Features
•High Pe rformance, Low Power AVR® 8-Bit Microcontroller
•Advanced RISC Architecture
– 120 Po we rful Instructions – Most Single Clock Cy cle Execu tion
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
•Non-volatile Program and Data Memories
– 2/4/8K Bytes of In-System Programmable Program Memory Flash
• Endurance: 10,000 Write/Erase Cycles
– 128/256/512 Bytes In-System Programmable EEPROM
• Endurance: 100,000 Write/Erase Cycles
– 128/256/512 Bytes Internal SR AM
– Programming Lock for Self-Programming Flash Program and EEPROM Data
Security
•Peripheral Features
– 8-bit Timer/Counter with Prescaler and Two PWM Channels
– 8-bit High Speed Timer/Counter with Separate Prescaler
• 2 High Frequency PWM Outputs with Sepa rate Output Compare Registe rs
• Programmable Dead Time Generator
– USI – Universal Serial Interface with Start Condition Detector
– 10-bit ADC
• 4 Single Ended Channels
• 2 Differential ADC Channel Pairs with Programmable Gain (1x, 20x)
• Temperature Measurement
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
•Special Microcontroller Features
– debugWIRE On-chip Debug System
– In-System Programmable via SPI Port
– External and Internal Interrupt Sources
– Low Power Idle, ADC Noise Reduction, and Power-down Modes
– Enhanced P ower-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated Oscillator
•I/O and Packages
– Six Programmable I/O Lines
– 8-pin PDIP, 8-pin SOIC, 20-pad QFN/MLF, and 8-pin TSSOP (only ATtiny45/V)
•Operatin g Voltage
– 1.8 - 5.5V for ATtiny25V/45V/85V
– 2.7 - 5.5V for ATtiny25/45/85
•Speed Grade
– ATtiny25V/45V/85V: 0 – 4 MHz @ 1.8 - 5.5V, 0 - 10 MHz @ 2.7 - 5.5V
– ATtiny25/45/85: 0 – 10 MHz @ 2.7 - 5.5V, 0 - 20 MHz @ 4.5 - 5.5V
•Industrial Temperature Range
•Low Power Consumption
– Active Mode:
• 1 MHz, 1.8V: 300 µA
– Power-down Mode:
• 0.1 µA at 1.8V
8-bit
Microcontroller
with 2/4/8K
Bytes In-System
Programmable
Flash
ATtiny25/V
ATtiny45/V
ATtiny85/V
Rev. 2586N–AVR–04/11
22586N–AVR–04/11
ATtiny25/45/85
1. Pin Configurations
Figure 1-1. Pinout ATtiny25 /4 5/85
1.1 Pin Descriptions
1.1.1 VCC Supply voltage.
1.1.2 GND Ground.
1.1.3 Port B (PB5:PB0)
Port B is a 6-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
1
2
3
4
8
7
6
5
(PCINT5/RESET/ADC0/dW) PB5
(PCINT3/XTAL1/CLKI/OC1B/ADC3) PB3
(PCINT4/XTAL2/CLKO/OC1B/ADC2) PB4
GND
VCC
PB2 (SCK/USCK/SCL/ADC1/T0/INT0/PCINT2)
PB1 (MISO/DO/AIN1/OC0B/OC1A/PCINT1)
PB0 (MOSI/DI/SDA/AIN0/OC0A/OC1A/AREF/PCINT0)
PDIP/SOIC/TSSOP
1
2
3
4
5
QFN/MLF
15
14
13
12
11
20
19
18
17
16
6
7
8
9
10
DNC
DNC
GND
DNC
DNC
DNC
DNC
DNC
DNC
DNC
NOTE: Bottom pad should be soldered to ground.
DNC: Do Not Connect
NOTE: TSSOP only for ATtiny45/V
(PCINT5/RESET/ADC0/dW) PB5
(PCINT3/XTAL1/CLKI/OC1B/ADC3) PB3
DNC
DNC
(PCINT4/XTAL2/CLKO/OC1B/ADC2) PB4
VCC
PB2 (SCK/USCK/SCL/ADC1/T0/INT0/PCINT2)
DNC
PB1 (MISO/DO/AIN1/OC0B/OC1A/PCINT1)
PB0 (MOSI/DI/SDA/AIN0/OC0A/OC1A/AREF/PCINT0)
3
2586N–AVR–04/11
ATtiny25/45/85
resistors are activated. Th e Port B pins are tri-stated when a reset co ndition becomes active,
even if the clock is not running.
Port B also serve s the functions of var ious special features of the ATtiny25/45/85 as listed in
“Alternate Functions of Port B” on page 62.
On ATtiny25, the programmable I/O ports PB3 and PB4 (pins 2 and 3) are exchanged in
ATtiny15 Compatibility Mode for supporting the backward compatibility with ATtiny15.
1.1.4 RESET Reset input. A low level on this pin for longer than the minimum pulse length will gen erate a
reset, even if the clock is not r unning and pr ovided the reset pin has not be en disabled . The min-
imum pulse length is given in Table 21-4 on page 170. Shorter pulses are not guaranteed to
generate a reset.
The reset pin can also be used as a (weak) I/O pin.
42586N–AVR–04/11
ATtiny25/45/85
2. Overview The ATtiny25/45/85 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerf ul instru ctio ns in a single clock cycle, the ATt iny25 /45/ 85
achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize
power consumption versus proc essing speed.
2.1 Block Diagram
Figure 2-1. Block Diagram
The AVR core combines a rich instruction set with 32 general purpose working registers. All 32
registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
PROGRAM
COUNTER
CALIBRATED
INTERNAL
OSCILLATOR
WATCHDOG
TIMER
STACK
POINTER
PROGRAM
FLASH SRAM
MCU CONTROL
REGISTER
GENERAL
PURPOSE
REGISTERS
INSTRUCTION
REGISTER
TIMER/
COUNTER0
SERIAL
UNIVERSAL
INTERFACE
TIMER/
COUNTER1
INSTRUCTION
DECODER
DATA DIR.
REG.PORT B
DATA REGISTER
PORT B
PROGRAMMING
LOGIC
TIMING AND
CONTROL
MCU STATUS
REGISTER
STATUS
REGISTER
ALU
PORT B DRIVERS
PB[0:5]
VCC
GND
CONTROL
LINES
8-BIT DATABUS
Z
ADC /
ANALOG COMPARATOR
INTERRUPT
UNIT
DATA
EEPROM OSCILLATORS
Y
X
RESET
5
2586N–AVR–04/11
ATtiny25/45/85
registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achiev ing throughputs up to ten times faster than con-
ventional CISC microcontrollers.
The ATtiny25/45/85 provides the following features: 2/4/8K bytes of In-System Programmable
Flash, 128/256/512 bytes EEPROM, 128/256/256 bytes SRAM, 6 general purpose I/O lines, 32
general purpose working registers, one 8-bit Timer/Counter with compare modes, one 8-bit high
speed Timer/Counter, Universal Serial Interface, Internal and External Interrupts, a 4-channel,
10-bit ADC, a programmable Watchdog Timer with internal Oscillator, and three software select-
able power saving modes. Idle mode stops the CPU while allowing the SRAM, Timer/Counter,
ADC, Analog Comparator, and Interrupt system to continue functioning. Power-down mode
saves the register content s, disabling all chip functions until the nex t Interrupt or Hardware
Reset. ADC Noise Reduction mode stop s the CPU and all I /O modules except ADC, to minimi ze
switching noise during ADC conversions.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip ISP Flash allows the Program memory to be re-programmed In-System through an SPI
serial interface, by a conventional non-volatile memory programmer or by an On-chip boot code
running on the AVR core.
The ATtiny25/45/ 85 AVR is suppor ted with a f ull suite of program and syst em developmen t tools
including: C Compilers, Macro Assemblers, Program Debugger/Simulators and Evaluation kits.
62586N–AVR–04/11
ATtiny25/45/85
3. About
3.1 Resources A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
3.2 Code Examples
This documentatio n contains simple co de examples that br iefly sh ow how to u se various parts of
the device. These code examp les assume that the part specific header file is included b efore
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt ha ndlin g in C is com piler d epe nd ent. Please con firm wit h the C com piler d ocume n-
tation for more details.
For I/O Registers located in the extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically, this
means “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. Note that not all
AVR devices include an exte nded I/O map.
3.3 Capacitive Touch Sensing
Atmel QTouch Library provides a simple to use solution for touch sensitive interfaces on Atmel
AVR microcontrollers. The QTouch Library includes support for QTouch® and QMatrix® acquisi-
tion methods.
Touch sensing is easily added to any application by linking the QTouch Library and using the
Application Progra mming In terface (API ) of the libra ry to defi ne the touch ch annels and sensors.
The application then calls the API to retrieve channel information and determine the state of the
touch sensor.
The QTouch Library is free and can be downloaded from the Atmel website. For more informa-
tion and details of implementation, refer to the QTouch Library User Guide – also available from
the Atmel website.
3.4 Data Retention
Reliability Qualification results show that the projected data retention failure rate is much less
than 1 PPM over 20 years at 85°C or 100 years at 25°C.
7
2586N–AVR–04/11
ATtiny25/45/85
4. AVR CPU Core
4.1 Introduction This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
4.2 Architectural Overview
Figure 4-1. Block Diagram of the AVR Architecture
In order to maximize performance and parallelism , the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the Program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruc-
tion is pre-fetche d from the Progr am memory. This concept enables instructions to be executed
in every clock cycle. The Program memory is In-System Reprogrammable Flash memory.
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Program
Counter
Control Lines
32 x 8
General
Purpose
Registrers
ALU
Status
and Control
I/O Lines
EEPROM
Data Bus 8-bit
Data
SRAM
Direct Addressing
Indirect Addressing
Interrupt
Unit
Watchdog
Timer
Analog
Comparator
I/O Module 2
I/O Module1
I/O Module n
82586N–AVR–04/11
ATtiny25/45/85
The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ-
ical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficien t address calculations. One of the these addre ss pointers
can also be used as an address pointer for look up ta bles in Flash Program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single regi ster operation s can also be executed in th e ALU. After an ar ithmetic opera-
tion, the Stat us Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word for-
mat, but there are also 32-bit instructions.
During interrupts an d subroutine calls, the retur n address Program Count er (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector posi-
tion. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis-
ters, SPI, and other I/O fun ctions. The I/O memory can be access ed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F.
4.3 ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or betwee n a re gister an d an immedi ate ar e execut ed . The ALU ope ra tio ns are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
4.4 Status Register
The Status Regist er conta ins infor mation a bout the result of th e most recently e xecuted ari thme-
tic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the I nstru ction Se t Re ference. This will in many case s re move the n eed f or using t he
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an inte rr up t. T his mu st be ha nd le d by so ftw ar e.
9
2586N–AVR–04/11
ATtiny25/45/85
4.4.1 SREG – AVR Status Register
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Globa l Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter-
rupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry is useful
in BCD arithmetic. See t he “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or betwee n 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 in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
Bit 76543210
0x3F I T H S V N Z C SREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
10 2586N–AVR–04/11
ATtiny25/45/85
4.5 General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruc tion set. In order t o achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit outpu t operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 4-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 4-2. AVR CPU General Purpose Working Registers
Most of the instructions operating on the Register File have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 4-2, each register is also assigned a Data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically imple-
mented as SRAM locations, this memo ry organization provides great fle xibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file .
4.5.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters are 16-bit address pointers for indirect ad dressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 4- 3.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers R17 0x11
…
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte
11
2586N–AVR–04/11
ATtiny25/45/85
Figure 4-3. The X-, Y-, and Z-registers
In the differ ent a ddr essing modes the se ad dr ess regist er s have fun cti ons a s fi xed d isp lacement ,
automatic increment, and automatic decrement (see the instruction set reference for details).
4.6 Stack Pointer The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of th e Stack. No te that the Sta ck is implement ed as growing from hig her memor y loca-
tions to lower memor y locat io ns. This im plies t hat a Stack PUSH co mmand decr ease s th e Stack
Pointer.
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 0x60. The Stack Point er is decrement ed by one when d ata is pushed onto the St ack
with the PUSH instruction, and it is decremented by two when the return add re ss is pushed on to
the Stack with subroutine call or inte rrupt. The Stack Point er is increme nted by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when data is
popped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
4.6.1 SPH and SPL — Stack Pointer Register
15 XH XL 0
X-register 707 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 707 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 7070
R31 (0x1F) R30 (0x1E)
Bit 151413121110 9 8
0x3E SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
0x3D SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
12 2586N–AVR–04/11
ATtiny25/45/85
4.7 Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly genera ted f rom th e selected clo ck source f or the
chip. No internal clock division is used.
Figure 4- 4 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 4-4. The Parallel Instruction Fetches and Instruction Executions
Figure 4-5 shows the int ernal timi ng con cept for th e Regi ster File . In a single clock cycl e an ALU
operation using two register operands is executed, and the result is stored back to the destina-
tion register.
Figure 4-5. Single Cycle ALU Operation
4.8 Reset and Interrupt Handling
The AVR provides several different inte rrupt sources. These interrupts and the separate Reset
Vector each have a separate Program Vector in the Program memo ry space. All interrupts are
assigned individual enable bits which must be wr itten logic one to gether with th e Global Inter rupt
Enable bit in the Stat us Register in order to enable the interrupt.
The lowest addresses in the Program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 50. 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.
clk
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
T1 T2 T3 T4
CPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
T1 T2 T3 T4
clkCPU
13
2586N–AVR–04/11
ATtiny25/45/85
When an interrupt occurs, th e Global Interrupt Enable I-bit is cleared and all interrup ts are dis-
abled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is au tomatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vec-
tor in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writ ing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. The se
interrupts do not nece ssarily have I nterrupt Fla gs. If t he interr upt condit ion disappear s before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The f ollowing e xa mple sho ws how this can be used to a void interrupts during the
timed EEPROM write sequence.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMPE ; start EEPROM write
sbi EECR, EEPE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
14 2586N–AVR–04/11
ATtiny25/45/85
When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-
cuted before any pending interrupts, as shown in this example.
4.8.1 Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-
mum. After fo ur clock cycles the Pro gram Vector addre ss for the actua l interrupt han dling routine
is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is in creased by fo ur clock cycles. This incre ase comes in additi on to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and t he I-bit in SREG is set.
Assembly Code Example
sei ; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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ATtiny25/45/85
5. AVR Memories
This section describes the different memories in the ATtiny25/45/85. The AVR architecture has
two main memory spaces, the Data memory and the Program memory space. In addition, the
ATtiny25/45/85 features an EEPROM Memory for data storage. All three memory spaces are lin-
ear and regular.
5.1 In-System Re-programmable Flash Program Memory
The ATtiny25/45/85 co ntains 2/4/8K bytes On-chip In-System Reprogrammable Flash memo ry
for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as
1024/2048 /4096 x 16.
The Flash memory has an endurance of at least 10,000 write/er ase cycles . The ATtiny25/45 /85
Program Counter (PC) is 10/11/12 bits wide, thus addressing the 1 024/2048/4096 Program
memory locations. “Me mory Programmin g” on page 151 contains a detailed descri ption on Flash
data serial downloading using the SPI pins.
Constant tables ca n be allocated within the entire Progra m memory address space (see the
LPM – Load Program memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim-
ing” on page 12.
Figure 5-1. Program Memory Map
5.2 SRAM Data Memory
Figure 5-2 shows how the ATtiny25/45/85 SRAM Memory is organized.
The lower 224/352/607 Data memory locations address both the Register File, the I/O memory
and the internal da ta SRAM. The first 32 locations addre ss the Register File, the next 64 loca -
tions the standard I/O memory, and the last 128/256 /512 locations address the internal data
SRAM.
The five different address ing modes for the Data memory cov er: Direct, Indirect with Displace-
ment, 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 Displacemen t mode reaches 63 add ress locations from the base address given
by the Y- or Z-register.
0x0000
0x03FF/0x07FF/0x0FFF
Program Memory
16 2586N–AVR–04/11
ATtiny25/45/85
When using register indirect addressing modes with automatic pre-decrement and post-incre-
ment, the address registers X, Y, and Z are decrement ed or incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 128/256/512 bytes of inter-
nal data SRAM in the ATtiny25/45/85 are all accessible through all these addressing modes.
The Register File is described in “General Purpos e Register File” on page 10.
Figure 5-2. Data Memory Map
5.2.1 Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figur e 5- 3.
Figure 5-3. On-chip Data SRAM Access Cycles
5.3 EEPROM Data Memory
The ATtiny25/45/85 contains 128/256/512 bytes of data EEPROM memory. It is organized as a
separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/e rase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPR OM
Data Register, and the EEPROM Control Register. For details see “Serial Downloading” on page
155.
5.3.1 EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
32 Registers
64 I/O Registers
Internal SRAM
(128/256/512 x 8)
0x0000 - 0x001F
0x0020 - 0x005F
0x0DF/0x015F/0x025F
0x0060
Data Memory
clk
WR
RD
Data
Data
Address
Address valid
T1 T2 T3
Compute Address
Read Write
CPU
Memory Access Instruction Next Instruction
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ATtiny25/45/85
The write access times for the EEPROM are given in Table 5-1 on page 21. A self-timing func-
tion, however, lets the user software detect when the next byte can be written. If the user code
contains instructions that write the EEPROM, some precautions must be taken. In heavily fil-
tered power supplies, VCC is likely to rise or fall slowly on Power-up/down. This causes the
device for some period of time to run at a voltage lower than specified as minimum for the clock
frequency used. See “Preventing EEPROM Co rruption” on page 19 for details on how to avoid
problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to “Atomic Byte Program ming” on page 17 and “Split Byte Programming” on page 17 for
details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
5.3.2 Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPRO M, the
user must write the address into the EEAR Register and data into EEDR Register. If the EEPMn
bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the erase/write
operation. Both the erase and write cycle are done in one operation and the total programming
time is given in Table 5-1 on page 21. The EEPE bit remains set until the erase and write opera-
tions are completed. While the device is busy with programming, it is not possible to do any
other EEPROM operations.
5.3.3 Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if
the system requires short access time for some limited period of time (typically if the power sup-
ply voltage falls). In order to take advantage of this method, it is required that the locations to be
written have been erased before the write operation. But since the erase and write operations
are split, it is possib le to do the erase operations when th e system allows doing time-critical
operations (typically after Power-up).
5.3.4 Erase To erase a byte, the address must be written to EEAR. If the EEPM n bits are 0b01, writing the
EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (program-
ming time is given in Table 5-1 on page 21). The EEPE bit remains set until the erase operation
completes. While the device is busy programming, it is not possible to do any other EEPROM
operations.
5.3.5 Write To write a location, the user must write the address into EEAR and the data into EEDR. If the
EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger
the write operation only (programming time is given in Table 5-1 on page 21). The EEPE bit
remains set until the write operation completes. If the location to be written has not been erased
before write, the data that is stored must be considered as lost. While the device is busy with
programming, it is not possible to do any other EEPROM operations.
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator fre-
quency is within the requirements described in “OSCCAL – Oscillator Calibration Register” on
page 32.
18 2586N–AVR–04/11
ATtiny25/45/85
The following code examples show one assembly and one C function for erase, write, or atomic
write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling
interrupts globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_write
; Set Programming mode
ldi r16, (0<<EEPM1)|(0<<EEPM0)
out EECR, r16
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r19) to data register
out EEDR, r19
; Write logical one to EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret
C Code Example
void EEPROM_write(unsigned char ucAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set Programming mode */
EECR = (0<<EEPM1)|(0<<EEPM0);
/* Set up address and data registers */
EEAR = ucAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
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ATtiny25/45/85
The next code examples show assembly and C functions for reading the EEPROM. The exam-
ples assume that interrupts are controlled so that no interrupts will occur during execution of
these functio ns.
5.3.6 Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supp ly voltage is
too low for the CPU and the EEPROM to operate properly. These issues a re the same as for
board level systems using 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 seque nce to the EEPROM requires a minimum voltage to operate correctly. Sec-
ondly, the CPU itself can execute instructions incorrectly , if the su pp ly voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
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 detection level of the internal
BOD does not match the neede d de te ction level, an e xterna l low VCC reset protection circuit can
be used. If a reset occurs while a write operation is in progress , the write operation will be com-
pleted provided that the power supply voltage is sufficient.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from data register
in r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned char ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
20 2586N–AVR–04/11
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5.4 I/O Memory The I/O space defin itio n of th e AT tiny 25 /4 5 /85 is sho w n in “Register Summary” on page 205.
All ATtiny25/45/85 I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD/L DS/LDD and ST/STS/STD in structions, transferring dat a between the 32
general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these re giste rs, the
value of single bits can b e checked b y using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, the
I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using
LD and ST instructions, 0x20 must be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flag s are cleared b y writing a lo gical one to t hem. Note th at the CBI a nd SBI
instructions will only operate on the specified bit, and can therefore be used on registers contain-
ing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
5.5 Register Description
5.5.1 EEARH and EEARL – EEPROM Address Register
• Bits 7:1 – Res: Reserved Bits
These bits are reserved for future use and will always read as 0 in ATtiny25/45/85.
• Bits 8:0 – EEAR[8:0]: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL – specifies the high EEPROM address
in the 128/256/512 bytes EEPROM space. The EEPROM data bytes are addressed linearly
between 0 and 127/255/511. The initial value of EEAR is undefined. A proper value must be writ-
ten before the EEPROM may be accessed.
5.5.2 EEDR – EEPROM Data Register
• Bits 7:0 – EEDR[7:0]: EEPROM Data
For the EEPROM write operation the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the
EEDR contains the data read out from the EEPROM at the address given by EEAR.
Bit 76543210
0x1F – – – – – – –EEAR8EEARH
0x1E EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
Bit 76543210
Read/Write RRRRRRRR/W
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
Initial ValueXXXXXXXX
Bit 76543210
0x1D EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.5.3 EECR – EEPROM Control Register
• Bit 7 – Res: Reserved Bit
This bit is reserved for future use and will always read as 0 in ATtiny25/45/85. For compatibility
with future AVR devices, always write this bit to zero. After reading, mask out this bit.
• Bit 6 – Res: Reserved Bit
This bit is reserved in the ATtiny25/45/85 and will always read as zero.
• Bits 5:4 – EEPM[1:0]: EEPROM Programming Mode Bits
The EEPROM Programming mode bits setting defines which programming action that will be
triggered when writing EEPE. It is possible to program data in one atomic operation (erase the
old value and program the new value) or to split the Erase and Write operations in two different
operations. The Pr ogramming t imes for the d ifferen t modes ar e shown in Table 5-1. While EEPE
is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00
unless the EEPROM is busy programming.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a constant inter-
rupt when Non-volatile memory is ready for programming.
• Bit 2 – EEMPE: EEPROM Master Program Enable
The EEMPE bit determines whether writing EEPE to one will have effect or not.
When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the
selected address. If EEMPE is zero, setting EEPE will have no effect. When EEMPE has been
written to one by software, hardware clears the bit to zero after four clock cycles.
• Bit 1 – EEPE: EEPROM Program Enable
The EEPROM Program Enable Signal EEPE is the programming enable signal to the EEPROM.
When EEPE is written, the EEPROM will be programmed according to the EEPMn bits setting.
The EEMPE bit must be written to one b efore a logical one is written to EEPE, otherwise no
EEPROM write takes place. When the write access time has elapsed, the EEPE bit is cleared
by hardware. When EEPE has been set, the CPU is halted for two cycles before the next
instruction is executed.
Bit 76543210
0x1C – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 X X 0 0 X 0
Table 5-1. EEPROM Mode Bits
EEPM1 EEPM0 Programming
Time Operation
0 0 3.4 ms Erase and Write in one operation (Atomic Operation)
0 1 1.8 ms Erase Only
1 0 1.8 ms Write Only
1 1 – Reserved for future use
22 2586N–AVR–04/11
ATtiny25/45/85
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the cor-
rect address is set up in the EEAR Register, the EERE bit must be written to one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed. The user should poll the EEPE bit before starting the read opera-
tion. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change
the EEAR Register.
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ATtiny25/45/85
6. System Clock and Clock Options
6.1 Clock Systems and their Distribution
Figure 6-1 presents the principal clock systems in the AVR and th eir distribution . All of the clocks
need not be active at a given time . In order to red uce power co nsumption, the clo cks to modu les
not being used can be halted by using different sleep modes, as described in “Power Manage-
ment and Sleep Modes” on page 35. The clock systems are detailed below.
Figure 6-1. Clock Distribution
6.1.1 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.
6.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority o f the I/O modules, like T imer/Counter. 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.
6.1.3 Flash Clock – clkFLASH
The Flash clock controls o peration of t he Flash in terface. Th e Flash clock is usually active simul-
taneously with the CPU clock.
General I/O
Modules CPU Core RAM
clk
I/O
AVR Clock
Control Unit clk
CPU
Flash and
EEPROM
clk
FLASH
Source clock W atchdog Timer
Watchdog
Oscillator
Reset Logic
Clock
Multiplexer
Watchdog clock
Calibrated RC
Oscillator
Calibrated RC
Oscillator
External Clock
ADC
clk
ADC
Crystal
Oscillator Low-Frequency
Crystal Oscillator
System Clock
Prescaler
PLL
Oscillator
clk
PCK
clk
PCK
24 2586N–AVR–04/11
ATtiny25/45/85
6.1.4 ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to re duce noise ge ner ated by digital cir cuit ry. Th is gives mo re accurat e ADC conversion
results.
6.1.5 Internal PLL for Fast Peripheral Clock Generation - clkPCK
The internal PLL in ATtiny25/45/85 generates a clock frequency that is 8x multiplied from a
source input. By default, the PLL uses the output of the internal, 8.0 MHz RC oscillator as
source. Alternatively, if bit LSM of PLLCSR is set the PLL will use the output of the RC oscillator
divided by two. Thus the output of the PLL, the fast peripheral clock is 64 MHz. The fast per iph-
eral clock, or a clock prescaled from that, can be selected as the clock source for
Timer/Counter1 or as a system clock. See Figure 6-2. The frequency of the fast peripheral clock
is divided by two when LSM of PLLCSR is set, resulting in a clock frequency of 32 MHz. Note,
that LSM can not be set if PLLCLK is used as system clock.
Figure 6-2. PCK Clocking System.
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 RC oscillator is taken to a
higher frequency than 8 MHz, the fast peripheral clock frequency saturates at 85 MHz (worst
case) and remains oscillating at the maximum frequency. It should be noted that the PLL in this
case is not locked any longer with the RC oscillator clock. Therefore, it is recommended not to
take the OSCCAL adjustments to a higher frequency than 8 MHz in order to keep the PLL in the
correct operating range.
The internal PLL is enabled when:
• The PLLE bit in the register PLLCSR is set.
• The CKSEL fuse is programmed to ‘0001’.
• The CKSEL fuse is programmed to ‘0011’.
The PLLCSR bit PLOCK is set when PLL is locked.
Both internal RC oscillator and PLL are switched off in power down and stand -by sleep modes.
6.1.6 Internal PLL in ATtiny15 Compatibility Mode
Since ATtiny25/45/85 is a migration device for ATtiny15 users there is an ATtiny15 compatibility
mode for backward compatibility. The ATtiny15 compatibility mode is selected by programming
the CKSEL fuses to ‘0011’.
25
2586N–AVR–04/11
ATtiny25/45/85
In the ATtiny15 compatibility mode the frequency of the internal RC oscillator is calibrated down
to 6.4 MHz and the multiplication factor of the PLL is set to 4x. See Figure 6-3. With these
adjustments the clocking system is ATtiny15-compatible and the resulting fast peripheral clock
has a frequency of 25.6 MHz (same as in ATtiny15).
Figure 6-3. PCK Clocking System in ATtiny15 Compatibility Mode.
Note that low speed mode is not implemented in ATtiny15 compatibility mode.
6.2 Clock SourcesThe device has the follo wing clock source options, selectable by Flash Fuse bits as shown
below. The cloc k fr om t he se lected so ur ce is i npu t t o th e AVR clo c k gene ra to r, an d rou te d t o the
appropriate modules.
Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.
2. The device is shipped with this option selected.
3. This will select ATtiny15 Compatibility Mode, where system clock is divided by f our, resulting in
a 1.6 MHz clock frequency. For more inormation, see “Calibrated Internal Oscillator” on page
27.
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down, the sele cted clo ck source is used to time t he start -up, ensuring sta-
ble Oscillator operatio n before instruction execution starts. When the CPU starts from reset,
there is an additional delay allowing the power to rea ch a stable level before commencing nor-
1/2
1.6 MHz
6.4 MHz
OSCILLATOR
PLL
8x
PLLEOSCCAL
3.2 MHz
LOCK
DETECTOR
SYSTEM
CLOCK
PLOCK
PCK
25.6 MHz
1/4
Table 6-1. Device Clocking Options Select
Device Clocking Option CKSEL[3:0](1)
External Clock (see page 26) 0000
High Frequency PLL Clock (see page 26) 0001
Calibrated Internal Oscillator (see page 27) 0010(2)
Calibrated Internal Oscillator (see page 27) 0011(3)
Internal 128 kHz Oscillator (see page 29) 0100
Low-Frequency Crystal Oscillator (see pag e 29) 0110
Crystal Oscillator / Ceramic Resonator (see page 30) 1000 – 1111
Reserved 0101, 0111
26 2586N–AVR–04/11
ATtiny25/45/85
mal 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 each time-out is shown in Table 6-2.
6.2.1 External ClockTo drive th e devic e from a n exter nal cl ock source, CLKI should be driven as shown in Figure 6-
4. To run the device on an external clock, the CKSEL Fuses must be programmed to “00”.
Figure 6-4. External Clock Drive Configuration
When this clock source is selected, start-up times are de termined by the SUT Fuses as sh own in
Table 6-3.
When applying an external clock, it is required t o avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
Note that the System Clock Prescaler can be used to implemen t run-time change s of the interna l
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
31 for details.
6.2.2 High Frequency PLL Clock
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
Table 6-2. Number of Watchdog Oscillator Cycles
Typ Time-out Number of Cycles
4 ms 512
64 ms 8K (8,192)
Table 6-3. Start-up Times for the External Clock Selection
SUT[1:0] Start-up Time from
Power-down Additional Delay from
Reset Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved
EXTERNAL
CLOCK
SIGNAL CLKI
GND
27
2586N–AVR–04/11
ATtiny25/45/85
a system clock source, by programming the CKSEL fuses to ‘0001’, it is divided by four like
shown in Table 6-4.
When this clock source i s select ed, st ar t-u p time s ar e dete rmin ed by the SUT fuses as shown in
Table 6-5.
6.2.3 Calibrated Internal Oscillator
By default, the Internal RC Oscillator provides an approximat e 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. See “Cali-
brated Internal RC Oscillator Accuracy” on page 169 and “Internal Oscillator Speed” on page
197 for more details. The device is shipped with the CKDIV8 Fuse programmed. See “System
Clock Prescaler” on page 31 for more details.
This clock may be sele ct ed as th e s ystem c loc k by p ro gram m in g th e CKS E L F us es as sh own in
Table 6-6 on page 28. If selected, it will operate with no external components. During reset,
hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby
automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory
calibration in Table 21-2 on page 169.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 32, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of th is calibration is shown as User calibration in Table 21-2 on page 169.
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the
Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed cali-
bration value, see the section “Calibration Bytes” on p age 154.
The internal oscillator can also be set to provide a 6.4 MHz clock by writing CKSEL fuses to
“0011”, as shown in Table 6-6 below. This setting is reffered to as ATtiny15 Compatibility Mode
and is intended to pr ovide a calibrated clock source at 6.4 MHz, as in ATtiny1 5. In ATtiny15
Compatibility Mode the PLL uses the internal oscillator running at 6.4 MHz to generate a
25.6 MHz peripheral clock signal for Timer/Counter1 (see “8-bit Timer/Counter1 in ATtiny15
Table 6-4. High Frequency PLL Clock Operating Modes
CKSEL[3:0] Nominal Frequency
0001 16 MHz
Table 6-5. Start-up Times for the High Frequency PLL Clock
SUT[1:0] Start-up Time from
Power Down Additional Delay from
Power-On Reset (VCC = 5.0V) Recommended
usage
00 14CK + 1K (1024) CK + 4 ms 4 ms BOD enabled
01 14CK + 16K (16384) CK + 4 ms 4 ms Fast rising power
10 14CK + 1K (1024) CK + 64 ms 4 ms Slowly rising power
11 14CK + 16K (16384) CK + 64 ms 4 ms Slowly rising power
28 2586N–AVR–04/11
ATtiny25/45/85
Mode” on pa ge 98). Note that in this mode of operation the 6.4 MHz clock signal is always
divided by four, providing a 1.6 MHz system clock.
Note: 1. The device is shipped with this option selected.
2. This setting will select ATtiny15 Compatibility Mode, where system clock is divided by four,
resulting in a 1.6 MHz clock frequency.
When the calibrated 8 MHz internal oscillator is selected as clock source the start-up times are
determined by the SUT Fuses as shown in Table 6-7 below.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increa sed to 14CK + 4 ms to
ensure programming mode can be entered.
2. The device is shipped with this option selected.
In ATtiny15 Compatibility Mode start-up times are determined by SUT fuses as shown in Table
6-8 below.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increa sed to 14CK + 4 ms to
ensure programming mode can be entered.
In summary, more information on ATtiny15 Compatibility Mode can be found in sections “Port B
(PB5:PB0)” on page 2, “Internal PLL in ATtiny15 Compatibility Mode” on page 24, “8-bit
Timer/Counter1 in ATtiny15 Mode” on page 98, “Limitations of debugWIRE” on page 144, “Cali-
bration Bytes” on page 154 and in table “Clock Prescaler Select” on page 34.
Table 6-6. Internal Calibrated RC Oscillator Operating Modes
CKSEL[3:0] Nominal Frequency
0010(1) 8.0 MHz
0011(2) 6.4 MHz
Table 6-7. Start-up Times for Internal Calibrated RC Oscillator Clock
SUT[1:0] Start-up Time
from Power-down Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK 14CK(1) BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10(2) 6 CK 14CK + 64 ms Slowly r ising power
11 Reserved
Table 6-8. Start-up Times for Internal Calibrated RC Oscillator Clock (in ATtiny15 Mode)
SUT[1:0] Start-up Time
from Power-down Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK 14CK + 64 ms
01 6 CK 14CK + 64 ms
10 6 CK 14CK + 4 ms
11 1 CK 14CK(1)
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6.2.4 Internal 128 kHz Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “0100”.
When this clock source is selected, start-up times are de termined by the SUT Fuses as sh own in
Table 6-9.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increa sed to 14CK + 4 ms to
ensure programming mode can be entered.
6.2.5 Low-Frequency Crystal Oscillator
To use a 32.7 68 kHz wat ch crystal as t he cl ock so urce for t he device, the Low-f reque ncy Crystal
Oscillator must be selected by setting CKSEL fuses to ‘0110’. The crystal should be connected
as shown in Figure 6-5. To find suitable load capacitance for a 32.768 kHz cr ysal, please consult
the manufacturer’s datasheet.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table 6-10.
Note: 1. These options should be used only if frequency stability at start-up is not important.
The Low-frequency Cr ystal Oscillator provid es an internal load capacitance, see Table 6-11 at
each TOSC pin.
Table 6-9. Start-up Times for the 128 kHz Internal Oscillator
SUT[1:0] Start-up Time from
Power-down Additional Delay from
Reset Recommended Usage
00 6 CK 14CK (1) BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 6-10. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
SUT[1:0] Start-up Time from
Power Down Additional Delay from
Reset (VCC = 5.0V) Recommended usage
00 1K (1024) CK(1) 4 ms Fast rising power or BOD enabled
01 1K (1024) CK(1) 64 ms Slowly rising power
10 32K (32768) CK 64 ms Stable frequency at start-up
11 Reserved
Table 6-11. Capacitance of Low-Frequency Cry stal Oscillator
Device 32 kHz Osc. Type Cap (Xtal1/Tosc1) Cap (Xtal2/Tosc2)
ATtiny25/45/85 System Osc. 16 pF 6 pF
30 2586N–AVR–04/11
ATtiny25/45/85
6.2.6 Crystal Oscillator / Ceramic Resonator
XTAL1 and XTAL2 are input and output , respectively, of an inver ting amplifier which ca n be con-
figured for use as an O n-chip Oscillator, as shown in Figure 6-5. Either a quartz crystal or a
ceramic resonator may be used.
Figure 6-5. Crystal Oscillator Connections
C1 and C2 should always be equal for both crystals and resonators. The optim al 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 give n in Table 6-12 below. For ceramic resona tors, the capacitor values
given by the manufacturer shou ld be used.
Notes: 1. This option should not be used with crystals, only with ceramic resonators.
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL[3:1] as shown in Table 6-12.
The CKSEL0 Fuse toget her wit h the SUT[ 1: 0] F uses select the sta rt -up t ime s as shown in Table
6-13.
Table 6-12. Crystal Osc illator Operating Modes
CKSEL[3:1] Frequency Range (MHz) Recommended Range for Capacitors C1 and
C2 for Use with Crystals (pF)
100(1) 0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 6-13. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT[1:0] Start-up Time from
Power-down Additional Delay
from Reset Recom mended Usag e
0 00 258 CK(1) 14CK + 4 ms Ceramic resonator,
fast rising power
0 01 258 CK(1) 14CK + 64 ms Ceramic resonator,
slowly rising power
0 10 1K (1024) CK(2) 14CK Ceramic resonator,
BOD enabled
XTAL2
XTAL1
GND
C2
C1
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Notes: 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. These
options are not suitable for crystals.
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 fre-
quency of the device, and if frequency stability at start-up is not important for the application.
6.2.7 Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is therefore the Internal RC Oscillator running at 8 MHz with longest start-up
time and an initial system clock prescaling of 8, resulting in 1.0 MHz system clock. This default
setting ensures that all users can make their desired clock source setting using an In-System or
High-voltage Programmer.
6.3 System Clock Prescaler
The ATtiny25/45/8 5 system clock can be divided by setting the “CLKPR – Clock Prescale Regis-
ter” on page 33. This feature can be used to decrease power consumption when the
requirement for processing power is low. This can be used with all clock source options, and it
will affect the clock frequency of the CP U and all synchronous peripherals. clkI/O, clkADC, clkCPU,
and clkFLASH are divided by a factor as shown in Table 6-15 on pag e 34.
6.3.1 Switching Time
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither the
clock frequency corresponding to the previous setting, nor the clock frequency corresponding to
the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, 2 active clock edges ar e produ ced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
0 11 1K (1024)CK(2) 14CK + 4 ms Ceramic resonator,
fast rising power
1 00 1K (1024)CK(2) 14CK + 64 ms Ceramic resonator,
slowly rising power
1 01 16K (16384) CK 14CK Crystal Oscillator,
BOD enabled
1 10 16K (16384) CK 14CK + 4 ms Crystal Oscillator,
fast rising power
1 11 16K (16384) CK 14CK + 64 ms Crystal Oscillator,
slowly rising power
Table 6-13. Start-up Times for the Crystal Oscillator Clock Selection (Continued)
CKSEL0 SUT[1:0] Start-up Time from
Power-down Additional Delay
from Reset Recom mended Usag e
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6.4 Clock Output Buffer
The device can output the system clock on the CLKO pin (when not used as XTAL2 pin). To
enable the out put, the CKOUT Fuse has to be pr ogrammed. This mode is suitable when the chip
clock is used to drive other circuits on the system. Note that the clock will not be output during
reset and that the normal operation of the I/O pin will be overridden when the fuse is pro-
grammed. Internal RC Oscillator, WDT Oscillator, PLL, and external clock (CLKI) can be
selected when the clock is output on CLKO. Crystal oscillators (XTAL1, XTAL2) can not be used
for clock output on CLKO. If the System Clock Prescaler is used, it is the divided system clock
that is output.
6.5 Register Description
6.5.1 OSCCAL – Oscillator Calibration Register
• Bits 7:0 – CAL[7:0]: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. A pre-programmed calibration v alue is
automatically writt en to this register du ring chip reset, giving the Factory calibrated frequency as
specified in Table 21-2 on page 169. The application software can write this register to change
the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 21-
2 on page 169. Calibration outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write acc esses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two fre-
quency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL[6:0] bits are used to tune th e frequency within the selected range . A setting of 0x00
gives the lowe st frequ ency in that range, a nd a setting of 0x7F g ives the highest fr equency in t he
range.
To ensure stable operation of the MCU the calibration value should be changed in small. A vari-
ation in frequency of more than 2% from one cycle to the next can lead to unpredicatble
behavior. Changes in OSCCAL should not exceed 0x20 for each calibration. It is required to
ensure that the MCU is kept in Reset during such changes in the clock frequency
Bit 76543210
0x31 CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
Table 6-14. Internal RC Oscillator Frequency Range
OSCCAL Value Typical Lowest Frequenc y
with Respect to Nominal Frequency T ypical Highest Frequency
with Respect to Nominal Frequency
0x00 50% 100%
0x3F 75% 150%
0x7F 100% 200%
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6.5.2 CLKPR – Clock Prescale Register
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE
bit is only updated when the other bits in CLKPR are simultaniosly written to zero. CLKPCE is
cleared by hardware four cycles after it is written or when the CLKPS bits are written. Rewriting
the CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the
CLKPCE bit.
• Bits 6:4 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bits 3:0 – CLKPS[3:0]: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As t he divider divide s the master clock input t o the MCU, the spe ed of all synchro-
nous peripherals is reduced when a division factor is used. The division factors are given in
Table 6-15.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (C LKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired v alue to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing presca ler setting to make sure the write proce dure is
not interrupted.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to
“0011”, giving a division factor of eight at start up. This feature sh ould be used if the selected
clock source has a higher frequency than the maximum frequency of the device at the present
operating conditions. Note that any value can be written to the CLKPS bits regardless of the
CKDIV8 Fuse setting. The Application software must ensure that a sufficien t division factor is
chosen if the selcted clock source has a higher frequency than the maximum frequency of the
Bit 76543210
0x26 CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR
Read/Write R/W R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
34 2586N–AVR–04/11
ATtiny25/45/85
device at the present operating conditions. The device is shipped with the CKDIV8 Fuse
programmed.
Note: The prescaler is disabled in ATtiny15 compatibility mode and neither writing to CLKPR, nor pro-
gramming the CKDIV8 fuse has any effect on the system clock (which will always be 1.6 MHz).
Table 6-15. Clock Presc aler Select
CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor
0000 1
0001 2
0010 4
0011 8
0100 16
0101 32
0110 64
0111 128
1000 256
1001 Reserved
1010 Reserved
1011 Reserved
1100 Reserved
1101 Reserved
1110 Reserved
1111 Reserved
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7. Power Management and Sleep Modes
The high performance and industry leading code efficiency makes the AVR microcontrollers an
ideal choise for low power applications. In addition, sleep modes enable the application to shut
down unused modules in the M CU, thereby saving power. The AVR provides various slee p
modes allowing the user to tailor the power consumption to the application’s requirements.
7.1 Sleep Modes Figure 6-1 on page 23 presents the different clock systems and their distribution in
ATtiny25/45/85. The figure is helpful in selecting an appropriate sleep mode. Table 7-1 shows
the differen t sleep modes and their wake up sources.
Note: 1. For INT0, only level interrupt.
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM[1:0] bits in the MCUCR Register select which
sleep mode (Idle, ADC Noise Reduction or Power-down) will be activated by the SLEEP instruc-
tion. See Table 7-2 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, exe cutes the interrupt routine, and
resumes execution from the instruction following SLEEP. The contents of the Register File and
SRAM are unaltered when the device wake s u p fr om slee p. I f a r eset occurs d uri ng sle ep mod e,
the MCU wakes up and executes from the Reset Vector.
Note that if a level triggered interrupt is used for wake-up the changed level must be held for
some time to wake up the MCU (and for the MCU to enter the interrupt service routine). See
“External Interrupts” on page 51 for details.
7.1.1 Idle Mode When the SM[1:0] bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing Analog Comparator, ADC, USI, Timer/Counter, 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 M CU to wake up from external triggered interrupts as well a s internal
ones like the Timer Over flow. If wake-up from th e Analog Compa rator interrupt is not require d,
Table 7-1. Active Clock Domains and Wake-up Sources in th e Different Sleep Modes
Active Clock Domains Oscillators Wake-up Sources
Sleep Mode
clkCPU
clkFLASH
clkIO
clkADC
clkPCK
Main Clock
Source Enabled
INT0 and
Pin Change
SPM/EEPROM
Ready
USI Start Condition
ADC
Other I/O
Watchdog
Interrupt
Idle XXX X XXXXXX
ADC Noise
Reduction XXX
(1) XXX X
Power-down X(1) XX
36 2586N–AVR–04/11
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the Analog Comparator can be powered down by setting the ACD bit in “ACSR – Analog Com-
parator Control and Status Register” on page 124. This will reduce power consumption in Idle
mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
7.1.2 ADC Noise Reduction Mode
When the SM[1:0] bits are written to 01, the SLEEP instruction makes the MCU enter ADC
Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the
Watchdog to continue operating (if enabled). This sleep mode h alts 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 conve rsion star ts automa tically when this mode is enter ed. Apart form the
ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out
Reset, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin change
interrupt can wake up the MCU from ADC Noise Reduction mode.
7.1.3 Power-down Mode
When the SM[1:0] bits are written to 10, the SLEEP instruction makes the MCU ente r Power-
down mode. In this mode, the Oscillator is stopped, while the external interrupts, the USI start
condition dete ctio n a nd t he Watc hdo g co nt inu e ope ra tin g (if e nabled ). Only a n Exter na l Reset , a
Watchdog Reset, a Brown-out Reset, USI start condition interupt, an external level interrupt on
INT0 or a pin change interrupt can wake up the MCU. This sleep mode halts all generated
clocks, allowing operation of asynchronous modules only.
7.2 Software BOD Disable
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 20-4 on page
152), the BOD is acti vely monit ori ng th e sup ply vo lt age during a sleep per iod. In some devices it
is possible to save power by disabling the BOD by software in Power-Down sleep mode. Th e
sleep mode power consumption will then be at the same level as when BOD is globally disabled
by fuses.
If BOD is disabled by software, the BOD function is turned off immediately after entering the
sleep mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe
operation in case the VCC level has dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be the same as that
for wakeing up from RESET. The user must manually configure the wake up times such that the
bandgap refe rence ha s time t o start an d the BO D is working co rrect ly bef ore the MCU co ntinu es
executing code. See SUT[1:0] and CKSEL[3:0] fuse bits in table “Fuse Low Byte” on page 153
BOD disable is contro lle d by the BOD S (BO D Slee p ) bit of MCU Co nt ro l Reg ist er , se e “MCUCR
– MCU Control Register” on page 38. Writing this bit to one turns off BOD in Power-Down, while
writing a zero keeps the BOD active. The default setting is zero, i.e. BOD active.
Writing to the BODS bit is controlled by a timed sequence and an enable bit, see “MCUCR –
MCU Control Register” on page 38.
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7.2.1 Limitations BOD disable functionality has been implemented in the following devices, only:
• ATtiny25, revision E, and newer
• ATtiny45, revision D, and newer
• ATtiny85, revision C, and newer
Revisions are marked on the device package and can be located as follows:
• Bottom side of packages 8P3 and 8S2
• Top side of package 20M1
7.3 Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 39, pro-
vides a method to reduce power consumption by stopping the clock to individual peripherals.
The current state of the peripheral is frozen and the I/O registers can no t be read or written.
Resources used by the peripheral when stopping the clock will remain occupied, hence the
peripheral should in most cases be disabled before stopping the clock. Waking up a module,
which is done by clearing t he bit in PRR, p uts th e module in t he sa me stat e a s bef ore shut down.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped. See “Supply Current
of I/O modules” on page 182 for examples.
7.4 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 possi ble of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
7.4.1 Analog to Digit al Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “Analog to Digital Converter” on page 126
for details on ADC operation.
7.4.2 An a log Co mp ara tor
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 th e Ana log C omp arat or is
set up to use the Internal Voltage Reference as input, the Analog Comparator should be dis-
abled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
independent of sleep mode. Refer to “Analog Comparator” on page 123 for details on how to
configure the Analo g Comparator.
38 2586N–AVR–04/11
ATtiny25/45/85
7.4.3 Brown-out Detector
If the Brown-ou t Detector is not needed in the applicat ion, this module sh ould be turned off . If the
Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes,
and hence, always consume power. In the deeper sleep modes, this will contribute significantly
to the total curren t consumpt ion. See “Brown-out Detection” on page 43 and “Software BOD Dis-
able” on page 36 for details on how to configure the Brown-out Detector.
7.4.4 Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disable d as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When
turned on again, the user must allow the reference to start up before the output is used. If the
reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal Volt-
age Reference” on page 44 for details on the start-up time.
7.4.5 Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be turn ed off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. Refer to “Watchdog Timer” on pa ge 44 for d et ails on ho w to configu re the Wa tchd og Time r.
7.4.6 Port Pins When entering a sleep mo de, 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 whe re
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 the section “Digital Input Enable and Sleep Modes” on page 59 for details on
which pins are enab led. If th e input buff er is enab led an d the in put signal is left f loat ing or has an
analog signal level close to VCC/2, the input buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to VCC/2 on an input pin can cause significan t current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Register (DIDR0). Refer to
“DIDR0 – Digital Input Disable Register 0” on page 125 for details.
7.5 Register Description
7.5.1 MCUCR – MCU Control Register
The MCU Control Register contains control bits for power management.
• Bit 7 – BODS: BOD Sleep
BOD disable functionality is ava ilable in some devices, only. See “Limitations” on page 37.
Bit 76543210
0x35 BODS PUD SE SM1 SM0 BODSE ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R/W R/W
Initial Value00000000
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In order to disable BOD du ring sleep (see Table 7-1 on page 35) the BODS bit must be written to
logic one. This is controlled by a timed sequence and the enable bit, BODSE in MCUCR. First,
both BODS and BODSE must be set to one. Second, within four clock cycles, BODS must be
set to one and BODSE must be set to zero. The BODS bit is active three clock cycles after it is
set. A sleep instruction must be executed while BODS is active in order to turn off the BOD for
the actual sleep mode. The BODS bit is automatically cleared after three clock cycles.
In devices where Sleeping BOD has not been implemented this bit is unused and will always
read zero.
• Bit 5 – SE: Sleep Enable
The SE bit must be written to lo gic one to make the MCU enter the sle ep mode when the SLEEP
instruction is execut ed. To avoid t he MCU ent erin g the sleep mode un less it is the programmer’s
purpose, it is recomm ended to write the Sle ep Enable ( SE) bit to o ne just bef ore the e xecution of
the SLEEP instruction and to clear it immediately after waking up.
• Bits 4:3 – SM[1:0]: Sleep Mode Select Bits 1 and 0
These bits select between the three available sleep modes as sh own in Table 7-2.
• Bit 2 – BODSE: BOD Sl eep Enable
BOD disable functionality is ava ilable in some devices, only. See “Limitations” on page 37.
The BODSE bit enables setting of BODS cont rol bit, as explained o n BODS bit description. BOD
disable is controlled by a timed sequence.
This bit is unused in devices where software BOD disable has not been implemented and will
read as zero in those devices.
7.5.2 PRR – Power Reduction Register
The Power Reduction Register provides a method to reduce power consumption by allowing
peripheral clock signals to be disabled.
• Bits 7:4 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bit 3 – PR TIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 mo dule. When the Timer/Counter1
is enabled, operation will continue like before the shutdown.
Table 7-2. Sleep Mode Select
SM1 SM0 Sleep Mode
00Idle
0 1 ADC Noise Reduction
1 0 Power-down
11Reserved
Bit 76543 210
0x20 – – – – PRTIM1 PRTIM0 PRUSI PRADC PRR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
40 2586N–AVR–04/11
ATtiny25/45/85
• Bit 2 – PR TIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 mo dule. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.
• Bit 1 – PRUSI: Power Reduction USI
Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When
waking up the USI again, the USI should be re initialized to ensure proper operation.
• Bit 0 – PRADC: Power Reduction ADC
Writing a logic one to th is bit shuts down t he ADC. The ADC must be disabled before sh ut down.
Note that the ADC clock is also used by some parts of th e analog comparator , which means that
the analogue comparator can not be used when this bit is high.
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8. System Control and Reset
8.1 Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a RJMP – Relative
Jump – instruction to the reset handling routine. If the program never enables an inter rupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. The circuit diagram in Figure 8-1 shows the reset logic. Electrical parameters of the
reset circuitry ar e giv en in “System and Reset Characteristics” on page 170.
Figure 8-1. Reset Logic
The I/O ports of the AVR are im mediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have g one inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The dif-
ferent selections f or the delay period are presented in “Clock Sources” on page 25.
8.2 Reset SourcesThe ATtiny25/45 /85 has four source s of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin f or longer
than the minim um pulse length.
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires an d the
Watchdog is enabled.
• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabl ed.
MCU Status
Register (MCUSR)
Brown-out
Reset Circuit
BODLEVEL[2:0]
Delay Counters
Reset Circuit
RESET
VCC
Watchdog
Timer
INTERNAL RESET
COUNTER RESET
CKSEL[3:0]
CK
TIMEOUT
WDRF
BORF
EXTRF
PORF
DATA BUS
R
SQ
Clock
Generator
SPIKE
FILTER
Pull-up Resistor
Watchdog
Oscillator
SUT[1:0]
Power-on Reset
Circuit
42 2586N–AVR–04/11
ATtiny25/45/85
8.2.1 Power-on Reset
A Power-on Reset (POR) pulse is ge nerated by an On-chip detection circuit. The detection level
is defined in “System and Reset Characteristics” on page 170. The POR is activated whenever
VCC is below the detection level. The POR circuit can be used to trigger the Start-up Reset, as
well as to detect a failure in supply voltage.
A Power-on Reset (POR) cir cuit ensures that the device is reset from Power-on . Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay,
when VCC decreases below the detection level.
Figure 8-2. MCU Start-up, RESET Tied to VCC
Figure 8-3. MCU Start-up, RESET Extended Externally
8.2.2 External ResetAn External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer
than the min imum pul se widt h ( see “Syste m a nd Re se t Charact er ist ics” o n p age 17 0) will gener-
ate 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 counter starts the MCU after the Time-out period – tTOUT – has expired.
V
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
CC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
VCC
43
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Figure 8-4. External Reset During Operation
8.2.3 Br own-out Detection
ATtiny25/45/8 5 has an On-chip Brown -out Detection (BOD ) circuit for monitorin g the VCC level
during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be
selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free
Brown-out Detection. The hysteresis on the detection level shou ld be interpreted as VBOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
8-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 8-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-
ger than tBOD given in “System and Reset Characteristics” o n page 170.
Figure 8-5. Brown-out Reset During Operation
8.2.4 Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
“Watchdo g T ime r” on pa g e 44 for details on operation of the Watchdog Timer.
CC
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT- VBOT+
tTOUT
44 2586N–AVR–04/11
ATtiny25/45/85
Figure 8-6. Watchdog Rese t Du rin g Oper a tion
8.3 Internal Voltage Reference
ATtiny25/45/85 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator or the ADC.
8.3.1 Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time tha t may influence the way it should be used. T he
start-up time is given in “System and Reset Characteristics” on page 170. To save power, the
reference is not always turned on. The reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL[2:0] Fuse Bits).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
AC BG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three
conditions above to ensure that the reference is turned off before entering Power-down mode.
8.4 Watchdog Timer
The Watchdog Timer is clocked from an On-chip Oscillator which runs at 128 kHz. By controlling
the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table
8-3 on page 48. The WDR – Watchdog Reset – instruction resets the Watchdog Timer. The
Watchdog Timer is also reset when it is disabled and when a Chip Rese t occurs. Ten d ifferent
clock cycle periods can be selected to determine the reset period. If the reset period expires
without another Watchdog Reset, the ATtiny25/45/85 resets and executes from the Reset Vec-
tor. For timing details on the Watchdog Reset, refer to Table 8-3 on page 48.
The Wathdog Timer can also be configured to generate an interrupt instead of a reset. This can
be very helpful when using the Watchdog to wake-up from Power-down.
To prevent uninte ntional disabling of the Wa tchdog or unintentional ch ange of time-out period ,
two different safety levels are selected by the fuse WDTON as shown in Table 8-1 Refer to
CK
CC
45
2586N–AVR–04/11
ATtiny25/45/85
“Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 45 for
details.
Figure 8-7. Watchdog Timer
8.4.1 Timed Sequences f or Changing the Configuration of the Watchdog Timer
The sequence for chan gin g configu ra tion dif f ers slightly between the two safety levels. Separate
procedures are described for each level.
8.4.1.1 Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to one without any restriction. A timed sequence is needed when disabling an enabled Watch-
dog Timer. To disable an enabled Watchdog Timer, the f ollowing procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be writ-
ten to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, in the same op eration, write the WDE and WDP bits
as desired, but with the WDCE bit cleared.
8.4.1.2 Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
always is set, the WDE must be written to one to start the timed sequence.
2. Within the next four clock cycles, in t he same o peration, write the WDP bits as de sired ,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
Table 8-1. WDT Configuration as a Function of the Fuse Settings of WDTON
WDTON Safety
Level WDT Initial
State How to Disable the
WDT How to Change Time-
out
Unprogrammed 1 Disabled Timed sequence No limitations
Programmed 2 Enabled Always enabled Timed sequence
OSC/2K
OSC/4K
OSC/8K
OSC/16K
OSC/32K
OSC/64K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K
MCU RESET
WATCHDOG
PRESCALER
128 kHz
OSCILLATOR
WATCHDOG
RESET
WDP0
WDP1
WDP2
WDP3
WDE
46 2586N–AVR–04/11
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8.4.2 Code ExampleThe following code example shows one assembly and one C function for turning off the WDT.
The example assumes that interrupts are cont rolled (e.g., by disab ling interrupts glob ally) so that
no interrupts will occur during execution of these functions.
Note: 1. See “Code Examples” on page 6.
8.5 Register Description
8.5.1 MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU Reset.
• Bits 7:4 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
Assembly Code Example(1)
WDT_off:
wdr
; Clear WDRF in MCUSR
ldi r16, (0<<WDRF)
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional Watchdog Reset
in r16, WDTCR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
C Code Example(1)
void WDT_off(void)
{
_WDR();
/* Clear WDRF in MCUSR */
MCUSR = 0x00
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
Bit 76543210
0x34 – – – – WDRF BORF EXTRF PORF MCUSR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
47
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• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset 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 if a Brown-out Reset occurs. The bit is reset by a Po wer-on Reset, or by writing a
logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occu rs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags t o identify a reset condition, the user shou ld read and t hen reset
the MCUSR as ear ly as possible in the pr ogram. If the regi ster is cleared before an other reset
occurs, the source of th e reset can be found by examining the Reset Flags.
8.5.2 WDTCR – Watchdog Timer Control Register
• Bit 7 – WDIF: Watchdog Timeout Interrupt Flag
This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is config-
ured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt
handling vector. Altern atively, WDIF is cle ared by writ ing a logic on e to the flag. Whe n the I -bit in
SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.
• Bit 6 – WDIE: Watch dog Timeout Interrupt Enable
When this bit is written to on e, WDE is cleared, and the I-bit in the Status Register is set, th e
Watchdog Time-out Interrupt is enabled. In this mode the corresponding interrupt is executed
instead of a reset if a timeout in the Watchdog Timer occurs.
If WDE is set, WDIE is automatically cleared by hard ware when a tim e-out occu rs. This is usefu l
for keeping the Watchdog Reset security while using the interrupt. After the WDIE bit is cleared,
the next time-out will generate a reset. To avoid the Watchdog Reset, WDIE must be set after
each interrupt.
Bit 76543210
0x21 WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000X000
Table 8-2. Watchdog Timer Configuration
WDE WDIE Watchdog Timer State Action on Time-out
0 0 Stopped None
0 1 Running Interrupt
1 0 Running Reset
1 1 Running Interrupt
48 2586N–AVR–04/11
ATtiny25/45/85
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the W DE bit is written to logic z ero. 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. This bit must also be set when
changing the prescaler bits. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 45.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written
to logic zero, the Wa tchdog Timer f unction is di sabled. WDE can only be cle ared if th e WDCE bit
has logic level one. To disable an enabled Watchdog Timer, the following procedure must be
followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be writ-
ten to WDE even though it is set to one befo re the disable operation starts.
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the Watchdog.
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm
described above. See “Timed Sequences for Changing the Configuration of the Watchdog
Timer” on page 45.
In safety level 1, WDE is overridden by WDRF in MCUSR. See “MCUSR – MCU Status Regis-
ter” on page 4 6 for descript ion of WDRF. This means t hat WDE is always set when WDRF is set.
To clear WDE, WDRF must be cleared before disabling the Watchdog with the procedure
described above. This feature ensures multiple resets during conditions causing failure, and a
safe start-up after the failure.
Note: If the watchdog timer is not going to be used in the application, it is important to go through a
watchdog disable procedure in the initialization of the device. If the Watchdog is accidentally
enabled, for example by a runaw ay pointer or brown-out condition, the device will be reset, which
in tur n will lead to a new watchdog reset. To avoid this situation, the application software should
always clear the WDRF flag and the WDE control bit in the initialization routine.
• Bits 5, 2:0 – WDP[3:0]: Watchdog Ti mer Prescaler 3, 2, 1, and 0
The WDP[3:0] bits determine the Watchdog Timer prescaling when the Watchdog Timer is
enabled. The different prescaling values and their corresponding Timeout Periods are shown in
Table 8-3.
Table 8-3. Watchdog Timer Prescale Select
WDP3 WDP2 WDP1 WDP0 Number of WDT Oscillator
Cycles Typical Time-out at
VCC = 5.0V
0 0 0 0 2K (2048) cycles 16 ms
0 0 0 1 4K (4096) cycles 32 ms
0 0 1 0 8K (8192) cycles 64 ms
0 0 1 1 16K (16384) cycles 0.125 s
0 1 0 0 32K (32764) cycles 0.25 s
0 1 0 1 64K (65536) cycles 0.5 s
0 1 1 0 128K (131072) cycles 1.0 s
0 1 1 1 256K (262144) cycles 2.0 s
1 0 0 0 512K (524288) cycles 4.0 s
49
2586N–AVR–04/11
ATtiny25/45/85
Note: 1. If selected, one of the valid settings below 0b1010 will be used.
1 0 0 1 1024K (1048576) cycles 8.0 s
1010
Reserved(1)
1011
1100
1101
1110
1111
Table 8-3. Watchdog Timer Prescale Select (Continued)
WDP3 WDP2 WDP1 WDP0 Number of WDT Oscillator
Cycles Typical Time-out at
VCC = 5.0V
50 2586N–AVR–04/11
ATtiny25/45/85
9. Interrupts This sectio n describes the specifics of the interrupt han dling as performed in ATtiny25/45/ 85.
For a general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling”
on page 12.
9.1 Interrupt Vectors in ATtiny25/45/85
The interrupt vector s of ATtiny25/45/85 are described in Table 9-1below.
If the progr am n ever e nab les an inte rr upt sou rce, the I nter rupt Vect ors ar e n ot used , and regu lar
program code can be placed at these locations.
Table 9-1. Reset and Interrupt Vect or s
Vector No. Program Address Source Interrupt Definition
1 0x0000 RESET External Pin, Power-on Reset,
Brown-out Reset, Watchdog Reset
2 0x0001 INT0 External Interrupt Request 0
3 0x0002 PCINT0 Pin Change Interrupt Request 0
4 0x0003 TIMER1_COMPA Timer/Counter1 Compare Match A
5 0x0004 TIMER1_OVF Timer/Counter1 Overflow
6 0x0005 TIMER0_OVF Timer/Counter0 Overflow
7 0x0006 EE_RDY EEPROM Ready
8 0x0007 ANA_COMP Analog Comparator
9 0x0008 ADC ADC Conversion Complete
10 0x0009 TIMER1_COMPB Timer/Counter1 Compare Match B
11 0x000A TIMER0_COMPA Timer/Counter0 Compare Match A
12 0x000B TIMER0_COMPB Timer/Counter0 Compare Match B
13 0x000C WDT Watchdog Time-out
14 0x000D USI_START USI START
15 0x000E USI_OVF USI Overflow
51
2586N–AVR–04/11
ATtiny25/45/85
A typical and general setup for interrupt vector addresses in ATtiny25/45/85 is shown in the pro-
gram examp l e be low.
Note: See “Code Examples” on page 6.
9.2 External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT[5:0] pins. Observe
that, if enabled, the interrupts will trigger even if the INT0 or PCINT[5:0] pins are configured as
outputs. This feature provid es a way of generating a software interrupt. Pin change interrupts
PCI will trigger if any enabled PCINT[5:0] pin toggles. The PCMSK Register control which pins
contribute to the pin change interrupts. Pin change interrupts on PCINT[5:0] are detected asyn-
chronously. This implies that these interrupts can b e used for waking the part also from sle ep
modes other than Idle mode.
The INT0 interrupts can be triggered by a falling or rising edge or a low level. This is set up as
indicated in the specification for the MCU Control Register – MCUCR. When the INT0 interrupt is
enabled and is configured as level triggered, the interrupt will trigger as long as the pin is held
low. Note that recognition of falling or rising edge interrupts on INT0 requires the presence of an
I/O clock, described in “Clock Systems and their Distribution” on page 23.
9.2.1 Low Level Interrupt
A low level interrupt on INT0 is detected asynchronously. This implies that this interrupt can be
used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in
all sleep modes except Idle mod e.
Assembly Code Example
.org 0x0000 ;Set address of next statement
rjmp RESET ; Address 0x0000
rjmp INT0_ISR ; Address 0x0001
rjmp PCINT0_ISR ; Address 0x0002
rjmp TIM1_COMPA_ISR ; Address 0x0003
rjmp TIM1_OVF_ISR ; Address 0x0004
rjmp TIM0_OVF_ISR ; Address 0x0005
rjmp EE_RDY_ISR ; Address 0x0006
rjmp ANA_COMP_ISR ; Address 0x0007
rjmp ADC_ISR ; Address 0x0008
rjmp TIM1_COMPB_ISR ; Address 0x0009
rjmp TIM0_COMPA_ISR ; Address 0x000A
rjmp TIM0_COMPB_ISR ; Address 0x000B
rjmp WDT_ISR ; Address 0x000C
rjmp USI_START_ISR ; Address 0x000D
rjmp USI_OVF_ISR ; Address 0x000E
RESET: ; Main program start
<instr> ; Address 0x000F
...
52 2586N–AVR–04/11
ATtiny25/45/85
Note that if a level trigger ed interrupt is used for wake-up from Power-down, the required le vel
must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If
the level disappears before the end of the Start-up Time, the MCU will still wake up, but no inter-
rupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described
in “System Clock and Clock Options” on page 23.
If the low level on the interrupt pin is removed before the device has woken up then program
execution will not be diverted to the interrupt service routine but continue from the instruction fol-
lowing the SLEEP command.
9.2.2 Pin Change Interrupt Timing
An example of timing of a pi n change interrupt is shown in Figure 9-1.
Figure 9-1. Timing of pin change interrupts
clk
PCINT(0)
pin_lat
pin_sync
pcint_in_(0)
pcint_syn
pcint_setflag
PCIF
PCINT(0) pin_sync pcint_syn
pin_lat
D Q
LE
pcint_setflag PCIF
clk clk
PCINT(0) in PCMSK(x)
pcint_in_(0) 0
x
53
2586N–AVR–04/11
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9.3 Register Description
9.3.1 MCUCR – MCU Control Register
The External Interrupt Control Register A contains control bits for interrupt sense control.
• Bits 1:0 – ISC0[1:0]: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corre-
sponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt ar e defined in Table 9-2. The value on the INT 0 pin is sampled before detecting edges.
If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate
an interrupt. Shorter pulses are not guaranteed to g enerate an interrupt. If low level interrupt is
selected, the low level must be held until the completion of the currently executing instruction to
generate an interr upt.
9.3.2 GIMSK – General Interrupt Mask Register
• Bits 7, 4:0 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bit 6 – INT0: External Interrupt Request 0 Enab le
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin inter rupt is enab led. The Interrupt Sense Cont rol0 bits 1/0 (ISC0 1 and I SC00) in t he MCU
Control Register ( MCUCR) define whether the ext ernal int errupt is activa ted on r ising a nd/or f all-
ing edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even
if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is
executed fro m th e INT0 Interr up t Vector.
• Bit 5 – PCIE: Pin Change Interrupt Enable
When the PCIE bit is set (one) and the I-bit in the Status Register (SREG ) is set (one), pin
change interrupt is enabled. Any change on any enabled PCINT[5:0] pin w ill cause an interrupt.
The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI Interrupt
Vector. PCINT[5:0] pins are enabled individually by the PCMSK0 Re gister.
Bit 76543210
0x35 BODS PUD SE SM1 SM0 BODSE ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R/W R/W
Initial Value00000000
Table 9-2. Interrupt 0 Sense Control
ISC01 ISC00 Description
0 0 The low level of INT0 generates an interrupt request.
0 1 Any logical change on INT0 generates an interrupt request.
1 0 The falling edge of INT0 generates an interrupt request.
1 1 The rising edge of INT0 generates an interrupt request.
Bit 76543210
0x3B –INT0PCIE–––––GIMSK
Read/Write RR/WR/WRRRRR
Initial Value00000000
54 2586N–AVR–04/11
ATtiny25/45/85
9.3.3 GIFR – General Interrupt Flag Register
• Bits 7, 4:0 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bit 6 – INTF0: External Interrupt Flag 0
When an edge or logic chang e on the INT0 pin trigger s an interr upt requ est, INT F0 becomes set
(one). If the I-bit in SREG and the INT0 bit in GIMSK are set (o ne), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT0 is configured as a level interrupt.
• Bit 5 – PCIF: Pin Change Interrupt Flag
When a logic change on any PCINT[5:0] pin triggers an interrupt request, PCIF becomes set
(one). If the I-bit in SREG and the PCIE bit in GIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be clea red by writing a logical one to it.
9.3.4 PCMSK – Pin Change Mask Register
• Bits 7:6 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bits 5:0 – PCINT[5: 0]: Pin Change Enable Mask 5:0
Each PCINT[5:0] bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT[5:0] is set and the PCIE bit in GIMSK is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT[5:0] is cleared, pin change interrupt on the correspondin g I/O
pin is disabled.
Bit 76543210
0x3A –INTF0PCIF–––––GIFR
Read/Write RR/WR/WRRRRR
Initial Value00000000
Bit 76543210
0x15 – – PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
55
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10. I/O Ports
10.1 Introduction All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when chang-
ing drive value (if conf igured a s output) or enablin g/disabling o f pull-up resistors (if con figured as
input). Each output buffer has symmetrical drive characteristics with both hig h sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have indi-
vidually 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 10-1. Refer to “Electrical Char-
acteristics” on page 166 for a complete list of parameters.
Figure 10-1. I/O Pin Equivalent Schematic
All registers and bit references in this sect ion are written in g eneral form. A lower case “x” repre-
sents the numbering letter for the p ort, and a lower case “n” represe nts the bit numb er. However,
when using the regist er or bit defin es in a program , the precise f orm must be used. For examp le,
PORTB3 for bit no. 3 in Port B, her e docume nt ed ge ner ally as PO RT xn. The physical I /O Regis-
ters and bit locations are listed in “Register Descri ption” on page 66.
Three I/O memory address locations are allocated for each port, one each for the Data Register
– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register and the Data Direction Register are read/write.
However, writing a logic one to a bit in the PINx Register, will result in a toggle in the correspond-
ing bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables the
pull-up function for all pins in all po rts when set.
Using the I/O port as G eneral Digital I/O is described in “Ports as General Digital I/O” on page
56. Most port pins are m ultiplexed with alternate function s for the peripheral features o n the
device. How each alternate function interferes with the port pin is described in “Alternate Port
Functions” on page 59. Refer to the individual module sections for a full description of the alter-
nate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the por t as general digital I/O.
Logic
Rpu
See Figure
"General Digital I/O" for
Details
Pxn
56 2586N–AVR–04/11
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10.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 10-2 show s a func-
tional description of one I/O-port pin, here generically called Pxn.
Figure 10-2. General Digital I/O(1)
Note: 1. WRx, WPx, WD x, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
10.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description” on page 66, the DDxn bits are accessed at the DDRx I/ O add re ss, the PO RT xn bits
at the PORTx I/O address, and the PINxn bits at the PINx I/O add ress.
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 t he pull-up resist or off, PORTxn h as to be written logic zero or the pi n has to
be configured as an output pin. The port pins are tr i-stated when rese t condition becomes a ctive,
even if no clocks are runn in g.
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).
clk
RPx
RRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clkI/O: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
Q
D
Q
QD
CLR
PORTxn
Q
QD
CLR
DDxn
PINxn
DATA BU S
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
WPx
0
1
WRx
WPx: WRITE PINx REGISTER
57
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10.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port.
10.2.3 Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}
= 0b11), an intermediate state with either pull- up enabled {DDxn, PORTxn} = 0b01) or output
low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully accept-
able, as a high-impedant environment will not notice the differenc e 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 e ither the tri-st ate ({DDxn, PORTxn} = 0b00) or th e output high state ({DDxn, PORTxn}
= 0b10) as an intermediate step.
Table 10-1 summarizes the control signals for the pin value.
10.2.4 Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit . As shown in Figur e 10-2, t he PINxn Register bit a nd the p recedin g latch con-
stitute a synchronizer. This is needed to avoid metastability if the physical pin changes value
near the edge of the internal clock, bu t it also introduces a delay. Figure 1 0-3 shows a timing dia-
gram of the synchronization when reading an externally ap plied pin value. The maximum and
minimum prop a ga tio n dela ys ar e de no te d tpd,max and tpd,min respectively.
Figure 10-3. Synchronization when Reading an Externally Applied Pin value
Table 10-1. P ort Pin Configurations
DDxn PORTxn PUD
(in MCUCR) I/O Pull-up Comment
0 0 X Input No Tri-state (Hi-Z)
0 1 0 Input Yes P xn 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)
XXX in r17, PINx
0x00 0xFF
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX
SYSTEM CLK
t
pd, max
t
pd, min
58 2586N–AVR–04/11
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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 transpa rent when the clock is high, as indicated by the
shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indi-
cated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed
between ½ and 1½ system clock pe riod depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indi-
cated in Figure 10-4. 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 10-4. Synchronization when Rea ding a Software Assigned Pin Value
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 5 as input with a pull-up assigned to port pin 4. The resulting pin values
are read back again, bu t as previou sly discussed, a nop instruction is included t o be able to read
back the value recently assigned to some of the pins.
Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-
ups are set on pins 0, 1 and 4, until the direction bits are correctly set, defining bit 2 and 3 as
low and redefining bits 0 and 1 as strong high drivers.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PB4)|(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
...
out PORTx, r16 nop in r17, PINx
0xFF
0x00 0xFF
SYSTEM CLK
r16
INSTRUCTIONS
SYNC LATCH
PINxn
r17
tpd
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10.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 10-2, the digital input signa l can be clamped to ground at the input of the
schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down mode to avoid high power consumption if some input signals are left floating, or
have an analog sig nal 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 59.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as
“Interrupt on Rising Edge , Falling Edge, or Any Logic Change on Pin” while the ext ernal interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from the
above mentioned Sleep mode, as the clamping in these sleep mode produces the requested
logic change.
10.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensur e that these pins have a def ined level. Even
though most of t he digital inputs are d isabled in the deep sleep modes as descr ibed above, fl oat-
ing inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset is
important, it is recommended to use an external pull-u p or pulldown. Connecting unused pins
directly to VCC or GND is not recommended, sin ce this may ca use excess ive curr ents if the pin is
accidentally configured as an output.
10.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 10-5
shows how the po rt pin control signals from the sim plified Figure 10-2 can be overridden by
alternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB4)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINB;
...
60 2586N–AVR–04/11
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Figure 10-5. Alternate Port Funct ions(1)
Note: 1. WRx, WPx, WD x, RRx, 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.
clk
RPx
RRx
WRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clkI/O: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
SET
CLR
0
1
0
1
0
1
DIxn
AIOxn
DIEOExn
PVOVxn
PVOExn
DDOVxn
DDOExn
PUOExn
PUOVxn
PUOExn: Pxn PULL-UP OVERRIDE ENABLE
PUOVxn: Pxn PULL-UP OVERRIDE VALUE
DDOExn: Pxn DATA DIRECTION OVERRIDE ENABLE
DDOVxn: Pxn DATA DIRECTION OVERRIDE VALUE
PVOExn: Pxn PORT VALUE OVERRIDE ENABLE
PVOVxn: Pxn PORT VALUE OVERRIDE VALUE
DIxn: DIGITAL INPUT PIN n ON PORTx
AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx
RESET
RESET
Q
QD
CLR
Q
QD
CLR
Q
Q
D
CLR
PINxn
PORTxn
DDxn
DATA BU S
0
1
DIEOVxn
SLEEP
DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
Pxn
I/O
0
1
PTOExn
PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE
WPx: WRITE PINx
WPx
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Table 10-2 summarizes th e fu nction of the overri ding signals. The pin and p ort ind exes from Fig-
ure 10-5 are not sh own in the succeed ing tabl es. The over ridi ng signals ar e gen erat ed intern ally
in the modules having the alternate function.
The following subsections shortly describe the alternate functions for each port, and relate the
overriding signals to the alternate function. Refer to the alternate function description for further
details.
Table 10-2. 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/disabl ed when PUOV is
set/cleared, regardless of the setting of the DDxn, PORTxn,
and PUD Register bits.
DDOE Data Directi on
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.
PTOE Port Toggle
Override Enable If PTOE is set, the PORTxn Register bit is inverted.
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 mode).
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 mode).
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 alter nate 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 bi-
directionally.
62 2586N–AVR–04/11
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10.3.1 Alternate Functions of Port B
The Port B pins with alternate function are shown in Table 10-3.
• Port B, Bit 5 – RESET/dW/ADC0/PCINT5
• RESET: External Reset input is active low and enabled by unprogramming (“1”) the
RSTDISBL Fuse. Pullup is acti vated and output driv e r and digita l input ar e deactivated when
the pin is used as the RESET pin.
• dW: When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are
unprogrammed, the debugWIRE system within the target device is activated. The RESET
port pin is configured as a wire-AND (ope n-drain) bi-directional I/O pin with pull-up enabled
and becomes the communication gateway between target and emulator.
• ADC0: Analog to Digital Converter, Channel 0.
• PCINT5: Pin Change Interrupt source 5.
Table 10-3. Port B Pins Alternate Functions
Port Pin Alternate Function
PB5
RESET:Reset Pin
dW: debugWIRE I/O
ADC0: ADC Input Channel 0
PCINT5:Pin Change Interrupt, Source 5
PB4
XTAL2: Cr ystal Oscillator Output
CLKO: System Clock Output
ADC2: ADC Input Channel 2
OC1B: Timer/Counter1 Compare Match B Output
PCINT4:Pin Change Interrupt 0, Source 4
PB3
XTAL1: Cr ystal Oscillator Input
CLKI: External Clock Input
ADC3: ADC Input Channel 3
OC1B: Complementary Timer/Counter1 Compare Match B Output
PCINT3:Pin Change Interrupt 0, Source 3
PB2
SCK: Serial Clock Input
ADC1: ADC Input Channel 1
T0: Timer/Counter0 Clock Source
USCK: USI Clock (Three Wire Mode)
SCL : USI Clock (Two Wire Mode)
INT0: External Interrupt 0 Input
PCINT2:Pin Change Interrupt 0, Source 2
PB1
MISO: SPI Master Data Input / Slave Data Output
AIN1: Analog Comparator, Negative Input
OC0B: Timer/Counter0 Compare Match B Output
OC1A: Timer/Counter1 Compare Match A Output
DO: USI Data Output (Three Wire Mode)
PCINT1:Pin Change Interrupt 0, Source 1
PB0
MOSI:: SPI Master Data Output / Slave Data Input
AIN0: Analog Comparator, Positi ve Input
OC0A: Timer/Counter0 Comp are Match A output
OC1A: Complementary Timer/Counter1 Compare Match A Output
DI: USI Data Input (Three Wire Mode)
SDA: USI Data Input (Two Wire Mode)
AREF: External Analog Reference
PCINT0:Pin Change Interrupt 0, Source 0
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• Port B, Bit 4 – XTAL2/CLKO/ADC2/OC1B/PCINT4
• XTAL2: Chip Clock Oscillator pin 2. Used as clock pin for all chip clock sources except
internal calibrateble RC Oscillator and exter nal clock. When used as a clock pin, the pin can
not be used as an I/O pin. When using internal calibratab le RC Oscillator or External clock as
a Chip clock sources, PB4 serves as an or dinary I/O pin.
• CLK O: The de vided system clock can be output on the pin PB4. The divided system clock will
be output if the CKOUT Fuse is programmed, r egardless of th e POR TB4 and DDB4 sett ings .
It will also be output during reset.
• ADC2: Analog to Digital Converter, Channel 2.
• OC1B: Output Compare Match output: The PB4 pin can serve as an external output for the
Timer/Counter1 Comp are Matc h B when configu red as an ou tput (DDB4 set). The OC1B pin
is also the output pin for the PWM mode timer function.
• PCINT4: Pin Change Interrupt source 4.
• Port B, Bit 3 – XTAL1/CLKI/ADC3/OC1B/PCINT3
• XTAL1: Chip Clock Oscillator pin 1. Used for all chip clock sources except internal
calibrateble RC oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
• CLKI: Clock Input from an external clock source, see “External Clock” on page 26.
• ADC3: Analog to Digital Converter, Channel 3.
•OC1B: Inv erted Output Compare Match output: The PB3 pin can serve as an external output
for the Timer/Counter1 Compare Match B when configured as an output (DDB3 set). The
OC1B pin is also the inverted output pin for the PWM mode timer function.
• PCINT3: Pin Change Interrupt source 3.
• Port B, Bit 2 – SCK/ADC1/T0/USCK/SCL/INT0/PCINT2
• SCK: Master Clock output, Slav e Clock input pin for SPI channel. When the SPI is enabled as
a Slave , this pin is configured as an input r egard less of the se tting of DDB2. When the SPI is
enabled as a Master, the da ta direction of this pin is contro lled by DDPB2. When the pin is
forced by the SPI to be an input, the pull-up can still be controlled by the PORTB2 bit.
• ADC1: Analog to Digital Converter, Channel 1.
• T0: Timer/Counter0 counter source.
• USCK: Three-wire mode Universal Serial Interface Clock.
• SCL: Two-wire mode Serial Clock for USI Two-wire mode.
• INT0: External Interrupt source 0.
• PCINT2: Pin Change Interrupt source 2.
• Port B, Bit 1 – MISO/AIN1/OC0B/OC1A/DO/PCINT1
• MISO: Master Data input, Sla v e Data out put pin f or SPI ch annel. When the SPI is enab led as
a Master, this pin is configured as an input regar dless of the setting of DDB1. When t he SPI
is enabled as a Slave, the data direction of this pin is controlled by DDB1. When the pin is
forced by the SPI to be an input, the pull-up can still be controlled by the PORTB1 bit.
• AIN1: Analog Comparator Negative Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the
Analog Comparator.
• OC0B: Output Compare Match output. The PB1 pin can serve as an external output for the
Timer/Counter0 Compare Match B. The PB1 pin has to be configured as an output (DDB1
64 2586N–AVR–04/11
ATtiny25/45/85
set (one)) to serve this f unction. The OC0B pin is also the ou tput pin f or the PWM mode ti mer
function.
• OC1A: Output Compare Match output: The PB1 pin can serve as an external output for the
Timer/Counter1 Comp are Matc h B when configu red as an ou tput (DDB1 set). The OC1A pin
is also the output pin for the PWM mode timer function.
• DO: Three-wire mode Universal Serial Interface Dat a output. Three-wire mode Data output
ov errides POR TB1 value and it is driven to the port when data direction bit DDB1 is set (one).
PORTB1 still enables the pull-up, if the direction is input and PORTB1 is set (one).
• PCINT1: Pin Change Interrupt source 1.
• Port B, Bit 0 – MOSI/AIN0/OC0A/OC1A/DI/SDA/AREF/PCINT0
• MOSI: SPI Master Data ou tput, Slav e Data input f or SPI channel. When the SPI is enabled as
a Slave , this pin is configured as an input r egard less of the se tting of DDB0. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDB0. When the pin is
forced by the SPI to be an input, the pull-up can still be controlled by the PORTB0 bit.
• AIN0: Analog Compar ator Positive Input. Configure t he 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.
• OC0A: Output Compare Match output. The PB0 pin can serve as an external output for the
Timer/Coun te r0 Com p ar e Ma tch A when configure d as an ou tpu t (DD B 0 se t (on e )). The
OC0A pin is also the output pin for the PWM mode timer function.
•OC1A
: In v erted Output Compare Match output: The PB0 pin can serve as an external output
for the Timer/Counter1 Compare Match B when configured as an output (DDB0 set). The
OC1A pin is also the inverted output pin for the PWM mode timer function.
• SDA: Two-wire mo d e Serial Interface Data.
• AREF: External Analog Reference for ADC. Pullup and output driver are disa bled on PB0
when the pin is used as an external reference or Internal Voltage Reference with external
capacitor at the AREF pin.
• 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 for DI function.
• PCINT0: Pin Change Interrupt source 0.
Table 10-4 and Table 10-5 relate the alternate functions of Port B to the overriding signals
shown in Figure 10-5 on page 60.
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Note: 1. 1 when the Fuse is “0” (Programmed).
Table 10-4. Overriding Signals for Alternate Functions in PB[5:3]
Signal
Name PB5/RESET/
ADC0/PCINT5 PB4/ADC2/XTAL2/
OC1B/PCINT4 PB3/ADC3/XTAL1/
OC1B/PCINT3
PUOE RSTDISBL(1) • DWEN(1) 00
PUOV100
DDOE RSTDISBL(1) • DWEN(1) 00
DDOV debugWire Transmit 0 0
PVOE 0 OC1B Enable OC1B Enable
PVOV 0 OC1B OC1B
PTOE000
DIEOE RSTDISBL(1) + (PCINT5 •
PCIE + ADC0D) PCINT4 • PCIE + ADC2D PCINT3 • PCIE + ADC3D
DIEOV ADC0D ADC2D ADC3D
DI PCINT5 Input PCINT4 Input PCINT3 Input
AIO RESET Input, ADC0 Input ADC2 Input ADC3 Input
Table 10-5. Overriding Signals for Alternate Functions in PB[2:0]
Signal
Name PB2/SCK/ADC1/T0/
USCK/SCL/INT0/PCINT2 PB1/MISO/DO/AIN1/
OC1A/OC0B/PCINT1
PB0/MOSI/DI/SDA/AIN0/AR
EF/OC1A/OC0A/
PCINT0
PUOE USI_TWO_WIRE 0 USI_TWO_WIRE
PUOV000
DDOE USI_TWO_WIRE 0 USI_TWO_WIRE
DDOV (USI_SCL_HOLD +
PORTB2) • DDB2 0(SDA
+ PORTB0) • DDB0
PVOE USI_TWO_WIRE • DDB2 OC0B Enable + OC1A
Enable +
USI_THREE_WIRE
OC0A Enable + OC1A
Enable + (USI_TWO_WIRE
• DDB0)
PVOV 0 OC0B + OC1A + DO OC0A + OC1A
PTOE USITC 0 0
DIEOE PCINT2 • PCIE + ADC1D +
USISIE PCINT1 • PCIE + AIN1D PCINT0 • PCIE + AIN0D +
USISIE
DIEOV ADC1D AIN1D AIN0D
DI T0/USCK/SCL/INT0/
PCINT2 Input PCINT1 Input DI/SDA/PCINT0 Input
AIO ADC1 Input Analog Comparator
Negative Input Analog Comparator Positive
Input
66 2586N–AVR–04/11
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10.4 Register Description
10.4.1 MCUCR – MCU Control Register
• Bit 6 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disab led even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-
figuring the Pin” on page 56 for more details about this feature.
10.4.2 PORTB – Port B Data Register
10.4.3 DDRB – Port B Data Direction Register
10.4.4 PINB – Port B Input Pins Address
Bit 7 6 5 4 3 2 1 0
0x35 BODS PUD SE SM1 SM0 BODSE ISC01 ISC00 MCUCR
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
Bit 76543210
0x18 – – PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x17 – – DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x16 – – PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 N/A N/A N/A N/A N/A N/A
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11. 8-bit Timer/Counter0 with PWM
11.1 Features •Tw o In depend ent Ou tpu t Compare Units
•Double Buffered Output Compare Registers
•Clear Timer on Compare Match (Auto Reload)
•Glitch Free, Phase Correct Pulse Width Modulator (PWM)
•Variable PWM Period
•Frequency Generator
•Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
11.2 Overview Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and wit h PWM support. It allows accurate program execut ion timing (eve nt man-
agement) and wave ge neration.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 11-1. For the actual
placement of I/O pins, re fer to “Pinout ATtiny25/45/85” on page 2. CPU accessible I/O Registers,
including I/O bit s and I/O pins, are sh own in bold. The de vice-specific I/O R egister and bit loca-
tions are listed in the “Register Description” on page 80.
Figure 11-1. 8-bit Timer/Counter Block Diagram
Clock Select
Timer/Counter
DATA BUS
OCRnA
OCRnB
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
=
Fixed
TOP
Value
Control Logic
= 0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
TCCRnA TCCRnB
Tn
Edge
Detector
( From Prescaler )
clkTn
68 2586N–AVR–04/11
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11.2.1 Registers The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0 B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the
Timer Interrupt Flag Register (TIFR). All interrupts are individually masked with the Timer Inter-
rupt Mask Register (TIMSK). TIFR and TIMSK are not shown in the figure.
The Timer/Counter can be clocked inter nally, via the pre scaler, or by an external clock source on
the T0 pin. T he Clock Se lect logic blo ck controls which clock so urce and edge the Timer/Cou nter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkT0).
The double buffered Output Com pare Registers (OCR0A and OCR0B) is compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Gen-
erator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and
OC0B). See “Output Compare Unit” on page 71. for details. The Compare Match event will als o
set the Compare Flag (OCF0A or OCF0B) which can be used to generate a n Output Compare
interrupt request.
11.2.2 Definitions Many register and bit reference s in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-
pare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter 0 counter value and so on.
The definitions in Table 11-1 are also used extensively throughout the documen t.
11.3 Timer/Counter0 Prescaler and Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (c) bits located in the
Timer/Counter0 Control Register (TCCR0B).
11.3.1 Internal Clock Source with Prescaler
Timer/Counter0 can be clocked directly by the system clock (by setting the CS0[2:0] = 1). This
provides the faste st operation, with a maximum timer/counter clock freque ncy equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024.
11.3.2 Prescaler Reset
The prescaler is free running, i.e. it operates independently of the Clock Select logic of
Timer/Counte r0. Sinc e the pr es caler is not af fecte d by the timer/c ount er’s cloc k select , the state
Table 11-1. Definitions
Constant Description
BOTTOM The counter reaches BOTTOM when it becomes 0x00
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
TOP The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fix ed value 0xFF (MAX) or the
value stored in the OCR0A Register. The assignment depends on the mode of operation
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of the prescaler will have implications for situations where a prescaled clock is used. One exam-
ple of a prescaling artifact is when the t imer/count er is enabled and clo cked by the prescaler (6 >
CS0[2:0] > 1). The number of system clock cycles from when the timer is enabled to the first
count occurs can be from 1 to N+1 system clock cycles, wher e N equals the pr escaler divisor (8,
64, 256, or 1024).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program
execution.
11.3.3 External Clock Source
An external clock source applied to th e T0 pin can b e used as timer/ counter clock (clk T0). The T0
pin is sampled once every system clock cycle by the pin synchronization logic. The synchro-
nized (sampled) sign al is then passed through t he edge d etector. F igure 11-2 shows a funct ional
equivalent block diagram of the T0 synchronization and edge detector logic. The registers are
clocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in the
high period of the internal system clock.
The edge detector generates one clkT0 pulse for each positive (CS0[2:0] = 7) or negative
(CS0[2:0] = 6) edge it detects.
Figure 11-2. T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has bee n applied to the T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T0 has been stable for at least one
system clock cycle, otherwise it is a risk that a false timer/counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the sys-
tem clock frequency (fExtClk < fclk_I/O/2) give n a 50/50% duty cycle. Since th e edge detecto r uses
sampling, the maximum frequency of an external clock it can detect is half the sampling fre-
quency (following the Nyquist sampling theorem). However, due to variation of the system clock
frequency and duty cycle caused by oscillator source (crystal, resonator, and capacitors) toler-
ances, it is recommended that maximum frequency of an external clock source is less than
fclk_I/O/2.5.
An external clock source can not be presca le d.
Tn_sync
(To Clock
Select Logic)
Edge DetectorSynchronization
DQDQ
LE
DQ
Tn
clk
I/O
70 2586N–AVR–04/11
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Figure 11-3. Timer/Counter0 Prescaler
The synchronization logic on the input pins (T0) in Figure 11-3 is shown in Figure 11-2 on page
69.
11.4 Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
11-4 shows a block diagram of the counter and its surroundings.
Figure 11-4. Counter Unit Block Diagram
Signal description (internal signals):
count Increment or de cre m en t TCNT0 by 1.
direction Select between increment and decrement.
clear Clear TCNT0 (set all bits to zero).
clkTnTimer/Co un te r clo ck, re fe rr ed to as clk T0 in the following.
top Signalize that TCNT0 has reached maximum value.
bottom Signalize that TCNT0 has reached minimum value (zero).
PSR10
Clear
clkT0
T0
clkI/O
Synchronization
DATA BUS
TCNTn Control Logic
count
TOVn
(Int.Req.)
Clock Select
top
Tn
Edge
Detector
( From Prescaler )
clk
Tn
bottom
direction
clear
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Depending of the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT0). clkT0 can be generated from an external or inte rnal clock source,
selected by the Clock Select bits (CS0[2:0]). When no clock source is selected (CS0[2:0] = 0)
the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of
whether clkT0 is present or not. A CPU write overrides (has priority over ) all counter clear or
count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in
the Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter
Control Register B (TCCR0B). There are close connections between how the counter behaves
(counts) and how waveforms are generated on the Output Compare output OC0A. For more
details about advanced counting sequences and waveform generation, see “Modes of Opera-
tion” on page 73.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by
the WGM0[1:0] bits. TOV0 can be used for generating a CPU interrupt.
11.5 Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers
(OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a
match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock
cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output
Compare interrupt . Th e Outp ut Co mpare Flag is aut om atica lly cleare d wh en the int errup t is exe-
cuted. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit
location. The Waveform Generator uses the match signal to generate an output according to
operating mod e set by the WGM0[2:0] bits and Compare Output mode (C OM0x[1:0]) bits. The
max and bottom signals are used by the Waveform Generator for handling the special cases of
the extreme values in some modes of operation (See “Modes of Operation” on page 73.).
Figure 11-5 shows a block diagram of the Output Compare unit.
Figure 11-5. Output Compare Unit, Block Diagram
OC Fnx (Int.Req.)
= (8-bit C omparator )
OCRnx
OCnx
DA TA B US
TCNTn
WGMn[1:0]
Waveform Generator
top
FOCn
COMnX[1:0]
bottom
72 2586N–AVR–04/11
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The OCR0x Registers are double buffered when using any of the Pulse Width Modulation
(PWM) modes. Fo r the nor mal and Clear Tim er on Compare ( CTC) modes of operation, the dou-
ble buffering is disabled. The double buffering synchronizes the update of the OCR0x Compare
Registers to either top or bottom of the coun ting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0x Register access may seem co mplex, but this is not case. Wh en the double buff ering
is enabled, the CPU has access to the OC R0x Buffer Register, and if double buffering is dis-
abled the CPU will access the OCR0x directly.
11.5.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOC0x) bit. Forcing Compare Match will not set the
OCF0x Flag or reload/clear the timer, but the OC0x pin will be updated as if a real Compare
Match had occurred ( the COM0x[1:0] bits setting s define wh ether the OC0x pi n is set, clear ed or
toggled).
11.5.2 Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any Compare Match that occur in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR0x to be initial-
ized to the same value as TCNT0 wit hout trigg ering an inte rrupt when t he Timer/Coun ter clock is
enabled.
11.5.3 Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all Compare Matches for one timer
clock cycle, there are risks involved when changing TCNT0 when using the Output Compare
Unit, independently of whet her the Timer/ Counter is runn ing or not. If the va lue written to TCNT0
equals the OCR0x value, the Compare Match will be missed, resulting in incorrect waveform
generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is
down-counting.
The setup of the OC0x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0x value is to use the Force Output Com-
pare (FOC0x) strobe bits in Normal mode. T he OC0x Registers keep their valu es even when
changing between Wa veform Generation modes.
Be aware that the COM0x[1:0] bits are not double buffered together with the compare value.
Changing the COM0x[1:0] bits will take effect immediately.
11.6 Compare Match Output Unit
The Compare Output mode (COM0x[1:0]) bits have two functions. The Waveform Generator
uses the COM0x[1:0] bits for defining the Output Compare (OC0x) state at the next Compare
Match. Also, the COM0x[1:0] bits control the OC0x pin output source. Figure 11-6 shows a sim-
plified schematic of the logic affected by the COM0x[1:0] bit setting. The I/O Registers, I/O bits,
and I/O pins in the fi gur e are shown in bo ld. On ly the par ts of t he gener al I/O Po rt Contr ol Regis-
ters (DDR and PORT) that are affected by the COM0x[1:0] bits are shown. When referring to the
OC0x state, the reference is for the internal OC0x Register, not the OC0x pin. If a system reset
occur, the OC0x Register is reset to “0”.
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Figure 11-6. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform
Generator if e ither of the COM0x[1:0 ] bits ar e set. However, the OC0x pin direct ion (inpu t or out-
put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x value is visi-
ble on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initializat ion of the OC0x state before t he out-
put is enabled. Note that some COM0x[1:0] bit settings are reserved for certain modes of
operation. See “Register Description” on page 80.
11.6.1 Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0x[1:0] bits differently in Normal, CTC, and PWM
modes. For all modes, setting the COM0x[1:0] = 0 tells the Waveform Generator that no action
on the OC0x Register is to be performed on the next Compare Match. For compare output
actions in the no n-PWM modes refer to Tab le 11-2 on page 80. For fast PWM mode, refer to
Table 11-3 on page 81, and for phase correct PWM re fe r to Table 11-4 on page 81.
A change of the COM0x[1:0] bits state will have effect at the first Compare Match after the bits
are written. For non-PWM modes, the action can be forced to have immediate effect by using
the FOC0x strobe bits.
11.7 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGM0[2:0]) and Compare Out-
put mode (COM0x[1:0]) bits. The Compare Output mode bits do not affect the counting
PORT
DDR
DQ
DQ
OCn
Pin
OCnx
DQ
Waveform
Generator
COMnx1
COMnx0
0
1
DATA BUS
FOCn
clk
I/O
74 2586N–AVR–04/11
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sequence, while the Waveform Generation mode bits do. T he COM0x[1:0] bits control whether
the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-
PWM modes the COM0x[1:0] bits control whether the output should be set, cleared, or toggled
at a Compare Matc h (See “Compare Match Output Unit” on page 72.).
For detailed timing information refer to Figure 11-10, Figure 11-11, Figure 11-12 and Figure 11-
13 in “Timer/Counter Timing Diagrams” on page 78.
11.7.1 Normal Mode The simplest mode of operation is the Normal mode (WGM0[2:0] = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bot-
tom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the same
timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflo w interrupt
that automatically clears the TOV0 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The Output Co mpare Un it can be used t o generate interrupts at some given time . Using the Ou t-
put Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
11.7.2 Clear Timer on Compare Match (CTC) Mode
In Clear Time r on Compare or CTC mode (WGM0[2:0] = 2), the OCR 0A Register is used to
manipulate the count er resolut io n. In CTC mode the counter is clear ed to zero wh en the counter
value (TCNT0) matches the OCR0A. The OCR0A de fines the top value for the counter, hence
also its resolution. This mode allows greater control of the Compare Match output frequency. It
also simplifies the op e ra tio n of coun tin g exte rn al ev en ts.
The timing diagram for the CTC mode is shown in Figure 11-7. The counter value (TCNT0)
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 11-7. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is run-
TCNTn
OCn
(Toggle)
OC nx Interrupt F lag S et
1 4
Period
2 3
( CO M nx[1 : 0 ] = 1 )
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ning with none or a low pres caler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum valu e (0xFF) and wrap around s tarting at 0x00 before the Comp are Match can
occur.
For generatin g a wavefor m out put in CT C mod e, t he OC0A ou tput can be se t to toggle it s logica l
level on each Compare Match by setting the Compare Output mode bits to toggle mode
(COM0A[1:0] = 1). The O C0A value will not be visible on the port pin unless the da ta direction
for the pin is set to output. The waveform generated will have a maximum frequency of fOC0 =
fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following
equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of op erat ion, the T OV0 Flag is se t in the same tim er clock cycle tha t the
counter counts from MAX to 0x00.
11.7.3 Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM0[2 :0] = 3 or 7) provides a high fre-
quency PWM waveform generation option. The fast PWM differs from the other PWM option by
its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOT-
TOM. TOP is defined as 0xFF when WGM0[2:0] = 3, and OCR0A when WGM0[2:0] = 7.
In non-inverti ng Compare Out put mode, the Out put Compar e (OC0x) is cleared on the Co mpare
Match between TCNT0 and OCR0x, and set at BOTTOM. In inverting Compare Output mode,
the output is set on Compare Match and cleared at BOTTOM.
Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice
as high as the phase correct PWM mode that use du al-slope operation. This high frequency
makes the fast PWM mode well suited for power regulation, rectification, and DAC applications.
High frequency a llows physically small sized external components (coils, capacitors), and there-
fore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 11-8. The TCNT0 value is in the timing diagram shown as a his-
togram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The sm all horizontal line marks on the TCNT0 slopes represent Com-
pare Matches between OCR0x and TCNT0.
fOCnx fclk_I/O
2 N 1 OCRnx+()⋅⋅
--------------------------------------------------=
76 2586N–AVR–04/11
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Figure 11-8. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the inter-
rupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare un it allows generation of PWM waveforms on the OC0x pins.
Setting the COM0x[1:0] bits to two will produce a non-inverted PWM and an inverted PWM out-
put can be generated by setting the COM0x[1 :0] to three: Setting the COM0A[1:0] bits to one
allowes the AC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not
available for the OC0B pin (Se e Ta ble 1 1- 3 on page 8 1). The actual OC0x value will only be vis-
ible on the port pin if the data direction for the port pin is set as output. The PWM waveform is
generated by setting (or clearing) the OC0x Register at the Compare Match between OCR0x
and TCNT0, and clearing (or setting) the OC0x Register at the timer clock cycle the counter is
cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the pre scale factor (1, 8, 64, 256, or 1024).
The extreme values for th e OCR0A Re gister rep resents sp ecial cases wh en gen erating a PW M
waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will result
in a constantly high or low output (dep ending on t he polarity of the output set by the COM0A[1:0]
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting OC0x to toggle its logical level on each Compar e Match (COM0x[1:0 ] = 1). The waveform
generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is set to zero. This
feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the Out-
put Compare unit is enabled in the fast PWM mode.
TCNTn
OC R nx Update and
TOVn Interrupt Flag Set
1
Period
2 3
OCn
OCn
( CO M nx[1 : 0 ] = 2 )
( CO M nx[1 : 0 ] = 3 )
OC R nx Interrupt F lag S et
4 5 6 7
fOCnxPWM fclk_I/O
N 256⋅
------------------=
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11.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM0[2:0] = 1 or 5) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dual-slope
operation. The coun ter counts repeatedly from BOTTOM to TOP and then from TOP to BOT-
TOM. TOP is defined as 0xFF when WGM0[2:0] = 1, and OCR0A when WGM0[2:0] = 5. In non-
inverting Compare Output mode, the O utput Compare (OC0x) is cleared on the Compare Match
between TCNT0 and OCR0x while upcounting, and set on the Compare Match while down-
counting. In inverting Outp ut Compar e mod e, the oper ation is in vert ed. The dual- slope o perat ion
has lower maximum operation frequency than single slope operation. However, due to the sym-
metric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correc t PWM mode the counter is increm ented until the counte r value matches TOP.
When the counter reaches TOP, it changes the count direction. The TCNT0 value will be equal
to TOP for one timer clo ck cycle. The tim ing dia gram fo r th e pha se correct PWM mode is shown
on F igure 11- 9. The TCNT0 value is in the timing diagram shown as a histogram for illustrating
the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The
small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x
and TCNT0.
Figure 11-9. Phase Correct PWM Mode , Tim in g Dia gr am
The Timer/Counter Over flow Flag (TOV0) is set each time the counter reache s BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC0x pins. Setting the COM0x[1:0] bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0x[1:0] to three: Setting the COM0A0 bits to
one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is
TOVn Interrupt Flag Set
OCnx Interrupt Flag Set
1 2 3
TCNTn
Period
OCn
OCn
(COMnx[1:0] = 2)
(COMnx[1:0] = 3)
OCRnx Update
78 2586N–AVR–04/11
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not available for the OC0B pin (See Table 11-4 on page 81). The actual OC0x value will only be
visible on the port pin if the data dir ection fo r th e por t pin is se t as o utput . The PWM wa ve f orm is
generated by clea ring (or setting) the OC0x Register at the Compare Mat ch between OCR0x
and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at Com-
pare Match between OCR0x and TCNT0 when the counter de crements. The PWM f requency for
the output when using phase correct PWM can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases wh en generating a PWM
waveform output in the phase correct PWM mo de. If the OCR0A is set equal to BO TTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 11-9 OCn has a transition from high to low even though
there is no Compare Match. The point of this transition is to guaratee symmetry around BOT-
TOM. There are two cases that give a transition without Compare Match, as follows:
• OCR0A changes its value from MAX, lik e in Figu re 11-9. When the OCR0A value is MAX the
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCn value at MAX must correspond to the result of an up-
counting Compare Match.
• The timer starts counting from a v alue higher than the one in OCR0A, and for that reason
misses the Compare Match and hence the OCn change that would have happened on the
way up.
11.8 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable sign al in the following figures. Th e figures include information on whe n Interrupt
Flags are set. Figure 11-10 con tains timing data for basic Timer/Co unter operat ion. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 11-10. Timer/Counter Timing Diagram, no Prescaling
Figure 11-11 shows the same timing data, but with th e prescaler enabled.
fOCnxPCPWM fclk_I/O
N510⋅
------------------=
clkTn
(clk
I/O
/1)
TOVn
clkI/O
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
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Figure 11-11. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 11-12 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC
mode and PWM mode, where OCR0A is TOP.
Figure 11-12. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
Figure 11-13 shows the setting of OCF0 A and the clearing of TCNT0 in CTC mode and fast
PWM mode where OCR0A is TOP.
Figure 11-13. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres-
caler (fclk_I/O/8)
TOVn
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
clkI/O
clkTn
(clk
I/O
/8)
OCFnx
OCRnx
TCNTn
OCRnx V alue
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clk
I/O
clk
Tn
(clk
I/O
/8)
OCFnx
OCRnx
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clk
I/O
/8)
80 2586N–AVR–04/11
ATtiny25/45/85
11.9 Register Description
11.9.1 GTCCR – General Timer/Counter Control Register
• Bit 7 – TSM: Timer/Counte r Synchronization Mode
Writing the TSM b i t to on e a ctiva te s the Tim er/Counter Synch r on iza tion Mode. In th is m o de, the
value written to PSR0 is kept, hence keeping the Prescaler Reset signal asserted. This ensures
that the timer/counter is halted and can be configured without the risk of advancing during con-
figuration. When the TSM bit is written to zero, the PSR0 bit is cleared by hardware, and the
timer/counter start counti ng.
• Bit 0 – PSR0: Prescaler Reset Timer/Counter0
When this bit is one, the Timer/Counter0 prescaler will be Reset. This bit is normally cleared
immediately by hardware, except if the TSM bit is set.
11.9.2 TCCR0A – Ti mer/ Co unt er Con t rol Register A
• Bits 7:6 – COM0A[1:0]: Compare Match Ou tput A Mode
• Bits 5:4 – COM0B[1:0]: Compare Match Ou tput B Mode
The COM0A[1:0] an d COM0B[1: 0] bits control t he behavio ur of Output Compar e pins OC0A and
OC0B, respecti vely. If any of t he COM0A[1:0] bi ts are set, the OC0A out put overrides the no rmal
port functionality of the I/O pin it is connected to. Similarly, if any of the COM0B[1:0] bits are set,
the OC0B output overrides the normal port functionality of the I/O pin it is connected to. How-
ever, note that the Data Direction Register ( DDR) bit co rrespondin g to t he OC0A and OC0B p ins
must be set in order to enable the output dr iver.
When OC0A/OC0B is connected to the I/O pin, the function of the COM0A[1:0]/COM0B[1:0] bits
depend on the WGM0[2:0] bit setting. Table 11-2 shows the COM0 x[1:0] bit functionality when
the WGM0[2:0] bits are set to a normal or CTC mode (non-PWM).
Bit 7 6 5 4 3 2 1 0
0x2C TSM PWM1B COM1B1 COM1B0 FOC1B FOC1A PSR1 PSR0 GTCCR
Read/Write R/W R R R R R R R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3210
0x2A COM0A1COM0A0COM0B1COM0B0––WGM01 WGM00 TCCR0A
Read/Write R/W R/W R/W R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 11-2. Compare Output Mode, non-PWM Mode
COM0A1
COM0B1 COM0A0
COM0B0 Description
0 0 Normal port operation, OC0A/OC0B disconnected.
0 1 Toggle OC0A/OC0B on Compare Match
1 0 Clear OC0A/OC0B on Compare Match
1 1 Set OC0A/OC0B on Compare Match
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Table 11-3 shows the COM0x[1:0] bit functionality when the WGM0[2:0] bits are set to fast PWM
mode.
Note: 1. A specia l case occurs when OCR0A or OCR0B equals TOP and COM0A1/COM0B1 is set. In
this case, the compare match is ignored, but the set or clear is done at BOTTOM. See “Fast
PWM Mode” on page 75 for more details.
Table 11-4 shows the COM0x[1:0] bit functionality wh en the WGM0[2:0] bits are set to phase
correct PWM mode.
Note: 1. A specia l case occurs when OCR0A or OCR0B equals TOP and COM0A1/COM0B1 is set. In
this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Cor-
rect PWM Mode” on page 77 for more details.
• Bits 3:2 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bits 1:0 – WGM0[1 :0]: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of wave-
form generation to be used, see Table 11-5. Modes of operation supported by th e Timer/Counter
Table 11-3. Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0B1 COM0A0
COM0B0 Description
0 0 Normal port operation, OC0A/OC0B disconnected.
01Reserved
10
Clear OC0A/OC0B on Compare Match , set OC0A/OC0B at BOTTOM
(non-inverting mode)
11
Set OC0A/OC0B on Compare Match, clea r OC0A/OC0B at BOTTOM
(inverting mode)
Table 11-4. Compare Output Mode, Phase Correct PWM Mod e(1)
COM0A1
COM0B1 COM0A0
COM0B0 Description
0 0 Normal port operation, OC0A/OC0B disconnected.
01Reserved
10
Clear OC0A/OC0B on Compare Match when up-counting.
Set OC0A/OC0B on Compare Match when down-counting.
11
Set OC0A/OC0B on Compare Match when up-counting.
Clear OC0A/OC0B on Compare Match when down-counting.
82 2586N–AVR–04/11
ATtiny25/45/85
unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode, and two types of
Pulse Width Modulation (PWM) mod es (s ee “Modes of Operation” on page 73).
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
11.9.3 TCCR0B – Ti mer/ Co unt er Con t rol Register B
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0A bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0A output is
changed accord ing to its CO M0A[1: 0] bits se tting. Note that the F OC0A bit is implemen ted as a
strobe. Th erefor e it is the va lue presen t in the CO M0A [1:0] bits that de termine s the effec t of th e
forced compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0B bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0B output is
changed accord ing to its CO M0B[1: 0] bits se tting. Note that the F OC0B bit is implemen ted as a
strobe. Th erefor e it is the va lue presen t in the CO M0B [1:0] bits that de termine s the effec t of th e
forced compare.
Table 11-5. Wa ve fo rm Ge ne ra tion Mo d e Bit Des crip tio n
Mode WGM
02 WGM
01 WGM
00 Timer/Counter Mode
of Operation TOP Update of
OCRx at TOV Flag
Set on
0 0 0 0 Normal 0xFF Immediate MAX(1)
1 0 0 1 PWM, Phase Correct 0xFF TOP BOTTOM(2)
2 0 1 0 CTC OCRA Immediate MAX(1)
3 0 1 1 Fast PWM 0xFF BOTTOM(2) MAX(1)
4 1 0 0 Reserved – – –
5 1 0 1 PWM, Phase Corre c t OCRA TOP B OTTOM(2)
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA BOTTOM(2) TOP
Bit 7 6 5 4 3 2 1 0
0x33 FOC0A FOC0B – – WGM02 CS02 CS01 CS00 TCCR0B
Read/Write W W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the descript ion in the “TCCR0A – Timer/Counter Control Register A” on page 80.
• Bits 2:0 – CS0[2:0]: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
11.9.4 TCNT0 – Timer/Counter Register
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers.
11.9.5 OCR0A – Output Compa re Re gi ster A
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT0 ). A match can be used to generate an Output Com pare interrupt, or to
generate a waveform output on the OC0A pin.
Table 11-6. Clock Select Bit Description
CS02 CS01 CS00 Description
0 0 0 No clock source (Timer/Counter stopped)
001clk
I/O/(No prescaling)
010clk
I/O/8 (From prescaler)
011clk
I/O/64 (From prescaler)
100clk
I/O/256 (From prescaler)
101clk
I/O/1024 (From prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.
Bit 76543210
0x32 TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x29 OCR0A[7:0] OCR0A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
84 2586N–AVR–04/11
ATtiny25/45/85
11.9.6 OCR0B – Output Compa re Re gi ster B
The Output Compare Register B contains an 8-bit value that is continuously compared with the
counter value (TCNT0 ). A match can be used to generate an Output Com pare interrupt, or to
generate a waveform output on the OC0B pin.
11.9.7 TIMSK – Timer/Counter Interrupt Mask Register
• Bits 7, 0 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
• Bit 4 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counte r0 Compare M a tch A interrupt is enabled. T h e co rr esponding int er rup t is executed
if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR0.
• Bit 3 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter Compar e Match B inte rrupt is enab led. The correspondin g interrup t is executed if
a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter
Interrupt Flag Register – TIFR0.
• Bit 1 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer /Counter0 occurs, i.e., when th e TOV0 bit is set in the Timer/ Counter 0 Inter-
rupt Flag Register – TIFR0.
11.9.8 TIFR – Timer/Counter Interrupt Flag Register
• Bits 7, 0 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
• Bit 4 – OCF0A: Out put Compare Flag 0 A
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare Regist er0. OCF0A is cleared by har dware when executin g the cor-
responding interrupt handling vector. Alternatively, OCF 0A is cleared by writing a logic one to
Bit 76543210
0x28 OCR0B[7:0] OCR0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x39 –OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 – TIMSK
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x38 –OCF1A OCF1B OCF0A OCF0B TOV1 TOV0 –TIFR
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial Value00000000
85
2586N–AVR–04/11
ATtiny25/45/85
the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable),
and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
• Bit 3 – OCF0B: Out put Compare Flag 0 B
The OCF0B bit is set when a Compare Ma tch occurs be tween th e Timer/Co unter and the da ta in
OCR0B – Output Compare Reg ister0 B. O CF0B is cleared by ha rdware when execut ing the cor-
responding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable),
and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed.
• Bit 1 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by
writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt
Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed.
The setting of this flag is dependen t of the WGM0[2:0] bit setting. Refer to Table 11-5, “Wave-
form Generation Mode Bit Description” on page 82.
86 2586N–AVR–04/11
ATtiny25/45/85
12. 8-bit Timer/Counter1
The Timer/Counter1 is a general purpose 8-bit Timer/Counter module that has a separate pres-
caling selection from the separ ate prescaler.
12.1 Timer/Counter1 Prescaler
Figure 12-1 shows the Timer/Counter1 prescaler that supports two clocking modes, a synchro-
nous clocking mode and an asynchron ous clocking mode. T he synchronous clocking 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 asyn-
chronous mode when it is set (‘1’).
Figure 12-1. Timer/Counter1 Prescaler
In the asynchronous clocking mode the clock selections are from PCK to PCK/16384 and stop,
and in the synchronous clocking mode the clock selections are from CK to CK/16384 and stop.
The clock options are described in Table 12-5 on pa ge 92 and the Timer/Counter1 Control Reg-
ister, TCCR1. Setting the PSR1 bit in GTCCR register resets the prescaler. The PCKE bit in the
PLLCSR register enables the asynchronous mode. The frequency of the fast peripheral clock is
64 MHz (or 32 MHz in Low Speed Mo de).
12.2 Counter and Compare Units
The Timer/Counter1 general operation is described in the asynchronous mode and the opera-
tion in the synchronous mode is mentioned on ly if there are difference s between these two
modes. Figure 12-2 shows Timer/Counter 1 synchronization register block diagram and syn-
chronization 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 regis-
ters TCCR1, GTCCR, 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.
The Timer/Counter1 features a high resolution and a high accuracy usage with the lower pres-
caling opportunities. It can also support two accurate, high speed, 8-bit Pulse Width Modulators
using clock speeds up to 64 MHz (or 32 MHz in Low Speed Mode). In this mode,
TIMER/COUNTER1 COUNT ENABLE
PSR1
CS10
CS11
CS12
PCK 64/32 MHz
0
CS13
14-BIT
T/C PRESCALER
T1CK/2
T1CK
T1CK/4
T1CK/8
T1CK/16
T1CK/32
T1CK/64
T1CK/128
T1CK/256
T1CK/512
T1CK/1024
T1CK/2048
T1CK/4096
T1CK/8192
T1CK/16384
CK
PCKE
T1CK
87
2586N–AVR–04/11
ATtiny25/45/85
Timer/Counter1 and the output compare registers serve as dual stand-alone PWMs with no n-
overlapping non-inverted and inverted outputs. Refer to page 89 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.
Figure 12-2. Timer/Counter 1 Synchronization Register Block Diagram.
Timer/Counter1 and the prescaler allow running the CPU from any clock source while the pres-
caler is operating on the fast 64 MHz (or 32 MHz in Low Speed Mode) PCK clock in the
asynchronous mode.
Note that the system clock frequency must be lower than one third of the PCK frequency. 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 12-3 shows the block diagram for Timer/Counter1.
8-BIT DATABUS
OCR1A OCR1A_SI
TCNT_SO
OCR1B OCR1B_SI
OCR1C OCR1C_SI
TCCR1 TCCR1_SI
GTCCR GTCCR_SI
TCNT1 TCNT1_SI
OCF1A OCF1A_SI
OCF1B OCF1B_SI
TOV1 TOV1_SITOV1_SO
OCF1B_SO
OCF1A_SO
TCNT1
S
AS
A
PCKE
CK
PCK
IO-registersInput synchronization
registers
Timer/Counter1 Output synchronization
registers
SYNC
MODE
ASYNC
MODE
1 CK Delay
~1 CK Delay1 PCK Delay No Delay
TCNT1
OCF1A
OCF1B
TOV1
1/2 CK Delay 1 CK Delay 1/2 CK Delay
1..2 PCK Delay
88 2586N–AVR–04/11
ATtiny25/45/85
Figure 12-3. Timer/Counter1 Block Diagram
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 TCCR1
and GTCCR. The interrupt enable/disable settings are found in the Timer/Counter Interrupt
Mask Register - TIMSK.
The Timer/Counter1 contains thr ee Output Compare Registers, OCR1A, OCR1B, and OCR1C
as the data source to be compared with the Timer/Counter1 contents. In normal mode the Out-
put 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, OCR1 B determines action on the OC1B pin (PB4 ) and it can
generate Timer1 OC1B interrupt in normal mode and in PWM mode. OCR1C holds the
Timer/Counte r maximum value, i.e. the clear on com pare match value. In the normal mode an
overflow interrupt (TOV1) is generated when Timer/Counter1 counts from $FF to $00, while in
the PWM mode t he overf low inter rupt is ge nerated when Timer/Coun ter1 counts e ither from $F F
to $00 or from OCR1C t o $00. The invert ed 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, OC 1B) are
generated. I n PWM mode, the Timer Count er count s up t o the value specified in the output com-
pare 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 prescale r options, flexible
PWM frequency selection is provided. Tab le 12-3 on page 91 lists clock selection and OCR1C
8-BIT DATABUS
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER1
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TIMER INT. MASK
REGISTER (TIMSK)
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
T/C1 CONTROL
LOGIC
TOV1
OCF1B OCF1B
TOV1
TOIE0
TOIE1
OCIE1B
OCIE1A
OCF1A
OCF1A
CK
PCK
T/C1 OVER-
FLOW IRQ T/C1 COMPARE
MATCH B IRQ OC1A
(PB1)
T/C1 COMPARE
MATCH A IRQ
T/C CONTROL
REGISTER 1 (TCCR1)
COM1B1
PWM1A
PWM1B
COM1B0
FOC1A
FOC1B
(OCR1A) (OCR1B) (OCR1C)
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TOV0
COM1A1
COM1A0
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
GLOBAL T/C CONTROL
REGISTER (GTCCR)
CS12
PSR1
CS11
CS10
CS13
CTC1
OC1A
(PB0) OC1B
(PB4) OC1B
(PB3)
DEAD TIME GENERATOR DEAD TIME GENERATOR
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2586N–AVR–04/11
ATtiny25/45/85
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 expe nse of resolution.
12.2.1 Timer/Counter1 Init ialization for Asynchronous Mode
To set Timer/Counter1 in asynchronous mode first enable PLL and then wait 100 µs for PLL to
stabilize. Next, poll the PLOCK bit until it is set and then set the PCKE bit.
12.2.2 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 PB4(OC1B) pins and invert ed outputs on pins PB0(OC1A) an d PB3(O C1B). As
default non-overlapping times for complemen tary output pairs are zero, but they can be inserted
using a Dead Time Generator (see description on page 100).
Figure 12-4. The PWM Output Pair
When the counte r value mat ch t he con tent s of OCR1A o r OCR1 B, th e O C1A an d O C1B o ut puts
are set or cleared according to the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the
Timer/Counter1 Co ntrol Register A - TCCR1, as shown in Table 12 -1.
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.
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/Coun ter reaches OCR1C. This prevents the occurrence of odd-length PWM
pulses (glitches) in the event of an unsynchronized OCR1A or OCR1 B. See Figure 12-5 for a n
example.
Table 12-1. Compare Mode Select in PWM Mode
COM1x1 COM1x0 Effect on Output Compare Pins
00
OC1x not connected.
OC1x not connected.
01
OC1x cleared on compare match. Set whenTCNT1 = $00.
OC1x set on compare match . Cleared when TCNT1 = $00.
10
OC1x cleared on compare match. Set when TCNT1 = $00.
OC1x not connected.
11
OC1x Set on compare match. Cleared when TCNT1= $00.
OC1x not connected.
PWM1x
PWM1x
x = A or B
t
non-overlap
=0
t
non-overlap
=0
90 2586N–AVR–04/11
ATtiny25/45/85
Figure 12-5. Effects of Unsynchronized OCR Latching
During the time between the write and the latch operation, a read from OCR1A or OCR 1B will
read the contents of the temporary lo cation. This means that the most recently written value
always will read out of OCR1A or OCR1B.
When OCR1A or OC R1B conta in $00 or t he top v alue, as specified in OCR1C register, the out-
put PB1(OC1A) or PB4(OC1B) is held low or high according to the settings of
COM1A1/COM1A0. This is shown in Table 12-2.
In PWM mode, the Timer Overflow Flag - TOV1 is set when the TCNT1 counts to the OCR1C
value and the TCNT1 is reset to $00. The Timer Overflow Interrupt1 is executed when TOV1 is
set provided that Tim er Over f low I nter rupt an d global interrupts are e nab led. This a lso ap plie s 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:
Resolution shows how ma ny bits are required to express th e value in the OCR1C register an d
can be calculated using the following equation:
Table 12-2. 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.
PWM Output OC1x
PWM Output OC1x
Unsynchronized OC1x Latch
Synchronized OC1x Latch
Counter Value
Compare Value
Counter Value
Compare Value
Compare Value changes
Glitch
Compare Value changes
fPWM fTCK1
OCR1C + 1()
------------------------------------=
91
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Table 12-3. Timer/Counter1 Clock Prescale Select in the Asynchronous Mode
PWM Frequency Clock Selection CS1[3:0] OCR1C RESOLUTION
20 kHz PCK/16 0101 199 7 .6
30 kHz PCK/16 0101 132 7 .1
40 kHz PCK/8 01 00 199 7 .6
50 kHz PCK/8 01 00 159 7 .3
60 kHz PCK/8 01 00 132 7 .1
70 kHz PCK/4 00 11 228 7 .8
80 kHz PCK/4 00 11 199 7 .6
90 kHz PCK/4 00 11 177 7 .5
100 kHz PCK/4 0011 159 7.3
110 kHz PCK/4 0011 144 7.2
120 kHz PCK/4 0011 132 7.1
130 kHz PCK/2 0010 245 7.9
140 kHz PCK/2 0010 228 7.8
150 kHz PCK/2 0010 212 7.7
160 kHz PCK/2 0010 199 7.6
170 kHz PCK/2 0010 187 7.6
180 kHz PCK/2 0010 177 7.5
190 kHz PCK/2 0010 167 7.4
200 kHz PCK/2 0010 159 7.3
250 kHz PCK 0001 255 8.0
300 kHz PCK 0001 212 7.7
350 kHz PCK 0001 182 7.5
400 kHz PCK 0001 159 7.3
450 kHz PCK 0001 141 7.1
500 kHz PCK 0001 127 7.0
R2OCR1C 1+()log=
92 2586N–AVR–04/11
ATtiny25/45/85
12.3 Register Description
12.3.1 TCCR1 – Timer/Counter1 Control Register
• 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/Counte r1
continues counting and is unaffected by a compare match.
• Bit 6 – PWM1A: Pulse Width Modulator A Enab le
When set (one) this b it enables PWM mode based on comparator OCR1A in Timer/Co unter1
and the co unter va lue is r eset to $0 0 in t he CPU clock cycle af ter a compar e matc h with OCR1C
register value.
• Bits 5:4 – COM1A[1: 0]: 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. Since the output pin action is an alternative
function to an I/O por t, the correspo nding direction con trol bit must be set (one ) in order to con-
trol an output pin.
In Normal mode, the COM1A1 and COM1A0 control bits determine the output pin actions that
affect pin PB1 (OC1A) as described in Table 12-4. Note that OC1A is not connected in normal
mode.
In PWM mode, th ese bits have differe n t func t ion s. Re fe r to Table 12-1 on page 89 for a detailed
description.
• Bits 3:0 - CS1[3:0]: Clock Select Bits 3, 2, 1, and 0
The Clock Select bits 3, 2, 1, and 0 define the pre scaling source of Timer/Counte r1.
Bit 7 6 5 4 3 2 1 0
0x30 CTC1 PWM1A COM1A1 COM1A0 CS13 CS12 CS11 CS10 TCCR1
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
Table 12-4. Comparator A Mode Select in Normal Mode
COM1A1 COM1A0 Description
0 0 Timer/Counter Comparator A disconnected from output pin OC1A.
0 1 Toggle the OC1A output line.
1 0 Clea r the OC1A output line.
1 1 Set the OC1A output line
Table 12-5. Timer/Counter1 Prescale Select
CS13 CS12 CS11 CS10 Asynchronous
Clocking Mode Synchronous
Clocking Mode
0 0 0 0 T/C1 stopped T/C1 stopped
0001PCK CK
0 0 1 0 PCK/2 CK/2
0 0 1 1 PCK/4 CK/4
93
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The Stop condition provides a Timer Enable/Disable function.
12.3.2 GTCCR – General Timer/Counter1 Control Regis ter
• Bit 6 – PWM1B: Pulse Width Modulator B Enab le
When set (one) this b it enables PWM mode based on comparator OCR1B in Timer/Co unter1
and the co unter va lue is r eset to $0 0 in t he CPU clock cycle af ter a compar e matc h with OCR1C
register value.
• Bits 5:4 – COM1B[1: 0]: 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. Since the output pin action is an alternative
function to an I/O por t, the correspo nding direction con trol bit must be set (one ) in order to con-
trol an output pin.
In Normal mode, the COM1B1 and COM1B0 control bits determine the output pin actions that
affect pin PB4 (OC1B) as described in Table 12-6. Note that OC1B is not connected in normal
mode.
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
Table 12-5. Timer/Counter1 Prescale Select (Continued)
CS13 CS12 CS11 CS10 Asynchronous
Clocking Mode Synchronous
Clocking Mode
Bit 7 6 5 4 3 2 1 0
0x2C TSM PWM1B COM1B1 COM1B0 FOC1B FOC1A PSR1 PSR0 GTCCR
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Table 12-6. Comparator B Mode Select in Normal Mode
COM1B1 COM1B0 Description
0 0 Timer/Counter Comparator B disconnected from output pin OC1B.
0 1 Toggle the OC1B output line.
1 0 Clea r the OC1B output line.
1 1 Set the OC1B output line
94 2586N–AVR–04/11
ATtiny25/45/85
In PWM mode, th ese bits have differe n t func t ion s. Re fe r to Table 12-1 on page 89 for a detailed
description.
• Bit 3 – FOC1B: Force Output Compare Match 1B
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 CO M1B1 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 pro-
grammed 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 2 – 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 CO M1A1 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 pro-
grammed 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 1 – PSR1 : Prescaler Reset Timer/Counter1
When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffec ted) 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.
12.3.3 TCNT1 – Timer/Counter1
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 and half CPU
clock cycles in synchronous mode and at most one CPU clock cycles for asynchronous mode.
12.3.4 OCR1A –Timer/Counter1 Output Compare RegisterA
The output compare re gister 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 TCCR1. A compare match does
only occur if Timer/Counter1 counts to the OCR1A value. A software 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 follow-
ing the compar e event.
Bit 76543210
0x2F MSB LSB TCNT1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 76543210
0x2E MSB LSB OCR1A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
95
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12.3.5 OCR1B – Timer/Counter1 Output Compare RegisterB
The output compare re gister 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 TCCR1. 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 follow-
ing the compar e event.
12.3.6 OCR1C – Timer/Counter1 Output Compare RegisterC
The output compare register C is an 8-bit read/writ e register.
The Timer/Counter O utput Comp are Regist er C contai ns data t o b e cont inu ously compa re d 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 TCCR1 is set, a compare match will clear TCNT1.
This register has the same function in normal mode and PWM mode.
12.3.7 TIMSK – Timer/Counter Interrupt Mask Register
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 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/Count er1 Compare MatchA , interrupt is enabled. The corresponding interru pt at vector
$003 is execut ed if a compa re matchA occur s. The Com pare Flag in Timer/Count er1 is set (on e)
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/Count er1 Compare MatchB , interrupt is enabled. The corresponding interru pt at vector
$009 is execut ed if a compa re matchB occur s. The Com pare Flag in Timer/Count er1 is set (on e)
in the Timer/Counter Interrupt Flag Register.
Bit 76543210
0x2B MSB LSB OCR1B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 76543210
0x2D MSB LSB OCR1C
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 1 1 1 1 1 1 1 1
Bit 7 6 5 4 3 2 1 0
0x39 – OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 – TIMSK
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial value 0 0 0 0 0 0 0 0
96 2586N–AVR–04/11
ATtiny25/45/85
• 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 Overflo w interrupt is enabled. The corresponding interrupt (at vector $004) is
executed if an overfl ow in Timer/ Co un ter1 occurs. The Overflow Flag (Timer1) is set (one) in the
Timer/Counter Interrupt Flag Register - TIFR.
• Bit 0 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
12.3.8 TIFR – Timer/Counter Interrupt Flag Register
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
• Bit 6 – OCF1A: Out put Compare Flag 1A
The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1A - Output Compare Regist er 1A. OCF1 A is cleared by ha rdware when executing
the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchroniza-
tion 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: Out put Compare Flag 1B
The OCF1B bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1B - Output Compare Regist er 1A. OCF1 B is cleared by ha rdware when executing
the corresponding interrupt handling vector. Alternatively, OCF1B is cleared, after synchroniza-
tion 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.
• Bit 2 – TOV1: Timer/Counter1 Overflow Flag
In normal mode (PWM1A=0 and PWM1B=0) the bit TOV1 is set (one) when an overflow occurs
in Timer/Counter1. The bit TOV1 is cleared by hardware when executing the corresponding
interrupt handling vec tor. Alternatively, TOV1 is cleared, after synchronization clock cycle, by
writing a logical one to the flag.
In PWM mode (either PWM1A=1 or PWM1B=1) the bit TOV1 is set (one) when compare match
occurs between Timer/Counter1 and data value in OCR1C - Outpu t Compare Register 1C.
When the SREG I-b it, and TO IE1 (Timer/Co unter1 Overflo w Interrup t Enable), and TOV1 are set
(one), the Timer/Counter1 Overflow interrupt is executed.
• Bit 0 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
Bit 7 6 5 4 3 2 1 0
0x38 –OCF1AOCF1B
OCF0A OCF0B TOV1 TOV0 – TIFR
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial value 0 0 0 0 0 0 0 0
97
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12.3.9 PLLCSR – PLL Control and Status Register
• Bit 7 – LSM: Low Speed Mode
The high speed mode is enabled as default and the fast peripheral clock is 64 MHz, but the low
speed mode can be set by writing the LSM bit to one. Then the fast peripheral clock is scaled
down to 32 MHz. The low speed mode must be set, if the supply voltage is below 2.7 volts,
because the Timer/Counter1 is not running f ast enough on low voltage levels. I t is highly recom-
mended that Timer/Counter1 is stopped whenever the LSM bit is changed.
Note, that LSM can not be set if PLLCLK is used as system clock.
• Bit 6:3 – Res : Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 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 (or 32 MHz in Low Speed Mode) 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. T he bit PCKE can
only be set, if the PLL has be en enabled earlier.
• Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started and if needed internal RC-oscillator is started as a PLL
reference clock. If PLL is selected as a system clock source the value for this bit is always 1.
• Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock. The PLOCK bit should be
ignored during initial PLL lock-in sequence when PLL frequency overshoots and undershoots,
before reaching steady state. The stea dy state is obtained within 100 µs. After PLL lock-in it is
recommended to check the PLOCK bit before enabling PCK for Timer/Counter1.
Bit 76543210
0x27 LSM - - - - PCKE PLLE PLOCK PLLCSR
Read/Write R/W R R R R R/W R/W R
Initial value 0 0 0 0 0 0 0/1 0
98 2586N–AVR–04/11
ATtiny25/45/85
13. 8-bit Timer/Counter1 in ATtiny15 Mode
The ATtiny15 compatibility mode is selected by writing the code “0011” to the CKSEL fuses (if
any other code is written, the T imer/Counter1 is working in normal mode). When selected the
ATtiny15 compatibility mode provides an ATtiny15 backward compatible prescaler and
Timer/Counter. Furt hermore, the clocking system has same clock frequencies as in ATtiny1 5.
13.1 Timer/Counter1 Prescaler
Figure 13 -1 shows an ATtiny15 compatible prescaler. It has two prescaler units, a 10-bit pres-
caler for the system clock (CK) and a 3-bit prescaler for the fast peripheral clock (PCK). The
clocking system of the Timer/Counter1 is always synchronous in the ATtiny15 compatibility
mode, because the same RC Oscillator is used as a PLL clock source (generates the input clock
for the prescaler) and the AVR core.
Figure 13-1. Timer/Counter1 Prescaler
The same clock selections as in ATtiny15 can be chosen for Timer/Counter1 from the output
multiplexer, because the frequency of the fast peripheral clock is 25.6 MHz and the prescaler is
similar in the ATtiny15 compatibility mode. The clock selections are PCK, PCK/2, PCK/4, PCK/8,
CK, CK/2, CK/4, CK/8, CK/16, CK/32, CK/64, CK/128, CK/256, CK/512, CK/1024 and stop.
13.2 Counter and Compare Units
Figure 13 -2 shows Timer/Counter 1 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 TCCR1,
GTCCR, OCR1A 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 and TOV1),
because of the input and output synchronization.
The Timer/Counter1 features a high resolution and a high accuracy usage with the lower pres-
caling opportunities. It can also support an accurate, high speed, 8-bit Pulse Width Modulator
(PWM) using clock speeds up to 25.6 MHz. In this mode, Timer/Counter1 and the Output Com-
pare Registers serve as a stand-alone PWM. Refer to “Timer/Counter1 in PWM Mode” on page
TIMER/COUNTER1 COUNT ENABLE
PSR1
CS10
CS11
CS12
PCK (25.6 MHz)
0
CS13
3-BIT T/C PRESCALER
PCK/2
PCK
PCK/4
PCK/8
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
CK/128
CK/256
CK/512
CK/1024
10-BIT T/C PRESCALER
CK (1.6 MHz)
CK
CLEAR
CLEAR
99
2586N–AVR–04/11
ATtiny25/45/85
101 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.
Figure 13-2. Timer/Counter 1 Synchronization Register Block Diagram.
Timer/Counter1 and the prescaler allow running the CPU from any clock source while the pres-
caler is operating on the fast 25.6 MHz PCK clock in the asynchronous mode.
The following Figure 13-3 shows the block diagram for Timer/Counter1.
8-BIT DATABUS
OCR1A OCR1A_SI
TCNT_SO
OCR1C OCR1C_SI
TCCR1 TCCR1_SI
GTCCR GTCCR_SI
TCNT1 TCNT1_SI
OCF1A OCF1A_SI
TOV1 TOV1_SITOV1_SO
OCF1A_SO
TCNT1
S
AS
A
PCKE
CK
PCK
IO-registersInput synchronization
registers
Timer/Counter1 Output synchronization
registers
SYNC
MODE
ASYNC
MODE
1 PCK Delay No Delay~1 CK Delay
1PCK Delay No Delay
TCNT1
OCF1A
TOV1
1..2 PCK Delay
~1 CK Delay1..2 PCK Delay
100 2586N–AVR–04/11
ATtiny25/45/85
Figure 13-3. Timer/Counter1 Block Diagram
Two status flags (overflow and compare m atch) are found in the Timer/Counter Interrupt Fla g
Register - TIFR . Control signals are found in the Timer/Counter Control Registers TCCR1 and
GTCCR. The interrupt enable/disable settings are found in the Timer/Counter Interrupt Mask
Register - TIMSK.
The Timer/Counter1 contains two Output Compare Registers, OCR1A and OCR1C as the data
source to be compared with the Timer/Counter1 contents. In normal mode the Output Compare
functions are operational with OCR1A only. OCR1A determines action on the OC1A pin (PB1),
and it can generate Timer1 OC1A interrupt in normal mode and in PWM mode. OCR1C holds
the Timer/Counter maximum value, i.e. the clear on compare match value. In the normal mode
an overflow interrupt (TOV1) is generated when Timer/Counter1 counts from $FF to $00, while
in the PWM mode the overflow interrupt is generated when the Timer/Counter1 counts either
from $FF to $00 or from OCR1C to $00.
In PWM mode, OCR1 A pr ovid e s th e da ta va lu e s against which the Timer Counter value is com-
pared. Upon compare match the PWM outputs (OC1A) is generated. In PWM mode, the Timer
Counter counts up to the va lue specified in the outp ut compare registe r OCR1C and starts again
from $00. This fea ture 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
12-3 on page 91 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 reso lution.
8-BIT DATABUS
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER1
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TIMER INT. MASK
REGISTER (TIMSK)
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
T/C1 CONTROL
LOGIC
TOV1
TOV1
TOIE0
TOIE1
OCIE1A
OCF1A
OCF1A
CK
PCK
T/C1 OVER-
FLOW IRQ OC1A
(PB1)
T/C1 COMPARE
MATCH A IRQ
GLOBAL T/C CONTROL
REGISTER 2 (GTCCR)
PWM1A
FOC1A
(OCR1A) (OCR1C)
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TOV0
COM1A1
COM1A0
T/C CONTROL
REGISTER 1 (TCCR1)
CS12
PSR1
CS11
CS10
CS13
CTC1
101
2586N–AVR–04/11
ATtiny25/45/85
13.2.1 Timer/Counter1 in PWM Mode
When the PWM mode is selected, Timer/Counter1 and the Output Compare Register A -
OCR1A form an 8-bit, free-running and glitch-free PWM generator with output on the
PB1(OC1A).
When the counter value match the content of OCR1A, the OC1 A and output is set or cleared
according to the COM1A1/COM1A0 bits in the Timer/Counter1 Control Register A - TCCR1, as
shown in Table 13-1.
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 OCR1C will
set an overflow interrup t flag (TOV1) after a synchronization delay following the compare event.
Note that in PWM mode, writing to the Output Compare Register OCR1A, the data value is first
transferred to a temporary location. The value is latched into OCR1A when the Timer/Counter
reaches OCR1C. Thi s prevents the occurrence of odd-length PWM pu lses (glitches) in t he event
of an unsynchr on ize d OC R1A. See Figure 13-4 for an e xample.
Figure 13-4. Effects of Unsynchronized OCR Latching
During the time between the write and the latch operation, a read from OCR1A will read the con-
tents of the temporary location. This means that the most recently written value always will read
out of OCR1A.
Table 13-1. Compare Mode Select in PWM Mode
COM1A1 COM1A0 Effect on Output Compare Pin
0 0 OC1A not connected.
0 1 OC1A not connected.
1 0 OC1A cleared on compare match. Set when TCNT1 = $00.
1 1 OC1A set on compare match. Cleared when TCNT1 = $00.
PWM Output OC1A
PWM Output OC1A
Unsynchronized OC1A Latch
Synchronized OC1A Latch
Counter Value
Compare Value
Counter Value
Compare Value
Compare Value changes
Glitch
Compare Value changes
102 2586N–AVR–04/11
ATtiny25/45/85
When OCR1A contains $00 or the top value, as specified in OCR1C register, the output
PB1(OC1A) is held low or high according to the settings of COM1A1/COM1A0. This is shown in
Table 13-2.
In PWM mode, the Timer Overflow Flag - TOV1 is set when the TCNT1 counts to the OCR1C
value and the TCNT1 is reset to $00. The Timer Overflow Interrupt1 is executed when TOV1 is
set provided that Tim er Over f low I nter rupt an d global interrupts are e nab led. This a lso ap plie s to
the Timer Output Compare flags and interrupts.
The PWM frequency can be derived from the timer/counter clock frequency using the following
equation:
The duty cycle of the PWM waveform can be calculated using the f ollowing equation:
...where TPCK is the period of the fast peripheral clock (1/25.6 MHz = 39.1 ns).
Resolution indicates how many bits are required to express the value in the OCR1C register. It
can be calculated using the following equation:
Table 13-2. PWM Outputs OCR1A = $00 or OCR1C
COM1A1 COM1A0 OCR1A Output OC1A
01$00L
0 1 OCR1C H
10$00L
1 0 OCR1C H
11$00H
1 1 OCR1C L
Table 13-3. Timer/Counter1 Clock Prescale Select in the Asynchronous Mode
PWM Frequency Clock Selection CS1[3:0] OCR1C RESOLUTION
20 kHz PCK/16 0101 199 7.6
30 kHz PCK/16 0101 132 7.1
40 kHz PCK/8 0100 199 7.6
50 kHz PCK/8 0100 159 7.3
60 kHz PCK/8 0100 132 7.1
70 kHz PCK/4 0011 228 7.8
ffTCK1
OCR1C + 1()
------------------------------------=
DOCR1A 1+()TTCK1 TPCK
–×
OCR1C 1+()TTCK1
×
----------------------------------------------------------------------------=
R2OCR1C 1+()log=
103
2586N–AVR–04/11
ATtiny25/45/85
13.3 Register Description
13.3.1 TCCR1 – Timer/Counter1 Control Register
• 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 OCR1A register. If the control bit is cleared, Timer/Counter1 contin-
ues counting and is unaffected by a compare match.
• Bit 6 – PWM1A: Pulse Width Modulator A Enab le
When set (one) this b it enables PWM mode based on comparator OCR1A in Timer/Co unter1
and the co unter va lue is r eset to $0 0 in t he CPU clock cycle af ter a compar e matc h with OCR1C
register value.
80 kHz PCK/4 0011 199 7.6
90 kHz PCK/4 0011 177 7.5
100 kHz PCK/4 0011 159 7.3
110 kHz PCK/4 0011 144 7.2
120 kHz PCK/4 0011 132 7.1
130 kHz PCK/2 0010 245 7.9
140 kHz PCK/2 0010 228 7.8
150 kHz PCK/2 0010 212 7.7
160 kHz PCK/2 0010 199 7.6
170 kHz PCK/2 0010 187 7.6
180 kHz PCK/2 0010 177 7.5
190 kHz PCK/2 0010 167 7.4
200 kHz PCK/2 0010 159 7.3
250 kHz PCK 0001 255 8.0
300 kHz PCK 0001 212 7.7
350 kHz PCK 0001 182 7.5
400 kHz PCK 0001 159 7.3
450 kHz PCK 0001 141 7.1
500 kHz PCK 0001 127 7.0
Table 13-3. Timer/Counter1 Clock Prescale Select in the Asynchronous Mode (Continued)
PWM Frequency Clock Selection CS1[3:0] OCR1C RESOLUTION
Bit 7 6 5 4 3 2 1 0
0x30 CTC1 PWM1A COM1A1 COM1A0 CS13 CS12 CS11 CS10 TCCR1A
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
104 2586N–AVR–04/11
ATtiny25/45/85
• Bits 5:4 – COM1A[1: 0]: 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 alterna tive function to a n I/O po rt, the corresponding direction control bit must be
set (one) in orde r to cont ro l an ou tp ut pi n.
In PWM mode, these bits have different functions. Refer to Table 13-1 on page 101 for a
detailed descrip tion .
• Bits 3:0 – CS1[3: 0]: Clock Sel ect Bits 3, 2, 1, and 0
The Clock Select bits 3, 2, 1, and 0 define the pre scaling source of Timer/Counte r1.
The Stop condition provides a Timer Enable/Disable function.
Table 13-4. 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 Clea r the OC1A output line.
1 1 Set the OC1A output line
Table 13-5. Timer/Counter1 Prescale Select
CS13 CS12 CS11 CS10 T/C1 Clock
0 0 0 0 T/C1 stopped
0001PCK
0 0 1 0 PCK/2
0 0 1 1 PCK/4
0 1 0 0 PCK/8
0101CK
0110CK/2
0111CK/4
1000CK/8
1001CK/16
1010CK/32
1011CK/64
1100CK/128
1101CK/256
1110CK/512
1 1 1 1 CK/1024
105
2586N–AVR–04/11
ATtiny25/45/85
13.3.2 GTCCR – General Timer/Counter1 Control Regis ter
• Bit 2 – 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 CO M1A1 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 pro-
grammed 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 1 – PSR1 : Prescaler Reset Timer/Counter1
When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffec ted) 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.
13.3.3 TCNT1 – Timer/Counter1
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.
13.3.4 OCR1A – Timer/Counter1 Output Compare RegisterA
The output compare re gister 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 TCCR1. A compare match does
only occur if Timer/Counter1 counts to the OCR1A value. A software 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 follow-
ing the compar e event.
Bit 7 6 5 4 3 2 1 0
0x2C TSM PWM1B COM1B1 COM1B0 FOC1B FOC1A PSR1 PSR0 GTCCR
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 76543210
0x2F MSB LSB TCNT1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 76543210
0x2E MSB LSB OCR1A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
106 2586N–AVR–04/11
ATtiny25/45/85
13.3.5 OCR1C – Timer/Counter1 Output Compare Register C
The Output Compare Register B - OCR1B from ATtiny15 is replaced with the output compare
register C - OCR1 C that is an 8-bit r ead/write register . This regist er has th e same function as the
Output Compare Register B in ATtiny15.
The Timer/Counter O utput Comp are Regist er C contai ns data t o b e cont inu ously compa re d 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 TCCR1 is set, a compare match will clear TCNT1.
13.3.6 TIMSK – Timer/Counter Interrupt Mask Register
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 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/Count er1 Compare MatchA , interrupt is enabled. The corresponding interru pt at vector
$003 is execut ed if a compa re matchA occur s. The Com pare Flag in Timer/Count er1 is set (on e)
in the Timer/Counter Interrupt Flag Register.
• 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 Overflo w interrupt is enabled. The corresponding interrupt (at vector $004) is
executed if an overfl ow in Timer/ Co un ter1 occurs. The Overflow Flag (Timer1) is set (one) in the
Timer/Counter Interrupt Flag Register - TIFR.
• Bit 0 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
13.3.7 TIFR – Timer/Counter Interrupt Flag Register
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
Bit 76543210
0x2D MSB LSB OCR1C
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 1 1 1 1 1 1 1 1
Bit 7 6 5 4 3 2 1 0
0x39 –OCIE1A
OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 – TIMSK
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
0x38 –OCF1A
OCF1B OCF0A OCF0B TOV1 TOV0 – TIFR
Read/Write R R/W R/W R/W R/W R/W R/W R
Initial value 0 0 0 0 0 0 0 0
107
2586N–AVR–04/11
ATtiny25/45/85
• Bit 6 – OCF1A: Out put Compare Flag 1A
The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1A - Output Compare Regist er 1A. OCF1 A is cleared by ha rdware when executing
the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchroniza-
tion 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 2 – TOV1: Timer/Counter1 Overflow Flag
The bit TOV1 is set (one) when an overflo w occurs in Time r/Coun te r1 . TO V1 is clear ed by har d-
ware 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 0 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
13.3.8 PLLCSR – PLL Control and Status Register
• Bits 6:3 – Res : Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and always read as zero.
• Bit 2 – PCKE: PCK Enable
The bit PCKE is always set in the ATtiny15 compatibility mode.
• Bit 1 – PLLE: PLL Enable
The PLL is always enabled in the ATtiny15 compatibility mode.
• Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock. The PLOCK bit should be
ignored during initial PLL lock-in sequence when PLL frequency overshoots and undershoots,
before reaching steady state. The stea dy state is obtained within 100 µs. After PLL lock-in it is
recommended to check the PLOCK bit before enabling PCK for Timer/Counter1.
Bit 76543210
0x27 LSM – – – – PCKE PLLE PLOCK PLLCSR
Read/Write R/W R R R R R/W R/W R
Initial value 0 0 0 0 0 0 0/1 0
108 2586N–AVR–04/11
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14. Dead Time Generator
The Dead Time Generator is provided for the Timer/Counter1 PWM output pairs to allow driving
external power c ontrol switches safe ly. The Dead T ime Generator is a separate block that can
be connected to Timer/Counter1 and it is used to insert dead times (non-overlapping times) for
the Timer/Counter1 complementary output pairs (OC1A-OC1A and OC1B-OC1B ). The sharing
of tasks is as follows: the timer/counter generates the PWM output and the Dead Time Genera-
tor generates the non-overlapping PWM output pair from the timer/counter PWM signal. Two
Dead Time Generators are provided, one for each PWM output. The non-overlap time is adjust-
able and the PWM output and it’s complementary output are adjusted separately, and
independently for both PWM outputs.
Figure 14-1. Timer/Counter1 & Dead Time Generators
The dead time generation is based on the 4-bit down counters that count the dead time, as
shown in Figure 46. Th ere is a dedicated prescaler in fr ont of the Dead Time Generator that can
divide the T imer/Counter1 c lock (PCK or CK) by 1, 2, 4 or 8. This pr ovides for large r ange of
dead times that ca n be generated. The presca ler is controlled by two control bits DT PS1[1:0]
from the I/O register at address 0x23. The block has also a rising and falling edge detector that
is used to start the dead time counting period. Depending on the edge, one of the transitions on
the rising edges, OC1x or OC1x is delayed until the counter has counted to zero. The compara-
tor is used to compare the counter with zero and stop the dead time insertion when zero has
been reached. The counter is loaded with a 4-bit DT1xH or DT1xL value from DT1x I/O register,
depending on the edge of the PWM generator output when the dead time insertion is started.
Figure 14-2. Dead Time Generator
TIMER/COUNTER1
OC1A OC1A OC1B OC1B
DEAD TIME GENERATOR
PWM GENERATOR
PCKE
T15M
PCK
CK
DT1AH DT1BH
DEAD TIME GENERATOR
PWM1BPWM1A
DT1AL DT1BL
CLOCK CONTROL
OC1x
OC1x
T/C1 CLOCK
PWM1x
4-BIT COUNTER
COMPARATOR
DT1xL
DT1xH
DT1x
I/O REGISTER
DEAD TIME
PRESCALER
DTPS1[1:0]
109
2586N–AVR–04/11
ATtiny25/45/85
The length of the counting period is user adjustable by selecting the dead time prescaler setting
in 0x23 register, and selecting then the dead time value in I/O register DT1x. The DT1x register
consists of two 4-b it fields, DT1xH and DT1xL that contr ol the dead time periods of the PW M
output and its’ complementary ou tput separately. Thus the rising edg e of OC1x and OC1x can
have different dead time periods. The dead time is adjusted as the number of prescaled dead
time generator clock cycles.
Figure 14-3. The Complementary Output Pair
14.1 Register Description
14.1.1 DTPS1 – Timer/Counter1 Dead Time Prescaler Register 1
The dead time prescaler register, DTPS1 is a 2-bit read/write register.
• Bits 1:0 – DTPS1[1:0]: Dead Time Prescaler
The dedicated Dead Time prescaler in front of the Dead Time Generator can divide the
Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8 providing a large range of dead times that can
be generated. The Dead Time prescaler is controlled by two bits DTPS1 [1:0] from the Dead
Time Prescaler register. These bits define the division factor of the Dead Time prescaler. The
division factors are given in table 46.
OC1x
x = A or B
t
non-overlap / rising edge
t
non-overlap / falling edge
OC1x
PWM1x
Bit 76543210
0x23 DTPS11 DTPS10 DTPS1
Read/WriteRRRRRRR/WR/W
Initial value 0 0 0 0 0 0 0 0
Table 14-1. Division factors of the Dead Time prescaler
DTPS11 DTPS10 Prescaler divides the T/C1 clock by
0 0 1x (no divisi on)
012x
104x
118x
110 2586N–AVR–04/11
ATtiny25/45/85
14.1.2 DT1A – Timer/Counter1 Dead Time A
The dead time value register A is an 8-bit read/write register.
The dead time delay of is adjusted by the dead time value register, DT1A. The register consists
of two fields, DT1AH[3:0] and DT1AL[3:0], one for each complementary output. Therefore a dif-
ferent dead ti me delay can be adju sted for t he rising edge o f OC1A and the rising edge of OC1A .
• Bits 7:4 – DT1AH[3:0]: Dead Time Value for OC1A Output
The dead time value for the OC1A output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
• Bits 3:0 – DT1AL[3:0]: Dead Time Value for OC1A Output
The dead time value for the OC1A output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
14.1.3 DT1B – Timer/Counter1 Dead Time B
The dead time value register Bis an 8-bit read/write register.
The dead time delay of is adjusted by the dead time value register, DT1B. The register consists
of two fields, DT1BH[3:0] and DT1BL[3:0], one for each complementary output. Therefore a dif-
ferent dead ti me delay can be adju sted for t he rising edge o f OC1A and the rising edge of OC1A .
• Bits 7:4 – DT1BH[3:0]: Dead Time Value for OC1B Output
The dead time value for the OC1B output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
• Bits 3:0 – DT1BL[3:0]: Dead Time Value for OC1B Output
The dead time value for the OC1B output. The dead time delay is set as a number of the pres-
caled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
Bit 76543210
0x25 DT1AH3 DT1AH2 DT1AH1 DT1AH0 DT1AL3 DT1AL2 DT1AL1 DT1AL0 DT1A
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 76543210
0x24 DT1BH3 DT1BH2 DT1BH1 DT1BH0 DT1BL3 DT1BL2 DT1BL1 DT1BL0 DT1B
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
111
2586N–AVR–04/11
ATtiny25/45/85
15. USI – Universal Serial Interface
15.1 Features •Two-wire Synchr on ous Data Transfer (Master or Slave)
•Three-wire Synchronous Data Transfer (Master or Slave)
•Data Received Interrupt
•Wakeup from Idle Mode
•Wake-up from All Sleep Modes In Two-wire Mode
•Two-wire Start Condition Detector with Interrupt Capability
15.2 Overview The Universal Serial Interface (USI), provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rat es and use s less code spa ce than solution s based on soft ware only. I nterr upts
are included to minimize the processor load.
A simplified block diagram of the USI is shown in Figure 15-1 For actual placem ent of I/O pins
refer to “Pinout ATtiny25/45/85” on page 2. Device-specific I/O Register and bit locations are
listed in the “Register Descriptions” on page 118.
Figure 15-1. Universal Serial Interface, Block Diagram
The 8-bit USI Data Register (USIDR) contains the incoming and outgoing data. It is directly
accessible via the data bus but a copy of the contents is also placed in the USI Buffer Register
(USIBR) where it can be retrieved later. If reading the USI Data Register dire ctly, the register
must be read as quickly as possible to ensure that no data is lost.
The most signif icant bi t of the USI Data Re gister is connected t o one of two outpu t pins (depen d-
ing on the mode configuration, see “USICR – USI Control Register” on page 120). There is a
transparent latch between the output of the USI Data Register and the output pin, which delays
DATA BUS
USIPF
USITC
USICLK
USICS0
USICS1
USIOIFUSIOIE
USIDC
USISIF
USIWM0
USIWM1
USISIE Bit7
Two-wire
Clock
Control Unit
DO (Output only)
DI/SDA (Input/Open Drain)
USCK/SCL (Input/Open Drain)
4-bit Counter
USIDR
USISR
DQ
LE
USICR
CLOCK
HOLD
TIM0 COMP
Bit0
[1]
3
0
1
2
3
0
1
2
0
1
2
USIBR
112 2586N–AVR–04/11
ATtiny25/45/85
the change o f 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 writt en via the data bus, and it can generate an overflow
interrupt. Both the USI Data Register and the count er 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 cou nts both clock edges. This means the counter registers the number of
clock edges and not the number of data bits. The clock can be selected from three different
sources: The USCK pin, Timer/Counter0 Compare Match or from software.
The two-wire clock control unit can be configured to generate an interrupt whe n a start condition
has been detected on the two-wire bus. It can also be set to generate wait states by holding the
clock pin low after a start co ndition is detected, or after the counter overflows.
15.3 Functional Descriptions
15.3.1 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 required. Pin names used in this mode are DI, DO, and USCK.
Figure 15-2. Three-wire Mode Operation, Simplified Diagram
Figure 15-2 shows two USI units opera ting in t hree-wire mode, one as Ma ste r and on e as Slave.
The two USI Data Registers are interconnected in such way that after eight USCK clocks, the
data in each register has been intercha nged. The same clock also incr ements 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 USCK pin via the PORTB register or by writing a one to bit USITC bit in USICR.
SLAVE
MASTER
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DO
DI
USCK
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DO
DI
USCK
PORTxn
113
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Figure 15-3. Three-Wire Mode, Timing Diagram
The three-wire mode timing is shown in Figure 15-3 At the top of the figure is a USCK cycle ref-
erence. One bit is shifted into the USI Data Register (USIDR) for each of these cycles. The
USCK 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 (USI Data Register is shifted by one) at nega-
tive edges . In external c lock mode 1 (U SICS0 = 1) the opposite edges with respect to mode 0
are used. In other words, data is sampled 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 15-3), a bus transfer involves the following steps:
1. The slave and master devices set up their data outputs and, depending on the protocol
used, enable their output drivers (mark A and B). The output is set up by writing the
data to be transmitted to the USI Data Register. The output is enabled by setting the
corresponding bit in the Data Direction Register of Port B. Note that there is not a pre-
ferred order of points A and B in the figure, but both must be at least one half USCK
cycle before point C , where the data is sampled. This is in order to ensure that the data
setup requirem e nt is sat isfie d. The 4-bit counter is reset to zero.
2. The master software generates a clock pulse by toggling the USCK line twice (C and
D). The bit values on the data input (DI) pins are 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 complete register (byte) transfer.
4. After eight clock pulses (i.e ., 16 cloc k edges) the counter will o verflow and indicate that
the tran sfe r has been completed. If USI Buffer Registers are not used the data bytes
that have been transferred must now be proc essed bef ore a new transfer can be initi-
ated. 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.
15.3.2 SPI Master Operation Example
The following code demonstrates how to use the USI as an 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
in r16, USISR
MSB
MSB
654321LSB
1 2 3 4 5 6 7 8
654321LSB
USCK
USCK
DO
DI
DCBA E
CYCLE ( Reference )
114 2586N–AVR–04/11
ATtiny25/45/85
sbrs r16, USIOIF
rjmp SPITransfer_loop
in r16,USIDR
ret
The code is size optimized using only eight instructions (plus return). The code example
assumes that the DO and USCK pins have been enabled as outputs in DDRB. The value stored
in register r16 prior to the function is called is transferred to the slave device, and when the
transfer is completed th e data received from the slave is stored back into the register r16.
The second and third instructions clear the USI Counter Overflow Flag and the USI counter
value. The fourth and fifth instructions set three-wire mode, positive edge clock, count at USITC
strobe, and toggle USCK. The loop is repeated 16 times.
The following code demonstrates ho w to use the USI as an 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
15.3.3 SPI Slave Operation Example
The following code demonst rates how to use the USI as an SPI slave:
init:
ldi r16,(1<<USIWM0)|(1<<USICS1)
out USICR,r16
115
2586N–AVR–04/11
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...
SlaveSPITransfer:
out USIDR,r16
ldi r16,(1<<USIOIF)
out USISR,r16
SlaveSPITransfer_loop:
in r16, USISR
sbrs r16, USIOIF
rjmp SlaveSPITransfer_loop
in r16,USIDR
ret
The code is size optimized using only eight instructions (plus return). The code example
assumes that the DO and USCK pins have been enabled as outputs in DDRB. The value stored
in register r16 prio r to the function is called is transferred to the master device, and when the
transfer is completed th e data received from the master is stor ed back into the register r16.
Note that the first two instructions is for initialization , only, and need only be execu ted once.
These instructions set three-wire mode and positive edge clock. The loop is repeated until the
USI Counter Overflow Flag is set.
15.3.4 Two-wire ModeThe USI two-wire mode is compliant to the In ter I C (TWI ) bus prot ocol, but witho ut slew rate lim-
iting on outp uts and wit hout input noise filtering. Pin names used in this mod e are SCL a nd SDA.
Figure 15-4. Two-wire Mode Operation, Simplified Diagram
MASTER
SLAVE
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SDA
SCL
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Two-wire Clock
Control Unit
HOLD
SCL
PORTxn
SDA
SCL
VCC
116 2586N–AVR–04/11
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Figure 15-4 shows t wo USI units o perat in g i n tw o- wire mo de, on e as ma ste r and one a s slave. It
is only the physical layer that is shown since the system operation is highly dependent of the
communica tion scheme used . The main differ ences betwee n the master and sla ve operation at
this level is the serial clock generation which is always done by the master. Only the slave uses
the clock control unit.
Clock generation must be implemented in software, but the shift operation is done automatically
in both devices. Note that clocking only on negative edges 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 comple ted. The clock is generated by the ma ster by toggling the USCK 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.
Figure 15-5. Two-wire Mode, Typical Timing Diag ram
Referring to the timing diagram (Figure 15-5), a bus transfer involves the following steps:
1. The start condition is g enerated by the master by forc ing the SDA low line while keep-
ing the SCL line high (A). SDA can be forced low either by writing a zero to bit 7 of the
USI Data Register, or by setting the corresponding bit in the PORTB register to zero.
Note that the Data Direction Register bit must be set to one for the output to be
enabled. The start detector logic of the slave device (see Figure 15-6 on page 117)
detects the start condition and sets the USISIF Flag. The flag can gene rate an interrupt
if necessar y.
2. In addition, the start detector will hold the SCL line low after the master has forced a
negative edge on this line (B). This allows the sla ve to w ake up from sleep or complet e
other tasks be fo re setting up th e USI Data Regist er to receiv e the add ress. T his is done
by clearing the start condition flag and rese ttin g the co un te r.
3. The master set the first bit to be transferred and r eleases the SCL line (C). The slave
samples the data and shifts it into the USI Data Register at the positive edge of the SCL
clock.
4. After eight bits containing slave address and data direction (read or write) have been
transferred, 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. When the slave is addressed, it holds the SDA line low during the acknowledgment
cycle before holding the SCL line low again (i.e., the USI Counter Register must be set
to 14 before releasing SCL at (D)). Depending on the R/W bit the master or slave
PS ADDRESS
1 - 7 8 9
R/W ACK ACK
1 - 8 9
DATA ACK
1 - 8 9
DATA
SDA
SCL
A B D EC F
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enab les its ou tput. If th e bi t is se t, a master read oper a tion is in pro g ress (i .e ., the sl av e
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 forcing the
acknowledge bit low after the last byte transmitted.
15.3.5 Start Condition Detector
The start condition detector is shown in Figure 15-6. 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.
Figure 15-6. Start Condition Detector, Logic Diagram
The start condition detect or is wor king asyn chronou sly and can there fore wake u p the pr ocessor
from power- down sleep mode. Ho wever, the protoc ol used might have re strictions on the SC L
hold time. Therefore, when using this feature the oscillator start-up time (set by CKSEL fuses,
see “Clock Systems and their Distribution” on page 23) must also be taken into consideration.
Refer to the descrip tion of th e USISI F bit on page 119 for further details.
15.3.6 Clock speed considerations
Maximum frequency for SCL and SCK is fCK / 2. This is also the maximum data transmit and
receive rate in both two- and three-wire mode. In two-wire slave mode the Two-wire Clock Con-
trol Unit will hold the SCL low until the slav e is ready to receive more data. This may reduce the
actual data rate in two -wir e m od e.
15.4 Alternative USI Usage
The flexible design of the USI allows it to be used for other tasks when serial communication is
not needed. Below ar e some examples.
15.4.1 Half-Duplex Asynchronous Data Transfer
Using the USI Data Register in three-wire mode it is possible to implement a more compact and
higher performance UART than by software, only.
15.4.2 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 increment the counter value.
SDA
SCL
Write( USISIF)
CLOCK
HOLD
USISIF
DQ
CLR
DQ
CLR
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15.4.3 12-Bit Timer/Counter
Combining the 4-bit USI counter with one of the 8-bit timer/counters creates a 12-bit counter.
15.4.4 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.
15.4.5 Software Interrupt
The counter over flow interrupt can be used as a software interrupt triggered by a clock strobe.
15.5 Register Descriptions
15.5.1 USIDR – USI Data Register
The USI Data Register can be accessed directly but a copy of the data can also be found in the
USI Buffer Register.
Depending on the USIC S[1:0] bits of th e USI Contr ol Register a (left ) shift oper ation may be pe r-
formed. The shift operation can be synchronised to an external clock edge, to a Timer/Counter0
Compare Match, or directly to software via the USICLK bit. 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.
Note that even whe n no wire mode is selected (USIWM[1:0] = 0) both the external data input
(DI/SDA) and the external clock input (USCK/SCL) can still be used by the USI Data Register.
The output pin (DO or SDA, depending on the wire mode) is connected via the output latch to
the most significant bit (bit 7) of the USI Data Register. The output latch ensures that data input
is sampled and data output is changed on opposite clock edges. The 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 is written as long as the latch is open.
Note that the Data Direction Register bit corresponding to the output pin must be set to one in
order to enable data output from the USI Data Register.
15.5.2 USIBR – USI Buffer Register
Instead of reading data from the USI Data Register the USI Buffer Register can be used. This
makes controlling the USI less time critical and gives the CPU more time to handle other pro-
gram tasks. USI flags as set similarly as when reading the USIDR register.
The content of th e USI Data Regis te r is loa de d to th e U SI Bu ffer Register wh e n t he tr an sf er ha s
been completed.
Bit 7 6 5 4 3 2 1 0
0x0F MSB LSB USIDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
0x10 MSB LSB USIBR
Read/Write R R R R R R R R
Initial Value 0 0 0 0 0 0 0 0
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15.5.3 USISR – USI Status Register
The Status Register contains interrupt flags, line status flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When two-wire mode is selected, the USISIF Flag is set (to one) when a start condition has
been detected. When three-wire mode or output disable mode has been selected any edge on
the SCK pin will set the flag.
If USISIE bit in USICR and the Global Interrupt Enable Flag are set, an interrupt will be gener-
ated when this flag is 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 USCL in two-wire mode.
A start condition interrupt will wakeup the processor from all 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). If the
USIOIE bit in USICR and the Global Interrupt Enable Flag are set an interrupt will also be gener-
ated when the flag is set. The flag will only be cl eared if a one is written to the USIOIF bit.
Clearing this bit will release the counter overflow hold of SCL in two-wire 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, th e USIPF Flag is set (on e) when a stop cond ition has been
detected. The flag is cleared b y writing a one to this bit. Note that this is not an interrup t flag.
This signal is useful when implementing two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when b it 7 in t he USI Data Register d iffer s from the physica l pin value. The
flag is only valid when two-wir e mo de is used. T his signal is usef ul wh en imple mentin g Two-wire
bus master arbit ration.
• Bits 3:0 – USICNT[3:0]: 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 Com pare Match, or by software using USICLK or USITC strobe
bits. The clock source depen ds on the setting of the USICS[1:0] bi ts.
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 choosing an external clock source
(USICS1 = 1) and writing a one to the USICLK bit.
Note that even when no wire mode is selected (USIWM[1:0] = 0) the external clock input
(USCK/SCL) can still be used by the counter.
Bit 7 6 5 4 3 2 1 0
0x0E USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 USISR
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
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15.5.4 USICR – USI Control Register
The USI Control Register includes bits for interrupt enable, setting the wire mode, selecting the
clock and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to on e ena bles t he start co nditi o n detect or interr up t. If th er e is a pe nding int er rupt
and USISIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed
immediately. Refer to the USISIF bit description on page 119 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the counter overflow interrupt. If there is a pending interrupt and
USIOIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed imme-
diately. Refer to the USIOIF bit description on page 119 for further details.
• Bits 5:4 – USIWM[1: 0]: Wire Mode
These bits set the type of wire mode to be used, as shown in Table 15-1 below.
Note: 1. The DI and USCK pins are renamed to Serial Data (SD A) and Serial Clock (SCL) respectiv ely
to av oid confusion between the modes of operation.
Bit 7 6 5 4 3 2 1 0
0x0D USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR
Read/Write R/W R/W R/W R/W R/W R/W W W
Initial Value 0 0 0 0 0 0 0 0
Table 15-1. Relationship between USIWM[1:0] and USI Operation
USIWM1 USIWM0 Description
00
Outputs, clock hold, and start detector disabled.
Port pins operates as normal.
01
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORTB register.
Howe v er , the corresponding DDRB bit still controls the data direction. When the port pin is
set as input the pin pull-up is controlled by the PORTB bit.
The Data Input (DI) and Serial Clock (USCK) pins do not affect the normal port operation.
When operating as master, clock pulses are software generated by toggling the PORTB
register , while the data direction is set to output. The USITC bit in the USICR Register can
be used for this purpose.
10
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins (1).
The Serial Data (SDA) and the Serial Clock (SCL) pins are bi-directional and use open-
collector output drives. The output drivers are enab led b y setting the corresponding bit f or
SDA and SCL in the DDRB register.
When the output driver is enabled for the SD A pin it will f orce the line SD A low if the output
of the USI Data Register or the corresponding 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 corresponding 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 b y enab ling this mode. Pull-ups on the SDA and SCL port pin are
disabled in Two-wire mode.
11
Two-wire mode. Uses SDA and SCL pins.
Same operation as in two-wire mode above, except that the SCL line is also held low
when a counter overflow occurs, and until the Counter Overflow Flag (USIOIF) is cleared.
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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 USI
Data Register can there fore be clocked externally and da ta input sampled, even when o utputs
are disabled.
• Bits 3:2 – USICS[1:0]: Clock Source Select
These bits set the clock source for the USI Data 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 (USCK/SCL). When software strobe or
Timer/Counter0 Compare Match clock option is selected, the output latch is transparent and
therefore the output is changed immediately.
Clearing the USICS[1:0] bits enables software strobe option. When using this option, writing a
one to the USICLK bit clocks both the USI Data Register and the counter. For external clock
source (USICS1 = 1), th e USICLK bit is no longe r used as a strobe, but selects between e xternal
clocking and software clocking by the USITC strobe bit.
Table 15-2 shows the relationship between the USICS[1:0] and USICLK setting and clock
source used for the USI Data Register and the 4-bit counter.
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the USI Data Register to shift one step and the counter
to increment by one, provided that the software clock strobe option has been selected by writing
USICS[1:0] bit s to zero. Th e output will ch ange immedia tely when the c lock strobe is executed,
i.e., during the same instruction cycle. The value shifted into the USI Data Register is sampled
the previous instruction cycle.
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 Tab le 15 -2 ).
The bit will be read as zero.
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0.
The toggling is independe nt of the setting in t he Data Direction Register, b ut if the PORT value is
to be shown on the pin the corresponding DDR pin must be set as output (to one). This feature
allows easy clock generation when implementing master devices.
Table 15-2. Relationship between the USICS[1:0] and USICLK Setting
USICS1 USICS0 USICLK Clock Source 4-bit Counter Clock Source
0 0 0 No Clock No Clock
0 0 1 Software clock strobe (USICLK) Software clock strobe (USICLK)
0 1 X Timer/Counter0 Compare Match Timer/Counter0 Compare Match
1 0 0 External, positive edge External, both edges
1 1 0 External, negative edge External, both edges
1 0 1 External, posi tive edge Software clock strobe (USITC)
1 1 1 External, negative edge Software clock strobe (USITC)
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When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writ-
ing 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.
The bit will read as zero.
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16. Analog Comparator
The Analog Comparat or compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator output, ACO, is set. The comparator can trigger a separate inter-
rupt, exclusi ve to the Anal og Comparat or. The use r can select Int errupt t riggering on comp arator
output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown
in Figure 16-1.
Figure 16-1. Analog Comparator Block Diagram
Notes: 1. See Table 16-1 below.
See Figure 1-1 on page 2 and Table 10-5 on page 65 for Analog Comparator pin placement.
16.1 Analog Comparator Multiplexed Input
When the Analog to Digital Converter (ADC) is configurated as single ended input channel, it is
possible to select a ny of the ADC[ 3:0] pins to replace t he nega tive input to th e Analog Com para-
tor. The ADC multiplexer is used to select this input, and consequently, the ADC must be
switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in
ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX[1:0] in ADMUX
select the input pin to replace the negative input to the Analog Comparator, as shown in Table
16-1. If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the Analog
Comparator.
ACD
+
_
VCC
ACBG
ACI
ACO
ACIE
ACIS1 ACIS0
INTERRUPT
SELECT
ANALOG
COMPARATO
R
IRQ
AIN0
AIN1
INT ERNAL 1.1V
REFERENCE
ADC MULT IP LEXER
OUTPUT
ACME
ADEN
(1)
Table 16-1. Analog Comparator Multiplexed In put
ACME ADEN MUX[1:0] Analog Comparator Negative Input
0x xxAIN1
11 xxAIN1
10 00ADC0
10 01ADC1
10 10ADC2
10 11ADC3
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16.2 Register Description
16.2.1 ADCSRB – ADC Control and Status Register B
• Bit 6 – ACME: Analog Compar ator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (A DEN in ADCSRA is zero), the
ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written
logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed
description of this bit, see “Analog Comparator Multiplexed Input” on page 123.
16.2.2 ACSR – Analo g Compa r at o r Cont rol and Status Re gi st er
• Bit 7 – ACD: Analog Comparat or Disable
When this bit is written logic one, the power to the Ana log Comparator is swit ched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is
changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the Analog
Comparator. When this bit is cleared, AI N0 is ap plied to the positive input of the Analog Compar-
ator. When the bandgap reference is used as input to the Analog Comparator, it will take a
certain time for the voltage to stabilize. If not stabilized, the first conversion may give a wrong
value. See “Internal Voltage Reference” on page 44.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Fla g
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is ex ecut ed if the ACIE bit is se t
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding inter-
rupt handling ve ctor. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is writte n logic one and t he I-bit in the Status Register is set, the Analog Com-
parator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and will always read as zero.
Bit 76543210
0x03 BIN ACME IPR – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R/W R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x08 ACD ACBG ACO ACI ACIE – ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R R/W R/W
Initial Value00N/A00000
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• Bits 1:0 – ACIS[1:0]: Analog Comparator Interrupt Mode Select
These bits determin e which comparator even ts that trigger the Analog Compa rator interr upt. The
different settings are shown in Table 16 -2.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by
clearing its Inte rrupt Enable bit in the ACSR Reg ister. Ot herwise an inter rupt can occu r when the
bits are changed.
16.2.3 DIDR0 – Digital Input Disable Register 0
• Bits 1:0 – AIN1D, AIN0D: AIN[1:0] Digital Input Disable
When this bit is writte n logic one , the digita l input buf fer on the AI N1/0 pin is disa bled. The corr e-
sponding PIN Register bit will always read as zero when this bit is set. When an analog signal is
applied to the AIN1/0 pin and the digital input from this pin is not needed, this bit should be writ-
ten logic one to reduce power consumption in the digital input buffer.
Table 16-2. ACIS1/ACIS0 Settings
ACIS1 ACIS0 Interrupt Mode
0 0 Comparator Interrupt on Output Toggle.
01Reserved
1 0 Comparator Interrupt on Falling Output Edge.
1 1 Comparator Interrupt on Rising Output Edge.
Bit 76543210
0x14 – – ADC0D ADC2D ADC3D ADC1D AIN1D AIN0D DIDR0
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
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17. Analog to Digital Converter
17.1 Features •10-bit Resolution
•1 LSB Integral Non-linearity
•± 2 LSB Absolute Accuracy
•65 - 260 µs Conversion Time
•Up to 15 kSPS at Maximum Resolution
•Four Multiplexed Single Ended Input Channels
•Two differential input c h annel s wit h selectab le gain
•Temperature sensor input channel
•Optional Left Adjust men t for ADC Result Readout
•0 - VCC ADC Input Voltage Range
•Selectable 1.1V / 2.56V ADC Voltage Reference
•Free Running or Single Conversion Mode
•ADC Start Conversion by Auto Triggering on Interrupt Sources
•Interrupt on ADC Conversion Complete
•Sleep Mode Noise Cancele
•Unipolar / Bibilar In put Mode
•Input Polarity Reversal Mode
17.2 Overview The ATtiny25/45/85 features a 10-bit successive approximation Analog to Digital Converter
(ADC). The ADC is connected to a 4-channel Analog Multiplexer which allo ws one differential
voltage input and four single-ended voltage inputs constructed from the pins of Port B. The dif-
ferential input (PB3, PB4 or PB2, PB5) is equipped with a programmable gain stage, provid ing
amplification step of 26 dB (20x) on the differential input voltage before the A/D conversion. The
single-ended voltage inputs refer to 0V (GND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is
held at a constant level during conversion. A block diagram of the ADC is shown in Figure 17-1
on page 127.
Internal reference voltages of nominally 1.1V / 2.56V are provided on-chip. Alternatively, VCC
can be used as reference voltage for single ended channels. There is also an option to use an
external voltage reference and turn-off the internal voltage reference.
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Figure 17-1. Analog to Digital Converter Block Schema tic
17.3 Operation The ADC converts an analog input voltage to a 10-bit digital value through successive approxi-
mation. The minimum value represents GND and the maximum value represents the voltage on
VCC, the voltage on the AREF pin or an internal 1.1V / 2.56V voltage reference.
The voltage reference for the ADC may be selected by writing to the REFS[2:0] bits in ADMUX.
The VCC supply, the AREF pin or an internal 1.1V / 2. 56V vo ltage re fere nce may be select ed as
the ADC voltage reference. Optionally the internal 2.56V voltage reference may 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[3:0] bits in
ADMUX. Any of the four ADC input pins ADC[3:0] can be selected as single ended inputs to the
ADC. ADC2 or ADC0 can be selected as positive input and ADC0, ADC1, ADC2 or ADC3 can
be selected as negative input to the differential gain amplifier.
If differential channels are selected, the differential gain stage amplifies the voltage difference
between the selected inp ut pai r b y the select ed gain f actor, 1x o r 20x, acco rding to th e sett ing of
the MUX[3:0] bits in ADMUX. This amplified value then becomes the analog input to the ADC. If
single ended channels are used, the gain amplifier is bypassed altogether.
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15 0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL. & STATUS A
REGISTER (ADCSRA) ADC DATA REGISTER
(ADCH/ADCL)
ADIE
ADATE
ADSC
ADEN
ADIF ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
INTERNAL 1.1V/2.56V
REFERENCE
MUX DECODER
MUX2
AREF
ADC3
ADC2
ADC1
ADC0
REFS[2:0]
ADLAR
CHANNEL SELECTION
ADC[9:0]
ADC MULTIPLEXER
OUTPUT
PRESCALER
INPUT
MUX
TRIGGER
SELECT
ADTS[2:0]
INTERRUPT
FLAGS
START
+
-
GAIN SELECTION
GAIN
AMPLIFIER
NEG.
INPUT
MUX
SINGLE ENDED / DIFFERENTIAL SELECTION
TEMPERATURE
SENSOR
ADC4
ADC CTRL. & STATUS B
REGISTER (ADCSRB)
BIN
IPR
VCC
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If ADC0 or ADC2 is selected as both the positive and negative input to the differential gain
amplifier (ADC0-ADC0 or ADC2-ADC2), the remaining offset in the gain stage and conversion
circuitry can be measured directly as the result of the conversion. This figure can be subtracted
from subsequent conversions with the same gain setting t o reduce offset error to below 1 LSW.
The on-chip temperature sensor is selected by writing the code “1111” to the MUX[3:0] bits in
ADMUX register when the ADC4 channel is used as an ADC input.
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage refe rence 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 recommende d to switch off the ADC befor e entering power
saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and
ADCL. By default, the result is presented right ad justed, but can optionally be presented left
adjusted by setting the ADLAR bit in ADMUX.
If the result is left ad justed and no more than 8-bit precision is requ ired, 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 interr upt which can be trigge red when a conversion co mpletes. When ADC
access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will
trigger even if the result is lost.
17.4 Starting a Conversion
A single 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 w ill be cleared by hardware
when the conversio n is com pleted . If a dif fere nt data channel is selected while a co nversion is in
progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is
enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is
selected by setting th e ADC Trigge r Se lect bit s, ADTS in ADCSRB (se e descr iption of the ADTS
bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal,
the ADC prescaler is reset and a conversion is started. This provides a method of starting con-
versions at fixed intervals. If the trigger signal still is set when the conversion completes, a new
conversion will not be started. If another positive edge occurs on the trigger signal during con-
version, the edge will be ignored. Note that an Interrupt Flag will be set even if the specific
interrupt is di sabled or t he Global In terr upt Enable b it in SREG is cleared. A conversion can th us
be triggered with out causing an interr upt. However, the Interrup t Flag must be cleare d in order to
trigger a new conversion at the next interrupt event.
Using the ADC Interrupt Flag as a trigger source make s the ADC start a new conver sion as soon
as the ongoing conversion has finished. The ADC then operates in Free Running mode, con-
stantly sampling and up dating the ADC Data Register . The first conversion must be started by
writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive
conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not.
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Figure 17-2. ADC Auto Trigger Logic
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to
one. ADSC can also be us ed to determine if a conversion is in pr ogress. The ADSC bit will be
read as one during a conversion, independently of how the conversio n was started.
17.5 Prescaling and Conversion Timing
Figure 17-3. ADC Prescaler
By default, the successive approximation circuitry requires an input clock frequency between
50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the
input clock frequency to the ADC can be h igher than 200 kHz to get a higher sam ple rate. It is
not recommended to use a higher input clock freq uency than 1 MHz.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit
in ADCSRA. The prescaler keeps runnin g for as long as the ADEN bit is set, and is continuously
reset when ADEN is low.
ADSC
ADIF
SOURCE 1
SOURCE n
ADTS[2:0]
CONVERSION
LOGIC
PRESCALER
START CLKADC
.
.
.
.EDGE
DETECTOR
ADATE
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
CK
ADPS0
ADPS1
ADPS2
CK/128
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
Reset
ADEN
START
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When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion
starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched
on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry,
as shown in Figure 17-4 below.
Figure 17-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
The actual sample- and-h old ta kes pla ce 1. 5 ADC clock cycles aft er t he sta rt of a norma l con ver-
sion and 13.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conver sion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
Figure 17-5. ADC Timing Diagram, Single Conversion
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures
a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold
takes place two ADC clock cycles after the rising edge on the trigger source signal. Three addi-
tional CPU clock cycles are used for synchr onization logic.
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
Sample & Hold
ADIF
ADCH
ADCL
Cycle Number
ADEN
1212
13 14 15 16 17 18 19 20 21 22 23 24 25 1 2
First Conversion Next
Conversion
3
MUX and REFS
Update MUX and REFS
Update
Conversion
Complete
123456789 10 11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
3
Sample & Hold
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
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Figure 17-6. ADC Timing Diagram, Auto Triggered Conversion
In Free Running mode, a new conversion will be started immediately after the conversion com-
pletes, while ADSC remains high.
Figure 17-7. ADC Timing Diagram, Free Running Conversion
For a summary of conversion times, see Table 17-1 .
Table 17-1. ADC Conversion Time
Condition Sample & Hold
(Cycles fr om Start of Conversion) Total Conversion Time
(Cycles)
First conversion 13.5 25
Nor m al conversions 1.5 13
A uto Triggered conv ersions 2 13.5
12345678910 11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
Trigger
Source
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
Conversion
Complete
Prescaler
Reset
ADATE
Prescaler
Reset
Sample &
Hold
MUX and REFS
Update
11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
34
Conversion
Complete Sample & Hold
MUX and REFS
Update
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17.6 Changing Channel or Reference Selection
The MUX[3:0] and REFS[2:0] bits in the ADMUX Register are single buffered through a tempo-
rary register to which the CPU has random access. This ensures that the channels and voltage
reference select ion only take s place at a sa fe point d uri ng the con version . The cha nne l an d vol t-
age reference selection is continuously updated until a conversion is started. Once the
conversion starts, the channel and voltage reference sele ction is locked to ensure a sufficient
sampling time for the ADC. Continuous updating resumes in the la st ADC clock cycle before the
conversion completes (ADIF in ADCSRA 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 voltage reference selection values to ADMUX until one ADC clock cycle after ADSC is written.
If Auto Triggering is used, the exact tim e of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot te ll if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
a. When ADATE or ADEN is cleared.
b. During conversion, min imum one ADC clock cycle after the trigger event.
c. After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
17.6.1 ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the chann el before sta rting the conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is t o wa it for the co nversio n to complete b efore cha nging the ch annel sele ction.
In Free Running mode, always select the channel before starting the first conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the first conversion to complete, and then change the cha nnel
selection. Since the next conversion has already started automatically, the next result will reflect
the previous channel selection. Subsequent conversions will reflect the new channel selection.
17.6.2 ADC Voltage Reference
The voltage refere nce for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either VCC, or internal 1.1V / 2.56V voltage reference, or external AREF pin. The first ADC con-
version result after switching voltage reference sou rce may be inaccurate, and the user is
advised to discard th is res ult .
17.7 ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise
induced from the CPU core and o ther I/O pe ripherals. The noise ca nceler can be used with ADC
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Noise Reduc tion an d Id le m ode. To m ake use of th is fe atur e, th e fo llowing proce dur e sh ould b e
used:
• Mak e sure that the ADC is enable d and is not busy con v erting. Single Con version mode must
be selected and the ADC conversion complete interrupt must be enabled.
• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the
CPU has been halted.
• If no other interrupts occur before the ADC con version completes , the ADC interrupt will wake
up the CPU and execute the ADC Conversion Complet e i nterrupt rout ine. If anothe r inter rupt
wakes up the CPU before the ADC conversion is complete, that interrupt will be executed,
and an ADC Conversion Complete interrupt request will be generated when the ADC
conversion completes. The CPU will remain in active mode until a new sleep command is
executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle
mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter-
ing such sleep modes to avoid excessive power consumption.
17.8 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 17-8. An ana log
source applied to ADCn is subjecte d to the pin ca pacitance and inp ut leakage of that pin, re gard-
less of whether that channel is selected as input for the ADC. When the channel is selected, the
source must dr ive the S/H capacitor th rough the series re sistance (combined resistance in the
input path).
Figure 17-8. Analog Input Circuitry
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the samp ling time wi ll be n egligible . I f a sour ce with higher impe d-
ance is used, the sampling time will depend on how long time the source needs to charge the
S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources
with slowly varying signals, since this minimizes the required charge transfer to the S/H
capacitor.
Signal componen ts higher than the Nyquist frequenc y (fADC/2) should not be present to avoid
distortion from unpredictab le signal convolution. Th e user is advised to remove high frequency
components with a low-pass filter before applying the signals as inputs to the ADC.
ADCn
IIH
1..100 kΩ
CS/H= 14 pF
VCC/2
IIL
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17.9 Noise Canceling Techniques
Digital circuitry inside and outside the device 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:
• Keep analog signal paths as short as possible .
• Make sure analog tracks run over the analog ground plane.
• Keep analog tracks well away from high-speed switching digital tracks.
• If any port pin is used as a digital output, it mustn’t switch wh ile a conversion is in progress.
• Place bypass capacitors as close to VCC and GND pins as possible.
Where high ADC accuracy is req uired it is recommend ed to u se ADC Noise Re duction Mode, as
described in Se ction 17.7 on pa ge 132. This is especially the case when system clock frequency
is above 1 MHz, or when the ADC is used for reading the internal temperature sensor, as
described in Section 17.12 on page 137. A good system design with properly placed, external
bypass capacitors does reduce the need for using ADC Noise Reduction Mode
17.10 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior, as follows:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Idea l value: 0 LSB.
Figure 17-9. Offset Error
Output Code
VREF Input Voltage
Ideal ADC
Actual ADC
Offset
Error
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• Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last
transit ion (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum).
Ideal value: 0 LSB
Figure 17-10. Gain Error
• Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal t ransition for any code. Ideal value: 0
LSB.
Figure 17-11. Integral Non-linearity (INL)
Output Code
VREF Input Voltage
Ideal ADC
Actual ADC
Gain
Error
Output Code
VREF Input Voltage
Ideal ADC
Actual ADC
INL
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• Diff erential Non-line arity (DNL): The maximum de via tion of the actual code width ( the interval
between two adjacent tr ansitions) from the ideal code width (1 LSB). Ideal value: 0 LSB.
Figure 17-12. Differential Non-linearity (DNL)
• Quantization Error: Due to the quantization of the input voltage into a finite n umber of codes ,
a range of input v oltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
• Absolute Accuracy: The m aximum deviation of an actual (una djusted) tr ansitio n compared to
an ideal transition for any code. This is the compound effect of offset, gain error, diff erential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
17.11 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversio as there are three types of conversions: single ended conversion, unipolar differential
conversion and bipolar diff erential conversion.
17.11.1 Single Ended Conversion
For single ended conversion, the result is
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 17-3 on page 138 an d Table 17-4 on page 139). 0x 000 represents analog ground, and
Output Code
0x3FF
0x000
0VREF Input Voltage
DNL
1 LSB
ADC VIN 1024⋅
VREF
--------------------------=
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0x3FF represents the selecte d voltage reference minu s one LSB. The result is presente d in one-
sided form, from 0x3FF to 0x000.
17.11.2 Unipolar Differential Conversion
If differential ch an ne ls an d an un i po lar input mode are used, the res ult is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference (see Table 17-3 on page 138 and Table 17-4 on page
139). The voltage on the positive pin must always be larger than the voltage on the negative pin
or otherwise the voltage difference is saturated to zero. The result is presented in one-sided
form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 1x or 20x.
17.11.3 Bipolar Differential Conversion
As default the ADC converter opera tes in the unipolar input mode , but the bipolar input mode
can be selected by writting the BIN bit in the ADCSRB to one. In the bipolar input mode two-
sided voltage differences are allowed and thus the voltage on the negat ive input pin can also be
larger than the voltage on the positive input pin. If differential channels and a bipolar input mode
are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the sele cted vo ltage ref erenc e. The result is prese nted in two’s compleme nt fo rm, from
0x200 (-512d) through 0x000 (+0d) to 0x 1FF (+511d). The GAIN is either 1x or 20x.
However, if the signal is not b ipolar by nature (9 bits + sign as the 10t h bit), this scheme loses
one bit of the conver ter dynamic range. The n, if the user wants to perform th e conversion with
the maximum dynamic range, the user can perform a quick polarity check of the result and use
the unipolar differential conversion with selectable differential input pairs (see the Input Polarity
Reversal mode ie. the IPR bit in the “ADCSRB – ADC Control and Status Register B” on pa ge
141). When the polari ty check is perform ed, it is sufficient to read the MSB of the result (ADC9 in
ADCH). If the bit is one, the result is negat ive, and if this bit is zero, the result is positive.
17.12 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC4 channel. Selecting the ADC4 channel by writing the MUX[3:0] bits in
ADMUX register to “1111 ” enables the temperature se nsor. The internal 1.1V refere nce must
also be selected for the ADC reference source in the temperature sensor measurement. When
the tempera ture sensor is enabled, th e ADC conver ter can b e used in single conver sion mode to
measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in Table 17-2
The sensitivity is approximat ely 1 LSB / °C and the accuracy depends on th e method of user cal-
ibration. Typically, the measurement accuracy after a single temperatu re calibration is ±10°C,
ADC VPOS VNEG
–()1024⋅
VREF
--------------------------------------------------------GAIN⋅=
ADC VPOS VNEG
–()512⋅
VREF
-----------------------------------------------------GAIN⋅=
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assuming calibration at room temperature. Better accuracies are achieved by using two
temperature points for calibration.
The values described in Table 17- 2 are typical values. However, due to process variatio n the
temperature sensor output voltage varies from one chip to another. To be capable of achieving
more accurate results the temperature measurement can be calibrated in the application soft-
ware. The sofware calibration can be done using the formula:
T = k * [(ADCH << 8) | ADCL] + TOS
where ADCH and ADCL are th e ADC data register s, k is the fixed slop e coefficient and T OS is the
temperature sensor offse t. Typically, k is very close to 1.0 and in single-point calibration th e
coefficient may be omitted. Where higher accuracy is required the slope coefficient should be
evaluated based on measurements at two temperatures.
17.13 Register Description
17.13.1 ADMUX – ADC Multiplexer Selection Register
• Bits 7:6, 4 – REFS[2:0]: Voltage Reference Selection Bits
These bits select the voltage reference (VREF) for the ADC, as shown in Table 17-3. 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). Whenever these bits are changed, the next conversion will
take 25 ADC clock cycles. When differential channels and gain are used, using VCC or an
external AREF higher than (VCC - 1V) as a voltage reference is not recommended as this will
affect the ADC accurac y.
Note: 1. The device requries a supply voltage of 3V in order to generate 2.56V reference voltage.
Table 17-2. Temperature vs. Sensor Output Voltage (Typical Case)
Temperature -40°C+25°C+85°C
ADC 230 LSB 300 LSB 370 LSB
Bit 76543210
0x07 REFS1 REFS0 ADLAR REFS2 MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 17-3. Voltage Reference Selections for ADC
REFS2 REFS1 REFS0 Voltage Reference (VREF) Selection
X00V
CC used as Voltage Reference, disconnected from PB0 (AREF).
X01
External Voltage Reference at PB0 (AREF) pin, Internal Voltage
Reference turned off.
0 1 0 Internal 1.1V Voltage Reference.
0 1 1 Reserved
110
Inter nal 2.56V Voltage Reference without external bypass
capacitor, disconnected from PB0 (AREF)(1).
111
Internal 2.56V Voltage Reference with e xternal bypass capacitor at
PB0 (AREF) pin(1).
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• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADL AR to left adjust the resu lt. Oth erwise, the r esult is ri ght adju sted. Changing t he
ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver-
sions. For a comple te description of this bit, see “ADCL and ADCH – The ADC Data Register”
on page 141.
• Bits 3:0 – MUX[3:0]: Analog Channel and Gain Selection Bits
The value of these b its sele cts which com bina tion o f ana log inp uts are conn ected to t he ADC. In
case of differential input (ADC0 - ADC1 or ADC2 - ADC3), gain selection is also made with these
bits. Selecting ADC2 or ADC0 as both inputs to the diffe rential gain stage en ables offset mea-
surements. Selecting the single-ended channel ADC4 enables the temperature sensor. Refer to
Table 17-4 for details. If these bits are changed during a conversion, the change will not go into
effect until this conversion is complete (ADIF in ADCSRA is set).
Note: 1. For offset calibration, only. See “Operation” on page 127.
2. After switching to internal voltage reference the ADC requires a settling time of 1ms before
measurements are stable. Con versions starting before this ma y not be reliable. The ADC must
be enabled during the settli ng time.
3. F or temperature sensor.
Table 17-4. Input Channel Selections
MUX[3:0] Single Ended
Input Positive
Differential Input Negative
Differential Input Gain
0000 ADC0 (PB5)
N/A
0001 ADC1 (PB2)
0010 ADC2 (PB4)
0011 ADC3 (PB3)
0100
N/A
ADC2 (PB4) ADC2 (PB4) 1x
0101 (1) ADC2 (PB4) ADC2 (PB4) 20x
0110 ADC2 (PB4) ADC3 (PB3) 1x
0111 ADC2 (PB4) ADC3 (PB3) 20x
1000 ADC0 (PB5) ADC0 (PB5) 1x
1001 ADC0 (PB5) ADC0 (PB5) 20x
1010 ADC0 (PB5) ADC1 (PB2) 1x
1011 ADC0 (PB5) ADC1 (PB2) 20x
1100 (2) VBG
N/A
1101 GND
1110 N/A
1111 (3) ADC4
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17.13.2 ADCSRA – ADC Control and Status Register A
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the
ADC off while a conversion is in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mod e, write this bit t o one to start ea ch conversion. In Free Running mode,
write this bit to one to st art th e first conversion. Th e first conversion af ter ADSC ha s been writt en
after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled,
will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initializa-
tion of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete,
it returns to zero. Writing zero to this bit has no effect.
• Bit 5 – ADATE: ADC A uto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a con-
version on a positive e dge of the select ed trigger signal. The trigger sou rce is selected by setting
the ADC Trigger Select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is se t wh en an ADC conversion co mple tes and t he data reg iste rs ar e upd at ed. Th e ADC
Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively,
ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify-Write on
ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions
are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is wr itte n to on e a n d t he I- bit in SREG is set, the ADC Conversion Complete Inter-
rupt is activated.
• Bits 2:0 – ADPS[2:0]: ADC Prescaler Select Bits
These bits determine the division f actor be twee n the syst em clock frequen cy and th e inpu t clock
to the ADC.
Bit 76543210
0x06 ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 17-5. ADC Prescaler Selections
ADPS2 ADPS1 ADPS0 Division Factor
000 2
001 2
010 4
011 8
100 16
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17.13.3 ADCL and ADCH – The ADC Data Register
17.13.3.1 ADLAR = 0
17.13.3.2 ADLAR = 1
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if
the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLA R is set, the result is left adjusted. If ADLAR is cleared (default), th e result
is right adjusted.
• Bits 9:0 - ADC[9:0]: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on
page 136.
17.13.4 ADCSRB – ADC Control and Status Register B
• Bit 7 – BIN: Bipolar Input Mode
The gain stag e is wo rking in the unip o l ar m ode as de fa ult, but the bipo la r m o de ca n be selected
by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided conversions
101 32
110 64
1 1 1 128
Table 17-5. ADC Prescaler Selections (Continued)
ADPS2 ADPS1 ADPS0 Division Factor
Bit 151413121110 9 8
0x05 ––––––ADC9 ADC8 ADCH
0x04 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 151413121110 9 8
0x05 ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
0x04 ADC1 ADC0 ––––––ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 76543210
0x03 BIN ACME IPR – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R/W R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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are supported and the voltage on the positive input must always be larger than the voltage on
the negative input . Otherwise th e result is satura ted to the voltag e reference. In the bipolar mode
two-sided conversions are supported and the result is represented in the two’s complement
form. In the unipo lar mode the resolu tion is 10 bits an d the bipolar mod e the reso lution is 9 bits +
1 sign bit.
• Bit 5 – IPR: Input Polarity Reversal
The Input Polarity mode allows software selectable differential input pairs and full 10 bit ADC
resolution, in the unipolar input mode, a ssuming a pre-determ ined input polarity. If the in put
polarity is not known it is actually possible to determine the polar ity first by using th e bipolar input
mode (with 9 bit resolution + 1 sign bit ADC measurem ent). And once determ ined, set or clear
the polarity reversal bit, as needed, for a succeeding 10 bit unipolar measurement.
• Bits 4:3 – Res: Reserved Bits
These bits are reserve d bits in the ATtiny25/45/85 and will always read as zero.
• Bits 2:0 – ADTS[2:0]: ADC Aut o Trigger Sourc e
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger
an ADC conversion. If ADATE is cleared, the ADTS[2:0] settings will have no effect. A conver-
sion will be triggered by the rising edge of the selected In terrupt Flag. Note that switching from a
trigger source that is cleared to a trigger source that is set, will generate a positive edge on the
trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running
mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
17.13.5 DIDR0 – Digital Input Disable Register 0
• Bits 5:2 – ADC3D:ADC0D: ADC[3:0] Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is dis-
abled. The corresponding PIN register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC[3:0] pin and the digital input from this pin is not needed, this
bit should be written logic one to r educe power consumption in the digital input buffer.
Table 17-6. ADC Auto Trigger Source Selections
ADTS2 ADTS1 ADTS0 Trigger Source
0 0 0 Free Running mode
0 0 1 Analog Comparator
0 1 0 External Interrupt Request 0
0 1 1 Timer/Counter0 Compare Match A
1 0 0 Timer/Counter0 Overflow
1 0 1 Timer/Counter0 Compare Match B
1 1 0 Pin Change Interrupt Req uest
Bit 76543210
0x14 –– ADC0D ADC2D ADC3D ADC1D AIN1D AIN0D DIDR0
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
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18. debugWIRE On-chip Debug System
18.1 Features •Complete Program Flow Control
•Emulates All On-chip Functions, Both Digital and An alog , except RESET Pin
•Real-time Operation
•Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)
•Unlimited Number of Program Break Points (Using Software Break Points)
•Non-intrusive Operation
•Electrical Characteristics Identical to Real Device
•A u tomatic Configuration System
•High-Speed Oper ation
•Programming of Non-volatile Memories
18.2 Overview Th e debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatile
memories.
18.3 Physical Interface
When the deb ugWIRE Enable (DW EN) Fuse is progr ammed and Loc k bits are unprog rammed,
the debugWIRE system within the target device is activated. The RESET port pin is configured
as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the commu-
nication gateway between target and emulator.
Figure 18-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.
Figure 18-1. The debugWIRE Setup
dW
GND
dW(RESET)
VCC
1.8 - 5.5V
144 2586N–AVR–04/11
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When designing a system where debugWIRE will be used, the following must be observed:
• Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 kΩ. However, the
pull-up resistor is optio nal.
• Connecting the RESET pin directly to VCC will not work.
• Capacitors inserted on the RESET pin must be disconnected when using debugWire.
• All external reset sources must be disconnected.
18.4 Software Break Points
debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a
Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruc-
tion replaced by the BREAK instruction will be stored. When program execution is continued, the
stored instruction will be executed before continuing from the Program memory. A break can be
inserted manually by putting the BREAK instruction in the program.
The Flash must be re-prog rammed each time a Break Point is changed. This is automatically
handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore
reduce the Fl ash Data ret ention. Devices used for d ebugging p urposes sho uld not b e shipped to
end customers.
18.5 Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is
enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken while
accessing some of the I/O Registers via the debugger (AVR Studio). See the debugWIRE docu-
mentation for detailed description of the limitations.
The debugWIRE interface is asynchronous, which means that the debugger needs to synchro-
nize to the system clock. If the system clock is changed by software (e.g. by writing CLKPS bits)
communication via debugWI RE may fail. Also, clock frequencie s below 100kHz may cause com-
munication problems.
A programmed DWEN Fuse enables some parts of the clock syst em to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should
be disabled when debugWir e is not used.
18.6 Register Description
The following sectio n descr ib es th e re gisters used with the de bug W ire .
18.6.1 DWDR – debugWire Dat a Reg i st er
The DWDR Register provides a communicatio n channel from the running program in the MCU
to the debugger. This register is only acce ssible by the debugWIRE and can therefore not be
used as a general purpo se register in the norma l operations.
Bit 76543210
0x22 DWDR7 DWDR6 DWDR5 DWDR4 DWDR3 DWDR2 DWDR1 DWDR0 DWDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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19. Self-Programming the Flash
The device provides a Self-Programming mechanism for downloading and uploading program
code by the MCU itself. The Self-Programming can use any available data interface and associ-
ated protocol to read code and write (program) that code into the Program memory. The SPM
instruction is disabled by default but it can be enabled by programming the SELFPRGEN fuse
(to “0”).
The Program memory is updated in a page by page fashion. Before programming a page with
the data stored in th e temporary page buf fer, the page must be erased. The temp orary page bu f-
fer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Writ e operation:
Alternative 1, fill the buffer before a Page Erase
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
Alternative 2, fill the buffer after Page Erase
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
If only a part of t he page needs to be changed, the rest of the page must be stored (for example
in the temporary page buf fer) befo re the erase, and then be re-written . When using alternat ive 1,
the Boot Loader pr ovides an effe ctive Rea d- Modify- Wr ite fe at ure which allo ws t he use r soft ware
to first read the page, do the necessary changes, and then write back the modified data. If alter-
native 2 is used, it is not p ossible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page addre ss used in both the Page Er ase and Page Write operat ion is addressing th e same
page.
19.1 Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “00000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Othe r bits in the Z-pointer will
be ignored during this operation.
Note: The CPU is halted during the Page Erase operation.
19.2 Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the CTPB bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each addr ess without erasing the temporary buffer.
146 2586N–AVR–04/11
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If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
19.3 Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPM CSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
Note: The CPU is halted during the Page Write operation.
19.4 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see Table 20-8 on page 154), the Program Counter can
be treated as havin g two different sections. One sect ion, consisting of the least signif icant bits, is
addressing the words within a page, while the most significant bits are addressing the pages.
This is shown in Figure 19-1. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the software addresses the
same page in both the Page Erase and Page Write operation.
The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the
Flash byte-b y-b yte, also the LSB (bit Z0) of th e Z- po in te r is used .
Figure 19-1. Addressing the Flash During SPM(1)
Note: 1. The different variables used in Figure 19-1 are listed in Table 20-8 on page 154.
Bit 1514131211109 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30)Z7Z6Z5Z4Z3Z2Z1Z0
76543210
PROGRAM MEMORY
0115
Z - REGISTER
BIT
0
ZPAGEMSB
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
INSTRUCTION WORD
PA G E PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PA G E
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
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19.5 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleare d before writing to the SPMCSR Register.
19.6 Reading Lock, Fuse and Signature Data from Software
It is possible to read fuse an d lock bits from firmware. In ad dition, firmware can also re ad data
from the device signature imprint table (see page 153).
Note: Fus e and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are unpro-
grammed, will be read as one.
19.6.1 Reading Lock Bits from Firmware
Issuing an LPM instruction within three CPU cycles after RFLB and SELFPRGEN bits have
been set in SPMCSR will return lock bit values in the destination register. The RFLB and SELF-
PRGEN bits automatica lly clear upon com pletion of read ing the lo ck bits, or if n o LPM instruct ion
is executed within three CPU cycles, or if no SPM instruction is executed withi n four CPU cycles.
When RFLB and SELFPRGEN are cleared LPM functions normally.
To read the lock bits, follow the below procedure:
1. Load the Z-pointer with 0x0001.
2. Set RFLB and SELFPRGEN bits in SPMCSR.
3. Issue an LPM instr uction within three clock cycles.
4. Read the lock bits from the LPM destination register.
If successful, the contents of the destination register are as follows.
See section “Program And Data Memory Lock Bits” on page 151 for more information.
19.6.2 Reading Fuse Bits from Firmware
The algorithm for reading fuse bytes is similar to the one described above for reading lock bits,
only the addresses are differe nt. To read the Fuse Low Byte (FLB), follow the below pro cedure:
1. Load the Z-pointer with 0x0000.
2. Set RFLB and SELFPRGEN bits in SPMCSR.
3. Issue an LPM instr uction within three clock cycles.
4. Read the FLB from the LPM destination register.
If successful, the contents of the destination register are as follows.
Refer to Table 20-5 on page 153 for a detailed description and mapping of the Fuse Low Byte.
Bit 76543210
Rd ––––––LB2LB1
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
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To read the Fuse High Byte (FHB), simply replace the address in the Z-pointer with 0x0003 and
repeat the pro cedure abo ve. If succe ssful, the co ntents of the destinat ion re gister ar e as follows.
Refer to Table 20-4 on page 152 for detailed description and mapping of the Fuse High Byte.
To read the Fuse Extended Byte (FEB), replace the address in the Z-pointer with 0x0002 and
repeat the previous procedure. If successful, the contents of the destination register are as
follows.
Refer to Table 20-3 on page 152 for detailed description and mapping of the Fuse Extended
Byte.
19.6.3 Reading Device Signature Imprint Table from Firmware
To read the contents of the device signature imprint table, follow the below procedure:
1. Load the Z- p oin te r wi th the ta ble index.
2. Set RSIG and SPMEN bits in SPMCSR.
3. Issue an LPM instr uction within three clock cycles.
4. Read table data from the LPM destination register.
See program example below.
Note: 1. See “Code Examples” on page 6.
If successful, the contents of the destination register are as described in section “Device Signa-
ture Imprint Table” on page 153.
Bit 76543210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
Bit 76543210
Rd FEB7 FEB6 FEB5 FEB4 FEB3 FEB2 FEB1 FEB0
Assembly Code Example(1)
DSIT_read:
; Uses Z-pointer as table index
ldi ZH, 0
ldi ZL, 1
; Preload SPMCSR bits into R16, then write to SPMCSR
ldi r16, (1<<RSIG)|(1<<SPMEN)
out SPMCSR, r16
; Issue LPM. Table data will be returned into r17
lpm r17, Z
ret
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19.7 Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and th e same design solutions should be applied.
A Flash program co rr up tion can be cau sed b y two situ a tions when th e voltag e is too low. F irst , a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these de sign recommendations (one is
sufficient):
1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enab ling the internal Brown-out Detector (BOD) if the operating
voltage matches the detection level. If not, an external low VCC reset protection circuit
can be used. If a r eset occurs while a write oper atio n is in prog r ess , the write oper ation
will be completed provided that the power supply voltage is sufficient.
2. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will pre-
v ent the CPU from attempti ng to decode and e x ecute instructions , eff ectiv ely protecting
the SPMCSR Register and thus the Flash from unintentional writes .
19.8 Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 19-1 shows the typical pro-
gramming time for Flash accesses fr om the CPU.
Note: 1. Minimum and maximum programming time is per individual operation.
19.9 Register Description
19.9.1 SPMCSR – Store Program Memory Control and Status Register
The Store Progr am Memory Contro l and Status Regist er contains the co ntrol bits nee ded to con-
trol the Program memory operations.
• Bits 7:6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and always read as zero.
• Bit 5 – RSIG: Read Device Signature Imprint Table
Issuing an LPM instruction within three cyc les after RSIG and SPMEN bits have been set in
SPMCSR will return the selected data (depending on Z-pointer value) from the device signature
imprint table into the destination register. See “Device Signature Imprint Table” on page 153 for
details.
Table 19-1. SPM Programming Time(1)
Symbol Min Programming Time Max Programming Time
Flash write (Page Erase , P age Write, and
write Lock bits by SPM) 3.7 ms 4.5 ms
Bit 7 654 3210
0x37 – – RSIG CTPB RFLB PGWRT PGERS SPMEN SPMCSR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 4 – CTPB: Clear Temporary Page Buffer
If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be
cleared and the data will be lost.
• Bit 3 – RFLB: Read Fuse and Lock Bits
An LPM instruction with in three cycles after RFL B and SPMEN are set in t he SPMCSR Registe r,
will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the destina-
tion register. See “EEPROM Write Prevents Writing to SPMCSR” on page 147 for details.
• Bit 2 – PGWRT: Page Write
If this bit is writt en to one at the same t ime as SPMEN, t he next SPM instru ctio n within f our clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address is
taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four
clock cycles. The CPU is halted during the entire Page Write operation.
• Bit 1 – PGERS: Page Erase
If this bit is writt en to one at the same t ime as SPMEN, t he next SPM instru ctio n within f our clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If set to one together with
RSIG, CTPB, RFLB, PGWRT or PGERS, the following LPM/SPM instruction will have a special
meaning, as described elsewhere.
If only SPMEN is written, the following SPM instruction will store the value in R 1:R0 in the tem-
porary page buf fer addre ssed by t he Z-point er. The L SB of th e Z-pointer is ignored. Th e SPMEN
bit will auto-clear upon completion of an SPM instruction, or if no SPM instruction is executed
within four clock cycles. During Page Erase and Page Write, the SPMEN bit remains high until
the operation is completed.
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20. Memory Programming
This section describes t he different methods for Programming the ATtiny25/45/85 memories.
20.1 Program And Data Memory Lock Bits
ATtiny25/45/85 provides two Lock bits which can be left unprogrammed (“1”) or can be pro-
grammed (“0”) to obtain the additional security listed in Table 20-2. Lock bits can be erased to
“1” with the Chip Erase command, only.
Program memory can be read out via the debugWIRE interface when the DWEN fuse is pro-
grammed, even if th e Lock Bits are set. Thus, when Lock Bit security is required de bugWIRE
should always be disabled (by clearing the DWEN fuse) .
Note: 1. “1 ” means unprogrammed, “0” means programmed
Notes: 1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Lock bits can also be read by device firmware. See section “Reading Lock, Fuse and Signature
Data from Software” on page 147.
Table 20-1. Lock Bit Byte(1)
Lock Bit Bit No 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)
Table 20-2. Lock Bit Protection Modes(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
210
Further programming of the Flash and EEPROM is disabled in
High-voltage and Serial Programming mode. The Fuse bits are
locked in both Serial and High-voltage Programming mode.(1)
debugWire is disabled.
300
Further programming and v erification of the Flash and EEPROM
is disabled in High-voltage and Serial Programming mode. The
Fuse bits are locked in both Serial and High-voltage
Programming mode.(1) debugWire is disabled.
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20.2 Fuse Bytes ATtiny25/45/85 has three fuse bytes, as described in Table 20-3, Table 20-4, and Table 20-5.
Note that fuses are rea d as logical zero, “0”, when programmed.
Notes: 1. Enables SPM instruction. See “Self-Programming the Flash” on page 145.
Notes: 1. Controls use of RESET pin. See “Alternate Functions of Port B” on page 62.
2. After this fuse has been programmed de vice can be progra mmed via high-voltage serial mode,
only.
3. Must be unprogrammed when lock bit security is required. See “Program And Data Memory
Lock Bits” on page 151.
4. This fuse is not accessible in SPI programming mode.
5. See “WDTCR – Watchdog Timer Control Register” on page 47 for details.
6. See table “BODLEVEL Fuse Coding. TA = -40°C to +85°C” on page 171.
Table 20-3. Fuse Extended Byte
Fuse High Byte Bit No Description Default Value
7 - 1 (unprogrammed)
6 - 1 (unprogrammed)
5 - 1 (unprogrammed)
4 - 1 (unprogrammed)
3 - 1 (unprogrammed)
2 - 1 (unprogrammed)
1 - 1 (unprogrammed)
SELFPRGEN (1) 0 Self-programming enabled 1 (unpro grammed)
Table 20-4. Fus e High Byte
Fuse High Byte Bit No Description Default Value
RSTDISBL (1) (2) 7 External reset disabled 1 (unprogrammed)
DWEN (1) (2) (3) 6 DebugWIR E en a bled 1 (unprogrammed)
SPIEN (4) 5Serial program and data download
enabled 0 (progr ammed)
(SPI prog. enabled)
WDTON (5) 4 Watchdog timer always on 1 (unprogrammed)
EESAVE 3 EEPROM preserves chip eras e 1 (unprogrammed)
(EEPROM not preserved)
BODLEVEL2 (6) 2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL1 (6) 1 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0 (6) 0 Brown-out Detector trigger level 1 (unprogrammed)
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Notes: 1. See “System Clock Prescaler” on pag e 31 for details.
2. Allows system clock to be output on pin. See “Clock Ou tput Buffer” on page 32 for details.
3. The default value gives maximum start-up time for the default clock source. See Table 6-7 on
page 28 for details.
4. The default setting selects internal, 8 MHz RC oscillator. See Table 6-6 on page 28 fo r details.
Note that fuse bits are locked if Lock Bit 1 (LB1) is programmed. Fu se bits should be pro-
grammed before lock bits. The status of fuse bits is not affected by chip erase.
Lock bits can also be read by device firmware. See section “Reading Lock, Fuse and Signature
Data from Software” on page 147.
20.2.1 Latching of Fuses
Fuse values are latch ed when the devi ce enter s programmin g mode and ch anges to fuse values
will have no effect until the part leaves programming mode. This does not apply to the EESAVE
Fuse which takes effect once it is programmed. Fuses are also latched on power-up.
20.3 Device Signature Imprint Table
The device signature imprint table is a dedicated memory area used for storing miscellaneous
device information, such as the device signature and oscillator calibration data. Most of this
memory segment is reserved for internal use, as outlined in Table 20-6.
Notes: 1. See section “Signature Bytes” for more information.
2. See section “Calibration Bytes” for more information.
Table 20-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8 (1) 7 Clock divided by 8 0 (programmed)
CKOUT (2) 6 Clock output enabled 1 (unprogrammed)
SUT1 (3) 5 Start-up time setting 1 (unprogrammed)(3)
SUT0 (3) 4 Start-up time setting 0 (programmed)(3)
CKSEL3 (4) 3 Clock source setting 0 (programmed)(4)
CKSEL2 (4) 2 Clock source setting 0 (programmed)(4)
CKSEL1 (4) 1 Clock source setting 1 (unprogrammed)(4)
CKSEL0 (4) 0 Clock source setting 0 (programmed)(4)
Table 20-6. Contents of Device Signature Imprint Table.
Address High Byte
0x00 Signature byte 0 (1)
0x01 Calibration data for internal oscillator at 8.0 MHz (2)
0x02 Signature byte 1 (1)
0x03 Calibration data for internal oscillator at 6.4 MHz (2)
0x04 Signature byte 2 (1)
0x05 ... 0x2A Reserved for internal use
154 2586N–AVR–04/11
ATtiny25/45/85
20.3.1 Signature Bytes
All Atmel microcontrollers have a three- byte signature code which identifies the device. This
code can be read in both serial and high-vo ltage programming mode, even when the device is
locked.
Signature bytes can also be read by the device firmware. See section “Reading Lock, Fuse and
Signature Data from Software” on page 147.
The three signature bytes reside in a separate address space called the device signature imprint
table. The signature data for ATtiny25/45/85 is given in Table 20-7.
20.3.2 Calibration Bytes
The device signature imprint table of ATtiny25/45/85 contains two bytes of calibration data for
the internal RC Oscillator, as shown in Table 20-6 on pa ge 153 . In nor mal mod e of ope ratio n the
calibration data f or 8 MHz op erat ion is auto mat ically fet che d a nd writte n to t he OSCCAL regist er
during reset. In ATtiny15 compatibility mode the calibration data for 6.4 MHz operation is used
instead. This procedure guarantees the internal oscillator is always calibrated to the correct
frequency.
Calibration bytes can also b e read by the device f irmware. Se e section “Rea ding Lock, Fuse and
Signature Data from Software” on page 147.
20.4 Page Size
Table 20-7. Device Signature Bytes
Part Signature Byte 0 Signature Byte 1 Signature Byte 0
ATtiny25 0x1E 0x91 0x08
ATtiny45 0x1E 0x92 0x06
ATtiny85 0x1E 0x93 0x0B
Table 20-8. No. of Words in a Page and No. of Pages in the Flash
Device Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
ATtiny25 1K words
(2K bytes) 16 words PC[3:0] 64 PC[9:4] 9
ATtiny45 2K words
(4K bytes) 32 words PC[4:0] 64 PC[10:5] 10
ATtiny85 4K words
(8K bytes) 32 words PC[4:0] 128 PC[11:5] 11
Table 20-9. No. of Words in a Page and No. of Pages in the EEPROM
Device EEPROM
Size Page Size PCWORD No. of Pages PCPAGE EEAMSB
ATtiny25 128 bytes 4 bytes EEA[1:0] 32 EEA[6:2] 6
ATtiny45 256 bytes 4 bytes EEA[1:0] 64 EEA[7:2] 7
ATtiny85 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
155
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20.5 Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while
RESET is pulled to GND. The se rial interface co nsists of pins SCK, MOSI (i nput) and MI SO (out-
put). See below.
Figure 20-1. Serial Programming and Verify(1)
Notes: 1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
CLKI pin.
After RESET is set low, the Programming Enable instruction needs to be executed first before
program/erase operations can be executed.
Note: In Table 20-10 above, the pin mapping for SPI programming is listed. Not all parts use the SPI
pins dedicated for the internal SPI interface.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
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
Table 20-10. Pin Mapping Serial Programming
Symbol Pins I/O Description
MOSI PB0 I Serial Data in
MISO PB1 O Seria l Data out
SCK PB2 I Serial Clo ck
VCC
GND
SCK
MISO
MOSI
RESET
+1.8 - 5.5V
156 2586N–AVR–04/11
ATtiny25/45/85
20.5.1 Serial Programming Algorithm
When writing serial data to the ATtiny25/45/85, data is clocked on the rising edge of SCK.
When reading data from the ATtiny25/45/85, data is clocked on the falling edge of SCK. See
Figure 21-4 and Figure 21-5 for timing details.
To program and verify the ATtiny25/45/85 in the Serial Programming mode, the following
sequence is recommended (see four byte instruction formats in Table 20-12):
1. Power-up sequence : ap ply 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 after SCK has been
set to '0'. The duration of the pulse must be at least tRST plus two CPU clock cycles.
See Table 21-4 on page 170 for minimum pulse width on RESET pin, tRST
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of syn-
chronization. When in sync. the second byte (0x53), will echo back when issuing the
third by te of the Progr amming Enab le instruction. Whether the echo is correct or not, all
four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give
RESET a positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at
a time b y supplying the 5 LSB of the address and data togethe r with the Loa d Prog r am
memory Page instruction. To ensure correct loading of the pa ge, the data lo w byte m ust
be loaded before data high byte is applied for a given address. The Program memory
Page is stored by loading the Write Program memory Page instruction with the 6 MSB
of the address. If polling (RDY/BSY) is not used, the user must wait at least t WD_FLASH
before issuing the next page. (See Table 20-11.) Accessing the serial programming
interface before the Flash write operation completes can result in incorrect
programming.
5. A: The EEPRO M arra y is prog rammed one byte at a time by su pplying the addres s and
data together with the appropriate Write instruction. An EEPROM memory location is
first automatically erased before new data is written. If polling (RDY/BSY) is not used,
the user must wait at least tWD_EEPROM before issuing the next byte. (See Table 20-11.)
In a chip erased device, no 0xFFs in the data file(s) need to be progr ammed.
B: The EEPR OM arra y is progr ammed one page a t a time . The Memory page is loaded
one byte at a time by supplying the 2 LSB of the address and data together with the
Load EEPROM Memory Page instruction. The EEPROM Memory Page is stored by
loading the Write EEPROM Memory Page Instruction with the 6 MSB of the address.
When using EEPROM page access only byte locations loaded with the Load EEPR OM
Memory Pa ge instruction is altered. The remaining locations remain unchanged. If poll-
ing (RDY/BSY) is not used, the used must wait at least tWD_EEPROM before issuing the
ne xt pa ge (See Tab le 20-9). In a chip er ased devi ce , no 0xFF in the data file (s) need to
be programmed.
6. Any memory location can be verified by using the Read instruction which ret urns the
content at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to co mmence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
157
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20.5.2 Serial Programming Instruction set
Table 20-12 on page 157 and Figure 20-2 on page 158 describes the Instruction set.
Table 20-11. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FLASH 4.5 ms
tWD_EEPROM 4.0 ms
tWD_ERASE 9.0 ms
tWD_FUSE 4.5 ms
Table 20-12. Serial Programming Instruction Set
Instruction/Operation
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
Programming Enab le $AC $53 $00 $00
Chip Erase (Program Memory/EEPROM) $AC $80 $00 $00
Poll RDY/BSY $F0 $00 $00 data b yte out
Load Instructions
Load Extended Address byte(1) $4D $00 Extended adr $0 0
Load Program Memory Page, High byte $48 adr MSB adr LSB high data byte in
Load Program Memor y Page, Low byte $40 adr MSB adr LSB low data byte in
Load EEPROM Memory Page (page access) $C1 $00 0000 000aa data byte in
Read Instructions
Read Program Memory, High byte $28 adr MSB adr LSB high data byte out
Read Program Memory, Low byte $20 adr MSB adr LSB low data byte out
Read EEPROM Memory $A0 $00 00aa aaaa data byte out
Read Lock bits $58 $00 $00 data byte out
Read Signature Byte $30 $00 0000 000aa data byte out
Read Fuse bits $50 $00 $00 data byte out
Read Fuse High bits $58 $08 $00 data byte out
Read Extended Fuse Bits $50 $08 $00 data byte out
Read Calibration Byte $38 $00 $00 data byte out
Write Instructions(6)
Write Progra m Me mo ry Page $4C adr MSB adr LSB $00
Write EEPROM Memory $C0 $00 00aa aaaa data byte in
Write EEPROM Memory Page (page access) $C2 $00 00aa aa00 $00
Write Lock bits $AC $E0 $00 data byte in
Write Fuse bits $AC $A0 $00 data byte in
Write Fuse High bits $AC $A8 $00 data byte in
Write Extended Fuse Bits $AC $A4 $00 data byte in
158 2586N–AVR–04/11
ATtiny25/45/85
Notes: 1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (‘1’) .
5. Refer to the correspondig section for Fuse and Lock bits, Calibration and Signature bytes and Page size.
6. Instructions accessing program memory use a word address. This address may be random within the page range.
7. See htt://www.atmel.com/avr for Application Notes regarding programming and programmers.
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until
this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 20-2 on page
158.
Figure 20-2. Serial Programming Instruction example
Byte 1 Byte 2 Byte 3 Byte 4
Adr LSB
Bit 15 B 0
Serial Programming Instruction
Program Memory/
EEPROM Memory
Page 0
Page 1
Page 2
Page N-1
Page Buffer
Write Program Memory Page/
Write EEPROM Memory Page
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Byte 1 Byte 2 Byte 3 Byte 4
Bit 15 B 0
Adr MSB
Page Offset
Page Number
Ad
r M
MS
SB
A
A
Adr
r L
LSB
B
159
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ATtiny25/45/85
20.6 High-voltage Serial Programming
This section describe s how to program an d verify Flash Program memory, EEPROM Data mem-
ory, Lock bits and Fuse bits in the ATtiny25/45/85.
Figure 20-3. High-voltage Serial Programming
The minimum period for the Serial Clock Input (SCI) during High-voltage Serial Programming is
220 ns.
20.7 High-voltage Serial Programming Algorithm
To program and verify the ATtiny25/45/85 in the High-voltage Serial Programming mode, the fol-
lowing sequence is recommended (See instruction formats in Table 20-16):
Table 20-13. Pin Name Mapping
Signal Name in High-voltage
Serial Programming Mode Pin Name I/O Function
SDI PB0 I Serial Data Input
SII PB1 I Serial Instruction Input
SDO PB2 O Serial Data Output
SCI PB3 I Serial Clock Input (min. 220ns period)
Table 20-14. Pin Values Used to Enter Programming Mode
Pin Symbol Value
SDI Prog_enable[0] 0
SII Prog_enable[1] 0
SDO Prog_enable[2] 0
VCC
GND
SDO
SII
SDI
(RESET)
+4.5 - 5.5V
PB0
PB1
PB2
PB5
+11.5 - 12.5V
PB3
SCI
160 2586N–AVR–04/11
ATtiny25/45/85
20.7.1 Enter High-voltage Serial Programming Mode
The following algorithm puts the device in High-voltage Serial Programming mode:
1. Set Prog_enable pins listed in Table 20-1 4 to “000”, RESET pin and VCC to 0V.
2. Apply 4.5 - 5. 5V be twee n VCC an d GN D. Ensure that VCC reache s at lea st 1. 8V with in
the next 20 µs.
3. Wait 20 - 60 µs, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog _enable pins unchanged for at least 10 µs after the High-voltage has
been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO
pin.
6. Wait at least 300 µs before giving any serial instructions on SDI/SII.
7. Exit Programming mode b y power the device down or by bringing RESET pin to 0V.
If the rise time of t he VCC is unable to fulfill the requirements listed above, the following alterna-
tive algorithm can be used:
1. Set Prog_enable pins listed in Table 20-1 4 to “000”, RESET pin and VCC to 0V.
2. Apply 4.5 - 5. 5V be twee n VCC and GND.
3. Monitor VCC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.
4. Keep the Prog _enable pins unchanged for at least 10 µs after the High-voltage has
been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO
pin.
6. Wait until VCC actually reaches 4.5 - 5.5V before giving any serial instructions on
SDI/SII.
7. Exit Programming mode b y power the device down or by bringing RESET pin to 0V.
20.7.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command need s only be loaded once when writing or reading multiple memory
locations.
• Skip writing the data value 0xFF that is the contents of the entire EEPR OM (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 256 word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.
Table 20-15. High-voltage Reset Characteristics
Supply Voltage RESET Pin High-voltage Threshold Minimum High-voltage Period for
Latching Prog_enable
VCC VHVRST tHVRST
4.5V 11.5V 100 ns
5.5V 11.5V 100 ns
161
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20.7.3 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 re-
programmed.
Note: 1. The EEPROM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
1. Load command “Chip Erase” (see Table 20-16).
2. Wait after Instr. 3 until SDO goes high for the “Ch ip Erase” cycle to finish.
3. Load Command “No Operation”.
20.7.4 Programming the Flash
The Flash is organized in pages, see Table 20-12 on page 157. When programming the Flash,
the program data is latched into a page buffer. This allows one page of program data to be pro-
grammed simultaneously. The following procedure describes how to program the entire Flash
memory:
1. Load Command “Write Flash” (see Table 20-16).
2. Load Flash Page Buffer.
3. Load Flash High Add ress and Progr am P age. W ait after Instr. 3 until SDO goes h igh f or
the “Page Programming” cycle to finish.
4. Repeat 2 through 3 until the entire Flash is programmed or until all data has been
programmed.
5. End Page Programming by Loading Command “No Operation”.
When writing or reading serial data to the ATtiny25/45/85, data is clocked on the rising edge of
the serial clock, see Figure 20-5, Figure 21-6 and Table 21 -1 2 for details.
Figure 20-4. Addressing the Flash which is Organized in Pages
PROGRAM MEMORY
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
INSTRUCTION WORD
PA G E PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PA G E
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
162 2586N–AVR–04/11
ATtiny25/45/85
Figure 20-5. High-voltage Serial Programming Waveforms
20.7.5 Programming the EEPROM
The EEPROM is organized in pages, see Table 21-11 on page 175. When programming the
EEPROM, the data is latched into a page buffer. This allows one page of data to be pro-
grammed simultaneously. The programming algo rithm for the EEPROM Data memory is as
follows (refer to Table 20-16):
1. Load Command “Write EEPROM”.
2. Load EEPROM Page Buffer.
3. Progr am EEPR OM Pa ge. Wait after Instr. 2 until SDO goes high f or t he “Page Pr ogr am-
ming” cycle to finish.
4. Repeat 2 through 3 until the entire EEPROM is programmed or until all data has been
programmed.
5. End Page Programming by Loading Command “No Operation”.
20.7.6 Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to Table 20-16):
1. Load Command "Read Flash".
2. Read Flash Lo w and Hig h Bytes. The contents at the se lected a ddress ar e available at
serial ou tp u t SDO.
20.7.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Table 20 -1 6):
1. Load Command “Read EEPROM”.
2. Read EEPR OM Byte. The contents at the selected address are available at serial out-
put SDO.
20.7.8 Programming and Reading the Fuse and Lock Bits
The algorithms for programming and reading the Fuse Low/High bits and Lock bits are shown in
Table 20-16.
20.7.9 Reading the Signature Bytes and Calibration Byte
The algorithms for reading the Signature byte s and Calibration byte are shown in Table 20-16.
20.7.10 Power-off sequence
Set SCI to “0”. Set RESET to “1”. Turn VCC po we r off .
MSB
MSB
MSB LSB
LSB
LSB
012345678910
SDI
PB0
SII
PB1
SDO
PB2
SCI
PB3
163
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ATtiny25/45/85
Table 20-16. High-voltage Serial Programming Instruction Set for ATtiny25/45/85
Instruction
Instruction Format
Operation RemarksInstr.1/5 Instr.2/6 Instr.3 Instr.4
Chip Erase SDI
SII
SDO
0_1000_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr.3 until SDO
goes high for the Chip Erase
cycle to finish.
Load “Write
Flash”
Command
SDI
SII
SDO
0_0001_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter Flash Programming
code.
Load Flash
Page Buffer
SDI
SII
SDO
0_bbbb_bbbb _00
0_0000_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_dddd_dddd_00
0_0011_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1101_00
x_xxxx_xxxx_xx
Repeat after Instr. 1 - 5 until
the entire page buffer is filled
or until all data within the
page is filled.(2)
SDI
SII
SDO
0_0000_0000_00
0_0111_1100_00
x_xxxx_xxxx_xx Instr 5.
Load Flash
High Address
and Program
Page
SDI
SII
SDO
0_0000_000a_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr 3 until SDO
goes high. Repeat Instr. 2 - 3
for each loaded Flash Page
until the entire Flash or all
data is programmed. Repeat
Instr. 1 for a new 256 byte
page.(2)
Load “Read
Flash”
Command
SDI
SII
SDO
0_0000_0010_00
0_0100_1100_00
x_xxxx_xxxx_xx Enter Flash Read mode.
Read Flash
Low and High
Bytes
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_000a_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqqx_xx
Repeat Instr. 1, 3 - 6 for each
new address. Repeat Instr. 2
for a new 256 byte page.
SDI
SII
SDO
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
p_pppp_pppx_xx Instr 5 - 6.
Load “Write
EEPROM”
Command
SDI
SII
SDO
0_0001_0001_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter EEPROM Programming
mode.
Load
EEPROM
Page Buffer
SDI
SII
SDO
0_00bb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
Repeat Instr. 1 - 5 until the
entire page buffer is filled or
until all data within the page is
filled.(3)
SDI
SII
SDO
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx Instr. 5
Program
EEPROM
Page
SDI
SII
SDO
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 2 until SDO
goes high. Repeat Instr. 1 - 2
for each loaded EEPROM
page until the entire
EEPROM or all data is
programmed.
164 2586N–AVR–04/11
ATtiny25/45/85
Write
EEPROM
Byte
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
Repeat Instr. 1 - 6 for each
new address. Wait after Instr.
6 until SDO goes high.(4)
SDI
SII
SDO
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx Instr. 6
Load “Read
EEPROM”
Command
SDI
SII
SDO
0_0000_0011_00
0_0100_1100_00
x_xxxx_xxxx_xx Enter EEPROM Read mode.
Read
EEPROM
Byte
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqq0_00
Repeat Instr. 1, 3 - 4 for each
new address. Repeat Instr. 2
for a new 256 byte page.
Write Fuse
Low Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_A987_6543_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write A - 3 = “0” to
program the Fuse bit.
Write Fuse
High Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_IHGF_EDCB_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write I - B = “0” to
program the Fuse bit.
Write Fuse
Extended Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_000J_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0110_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1110_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write J = “0” to
program the Fuse bit.
Write Lock
Bits
SDI
SII
SDO
0_0010_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0021_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write 2 - 1 = “0” to
program the Lock bit.
Read Fuse
Low Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
A_9876_543x_xx
Reading A - 3 = “0” means
the Fuse bit is programmed.
Read Fuse
High Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1010_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1110_00
I_HGFE_DCBx_xx
Reading I - B = “0” means the
Fuse bit is programmed.
Read Fuse
Extended Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1010_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1110_00
x_xxxx_xxJx_xx
Reading J = “0” means the
Fuse bit is programmed.
Read Lock
Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
x_xxxx_x21x_xx
Reading 2, 1 = “0” means the
Lock bit is programmed.
Read
Signature
Bytes
SDI
SII
SDO
0_0000_1000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_00bb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqqx_xx
Repeats Instr 2 4 for each
signature byte address.
Read
Calibration
Byte
SDI
SII
SDO
0_0000_1000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
p_pppp_pppx_xx
Load “No
Operation”
Command
SDI
SII
SDO
0_0000_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
Table 20-16. High-voltage Serial Progra mming Instruction Set for ATtiny25/45/85 (Continued)
Instruction
Instruction Format
Operation RemarksInstr.1/5 Instr.2/6 Instr.3 Instr.4
165
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Notes: 1. a = address high bits, b = address low bits , d = data in high bits, e = data in lo w bits, p = data ou t high bits, q = data out low
bits, x = don’t care, 1 = Lock Bit1, 2 = Lock Bit2, 3 = CKSEL0 Fuse, 4 = CKSEL1 Fuse, 5 = CKSEL2 Fuse, 6 = CKSEL3
Fuse, 7 = SUT0 Fuse, 8 = SUT1 Fuse, 9 = CKOUT Fuse, A = CKDIV8 Fuse, B = BODLEVEL0 Fuse, C = BODLEVEL1
Fuse, D = BODLEVEL2 Fuse, E = EESAVE Fuse, F = WDTON Fuse, G = SPIEN Fuse, H = DWEN Fuse, I = RSTDISBL
Fuse, J = SELFPRGEN Fuse
2. For page sizes less than 256 words, parts of the address (bbbb_bbbb) will be parts of the page address.
3. For page sizes less than 256 bytes, parts of the address (bbbb_bbbb) will be parts of the page address.
4. The EEPROM is written page-wise. But only the bytes that are loade d into the page are actually written to the EEPROM.
Page-wise EEPROM access is more efficient when multiple bytes are to be written to the same page. Note that auto-erase
of EEPROM is not available in High-voltage Serial Programming, only in SPI Programming.
166 2586N–AVR–04/11
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21. Electrical Characteristics
21.1 Absolute Maximum Ratings*
21.2 DC Characteristics
Operating Temperature.................................. -55°C to +125°C*NOTICE: Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age 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.
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
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA
Table 21-1. DC Characteristics. TA = -40°C to +85°C
Symbol Parameter Condition Min. Typ.(1) Max. Units
VIL Input Low-voltage, except
XTAL1 and RESET pin VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V -0.5
-0.5 0.2VCC(3)
0.3VCC(3) V
V
VIH Input High-voltage, except
XTAL1 and RESET pin VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V 0.7VCC(2)
0.6VCC(2) VCC +0.5
VCC +0.5 V
V
VIL1 Input Low-voltage, XTAL1 pin,
External Clock Selected VCC = 1.8V - 5.5V -0.5 0.1VCC(3) V
VIH1 Input High-voltage, XTAL1 pin,
External Clock Selected VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V 0.8VCC(2)
0.7VCC(2) VCC +0.5
VCC +0.5 V
V
VIL2 Input Low-voltage,
RESET pin VCC = 1.8V - 5.5V -0.5 0.2VCC(3) V
V
VIH2 Input High-voltage,
RESET pin VCC = 1.8V - 5.5V 0.9VCC(2) VCC +0.5 V
VIL3 Input Low-voltage,
RESET pin as I/O VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V -0.5
-0.5 0.2VCC(3)
0.3VCC(3) V
V
VIH3 Input High-voltage,
RESET pin as I/O VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V 0.7VCC(2)
0.6VCC(2) VCC +0.5
VCC +0.5 V
V
VOL Output Low-voltage,(4)
Port B (except RESET) (6) IOL = 10 mA, VCC = 5V
IOL = 5 mA, VCC = 3V 0.6
0.5 V
V
VOH Output High-voltage, (5)
Port B (except RESET) (6) IOH = -10 mA, V CC = 5V
IOH = -5 mA, VCC = 3V 4.3
2.5 V
V
IIL Input Leakage
Current I/O Pin VCC = 5.5V, pin low
(absolute value) < 0.05 1 µA
IIH Input Leakage
Current I/O Pin VCC = 5.5V, pin hig h
(absolute value) < 0.05 1 µA
167
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Notes: 1. Typical values at 25°C.
2. “Min” means the lowest value where the pin is guaranteed to be read as high.
3. “Max” means the highest value where the pin is guaranteed to be read as low.
4. Although each I/O port can sink more th an the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be obser ved:
1] The sum of all IOL, for all ports, should not exceed 60 mA.
If IOL e xceeds the test condition, V OL may e x ceed 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 (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be obser ved:
1] The sum of all IOH, for all ports, should not exceed 60 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. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence,
has a weak drive strength as compared to regular I/O pins. See Figure 22-23, Figure 22-24, Figure 22-25, and Figure 22-26
(starting on page 189).
7. V alues are with e xternal clock using methods described in “Minimizing Power Consumption” on page 37. P ower Reduction is
enabled (PRR = 0xFF) and there is no I/O drive.
8. Brown-Out Detection (BOD) disabled.
RRST Reset Pull-up Resistor VCC = 5.5V, inp u t low 30 60 kΩ
Rpu I/O Pin Pull-up Resistor VCC = 5.5V, input low 20 50 kΩ
ICC
Power Supply Current (7)
Active 1 MHz, VCC = 2V 0.3 0.55 mA
Active 4 MHz, VCC = 3V 1.5 2.5 mA
Active 8 MHz, VCC = 5V 5 8 mA
Idle 1 MHz, VCC = 2V 0.1 0.2 mA
Idle 4 MHz, VCC = 3V 0.35 0.6 mA
Idle 8 MHz, VCC = 5V 1.2 2 mA
Power-down mode (8) WDT enabled, VCC = 3V 10 µA
WDT disabled, VCC = 3V 2 µA
Table 21-1. DC Characteristics. TA = -40°C to +85°C (Continued)
Symbol Parameter Condition Min. Typ.(1) Max. Units
168 2586N–AVR–04/11
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21.3 Speed
Figure 21-1. Maximum Frequency vs. VCC
Figure 21-2. Maximum Frequency vs. VCC
10 MHz
4 MHz
1.8V 2.7V 5.5V
Safe Operating Area
20 MHz
10 MHz
2.7V 4.5V 5.5V
Safe Operating Area
169
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21.4 Clock Characteristics
21.4.1 Calibrated Internal RC Oscillator Accuracy
It is possible to manually calibrate the internal oscillator to be more accurate than default factory
calibration. Please note that the oscillator frequency depends on temperature and voltage. Volt-
age and temperature characteristics can be found in Figure 22-40 on page 198 and Figure 22-
41 on page 198.
Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
2. ATtiny25/V, only: 6.4 MHz in ATtiny15 Compatibility Mode.
3. Volta ge range for ATtiny25V/45V/85V.
4. Voltage range for ATtiny25/45/85.
21.4.2 External Clock Drive
Figure 21-3. External Clock Drive Waveforms
Table 21-2. Calibration Accuracy of Internal RC Oscillator
Calibration
Method Target Frequency VCC Temperature Accuracy at given V oltage
& Temperature (1)
Factory
Calibration 8.0 MHz (2) 3V 25°C±10%
User
Calibration
Fix ed frequency within:
6 – 8 MHz
Fixed voltage within:
1.8V - 5.5V (3)
2.7V - 5.5V (4)
Fixed temperature
within:
-40°C to +85°C±1%
VIL1
VIH1
Table 21-3. External Clock Drive Characteristics
Symbol Parameter
VCC = 1.8 - 5.5V VCC = 2.7 - 5.5V VCC = 4.5 - 5.5V
UnitsMin. Max. Min. Max. Min. Max.
1/tCLCL Clock Frequency 0 4 0 10 0 20 MHz
tCLCL Clock Period 250 100 50 ns
tCHCX High Time 100 40 20 ns
tCLCX Low Time 100 40 20 ns
tCLCH Rise Time 2.0 1.6 0.5 µs
tCHCL Fall Time 2.0 1.6 0.5 µs
ΔtCLCL Change in peri od from one clock cycle to the next 2 2 2 %
170 2586N–AVR–04/11
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21.5 System and Reset Characteristics
Note: 1. Values are guidelines only.
Two versions of power-on reset have been implemented, as follows.
21.5.1 Standard Power-On Reset
This implementation of power-on reset existed in early versions of ATtiny25/45/85. The table
below describes the characte ristics of this power-on reset and it is valid for the followin g devices,
only:
• ATtiny25, revision D, and older
• ATtiny4 5, revision F, and older
• ATtiny85, revision B, and newer
Note: Revisions are marked on the package (packages 8P3 and 8S2: bottom, package 20M1: top)
Note: 1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is risin g
3. The power-on reset will not work unless the supply voltage has been below VPOA
Table 21-4. Re se t, Brown-ou t an d Inte rna l Voltage Characteristics
Symbol Parameter Condition Min(1) Typ(1) Max(1) Units
VRST RESET Pin Threshold Voltage VCC = 3V 0.2 VCC 0.9 VCC V
tRST Minimum pulse width on
RESET Pin VCC = 3V 2.5 µs
VHYST Brown-out Detector Hysteresis 50 mV
tBOD Min Pulse Width on
Brown-out Reset 2µs
VBG Bandgap reference
voltage VCC = 5.5V
TA= 25°C 1.0 1.1 1.2 V
tBG Bandgap reference
start-up time VCC = 2.7V
TA= 25°C 40 70 µs
IBG Bandgap reference
current consumption VCC = 2.7V
TA= 25°C 15 µA
Table 21-5. Characteristics of Standard Power-On Reset. TA = -40° to +85°C
Symbol Parameter Min(1) Typ(1) Max(1) Units
VPOR Release threshold of power-on reset (2) 0.7 1.0 1.4 V
VPOA Activation threshold of pow e r-on reset (3) 0.05 0.9 1.3 V
SRON Power-on slope rate 0.01 4.5 V/ms
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21.5.2 Enhanced Power-On Reset
This implementation of power-on reset exists in newer versions of ATtiny25/45/85. The table
below describes the characte ristics of this power-on reset and it is valid for the followin g devices,
only:
• ATtiny25, revision E, and newer
• ATtiny45, revision G, and newer
• ATtiny85, revision C, and newer
Note: 1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is risin g
3. The Power-on Reset will not work unless the supply voltage has been below VPOT (falling)
21.6 Brown-Out Detection
Note: 1. VBOT ma y be belo w nominal minimum operating v oltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT dur ing the production test. This guar-
antees that a Brown-out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed.
Table 21-6. Characteristics of Enhanced Power-On Reset. TA = -40°C to +85°C
Symbol Parameter Min(1) Typ(1) Max(1) Units
VPOR Release threshold of power-on reset (2) 1.1 1.4 1.6 V
VPOA Activation threshold of pow e r-on reset (3) 0.6 1.3 1.6 V
SRON Power-On Slope Rate 0.01 V/ms
Table 21-7. BODLEVEL Fuse Coding. TA = -40°C to +85°C
BODLEVEL[2:0] Fuses Min(1) Typ(1) Max(1) Units
111 BOD Disabled
110 1.7 1.8 2.0
V101 2.5 2.7 2.9
100 4.1 4.3 4.5
0XX Reserved
172 2586N–AVR–04/11
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21.7 ADC Characteristics
Note: 1. Values are guidelines only.
Table 21-8. ADC Characteristics, Single Ended Channels. TA = -40°C to +85°C
Symbol Parameter Condition Min Typ Max Units
Resolution 10 Bits
Absolute accuracy
(Including INL, DNL, and
Quantization, Gain and
Offset errors)
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz 2LSB
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz 3LSB
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
Noise Reduction Mode 1.5 LSB
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
Noise Reduction Mode 2.5 LSB
Integral Non-linearity (INL)
(Accura cy after offset and ga in
calibration)
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz 1LSB
Differential Non-l inearity (DNL) VREF = 4V, VCC = 4V,
ADC clock = 200 kHz 0.5 LSB
Gain Error VREF = 4V, VCC = 4V,
ADC clock = 200 kHz 2.5 LSB
Offset Error VREF = 4V, VCC = 4V,
ADC clock = 200 kHz 1.5 LSB
Conversion Time Free Running Conversion 14 280 µs
Clock Frequency 50 1000 kHz
VIN Input Voltage GND VREF V
Input Bandwidth 38.4 kHz
AREF External Reference Voltage 2.0 VCC V
VINT Internal Voltage Reference 1.0 1.1 1.2 V
Internal 2.56V Reference (1) VCC > 3.0V 2.3 2.56 2.8 V
RREF 32 kΩ
RAIN Analog Input Resistance 100 MΩ
ADC Output 0 1023 LSB
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Note: 1. Values are guidelines only.
Table 21-9. ADC Characteristics, Differential Channels (Unipolar Mode). TA = -40°C to +85°C
Symbol Parameter Condition Min Typ Max Units
Resolution Gain = 1x 10 Bits
Gain = 20x 10 Bits
Absolute accuracy
(Including INL, DNL, and
Quantization, Gain and Offset
Errors)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 10.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 20.0 LSB
Integral Non-Linearity (INL)
(Accuracy after Offset and
Gain Calibration)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 4.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 10.0 LSB
Gain Error Gain = 1x 10.0 LSB
Gain = 20x 15.0 LSB
Offset Error
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 3.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 4.0 LSB
Conversion Time Free Running Conversion 70 280 µs
Clock Frequency 50 200 kHz
VIN Input Voltage GND VCC V
VDIFF Input Differential Voltage VREF/Gain V
Input Bandwidth 4 kHz
AREF External Reference Voltage 2.0 VCC - 1.0 V
VINT Internal Voltage Reference 1.0 1.1 1.2 V
Internal 2.56V Reference (1) VCC > 3.0V 2.3 2.56 2.8 V
RREF Reference Input Resistance 32 kΩ
RAIN Analog Input Resistance 100 MΩ
ADC Conversion Output 0 10 23 LSB
174 2586N–AVR–04/11
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Note: 1. Values are guidelines only.
Table 21-10. ADC Characteristics, Differential Ch annels (Bipolar Mode). TA = -40°C to +85°C
Symbol Parameter Condition Min Typ Max Units
Resolution Gain = 1x 10 Bits
Gain = 20x 10 Bits
Absolute accuracy
(Including INL, DNL, and
Quantization, Gain and Offset
Errors)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 8.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 8.0 LSB
Integral Non-Linearity (INL)
(Accuracy after Offset and
Gain Calibration)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 4.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 5.0 LSB
Gain Error Gain = 1x 4.0 LSB
Gain = 20x 5.0 LSB
Offset Error
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 3.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz 4.0 LSB
Conversion Time Free Running Conversion 70 280 µs
Clock Frequency 50 200 kHz
VIN Input Voltage GND VCC V
VDIFF Input Differential Voltage VREF/Gain V
Input Bandwidth 4 kHz
AREF External Reference Voltage 2.0 VCC - 1.0 V
VINT Internal Voltage Reference 1.0 1.1 1.2 V
Internal 2.56V Reference (1) VCC > 3.0V 2.3 2.56 2.8 V
RREF Reference Input Resistance 32 kΩ
RAIN Analog Input Resistance 100 MΩ
ADC Conversion Output -512 511 LSB
175
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21.8 Serial Programming Characteristics
Figure 21-4. Serial Programming Waveforms
Figure 21-5. Serial Programming Timing
Note: 1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
Table 21-11. Serial Programming Character istics, TA = -40°C to +85°C, VCC = 1.8 - 5.5 V
(Unless Otherwise Noted)
Symbol Parameter Min Typ Max Units
1/tCLCL Oscillator Frequency (VCC = 1.8 - 5.5V) 0 4 MHz
tCLCL Oscillator Period (VCC = 1.8 - 5.5V) 250 ns
1/tCLCL Oscillator Frequency (VCC = 2.7 - 5.5V) 0 10 MHz
tCLCL Oscillator Period (VCC = 2.7 - 5.5V) 100 ns
1/tCLCL Oscillator Frequency (VCC = 4.5V - 5.5V) 0 20 MHz
tCLCL Oscillator Period (VCC = 4.5V - 5.5V) 50 ns
tSHSL SCK Pulse Width High 2 tCLCL* ns
tSLSH SCK Pulse Width Low 2 tCLCL* ns
tOVSH MOSI Setup to SCK High tCLCL ns
tSHOX MOSI Hold after SCK High 2 tCLCL ns
tSLIV SCK Low to MISO Valid 100 ns
MSB
MSB
LSB
LSB
SERIAL CLOCK INPUT
(SCK)
SERIAL DATA INPUT
(MOSI)
(MISO)
SAMPLE
SERIAL DATA OUTPUT
MOSI
MISO
SCK
tOVSH
tSHSL
tSLSH
tSHOX
tSLIV
176 2586N–AVR–04/11
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21.9 High-voltage Serial Programming Characteristics
Figure 21-6. High-voltage Serial Programming Timing
Table 21-12. High-voltage Serial Progr amming Ch ar acterist ics TA = 25°C ± 10%, VCC = 5.0V ±
10% (Unless otherwise noted)
Symbol Parameter Min Typ Max Units
tSHSL SCI (PB3) Pulse Width High 125 ns
tSLSH SCI (PB3) Pulse Width Low 125 ns
tIVSH SDI (PB0), SII (PB1) Valid to SCI (PB3) High 50 ns
tSHIX SDI (PB0), SII (PB1) Hold after SCI (PB3) High 50 ns
tSHOV SCI (PB3) High to SDO (PB2) Valid 16 ns
tWLWH_PFB Wait after Instr. 3 for Write Fuse Bits 2.5 ms
SDI (PB0), SII (PB1)
SDO (PB2)
SCI (PB3)
tIVSH
tSHSL
tSLSH
tSHIX
tSHOV
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22. Typical Characteristics
The data contained in this section is largely based on simulat ions and characterization of similar
devices in the same process and design methods. Thus, the data should be treated as indica-
tions of how the part will behave.
The following charts show typical behavior. These figures are not tested during m anufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock
source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient tempera-
ture. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as 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 cur-
rent drawn by the Watchdog Timer.
22.1 Active Supply Current
Figure 22-1. Active Supply Current vs. Low frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY
0.1 -1.0 MHz
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0,2
0,4
0,6
0,8
1
1,2
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Frequency (MHz)
I
CC
(mA)
178 2586N–AVR–04/11
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Figure 22-2. Active Supply Current vs. Frequency (1 - 20 MHz)
Figure 22-3. Active Supply Current vs. VCC (Internal RC oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
5.5 V
5.0 V
4.5 V
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16 18 20
Frequency (MHz)
I
CC
(mA)
1.8V
2.7V
3.3V
4.0V
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
85 ˚C
25 ˚C
-40 ˚C
0
1
2
3
4
5
6
7
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
I
CC
(mA)
179
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Figure 22-4. Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
Figure 22-5. Active Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
ACTIVE SUPPLY CURRENT vs. V
CC
INTERNAL RC OSCILLATOR, 1 MHz
85 ˚C
25 ˚C
-40 ˚C
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,5 2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
I
CC
(mA)
ACTIVE SUPPLY CURRENT vs. V
CC
INTERNAL RC OSCILLATOR, 128 KHz
85 ˚C
25 ˚C
-40 ˚C
0
0,05
0,1
0,15
0,2
0,25
1,5 2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
ICC
(mA)
180 2586N–AVR–04/11
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22.2 Idle Supply Current
Figure 22-6. Idle Supply Current vs. low Frequency (0.1 - 1.0 MHz)
Figure 22-7. Idle Supply Current vs. Frequency (1 - 20 MHz)
IDLE SUPPLY CURRENT vs. LOW FREQUENCY
0.1 - 1.0 MHz
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0,05
0,1
0,15
0,2
0,25
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Frequency (MHz)
I
CC
(mA)
IDLE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
5.5 V
5.0 V
4.5 V
0
0,5
1
1,5
2
2,5
3
3,5
4
0 2 4 6 8 101214161820
Frequency (MHz)
I
CC
(mA)
1.8V
2.7V
3.3V
4.0V
181
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-8. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)I
Figure 22-9. Idle Supply Current vs. VCC (Internal RC Oscilllator, 1 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
85 ˚C
25 ˚C
-40 ˚C
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
I
CC
(mA)
IDLE SUPPLY CURRENT vs. V
CC
INTERNAL RC OSCILLATOR, 1 MHz
85 ˚C
25 ˚C
-40 ˚C
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
1,5 2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
ICC
(mA)
182 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-10. Idle Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
22.3 Supply Current of I/O modules
The tables and formulas below can b e used to calculate the additional current consumption for
the different I/O modules in Active and Idle mode. The enabling or disabling of the I/O modules
are controlled by the Power Reduction Register. See “PRR – Power Reduction Register” on
page 39 for details.
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 128 kHz
85 ˚C
25 ˚C
-40 ˚C
0
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
0,09
0,1
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
I
CC
(mA)
Table 22-1. Additional Current Consumption for the different I/O modules (absolute values)
PRR bit Typical numbers
VCC = 2V, f = 1 MHz VCC = 3V, f = 4 MHz V CC = 5V, f = 8 MHz
PRTIM1 45 uA 300 uA 1100 uA
PRTIM0 5 uA 30 uA 110 uA
PRUSI 5 uA 25 uA 100 uA
PRADC 15 uA 85 uA 340 uA
Table 22-2. Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external clock
(see Figure 22-1 and Figure 22-2)
Additional Current consumption
compared to Idle with external clock
(see Figure 22-6 and Figure 22-7)
PRTIM1 20 % 80 %
PRTIM0 2 % 10 %
PRUSI 2 % 10 %
PRADC 5 % 25 %
183
2586N–AVR–04/11
ATtiny25/45/85
It is possible to calcu late t he typical cur rent co nsumption b ased on the n umber s from Tab le 22-2
for other VCC and frequency settings that listed in Table 22-1.
22.3.1 Example Calculate the expected current consumption in idle mode with USI, TIMER0, and ADC enabled
at VCC = 2.0V and f = 1 MHz. From Table 22-2 on page 182, third column, we see that we nee d
to add 10% for the USI, 25 % for the ADC, a nd 10% for t he TIMER0 module. Reading fr om Figure
22-9, we find that the idle current consumption is ~0,18 mA at VCC = 2.0V and f = 1 MHz. The
total current consumpt ion in idle mode with USI, TIMER0, and ADC enable d, gives:
22.4 Power-down Supply Current
Figure 22-11. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
ICC 018mA,101,025,01,++ +()×0261mA,≈=
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER DISABLED
85 ˚C
25 ˚C
-40 ˚C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
I
CC
(uA)
184 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-12. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
22.5 Pin Pull-up
Figure 22-13. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
POWER-DOWN SUPPLY CURRENT vs. V
CC
WATCHDOG TIMER ENABLED
85 ˚C
25 ˚C
-40 ˚C
0
2
4
6
8
10
12
14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
V
CC
= 1.8V
85 ˚C
25 ˚C
-40 ˚C
0
10
20
30
40
50
60
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2
V
OP
(V)
IOP
(uA
)
185
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-14. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
Figure 22-15. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
V
CC
= 2.7V
85 ˚C
25 ˚C
-40 ˚C
0
10
20
30
40
50
60
70
80
0 0,5 1 1,5 2 2,5 3
V
OP
(V)
I
OP
(uA)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
V
CC
= 5V
85 ˚C
25 ˚C
-40 ˚C
0
20
40
60
80
100
120
140
160
0123456
V
OP
(V)
I
OP
(uA)
186 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-16. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V CC = 1.8V)
Figure 22-17. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V CC = 2.7V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
V
CC
= 1.8V
85 ˚C
25 ˚C
-40 ˚C
0
5
10
15
20
25
30
35
40
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2
V
RESET
(V)
I
R
ESET
(uA)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
V
CC
=2.7V
85 ˚C
25 ˚C
-40 ˚C
0
10
20
30
40
50
60
0 0,5 1 1,5 2 2,5 3
V
RESET
(V)
I
RESET
(uA)
187
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-18. Reset Pull-up Resistor Current vs. Reset Pin Voltage (V CC = 5V)
22.6 Pin Driver Strength
Figure 22-19. I/O Pin Output Voltage vs. Sink Current (VCC = 3V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
V
CC
= 5V
85 ˚C
25 ˚C
-40 ˚C
0
20
40
60
80
100
120
0123456
V
RESET
(V)
I
RESET
(uA)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
V
CC
= 3V
85
25
-40
0
0,2
0,4
0,6
0,8
1
1,2
0 5 10 15 20 25
I
OL
(mA)
V
OL
(V)
188 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-20. I/O Pin Output Voltage vs. Sink Current (VCC = 5V)
Figure 22-21. I/O Pin Output Voltage vs. Source Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
V
CC
= 5V
85
25
-40
0
0,1
0,2
0,3
0,4
0,5
0,6
0 5 10 15 20 25
I
OL
(mA)
V
OL
(V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
V
CC
= 3V
85
25
-40
0
0,5
1
1,5
2
2,5
3
3,5
0 5 10 15 20 25
I
OH
(mA)
V
OH
(V)
189
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-22. I/O Pin Output Voltage vs. Source Current (VCC = 5V)
Figure 22-23. Reset Pin Output Voltage vs. Sink Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 5V
85
25
-40
4,4
4,5
4,6
4,7
4,8
4,9
5
5,1
0 5 10 15 20 25
IOH (mA)
V
OH
(V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 3V
-45 °C
0 °C
85 °C
0
0.5
1
1.5
00.511.522.53
IOL (mA)
VOL (V)
190 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-24. Reset Pin Output Voltage vs. Sink Current (VCC = 5V)
Figure 22-25. Reset Pin Output Voltage vs. Source Current (VCC = 3V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 5V
-45 °C
0 °C
85 °C
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
IOL (mA)
VOL (V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 3V
-45 °C
25 °C
85 °C
0
0.5
1
1.5
2
2.5
3
3.5
00.511.52
IOH (mA)
VOH (V)
191
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-26. Reset Pin Output Voltage vs. Source Current (VCC = 5V)
22.7 Pin Threshold and Hysteresis
Figure 22-27. I/O Pin Input Threshold Voltage vs. VCC (VIH, IO Pin Read as ‘1’)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 5V
-45 °C
25 °C
85 °C
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2
IOH (mA)
VOH (V)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
85 ˚C
25 ˚C
-40 ˚C
0
0,5
1
1,5
2
2,5
3
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
Threshold (V)
192 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-28. I/O Pin Input Threshold Voltage vs. VCC (VIL, IO Pin Read as ‘0’)
Figure 22-29. I/O Pin Input Hysteresis vs. VCC
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIL, IO PIN READ AS '0'
85 ˚C
25 ˚C
-40 ˚C
0
0,5
1
1,5
2
2,5
3
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
Threshold (V)
85 °C
25 °C
-40 °C
0
0,1
0,2
0,3
0,4
0,5
0,6
1,5 2 2,5 3 3,5 4 4,5 5 5,5
Input Hysteresis (V)
V
CC
(V)
I/O PIN INPUT HYSTERESIS vs. VCC
193
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-30. Reset Input Threshold Voltage vs. VCC (VIH, IO Pin Read as ‘1’)
Figure 22-31. Reset Input Threshold Voltage vs. VCC (VIL, IO Pin Read as ‘0’)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
85 °C
25 °C
-40 °C
0
0,5
1
1,5
2
2,5
1,5 2 2,5 33,544,555,5
VCC (V)
Threshold (V)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIL, IO PIN READ AS '0'
85 °C
25 °C
-40 °C
0
0,5
1
1,5
2
2,5
1,5 2 2,5 33,5 4 4,5 5 5,5
VCC (V)
Threshold (V)
194 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-32. Reset Pin Input Hysteresis vs. VCC
22.8 BOD Threshold
Figure 22-33. BOD Threshold vs. Temperature (BOD Le vel is 4.3V)
RESET PIN INPUT HYSTERESIS vs. VCC
85 °C
25 °C
-40 °C
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
Input Hysteresis (V)
BOD THRESHOLDS vs. TEMPERATURE
Rising VCC
Falling VCC
4,26
4,28
4,3
4,32
4,34
4,36
4,38
4,4
-50 -40 -30 -20 -10 0 10 20 30405060708090100
Temperature (C)
Threshold (V)
195
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-34. BOD Threshold vs. Temperature (BOD Le vel is 2.7V)
Figure 22-35. BOD Threshold vs. Temperature (BOD Le vel is 1.8V)
BOD THRESHOLDS vs. TEMPERATURE
Rising VCC
Falling VCC
2,68
2,7
2,72
2,74
2,76
2,78
2,8
-50 -40 -30 -20 -10 0 10 20 304050607080 90 100
Temperature (C)
Threshold (V)
BOD THRESHOLDS vs. TEMPERATURE
Rising VCC
Falling VCC
1,795
1,8
1,805
1,81
1,815
1,82
1,825
1,83
1,835
1,84
1,845
1,85
-50 -40 -30 -20 -10 0 10 20 304050607080 90 100
Temperature (C)
Threshold (V)
196 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-36. Bandgap Voltage vs. Supply Voltage
Figure 22-37. Bandgap Voltage vs. Temperature
BANDGAP VOLTAGE vs. VCC
85 °C
25 °C
-40 °C
1
1,02
1,04
1,06
1,08
1,1
1,12
1,14
1,16
1,18
1,2
1,5 2 2,5 3 3,5 4 4,5 5 5,5
Vcc (V)
Bandgap Voltage (V)
BANDGAP VOLTAGE vs. Temperature
5 V
3 V
1.8 V
1
1,02
1,04
1,06
1,08
1,1
1,12
1,14
1,16
1,18
1,2
-40 -20 0 20 40 60 80 100
Temperature
Bandgap Voltage (V)
197
2586N–AVR–04/11
ATtiny25/45/85
22.9 Internal Oscillator Speed
Figure 22-38. Watchdog Oscillator Frequency vs. VCC
Figure 22-39. Watchdog Oscillator Frequency vs. Temperature
WATCHDOG OSCILLATOR FREQUENCY vs. V
CC
85 ˚C
25 ˚C
-40 ˚C
0,112
0,114
0,116
0,118
0,12
0,122
0,124
0,126
0,128
2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
F
RC
(MHz)
WATCHDOG OSCILLATOR FREQUENCY vs. TEMPERATURE
5.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0,108
0,11
0,112
0,114
0,116
0,118
0,12
-40 -30 -20 -10 0 10 20 30405060708090100
Temperature
FRC (MHz)
198 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-40. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
Figure 22-41. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. V
CC
85 ˚C
25 ˚C
-40 ˚C
7,5
7,6
7,7
7,8
7,9
8
8,1
8,2
1,5 2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
F
RC
(M
Hz)
CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
5.0 V
3.0 V
7,7
7,75
7,8
7,85
7,9
7,95
8
8,05
8,1
8,15
-60 -40 -20 0 20 40 60 80 100
Temperature
F
RC
(MHz)
199
2586N–AVR–04/11
ATtiny25/45/85
Figure 22-42. Calibrated 8 MHz RC Oscillator Frequency vs. OSCCAL Value
Figure 22-43. Calibrated 1.6 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
85 ˚C
25 ˚C
-40 ˚C
0
2
4
6
8
10
12
14
16
18
0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
OSCCAL (X1)
FRC
(MHz)
CALIBRATED 1.6 MHz RC OSCILLATOR FREQUENCY vs. V
CC
85 ˚C
25 ˚C
-40 ˚C
1,4
1,45
1,5
1,55
1,6
1,65
1,5 2 2,5 3 3,5 4 4,5 5 5,5
V
CC
(V)
F
RC
(MHz)
200 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-44. Calibrated 1.6 MHz RC Oscillator Frequency vs. Temperature
Figure 22-45. Calibrated 1.6 MHz RC Oscillator Frequency vs. OSCCAL Value
CALIBRATED 1.6MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
5.0 V
3.0 V
1,5
1,52
1,54
1,56
1,58
1,6
1,62
1,64
-60 -40 -20 0 20 40 60 80 100
Temperature
F
RC
(MHz)
CALIBRATED 1.6 MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
85 ˚C
25 ˚C
-40 ˚C
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
OSCCAL (X1)
F
RC
(MHz)
201
2586N–AVR–04/11
ATtiny25/45/85
22.10 Current Consumption of Peripheral Units
Figure 22-46. Brownout Detector Current vs. VCC
Figure 22-47. ADC Current vs. VCC (AREF = AVCC)
BROWNOUT DETECTOR CURRENT vs. VCC
85 °C
25 °C
-40 °C
0
5
10
15
20
25
30
1,5 2 2,5 33,5 4 4,5 5 5,5
VCC (V)
ICC (uA)
ADC CURRENT vs. VCC
AREF = AVCC
85 °C
25 °C
-40 °C
0
50
100
150
200
250
1,5 2 2,5 33,5 4 4,5 5 5,5
VCC (V)
ICC (uA)
202 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-48. Analog Comparator Current vs. VCC
Figure 22-49. Programming Current vs. VCC
ANALOG COMPARATOR CURRENT vs. VCC
85 °C
25 °C
-40 °C
0
5
10
15
20
25
30
35
40
45
50
1,5 2 2,5 33,5 4 4,5 5 5,5
VCC (V)
ICC (uA)
PROGRAMMING CURRENT vs. Vcc
Ext Clk
85 °C
25 °C
-40 °C
0
2
4
6
8
10
12
1,5 2 2,5 33,5 4 4,5 5 5,5
VCC (V)
ICC (mA)
203
2586N–AVR–04/11
ATtiny25/45/85
22.11 Current Consumption in Reset and Reset Pulsewidth
Figure 22-50. Reset Supply Current vs. VCC (0.1 - 1.0 MHz, Excluding Current Through The
Reset Pull-up)
Figure 22-51. Reset Supply Current vs. VCC (1 - 20 MHz, Excluding Curr ent Through The Reset
Pull-up)
RESET SUPPLY CURRENT vs. V
CC
0.1 - 1.0 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Frequency (MHz)
I
CC
(mA)
RESET SUPPLY CURRENT vs. VCC
1 - 20 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
5.5 V
5.0 V
4.5 V
0
0,5
1
1,5
2
2,5
0 2 4 6 8 101214161820
Frequency (MHz)
I
CC
(mA)
1.8V
2.7V
3.3V
4.0V
204 2586N–AVR–04/11
ATtiny25/45/85
Figure 22-52. Minimum Reset Pulse Width vs. VCC
MINIMUM RESET PULSE WIDTH vs. V
CC
85 ˚C
25 ˚C
-40 ˚C
0
500
1000
1500
2000
2500
1,5 2 2,5 3 3,5 4 4,5 5 5,5
VCC (V)
Pulsewidth (ns)
205
2586N–AVR–04/11
ATtiny25/45/85
23. Register Summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
0x3F SREG I T H S V N Z C page 8
0x3E SPH – – – – – – SP9 SP8 page 11
0x3D SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 page 11
0x3C Reserved –
0x3B GIMSK – INT0 PCIE – – – – – page 53
0x3A GIFR – INTF0 PCIF – – – – – page 54
0x39 TIMSK – OCIE1A OCIE1B OCIE0A OCIE0B TOIE1 TOIE0 – pages 84, 106
0x38 TIFR – OCF1A OCF1B OCF0A OCF0B TOV1 TOV0 –page 84
0x37 SPMCSR –– RSIG CTPB RFLB PGWRT PGERS SPMEN page 149
0x36 Reserved –
0x35 MCUCR BODS PUD SE SM1 SM0 BODSE ISC01 ISC00 pages 38, 53, 66
0x34 MCUSR – – – – WDRF BORF EXTRF PORF page 46,
0x33 TCCR0B FOC0A FOC0B –– WGM02 CS02 CS01 CS00 page 82
0x32 TCNT0 Timer/Counter0 page 83
0x31 OSCCAL Oscillator Calibration Re gister page 32
0x30 TCCR1 CTC1 PWM1A COM1A1 COM1A0 CS13 CS12 CS11 CS10 pages 92, 103
0x2F TCNT1 Timer/Counter1 pages 94, 105
0x2E OCR1A Timer/Counter1 Output Compare Register A pages 94, 105
0x2D OCR1C Timer/Counter1 Output Compare Register C pages 95, 106
0x2C GTCCR TSM PWM1B COM1B1 COM1B0 FOC1B FOC1A PSR1 PSR0 pages 80, 93, 105
0x2B OCR1B Timer/Counter1 Output Compare Register B page 95
0x2A TCCR0A COM0A1 COM0A0 COM0B1 COM0B0 –WGM01 WGM00 page 80
0x29 OCR0A Timer/Counter0 – Output Compare Register A page 83
0x28 OCR0B Timer/Counter0 – Output Compare Register B page 84
0x27 PLLCSR LSM –––– PCKE PLLE PLOCK pages 97, 107
0x26 CLKPR CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 page 33
0x25 DT1A DT1AH3 DT1AH2 DT1AH1 DT1AH0 DT1AL3 DT1AL2 DT1AL1 DT1AL0 page 110
0x24 DT1B DT1BH3 DT1BH2 DT1BH1 DT1BH0 DT1BL3 DT1BL2 DT1BL1 DT1BL0 page 110
0x23 DTPS1 - - - - - - DTPS11 DTPS10 page 109
0x22 DWDR DWDR[7:0] page 144
0x21 WDTCR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 page 47
0x20 PRR –PRTIM1 PRTIM0 PRUSI PRADC page 37
0x1F EEARH EEAR8 page 20
0x1E EEARL EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 page 20
0x1D EEDR EEPROM Data Register page 20
0x1C EECR –– EEPM1 EEPM0 EERIE EEMPE EEPE EERE page 21
0x1B Reserved –
0x1A Reserved –
0x19 Reserved –
0x18 PORTB –– PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 page 66
0x17 DDRB –– DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 page 66
0x16 PINB –– PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 page 66
0x15 PCMSK –– PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 page 54
0x14 DIDR0 –– ADC0D ADC2D ADC3D ADC1D AIN1D AIN0D pages 125, 142
0x13 GPIOR2 General Purpose I/O Register 2 page 10
0x12 GPIOR1 General Purpose I/O Register 1 page 10
0x11 GPIOR0 General Purpose I/O Register 0 page 10
0x10 USIBR USI Buffer Register page 118
0x0F USIDR USI Data Register page 118
0x0E USISR USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 page 119
0x0D USICR USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC page 120
0x0C Reserved –
0x0B Reserved –
0x0A Reserved –
0x09 Reserved –
0x08 ACSR ACD ACBG ACO ACI ACIE –ACIS1 ACIS0 page 124
0x07 ADMUX REFS1 REFS0 ADLAR REFS2 MUX3 MUX2 MUX1 MUX0 page 138
0x06 ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 page 140
0x05 ADCH ADC Data Register High Byte page 141
0x04 ADCL ADC Data Register Low Byte page 141
0x03 ADCSRB BIN ACME IPR –– ADTS2 ADTS1 ADTS0 pages 124, 141
0x02 Reserved –
0x01 Reserved –
0x00 Reserved –
206 2586N–AVR–04/11
ATtiny25/45/85
Note: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
207
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24. Instruction Set Summary
Mnemonics Operands Description Operation Flags #Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD Rd, Rr Add two Registers Rd ← Rd + Rr Z,C,N,V,H 1
ADC Rd, Rr Add with Carry two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1
ADIW Rdl,K Add Immediate to Word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2
SUB Rd, Rr Subtract two Registers Rd ← Rd - Rr Z,C,N,V,H 1
SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1
SBC Rd, Rr Subtract with Carry two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1
SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1
SBIW Rdl,K Subtract Immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z,C,N,V,S 2
AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1
ANDI Rd, K Logical AND Register and Constant Rd ← Rd • K Z,N,V 1
OR Rd, Rr Logical OR Registe rs Rd ← Rd v Rr Z,N,V 1
ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1
EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕ Rr Z,N,V 1
COM Rd One’s Complement Rd ← 0xFF − Rd Z,C,N,V 1
NEG Rd Two’s Complement Rd ← 0x00 − Rd Z,C,N,V,H 1
SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1
CBR Rd,K Clear Bit(s) in Register Rd ← Rd • (0xFF - K) Z,N,V 1
INC Rd Increment Rd ← Rd + 1 Z,N,V 1
DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1
TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V 1
CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V 1
SER Rd Set Register Rd ← 0xFF None 1
BRANCH INSTRUCTIONS
RJMP k Relative Jump PC ← PC + k + 1 None 2
IJMP Indirect Jump to (Z) PC ← Z None 2
RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3
ICALL Indirect Call to (Z) PC ← ZNone3
RET Subroutine Return PC ← STACK None 4
RETI Interrupt Return PC ← STACK I 4
CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1
CPC Rd,Rr Compare with Carry Rd − Rr − C Z, N,V,C,H 1
CPI Rd,K Compare Register with Immediate Rd − K Z, N,V,C,H 1
SBRC Rr, b Ski p if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if Bit in Register is Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if Bit in I/O Register Cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if Bit in I/O Register is Set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2
BRBC s, k Branch if Status Flag Cleared if (S REG(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 N one 1/2
BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1 /2
BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1 /2
BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if Less Than Zero, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1/2
BRTC k Branch if T Flag Cleared if (T = 0) then PC ← PC + k + 1 None 1/2
BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1/2
BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1/2
BRIE k Branch if Interrupt Enabled if ( I = 1) then PC ← PC + k + 1 None 1/2
BRID k Branch if Interrupt Disabled if ( I = 0) then PC ← PC + k + 1 None 1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI P,b Set Bit in I/O Register I/O(P,b) ← 1None2
CBI P, b Clear Bit in I/O Register I/O(P,b) ← 0None2
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
208 2586N–AVR–04/11
ATtiny25/45/85
ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1
SWAP Rd Swap Nibbles Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0) None 1
BSET s Flag Set SREG(s) ← 1 SREG(s) 1
BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1
BST Rr, b Bit Store from Register to T T ← Rr(b) T 1
BLD Rd, b Bit load from T to Register Rd(b) ← TNone1
SEC Set Carry C ← 1C1
CLC Clear Carry C ← 0 C 1
SEN Set Negative Flag N ← 1N1
CLN Clear Negative Flag N ← 0 N 1
SEZ Set Zero Flag Z ← 1Z1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1I1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1S1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Twos Complement Overflow. V ← 1V1
CLV Clear Twos Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1T1
CLT Clear T in SREG T ← 0 T 1
SEH Set Hal f Carry Flag in SREG H ← 1H1
CLH Clear Half Carry Flag in SREG H ← 0 H 1
DATA TRANSFER INSTRUCTIONS
MOV Rd, Rr Move Between Registers Rd ← Rr None 1
MOVW Rd, Rr Copy Register Word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load Immediate Rd ← KNone1
LD Rd, X Load Indirect Rd ← (X) None 2
LD Rd, X+ Load Indirect and Post-Inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load Indirect and Pre-Dec. X ← X - 1, Rd ← (X) None 2
LD Rd, Y Load Indirect Rd ← (Y) None 2
LD Rd, Y+ Load Indirect and Post-Inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load Indirect and Pre-Dec. Y ← Y - 1, Rd ← (Y) None 2
LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2
LD Rd, Z Load Indirect Rd ← (Z) None 2
LD Rd, Z+ Load Indirect and Post-Inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load Indirect and Pre-Dec. Z ← Z - 1, Rd ← (Z) None 2
LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2
LDS Rd, k Load Dir ect 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 N one 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 S t ore Dir ect to SRAM (k) ← Rr None 2
LPM Load Program Memory R0 ← (Z) None 3
LPM Rd, Z Load Progra m Memory Rd ← (Z) None 3
LPM Rd, Z+ Loa d Program Memory and Post-Inc Rd ← (Z), Z ← Z+1 None 3
SPM Store Program Memory (z) ← R1:R0 None
IN Rd, P In Port Rd ← PNone1
OUT P, Rr Out Port P ← Rr None 1
PUSH Rr Push Register on Stack STACK ← Rr None 2
POP Rd Pop Register from Stack Rd ← STACK None 2
MCU CONTROL INSTRUCTIONS
NOP No Operation None 1
SLEEP Sleep (see specific descr. for Sleep function) None 1
WDR Watchdog Reset (see specific descr. for WDR/Timer) None 1
BREAK Break For On-chip Debug Only None N/A
Mnemonics Operands Description Operation Flags #Clocks
209
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25. Ordering Information
Notes: 1. For speed vs. supply voltage, see section 21.3 “Speed” on page 168.
2. All packages are Pb-free, halide-free and fully green, and they comply with the European directive for Restriction of Hazard-
ous Substances (RoHS).
3. Code indicators: – H: NiPdAu lead finish
– U or N: matte tin
– R: tape & reel
4. Can also be supplied in wafer form. Contact your local Atmel sales office for ordering inf ormation and minimum quantities.
5. For Typical and Electrical character istics for this device please consult Appendix A, ATtiny25/V Specifi c ation at 105°C.
25.1 ATtiny25
Speed (MHz) (1) Supply Voltage (V) Temperature Range Package (2) Ordering Code (3)
10 1.8 – 5.5
Industrial
(-40°C to +85°C) (4)
8P3 ATtiny25V-10PU
8S2 ATtiny25V-10SU
ATtiny25V-10SUR
ATtiny25V-10SH
S8S1 ATtiny25V-10SSU
ATtiny25V-10SSUR
ATtiny25V-10SSH
20M1 ATtiny25V-10MU
ATtiny25V-10MUR
Industrial
(-40°C to +105°C) (5)
8S2 ATtiny25V-10SN
ATtiny25V-10SNR
S8S1 ATtiny25V-10SSN
ATtiny25V-10SSNR
20 2.7 – 5.5
Industrial
(-40°C to +85°C) (4)
8P3 ATtiny25-20PU
8S2 ATtiny25-20SU
ATtiny25-20SUR
ATtiny25-20SH
S8S1 ATtiny25-20SSU
ATtiny25-20SSUR
ATtiny25-20SSH
20M1 ATtiny25-20MU
ATtiny25-20MUR
Industrial
(-40°C to +105°C) (5)
8S2 ATtiny25-20SN
ATtiny25-20SNR
S8S1 ATtiny25-20SSN
ATtiny25-20SSNR
Package Types
8P3 8-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
8S2 8-lead, 0.208" Wide, Plastic Gull-Wing Small Outline (EIAJ SOIC)
S8S1 8-lead, 0.150" Wide, Plastic Gull-Wing Small Outline (JEDEC SOIC)
20M1 20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
210 2586N–AVR–04/11
ATtiny25/45/85
Notes: 1. For speed vs. supply voltage, see section 21.3 “Speed” on page 168.
2. All packages are Pb-free, halide-free and fully green and they comply with the European directive for Restriction of Hazard-
ous Substances (RoHS).
3. Code indicators: – H: NiPdAu lead finish
– U: matte tin
– R: tape & reel
4. These devices can also be supplied in waf er form. Please contact your local Atmel sales office for detailed ordering informa-
tion and minimum quantities.
25.2 ATtiny45
Speed (MHz) (1) Supply Voltage (V) Temperature Range Package (2) Ordering Code (3)
10 1.8 – 5.5 Industrial
(-40°C to +85°C) (4)
8P3 ATtiny45V-10PU
8S2 ATtiny45V-10SU
ATtiny45V-10SUR
ATtiny45V-10SH
8X ATtiny45V-10XU
ATtiny45V-10XUR
20M1 ATtiny45V-10MU
ATtiny45V-10MUR
20 2.7 – 5.5 Industrial
(-40°C to +85°C) (4)
8P3 ATtiny45-20PU
8S2 ATtiny45-20SU
ATtiny45-20SUR
ATtiny45-20SH
8X ATtiny45-20XU
ATtiny45-20XUR
20M1 ATtiny45-20MU
ATtiny45-20MUR
Package Types
8P3 8-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
8S2 8-lead, 0.208" Wide, Plastic Gull-Wing Small Outline (EIAJ SOIC)
8X 8-lead, 4.4 mm Wide, Plastic Thin Shrink Small Outline Package (TSSOP)
20M1 20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
211
2586N–AVR–04/11
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Notes: 1. For speed vs. supply voltage, see section 21.3 “Speed” on page 168.
2. All packages are Pb-free, halide-free and fully green and they comply with the European directive for Restriction of Hazard-
ous Substances (RoHS).
3. Code indicators: – H: NiPdAu lead finish
– U: matte tin
– R: tape & reel
4. These devices can also be supplied in waf er form. Please contact your local Atmel sales office for detailed ordering informa-
tion and minimum quantities.
25.3 ATtiny85
Speed (MHz) (1) Supply Voltage (V) Temperature Range Package (2) Ordering Code (3)
10 1.8 – 5.5 Industrial
(-40°C to +85°C) (4)
8P3 ATtiny85V-10PU
8S2 ATtiny85V-10SU
ATtiny85V-10SUR
ATtiny85V-10SH
20M1 ATtiny85V-10MU
ATtiny85V-10MUR
20 2.7 – 5.5 Industrial
(-40°C to +85°C) (4)
8P3 ATtiny85-20PU
8S2 ATtiny85-20SU
ATtiny85-20SUR
ATtiny85-20SH
20M1 ATtiny85-20MU
ATtiny85-20MUR
Package Types
8P3 8-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
8S2 8-lead, 0.208" Wide, Plastic Gull-Wing Small Outline (EIAJ SOIC)
20M1 20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
212 2586N–AVR–04/11
ATtiny25/45/85
26. Packaging Information
26.1 8P3
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
8P3, 8-lead, 0.300" Wide Body, Plastic Dual
In-line Package (PDIP)
01/09/02
8P3 B
D
D1
E
E1
e
L
b2
b
A2 A
1
N
eA
c
b3
4 PLCS
Top View
Side View
End View
COMMON DIMENSIONS
(Unit of Measure = inches)
SYMBOL MIN NOM MAX NOTE
Notes: 1. This drawing is for general information only; refer to JEDEC Drawing MS-001, Variation BA for additional information.
2. Dimensions A and L are measured with the package seated in JEDEC seating plane Gauge GS-3.
3. D, D1 and E1 dimensions do not include mold Flash or protrusions. Mold Flash or protrusions shall not exceed 0.010 inch.
4. E and eA measured with the leads constrained to be perpendicular to datum.
5. Pointed or rounded lead tips are preferred to ease insertion.
6. b2 and b3 maximum dimensions do not include Dambar protrusions. Dambar protrusions shall not exceed 0.010 (0.25 mm).
A 0.210 2
A2 0.115 0.130 0.195
b 0.014 0.018 0.022 5
b2 0.045 0.060 0.070 6
b3 0.030 0.039 0.045 6
c 0.008 0.010 0.014
D 0.355 0.365 0.400 3
D1 0.005 3
E 0.300 0.310 0.325 4
E1 0.240 0.250 0.280 3
e 0.100 BSC
eA 0.300 BSC 4
L 0.115 0.130 0.150 2
213
2586N–AVR–04/11
ATtiny25/45/85
26.2 8S2
TITLE DRAWING NO. GPC REV.
Package Drawing Contact:
packagedrawings@atmel.com 8S2STN F
8S2, 8-lead, 0.208” Body, Plastic Small
Outline Package (EIAJ)
4/15/08
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
Notes: 1. This drawing is for general information only; refer to EIAJ Drawing EDR-7320 for additional information.
2. Mismatch of the upper and lower dies and resin burrs aren't included.
3. Determines the true geometric position.
4. Values b,C apply to plated terminal. The standard thickness of the plating layer shall measure between 0.007 to .021 mm.
A 1.70 2.16
A1 0.05 0.25
b 0.35 0.48 4
C 0.15 0.35 4
D 5.13 5.35
E1 5.18 5.40 2
E 7.70 8.26
L 0.51 0.85
θ 0° 8°
e 1.27 BSC 3
θθ
11
NN
EE
TOP VIEWTOP VIEW
CC
E1E1
END VIEWEND VIEW
AA
bb
LL
A1A1
ee
DD
SIDE VIEWSIDE VIEW
214 2586N–AVR–04/11
ATtiny25/45/85
26.3 S8S1
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
S8S1, 8-lead, 0.150" Wide Body, Plastic Gull Wing Small
Outline (JEDEC SOIC)
7/28/03
S8S1A
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
Notes:1.This drawing is for general information only; refer to JEDEC Drawing MS-012 for proper dimensions, tolerances, datums,etc.
E 5.79 6.20
E1 3.813.99
A1.35 1.75
A1 0.1 0.25
D4.80 4.98
C 0.17 0.25
b0.31 0.51
L 0.4 1.27
e 1.27 BSC
0o 8o
Top View
Side View
End View
1
N
C
A
A1
b
L
e
D
E1 E
215
2586N–AVR–04/11
ATtiny25/45/85
26.4 8X
TITLE DRAWING NO.
R
REV.
Note: These drawings are for general information only. Refer to JEDEC Drawing MO-153AC.
2325 Orchard Parkway
San Jose, CA 95131
4/14/05
8X, 8-lead, 4.4 mm Body Width, Plastic Thin Shrink
Small Outline Package (TSSOP) 8XA
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A 1.05 1.10 1.20
A1 0.05 0.10 0.15
b 0.25 – 0.30
C – 0.127 –
D 2.90 3.05 3.10
E1 4.30 4.40 4.50
E 6.20 6.40 6.60
e 0.65 TYP
L 0.50 0.60 0.70
Ø
0
o – 8o
CC
AA
bb
LL
A1A1
D
Side View
Top View
End View
EE
11
E1E1
e
ØØ
216 2586N–AVR–04/11
ATtiny25/45/85
26.5 20M1
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
20M1, 20-pad, 4 x 4 x 0.8 mm Body, Lead Pitch 0.50 mm, A
20M1
10/27/04
2.6 mm Exposed Pad, Micro Lead Frame Package (MLF)
A 0.70 0.75 0.80
A1 – 0.01 0.05
A2 0.20 REF
b 0.18 0.23 0.30
D 4.00 BSC
D2 2.45 2.60 2.75
E 4.00 BSC
E2 2.45 2.60 2.75
e 0.50 BSC
L 0.35 0.40 0.55
SIDE VIEW
Pin 1 ID
Pin #1
Notch
(0.20 R)
BOTTOM VIEW
TOP VIEW
Note: Reference JEDEC Standard MO-220, Fig. 1 (SAW Singulation) WGGD-5.
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
D
E
e
A2
A1
A
D2
E2
0.08 C
L
1
2
3
b
1
2
3
217
2586N–AVR–04/11
ATtiny25/45/85
27. Errata
27.1 Errata ATtiny25
The revision letter in this section refers to the revision of the ATtiny25 device.
27.1.1 Rev D and E No known errata.
27.1.2 Rev B and C •EEPROM read may fail at lo w supply v oltage / low clock frequency
1. EEPROM read may fail at low supply voltage / low clock frequency
Trying to read EEPROM at low clock frequencies and/or low supply voltage may result in
invalid data.
Problem Fix/Workaround
Do not use the EEPROM when clock frequency is below 1MHz and supply voltage is below
2V. If operating frequency can not be raised above 1MHz then supply voltage should be
more than 2V. Similarly, if supply voltage can not be raised above 2V then operating fre-
quency should be more than 1MHz.
This feature is known to be temperature dependent but it has not been characterised.
Guidelines are given for room temperature, only.
27.1.3 Rev A Not sampled.
27.2 Errata ATtiny45
The revision letter in this section refers to the revision of the ATtiny45 device.
27.2.1 Rev F and G No known errata
27.2.2 Rev D and E •EEPROM read may fail at low supply voltage / low cl ock frequency
1. EEPROM read may fail at low supply voltage / low clock frequency
Trying to read EEPROM at low clock frequencies and/or low supply voltage may result in
invalid data.
Problem Fix/Workaround
Do not use the EEPROM when clock frequency is below 1MHz and supply voltage is below
2V. If operating frequency can not be raised above 1MHz then supply voltage should be
more than 2V. Similarly, if supply voltage can not be raised above 2V then operating fre-
quency should be more than 1MHz.
This feature is known to be temperature dependent but it has not been characterised.
Guidelines are given for room temperature, only.
218 2586N–AVR–04/11
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27.2.3 Rev B and C •PLL not locking
•EEPROM read from application code does not work in Lock Bit Mode 3
•EEPROM read ma y fail at low supply voltage / low c l ock frequency
•Timer Counter 1 PWM output generation on OC1B- XOC1B does not work correctly
1. PLL not locking
When at frequencies below 6.0 MHz, the PLL will not lock
Problem fix / Workaround
When using the PLL, run at 6.0 MHz or hi gher.
2. EEPROM read from application code does not work in Lock Bit Mode 3
When the Memory Lock Bits LB2 and LB1 are programmed to mode 3, EEPROM read does
not work from the ap plication code.
Problem Fix/Work around
Do not set Lock Bit Protection Mode 3 when the application code needs to read from
EEPROM.
3. EEPROM read may fail at low supply voltage / low clock frequency
Trying to read EEPROM at low clock frequencies and/or low supply voltage may result in
invalid data.
Problem Fix/Workaround
Do not use the EEPROM when clock frequency is below 1MHz and supply voltage is below
2V. If operating frequency can not be raised above 1MHz then supply voltage should be
more than 2V. Similarly, if supply voltage can not be raised above 2V then operating fre-
quency should be more than 1MHz.
This feature is known to be temperature dependent but it has not been characterised.
Guidelines are given for room temperature, only.
4. Timer Counter 1 PWM output generati on on OC1B – XOC1B does not work correctly
Timer Counter1 PWM output OC1B-XOC1B does not work correctly. Only in the case when
the control bits, COM1B1 and COM1B0 are in the same mode as COM1A1 and COM1A0,
respectively, the OC1B-XOC1B output works correctly.
Problem Fix/Work around
The only workaroun d is to us e same co ntro l setti ng on COM1A[1: 0] and COM1B[ 1:0] cont rol
bits, see table 14-4 in the data sheet. The problem has been f ixed for Tiny45 rev D.
27.2.4 Rev A •Too high power down power consumption
•DebugWIRE looses communication when single stepping into interrupts
•PLL not locking
•EEPROM read from application code does not work in Lock Bit Mode 3
•EEPROM read ma y fail at low supply voltage / low c l ock frequency
1. Too high power down power consumption
Three situations will lead to a too high power down power consumption. These are:
– An external clock is selected by fuses , b ut the I/O POR T is still enab led as an output.
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– The EEPROM is read before entering power down.
– VCC is 4.5 volts or higher.
Problem fix / Workaround
– When using external clock, avoid setting the clock pin as Output.
– Do not read the EEPROM if power down power consumption is important.
– Use VCC lower than 4.5 Volts.
2. DebugWIRE looses communication when single stepping into interrupts
When receiving an interrupt during single stepping, debugwire will loose
communication.
Problem fix / Workaround
– When singlestepping, disable interrupts.
– When debugging interrupts , use breakpoints within the inter rupt routine, and run into
the interrupt.
3. PLL not locking
When at frequencies below 6.0 MHz, the PLL will not lock
Problem fix / Workaround
When using the PLL, run at 6.0 MHz or hi gher.
4. EEPROM read from application code does not work in Lock Bit Mode 3
When the Memory Lock Bits LB2 and LB1 are programmed to mode 3, EEPROM read does
not work from the ap plication code.
Problem Fix/Work around
Do not set Lock Bit Protection Mode 3 when the application code needs to read from
EEPROM.
5. EEPROM read may fail at low supply voltage / low clock frequency
Trying to read EEPROM at low clock frequencies and/or low supply voltage may result in
invalid data.
Problem Fix/Workaround
Do not use the EEPROM when clock frequency is below 1MHz and supply voltage is below
2V. If operating frequency can not be raised above 1MHz then supply voltage should be
more than 2V. Similarly, if supply voltage can not be raised above 2V then operating fre-
quency should be more than 1MHz.
This feature is known to be temperature dependent but it has not been characterised.
Guidelines are given for room temperature, only.
220 2586N–AVR–04/11
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27.3 Errata ATtiny85
The revision letter in this section refers to the revision of the ATtiny85 device.
27.3.1 Rev B and C No known errata.
27.3.2 Rev A •EEPROM read may fail at low supply voltage / low cl ock frequency
1. EEPROM read may fail at low supply voltage / low clock frequency
Trying to read EEPROM at low clock frequencies and/or low supply voltage may result in
invalid data.
Problem Fix/Workaround
Do not use the EEPROM when clock frequency is below 1MHz and supply voltage is below
2V. If operating frequency can not be raised above 1MHz then supply voltage should be
more than 2V. Similarly, if supply voltage can not be raised above 2V then operating fre-
quency should be more than 1MHz.
This feature is known to be temperature dependent but it has not been characterised.
Guidelines are given for room temperature, only.
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28. Datasheet Revision History
28.1 Rev. 2586N-04/11
1. Added:
– Section “Capacitive Touch Sensing” on page 6.
2. Updated:
– Document template.
– Removed “Preliminary” on front page. All devices now final and in production.
– Section “Limitations” on page 37.
– Program example on page 51.
– Section “Overview” on page 126.
–Table 17-4 on page 139.
– Section “Limitations of debugWIRE” on page 144.
– Section “Serial Programming Algorithm” on page 15 6.
–Table 21-7 on page 171.
– EEPROM errata on pages 217, 217, 218, 219, and 220
– Ordering information on pages 209, 210, and 211.
28.2 Rev. 2586M-07/10
1. Clarified Section 6.4 “Clock Outp ut Buffe r” on pag e 32 .
2. Added Ordering Codes -SN and -SNR for ATtiny25 extended temperatu re.
28.3 Rev. 2586L-06/10
1. Added:
– TSSOP f or ATtiny45 in “Features” on page 1, Pinout Figure 1-1 on page 2, Ordering
Information in Section 25.2 “ATtiny45” on page 210, and Packaging Information in
Section 26.4 “8X” on page 215
–Table 6-11, “Capacitance of Low-Frequency Crystal Oscillator,” on page 29
–Figure 22-36 on page 196 and Figure 22-37 on page 196, Typical Characteristics
plots for Bandgap Voltage vs. VCC and Temperature
– Extended temperature in Section 25.1 “ATtiny25” on page 209, Ordering Information
– Tape & reel part numbers in Ordering Information, in Section 25.1 “ATtiny25” on
page 209 an d Section 25.2 “ATtiny45” on page 210
2. Updated:
–“Features” on page 1, removed Preliminary from ATtiny25
–Section 8.4.2 “Code Example” on page 46
–“PCMSK – Pin Change Mask Register” on page 54, Bit Descriptions
–“TCCR1 – Timer/Counter1 Control Register” on page 92 and “GTCCR – General
Timer/Counter1 Control Register” on page 93, COM bit descriptions clarified
–Section 20.3.2 “Calibration Bytes” on page 154, frequencies (8 MHz, 6.4 MHz)
–Table 20-11, “Minimum Wait Delay Before Writing the Next Flash or EEPROM
Location,” on page 157, value for tWD_ERASE
222 2586N–AVR–04/11
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–Table 20-16, “High-voltage Serial Programming Instruction Set for ATtiny25/45/85,”
on page 163
–Table 21-1, “DC Characteri stics. TA = -40°C to +85°C,” on page 166, notes adjusted
–Table 21-11, “Serial Programming Characteristics, TA = -40°C to +85°C, VCC = 1.8 -
5.5V (Unless Otherwise Noted),” on page 175, added tSLIV
– Bit syntax throughout the datasheet, e.g. from CS02:0 to CS0[2:0].
28.4 Rev. 2586K-01/08
1. Updated Document Template.
2. Added Sections:
–“Data Retention ” on page 6
–“Low Level Interrupt” on page 51
–“Device Signature Imprint Table” on page 153
3. Updated Sections:
–“Internal PLL for Fast Peripheral Clock Generation - clkPCK” on page 24
–“System Clock and Clock Options” on page 23
–“Internal PLL in ATtiny15 Compatibility Mode” on page 24
–“Sleep Modes” on page 35
–“Software BOD Disabl e” on page 36
–“External Interrupts” on page 51
–“Timer/Counter1 in PWM Mode” on page 101
–“USI – Universal Serial Interface” on page 11 1
–“Temperature Measurement” on page 137
–“Reading Lock, Fuse an d Signature Data from Software” on page 147
–“Program And Data Memory Lock Bits” on page 151
–“Fuse Bytes” on page 152
–“Signature Bytes” on page 154
–“Calibration Bytes” on page 154
–“System and Reset Characteristics” on page 170
4. Added Figures:
–“Reset Pin Output Voltage vs. Sink Current (VCC = 3V)” on page 189
–“Reset Pin Output Voltage vs. Sink Current (VCC = 5V)” on page 190
–“Reset Pin Output Voltage vs. Source Current (VCC = 3V)” on page 190
–“Reset Pin Output Voltage vs. Source Current (VCC = 5V)” on page 191
5. Updated Figure:
–“Reset Logic ” on page 41
6. Updated Tables:
–“Start-up Times for Internal Calibrated RC Oscillator Clock” on page 28
–“Start-up Times for Internal Calibrated RC Oscillator Clock (in ATtiny15 Mode)” on
page 28
–“Start-up Times for the 128 kHz Internal Oscillator” on page 29
–“Compare Mode Select in PWM Mode” on page 89
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2586N–AVR–04/11
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–“Compare Mode Select in PWM Mode” on page 101
–“DC Characteristics. TA = -40°C to +85°C” on page 166
–“Calibration Accuracy of Internal RC Oscillator” on page 169
–“ADC Characteristics” on page 172
7. Updated Code Example in Section:
–“Write” on page 17
8. Updated Bit Descriptions in:
–“MCUCR – MCU Control Register” on page 38
–“Bits 7:6 – COM0A[ 1:0]: Compare Match Output A Mode” on page 80
–“Bits 5:4 – COM0B[ 1:0]: Compare Match Output B Mode” on page 80
–“Bits 2:0 – ADTS[2:0 ]: ADC Auto Trigger Source” on page 142
–“SPMCSR – Store Program Memory Control and Status Register” on page 149.
9. Updated description of feature “EEPR OM read may f ail at lo w supply voltage / low cloc k
frequency” in Sections:
–“Errata ATtiny25” on page 2 1 7
–“Errata ATtiny45” on page 2 1 7
–“Errata ATtiny85” on page 2 2 0
10. Updated Package Description in Sections:
–“ATtiny25” on page 209
–“ATtiny45” on page 210
–“ATtiny85” on page 211
11. Updated Package Drawing:
–“S8S1” on page 214
12. Updated Order Codes for:
–“ATtiny25” on page 209
28.5 Rev. 2586J-12/06
1. Updated “Low Power Consumption” on page 1.
2. Update d de sc rip tio n of instruction length in “Architectur al Ove r view ” .
3. Updated Flash size in “In-System Re-programmable Flash Program Memory” on
page 15.
4. Updated cross-references in sections “Atomic Byte Programming” , “Erase” an d
“Write” , starting on page 17.
5. Updated “Atomic Byte Programming” on page 17.
6. Updated “Internal PLL for Fast Peripheral Clock Generation - clkPCK” on page 24.
7. Replaced single clocking system figure with two: Figure 6-2 and Figure 6-3.
8. Updated Table 6-1 on page 25, Table 6-13 on page 30 and Table 6-6 on page 28.
9. Updated “Calibrated Internal Oscillator” on page 27.
10. Updated Table 6-5 on page 27.
11. Updated “OSCCAL – Oscillator Calibration Register” on page 32.
12. Updated “CLKPR – Clock Prescale Register” on page 33.
13. Updated “Power-down Mode” on page 36.
224 2586N–AVR–04/11
ATtiny25/45/85
28.6 Rev. 2586I-09/06
14. Updated “Bit 0” in “PRR – Power Reduction Register” on page 39.
15. Added footnote to Table 8-3 on page 48.
16. Updated Table 10-5 on page 65.
17. Deleted “Bits 7, 2” in “MCUCR – MCU Control Register” on page 66.
18. Updated and moved section “Timer/Counter0 Prescaler and Clock Sources”, now
located on page 68.
19. Updated “Timer/Counter1 Initialization for Asynchro nous Mode” on page 89.
20. Updated bit description in “PLLCSR – PLL Control and Status Register” on page 97
and “PLLCSR – PLL Control and Status Register” on page 107.
21. Added recommended maximum frequency in“Prescaling and Conversion Timing” on
page 129.
22. Updated Figure 17-8 on page 133 .
23. Updated “Temperature Measurement” on page 137.
24. Updated Table 17-3 on page 138.
25. Updated bit R/W descriptions in:
“TIMSK – Timer/Counter Interrupt Mask Register” on page 84,
“TIFR – Timer/Counter Interrupt Flag Register” on page 84,
“TIMSK – Timer/Counter Interrupt Mask Register” on page 95,
“TIFR – Timer/Counter Interrupt Flag Register” on page 96,
“PLLCSR – PLL Control and Status Register” on page 97,
“TIMSK – Timer/Counter Interrupt Mask Register” on page 106,
“TIFR – Timer/Counter Interrupt Flag Register” on page 106,
“PLLCSR – PLL Control and Status Register” on page 107 and
“DIDR0 – Digital Input Disable Register 0” on pa ge 142.
26. Added limitation to “Limitations of debugWIRE” on page 144.
27. Updated “DC Characteristics” on page 166.
28. Updated Table 21-7 on page 171.
29. Updated Figure 21-6 on page 176.
30. Updated Table 21-12 on page 176.
31. Updated Table 22-1 on page 182.
32. Updated Table 22-2 on page 182.
33. Updated Table 22-30, Table 22-31 and Table 22-32, starting on page 193.
34. Updated Table 22-33, Table 22-34 and Table 22-35, starting on page 194.
35. Updated Table 22-39 on page 197.
36. Updated Table 22-46, Table 22-47, Table 22-48 and Table 22-49.
1. All Characterization data moved to “Electrical Characteristics” on page 166.
2. All Register Descriptions are gathered up in seperate sections in the end of each
chapter.
3. Updated Table 11-3 on pa ge 81, Table 11-5 on page 82, Table 11-6 on page 83 and
Table 20-4 on page 152.
4. Updated “Calibrated Internal Oscillator” on page 27.
5. Updated Note in Table 7-1 on page 35.
6. Updated “System Control and Re set” on page 41.
7. Update d Re gis ter Desc rip tion in “I/O Ports” on page 55.
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28.7 Rev. 2586H-06/06
28.8 Rev. 2586G-05/06
28.9 Rev. 2586F-04/06
28.10 Rev. 2586E-03/06
8. Updated Features in “USI – Universal Serial Inter fac e” on pa g e 111.
9. Updated Code Example in “SPI Master Operation Example” on page 113 and “SPI
Slave Operatio n E xam p le” on pa g e 11 4.
10. Updated “Analog Comparator Multiplexed Input” on page 123.
11. Updated Figure 17-1 on page 127.
12. Updated “Signature Bytes” on page 154.
13. Updated “Electrical Characteri stics” on page 166.
1. Updated “Calibrated Internal Oscillator” on page 27.
2. Updated Table 6.5.1 on page 32.
3. Added Table 21-2 on page 169.
1. Updated “Internal PLL for Fast Peripheral Clock Generation - clkPCK” on page 24.
2. Updated “Default Clock Source” on page 31.
3. Updated “Low-Frequency Crystal Oscillator” on page 29.
4. Updated “Calibrated Internal Oscillator” on page 27.
5. Updated “Clock Output Buffer” on page 32.
6. Updated “Power Management and Sleep Modes” on page 35.
7. Added “Software BOD Disab le” on pag e 36.
8. Updated Figure 16-1 on page 123.
9. Updated “Bit 6 – ACBG: Analog Comparator Bandgap Select” on page 124.
10. Added note for Ta ble 17-2 on page 129.
11. Updated “Register Summary” on page 205.
1. Updated “Digital Input Enable and Sleep Modes” on page 59.
2. Updated Table 20-16 on page 163.
3. Updated “Ordering Information” on page 209.
1. Updated Features in “Analog to Digital Converter” on page 126.
2. Updated Operation in “Analog to Digital Converter” on page 126.
3. Updated Table 17-2 on page 138.
4. Updated Table 17-3 on page 138.
5. Updated “Errata” on pa ge 217.
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28.11 Rev. 2586D-02/06
28.12 Rev. 2586C-06/05
28.13 Rev. 2586B-05/05
28.14 Rev. 2586A-02/05
Initial revision.
1. Updated Table 6-13 on page 30, Table 6-10 on page 29, Table 6-3 on page 26,
Table 6-9 on page 29, Table 6-5 on page 27, Table 9-1 on page 50,Table 17-4 on
page 139, Table 20-16 on page 163, Table 21-8 on page 172.
2. Updated “Timer/Counte r1 in PWM Mode” on page 89.
3. Update d te xt “Bit 2 – TO V1 : Tim er /Counter1 Over flo w Fla g” on pa ge 96 .
4. Updated values in “DC Characteristics” on page 16 6.
5. Updated “Register Summary” on page 205.
6. Updated “Ordering Information” on page 209.
7. Updated Re v B and C in “Err ata ATtiny45” on pa ge 217 .
8. All references to power-save mode are removed.
9. Update d Re gis ter Adre ss es .
1. Updated “Features” on page 1.
2. Updated Figure 1-1 on page 2.
3. Update d Co de Exam p les on page 18 and page 19.
4. Moved “Temperature Measurement” to Section 17.12 page 137.
5. Updated “Register Summary” on page 205.
6. Updated “Ordering Information” on page 209.
1. CLKI added, instances of EEMWE/EEWE renamed EEMPE/EEPE, removed some
TBD.
Removed “Preliminary Description” from “Temperature Measurement” on page 137.
2. Updated “Features” on page 1.
3. Updated Figure 1-1 on page 2 and Figure 8-1 on page 41.
4. Updated Table 7-2 on page 39, Table 10-4 on page 65, Table 10-5 on page 65
5. Updated “Serial Programming Instruction set” on page 157.
6. Update d SPH re gis ter in “Instruction Set Summary” on page 207.
7. Updated “DC Characteristics” on page 166.
8. Updated “Ordering Information” on page 209.
9. Updated “Errata” on pa ge 217.
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Table of Contents
Features..................................................................................................... 1
1 Pin Configurations ................................................................................... 2
1.1 Pin Descriptions .................................................................................................2
2 Overview ................................................................................................... 4
2.1 Block Diagram ....... ... ... ... .... ................ ... ... ... .... ................ ... ... ... ................. ... ... ..4
3 About ......................................................................................................... 6
3.1 Resources .........................................................................................................6
3.2 Code Examples .................................................................................................6
3.3 Capacitive Touch Sensing .................................................................................6
3.4 Data Retention ...................................................................................................6
4 AVR CPU Core ..........................................................................................7
4.1 Introduction ........................................................................................................7
4.2 Architectural Overview .......................................................................................7
4.3 ALU – Arithmetic Logic Unit ...............................................................................8
4.4 Status Register ...... ... ... ... .... ................ ... ... ... ................. ... ... ... ................ .... ... .....8
4.5 General Purpose Register File ........................................................................10
4.6 Stack Pointer ...................................................................................................11
4.7 Instruction Executio n Tim in g . ... ... ................ .... ... ... ... ................ .... ... ... .............12
4.8 Reset and Interrupt Handling ...........................................................................12
5 AVR Memories ........................................................................................ 15
5.1 In-System Re-programmable Flash Program Memory ....................................15
5.2 SRAM Data Memory .............. ... ... ................ .... ... ... ................ ... .... ... ................15
5.3 EEPROM Data Memory ..................................................................................16
5.4 I/O Memory ........ .... ... ................ ... .... ... ................ ... ... ................ .... ... ... .............20
5.5 Register Descriptio n .... ... ................. ... ... ................ ... .... ... ................ ... ... .... ......20
6 System Clock and Clock Options ......................................................... 23
6.1 Clock Systems and their Distr i bu tio n .. ... ... ... ................. ... ... ... ... .... ................ ...23
6.2 Clock Sources .......... ... ... ................. ... ... ... ... ................. ... ... ... ................ .... ... ...25
6.3 System Clock Prescaler . .... ... ... ................ ... .... ... ... ................ ... .... ... ... .............31
6.4 Clock Output Buffer ..... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ ...32
6.5 Register Descriptio n .... ................ .... ... ................ ... ... .... ................ ... ... .............32
7 Power Management and Sleep Modes ................................................. 35
ii 2586N–AVR–04/11
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7.1 Sleep Modes ....................................................................................................35
7.2 Software BOD Disab le . ... ................. ... ... ... ................ .... ... ................ ... ... .... ......36
7.3 Power Reduction Register ...............................................................................37
7.4 Minimizing Power Consumption ......................................................................37
7.5 Register Descriptio n .... ... ................. ... ... ................ ... .... ... ................ ... ... .... ......38
8 System Control and Reset .................................................................... 41
8.1 Resetting the AVR ...........................................................................................41
8.2 Reset Sources .................................................................................................41
8.3 Internal Voltage Reference ..............................................................................44
8.4 Watchdog Timer ..............................................................................................44
8.5 Register Descriptio n .... ... ................. ... ... ................ ... .... ... ................ ... ... .... ......46
9 Interrupts ................................................................................................ 50
9.1 Interrupt Vectors in ATtiny 25 /4 5 /85 ................. ... ... ... .... ................ ... ... ... .... ......5 0
9.2 External Interrupts ...........................................................................................51
9.3 Register Descriptio n .... ... ................. ... ... ................ ... .... ... ................ ... ... .... ......53
10 I/O Ports .................................................................................................. 55
10.1 Introduction ...................................................................................................... 55
10.2 Ports as General Digital I/O .............................................................................56
10.3 Alternate Port Functions ..................................................................................59
10.4 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ ...66
11 8-bit Timer/Counter0 with PWM ............................................................ 67
11.1 Features ..........................................................................................................67
11.2 Overview ... ...... ....... ...... ... ....... ...... ....... ...... ....... ...... ... ....... ...... ....... ...... ....... ......67
11.3 Timer/Counter0 Prescaler and Clock Sources ................................................68
11.4 Counter Unit ....................................................................................................70
11.5 Output Compare Unit .......................................................................................71
11.6 Compare Match Output Unit ............................................................................72
11.7 Modes of Operation .........................................................................................73
11.8 Timer/Counte r Timin g Diagr am s .............. ... .... ... ... ... ................ .... ... ... ... .... ......78
11.9 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ ...80
12 8-bit Timer/Counter1 .............................................................................. 86
12.1 Timer/Counter1 Prescaler ...............................................................................86
12.2 Counter and Compare Units ............................................................................86
12.3 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ ...92
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13 8-bit Timer/Counter1 in ATtiny15 Mode ............................................... 98
13.1 Timer/Counter1 Prescaler ...............................................................................98
13.2 Counter and Compare Units ............................................................................98
13.3 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ .103
14 Dead Time Generator ........................................................................... 108
14.1 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ .109
15 USI – Universal Serial Interface .......................................................... 111
15.1 Features ........................................................................................................111
15.2 Overview ... ...... ....... ...... ... ....... ...... ....... ...... ....... ...... ... ....... ...... ....... ...... ....... ....111
15.3 Functional De scr ipt ion s ............... .... ... ... ................ ... .... ... ... ................ ... .... ... .112
15.4 Alternative USI Usage ...................................................................................117
15.5 Register Des crip tio n s .. ... .... ... ................ ... ... .... ... ................ ... ... .... ... ..............118
16 Analog Comparator ............................................................................. 123
16.1 Analog Comparator Multiplexed Input ...........................................................123
16.2 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ .124
17 Analog to Digital Converter ................................................................ 126
17.1 Features ........................................................................................................126
17.2 Overview ... ...... ....... ...... ... ....... ...... ....... ...... ....... ...... ... ....... ...... ....... ...... ....... ....126
17.3 Operation .......................................................................................................127
17.4 Starting a Conversion ....................................................................................128
17.5 Prescaling and Conversion Timing ................................................................129
17.6 Changing Channel or Reference Selection ...................................................132
17.7 ADC Noise Canceler .....................................................................................132
17.8 Analog Input Circuitry ....................................................................................133
17.9 Noise Canceling Techniques .........................................................................134
17.10 ADC Accuracy Definitions .............................................................................134
17.11 ADC Conversion Result .................................................................................136
17.12 Temperature Measurement ...........................................................................137
17.13 Regi ste r Des crip tio n .... ... .... ................ ... ... ... .... ................ ... ... ... .... ................ .138
18 debugWIRE On-chip Debug System .................................................. 143
18.1 Features ........................................................................................................143
18.2 Overview ... ...... ....... ...... ... ....... ...... ....... ...... ....... ...... ... ....... ...... ....... ...... ....... ....143
18.3 Physical Interfa c e ..... ... ... .... ... ... ................ ... .... ... ................ ... ... .... ... ..............143
18.4 Software Bre ak Point s .... .... ... ... ... .... ................ ... ... ... .... ................ ... ... ... .... ....1 4 4
iv 2586N–AVR–04/11
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18.5 Limitations of debugWIRE .............................................................................144
18.6 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ .144
19 Self-Programming the Flash ............................................................... 145
19.1 Performing Page Erase by SPM ....................................................................145
19.2 Filling the Temporary Buffer (Page Loading) .................................................145
19.3 Performing a Page Write ...............................................................................146
19.4 Addressing the Flash During Self-Programming ...........................................146
19.5 EEPROM Write Prevents Writing to SPMCSR ..............................................147
19.6 Reading Lock, Fuse and Signature Data from Software ...............................147
19.7 Preventin g Flas h Corru pt i on ..... ... .... ................ ... ... ... .... ................ ... ... ... ........149
19.8 Programming Time for Flash when Using SPM ............................................149
19.9 Register Des crip tio n .... ... .... ... ................ ... ... .... ................ ... ... ... .... ................ .149
20 Memory Programming ......................................................................... 151
20.1 Program And Da ta M em o ry Lo ck Bits ................ ... ... .... ... ... ................ ... .... ... .151
20.2 Fuse Bytes ... ... ... .... ... ................ ... .... ... ................ ... ... .... ... ................ ... ... .... ... .152
20.3 Device Signature Imprint Table .....................................................................153
20.4 Page Size ......................................................................................................154
20.5 Serial Downloading ........................................................................................155
20.6 High-voltage Serial Programming ..................................................................159
20.7 High-voltage Serial Programming Algorithm .................................................159
21 Electrical Characteristics .................................................................... 166
21.1 Absolute Maxim u m Ra ting s* . ... ... .... ... ... ................ ... .... ... ... ... ................ .... ... .166
21.2 DC Characteristics .........................................................................................166
21.3 Speed ............................................................................................................168
21.4 Clock Charac te rist ics ... ................ .... ... ... ... ................ .... ... ... ................ ... .... ... .169
21.5 System and Reset Characteristics ................................................................170
21.6 Brown-Out Detection .....................................................................................171
21.7 ADC Characteristics ......................................................................................172
21.8 Serial Programming Characteristics ..............................................................175
21.9 High-voltage Serial Programming Characteristics .........................................176
22 Typical Characteristics ........................................................................ 177
22.1 Active Supply Current ....................................................................................177
22.2 Idle Supply Current ........................................................................................180
22.3 Supply Curren t of I/O mod u les .... ................ .... ... ... ................ ... .... ... ... ...........182
22.4 Power-down Supply Current ..........................................................................183
v
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22.5 Pin Pull-up .....................................................................................................184
22.6 Pin Driver Strength ........................................................................................187
22.7 Pin Threshold and Hysteresis ........................................................................191
22.8 BOD Threshold ..............................................................................................194
22.9 Internal Oscillator Speed ...............................................................................197
22.10 Curren t Co ns um p tion of Per iph e ra l Units .............. ... ................ .... ... ... ... ........201
22.11 Current Consumption in Reset and Reset Pulsewidth ..................................203
23 Register Summary ............................................................................... 205
24 Instruction Set Summary .................................................................... 207
25 Ordering Information ........................................................................... 209
25.1 ATtiny25 ........................................................................................................209
25.2 ATtiny45 ........................................................................................................210
25.3 ATtiny85 ........................................................................................................211
26 Packaging Information ........................................................................ 212
26.1 8P3 ................................................................................................................212
26.2 8S2 ................................................................................................................213
26.3 S8S1 ..............................................................................................................214
26.4 8X ..................................................................................................................215
26.5 20M1 .................. .... ... ................ ... .... ... ................ ... ... .... ................ ... ... ...........216
27 Errata ..................................................................................................... 217
27.1 Errata ATtiny25 ..............................................................................................217
27.2 Errata ATtiny45 ..............................................................................................217
27.3 Errata ATtiny85 ..............................................................................................220
28 Datasheet Revision History ................................................................ 221
28.1 Rev. 2586N-04/11 .........................................................................................221
28.2 Rev. 2586M-07/10 .........................................................................................221
28.3 Rev. 2586L-06/10 ..........................................................................................221
28.4 Rev. 2586K-01/08 ..........................................................................................222
28.5 Rev. 2586J-12/06 ..........................................................................................223
28.6 Rev. 2586I-09/06 ...........................................................................................224
28.7 Rev. 2586H-06/06 .........................................................................................225
28.8 Rev. 2586G-05/06 .........................................................................................225
28.9 Rev. 2586F-04/06 ..........................................................................................225
28.10 Rev. 2586E-03/06 ..........................................................................................225
vi 2586N–AVR–04/11
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28.11 Rev. 2586D-02/06 .........................................................................................226
28.12 Rev. 2586C-06/05 .........................................................................................226
28.13 Rev. 2586B-05/05 ..........................................................................................226
28.14 Rev. 2586A-02/05 ..........................................................................................226
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