
2.15
2.1
-40°C
2.05
25°C
FRC (MHz)
2
85°C
1.95
1.9
1.85
1.8
1.75
1.7
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
163
1477I–AVR–10/06
Figure 132. Calibrated 2 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 2MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
4.3
3.8
FRC (MHz)
3.3
2.8
2.3
1.8
1.3
0.8
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL VALUE
Figure 133. Calibrated 1 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 1 MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
1.04
1.02
FRC (MHz)
1
0.98
5.0V
0.96
3.5V
0.94
2.7V
0.92
0.9
-60
-40
-20
0
20
40
60
80
100
VCC (V)
164
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 134. Calibrated 1 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 1MHz RC OSCILLATOR FREQUENCY vs. VCC
1.1
1.05
-40°C
FRC (MHz)
25°C
1
85°C
0.95
0.9
0.85
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 135. Calibrated 1 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 1MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
2
1.8
FRC (MHz)
1.6
1.4
1.2
1
0.8
0.6
0.4
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL VALUE
165
1477I–AVR–10/06
Current Consumption of
Peripheral Units
Figure 136. Brown-out Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs. VCC
0.035
0.03
ICC (mA)
0.025
-40°C
25°C
85°C
0.02
0.015
0.01
0.005
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 137. ADC Current vs. VCC (AREF = AVCC)
ADC CURRENT vs. VCC
AREF = AVCC
250
-40°C
25°C
200
85°C
ICC (uA)
150
100
50
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
166
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 138. AREF External Reference Current vs. VCC
AREF EXTERNAL REFERENCE CURRENT vs. VCC
250
-40°C
25°C
85°C
200
ICC (uA)
150
100
50
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 139. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. VCC
120
100
85°C
80
-40°C
ICC (uA)
25°C
60
40
20
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
167
1477I–AVR–10/06
Figure 140. Programming Current vs. VCC
PROGRAMMING CURRENT vs. VCC
5
ICC (mA)
4
-40°C
3
25°C
85°C
2
1
0
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Current Consumption in
Reset and Reset Pulsewidth
Figure 141. Reset Supply Current vs. VCC
(0.1 - 1.0 MHz, Excluding Current Through The Reset Pull-up)
RESET SUPPLY CURRENT vs. VCC
0.1 - 1.0 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
3.5
5.5V
3
5.0V
2.5
ICC (mA)
4.5V
4.0V
2
3.3V
3.0V
2.7V
1.5
1
0.5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
168
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Figure 142. Reset Supply Current vs. VCC
(1 - 20 MHz, Excluding Current Through The Reset Pull-up)
RESET SUPPLY CURRENT vs. VCC
1 - 20 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
20
18
5.5V
ICC (mA)
16
14
5.0V
12
4.5V
10
4.0V
8
3.3V
3.0V
2.7V
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 143. Reset Pulsewidth vs. VCC
RESET PULSE WIDTH vs. VCC
1200
85°C
1000
Pulsewidth (ns)
25°C
800
-40°C
600
400
200
0
0
1
2
3
VCC (V)
169
1477I–AVR–10/06
Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
$3F ($5F)
SREG
I
T
H
S
V
N
Z
C
11
$3E ($5E)
Reserved
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
12
$3D ($5D)
SP
$3C ($5C)
Reserved
$3B ($5B)
GIMSK
-
INT0
PCIE1
PCIE0
-
-
-
-
60
$3A ($5A)
GIFR
-
INTF0
PCIF
-
-
-
-
-
61
$39 ($59)
TIMSK
-
OCIE1A
OCIE1B
-
-
TOIE1
TOIE0
-
61
$38 ($58)
TIFR
-
OCF1A
OCF1B
-
-
TOV1
TOV0
-
62
$37 ($57)
Reserved
$36 ($56)
Reserved
$35 ($55)
MCUCR
-
PUD
SE
SM1
SM0
-
ISC01
ISC00
38
$34 ($54)
MCUSR
-
-
-
-
WDRF
BORF
EXTRF
PORF
37
$33 ($53)
TCCR0
-
-
-
-
PSR0
CS02
CS01
CS00
$32 ($52)
TCNT0
$31 ($51)
OSCCAL
$30 ($50)
TCCR1A
COM1A1
COM1A0
COM1B1
CTC1
PSR1
-
Timer/Counter0 (8-Bit)
68
69
Oscillator Calibration Register
30
COM1B0
FOC1A
FOC1B
PWM1A
PWM1B
-
CS13
CS12
CS11
CS10
72
$2F ($4F)
TCCR1B
$2E ($4E)
TCNT1
Timer/Counter1 (8-Bit)
74
$2D ($4D)
OCR1A
Timer/Counter1 Output Compare Register A (8-Bit)
74
$2C ($4C)
OCR1B
Timer/Counter1 Output Compare Register B (8-Bit)
75
$2B ($4B)
OCR1C
Timer/Counter1 Output Compare Register C (8-Bit)
75
$2A ($4A)
Reserved
$29 ($49)
PLLCSR
$28 ($48)
Reserved
$27 ($47)
Reserved
$26 ($46)
Reserved
$25 ($45)
Reserved
$24 ($44)
Reserved
$23 ($43)
Reserved
$22 ($42)
Reserved
$21 ($41)
WDTCR
$20 ($40)
Reserved
$1F ($3F)
Reserved
73
-
-
-
-
-
PCKE
PLLE
PLOCK
-
-
-
WDCE
WDE
WDP2
WDP1
WDP0
80
-
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
19
20
$1E ($3E)
EEAR
$1D ($3D)
EEDR
$1C ($3C)
EECR
-
-
-
-
EERIE
EEMWE
EEWE
EERE
$1B ($3B)
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
$1A ($3A)
DDRA
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
$19 ($39)
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
$18 ($38)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
$17 ($37)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
$16 ($36)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
$15 ($35)
Reserved
$14 ($34)
Reserved
$13 ($33)
Reserved
$12 ($32)
Reserved
$11 ($31)
Reserved
$10 ($30)
Reserved
$0F ($2F)
USIDR
$0E ($2E)
USISR
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
83
$0D ($2D)
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
84
$0C ($2C)
Reserved
170
$0B ($2)B
Reserved
$0A ($2A)
Reserved
$09 ($29)
Reserved
EEPROM Data Register (8-Bit)
20
Universal Serial Interface Data Register (8-Bit)
83
$08 ($28)
ACSR
ACD
ACBG
ACO
ACI
ACIE
ACME
ACIS1
ACIS0
93
$07 ($27)
ADMUX
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
103
$06 ($26)
ADCSR
ADEN
ADSC
ADFR
ADIF
ADIE
ADPS2
ADPS1
ADPS0
$05 ($25)
ADCH
ADC Data Register High Byte
106
$04 ($24)
ADCL
ADC Data Register Low Byte
106
…
Reserved
$00 ($20)
Reserved
105
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Instruction Set Summary
Mnemonic
Operands
Description
Operation
Flags
# Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD
Rd, Rr
Add Two Registers
Rd ← Rd + Rr
Z,C,N,V,H
ADC
Rd, Rr
Add with Carry Two Registers
Rd ← Rd + Rr + C
Z,C,N,V,H
1
ADIW
Rdl, K
Add Immediate to Word
Rdh:Rdl ← Rdh:Rdl + K
Z,C,N,V,S
2
SUB
Rd, Rr
Subtract Two Registers
Rd ← Rd - Rr
Z,C,N,V,H
1
SUBI
Rd, K
Subtract Constant from Register
Rd ← Rd - K
Z,C,N,V,H
1
SBC
Rd, Rr
Subtract with Carry Two Registers
Rd ← Rd - Rr - C
Z,C,N,V,H
1
1
SBCI
Rd, K
Subtract with Carry Constant from Reg.
Rd ← Rd - K - C
Z,C,N,V,H
1
SBIW
Rdl, K
Subtract Immediate from Word
Rdh:Rdl ← Rdh:Rdl - K
Z,C,N,V,S
2
AND
Rd, Rr
Logical AND Registers
Rd ← Rd • Rr
Z,N,V
1
ANDI
Rd, K
Logical AND Register and Constant
Rd ← Rd • K
Z,N,V
1
OR
Rd, Rr
Logical OR Registers
Rd ← Rd v Rr
Z,N,V
1
ORI
Rd, K
Logical OR Register and Constant
Rd ← Rd v K
Z,N,V
1
EOR
Rd, Rr
Exclusive OR Registers
Rd ← Rd ⊕ Rr
Z,N,V
1
COM
Rd
One’s Complement
Rd ← $FF - Rd
Z,C,N,V
1
NEG
Rd
Two’s Complement
Rd ← $00 - Rd
Z,C,N,V,H
1
SBR
Rd, K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
1
CBR
Rd, K
Clear Bit(s) in Register
Rd ← Rd • ($FF - K)
Z,N,V
1
INC
Rd
Increment
Rd ← Rd + 1
Z,N,V
1
DEC
Rd
Decrement
Rd ← Rd - 1
Z,N,V
1
TST
Rd
Test for Zero or Minus
Rd ← Rd • Rd
Z,N,V
1
CLR
Rd
Clear Register
Rd ← Rd ⊕ Rd
Z,N,V
1
SER
Rd
Set Register
Rd ← $FF
None
1
2
BRANCH INSTRUCTIONS
RJMP
k
IJMP
RCALL
k
Relative Jump
PC ← PC + k + 1
None
Indirect Jump to (Z)
PC ← Z
None
2
Relative Subroutine Call
PC ← PC + k + 1
None
3
3
ICALL
Indirect Call to (Z)
PC ← Z
None
RET
Subroutine Return
PC ← STACK
None
4
RETI
Interrupt Return
PC ← STACK
I
4
CPSE
Rd, Rr
Compare, Skip if Equal
if (Rd = Rr) PC ← PC + 2 or 3
None
CP
Rd, Rr
Compare
Rd - Rr
Z,N,V,C,H
1
CPC
Rd, Rr
Compare with Carry
Rd - Rr - C
Z,N,V,C,H
1
CPI
Rd, K
Compare Register with Immediate
Rd - K
Z,N,V,C,H
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b) = 0) PC ← PC + 2 or 3
None
1/2/3
1
1/2/3
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b) = 1) PC ← PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b) = 0) PC ← PC + 2 or 3
None
1/2/3
SBIS
P, b
Skip if Bit in I/O Register is Set
if (P(b) = 1) PC ← PC + 2 or 3
None
1/2/3
BRBS
s, k
Branch if Status Flag Set
if (SREG(s) = 1) then PC ← PC + k + 1
None
1/2
BRBC
s, k
Branch if Status Flag Cleared
if (SREG(s) = 0) then PC ← PC + k + 1
None
1/2
BREQ
k
Branch if Equal
if (Z = 1) then PC ← PC + k + 1
None
1/2
BRNE
k
Branch if Not Equal
if (Z = 0) then PC ← PC + k + 1
None
1/2
BRCS
k
Branch if Carry Set
if (C = 1) then PC ← PC + k + 1
None
1/2
BRCC
k
Branch if Carry Cleared
if (C = 0) then PC ← PC + k + 1
None
1/2
BRSH
k
Branch if Same or Higher
if (C = 0) then PC ← PC + k + 1
None
1/2
BRLO
k
Branch if Lower
if (C = 1) then PC ← PC + k + 1
None
1/2
BRMI
k
Branch if Minus
if (N = 1) then PC ← PC + k + 1
None
1/2
BRPL
k
Branch if Plus
if (N = 0) then PC ← PC + k + 1
None
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V = 0) then PC ← PC + k + 1
None
1/2
BRLT
k
Branch if Less than Zero, Signed
if (N ⊕ V = 1) then PC ← PC + k + 1
None
1/2
BRHS
k
Branch if Half-carry Flag Set
if (H = 1) then PC ← PC + k + 1
None
1/2
BRHC
k
Branch if Half-carry Flag Cleared
if (H = 0) then PC ← PC + k + 1
None
1/2
BRTS
k
Branch if T-flag Set
if (T = 1) then PC ← PC + k + 1
None
1/2
BRTC
k
Branch if T-flag Cleared
if (T = 0) then PC ← PC + k + 1
None
1/2
BRVS
k
Branch if Overflow Flag is Set
if (V = 1) then PC ← PC + k + 1
None
1/2
BRVC
k
Branch if Overflow Flag is Cleared
if (V = 0) then PC ← PC + k + 1
None
1/2
BRIE
k
Branch if Interrupt Enabled
if (I = 1) then PC ← PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if (I = 0) then PC ← PC + k + 1
None
1/2
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move between Registers
Rd ← Rr
None
1
LDI
Rd, K
Load Immediate
Rd ← K
None
1
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-inc.
Rd ← (X), X ← X + 1
None
2
LD
Rd, -X
Load Indirect and Pre-dec.
X ← X - 1, Rd ← (X)
None
2
171
1477I–AVR–10/06
Instruction Set Summary (Continued)
Mnemonic
Operands
Description
Operation
Flags
LD
Rd, Y
Load Indirect
Rd ← (Y)
None
# Clocks
2
LD
Rd, Y+
Load Indirect and Post-inc.
Rd ← (Y), Y ← Y + 1
None
2
LD
Rd, -Y
Load Indirect and Pre-dec.
Y ← Y - 1, Rd ← (Y)
None
2
LDD
Rd,Y+q
Load Indirect with Displacement
Rd ← (Y + q)
None
2
LD
Rd, Z
Load Indirect
Rd ← (Z)
None
2
LD
Rd, Z+
Load Indirect and Post-inc.
Rd ← (Z), Z ← Z + 1
None
2
LD
Rd, -Z
Load Indirect and Pre-dec.
Z ← Z - 1, Rd ← (Z)
None
2
LDD
Rd, Z+q
Load Indirect with Displacement
Rd ← (Z + q)
None
2
LDS
Rd, k
Load Direct from SRAM
Rd ← (k)
None
2
ST
X, Rr
Store Indirect
(X) ← Rr
None
2
ST
X+, Rr
Store Indirect and Post-inc.
(X) ← Rr, X ← X + 1
None
2
ST
-X, Rr
Store Indirect and Pre-dec.
X ← X - 1, (X) ← Rr
None
2
ST
Y, Rr
Store Indirect
(Y) ← Rr
None
2
ST
Y+, Rr
Store Indirect and Post-inc.
(Y) ← Rr, Y ← Y + 1
None
2
ST
-Y, Rr
Store Indirect and Pre-dec.
Y ← Y - 1, (Y) ← Rr
None
2
STD
Y+q, Rr
Store Indirect with Displacement
(Y + q) ← Rr
None
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
2
ST
Z+, Rr
Store Indirect and Post-inc.
(Z) ← Rr, Z ← Z + 1
None
2
ST
-Z, Rr
Store Indirect and Pre-dec.
Z ← Z - 1, (Z) ← Rr
None
2
STD
Z+q, Rr
Store Indirect with Displacement
(Z + q) ← Rr
None
2
STS
k, Rr
Store Direct to SRAM
(k) ← Rr
None
2
Load Program Memory
R0 ← (Z)
None
3
LPM
LPM
Rd, Z
Load Program Memory
Rd ← (Z)
None
3
IN
Rd, P
In Port
Rd ← P
None
1
OUT
P, Rr
Out Port
P ← Rr
None
1
PUSH
Rr
Push Register on Stack
STACK ← Rr
None
2
POP
Rd
Pop Register from Stack
Rd ← STACK
None
2
BIT AND BIT-TEST INSTRUCTIONS
SBI
P, b
Set Bit in I/O Register
I/O(P,b) ← 1
None
2
CBI
P, b
Clear Bit in I/O Register
I/O(P,b) ← 0
None
2
LSL
Rd
Logical Shift Left
Rd(n+1) ← Rd(n), Rd(0) ← 0
Z,C,N,V
1
LSR
Rd
Logical Shift Right
Rd(n) ← Rd(n+1), Rd(7) ← 0
Z,C,N,V
1
ROL
Rd
Rotate Left through Carry
Rd(0) ← C, Rd(n+1) ← Rd(n), C ← Rd(7)
Z,C,N,V
1
ROR
Rd
Rotate Right through Carry
Rd(7) ← C, Rd(n) ← Rd(n+1), C ← Rd(0)
Z,C,N,V
1
ASR
Rd
Arithmetic Shift Right
Rd(n) ← Rd(n+1), n = 0..6
Z,C,N,V
1
1
SWAP
Rd
Swap Nibbles
Rd(3..0) ← Rd(7..4), Rd(7..4) ← Rd(3..0)
None
BSET
s
Flag Set
SREG(s) ← 1
SREG(s)
1
BCLR
s
Flag Clear
SREG(s) ← 0
SREG(s)
1
BST
Rr, b
Bit Store from Register to T
T ← Rr(b)
T
1
BLD
Rd, b
Bit Load from T to Register
Rd(b) ← T
None
1
SEC
Set Carry
C←1
C
1
CLC
Clear Carry
C←0
C
1
SEN
Set Negative Flag
N←1
N
1
CLN
Clear Negative Flag
N←0
N
1
SEZ
Set Zero Flag
Z←1
Z
1
CLZ
Clear Zero Flag
Z←0
Z
1
SEI
Global Interrupt Enable
I←1
I
1
CLI
Global Interrupt Disable
I←0
I
1
SES
Set Signed Test Flag
S←1
S
1
CLS
Clear Signed Test Flag
S←0
S
1
SEV
Set Two’s Complement Overflow
V←1
V
1
CLV
Clear Two’s Complement Overflow
V←0
V
1
SET
Set T in SREG
T←1
T
1
CLT
Clear T in SREG
T←0
T
1
SEH
Set Half-carry Flag in SREG
H←1
H
1
CLH
Clear Half-carry Flag in SREG
H←0
H
1
NOP
No Operation
None
1
SLEEP
Sleep
(see specific descr. for Sleep function)
None
1
WDR
Watchdog Reset
(see specific descr. for WDR/timer)
None
1
172
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Ordering Information
Speed (MHz)
8
16
Notes:
Power Supply
2.7 - 5.5V
4.5 - 5.5V
Ordering Code
Package(1)
Operational Range
ATtiny26L-8PC
ATtiny26L-8SC
ATtiny26L-8MC
20P3
20S
32M1-A
Commercial
(0°C to 70°C)
ATtiny26L-8PI
ATtiny26L-8SI
ATtiny26L-8MI
ATtiny26L-8PU(2)
ATtiny26L-8SU(2)
ATtiny26L-8MU(2)
20P3
20S
32M1-A
20P3
20S
32M1-A
Industrial
(-40°C to 85°C)
ATtiny26-16PC
ATtiny26-16SC
ATtiny26-16MC
20P3
20S
32M1-A
Commercial
(0°C to 70°C)
ATtiny26-16PI
ATtiny26-16SI
ATtiny26-16MI
ATtiny26-16PU(2)
ATtiny26-16SU(2)
ATtiny26-16MU(2)
20P3
20S
32M1-A
20P3
20S
32M1-A
Industrial
(-40°C to 85°C)
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green.
Package Type
20P3
20-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
20S
20-lead, 0.300" Wide, Plastic Gull Wing Small Outline (SOIC)
32M1-A
32-pad, 5 x 5 x 1.0 body, Lead Pitch 0.50 mm Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
173
1477I–AVR–10/06
Packaging Information
20P3
D
PIN
1
E1
A
SEATING PLANE
A1
L
B
B1
e
E
COMMON DIMENSIONS
(Unit of Measure = mm)
C
eC
eB
Notes:
1. This package conforms to JEDEC reference MS-001, Variation AD.
2. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25 mm (0.010").
SYMBOL
MIN
NOM
MAX
A
–
–
5.334
A1
0.381
–
–
D
25.493
–
25.984
E
7.620
–
8.255
E1
6.096
–
7.112
B
0.356
–
0.559
B1
1.270
–
1.551
L
2.921
–
3.810
C
0.203
–
0.356
eB
–
–
10.922
eC
0.000
–
1.524
e
NOTE
Note 2
Note 2
2.540 TYP
1/12/04
R
174
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20P3, 20-lead (0.300"/7.62 mm Wide) Plastic Dual
Inline Package (PDIP)
DRAWING NO.
20P3
REV.
C
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
20S
C
1
L
E H
N
A1
Top View
End View
COMMON DIMENSIONS
(Unit of Measure = inches)
e
SYMBOL
b
A
D
Side View
MIN
NOM
MAX
A
0.0926
0.1043
A1
0.0040
0.0118
b
0.0130
0.0200
C
0.0091
0.0125
NOTE
4
D
0.4961
0.5118
1
E
0.2914
0.2992
2
H
0.3940
0.4190
L
0.0160
0.050
e
3
0.050 BSC
Notes: 1. This drawing is for general information only; refer to JEDEC Drawing MS-013, Variation AC for additional information.
2. Dimension "D" does not include mold Flash, protrusions or gate burrs. Mold Flash, protrusions and gate burrs shall not exceed
0.15 mm (0.006") per side.
3. Dimension "E" does not include inter-lead Flash or protrusion. Inter-lead Flash and protrusions shall not exceed 0.25 mm
(0.010") per side.
4. "L" is the length of the terminal for soldering to a substrate.
5. The lead width "b", as measured 0.36 mm (0.014") or greater above the seating plane, shall not exceed a maximum value of 0.61 mm
1/9/02
(0.024") per side.
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20S2, 20-lead, 0.300" Wide Body, Plastic Gull
Wing Small Outline Package (SOIC)
DRAWING NO.
20S2
REV.
A
175
1477I–AVR–10/06
32M1-A
D
D1
1
2
3
0
Pin 1 ID
E1
SIDE VIEW
E
TOP VIEW
A3
A2
A1
A
K
0.08 C
P
D2
1
2
3
P
Pin #1 Notch
(0.20 R)
K
e
SYMBOL
MIN
NOM
MAX
A
0.80
0.90
1.00
A1
–
0.02
0.05
A2
–
0.65
1.00
A3
E2
b
COMMON DIMENSIONS
(Unit of Measure = mm)
L
BOTTOM VIEW
0.20 REF
b
0.18
0.23
0.30
D
4.90
5.00
5.10
D1
4.70
4.75
4.80
D2
2.95
3.10
3.25
5.10
E
4.90
5.00
E1
4.70
4.75
4.80
E2
2.95
3.10
3.25
e
Note: JEDEC Standard MO-220, Fig. 2 (Anvil Singulation), VHHD-2.
NOTE
0.50 BSC
L
0.30
0.40
0.50
0.60
12o
P
–
–
0
–
–
K
0.20
–
–
5/25/06
R
176
2325 Orchard Parkway
San Jose, CA 95131
TITLE
32M1-A, 32-pad, 5 x 5 x 1.0 mm Body, Lead Pitch 0.50 mm,
3.10 mm Exposed Pad, Micro Lead Frame Package (MLF)
DRAWING NO.
32M1-A
REV.
E
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Errata
The revision letter refers to the revision of the device.
ATtiny26 Rev. B/C/D
• First Analog Comparator conversion may be delayed
1. First Analog Comparator conversion may be delayed
If the device is powered by a slow rising VCC, the first Analog Comparator conversion will take longer than expected on some devices.
Problem Fix/Workaround
When the device has been powered or reset, disable then enable the Analog Comparator before the first conversion.
177
1477I–AVR–10/06
Datasheet Revision
History
Please note that the referring page numbers in this section are referred to this document. The referring revision in this section are referring to the document revision.
Rev. 1477I-10/06
1. Updated “Errata” on page 177
Rev. 1477H-04/06
1. Updated typos.
2. Added “Resources” on page 6.
3. Updated features in “System Control and Reset” on page 33.
4. Updated “Prescaling and Conversion Timing” on page 98.
5. Updated algorithm for “Enter Programming Mode” on page 114.
Rev. 1477G-03/05
1. MLF-package alternative changed to “Quad Flat No-Lead/Micro Lead Frame
Package QFN/MLF”.
2. Updated “Electrical Characteristics” on page 128
3. Updated “Ordering Information” on page 173
Rev. 1477F-12/04
1. Updated Table 16 on page 34, Table 9 on page 29, and Table 29 on page 59.
2. Added Table 20 on page 41.
3. Added “Changing Channel or Reference Selection” on page 100.
4. Updated “Offset Compensation Schemes” on page 107.
5. Updated “Electrical Characteristics” on page 128.
6. Updated package information for “20P3” on page 174.
7. Rearranged some sections in the datasheet.
Rev. 1477E-10/03
1. Removed Preliminary references.
2. Updated “Features” on page 1.
3. Removed SSOP package reference from “Pin Configuration” on page 2.
4. Updated VRST and tRST in Table 16 on page 34.
5. Updated “Calibrated Internal RC Oscillator” on page 30.
6. Updated DC Characteristics for VOL, IIL, IIH, ICC Power Down and VACIO in “Electrical Characteristics” on page 128.
7. Updated VINT, INL and Gain Error in “ADC Characteristics” on page 131 and
page 132. Fixed typo in “Absolute Accuracy” on page 132.
178
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
8. Added Figure 106 in “Pin Driver Strength” on page 148, Figure 120, Figure 121
and Figure 122 in “BOD Thresholds and Analog Comparator Offset” on page
157. Updated Figure 117 and Figure 118.
9. Removed LPM Rd, Z+ from “Instruction Set Summary” on page 171. This
instruction is not supported in ATtiny26.
Rev. 1477D-05/03
1. Updated “Packaging Information” on page 174.
2. Removed ADHSM from “ADC Characteristics” on page 131.
3. Added section “EEPROM Write During Power-down Sleep Mode” on page 21.
4. Added section “Default Clock Source” on page 27.
5. Corrected PLL Lock value in the “Bit 0 – PLOCK: PLL Lock Detector” on page
76.
6. Added information about conversion time when selecting differential channels on page 99.
7. Corrected {DDxn, PORTxn} value on page 45.
8. Added section “Unconnected Pins” on page 48.
9. Added note for RSTDISBL Fuse in Table 50 on page 110.
10. Corrected DATA value in Figure 61 on page 118.
11. Added WD_FUSE period in Table 60 on page 125.
12. Updated “ADC Characteristics” on page 131 and added Table 66, “ADC Characteristics, Differential Channels, TA = -40×C to 85×C,” on page 132.
13. Updated “ATtiny26 Typical Characteristics” on page 133.
14. Added LPM Rd, Z and LPM Rd, Z+ in “Instruction Set Summary” on page 171.
Rev. 1477C-09/02
1. Changed the Endurance on the Flash to 10,000 Write/Erase Cycles.
Rev. 1477B-04/02
1. Removed all references to Power Save sleep mode in the section “System
Clock and Clock Options” on page 24.
2. Updated the section “Analog to Digital Converter” on page 96 with more
details on how to read the conversion result for both differential and singleended conversion.
3. Updated “Ordering Information” on page 173 and added QFN/MLF package
information.
Rev. 1477A-03/02
1. Initial version.
179
1477I–AVR–10/06
180
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Table of Contents
Features................................................................................................ 1
Pin Configuration................................................................................. 2
Description ........................................................................................... 3
Block Diagram ...................................................................................................... 4
Pin Descriptions.................................................................................................... 5
Resources ............................................................................................ 6
About Code Examples......................................................................... 7
AVR CPU Core ..................................................................................... 8
Architectural Overview.......................................................................................... 8
General Purpose Register File ............................................................................. 9
ALU – Arithmetic Logic Unit................................................................................ 10
Status Register – SREG ..................................................................................... 11
Stack Pointer – SP.............................................................................................. 12
Program and Data Addressing Modes................................................................ 12
Memories ............................................................................................ 17
In-System Programmable Flash Program Memory ............................................
SRAM Data Memory...........................................................................................
EEPROM Data Memory......................................................................................
I/O Memory .........................................................................................................
18
18
19
22
System Clock and Clock Options .................................................... 24
Clock Systems and their Distribution ..................................................................
Clock Sources.....................................................................................................
Default Clock Source ..........................................................................................
Crystal Oscillator.................................................................................................
Low-frequency Crystal Oscillator ........................................................................
External RC Oscillator ........................................................................................
Calibrated Internal RC Oscillator ........................................................................
External Clock.....................................................................................................
High Frequency PLL Clock – PLLCLK................................................................
24
26
27
27
28
29
30
31
32
System Control and Reset ................................................................ 33
Power-on Reset ..................................................................................................
External Reset ....................................................................................................
Brown-out Detection ...........................................................................................
Watchdog Reset .................................................................................................
MCU Status Register – MCUSR.........................................................................
34
35
36
36
37
Power Management and Sleep Modes............................................. 38
MCU Control Register – MCUCR ....................................................................... 38
i
1477I–AVR–10/06
Idle Mode ............................................................................................................
ADC Noise Reduction Mode...............................................................................
Power-down Mode..............................................................................................
Standby Mode.....................................................................................................
Minimizing Power Consumption .........................................................................
39
39
39
40
41
I/O Ports.............................................................................................. 43
Introduction .........................................................................................................
Ports as General Digital I/O ................................................................................
Alternate Port Functions .....................................................................................
Register Description for I/O Ports .......................................................................
43
44
48
58
Interrupts ............................................................................................ 59
Interrupt Vectors ................................................................................................. 59
Interrupt Handling ............................................................................................... 60
External Interrupt............................................................................... 64
Pin Change Interrupt........................................................................................... 64
Timer/Counters .................................................................................. 66
Timer/Counter0 Prescaler...................................................................................
Timer/Counter1 Prescaler...................................................................................
8-bit Timer/Counter0...........................................................................................
8-bit Timer/Counter1...........................................................................................
66
67
67
69
Watchdog Timer................................................................................. 80
Universal Serial Interface – USI........................................................ 82
Overview.............................................................................................................
Register Descriptions..........................................................................................
Functional Descriptions ......................................................................................
Alternative USI Usage ........................................................................................
82
83
87
92
Analog Comparator ........................................................................... 93
Analog to Digital Converter .............................................................. 96
Features.............................................................................................................. 96
Operation ............................................................................................................ 97
Prescaling and Conversion Timing ..................................................................... 98
Changing Channel or Reference Selection ...................................................... 100
ADC Noise Canceler Function.......................................................................... 101
ADC Conversion Result.................................................................................... 101
Scanning Multiple Channels ............................................................................. 107
ADC Noise Canceling Techniques ................................................................... 107
Offset Compensation Schemes ........................................................................ 107
ii
ATtiny26(L)
1477I–AVR–10/06
ATtiny26(L)
Memory Programming..................................................................... 109
Program and Data Memory Lock Bits...............................................................
Fuse Bits...........................................................................................................
Signature Bytes ................................................................................................
Calibration Byte ................................................................................................
Page Size .........................................................................................................
Parallel Programming Parameters, Pin Mapping, and Commands ..................
Parallel Programming .......................................................................................
Serial Downloading...........................................................................................
Serial Programming Pin Mapping .....................................................................
109
110
111
111
111
111
114
123
123
Electrical Characteristics................................................................ 128
Absolute Maximum Ratings*.............................................................................
DC Characteristics............................................................................................
External Clock Drive Waveforms ......................................................................
External Clock Drive .........................................................................................
ADC Characteristics .........................................................................................
128
128
130
130
131
ATtiny26 Typical Characteristics ................................................... 133
Register Summary ........................................................................... 170
Instruction Set Summary ................................................................ 171
Ordering Information....................................................................... 173
Packaging Information .................................................................... 174
20P3 ................................................................................................................. 174
20S ................................................................................................................... 175
32M1-A ............................................................................................................. 176
Errata ................................................................................................ 177
ATtiny26, all revisions....................................................................................... 177
Datasheet Revision History ............................................................ 178
Changes from Rev. 1477G-03/05 to Rev. 1477H-04/06...................................
Changes from Rev. 1477F-12/04 to Rev. 1477G-03/05 ...................................
Changes from Rev. 1477E-10/03 to Rev. 1477F-12/04 ...................................
Changes from Rev. 1477D-05/03 to Rev. 1477E-10/03 ...................................
Changes from Rev. 1477C-09/02 to Rev. 1477D-05/03...................................
Changes from Rev. 1477B-04/02 to Rev. 1477C-09/02 ...................................
Changes from Rev. 1477A-03/02 to Rev. 1477B-04/02 ...................................
178
178
178
178
179
179
179
Table of Contents ................................................................................. i
iii
1477I–AVR–10/06
iv
ATtiny26(L)
1477I–AVR–10/06
Atmel Corporation
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1477I–AVR–10/06