ATMEL ATTINY25

Features
• High Performance, Low Power AVR® 8-Bit Microcontroller
• Advanced RISC Architecture
•
•
•
•
•
•
•
•
– 120 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
Non-volatile Program and Data Memories
– 2/4/8K Byte of In-System Programmable Program Memory Flash (ATtiny25/45/85)
• Endurance: 10,000 Write/Erase Cycles
– 128/256/512 Bytes In-System Programmable EEPROM (ATtiny25/45/85)
• Endurance: 100,000 Write/Erase Cycles
– 128/256/512 Bytes Internal SRAM (ATtiny25/45/85)
– 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 Separate Output Compare Registers
• Programmable Dead Time Generator
– Universal Serial Interface with Start Condition Detector
– 10-bit ADC
• 4 Single Ended Channels
• 2 Differential ADC Channel Pairs with Programmable Gain (1x, 20x)
– 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 Power-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated Oscillator
I/O and Packages
– Six Programmable I/O Lines
– 8-pin SOIC
– 20-pin QFN
Operating Voltage
– 2.7 - 5.5V for ATtiny25/45/85
Speed Grade
– ATtiny25/45/85: 0 - 8 MHz @ 2.7 - 5.5V, 0 - 16 MHz @ 4.5 - 5.5V
Automotive Temperature Range
– -40°C to +125°C
Low Power Consumption
– Active Mode:
• 1 MHz, 2.7V: 500µA
– Power-down Mode:
• 0.2µA at 2.7V
8-bit
Microcontroller
with 2/4/8K
Bytes In-System
Programmable
Flash
ATtiny25
ATtiny45
ATtiny85
Automotive
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1. Pin Configurations
Figure 1-1.
Pinout ATtiny25/45/85
SOIC
(PCINT5/RESET/ADC0/dW) PB5
(PCINT3/XTAL1/OC1B/ADC3) PB3
(PCINT4/XTAL2/CLKO/OC1B/ADC2) PB4
GND
1
2
3
4
8
7
6
5
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)
2. Overview
The ATtiny25/45/85 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerful instructions in a single clock cycle, the ATtiny25/45/85
achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize
power consumption versus processing speed.
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2.1
Block Diagram
Figure 2-1.
Block Diagram
8-BIT DATABUS
CALIBRATED
INTERNAL
OSCILLATOR
PROGRAM
COUNTER
STACK
POINTER
PROGRAM
FLASH
SRAM
WATCHDOG
TIMER
TIMING AND
CONTROL
VCC
MCU CONTROL
REGISTER
MCU STATUS
REGISTER
GND
INSTRUCTION
REGISTER
INSTRUCTION
DECODER
CONTROL
LINES
GENERAL
PURPOSE
REGISTERS
TIMER/
COUNTER0
X
Y
Z
TIMER/
COUNTER1
ALU
UNIVERSAL
SERIAL
INTERFACE
STATUS
REGISTER
INTERRUPT
UNIT
PROGRAMMING
LOGIC
DATA
EEPROM
DATA REGISTER
PORT B
DATA DIR.
REG.PORT B
OSCILLATORS
ADC /
ANALOG COMPARATOR
PORT B DRIVERS
RESET
PB0-PB5
The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
The ATtiny25/45/85 provides the following features: 2/4/8K byte 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
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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 selectable power saving modes. The Idle mode stops the CPU while allowing the SRAM,
Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. The
Power-down mode saves the register contents, disabling all chip functions until the next Interrupt or Hardware Reset. The ADC Noise Reduction mode stops the CPU and all I/O modules
except ADC, to minimize 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 supported with a full suite of program and system development tools
including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators,
and Evaluation kits.
2.2
Automotive Quality Grade
The ATtiny25/45/85 have been developed and manufactured according to the most stringent
requirements of the international standard ISO-TS-16949. This data sheet contains limit values
extracted from the results of extensive characterization (Temperature and Voltage). The quality
and reliability of the ATtiny25/45/85 have been verified during regular product qualification as
per AEC-Q100 grade 1.
As indicated in the ordering information paragraph, the products are available in three different
temperature grades, but with equivalent quality and reliability objectives. Different temperature
identifiers have been defined as listed in Table 2-1.
Table 2-1.
Temperature
4
Temperature Grade Identification for Automotive Products
Temperature
Identifier
Comments
-40 ; +85
T
Similar to Industrial Temperature Grade but with Automotive
Quality
-40 ; +105
T1
Reduced Automotive Temperature Range
-40 ; +125
Z
Full AutomotiveTemperature Range
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2.3
2.3.1
Pin Descriptions
VCC
Supply voltage.
2.3.2
GND
Ground.
2.3.3
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
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the ATtiny25/45/85 as listed on
page 54.
On the ATtiny25 device the programmable I/O ports PB3 and PB4 (pins 2 and 3) are exchanged
in the ATtiny15 compatibility mode for supporting the backward compatibility with ATtiny15.
2.3.4
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a
reset, even if the clock is not running. The minimum pulse length is given in Table 8-1 on page
36. Shorter pulses are not guaranteed to generate a reset.
3. About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation for more details.
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.
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4.2
Architectural Overview
Figure 4-1.
Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
Control Lines
Direct Addressing
Instruction
Decoder
Indirect Addressing
Instruction
Register
Interrupt
Unit
Watchdog
Timer
ALU
Analog
Comparator
I/O Module1
Data
SRAM
I/O Module 2
I/O Module n
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the Program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the Program memory. This concept enables instructions to be executed
in every clock cycle. The Program memory is In-System Reprogrammable Flash memory.
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 typical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash Program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
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The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word format. Every Program memory address contains a 16- or 32-bit instruction.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The 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 position. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F.
4.3
ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
4.4
Status Register
The Status Register contains information about the result of the most recently executed arithmetic 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 Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
The AVR Status Register – SREG – is defined as:
Bit
7
6
5
4
3
2
1
0
I
T
H
S
V
N
Z
C
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SREG
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global Interrupt Enable
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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 destination for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result 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.
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4.5
General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit output 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
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
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 implemented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
4.5.1
The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 4-3.
Figure 4-3.
The X-, Y-, and Z-registers
15
X-register
XH
7
R27 (0x1B)
15
XL
0
7
0
0
R26 (0x1A)
YH
YL
0
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Y-register
7
0
R29 (0x1D)
Z-register
7
0
R28 (0x1C)
15
ZH
7
0
ZL
7
R31 (0x1F)
0
0
R30 (0x1E)
In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
4.6
Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations to lower memory locations. This implies that a Stack PUSH command decreases the 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 Pointer is decremented by one when data is pushed onto the Stack
with the PUSH instruction, and it is decremented by two when the return address is pushed onto
the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when 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 implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
Bit
Read/Write
Initial Value
4.7
15
14
13
12
11
10
9
8
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
1
0
0
1
1
1
1
1
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 generated from the selected clock source for the
chip. No internal clock division is used.
Figure 4-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
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ATtiny25/45/85 Auto
Figure 4-4.
The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 4-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destination register.
Figure 4-5.
Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
4.8
Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate Program Vector in the Program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt.
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 45. 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.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
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cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence..
Assembly Code Example
in r16, SREG
cli
; store SREG value
; disable interrupts during timed sequence
sbi EECR, EEMWE
; start EEPROM write
sbi EECR, EEWE
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<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in this example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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4.8.1
Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. After four clock cycles the Program Vector address for the actual interrupt handling routine
is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is increased by four clock cycles. This increase comes in addition to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and the I-bit in SREG is set.
5. AVR ATtiny25/45/85 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 linear and regular.
5.1
In-System Re-programmable Flash Program Memory
The ATtiny25/45/85 contains 2/4/8K byte On-chip In-System Reprogrammable Flash memory
for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as
1024/2049/4096 x 16.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny25/45/85
Program Counter (PC) is 10/11/12 bits wide, thus addressing the 1024/2048/4096 Program
memory locations. “Memory Programming” on page 139 contains a detailed description on Flash
data serial downloading using the SPI pins.
Constant tables can be allocated within the entire Program memory address space (see the
LPM – Load Program memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 10.
Figure 5-1.
Program Memory Map
Program Memory
0x0000
0x03FF/0x07FF
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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 data SRAM. The first 32 locations address the Register File, the next 64 locations the standard I/O memory, and the last 128/256/512 locations address the internal data
SRAM.
The five different addressing modes for the Data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register
File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address given
by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 128/256/512 bytes of internal data SRAM in the ATtiny25/45/85 are all accessible through all these addressing modes.
The Register File is described in “General Purpose Register File” on page 9.
Figure 5-2.
Data Memory Map
Data Memory
32 Registers
64 I/O Registers
0x0000 - 0x001F
0x0020 - 0x005F
0x0060
Internal SRAM
(128/256/512 x 8)
0x0DF/0x015F/0x025F
5.2.1
14
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 Figure 5-3.
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Figure 5-3.
On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Compute Address
Address valid
Write
Data
WR
Read
Data
RD
Memory Access Instruction
5.3
Next Instruction
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/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register. For a detailed description of Serial data
downloading to the EEPROM, see page 143.
5.3.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access times for the EEPROM are given in Table 5-1. A self-timing function, 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 filtered 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 Corruption” on page 20 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 Programming” on page 17 and “Split Byte Programming” on page 18 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
EEPROM Address Register High – EEARH
Bit
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
EEAR8
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
X
X
X
X
X
X
X
X
EEARH
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• Bit 7..1 – Res6..0: Reserved Bits
These bits are reserved for future use and will always read as 0 in ATtiny25/45/85.
• Bits 0 – EEAR8: EEPROM Address
The EEPROM Address Register – EEARH – 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 written before
the EEPROM may be accessed.
5.3.3
EEPROM Address Register – EEARL
Bit
7
6
5
4
3
2
1
0
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
X
X
X
X
X
X
X
X
EEARL
• Bits 7..0 – EEAR7..0: EEPROM Address
The EEPROM Address Register – EEARL – specifies the low 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 written before
the EEPROM may be accessed.
5.3.4
EEPROM Data Register – EEDR
Bit
7
6
5
4
3
2
1
0
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
X
X
X
X
X
X
X
X
EEDR
• Bits 7..0 – EEDR7..0: EEPROM Data
For the EEPROM write operation the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the
EEDR contains the data read out from the EEPROM at the address given by EEAR.
5.3.5
EEPROM Control Register – EECR
Bit
7
6
5
4
3
2
1
0
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
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
EECR
• 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 – EEPM1 and EEPM0: 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
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operations. The Programming times for the different modes are 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.
Table 5-1.
EEPROM Mode Bits
EEPM1
EEPM0
Programming
Time
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
–
Operation
Reserved for future use
• 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 interrupt 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 before 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 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the correct address is set up in the EEAR Register, the EERE bit must be 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 operation. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change
the EEAR Register.
5.3.6
Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the
user must write the address into the EEARL 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 1. The EEPE bit remains set until the erase and write operations are completed. While the device is busy with programming, it is not possible to do any
other EEPROM operations.
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5.3.7
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 supply 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 possible to do the erase operations when the system allows doing time-critical
operations (typically after Power-up).
5.3.8
Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the
EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (programming time is given in Table 1). 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.
5.3.9
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 1). 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 frequency is within the requirements described in “Oscillator Calibration Register – OSCCAL” on
page 27.
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
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.
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 (r17) in address register
out EEARL, r17
; Write data (r16) to data register
out EEDR,r16
; Write logical one to EEMWE
sbi EECR,EEMWE
; Start eeprom write by setting EEWE
sbi EECR,EEWE
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 */
EEARL = ucAddress;
EEDR = ucData;
/* Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r17) in address register
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 */
EEARL = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
5.3.10
Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage 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 needed detection level, an external low VCC reset protection circuit can
be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient.
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5.4
I/O Memory
The I/O space definition of the ATtiny25/45/85 is shown in “Register Summary” on page 188.
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/LDS/LDD and ST/STS/STD instructions, transferring data 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 registers, the
value of single bits can be checked by 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 Flags are cleared by writing a logical one to them. Note that, unlike most
other AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore
be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
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 their distribution. All of the clocks
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in “Power Management and Sleep Modes” on page 31. The clock systems are detailed below.
Figure 6-1.
Clock Distribution
General I/O
Modules
ADC
CPU Core
Flash and
EEPROM
RAM
clkPCK
clkI/O
clkCPU
AVR Clock
Control Unit
clkFLASH
clkADC
Reset Logic
Watchdog Timer
Source clock
Watchdog clock
Clock
Multiplexer
External Clock
Calibrated
Crystal RC
Oscillator
clkPCK
System Clock
Prescaler
Watchdog
Oscillator
Low-Frequency
Crystal Oscillator
PLL
Oscillator
Calibrated RC
Oscillator
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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 of the I/O modules, like Timer/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 operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.
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 reduce noise generated by digital circuitry. This gives more accurate 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. The source of the PLL input clock is the output of the internal RC oscillator having
a frequency of 8.0 MHz. Thus the output of the PLL, the fast peripheral clock is 64 MHz. The fast
peripheral clock, or a clock prescaled from that, can be selected as the clock source for
Timer/Counter1. See the Figure 6-2 on page 23.
Since the ATtiny25/45/85 device is a migration path for ATtiny15, there is an ATtiny15 compatibility mode for supporting the backward compatibility with ATtiny15. The ATtiny15 compatibility
mode is selected by programming the CKSEL fuses to ‘0011’. 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. 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).
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 only
when the PLLE bit in the register PLLCSR is set or the PLLCK fuse is programmed (‘0’). The bit
PLOCK from the register PLLCSR is set when PLL is locked.
Both internal RC oscillator and PLL are switched off in power down and stand-by sleep modes.
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ATtiny25/45/85 Auto
PCK Clocking System
Figure 6-2.
OSCCAL PLLE
PLLCK & CKSEL FUSES
CLKPS3..0
PLOCK
Lock
Detector
RC OSCILLATOR
8.0 MHz / 6.4 MHz
PCK
PLL
8x / 4x
64 / 25.6 MHz
DIVIDE
BY 4
XTAL1
XTAL2
6.2
System
Clock
Prescaler
SYSTEM
CLOCK
OSCILLATORS
Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the AVR clock generator, and routed to the
appropriate modules.
Table 6-1.
Device Clocking Options Select(1)
Device Clocking Option
CKSEL3..0
External Clock
0000
PLL Clock
0001
Calibrated Internal RC Oscillator 8.0 MHz
0010
Calibrated Internal RC Oscillator 6.4 MHz
0011
Watchdog Oscillator 128 kHz
0100
External Low-frequency Oscillator
0110
External Crystal/Ceramic Resonator
1000-1111
Reserved
0101, 0111
Note:
1. For all fuses “1” means unprogrammed while “0” means programmed.
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down or Power-save, the selected clock source is used to time the startup, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts
from reset, there is an additional delay allowing the power to reach a stable level before commencing normal operation. The Watchdog Oscillator is used for timing this real-time part of the
start-up time. The number of WDT Oscillator cycles used for each time-out is shown in Table 62.
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Table 6-2.
6.3
Number of Watchdog Oscillator Cycles
Typ Time-out
Number of Cycles
4 ms
512
64 ms
8K (8,192)
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. This default setting ensures that all users can
make their desired clock source setting using an In-System or High-voltage Programmer.
6.4
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an On-chip Oscillator, as shown in Figure 6-3. Either a quartz crystal or a
ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in Table 6-3. For ceramic resonators, the capacitor values given by
the manufacturer should be used.
Figure 6-3.
Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 6-3.
Table 6-3.
Crystal Oscillator Operating Modes
CKSEL3..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
Notes:
1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
6-4.
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ATtiny25/45/85 Auto
Table 6-4.
Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
SUT1..0
Start-up Time from
Power-down and
Power-save
0
00
258 CK(1)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
258 CK(1)
14CK + 65 ms
Ceramic resonator, slowly
rising power
0
10
1K CK(2)
14CK
Ceramic resonator, BOD
enabled
0
11
1K CK(2)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K CK(2)
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
14CK + 65 ms
Crystal Oscillator, slowly
rising power
Notes:
Additional Delay
from Reset
(VCC = 5.0V)
Recommended Usage
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 frequency of the device, and if frequency stability at start-up is not important for the application.
6.5
Low-frequency Crystal Oscillator
To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal
oscillator must be selected by setting CKSEL fuses to ‘0110’. The crystal should be connected
as shown in Figure 6-3. Refer to the 32 kHz Crystal Oscillator Application Note for details on
oscillator operation and how to choose appropriate values for C1 and C2.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table 6-5.
Table 6-5.
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time from
Power Down and Power
Save
Additional Delay from
Reset (VCC = 5.0V)
00
1K CK(1)
4 ms
Fast rising power or BOD
enabled
01
1K CK(1)
64 ms
Slowly rising power
10
32K CK
64 ms
Stable frequency at start-up
11
Notes:
Recommended usage
Reserved
1. These options should only be used if frequency stability at start-up is not important for the
application.
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6.6
Calibrated Internal RC Oscillator
The calibrated internal RC Oscillator provides an 8.0 MHz clock. The frequency is the nominal
value at 3V and 25°C. If the frequency exceeds the specification of the device (depends on VCC),
the CKDIV8 Fuse must be programmed in order to divide the internal frequency by 8 during
start-up. See “System Clock Prescaler” on page 29. for more details. This clock may be selected
as the system clock by programming the CKSEL Fuses as shown in Table 6-6. If selected, it will
operate with no external components. During reset, hardware loads the calibration byte into the
OSCCAL Register and thereby automatically calibrates the RC Oscillator. At 3V and 25°C, this
calibration gives a frequency within ± 1% of the nominal frequency. When this Oscillator is used
as the chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the
Reset Time-out. For more information on the pre-programmed calibration value, see the section
“Calibration Byte” on page 142.
In addition the calibrated internal RC Oscillator provides a 6.4 MHz clock that is chosen by writing the CKSEL fuses to “0011” as shown in Table 7. When this CKSEL setting is written the
nominal frequency of the calibrated internal RC Oscillator is calibrated down to 6.4 MHz. This
clock frequency is needed for the ATtiny15 compatibility mode. In the ATtiny15 compatibility
mode the 6.4 MHz internal RC oscillator is used as a reference clock for the PLL that is generating a 4x multiplied frequency from the reference clock. The resulting frequency is 25.6 MHz and
it is needed for supporting the same PWM frequencies as in ATtiny15.
Table 6-6.
Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
0010
Nominal Frequency
(1)
8.0 MHz
0011
Note:
6.4 MHz
1. The device is shipped with this option selected.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-7 and the start-up times in ATtiny15 compatibility mode in Table 9.
Table 6-7.
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK
01
6 CK
14CK + 4 ms
Fast rising power
10(1)
6 CK
14CK + 64 ms
Slowly rising power
11
Note:
BOD enabled
Reserved
1. The device is shipped with this option selected.
Table 6-8.
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK + 64 ms
01
6 CK
14CK + 64 ms
6 CK
14CK + 4 ms
1 CK
14CK
(1)
10
11
26
Recommended Usage
Recommended Usage
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6.6.1
Oscillator Calibration Register – OSCCAL
Bit
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
OSCCAL
Device Specific Calibration Value
• Bits 7..0 – CAL7..0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the internal Oscillator to remove process variations from the Oscillator frequency. This is done automatically during Chip Reset. When
OSCCAL is zero, the lowest available frequency is chosen. Writing non-zero values to this register will increase the frequency of the internal Oscillator. Writing 0xFF to the register gives the
highest available frequency. The calibrated Oscillator is used to time EEPROM and Flash
access. If EEPROM or Flash is written, do not calibrate to more than 8.8 MHz frequency. 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 frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the
range. Incrementing CAL6..0 by 1 will give a frequency increment of less than 2% in the frequency range 7.3 - 8.1 MHz.
Avoid changing the calibration value in large steps when calibrating the calibrated internal RC
Oscillator to ensure stable operation of the MCU. A variation 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
Table 6-9.
6.7
Internal RC Oscillator Frequency Range
OSCCAL Value
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
0x00
50%
100%
0x3F
75%
150%
0x7F
100%
200%
External Clock
To drive the device from an external clock source, CLKI should be driven as shown in Figure 64. To run the device on an external clock, the CKSEL Fuses must be programmed to “00”.
Figure 6-4.
External Clock Drive Configuration
EXTERNAL
CLOCK
SIGNAL
CLKI
GND
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7598D–AVR–02/07
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-10.
Table 6-10.
Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset
00
6 CK
14CK
01
6 CK
14CK + 4 ms
Fast rising power
10
6 CK
14CK + 64 ms
Slowly rising power
11
Recommended Usage
BOD enabled
Reserved
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
29 for details.
6.7.1
High Frequency PLL Clock - PLLCLK
There is an internal PLL that provides nominally 64 MHz clock rate locked to the RC Oscillator
for the use of the Peripheral Timer/Counter1 and for the system clock source. When selected as
a system clock source, by programming the CKSEL fuses to ‘0001’, it is divided by four like
shown in Table 6-11. When this clock source is selected, start-up times are determined by the
SUT fuses as shown in Table 6-12. See also “PCK Clocking System” on page 23.
Table 6-11.
Table 6-12.
6.8
PLLCK Operating Modes
CKSEL3..0
Nominal Frequency
0001
16 MHz
Start-up Times for the PLLCK
SUT1..0
Start-up Time from Power
Down and Power Save
Additional Delay from
Reset (VCC = 5.0V)
00
1K CK
14CK + 8ms
BOD enabled
01
16K CK
14CK + 8ms
Fast rising power
10
1K CK
14CK + 68 ms
Slowly rising power
11
16K CK
14CK + 68 ms
Slowly rising power
Recommended usage
128 kHz Internal Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The frequency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “11”.
28
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ATtiny25/45/85 Auto
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-13.
Table 6-13.
Start-up Times for the 128 kHz Internal Oscillator
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset
00
6 CK
14CK
01
6 CK
14CK + 4 ms
Fast rising power
10
6 CK
14CK + 64 ms
Slowly rising power
11
6.9
Recommended Usage
BOD enabled
Reserved
Clock Output Buffer
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other circuits on the system. Note that the clock will not be output during reset and the normal operation
of I/O pin will be overridden when the fuse is programmed. Any clock source, including the internal RC Oscillator, can be selected when the clock is output on CLKO. If the System Clock
Prescaler is used, it is the divided system clock that is output.
6.10
System Clock Prescaler
The ATtiny25/45/85 system clock can be divided by setting the Clock Prescale Register –
CLKPR. 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 CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH
are divided by a factor as shown in Table 6-14.
6.10.1
Clock Prescale Register – CLKPR
Bit
7
6
5
4
3
2
1
0
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
CLKPR
See Bit Description
• 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 reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 3..0 – CLKPS3..0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As the divider divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given in
Table 6-14.
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7598D–AVR–02/07
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 (CLKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is
not interrupted.
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 should 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 sufficient division factor is
chosen if the selcted clock source has a higher frequency than the maximum frequency of the
device at the present operating conditions. The device is shipped with the CKDIV8 Fuse
programmed.
Table 6-14.
6.10.2
Clock Prescaler Select
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Clock Division Factor
0
0
0
0
1
0
0
0
1
2
0
0
1
0
4
0
0
1
1
8
0
1
0
0
16
0
1
0
1
32
0
1
1
0
64
0
1
1
1
128
1
0
0
0
256
1
0
0
1
Reserved
1
0
1
0
Reserved
1
0
1
1
Reserved
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
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
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ATtiny25/45/85 Auto
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 are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
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.
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving
power. The AVR provides various sleep modes allowing the user to tailor the power consumption to the application’s requirements.
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM1..0 bits in the MCUCR Register select which
sleep mode (Idle, ADC Noise Reduction, or Power-down) will be activated by the SLEEP instruction. See Table 7-1 for a summary. If an enabled interrupt occurs while the MCU is in a sleep
mode, the MCU wakes up. The MCU is then halted for four cycles in addition to the start-up time,
executes the interrupt routine, and resumes execution from the instruction following SLEEP. The
contents of the Register File and SRAM are unaltered when the device wakes up from sleep. If a
reset occurs during sleep mode, the MCU wakes up and executes from the Reset Vector.
Figure 6-1 on page 21 presents the different clock systems in the ATtiny25/45/85, and their distribution. The figure is helpful in selecting an appropriate sleep mode.
7.0.1
MCU Control Register – MCUCR
The MCU Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
–
PUD
SE
SM1
SM0
—
ISC01
ISC00
Read/Write
R
R/W
R/W
R/W
R/W
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 5 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s
purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.
• Bits 4, 3 – SM1..0: Sleep Mode Select Bits 2..0
These bits select between the three available sleep modes as shown in Table 7-1.
Table 7-1.
Sleep Mode Select
SM1
SM0
Sleep Mode
0
0
Idle
0
1
ADC Noise Reduction
1
0
Power-down
1
1
Stand-by mode
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• Bit 2 – Res: Reserved Bit
This bit is a reserv ed bit in the ATtiny25/45/85 and will always read as zero.
7.1
Idle Mode
When the SM1..0 bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing Analog Comparator, ADC, 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 MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow. If wake-up from the Analog Comparator interrupt is not required,
the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator
Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If the
ADC is enabled, a conversion starts automatically when this mode is entered.
7.2
ADC Noise Reduction Mode
When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise
Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the
Watchdog to continue operating (if enabled). This sleep mode halts clkI/O, clkCPU, and clkFLASH,
while allowing the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If
the ADC is enabled, a conversion starts automatically when this mode is entered. Apart form the
ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out
Reset, 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.
7.3
Power-down Mode
When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter Powerdown mode. In this mode, the Oscillator is stopped, while the external interrupts, and the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out
Reset, 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.
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ATtiny25/45/85 Auto
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 58
for details..
Table 7-2.
Active Clock Domains and Wake-up Sources in the Different Sleep Modes
clkPCK
Main Clock
Source Enabled
INT0 and
Pin Change
SPM/
EEPROM
Ready
ADC
Other I/O
Watchdog
Interrupt
X
X
X
X
X
X
X
X
X
ADC Noise
Reduction
X
X
X(1)
X
X
X(1)
Power-down
Note:
7.4
Wake-up Sources
clkADC
Idle
Oscillators
clkIO
Sleep Mode
clkFLASH
clkCPU
Active Clock Domains
X
X
1. For INT0, only level interrupt.
Power Reduction Register
The Power Reduction Register, PRR, provides a method to stop the clock to individualperipherals to reduce power consumption. The current state of the peripheral is frozenand the I/O
registers can not be read or written. Resources used by the peripheral when stopping the clock
will remain occupied, hence the peripheral should in most cases be disabled before stopping the
clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the
same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.
Bit
7
6
5
4
3
2
1
0
–
-
-
-
PRTIM1
PRTIM0
PRUSI
PRADC
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PRR
• Bits 7, 6, 5, 4- Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 3- PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1
is enabled, operation will continue like before the shutdown.
• Bit 2- PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.
• 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
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7598D–AVR–02/07
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.
The analog comparator cannot use the ADC input MUX when the ADC is shut down.
7.5
Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
7.5.1
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “Analog to Digital Converter” on page 117
for details on ADC operation.
7.5.2
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering
ADC Noise Reduction mode, the Analog Comparator should be disabled. In the other sleep
modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is
set up to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
independent of sleep mode. Refer to “Analog Comparator” on page 114 for details on how to
configure the Analog Comparator.
7.5.3
Brown-out Detector
If the Brown-out Detector is not needed in the application, this module should be turned off. If the
Brown-out Detector is enabled by the 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 current consumption. Refer to “Brown-out Detection” on page 38 for details on how to
configure the Brown-out Detector.
7.5.4
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When
turned on again, the user must allow the reference to start up before the output is used. If the
reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal Voltage Reference” on page 40 for details on the start-up time.
7.5.5
Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Watchdog Timer” on page 40 for details on how to configure the Watchdog Timer.
7.5.6
Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important thing is then to ensure that no pins drive resistive loads. In sleep modes where
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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 51 for details on
which pins are enabled. If the input buffer is enabled and the input signal is left floating 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 significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Register (DIDR0). Refer to
“Digital Input Disable Register 0 – DIDR0” on page 117 for details.
8. System Control and Reset
8.0.1
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 interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. The circuit diagram in Figure 8-1 shows the reset logic. Table 8-1 defines the electrical
parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The different selections for the delay period are presented in “Clock Sources” on page 23.
8.0.2
Reset Sources
The ATtiny25/45/85 has four sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog is enabled.
• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
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7598D–AVR–02/07
Figure 8-1.
Reset Logic
DATA BUS
PORF
BORF
EXTRF
WDRF
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
Brown-out
Reset Circuit
BODLEVEL [1..0]
Pull-up Resistor
SPIKE
FILTER
Watchdog
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[1:0]
SUT[1:0]
8.0.3
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in Table 8-1. 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) circuit ensures that the device is reset from Power-on. Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after 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
VCC
RESET
TIME-OUT
VPOT
VRST
tTOUT
INTERNAL
RESET
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ATtiny25/45/85 Auto
Figure 8-3.
MCU Start-up, RESET Extended Externally
Table 8-1.
Power On Reset Specifications
Symbol
Parameter
Power-on Reset Threshold Voltage (rising)
VPOT
Power-on Reset Threshold Voltage (falling)
(1)
VPOR
VDD Start Voltage to ensure internal Power-on
Reset signal
-0.1
VDDRR
VDD Rise Rate to ensure
0.01
VRST
RESET Pin Threshold Voltage
tRST
Minimum pulse width on RESET Pin
Note:
8.0.4
Min
0.1 VCC
Typ
Max
Units
1.0
1.4
V
0.9
1.3
V
VSS
0.4
V
V/ms
0.9VCC
V
2.5
µs
1. The Power-on Reset will not work unless the supply voltage has been below VPOR.
External Reset
An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer
than the minimum pulse width (see Table 8-1) will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches
the Reset Threshold Voltage – VRST – on its positive edge, the delay counter starts the MCU
after the Time-out period – tTOUT – has expired.
External Reset During Operation
Figure 8-4.
CC
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7598D–AVR–02/07
8.0.5
Brown-out Detection
ATtiny25/45/85 has an On-chip Brown-out Detection (BOD) circuit for monitoring 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 should be interpreted as V BOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
Table 8-2.
BODLEVEL Fuse Coding(1)
BODLEVEL [2..0] Fuses
Min VBOT
111
Max VBOT
Units
BOD Disabled
110
1.7
1.8
2.0
101
2.5
2.7
2.9
100
4.0
4.3
4.6
2.3
(2)
010
2.2
(2)
001
1.9(2)
000
2.0(2)
011
Note:
Typ VBOT
V
1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guarantees that a Brown-out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed.
2. Centered value, not tested.
Table 8-3.
Symbol
Brown-out Characteristics
Parameter
VRAM
RAM Retention Voltage
VHYST
tBOD
Notes:
Min
(1)
Typ
Max
Units
50
mV
Brown-out Detector Hysteresis
50
mV
Min Pulse Width on Brown-out Reset
2
µs
1. This is the limit to which VDD can be lowered without losing RAM data
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
(V BOT+ 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 V CC if the voltage stays below the trigger level for
longer than tBOD given in Table 8-1.
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ATtiny25/45/85 Auto
Figure 8-5.
Brown-out Reset During Operation
VCC
VBOT+
VBOT-
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
8.0.6
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
page 40 for details on operation of the Watchdog Timer.
Figure 8-6.
Watchdog Reset During Operation
CC
CK
8.0.7
MCU Status Register – MCUSR
The MCU Status Register provides information on which reset source caused an MCU Reset.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
MCUSR
See Bit Description
• Bits 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• 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 Power-on Reset, or by writing a
logic zero to the flag.
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7598D–AVR–02/07
• 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 occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and then reset
the MCUSR as early as possible in the program. If the register is cleared before another reset
occurs, the source of the reset can be found by examining the Reset Flags.
8.1
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.
8.1.1
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 8-4. 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).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three
conditions above to ensure that the reference is turned off before entering Power-down mode.
Table 8-4.
Symbol
8.2
Internal Voltage Reference Characteristics
Parameter
Condition
Min
Typ
Max
Units
VCC = 1.1V / 2.7V,
TA = 25°C
1.0
1.1
1.2
V
70
µs
VBG
Bandgap reference voltage
tBG
Bandgap reference start-up time
VCC = 2.7V,
TA = 25°C
40
IBG
Bandgap reference current
consumption
VCC = 2.7V,
TA = 25°C
15
µA
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
8-7 on page 43. The WDR – Watchdog Reset – instruction resets the Watchdog Timer. The
Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs. Ten different
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 Vector. For timing details on the Watchdog Reset, refer to Table 8-7 on page 43.
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.
40
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period,
two different safety levels are selected by the fuse WDTON as shown in Table 8-5. Refer to
“Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 44 for
details.
Table 8-5.
WDT Configuration as a Function of the Fuse Settings of WDTON
Safety
Level
WDTON
WDT Initial
State
How to Disable the
WDT
How to Change Timeout
Unprogrammed
1
Disabled
Timed sequence
No limitations
Programmed
2
Enabled
Always enabled
Timed sequence
Watchdog Timer
OSC/512K
OSC/1024K
OSC/256K
OSC/64K
OSC/8K
OSC/16K
OSC/4K
OSC/2K
WATCHDOG
RESET
OSC/128K
WATCHDOG
PRESCALER
128 kHz
OSCILLATOR
OSC/32K
Figure 8-7.
WDP0
WDP1
WDP2
WDP3
WDE
MCU RESET
8.2.1
Watchdog Timer Control Register – WDTCR
Bit
7
6
5
4
3
2
1
0
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
0
0
0
WDTCR
• 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 configured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt
handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in
SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.
• Bit 6 – WDIE: Watchdog Timeout Interrupt Enable
When this bit is written to one, WDE is cleared, and the I-bit in the Status Register is set, the
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 hardware when a time-out occurs. This is useful
for keeping the Watchdog Reset security while using the interrupt. After the WDIE bit is cleared,
41
7598D–AVR–02/07
the next time-out will generate a reset. To avoid the Watchdog Reset, WDIE must be set after
each interrupt.
Table 8-6.
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
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not
be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the
description of the WDE bit for a Watchdog disable procedure. This bit must also be set when
changing the prescaler bits. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 44.
• 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 Watchdog Timer function is disabled. WDE can only be cleared if the 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 written to WDE even though it is set to one before 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 44.
In safety level 1, WDE is overridden by WDRF in MCUSR. See “MCU Status Register –
MCUSR” on page 39 for description of WDRF. This means that 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 runaway pointer or brown-out condition, the device will be reset, which
in turn 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 – WDP3..0: Watchdog Timer Prescaler 3, 2, 1, and 0
42
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
The WDP3..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 8-7.
Watchdog Timer Prescale Select
Table 8-7.
WDP3
WDP2
WDP1
WDP0
Number of WDT Oscillator
Cycles
Typical Time-out at
VCC = 5.0V
0
0
0
0
2K cycles
16 ms
0
0
0
1
4K cycles
32 ms
0
0
1
0
8K cycles
64 ms
0
0
1
1
16K cycles
0.125 s
0
1
0
0
32K cycles
0.25 s
0
1
0
1
64K cycles
0.5 s
0
1
1
0
128K cycles
1.0 s
0
1
1
1
256K cycles
2.0 s
1
0
0
0
512K cycles
4.0 s
1
0
0
1
1024K cycles
8.0 s
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
Reserved
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7598D–AVR–02/07
The following code example shows one assembly and one C function for turning off the WDT.
The example assumes that interrupts are controlled (e.g., by disabling interrupts globally) so that
no interrupts will occur during execution of these functions.
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;
}
Note:
8.3
1. The example code assumes that the part specific header file is included.
Timed Sequences for Changing the Configuration of the Watchdog Timer
The sequence for changing configuration differs slightly between the two safety levels. Separate
procedures are described for each level.
8.3.1
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 Watchdog Timer. 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 written to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits
as desired, but with the WDCE bit cleared.
44
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
8.3.2
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 the same operation, write the WDP bits as desired,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
9. Interrupts
This section describes the specifics of the interrupt handling as performed in ATtiny25/45/85.
For a general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling”
on page 11.
9.1
Interrupt Vectors in ATtiny25/45/85
Table 9-1.
Reset and Interrupt Vectors
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
TIM1_COMPA
Timer/Counter1 Compare Match A
5
0x0004
TIM1_OVF
Timer/Counter1 Overflow
6
0x0005
TIM0_OVF
Timer/Counter0 Overflow
7
0x0006
EE_RDY
EEPROM Ready
8
0x0007
ANA_COMP
Analog Comparator
9
0x0008
ADC
ADC Conversion Complete
10
0x0009
TIM1_COMPB
Timer/Counter1 Compare Match B
11
0x000A
TIM0_COMPA
Timer/Counter0 Compare Match A
12
0x000B
TIM0_COMPB
Timer/Counter0 Compare Match B
13
0x000C
WDT
Watchdog Time-out
14
0x000D
USI_START
USI START
15
0x000E
USI_OVF
USI Overflow
If the program never enables an interrupt source, the Interrupt Vectors are not used, and regular
program code can be placed at these locations. The most typical and general program setup for
the Reset and Interrupt Vector Addresses in ATtiny25/45/85 is:
Address Labels Code
Comments
0x0000
rjmp
RESET
; Reset Handler
0x0001
rjmp
EXT_INT0
; IRQ0 Handler
0x0002
rjmp
PCINT0
; PCINT0 Handler
45
7598D–AVR–02/07
0x0003
rjmp
TIM1_COMPA
; Timer1 CompareA Handler
0x0004
rjmp
TIM1_OVF
; Timer1 Overflow Handler
0x0005
rjmp
TIM0_OVF
; Timer0 Overflow Handler
0x0006
rjmp
EE_RDY
; EEPROM Ready Handler
0x0007
rjmp
ANA_COMP
; Analog Comparator Handler
0x0008
rjmp
ADC
; ADC Conversion Handler
0x0009
rjmp
TIM1_COMPB
; Timer1 CompareB Handler
0x000A
rjmp
TIM0_COMPA
;
0x000B
rjmp
TIM0_COMPB
;
0x000C
rjmp
WDT
;
0x000D
rjmp
USI_START
;
0x000E
rjmp
USI_OVF
;
0x000F
RESET: ldi
0x0010
ldi
r17, high(RAMEND); Tiny85 has also SPH
0x0011
out
SPL, r16
; Set Stack Pointer to top of RAM
0x0012
out
SPH, r17
; Tiny85 has also SPH
0x0013
sei
0x0014
...
<instr>
...
r16, low(RAMEND); Main program start
; Enable interrupts
xxx
...
...
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 changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as
input). Each output buffer has symmetrical drive characteristics with both high sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have
protection diodes to both VCC and Ground as indicated in Figure 10-1. Refer to “Electrical Characteristics” on page 156 for a complete list of parameters.
46
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 10-1. I/O Pin Equivalent Schematic
Rpu
Logic
Pxn
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for the port, and a lower case “n” represents the bit number. However,
when using the register or bit defines in a program, the precise form must be used. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description for I/O-Ports” on page 57.
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 corresponding bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables the
pull-up function for all pins in all ports when set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page
47. Most port pins are multiplexed with alternate functions for the peripheral features on the
device. How each alternate function interferes with the port pin is described in “Alternate Port
Functions” on page 52. Refer to the individual module sections for a full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the port as general digital I/O.
10.2
Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 10-2 shows a functional description of one I/O-port pin, here generically called Pxn.
47
7598D–AVR–02/07
Figure 10-2. General Digital I/O(1)
PUD
Q
D
DDxn
Q CLR
WDx
RESET
DATA BUS
RDx
1
Q
Pxn
D
0
PORTxn
Q CLR
RESET
WRx
SLEEP
WPx
RRx
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD:
SLEEP:
clkI/O:
Note:
10.2.1
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description for I/O-Ports” on page 57, the DDxn bits are accessed at the DDRx I/O address, the
PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one,
Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input
pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is
activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to
be configured as an output pin. The port pins are tri-stated when reset condition becomes active,
even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven
high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port
pin is driven low (zero).
10.2.2
48
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.
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
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 acceptable, as a high-impedant environment will not notice the difference between a strong high driver
and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all
pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}
= 0b10) as an intermediate step.
Table 10-1 summarizes the control signals for the pin value.
Table 10-1.
10.2.4
Port Pin Configurations
DDxn
PORTxn
PUD
(in MCUCR)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output Low (Sink)
1
1
X
Output
No
Output High (Source)
Comment
Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 10-2, the PINxn Register bit and the preceding latch constitute a synchronizer. This is needed to avoid metastability if the physical pin changes value
near the edge of the internal clock, but it also introduces a delay. Figure 10-3 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and
minimum propagation delays are denoted tpd,max and tpd,min respectively.
Figure 10-3. Synchronization when Reading an Externally Applied Pin value
SYSTEM CLK
INSTRUCTIONS
XXX
XXX
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd, max
t pd, min
49
7598D–AVR–02/07
Consider the clock period starting shortly after the first falling edge of the system clock. The latch
is closed when the clock is low, and goes transparent when the clock is high, as indicated by the
shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed
between ½ and 1½ system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 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 Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
0xFF
out PORTx, r16
nop
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
t
0xFF
pd
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 5 as input with a pull-up assigned to port pin 4. The resulting pin values
are read back again, but as previously discussed, a nop instruction is included to be able to read
back the value recently assigned to some of the pins.
50
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
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
...
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;
...
Note:
10.2.5
1. For the assembly program, two temporary registers are used to minimize the time from pullups 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.
Digital Input Enable and Sleep Modes
As shown in Figure 10-2, the digital input signal can be clamped to ground at the input of the
schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down mode, Power-save mode, and Standby mode to avoid high power consumption if
some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt
request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various
other alternate functions as described in “Alternate Port Functions” on page 52.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as
“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from the
above mentioned Sleep mode, as the clamping in these sleep mode produces the requested
logic change.
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7598D–AVR–02/07
10.2.6
Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even
though most of the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset is
important, it is recommended to use an external pull-up or pulldown. Connecting unused pins
directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is
accidentally configured as an output.
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 port pin control signals from the simplified Figure 10-2 can be overridden by
alternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
Figure 10-5. Alternate Port Functions(1)
PUOExn
PUOVxn
1
PUD
0
DDOExn
DDOVxn
1
Q
D
DDxn
0
Q CLR
WDx
PVOExn
RESET
RDx
1
DATA BUS
PVOVxn
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
WPx
RESET
DIEOVxn
WRx
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
Q
D
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
52
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP CONTROL
Pxn, PORT TOGGLE OVERRIDE ENABLE
PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clkI/O:
DIxn:
AIOxn:
PULLUP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
ATtiny25/45/85 Auto
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ATtiny25/45/85 Auto
Note:
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.
Table 10-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 10-5 are not shown in the succeeding tables. The overriding signals are generated internally
in the modules having the alternate function.
Table 10-2.
Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
PUOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, PUD} = 0b010.
PUOV
Pull-up Override
Value
If PUOE is set, the pull-up is enabled/disabled when PUOV is
set/cleared, regardless of the setting of the DDxn, PORTxn,
and PUD Register bits.
DDOE
Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled by the
DDOV signal. If this signal is cleared, the Output driver is
enabled by the DDxn Register bit.
DDOV
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled when
DDOV is set/cleared, regardless of the setting of the DDxn
Register bit.
PVOE
Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the port
value is controlled by the PVOV signal. If PVOE is cleared, and
the Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.
PVOV
Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless of the
setting of the PORTxn Register bit.
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 alternate function will use its
own synchronizer.
AIO
Analog
Input/Output
This is the Analog Input/Output to/from alternate functions. The
signal is connected directly to the pad, and can be used bidirectionally.
The following subsections shortly 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.
10.3.1
MCU Control Register – MCUCR
Bit
7
6
5
4
3
2
1
0
–
PUD
SE
SM1
SM0
–
ISC01
ISC00
MCUCR
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Read/Write
R
R/W
R/W
R/W
R/W
R
R
R
Initial Value
0
0
0
0
0
0
0
0
• Bits 7, 2– Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 6 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Configuring the Pin” on page 48 for more details about this feature.
10.3.2
Alternate Functions of Port B
The Port B pins with alternate function are shown in Table 10-3.
Table 10-3.
Port B Pins Alternate Functions
Port Pin
Notes:
Alternate Function
PB5
RESET / dW / ADC0 / PCINT5(1)
PB4
XTAL2 / CLKO / ADC2 / OC1B / PCINT4(2)
PB3
XTAL1 / ADC3 / OC1B / PCINT3(3)
PB2
SCK / ADC1 / T0 / USCK / SCL / INT0 / PCINT2(4)
PB1
MISO / AIN1 / OC0B / OC1A / DO / PCINT1(5)
PB0
MOSI / AIN0 / OC0A / OC1A / DI / SDA / AREF / PCINT0(6)
1. Reset Pin, debugWIRE I/O, ADC Input Channel or Pin Change Interrupt.
2. XOSC Output, Divided System Clock Output, ADC Input Channel, Timer/Counter1 Output
Compare and PWM Output B, or Pin Change Interrupt.
3. XOSC Input / External Clock Input, ADC Input Channel, Timer/Counter1 Inverted Output Compare and PWM Output B, or Pin Change Interrupt.
4. Serial Clock Input, ADC Input Channel, Timer/Counter Clock Input, USI Clock (three-wire
mode), USI Clock (two-wire mode), External Interrupt, or Pin Change Interrupt.
5. Serial Data Input, Analog Comparator Negative Input, Timer/Counter0 Output Compare and
PWM Output B, Timer/Counter1 Output Compare and PWM Output A, USI Data Output (threewire mode), or Pin Change Interrupt.
6. Serial Data Output, Analog Comparator Positive Input, Timer/Counter0 Output Compare and
PWM Output A, Timer/Counter1 Inverted Output Compare and PWM Output A, USI Data Input
(three-wire mode), USI Data (two-wire mode), Voltage Ref., or Pin Change Interrupt.
• 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 activated and output driver and digital input are 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 (open-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.
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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 external clock. When used as a clock pin, the pin can not be used
as an I/O pin. When using internal calibratable RC Oscillator or External clock as a Chip clock
sources, PB4 serves as an ordinary I/O pin.
CLKO: The devided system clock can be output on the pin PB4. The divided system clock will be
output if the CKOUT Fuse is programmed, regardless of the PORTB4 and DDB4 settings. 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 Compare Match B when configured as an output (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/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.
ADC3: Analog to Digital Converter, Channel 3.
OC1B: Inverted 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, Slave Clock input pin for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB2. When the SPI is
enabled as a Master, the data direction of this pin is controlled 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, Slave Data output pin for SPI channel. When the SPI is enabled as a
Master, this pin is configured as an input regardless of the setting of DDB1. When the 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.
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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 set
(one)) to serve this function. The OC0B pin is also the output pin for the PWM mode timer
function.
OC1A: Output Compare Match output: The PB1 pin can serve as an external output for the
Timer/Counter1 Compare Match B when configured as an output (DDB1 set). The OC1A pin is
also the output pin for the PWM mode timer function.
DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output overrides PORTB1 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 output, Slave Data input for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of 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 Comparator Positive Input. Configure the port pin as input with the internal pull-up
switched off to avoid the digital port function from interfering with the function of the Analog
Comparator.
OC0A: Output Compare Match output. The PB0 pin can serve as an external output for the
Timer/Counter0 Compare Match A when configured as an output (DDB0 set (one)). The OC0A
pin is also the output pin for the PWM mode timer function.
OC1A: Inverted 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 mode Serial Interface Data.
AREF: External Analog Reference for ADC. Pullup and output driver are disabled 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.
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ATtiny25/45/85 Auto
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 52.
Table 10-4.
Overriding Signals for Alternate Functions in PB5..PB3
Signal
Name
PB5/RESET/
ADC0/PCINT5
PB4/ADC2/XTAL2/
OC1B/PCINT4
PB3/ADC3/XTAL1/
_OC1B/PCINT3
PUOE
RSTDISBL(1) • DWEN(1)
0
0
PUOV
1
0
0
0
0
(1)
(1)
DDOE
RSTDISBL
• DWEN
DDOV
debugWire Transmit
0
0
PVOE
0
OC1B Enable
_OC1B Enable
PVOV
0
OC1B
_OC1B
PTOE
0
0
0
(1)
DIEOE
RSTDISBL + (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
Note:
1. 1 when the Fuse is “0” (Programmed).
Table 10-5.
10.4
Overriding Signals for Alternate Functions in PB3..PB0
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
0
0
0
PUOV
0
0
0
DDOE
USI_TWO_WIRE
0
USI_TWO_WIRE
DDOV
(USI_SCL_HOLD +
PORTB2) • DDB2
0
(SDA + PORTD) • DDRB0
PVOE
USI_TWO_WIRE • DDRB2
OC0B Enable + OC1A
Enable +
USI_THREE_WIRE
OC0A Enable + _OC1A
Enable + (USI_TWO_WIRE
• DDRB0)
PVOV
0
OC0B + OC1A + DO
OC0A + _OC1A
PTOE
USI_PTOE
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
Register Description for I/O-Ports
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10.4.1
Port B Data Register – PORTB
Bit
10.4.2
7
6
5
4
3
2
1
0
–
–
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
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
Port B Data Direction Register – DDRB
Bit
10.4.3
PORTB
7
6
5
4
3
2
1
0
–
–
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
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
DDRB
Port B Input Pins Address – PINB
Bit
7
6
5
4
3
2
1
0
–
–
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
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
PINB
11. External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT5..0 pins. Observe that,
if enabled, the interrupts will trigger even if the INT0 or PCINT5..0 pins are configured as outputs. This feature provides a way of generating a software interrupt. Pin change interrupts PCI
will trigger if any enabled PCINT5..0 pin toggles. The PCMSK Register control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT5..0 are detected
asynchronously. This implies that these interrupts can be used for waking the part also from
sleep 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 21. 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 mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the required level
must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If
the level disappears before the end of the Start-up Time, the MCU will still wake up, but no interrupt 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 21.
11.0.1
MCU Control Register – MCUCR
The External Interrupt Control Register A contains control bits for interrupt sense control.
Bit
7
6
5
4
3
2
1
0
–
PUD
SE
SM1
SM0
–
ISC01
ISC00
Read/Write
R
R/W
R/W
R/W
R/W
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bits 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
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ATtiny25/45/85 Auto
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt are defined in Table 11-1. The value on the INT0 pin is sampled before detecting
edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will
generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level
interrupt is selected, the low level must be held until the completion of the currently executing
instruction to generate an interrupt.
Table 11-1.
11.0.2
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.
General Interrupt Mask Register – GIMSK
Bit
7
6
5
4
3
2
1
0
–
INT0
PCIE
–
–
–
–
–
Read/Write
R
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIMSK
• Bits 7, 4..0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 6 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU
Control Register (MCUCR) define whether the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even
if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is
executed from the INT0 Interrupt Vector.
• 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 PCINT5..0 pin will cause an
interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from
the PCI Interrupt Vector. PCINT5..0 pins are enabled individually by the PCMSK0 Register.
11.0.3
General Interrupt Flag Register – GIFR
Bit
7
6
5
4
3
2
1
0
–
INTF0
PCIF
–
–
–
–
–
Read/Write
R
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIFR
• Bits 7, 4..0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 6 – INTF0: External Interrupt Flag 0
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When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set
(one). If the I-bit in SREG and the INT0 bit in GIMSK are set (one), the MCU will jump to the corresponding 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 PCINT5..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 corresponding 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.
11.0.4
Pin Change Mask Register – PCMSK
Bit
7
6
5
4
3
2
1
0
–
–
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
1
1
1
1
1
1
PCMSK
• Bits 7, 6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 5..0 – PCINT5..0: Pin Change Enable Mask 5..0
Each PCINT5..0 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT5..0 is set and the PCIE bit in GIMSK is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT5..0 is cleared, pin change interrupt on the corresponding I/O pin
is disabled.
12. 8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and with PWM support. It allows accurate program execution timing (event management) and wave generation. The main features are:
•
•
•
•
•
•
•
12.1
Two Independent Output 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)
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 12-1. For the actual
placement of I/O pins, refer to “Pinout ATtiny25/45/85” on page 2. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “8-bit Timer/Counter Register Description” on page 71.
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ATtiny25/45/85 Auto
Figure 12-1. 8-bit Timer/Counter Block Diagram
Count
Clear
Direction
TOVn
(Int.Req.)
Control Logic
clkTn
Clock Select
Edge
Detector
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCnA
DATA BUS
OCRnA
Fixed
TOP
Value
Waveform
Generation
=
OCnB
OCRnB
TCCRnA
12.1.1
OCnB
(Int.Req.)
TCCRnB
Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the
Timer Interrupt Flag Register (TIFR). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and TIMSK are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (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 Compare 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 Generator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and
OC0B). See “Output Compare Unit” on page 63. for details. The Compare Match event will also
set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compare
interrupt request.
12.1.2
Definitions
Many register and bit references 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 Compare 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/Counter0 counter value and so on.
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The definitions in Table 34 are also used extensively throughout the document.
12.2
BOTTOM
The counter reaches the 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
fixed value 0xFF (MAX) or the value stored in the OCR0A Register. The
assignment is dependent on the mode of operation.
Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and prescaler, see “Timer/Counter Prescaler” on page 77.
12.3
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
12-2 shows a block diagram of the counter and its surroundings.
Figure 12-2. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
count
clear
TCNTn
Control Logic
clkTn
Edge
Detector
Tn
direction
( From Prescaler )
bottom
top
Signal description (internal signals):
count
Increment or decrement TCNT0 by 1.
direction
Select between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT0 in the following.
top
Signalize that TCNT0 has reached maximum value.
bottom
Signalize that TCNT0 has reached minimum value (zero).
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 internal clock source,
selected by the Clock Select bits (CS02:0). When no clock source is selected (CS02:0 = 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
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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 Operation” on page 65.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by
the WGM01:0 bits. TOV0 can be used for generating a CPU interrupt.
12.4
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers
(OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a
match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock
cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output
Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. 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 mode set by the WGM02:0 bits and Compare Output mode (COM0x1:0) 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 65.).
Figure 12-3 shows a block diagram of the Output Compare unit.
Figure 12-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator )
OCFnx (Int.Req.)
top
bottom
Waveform Generator
OCnx
FOCn
WGMn1:0
COMnX1:0
The OCR0x Registers are double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR0x Compare
Registers to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
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The OCR0x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR0x Buffer Register, and if double buffering is disabled the CPU will access the OCR0x directly.
12.4.1
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 COM0x1:0 bits settings define whether the OC0x pin is set, cleared or
toggled).
12.4.2
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 initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.
12.4.3
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 whether the Timer/Counter is running or not. If the value written to TCNT0
equals the OCR0x value, the Compare Match will be missed, resulting in incorrect waveform
generation. 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 Compare (FOC0x) strobe bits in Normal mode. The OC0x Registers keep their values even when
changing between Waveform Generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value.
Changing the COM0x1:0 bits will take effect immediately.
12.5
Compare Match Output Unit
The Compare Output mode (COM0x1:0) bits have two functions. The Waveform Generator uses
the COM0x1:0 bits for defining the Output Compare (OC0x) state at the next Compare Match.
Also, the COM0x1:0 bits control the OC0x pin output source. Figure 12-4 shows a simplified
schematic of the logic affected by the COM0x1:0 bit setting. The I/O Registers, I/O bits, and I/O
pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers
(DDR and PORT) that are affected by the COM0x1:0 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 12-4. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCn
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform
Generator if either of the COM0x1:0 bits are set. However, the OC0x pin direction (input or output) 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 visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0x state before the output is enabled. Note that some COM0x1:0 bit settings are reserved for certain modes of
operation. See “8-bit Timer/Counter Register Description” on page 71.
12.5.1
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0x1:0 bits differently in Normal, CTC, and PWM modes.
For all modes, setting the COM0x1:0 = 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 non-PWM modes refer to Table 12-1 on page 72. For fast PWM mode, refer to Table 12-2 on
page 72, and for phase correct PWM refer to Table 12-3 on page 72.
A change of the COM0x1:0 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.
12.6
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGM02:0) and Compare Output
mode (COM0x1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM0x1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM0x1:0 bits control whether the output should be set, cleared, or toggled at a Compare
Match (See “Compare Match Output Unit” on page 64.).
For detailed timing information refer to Figure 12-8, Figure 12-9, Figure 12-10 and Figure 12-11
in “Timer/Counter Timing Diagrams” on page 70.
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12.6.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM02:0 = 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 bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the same
timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that 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 Compare Unit can be used to generate interrupts at some given time. Using the Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
12.6.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used to
manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter
value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter, hence
also its resolution. This mode allows greater control of the Compare Match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 12-5. The counter value (TCNT0)
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 12-5. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCn
(Toggle)
Period
(COMnx1:0 = 1)
1
2
3
4
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 running with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can
occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical
level on each Compare Match by setting the Compare Output mode bits to toggle mode
(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction for
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the pin is set to output. The waveform generated will have a maximum frequency of f OC0 =
fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following
equation:
f clk_I/O
f OCnx = -------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnx )
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
12.6.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency 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 BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the Compare 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 dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore 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 12-6. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x and TCNT0.
Figure 12-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCn
(COMnx1:0 = 2)
OCn
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
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In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins.
Setting the COM0x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM0x1:0 to three: Setting the COM0A1:0 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 (See Table 12-2 on page 72). The actual OC0x value will only be visible 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:
f clk_I/O
f OCnxPWM = -----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating a PWM
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 (depending on the polarity of the output set by the COM0A1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical level on each Compare Match (COM0x1:0 = 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 Output Compare unit is enabled in the fast PWM mode.
12.6.4
Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 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 counter counts repeatedly from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the Compare Match
between TCNT0 and OCR0x while upcounting, and set on the Compare Match while downcounting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation
has lower maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP.
When the counter reaches TOP, it changes the count direction. The TCNT0 value will be equal
to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown
on Figure 12-7. 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.
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Figure 12-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCn
(COMnx1:0 = 2)
OCn
(COMnx1:0 = 3)
Period
1
2
3
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches 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 COM0x1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0x1:0 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
not available for the OC0B pin (See Table 12-3 on page 72). The actual OC0x value will only be
visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is
generated by clearing (or setting) the OC0x Register at the Compare Match between OCR0x
and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at Compare Match between OCR0x and TCNT0 when the counter decrements. The PWM frequency for
the output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = -----------------N ⋅ 510
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, 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 12-7 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 BOTTOM. There are two cases that give a transition without Compare Match.
• OCR0A changes its value from MAX, like in Figure 12-7. When the OCR0A value is MAX the
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
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symmetry around BOTTOM the OCn value at MAX must correspond to the result of an upcounting Compare Match.
• The timer starts counting from a value 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.
12.7
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set. Figure 12-8 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 12-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 12-9 shows the same timing data, but with the prescaler enabled.
Figure 12-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 12-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC
mode and PWM mode, where OCR0A is TOP.
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Figure 12-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
OCRnx - 1
TCNTn
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCRnx
OCFnx
Figure 12-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast
PWM mode where OCR0A is TOP.
Figure 12-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
TOP - 1
TOP
BOTTOM
OCRnx
BOTTOM + 1
TOP
OCFnx
12.8
8-bit Timer/Counter Register Description
12.8.1
Timer/Counter Control Register A – TCCR0A
Bit
7
6
5
4
3
2
1
0
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
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
TCCR0A
• Bits 7:6 – COM01A:0: Compare Match Output A Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A1:0
bits are set, the OC0A output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0A pin
must be set in order to enable the output driver.
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When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM02:0 bit setting. Table 12-1 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 12-1.
Compare Output Mode, non-PWM Mode
COM01
COM00
Description
0
0
Normal port operation, OC0A disconnected.
0
1
Toggle OC0A on Compare Match
1
0
Clear OC0A on Compare Match
1
1
Set OC0A on Compare Match
Table 12-2 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Table 12-2.
Compare Output Mode, Fast PWM Mode(1)
COM01
COM00
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match, set OC0A at TOP
1
1
Set OC0A on Compare Match, clear OC0A at TOP
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 67
for more details.
Table 12-3 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 12-3.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.
1
1
Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 68 for more details.
• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
These bits control the Output Compare pin (OC0B) behavior. If one or both of the COM0B1:0
bits are set, the OC0B output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0B pin
must be set in order to enable the output driver.
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When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the
WGM02:0 bit setting. Table 12-1 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 12-4.
Compare Output Mode, non-PWM Mode
COM01
COM00
Description
0
0
Normal port operation, OC0B disconnected.
0
1
Toggle OC0B on Compare Match
1
0
Clear OC0B on Compare Match
1
1
Set OC0B on Compare Match
Table 12-2 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM
mode.
Table 12-5.
Compare Output Mode, Fast PWM Mode(1)
COM01
COM00
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match, set OC0B at TOP
1
1
Set OC0B on Compare Match, clear OC0B at TOP
Note:
Description
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 67
for more details.
Table 12-3 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 12-6.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.
1
1
Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.
Note:
Description
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 68 for more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 1:0 – WGM01:0: 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 waveform generation to be used, see Table 12-7. Modes of operation supported by the Timer/Counter
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unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode, and two types of
Pulse Width Modulation (PWM) modes (see “Modes of Operation” on page 65).
Waveform Generation Mode Bit Description
Table 12-7.
Timer/Counter
Mode of
Operation
TOP
Update of
OCRx at
TOV Flag
Set on(1)(2)
Mode
WGM2
WGM1
WGM0
0
0
0
0
Normal
0xFF
Immediate
MAX
1
0
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
2
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
TOP
MAX
4
1
0
0
Reserved
–
–
–
5
1
0
1
PWM, Phase
Correct
OCRA
TOP
BOTTOM
6
1
1
0
Reserved
–
–
–
7
1
1
1
Fast PWM
OCRA
TOP
TOP
Notes:
1. MAX
= 0xFF
2. BOTTOM = 0x00
12.8.2
Timer/Counter Control Register B – TCCR0B
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
Read/Write
W
W
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0B
• 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 according to its COM0A1:0 bits setting. Note that the FOC0A bit is implemented as a
strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the
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 according to its COM0B1:0 bits setting. Note that the FOC0B bit is implemented as a
74
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the
forced compare.
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 reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR0A” on page 71.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Clock Select Bit Description
Table 12-8.
CS02
CS01
CS00
Description
0
0
0
No clock source (Timer/Counter stopped)
0
0
1
clkI/O/(No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/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.
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.
12.8.3
Timer/Counter Register – TCNT0
Bit
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers.
12.8.4
Output Compare Register A – OCR0A
Bit
7
6
5
4
3
2
1
0
OCR0A[7:0]
OCR0A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
75
7598D–AVR–02/07
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0A pin.
12.8.5
Output Compare Register B – OCR0B
Bit
7
6
5
4
3
2
1
0
OCR0B[7:0]
OCR0B
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register B contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0B pin.
12.8.6
Timer/Counter Interrupt Mask Register – TIMSK
Bit
7
6
5
4
3
2
1
0
–
OCIE1A
OCIE1B
OCIE0A
OCIE0B
TOIE1
TOIE0
–
Read/Write
R
R
R
R
R/W
R/W
R/W
R
Initial Value
0
0
0
0
0
0
0
0
TIMSK
• Bits 7..4, 0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• 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 Compare Match B interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter
Interrupt Flag Register – TIFR0.
• Bit 2 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR0.
• 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 the TOV0 bit is set in the Timer/Counter 0 Interrupt Flag Register – TIFR0.
12.8.7
Timer/Counter 0 Interrupt Flag Register – TIFR
Bit
7
6
5
4
3
2
1
0
–
OCF1A
OCF1B
OCF0A
OCF0B
TOV1
TOV0
–
Read/Write
R
R
R
R
R/W
R/W
R/W
R
Initial Value
0
0
0
0
0
0
0
0
TIFR
• Bits 7, 0 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bit 4– OCF0A: Output Compare Flag 0 A
76
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable),
and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
• Bit 3 – OCF0B: Output Compare Flag 0 B
The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in
OCR0B – Output Compare Register0 B. OCF0B is cleared by hardware when executing the corresponding 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 dependent of the WGM02:0 bit setting. Refer to Table 12-7, “Waveform
Generation Mode Bit Description” on page 74.
13. Timer/Counter Prescaler
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency 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.
13.0.1
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/Counter. Since the prescaler is not affected by the Timer/Counter’s clock select, the state
of the prescaler will have implications for situations where a prescaled clock is used. One example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 >
CSn2:0 > 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, where N equals the prescaler divisor (8, 64,
256, or 1024).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program
execution.
13.0.2
External Clock Source
An external clock source applied to the T0 pin can be used as Timer/Counter clock (clkT0). The
T0 pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 13-1 shows a functional
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.
77
7598D–AVR–02/07
The edge detector generates one clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0
= 6) edge it detects.
Figure 13-1. T0 Pin Sampling
D
Tn
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the 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 system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, 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 prescaled.
Figure 13-2. Prescaler for Timer/Counter0
clk I/O
Clear
PSR10
T0
Synchronization
clkT0
Note:
13.0.3
General Timer/Counter Control Register – GTCCR
Bit
78
1. The synchronization logic on the input pins (T0) is shown in Figure 13-1.
7
6
5
4
3
2
1
0
TSM
PWM1B
COM1B1
COM1B0
FOC1B
FOC1A
PSR1
PSR0
GTCCR
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Read/Write
R/W
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the
value that is written to the PSR0 bit 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 configuration. When the TSM bit is written to zero, the PSR0 bit is cleared by
hardware, and the Timer/Counter start counting.
• 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.
14. 8-bit Timer/Counter1
The Timer/Counter1 is a general purpose 8-bit Timer/Counter module that has a separate prescaling selection from the separate prescaler.
Figure 14-1 shows the Timer/Counter1 prescaler that supports two clocking modes, a syncrhonous clocking mode and an asynchronous clocking mode. The 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 asynchronous mode when it is set (‘1’).
Figure 14-1. Timer/Counter1 Prescaler
PSR1
T1CK
T1CK/16384
T1CK/8192
T1CK/4096
T1CK/2048
T1CK/1024
T1CK/512
T1CK/256
T1CK/128
T1CK/64
T1CK/32
T1CK/16
T1CK/8
0
T1CK/4
14-BIT
T/C PRESCALER
T1CK/2
CK
S
PCK 64/32 MHz A
T1CK
PCKE
CS10
CS11
CS12
CS13
TIMER/COUNTER1 COUNT ENABLE
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 14-2 on page 83 and the Timer/Counter1 Control Register, 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 Mode).
79
7598D–AVR–02/07
14.1
Timer/Counter1
The Timer/Counter1 general operation is described in the asynchronous mode and the operation in the synchronous mode is mentioned only if there are differences between these two
modes. Figure 14-2 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, 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 prescaling 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 and the output compare registers serve as dual stand-alone PWMs with nonoverlapping non-inverted and inverted outputs. Refer to page 88 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 14-2. Timer/Counter 1 Synchronization Register Block Diagram.
8-BIT DATABUS
IO-registers
Input synchronization
registers
OCR1A
OCR1A_SI
OCR1B
OCR1B_SI
OCR1C
OCR1C_SI
TCCR1
TCCR1_SI
GTCCR
GTCCR_SI
TCNT1
TCNT1_SI
OCF1A
OCF1A_SI
OCF1B
OCF1B_SI
TOV1
TOV1_SI
Timer/Counter1
Output synchronization
registers
TCNT1
TCNT_SO
OCF1A
OCF1A_SO
TCNT1
OCF1B
OCF1B_SO
TOV1
TOV1_SO
PCKE
CK
S
A
PCK
80
S
A
SYNC
MODE
1/2 CK Delay
1 CK Delay
1/2 CK Delay
No Delay
ASYNC
MODE
~1/2 CK Delay
1 PCK Delay
1/2 PCK - 1 CK Delay
No Delay
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Timer/Counter1 and the prescaler allow running the CPU from any clock source while the prescaler 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 14-3 shows the block diagram for Timer/Counter1.
Figure 14-3. Timer/Counter1 Block Diagram
T/C1 OVER- T/C1 COMPARE T/C1 COMPARE
FLOW IRQ MATCH A IRQ MATCH B IRQ
OC1A
(PB1)
OC1B
(PB4)
OC1A
(PB0)
DEAD TIME GENERATOR
TOV0
PSR1
FOC1B
FOC1A
COM1B0
PWM1B
GLOBAL T/C CONTROL
REGISTER (GTCCR)
COM1B1
CS11
CS10
CS12
CS13
COM1A0
COM1A1
CTC1
TOV1
T/C CONTROL
REGISTER 1 (TCCR1)
PWM1A
OCF1B
TOV1
OCF1A
OCF1A
TIMER INT. FLAG
REGISTER (TIFR)
OCF1B
TOIE1
TOIE0
OCIE1A
OCIE1B
DEAD TIME GENERATOR
TIMER INT. MASK
REGISTER (TIMSK)
OC1B
(PB3)
TIMER/COUNTER1
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
T/C1 CONTROL
LOGIC
8-BIT COMPARATOR
8-BIT COMPARATOR
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
(OCR1A)
T/C1 OUTPUT
COMPARE REGISTER
(OCR1B)
T/C1 OUTPUT
COMPARE REGISTER
(OCR1C)
CK
PCK
8-BIT DATABUS
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 three Output Compare Registers, OCR1A, OCR1B, and OCR1C
as the data source to be compared with the Timer/Counter1 contents. In normal mode the Output Compare functions are operational with all three output compare registers. OCR1A
determines action on the OC1A pin (PB1), and it can generate Timer1 OC1A interrupt in normal
mode and in PWM mode. Likewise, OCR1B determines action on the OC1B pin (PB3) and it can
generate Timer1 OC1B interrupt in normal mode and in PWM mode. OCR1C holds the
Timer/Counter maximum value, i.e. the clear on compare match value. 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 Timer/Counter1 counts either from $FF
81
7598D–AVR–02/07
to $00 or from OCR1C to $00. The inverted PWM outputs OC1A and OC1B are not connected in
normal mode.
In PWM mode, OCR1A and OCR1B provide the data values against which the Timer Counter
value is compared. Upon compare match the PWM outputs (OC1A, OC1A, OC1B, OC1B) are
generated. In PWM mode, the Timer Counter counts up to the value specified in the output compare register OCR1C and starts again from $00. This feature allows limiting the counter “full”
value to a specified value, lower than $FF. Together with the many prescaler options, flexible
PWM frequency selection is provided. Table 14-6 lists clock selection and OCR1C values to
obtain PWM frequencies from 20 kHz to 250 kHz in 10 kHz steps and from 250 kHz to 500 kHz
in 50 kHz steps. Higher PWM frequencies can be obtained at the expense of resolution.
14.1.1
Timer/Counter1 Control Register - TCCR1
Bit
7
6
5
4
3
2
1
0
$30 ($50)
CTC1
PWM1A
COM1A1
COM1A0
CS13
CS12
CS11
CS10
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
TCCR1
• Bit 7- CTC1 : Clear Timer/Counter on Compare Match
When the CTC1 control bit is set (one), Timer/Counter1 is reset to $00 in the CPU clock cycle
after a compare match with OCR1C register value. If the control bit is cleared, Timer/Counter1
continues counting and is unaffected by a compare match.
• Bit 6- PWM1A: Pulse Width Modulator A Enable
When set (one) this bit enables PWM mode based on comparator OCR1A in Timer/Counter1
and the counter value is reset to $00 in the CPU clock cycle after a compare match with OCR1C
register value.
• Bits 5,4 - COM1A1, COM1A0: Comparator A Output Mode, Bits 1 and 0
The COM1A1 and COM1A0 control bits determine any output pin action following a compare
match with compare register A in Timer/Counter1. Output pin actions affect pin PB1 (OC1A).
Since this is an alternative function to an I/O port, the corresponding direction control bit must be
set (one) in order to control an output pin. Note that OC1A is not connected in normal mode.
Table 14-1.
Comparator A Mode Select
COM1A1
COM1A0
Description
0
0
Timer/Counter Comparator A disconnected from output pin OC1A.
0
1
Toggle the OC1A output line.
1
0
Clear the OC1A output line.
1
1
Set the OC1A output line
In PWM mode, these bits have different functions. Refer to Table 14-4 on page 88 for a detailed
description.
• Bits 3 .. 0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0
82
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1.
Table 14-2.
Timer/Counter1 Prescale Select
Asynchronous
Clocking Mode
Synchronous
Clocking Mode
0
T/C1 stopped
T/C1 stopped
0
1
PCK
CK
0
1
0
PCK/2
CK/2
0
0
1
1
PCK/4
CK/4
0
1
0
0
PCK/8
CK/8
0
1
0
1
PCK/16
CK/16
0
1
1
0
PCK/32
CK/32
0
1
1
1
PCK/64
CK/64
1
0
0
0
PCK/128
CK/128
1
0
0
1
PCK/256
CK/256
1
0
1
0
PCK/512
CK/512
1
0
1
1
PCK/1024
CK/1024
1
1
0
0
PCK/2048
CK/2048
1
1
0
1
PCK/4096
CK/4096
1
1
1
0
PCK/8192
CK/8192
1
1
1
1
PCK/16384
CK/16384
CS13
CS12
CS11
CS10
0
0
0
0
0
0
The Stop condition provides a Timer Enable/Disable function.
14.1.2
General Timer/Counter1 Control Register - GTCCR
Bit
7
6
5
4
3
2
1
0
$2C ($4C)
TSM
PWM1B
COM1B1
COM1B0
FOC1B
FOC1A
PSR1
PSR0
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
GTCCR
• Bit 6- PWM1B: Pulse Width Modulator B Enable
When set (one) this bit enables PWM mode based on comparator OCR1B in Timer/Counter1
and the counter value is reset to $00 in the CPU clock cycle after a compare match with OCR1C
register value.
• Bits 5,4 - COM1B1, COM1B0: Comparator B Output Mode, Bits 1 and 0
The COM1B1 and COM1B0 control bits determine any output pin action following a compare
match with compare register B in Timer/Counter1. Output pin actions affect pin PB3 (OC1B).
83
7598D–AVR–02/07
Since this is an alternative function to an I/O port, the corresponding direction control bit must be
set (one) in order to control an output pin. Note that OC1B is not connected in normal mode.
Table 14-3.
Comparator B Mode Select
COM1B1
COM1B0
Description
0
0
Timer/Counter Comparator B disconnected from output pin OC1B.
0
1
Toggle the OC1B output line.
1
0
Clear the OC1B output line.
1
1
Set the OC1B output line
In PWM mode, these bits have different functions. Refer to Table 14-4 on page 88 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 COM1B1 and COM1B0 written
in the same cycle as FOC1B, the new settings will be used. The Force Output Compare bit can
be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1B1 and COM1B0 takes place as if a compare match had occurred, but no
interrupt is generated. The FOC1B bit always reads as zero. FOC1B is not in use if PWM1B bit
is set.
• Bit 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 COM1A1 and COM1A0 written
in the same cycle as FOC1A, the new settings will be used. The Force Output Compare bit can
be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1A1 and COM1A0 takes place as if a compare match had occurred, but no
interrupt is generated. The FOC1A bit always reads as zero. FOC1A is not in use if PWM1A bit
is set.
• Bit 1- PSR1 : Prescaler Reset Timer/Counter1
When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffected) 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.
14.1.3
Timer/Counter1 - TCNT1
Bit
7
6
5
4
3
2
1
0
$2F ($4F)
MSB
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
LSB
TCNT1
This 8-bit register contains the value of Timer/Counter1.
Timer/Counter1 is realized as an up counter with read and write access. Due to synchronization
of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one and half CPU
clock cycles in synchronous mode and at most one CPU clock cycles for asynchronous mode.
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ATtiny25/45/85 Auto
14.1.4
Timer/Counter1 Output Compare RegisterA - OCR1A
Bit
7
6
5
4
3
2
1
0
$2E ($4E)
MSB
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
LSB
OCR1A
The output compare register A is an 8-bit read/write register.
The Timer/Counter Output Compare Register A contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in 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 following the compare event.
14.1.5
Timer/Counter1 Output Compare RegisterB - OCR1B
Bit
7
6
5
4
3
2
1
0
$2D ($4D)
MSB
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
LSB
OCR1B
The output compare register B is an 8-bit read/write register.
The Timer/Counter Output Compare Register B contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in 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 following the compare event.
14.1.6
Timer/Counter1 Output Compare RegisterC - OCR1C
Bit
7
6
5
4
3
2
1
0
$2B ($4B)
MSB
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
LSB
OCR1C
The output compare register C is an 8-bit read/write register.
The Timer/Counter Output Compare Register C contains data to be continuously compared with
Timer/Counter1. A compare match does only occur if Timer/Counter1 counts to the OCR1C
value. A software write that sets TCNT1 and OCR1C to the same value does not generate a
compare match. If the CTC1 bit in TCCR1 is set, a compare match will clear TCNT1.
This register has the same function in normal mode and PWM mode.
14.1.7
Timer/Counter Interrupt Mask Register - TIMSK
Bit
7
6
5
4
3
2
1
$39 ($59)
-
OCIE1A
OCIE1B
OCIE0A
OCIE0B
TOIE1
TOIE0
0
-
Read/Write
R
R/W
R/W
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0
0
TIMSK
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• 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/Counter1 Compare MatchA, interrupt is enabled. The corresponding interrupt at vector
$003 is executed if a compare matchA occurs. The Compare Flag in Timer/Counter1 is set (one)
in the Timer/Counter Interrupt Flag Register.
• Bit 5 - OCIE1B: Timer/Counter1 Output Compare Interrupt Enable
When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare MatchB, interrupt is enabled. The corresponding interrupt at vector
$009 is executed if a compare matchB occurs. The Compare Flag in Timer/Counter1 is set (one)
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 Overflow interrupt is enabled. The corresponding interrupt (at vector $004) is
executed if an overflow in Timer/Counter1 occurs. The Overflow Flag (Timer1) is set (one) in the
Timer/Counter Interrupt Flag Register - TIFR.
• Bit 0 - Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
14.1.8
Timer/Counter Interrupt Flag Register - TIFR
Bit
7
6
5
4
3
2
1
$38 ($58)
-
OCF1A
OCF1B
OCF0A
OCF0B
TOV1
TOV0
0
-
Read/Write
R
R/W
R/W
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0
0
TIFR
• Bit 7 - Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
• Bit 6 - OCF1A: Output Compare Flag 1A
The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1A - Output Compare Register 1A. OCF1A is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1A, and OCF1A
are set (one), the Timer/Counter1 A compare match interrupt is executed.
• Bit 5 - OCF1B: Output Compare Flag 1B
The OCF1B bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1B - Output Compare Register 1A. OCF1B is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1B is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1B, and OCF1B
are set (one), the Timer/Counter1 B compare match interrupt is executed.
• Bit 2 - TOV1: Timer/Counter1 Overflow Flag
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ATtiny25/45/85 Auto
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 vector. 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 - Output Compare Register 1C.
Clearing the Timer/Counter1 with the bit CTC1 does not generate an overflow.
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.
14.1.9
PLL Control and Status Register - PLLCSR
Bit
7
6
5
4
3
2
1
0
LSM
-
-
-
-
PCKE
PLLE
PLOCK
Read/Write
R
R
R
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0/1
0
$27 ($27)
PLLCSR
• 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 fast enough on low voltage levels. It is highly recommended that Timer/Counter1 is stopped whenever the LSM bit is changed.
• 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. The bit PCKE can
only be set, if the PLL has been 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, and it is safe to enable PCK
for Timer/Counter1. After the PLL is enabled, it takes about 100 micro seconds for the PLL to
lock.
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14.1.10
Timer/Counter1 Initialization for Asynchronous Mode
To change Timer/Counter1 to the asynchronous mode, first enable PLL, and poll the PLOCK bit
until it is set, and then set the PCKE bit.
14.1.11
Timer/Counter1 in PWM Mode
When the PWM mode is selected, Timer/Counter1 and the Output Compare Register C OCR1C form a dual 8-bit, free-running and glitch-free PWM generator with outputs on the
PB1(OC1A) and PB3(OC1B) pins and inverted outputs on pins PB0(OC1A) and PB2(OC1B). As
default non-overlapping times for complementary output pairs are zero, but they can be inserted
using a Dead Time Generator (see description on page 100).
Figure 14-4. The PWM Output Pair
PWM1x
PWM1x
t non-overlap =0
t non-overlap =0
x = A or B
When the counter value match the contents of OCR1A or OCR1B, the OC1A and OC1B outputs
are set or cleared according to the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the
Timer/Counter1 Control Register A - TCCR1, as shown in Table 14-4.
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.
Table 14-4.
Compare Mode Select in PWM Mode
COM11
COM10
Effect on Output Compare Pins
0
0
OC1x not connected.
OC1x not connected.
0
1
OC1x cleared on compare match. Set whenTCNT1 = $01.
OC1x set on compare match. Cleared when TCNT1 = $00.
1
0
OC1x cleared on compare match. Set when TCNT1 = $01.
OC1x not connected.
1
1
OC1x Set on compare match. Cleared when TCNT1= $01.
OC1x not connected.
Note that in PWM mode, writing to the Output Compare Registers OCR1A or OCR1B, the data
value is first transferred to a temporary location. The value is latched into OCR1A or OCR1B
when the Timer/Counter reaches OCR1C. This prevents the occurrence of odd-length PWM
pulses (glitches) in the event of an unsynchronized OCR1A or OCR1B. See Figure 14-5 for an
example.
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ATtiny25/45/85 Auto
Figure 14-5. Effects of Unsynchronized OCR Latching
Compare Value changes
Counter Value
Compare Value
PWM Output OC1x
Synchronized OC1x Latch
Compare Value changes
Counter Value
Compare Value
PWM Output OC1x
Glitch
Unsynchronized OC1x Latch
During the time between the write and the latch operation, a read from OCR1A or OCR1B will
read the contents of the temporary location. This means that the most recently written value
always will read out of OCR1A or OCR1B.
When OCR1A or OCR1B contain $00 or the top value, as specified in OCR1C register, the output PB1(OC1A) or PB3(OC1B) is held low or high according to the settings of
COM1A1/COM1A0. This is shown in Table 14-5.
Table 14-5.
PWM Outputs OCR1x = $00 or OCR1C, x = A or B
COM1x1
COM1x0
OCR1x
Output OC1x
Output OC1x
0
1
$00
L
H
0
1
OCR1C
H
L
1
0
$00
L
Not connected.
1
0
OCR1C
H
Not connected.
1
1
$00
H
Not connected.
1
1
OCR1C
L
Not connected.
In PWM mode, the Timer Overflow Flag - TOV1 is set 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 Timer Overflow Interrupt and global interrupts are enabled. This also applies to
the Timer Output Compare flags and interrupts.
The frequency of the PWM will be Timer Clock 1 Frequency divided by (OCR1C value + 1). See
the following equation:
f TCK1
f PWM = -----------------------------------( OCR1C + 1 )
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7598D–AVR–02/07
Resolution shows how many bit is required to express the value in the OCR1C register. It is calculated by following equation
ResolutionPWM = log2(OCR1C + 1).
Table 14-6.
Timer/Counter1 Clock Prescale Select in the Asynchronous Mode
PWM Frequency
Clock Selection
CS13..CS10
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
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
15. 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 Timer/Counter1 is working in normal mode). When selected the
ATtiny15 compatibility mode provides an ATtiny15 backward compatible prescaler and
Timer/Counter. Furthermore, the clocking system has same clock frequencies as in ATtiny15.
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ATtiny25/45/85 Auto
15.1
Timer/Counter1 Prescaler
Figure 15-1 shows an ATtiny15 compatible prescaler. It has two prescaler units, the 3-bit prescaler for the the system clock (CK) and the 10-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 15-1. Timer/Counter1 Prescaler
PSR1
CK (1.6 MHz)
CLEAR
CK/1024
CK/512
CK/256
CK/128
CK/64
CK/32
CK/16
CK/8
CK/4
CK/2
10-BIT T/C PRESCALER
CK
PCK/4
PCK/8
0
PCK/2
CLEAR
3-BIT T/C PRESCALER
PCK
PCK (25.6 MHz)
CS10
CS11
CS12
CS13
TIMER/COUNTER1 COUNT ENABLE
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.
15.2
Timer/Counter1
Figure 15-2 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 prescaling 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 Compare Registers serve as a stand-alone PWM. Refer to page 98 for a detailed description on this
function. Similarly, the high prescaling opportunities make this unit useful for lower speed functions or exact timing functions with infrequent actions.
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7598D–AVR–02/07
Figure 15-2. Timer/Counter 1 Synchronization Register Block Diagram.
8-BIT DATABUS
IO-registers
Input synchronization
registers
OCR1A
OCR1A_SI
OCR1C
OCR1C_SI
TCCR1
TCCR1_SI
GTCCR
GTCCR_SI
TCNT1
TCNT1_SI
Timer/Counter1
Output synchronization
registers
TCNT1
TCNT_SO
TCNT1
OCF1A
OCF1A_SO
OCF1A
OCF1A_SI
TOV1
TOV1_SI
TOV1
TOV1_SO
PCKE
CK
S
A
PCK
S
A
SYNC
MODE
1/2 CK Delay
ASYNC
MODE
~1/2 CK Delay
1CK Delay
1PCK Delay
1/2 CK Delay
1/2PCK - 1CK Delay
No Delay
No Delay
Timer/Counter1 and the prescaler allow running the CPU from any clock source while the prescaler is operating on the fast 25.6 MHz PCK clock in the asynchronous mode.
The following Figure 15-3 shows the block diagram for Timer/Counter1.
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ATtiny25/45/85 Auto
Figure 15-3. Timer/Counter1 Block Diagram
PSR1
GLOBAL T/C CONTROL
REGISTER 2 (GTCCR)
FOC1A
CS10
CS12
CS11
CS13
COM1A1
COM1A0
T/C CONTROL
REGISTER 1 (TCCR1)
CTC1
PWM1A
TOV1
TOV0
OCF1A
TIMER INT. FLAG
REGISTER (TIFR)
OCF1A
TIMER INT. MASK
REGISTER (TIMSK)
OC1A
(PB1)
TOV1
TOIE1
TOIE0
OCIE1A
T/C1 OVER- T/C1 COMPARE
FLOW IRQ MATCH A IRQ
TIMER/COUNTER1
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
8-BIT COMPARATOR
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
(OCR1A)
T/C1 OUTPUT
COMPARE REGISTER
(OCR1C)
T/C1 CONTROL
LOGIC
CK
PCK
8-BIT DATABUS
Two status flags (overflow and compare match) 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 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, OCR1A provides the data values against which the Timer Counter value is compared. Upon compare match the PWM outputs (OC1A) is generated. In PWM mode, the Timer
Counter counts up to the value specified in the output compare register OCR1C and starts again
from $00. This feature allows limiting the counter “full” value to a specified value, lower than $FF.
Together with the many prescaler options, flexible PWM frequency selection is provided. Table
14-6 lists clock selection and OCR1C values to obtain PWM frequencies from 20 kHz to 250 kHz
in 10 kHz steps and from 250 kHz to 500 kHz in 50 kHz steps. Higher PWM frequencies can be
obtained at the expense of resolution.
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7598D–AVR–02/07
15.2.1
15.2.2
Timer/Counter1 Control Register - TCCR1
Bit
7
6
5
4
3
2
1
0
$30 ($50)
CTC1
PWM1A
COM1A1
COM1A0
CS13
CS12
CS11
CS10
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
TCCR1A
• 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 continues counting and is unaffected by a compare match.
• Bit 6- PWM1A: Pulse Width Modulator A Enable
When set (one) this bit enables PWM mode based on comparator OCR1A in Timer/Counter1
and the counter value is reset to $00 in the CPU clock cycle after a compare match with OCR1C
register value.
• Bits 5,4 - COM1A1, COM1A0: Comparator A Output Mode, Bits 1 and 0
The COM1A1 and COM1A0 control bits determine any output pin action following a compare
match with compare register A in Timer/Counter1. Output pin actions affect pin PB1 (OC1A).
Since this is an alternative function to an I/O port, the corresponding direction control bit must be
set (one) in order to control an output pin.
Table 15-1.
Comparator A Mode Select
COM1A1
COM1A0
Description
0
0
Timer/Counter Comparator A disconnected from output pin OC1A.
0
1
Toggle the OC1A output line.
1
0
Clear the OC1A output line.
1
1
Set the OC1A output line
In PWM mode, these bits have different functions. Refer to Table 15-3 on page 98 for a detailed
description.
• Bits 3 .. 0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0
The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1.
Table 15-2.
94
Timer/Counter1 Prescale Select
CS13
CS12
CS11
CS10
T/C1 Clock
0
0
0
0
T/C1 stopped
0
0
0
1
PCK
0
0
1
0
PCK/2
0
0
1
1
PCK/4
0
1
0
0
PCK/8
0
1
0
1
CK
0
1
1
0
CK/2
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Table 15-2.
Timer/Counter1 Prescale Select (Continued)
CS13
CS12
CS11
CS10
T/C1 Clock
0
1
1
1
CK/4
1
0
0
0
CK/8
1
0
0
1
CK/16
1
0
1
0
CK/32
1
0
1
1
CK/64
1
1
0
0
CK/128
1
1
0
1
CK/256
1
1
1
0
CK/512
1
1
1
1
CK/1024
The Stop condition provides a Timer Enable/Disable function.
15.2.3
General Timer/Counter1 Control Register - GTCCR
Bit
7
6
5
4
3
2
1
0
$2C ($4C)
TSM
PWM1B
COM1B1
COM1B0
FOC1B
FOC1A
PSR1
PSR0
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
GTCCR
• 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 COM1A1 and COM1A0 written
in the same cycle as FOC1A, the new settings will be used. The Force Output Compare bit can
be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1A1 and COM1A0 takes place as if a compare match had occurred, but no
interrupt is generated. The FOC1A bit always reads as zero. FOC1A is not in use if PWM1A bit
is set.
• Bit 1- PSR1 : Prescaler Reset Timer/Counter1
When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffected) 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.
15.2.4
Timer/Counter1 - TCNT1
Bit
7
6
5
4
3
2
1
0
$2F ($4F)
MSB
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
LSB
TCNT1
This 8-bit register contains the value of Timer/Counter1.
Timer/Counter1 is realized as an up counter with read and write access. Due to synchronization
of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one CPU clock cycle
in synchronous mode and at most two CPU clock cycles for asynchronous mode.
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15.2.5
Timer/Counter1 Output Compare RegisterA - OCR1A
Bit
7
6
5
4
3
2
1
0
$2E ($4E)
MSB
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
LSB
OCR1A
The output compare register A is an 8-bit read/write register.
The Timer/Counter Output Compare Register A contains data to be continuously compared with
Timer/Counter1. Actions on compare matches are specified in 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 following the compare event.
15.2.6
Timer/Counter1 Output Compare Register C - OCR1C
Bit
7
6
5
4
3
2
1
0
$2B ($4B)
MSB
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
LSB
OCR1C
The Output Compare Register B - OCR1B from ATtiny15 is replaced with the output compare
register C - OCR1C that is an 8-bit read/write register. This register has the same function as the
Output Compare Register B in ATtiny15.
The Timer/Counter Output Compare Register C contains data to be continuously compared with
Timer/Counter1. A compare match does only occur if Timer/Counter1 counts to the OCR1C
value. A software write that sets TCNT1 and OCR1C to the same value does not generate a
compare match. If the CTC1 bit in TCCR1 is set, a compare match will clear TCNT1.
Bit
7
6
5
4
3
2
1
$39 ($59)
-
OCIE1A
OCIE1B
OCIE0A
OCIE0B
TOIE1
TOIE0
0
-
Read/Write
R
R/W
R/W
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0
0
TIMSK
• 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/Counter1 Compare MatchA, interrupt is enabled. The corresponding interrupt at vector
$003 is executed if a compare matchA occurs. The Compare Flag in Timer/Counter1 is set (one)
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 Overflow interrupt is enabled. The corresponding interrupt (at vector $004) is
executed if an overflow in Timer/Counter1 occurs. The Overflow Flag (Timer1) is set (one) in the
Timer/Counter Interrupt Flag Register - TIFR.
• Bit 0 - Res: Reserved Bit
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ATtiny25/45/85 Auto
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
15.2.7
Timer/Counter Interrupt Flag Register - TIFR
Bit
7
6
5
4
3
2
1
$38 ($58)
-
OCF1A
OCF1B
OCF0A
OCF0B
TOV1
TOV0
0
-
Read/Write
R
R/W
R/W
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0
0
TIFR
• Bit 7 - Res: Reserved Bit
This bit is a reserved bit in the ATtiny25/45/85 and always reads as zero.
• Bit 6 - OCF1A: Output Compare Flag 1A
The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data
value in OCR1A - Output Compare Register 1A. OCF1A is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1A, and OCF1A
are set (one), the Timer/Counter1 A compare match interrupt is executed.
• Bit 2 - TOV1: Timer/Counter1 Overflow Flag
The bit TOV1 is set (one) when an overflow occurs in Timer/Counter1. TOV1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV1 is
cleared, after synchronization clock cycle, by writing a logical one to the flag. When the SREG Ibit, 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.
15.2.8
PLL Control and Status Register - PLLCSR
Bit
7
6
5
4
3
2
1
0
LSM
-
-
-
-
PCKE
PLLE
PLOCK
Read/Write
R
R
R
R
R
R/W
R/W
R
Initial value
0
0
0
0
0
0
0/1
0
$27 ($27)
PLLCSR
• Bit 7.. 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.
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15.2.9
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 OC1A and output is set or cleared
according to the COM1A1/COM1A0 bits in the Timer/Counter1 Control Register A - TCCR1, as
shown in Table 15-3.
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 interrupt flag (TOV1) after a synchronization delay following the compare event.
Table 15-3.
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 = $01.
1
1
OC1A set on compare match. Cleared when TCNT1 = $01.
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. This prevents the occurrence of odd-length PWM pulses (glitches) in the event
of an unsynchronized OCR1A. See Figure 15-4 for an e xample.
Figure 15-4. Effects of Unsynchronized OCR Latching
Compare Value changes
Counter Value
Compare Value
PWM Output OC1A
Synchronized OC1A Latch
Compare Value changes
Counter Value
Compare Value
PWM Output OC1A
Unsynchronized OC1A Latch
Glitch
During the time between the write and the latch operation, a read from OCR1A will read the contents of the temporary location. This means that the most recently written value always will read
out of OCR1A.
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ATtiny25/45/85 Auto
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 15-4.
Table 15-4.
PWM Outputs OCR1A = $00 or OCR1C
COM1A1
COM1A0
OCR1A
Output OC1A
0
1
$00
L
0
1
OCR1C
H
1
0
$00
L
1
0
OCR1C
H
1
1
$00
H
1
1
OCR1C
L
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 Timer Overflow Interrupt and global interrupts are enabled. This also applies to
the Timer Output Compare flags and interrupts.
The frequency of the PWM will be Timer Clock 1 Frequency divided by (OCR1C value + 1). See
the following equation:
f TCK1
f PWM = -----------------------------------( OCR1C + 1 )
Resolution shows how many bit is required to express the value in the OCR1C register. It is calculated by following equation
ResolutionPWM = log2(OCR1C + 1).
Table 15-5.
Timer/Counter1 Clock Prescale Select in the Asynchronous Mode
PWM Frequency
Clock Selection
CS13..CS10
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
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
99
7598D–AVR–02/07
Table 15-5.
Timer/Counter1 Clock Prescale Select in the Asynchronous Mode
PWM Frequency
Clock Selection
CS13..CS10
OCR1C
RESOLUTION
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
16. Dead Time Generator
The Dead Time Generator is provided for the Timer/Counter1 PWM output pairs to allow driving
external power control switches safely. The Dead Time 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 Generator 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 adjustable and the PWM output and it’s complementary output are adjusted separately, and
independently for both PWM outputs.
Figure 16-1. Timer/Counter1 & Dead Time Generators
PCKE
TIMER/COUNTER1
T15M
CK
PWM GENERATOR
PWM1A
PWM1B
PCK
DT1AH
DT1BH
DEAD TIME GENERATOR
DT1AL
DT1BL
OC1A
100
DEAD TIME GENERATOR
OC1A
OC1B
OC1B
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
The dead time generation is based on the 4-bit down counters that count the dead time, as
shown in Figure 46. There is a dedicated prescaler in front of the Dead Time Generator that can
divide the Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8. This provides for large range of
dead times that can be generated. The prescaler is controlled by two control bits DTPS11..10
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 comparator 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 16-2. Dead Time Generator
DTPS11..10
T/C1 CLOCK
COMPARATOR
OC1x
DEAD TIME
PRESCALER
CLOCK CONTROL
4-BIT COUNTER
DT1xL
DT1xH
OC1x
DT1x
I/O REGISTER
PWM1x
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-bit fields, DT1xH and DT1xL that control the dead time periods of the PWM
output and its’ complementary output separately. Thus the rising edge 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 16-3. The Complementary Output Pair
PWM1x
OC1x
OC1x
x = A or B
t non-overlap / rising edge
16.0.1
t non-overlap / falling edge
Timer/Counter1 Dead Time Prescaler register 1 - DTPS1
Bit
7
6
5
4
3
2
$23 ($43)
1
0
DTPS11
DTPS10
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial value
0
0
0
0
0
0
0
0
DTPS1
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7598D–AVR–02/07
The dead time prescaler register, DTPS1 is a 2-bit read/write register.
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 DTPS11..10 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..
Table 16-1.
16.0.2
Division factors of the Dead Time prescaler
DTPS11
DTPS10
Prescaler divides the T/C1 clock by
0
0
1x (no division)
0
1
2x
1
0
4x
1
1
8x
Timer/Counter1 Dead Time A - DT1A
Bit
7
6
5
4
3
2
1
0
DT1AH3
DT1AH2
DT1AH1
DT1AH0
DT1AL3
DT1AL2
DT1AL1
DT1AL0
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
$25 ($45)
DT1A
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, DT1AH3..0 and DT1AL3..0, one for each complementary output. Therefore a different dead time delay can be adjusted for the rising edge of OC1A and the rising edge of OC1A.
• Bits 7..4- DT1AH3..DT1AH0: 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 prescaled 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- DT1AL3..DT1AL0: 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 prescaled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
16.0.3
Timer/Counter1 Dead Time B - DT1B
Bit
7
6
5
4
3
2
1
0
DT1BH3
DT1BH2
DT1BH1
DT1BH0
DT1BL3
DT1BL2
DT1BL1
DT1BL0
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
$25 ($45)
DT1B
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, DT1BH3..0 and DT1BL3..0, one for each complementary output. Therefore a different dead time delay can be adjusted for the rising edge of OC1A and the rising edge of OC1A.
• Bits 7..4- DT1BH3..DT1BH0: Dead Time Value for OC1B Output
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ATtiny25/45/85 Auto
The dead time value for the OC1B output. The dead time delay is set as a number of the prescaled 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- DT1BL3..DT1BL0: 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 prescaled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the
prescaled time/counter clock period multiplied by 15.
17. Universal Serial Interface – USI
The Universal Serial Interface, or USI, provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rates and uses less code space than solutions based on software only. Interrupts
are included to minimize the processor load. The main features of the USI are:
•
•
•
•
•
•
17.1
Two-wire Synchronous Data Transfer (Master or Slave, fSCLmax = fCK/16)
Three-wire Synchronous Data Transfer (Master or Slave fSCKmax = fCK/4)
Data Received Interrupt
Wakeup from Idle Mode
In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
Two-wire Start Condition Detector with Interrupt Capability
Overview
A simplified block diagram of the USI is shown on Figure 17-1. For the actual placement of I/O
pins, refer to “Pinout ATtiny25/45/85” on page 2. CPU accessible I/O Registers, including I/O
bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed
in the “USI Register Descriptions” on page 110.
Figure 17-1. Universal Serial Interface, Block Diagram
Bit7
Bit0
D Q
LE
DO
(Output only)
DI/SDA
(Input/Open Drain)
USCK/SCL
(Input/Open Drain)
3
2
USIDR
1
0
TIM0 COMP
USIPF
4-bit Counter
USIDC
USISIF
USIOIF
DATA BUS
USIDB
3
2
0
1
1
0
CLOCK
HOLD
[1]
USISR
Two-wire Clock
Control Unit
USITC
USICLK
USICS0
USICS1
USIWM0
USIWM1
USISIE
USIOIE
2
USICR
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7598D–AVR–02/07
The 8-bit Shift Register is directly accessible via the data bus and contains the incoming and
outgoing data. The register has no buffering so the data must be read as quickly as possible to
ensure that no data is lost. The most significant bit is connected to one of two output pins
depending of the wire mode configuration. A transparent latch is inserted between the Serial
Register Output and output pin, which delays the change of data output to the opposite clock
edge of the data input sampling. The serial input is always sampled from the Data Input (DI) pin
independent of the configuration.
The 4-bit counter can be both read and written via the data bus, and can generate an overflow
interrupt. Both the Serial Register and the counter are clocked simultaneously by the same clock
source. This allows the counter to count the number of bits received or transmitted and generate
an interrupt when the transfer is complete. Note that when an external clock source is selected
the counter counts both clock edges. In this case the counter counts the number of edges, and
not the number of bits. The clock can be selected from three different sources: The USCK pin,
Timer/Counter0 Compare Match or from software.
The Two-wire clock control unit can generate an interrupt when a start condition is detected on
the Two-wire bus. It can also generate wait states by holding the clock pin low after a start condition is detected, or after the counter overflows.
17.2
17.2.1
Functional Descriptions
Three-wire Mode
The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0 and 1, but
does not have the slave select (SS) pin functionality. However, this feature can be implemented
in software if necessary. Pin names used by this mode are: DI, DO, and USCK.
Figure 17-2. Three-wire Mode Operation, Simplified Diagram
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
SLAVE
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
PORTxn
MASTER
Figure 17-2 shows two USI units operating in Three-wire mode, one as Master and one as
Slave. The two Shift Registers are interconnected in such way that after eight USCK clocks, the
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data in each register are interchanged. The same clock also increments the USI’s 4-bit counter.
The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be used to determine when a
transfer is completed. The clock is generated by the Master device software by toggling the
USCK pin via the PORT Register or by writing a one to the USITC bit in USICR.
Figure 17-3. Three-wire Mode, Timing Diagram
CYCLE
1
( Reference )
2
3
4
5
6
7
8
USCK
USCK
DO
MSB
DI
MSB
A
B
C
6
5
4
3
2
1
LSB
6
5
4
3
2
1
LSB
D
E
The Three-wire mode timing is shown in Figure 17-3. At the top of the figure is a USCK cycle reference. One bit is shifted into the USI Shift 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 (Data Register is shifted by one) at negative
edges. External Clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., samples data at negative and changes the output at positive edges. The USI clock modes
corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 17-3.), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on the protocol used, enables its output driver (mark A and B). The output is set up by writing the
data to be transmitted to the Serial Data Register. Enabling of the output is done by setting the corresponding bit in the port Data Direction Register. Note that point A and B
does not have any specific order, but both must be at least one half USCK cycle before
point C where the data is sampled. This must be done to ensure that the data setup
requirement is satisfied. The 4-bit counter is reset to zero.
2. The Master generates a clock pulse by software toggling the USCK line twice (C and
D). The bit value on the slave and master’s data input (DI) pin is sampled by the USI on
the first edge (C), and the data output is changed on the opposite edge (D). The 4-bit
counter will count both edges.
3. Step 2. is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that
the transfer is completed. The data bytes transferred must now be processed before a
new transfer can be initiated. The overflow interrupt will wake up the processor if it is
set to Idle mode. Depending of the protocol used the slave device can now set its output to high impedance.
17.2.2
SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
ldi
r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
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SPITransfer_loop:
sts
USICR,r16
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SPITransfer_loop
lds
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that
the DO and USCK pins are enabled as output in the DDRE Register. The value stored in register
r16 prior to the function is called is transferred to the Slave device, and when the transfer is completed the data received from the Slave is stored back into the r16 Register.
The second and third instructions clears the USI Counter Overflow Flag and the USI counter
value. The fourth and fifth instruction set Three-wire mode, positive edge Shift Register clock,
count at USITC strobe, and toggle USCK. The loop is repeated 16 times.
The following code demonstrates how to use the USI module as a SPI Master with maximum
speed (fsck = fck/4):
SPITransfer_Fast:
sts
USIDR,r16
ldi
r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi
r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
sts
USICR,r16 ; MSB
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16 ; LSB
sts
USICR,r17
lds
r16,USIDR
ret
17.2.3
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
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ldi
r16,(1<<USIWM0)|(1<<USICS1)
sts
USICR,r16
...
SlaveSPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
SlaveSPITransfer_loop:
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SlaveSPITransfer_loop
lds
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that
the DO is configured as output and USCK pin is configured as input in the DDR Register. The
value stored in register r16 prior to the function is called is transferred to the master device, and
when the transfer is completed the data received from the Master is stored back into the r16
Register.
Note that the first two instructions is for initialization only and needs only to be executed
once.These instructions sets Three-wire mode and positive edge Shift Register clock. The loop
is repeated until the USI Counter Overflow Flag is set.
17.2.4
Two-wire Mode
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate limiting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.
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Figure 17-4. Two-wire Mode Operation, Simplified Diagram
VCC
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
HOLD
SCL
Two-wire Clock
Control Unit
SLAVE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
PORTxn
MASTER
Figure 17-4 shows two USI units operating in Two-wire mode, one as Master and one as Slave.
It is only the physical layer that is shown since the system operation is highly dependent of the
communication scheme used. The main differences between the Master and Slave operation at
this level, is the serial clock generation which is always done by the Master, and only the Slave
uses the clock control unit. Clock generation must be implemented in software, but the shift
operation is done automatically by both devices. Note that only clocking on negative edge for
shifting data is of practical use in this mode. The slave can insert wait states at start or end of
transfer by forcing the SCL clock low. This means that the Master must always check if the SCL
line was actually released after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate that the
transfer is completed. The clock is generated by the master by toggling the USCK pin via the
PORT Register.
The data direction is not given by the physical layer. A protocol, like the one used by the TWIbus, must be implemented to control the data flow.
Figure 17-5. Two-wire Mode, Typical Timing Diagram
SDA
SCL
S
A
B
1 - 7
8
9
1 - 8
9
1 - 8
9
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
C
D
E
P
F
Referring to the timing diagram (Figure 17-5.), a bus transfer involves the following steps:
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1. The a start condition is generated by the Master by forcing the SDA low line while the
SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of the Shift
Register, or by setting the corresponding bit in the PORT Register to zero. Note that the
Data Direction Register bit must be set to one for the output to be enabled. The slave
device’s start detector logic (Figure 17-6.) detects the start condition and sets the
USISIF Flag. The flag can generate an interrupt if necessary.
2. In addition, the start detector will hold the SCL line low after the Master has forced an
negative edge on this line (B). This allows the Slave to wake up from sleep or complete
its other tasks before setting up the Shift Register to receive the address. This is done
by clearing the start condition flag and reset the counter.
3. The Master set the first bit to be transferred and releases the SCL line (C). The Slave
samples the data and shift it into the Serial Register at the positive edge of the SCL
clock.
4. After eight bits are transferred containing slave address and data direction (read or
write), the Slave counter overflows and the SCL line is forced low (D). If the slave is not
the one the Master has addressed, it releases the SCL line and waits for a new start
condition.
5. If the Slave is addressed it holds the SDA line low during the acknowledgment cycle
before holding the SCL line low again (i.e., the Counter Register must be set to 14
before releasing SCL at (D)). Depending of the R/W bit the Master or Slave enables its
output. If the bit is set, a master read operation is in progress (i.e., the slave drives the
SDA line) The slave can hold the SCL line low after the acknowledge (E).
6. Multiple bytes can now be transmitted, all in same direction, until a stop condition is
given by the Master (F). Or a new start condition is given.
If the Slave is not able to receive more data it does not acknowledge the data byte it has last
received. When the Master does a read operation it must terminate the operation by force the
acknowledge bit low after the last byte transmitted.
Figure 17-6. Start Condition Detector, Logic Diagram
USISIF
D
Q
D
Q
CLOCK
HOLD
SDA
CLR
CLR
SCL
Write( USISIF)
17.2.5
Start Condition Detector
The start condition detector is shown in Figure 17-6. 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.
The start condition detector is working asynchronously and can therefore wake up the processor
from the Power-down sleep mode. However, the protocol used might have restrictions on the
SCL hold time. Therefore, when using this feature in this case the Oscillator start-up time set by
the CKSEL Fuses (see “Clock Systems and their Distribution” on page 21) must also be taken
into the consideration. Refer to the USISIF bit description on page 111 for further details.
17.3
Alternative USI Usage
When the USI unit is not used for serial communication, it can be set up to do alternative tasks
due to its flexible design.
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17.3.1
Half-duplex Asynchronous Data Transfer
By utilizing the Shift Register in Three-wire mode, it is possible to implement a more compact
and higher performance UART than by software only.
17.3.2
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 generate an increment.
17.3.3
12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
17.3.4
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.
17.3.5
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.
17.4
USI Register Descriptions
17.4.1
USI Data Register – USIDR
Bit
7
6
5
4
3
2
1
MSB
0
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USIDR
When accessing the USI Data Register (USIDR) the Serial Register can be accessed directly. If
a serial clock occurs at the same cycle the register is written, the register will contain the value
written and no shift is performed. A (left) shift operation is performed depending of the
USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a
Timer/Counter0 Compare Match, or directly by software using the USICLK strobe bit. Note that
even when no wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and
the external clock input (USCK/SCL) can still be used by the Shift Register.
The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch
to the most significant bit (bit 7) of the Data Register. The output latch is open (transparent) during the first half of a serial clock cycle when an external clock source is selected (USICS1 = 1),
and constantly open when an internal clock source is used (USICS1 = 0). The output will be
changed immediately when a new MSB written as long as the latch is open. The latch ensures
that data input is sampled and data output is changed on opposite clock edges.
Note that the corresponding Data Direction Register to the pin must be set to one for enabling
data output from the Shift Register.
17.4.2
USI Buffer Register – USIBR
Bit
7
6
5
4
3
2
1
MSB
110
0
LSB
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
USIBR
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The content of the Serial Register is loaded to the USI Buffer Register when the trasfer is completed, and instead of accessing the USI Data Register (the Serial Register) the USI Data Buffer
can be accessed when the CPU reads the received data. This gives the CPU time to handle
other program tasks too as the controlling of the USI is not so timing critical. The USI flags as set
same as when reading the USIDR register.
17.4.3
USI Status Register – USISR
Bit
7
6
5
4
3
2
1
0
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
Read/Write
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USISR
The Status Register contains Interrupt Flags, line Status Flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When Two-wire mode is selected, the USISIF Flag is set (to one) when a start condition is
detected. When output disable mode or Three-wire mode is selected and (USICSx = 0b11 &
USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the SCK pin sets the flag.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the Global
Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one to the USISIF
bit. Clearing this bit will release the start detection hold of 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). An
interrupt will be generated when the flag is set while the USIOIE bit in USICR and the Global
Interrupt Enable Flag are set. The flag will only be cleared if a one is written 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, the USIPF Flag is set (one) when a stop condition is detected.
The flag is cleared by writing a one to this bit. Note that this is not an Interrupt Flag. This signal is
useful when implementing Two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the Shift Register differs from the physical pin value. The flag
is only valid when Two-wire mode is used. This signal is useful when implementing Two-wire
bus master arbitration.
• Bits 3..0 – USICNT3..0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or
written by the CPU.
The 4-bit counter increments by one for each clock generated either by the external clock edge
detector, by a Timer/Counter0 Compare Match, or by software using USICLK or USITC strobe
bits. The clock source depends of the setting of the USICS1..0 bits. For external clock operation
a special feature is added that allows the clock to be generated by writing to the USITC strobe
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bit. This feature is enabled by write a one to the USICLK bit while setting an external clock
source (USICS1 = 1).
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) are can still be used by the counter.
17.4.4
USI Control Register – USICR
Bit
7
6
5
4
3
2
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
W
W
Initial Value
0
0
0
0
0
0
0
0
USICR
The Control Register includes interrupt enable control, wire mode setting, Clock Select setting,
and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be
executed. Refer to the USISIF bit description on page 111 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when
the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed.
Refer to the USIOIF bit description on page 111 for further details.
• Bit 5..4 – USIWM1..0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are
affected by these bits. Data and clock inputs are not affected by the mode selected and will
always have the same function. The counter and Shift Register can therefore be clocked externally, and data input sampled, even when outputs are disabled. The relations between
USIWM1..0 and the USI operation is summarized in Table 17-1.
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Table 17-1.
Relations between USIWM1..0 and the USI Operation
USIWM1
USIWM0
0
0
Outputs, clock hold, and start detector disabled. Port pins operates as
normal.
1
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORT
Register in this mode. However, the corresponding DDR bit still controls the
data direction. When the port pin is set as input the pins pull-up is controlled
by the PORT 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 PORT Register, while the data direction is set to
output. The USITC bit in the USICR Register can be used for this purpose.
0
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
uses open-collector output drives. The output drivers are enabled by setting
the corresponding bit for SDA and SCL in the DDR Register.
When the output driver is enabled for the SDA pin, the output driver will force
the line SDA low if the output of the Shift Register or the corresponding bit in
the PORT 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 PORT Register is zero, or by the
start detector. Otherwise the SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition and
the output is enabled. Clearing the Start Condition Flag (USISIF) releases the
line. The SDA and SCL pin inputs is not affected by enabling this mode. Pullups on the SDA and SCL port pin are disabled in Two-wire mode.
1
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the Two-wire mode described above, except that the
SCL line is also held low when a counter overflow occurs, and is held low until
the Counter Overflow Flag (USIOIF) is cleared.
0
1
1
Note:
Description
1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL) respectively
to avoid confusion between the modes of operation.
• Bit 3..2 – USICS1..0: Clock Source Select
These bits set the clock source for the Shift Register and counter. The data output latch ensures
that the output is changed at the opposite edge of the sampling of the data input (DI/SDA) when
using external clock source (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 USICS1..0 bits enables software strobe option. When using
this option, writing a one to the USICLK bit clocks both the Shift Register and the counter. For
external clock source (USICS1 = 1), the USICLK bit is no longer used as a strobe, but selects
between external clocking and software clocking by the USITC strobe bit.
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Table 17-2 shows the relationship between the USICS1..0 and USICLK setting and clock source
used for the Shift Register and the 4-bit counter.
Table 17-2.
Relations between the USICS1..0 and USICLK Setting
USICS1
USICS0
USICLK
Shift Register 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, positive edge
Software clock strobe (USITC)
1
1
1
External, negative edge
Software clock strobe (USITC)
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the Shift Register to shift one step and the counter to
increment by one, provided that the USICS1..0 bits are set to zero and by doing so the software
clock strobe option is selected. The output will change immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value shifted into the Shift Register is sampled the
previous instruction cycle. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1), the USICLK function is changed from
a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the
USITC strobe bit as clock source for the 4-bit counter (see Table 17-2).
• 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 independent of the setting in the Data Direction Register, but if the PORT value is
to be shown on the pin the DDRE4 must be set as output (to one). This feature allows easy clock
generation when implementing master devices. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writing to the USITC strobe bit will directly clock the 4-bit counter. This allows an early detection of
when the transfer is done when operating as a master device.
18. Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator output, ACO, is set. The comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator
output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown
in Figure 18-1.
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Figure 18-1. Analog Comparator Block Diagram(2)
BANDGAP
REFERENCE
ACBG
ACME
ADEN
ADC MULTIPLEXER
OUTPUT (1)
Notes:
1. See Table 18-2 on page 116.
2. Refer to Figure 1-1 on page 2 and Table 10-5 on page 57 for Analog Comparator pin
placement.
18.0.1
ADC Control and Status Register B – ADCSRB
Bit
7
6
5
4
3
2
1
0
BIN
ACME
IPR
–
–
ADTS2
ADTS1
ADTS0
Read/Write
R
R/W
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the
ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written
logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed
description of this bit, see “Analog Comparator Multiplexed Input” on page 116.
18.0.2
Analog Comparator Control and Status Register – ACSR
Bit
7
6
5
4
3
2
1
0
ACD
ACBG
ACO
ACI
ACIE
–
ACIS1
ACIS0
Read/Write
R/W
R/W
R
R/W
R/W
R
R/W
R/W
Initial Value
0
0
N/A
0
0
0
0
0
ACSR
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is
changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set an internal 1.1V / 2.56V reference voltage replaces the positive input to the
Analog Comparator. The selection of the internal voltage reference is done by writing the
REFS2..0 bits in ADMUX register. When this bit is cleared, AIN0 is applied to the positive input
of the Analog Comparator.
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• 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 Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Comparator 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.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 18-1.
Table 18-1.
ACIS1/ACIS0 Settings
ACIS1
ACIS0
Interrupt Mode
0
0
Comparator Interrupt on Output Toggle.
0
1
Reserved
1
0
Comparator Interrupt on Falling Output Edge.
1
1
Comparator Interrupt on Rising Output Edge.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by
clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the
bits are changed.
18.1
Analog Comparator Multiplexed Input
It is possible to select any of the ADC3..0 pins to replace the negative input to the Analog Comparator. 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), MUX1..0 in ADMUX
select the input pin to replace the negative input to the Analog Comparator, as shown in Table
18-2. If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the Analog
Comparator.
Table 18-2.
116
Analog Comparator Multiplexed Input
ACME
ADEN
MUX1..0
Analog Comparator Negative Input
0
x
xx
AIN1
1
1
xx
AIN1
1
0
00
ADC0
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Table 18-2.
18.1.1
Analog Comparator Multiplexed Input
ACME
ADEN
MUX1..0
Analog Comparator Negative Input
1
0
01
ADC1
1
0
10
ADC2
1
0
11
ADC3
Digital Input Disable Register 0 – DIDR0
Bit
7
6
5
4
3
2
1
0
–
–
ADC0D
ADC2D
ADC3D
ADC1D
AIN1D
AIN0D
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
DIDR0
• Bits 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corresponding 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 written logic one to reduce power consumption in the digital input buffer.
19. Analog to Digital Converter
19.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
10-bit Resolution
0.5 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 channels with selectable gain
Temperature sensor input channel
Optional Left Adjustment 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 Input Mode
Input Polarity Reversal Mode
The ATtiny25/45/85 features a 10-bit successive approximation ADC. The ADC is connected to
a 4-channel Analog Multiplexer which allows one differential voltage input and four single-ended
voltage inputs constructed from the pins of Port B. The differential input (PB3, PB4 or PB2, PB5)
is equipped with a programmable gain stage, providing 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 19-1.
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Internal voltage references of nominally 1.1V or 2.56V are provided On-chip and these voltage
references can optionally be externally decoupled at the AREF (PB0) pin by a capacitor, for better noise performance. Alternatively, VCC can be used as voltage reference for single ended
channels. There is also an option to use an external voltage reference and turn-off the internal
voltage reference. These options are selected using the REFS2..0 bits of the ADMUX control
register.
Figure 19-1. Analog to Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
INTERRUPT
FLAGS
ADTS[2:0]
AREF
INTERNAL 1.1V/2.56V
REFERENCE
PRESCALER
START
CONVERSION LOGIC
TEMPERATURE
SENSOR
SAMPLE & HOLD
COMPARATOR
10-BIT DAC
ADC4
ADC3
ADC2
ADC[9:0]
ADPS0
ADPS1
ADPS2
ADIF
ADSC
ADATE
ADEN
MUX0
ADLAR
MUX1
MUX DECODER
CHANNEL SELECTION
VCC
0
ADC DATA REGISTER
(ADCH/ADCL)
TRIGGER
SELECT
GAIN SELECTION
REFS2..0
BIN
IPR
15
ADC CTRL. & STATUS A
REGISTER (ADCSRA)
ADC MULTIPLEXER
SELECT (ADMUX)
MUX2
ADC CTRL. & STATUS B
REGISTER (ADCSRB)
ADIE
ADIF
8-BIT DATA BUS
+
SINGLE ENDED / DIFFERENTIAL SELECTION
INPUT
MUX
ADC1
ADC0
+
GAIN
AMPLIFIER
ADC MULTIPLEXER
OUTPUT
NEG.
INPUT
MUX
19.2
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value represents GND and the maximum value represents the voltage on
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 REFS2..0 bits in ADMUX.
The VCC supply, the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as
the ADC voltage reference. Optionally the internal 1.1V / 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 MUX3..0 bits in
ADMUX. Any of the four ADC input pins ADC3..0 can be selected as single ended inputs to the
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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 input pair by the selected gain factor, 1x or 20x, according to the setting of
the MUX3..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.
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 to reduce offset error to below 1 LSW.
The on-chip temperature sensor is selected by writing the code “1111” to the MUX3..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 reference and
input channel selections will not go into effect until ADEN is set. The ADC does not consume
power when ADEN is cleared, so it is recommended to switch off the ADC before entering power
saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and
ADCL. By default, the result is presented right adjusted, but can optionally be presented left
adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the data
registers belongs to the same conversion. Once ADCL is read, ADC access to data registers is
blocked. This means that if ADCL has been read, and a conversion completes before ADCH is
read, neither register is updated and the result from the conversion is lost. When ADCH is read,
ADC access to the ADCH and ADCL Registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When ADC
access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will
trigger even if the result is lost.
19.3
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 will be cleared by hardware
when the conversion is completed. If a different data channel is selected while a conversion is in
progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is
enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is
selected by setting the ADC Trigger Select bits, ADTS in ADCSRB (see description of the ADTS
bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal,
the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions 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 conversion, the edge will be ignored. Note that an Interrupt Flag will be set even if the specific
interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus
be triggered without causing an interrupt. However, the Interrupt Flag must be cleared in order to
trigger a new conversion at the next interrupt event.
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Figure 19-2. ADC Auto Trigger Logic
ADTS[2:0]
PRESCALER
START
ADIF
CLKADC
ADATE
SOURCE 1
.
.
.
.
CONVERSION
LOGIC
EDGE
DETECTOR
SOURCE n
ADSC
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon
as the ongoing conversion has finished. The ADC then operates in Free Running mode, constantly sampling and updating the ADC Data Register. The first conversion must be started by
writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive
conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to
one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be
read as one during a conversion, independently of how the conversion was started.
19.4
Prescaling and Conversion Timing
Figure 19-3. ADC Prescaler
ADEN
START
Reset
7-BIT ADC PRESCALER
CK/64
CK/128
CK/32
CK/8
CK/16
CK/4
CK/2
CK
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
By default, the successive approximation circuitry requires an input clock frequency between 50
kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the
input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate.
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.
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The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit
in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously
reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion
starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched
on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 14.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
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 additional CPU clock cycles are used for synchronization logic.
In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. For a summary of conversion times, see Table 19-1.
????????????????
??
????
??
????
??
??
????
????????????
????
????
????????????
??
????????
????????????
??
Figure 19-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
Cycle Number
1
2
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
2
3
ADC Clock
ADEN
ADSC
ADIF
Sign and MSB of Result
ADCH
LSB of Result
ADCL
MUX and REFS
Update
?
Conversion
Complete
Sample & Hold
MUX and REFS
Update
Figure 19-5. ADC Timing Diagram, Single Conversion
Cycle Number
1
One Conversion
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
3
ADC Clock
ADSC
ADIF
ADCH
ADCL
??
?
Sign and MSB of Result
LSB of Result
Sample & Hold
MUX and REFS
Update
Conversion
Complete
MUX and REFS
Update
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?
Figure 19-6. ADC Timing Diagram, Auto Triggered Conversion
Cycle Number
One Conversion
1
2
3
4
5
6
7
8
Next Conversion
10
9
11
12
13
1
2
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
ADCL
??
Prescaler
Reset
Sign and MSB of Result
LSB of Result
Sample &
Hold
Prescaler
Reset
Conversion
Complete
MUX and REFS
Update
Figure 19-7. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
11
12
Next Conversion
13
1
2
3
4
ADC Clock
??
?
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
Table 19-1.
ADC Conversion Time
Condition
Sample & Hold (Cycles
from Start of Conversion)
Conversion Time (Cycles)
First conversion
13.5
25
Normal conversions
1.5
13
2
13.5
Auto Triggered conversions
19.5
MUX and REFS
Update
Changing Channel or Reference Selection
The MUX3..0 and REFS2..0 bits in the ADMUX Register are single buffered through a temporary register to which the CPU has random access. This ensures that the channels and voltage
reference selection only takes place at a safe point during the conversion. The channel and voltage reference selection is continuously updated until a conversion is started. Once the
conversion starts, the channel and voltage reference selection is locked to ensure a sufficient
sampling time for the ADC. Continuous updating resumes in the last ADC clock cycle before the
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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 time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
a. When ADATE or ADEN is cleared.
b. During conversion, minimum 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.
19.5.1
ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion. The channel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the conversion to complete before changing the channel selection.
In Free Running mode, always select the channel before starting the first conversion. The channel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the first conversion to complete, and then change the channel
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.
19.5.2
19.6
ADC Voltage Reference
The voltage reference 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 conversion result after switching voltage reference source may be inaccurate, and the user is
advised to discard this result.
ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise
induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC
Noise Reduction and Idle mode. To make use of this feature, the following procedure should be
used:
a. Make sure that the ADC is enabled and is not busy converting. Single Conversion
mode must be selected and the ADC conversion complete interrupt must be
enabled.
b. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion
once the CPU has been halted.
c.
If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt
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routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt
request will be generated when the ADC conversion completes. The CPU will
remain in active mode until a new sleep command is executed.
Note that the ADC will not 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 entering such sleep modes to avoid excessive power consumption.
19.6.1
Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 19-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the ADC. When the channel is selected, the
source must drive the S/H capacitor through the series resistance (combined resistance in the
input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher impedance 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 components higher than the Nyquist frequency (fADC/2) should not be present to avoid
distortion from unpredictable signal convolution. The user is advised to remove high frequency
components with a low-pass filter before applying the signals as inputs to the ADC.
Figure 19-8. Analog Input Circuitry
IIH
ADCn
1..100 kΩ
CS/H= 14 pF
IIL
VCC/2
19.6.2
124
Analog 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:
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ATtiny25/45/85 Auto
a. Keep analog signal paths as short as possible. Make sure analog tracks run over
the analog ground plane, and keep them well away from high-speed switching digital tracks.
b. Use the ADC noise canceler function to reduce induced noise from the CPU.
c.
19.6.3
If any port pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress.
ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and V REF 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:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Ideal value: 0 LSB.
Figure 19-9. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
VREF Input Voltage
• Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last
transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum).
Ideal value: 0 LSB
Figure 19-10. Gain Error
Output Code
Gain
Error
Ideal ADC
Actual ADC
VREF Input Voltage
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• Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0
LSB.
Figure 19-11. Integral Non-linearity (INL)
Output Code
INL
Ideal ADC
Actual ADC
VREF
Input Voltage
• Differential Non-linearity (DNL): The maximum deviation of the actual code width (the interval
between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB.
Figure 19-12. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
VREF Input Voltage
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes,
a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to
an ideal transition for any code. This is the compound effect of offset, gain error, differential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
19.7
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
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conversio as there are three types of conversions: single ended conversion, unipolar differential
conversion and bipolar differential conversion.
19.7.1
Single Ended Conversion
For single ended conversion, the result is
V IN ⋅ 1024
ADC = -------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 19-3 on page 129 and Table 19-4 on page 129). 0x000 represents analog ground, and
0x3FF represents the selected voltage reference minus one LSB. The result is presented in onesided form, from 0x3FF to 0x000.
19.7.2
Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is
( V POS – V NEG ) ⋅ 1024
ADC = -------------------------------------------------------- ⋅ GAIN
V REF
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 19-3 on page 129 and Table 19-4 on page
129). 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.
19.7.3
Bipolar Differential Conversion
As default the ADC converter operates 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 twosided voltage differences are allowed and thus the voltage on the negative 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
( V POS – V NEG ) ⋅ 512
ADC = ----------------------------------------------------- ⋅ GAIN
V REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference. The result is presented in two’s complement form, from
0x200 (-512d) through 0x000 (+0d) to 0x1FF (+511d). The GAIN is either 1x or 20x.
However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses
one bit of the converter dynamic range. Then, if the user wants to perform the 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 register on page 135). When the polarity check is
performed, it is sufficient to read the MSB of the result (ADC9 in ADCH). If the bit is one, the
result is negative, and if this bit is zero, the result is positive.
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19.7.4
Temperature Measurement (Preliminary description)
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 MUX3..0 bits in ADMUX
register to “1111” enables the temperature sensor. The internal 1.1V voltage reference must
also be selected for the ADC voltage reference source in the temperature sensor measurement.
When the temperature sensor is enabled, the ADC converter can be used in single conversion
mode to measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in Table 51. The
voltage sensitivity is approximately 1 mV / °C and the accuracy of the temperature measurement
is +/- 10°C after bandgap calibration.
Table 19-2.
Temperature vs. Sensor Output Voltage (Typical Case)
-45 °C
Temperature / °C
Voltage / mV
+25 °C
242 mV
+105 °C
314 mv
403 mV
The values described in Table 51 are typical values. However, due to the process variation the
temperature sensor output voltage varies from one chip to another. To be capable of achieving
more accurate results the temperature measurement can be calibrated in the application software. The software calibration requires that a calibration value is measured and stored in a
register or EEPROM for each chip, as a part of the production test. The sofware calibration can
be done utilizing the formula:
Temperature = k ⋅ V TEMP + T OS
where VTEMP is the ADC reading of the temperature sensor signal, k is a fixed coefficient and TOS
is the temperature sensor offset value determined and stored into EEPROM as a part of production test.
19.7.5
ADC Multiplexer Selection Register – ADMUX
Bit
7
6
5
4
3
2
1
0
REFS1
REFS0
ADLAR
REFS2
MUX3
MUX2
MUX1
MUX0
Read/Write
R
R/W
R/W
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADMUX
• Bit 7..6,4 – REFS2..REFS0: Voltage Reference Selection Bits
These bits select the voltage reference (VREF) for the ADC, as shown in Table 19-3. 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
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take 25 ADC clock cycles. If active channels 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 accuracy.
Table 19-3.
Voltage Reference Selections for ADC
REFS2
REFS1
REFS0
Voltage Reference (VREF) Selection
0
0
0
VCC used as Voltage Reference, disconnected from PB0 (AREF).
0
0
1
External Voltage Reference at PB0 (AREF) pin, Internal Voltage
Reference turned off.
0
1
0
Internal 1.1V Voltage Reference without external bypass capacitor,
disconnected from PB0 (AREF).
0
1
1
Internal 1.1V Voltage Reference with external bypass capacitor at
PB0 (AREF) pin.
1
1
0
Internal 2.56V Voltage Reference without external bypass
capacitor, disconnected from PB0 (AREF).
1
1
1
Internal 2.56V Voltage Reference with external bypass capacitor at
PB0 (AREF) pin.
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the
ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conversions. For a comple te description of this bit, see “The ADC Data Register – ADCL and ADCH”
on page 131.
• Bits 3:0 – MUX3:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the 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 differential gain stage enables offset measurements. Selecting the single-ended channel ADC4 enables the temperature sensor. Refer to
Table 19-4 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).
Table 19-4.
Input Channel Selections
MUX3..0
Single Ended
Input
0000
ADC0 (PB5)
0001
ADC1 (PB2)
0010
ADC2 (PB4)
0011
ADC3 (PB3)
Positive
Differential Input
Negative
Differential Input
Gain
N/A
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Table 19-4.
Input Channel Selections
Single Ended
Input
Positive
Differential Input
Negative
Differential Input
Gain
0100
ADC2 (PB3)
ADC2 (PB3)
1x
0101 (1)
ADC2 (PB3)
ADC2 (PB3)
20x
0110
ADC2 (PB3)
ADC3 (PB4)
1x
ADC2 (PB3)
ADC3 (PB4)
20x
ADC0 (PB5)
ADC0 (PB5)
1x
1001
ADC0 (PB5)
ADC0 (PB5)
20x
1010
ADC0 (PB5)
ADC1 (PB2)
1x
1011
ADC0 (PB5)
ADC1 (PB2)
20x
MUX3..0
0111
N/A
1000
19.7.6
1100
1.1V/2.56V
1101
0V
1110
N/A
1111
ADC4
N/A
(2)
1.
For offset calibration only . See “Operation” on page 118.
2.
For Temperature Sensor
ADC Control and Status Register A – ADCSRA
Bit
7
6
5
4
3
2
1
0
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRA
• 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 mode, write this bit to one to start each conversion. In Free Running mode,
write this bit to one to start the first conversion. The first conversion after ADSC has been written
after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled,
will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete,
it returns to zero. Writing zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a conversion on a positive edge of the selected trigger signal. The trigger source is selected by setting
the ADC Trigger Select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The ADC
Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is
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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 written to one and the I-bit in SREG is set, the ADC Conversion Complete Interrupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the system clock frequency and the input clock
to the ADC.
Table 19-5.
19.7.7
19.7.7.1
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
The ADC Data Register – ADCL and ADCH
ADLAR = 0
Bit
Read/Write
Initial Value
19.7.7.2
ADC Prescaler Selections
15
14
13
12
11
10
9
8
–
–
–
–
–
–
ADC9
ADC8
ADCH
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ADLAR = 1
Bit
Read/Write
Initial Value
15
14
13
12
11
10
9
8
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
ADC1
ADC0
–
–
–
–
–
–
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
When an ADC conversion is complete, the result is found in these two registers.
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When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if
the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result
is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on
page 126.
19.7.8
ADC Control and Status Register B – ADCSRB
Bit
7
6
5
4
3
2
1
0
BIN
ACME
IPR
–
–
ADTS2
ADTS1
ADTS0
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
ADCSRB
• Bits 7– BIN: Bipolar Input Mode
The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected
by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided conversions
are supported and the voltage on the positive input must always be larger than the voltage on
the negative input. Otherwise the result is saturated to the voltage reference. In the bipolar mode
two-sided conversions are supported and the result is represented in the two’s complement
form. In the unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits +
1 sign bit.
• Bits 5 – IPR: Input Polarity Mode
The Input Polarity mode allows software selectable differential input pairs and full 10 bit ADC
resolution, in the unipolar input mode, assuming a pre-determined input polarity. If the input
polarity is not known it is actually possible to determine the polarity first by using the bipolar input
mode (with 9 bit resolution + 1 sign bit ADC measurement). And once determined, 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 reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger
an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion
will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive edge on the
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trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running
mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
Table 19-6.
19.7.9
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/Counter Compare Match A
1
0
0
Timer/Counter Overflow
1
0
1
Timer/Counter Compare Match B
1
1
0
Pin Change Interrupt Request
Digital Input Disable Register 0 – DIDR0
Bit
7
6
5
4
3
2
1
0
–
–
ADC0D
ADC2D
ADC3D
ADC1D
AIN1D
AIN0D
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
DIDR0
• Bits 5..2 – ADC3D..ADC0D: ADC3..0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC3..0 pin and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
20. debugWIRE On-chip Debug System
20.1
Features
•
•
•
•
•
•
•
•
•
•
20.2
Complete Program Flow Control
Emulates All On-chip Functions, Both Digital and Analog , 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
Automatic Configuration System
High-Speed Operation
Programming of Non-volatile Memories
Overview
The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatile
memories.
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20.3
Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed,
the debugWIRE system within the target device is activated. The RESET port pin is configured
as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway between target and emulator.
Figure 20-1. The debugWIRE Setup
1.8 - 5.5V
VCC
dW
dW(RESET)
GND
Figure 20-1 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.
When designing a system where debugWIRE will be used, the following observations must be
made for correct operation:
• Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 kΩ. However, the
pull-up resistor is optional.
• 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.
20.4
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 instruction replaced by the BREAK instruction will be stored. When program execution is continued, the
stored instruction will be executed before continuing from the Program memory. A break can be
inserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a Break Point is changed. This is automatically
handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore
reduce the Falsh Data retention. Devices used for debugging purposes should not be shipped to
end customers.
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20.5
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).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should
be disabled when debugWire is not used.
20.6
debugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.
20.6.1
debugWire Data Register – DWDR
Bit
7
6
5
4
3
2
1
0
DWDR[7:0]
DWDR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The DWDR Register provides a communication channel from the running program in the MCU
to the debugger. This register is only accessible by the debugWIRE and can therefore not be
used as a general purpose register in the normal operations.
21. 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 associated protocol to read code and write (program) that code into the Program memory.
The Program memory is updated in a page by page fashion. Before programming a page with
the data stored in the temporary page buffer, the page must be erased. The temporary page
buffer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase
• 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 the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be re-written. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already
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erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page address used in both the Page Erase and Page Write operation is addressing the
same page.
21.0.1
Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “00000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will
be ignored during this operation.
• The CPU is halted during the Page Erase operation.
21.0.2
Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the CTPB bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
21.0.3
Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
• The CPU is halted during the Page Write operation.
21.1
Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Bit
15
14
13
12
11
10
9
8
ZH (R31)
Z15
Z14
Z13
Z12
Z11
Z10
Z9
Z8
ZL (R30)
Z7
Z6
Z5
Z4
Z3
Z2
Z1
Z0
7
6
5
4
3
2
1
0
Since the Flash is organized in pages (see Table 22-6 on page 142), the Program Counter can
be treated as having two different sections. One section, consisting of the least significant bits, is
addressing the words within a page, while the most significant bits are addressing the pages.
This is shown in Figure 21-1. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the software addresses the
same page in both the Page Erase and Page Write operation.
The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
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Figure 21-1. Addressing the Flash During SPM(1)
BIT
15
ZPCMSB
ZPAGEMSB
1 0
Z - REGISTER
0
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
PCWORD[PAGEMSB:0]:
00
INSTRUCTION WORD
01
02
PAGEEND
Note:
21.1.1
1. The different variables used in Figure 21-1 are listed in Table 22-6 on page 142.
Store Program Memory Control and Status Register – SPMCSR
The Store Program Memory Control and Status Register contains the control bits needed to control the Program memory operations.
Bit
7
6
5
4
3
2
1
0
–
–
–
CTPB
RFLB
PGWRT
PGERS
SPMEN
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPMCSR
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and always read as zero.
• 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 within three cycles after RFLB and SPMEN are set in the SPMCSR Register,
will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the destination register. See “EEPROM Write Prevents Writing to SPMCSR” on page 138 for details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address is
taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
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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 written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted 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 written to one together with
either CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction will have a special
meaning, see description above. If only SPMEN is written, the following SPM instruction will
store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of
the Z-pointer is ignored. The 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.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower
five bits will have no effect.
21.1.2
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 (EEWE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
21.1.3
Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction
is executed within three CPU cycles after the RFLB and SPMEN bits are set in SPMCSR, the
value of the Lock bits will be loaded in the destination register. The RFLB and SPMEN bits will
auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed within
three CPU cycles or no SPM instruction is executed within four CPU cycles. When RFLB and
SPMEN are cleared, LPM will work as described in the Instruction set Manual.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
–
–
–
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the RFLB and
SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the
RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will be
loaded in the destination register as shown below. Refer to Table 22-5 on page 141 for a
detailed description and mapping of the Fuse Low byte.
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the
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value of the Fuse High byte (FHB) will be loaded in the destination register as shown below.
Refer to Table XXX on page XXX for detailed description and mapping of the Fuse High byte.
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
21.1.4
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 the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating
voltage matches the detection level. If not, an external low VCC reset protection circuit
can be used. If a reset occurs while a write operation is in progress, the write operation
will be completed provided that the power supply voltage is sufficient.
2. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will prevent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
21.1.5
Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 21-1 shows the typical programming time for Flash accesses from the CPU.
Table 21-1.
SPM Programming Time
Symbol
Min Programming Time
Max Programming Time
Flash write (Page Erase, Page Write, and
write Lock bits by SPM)
3.7 ms
4.5 ms
22. Memory Programming
This section describes the different methods for Programming the ATtiny25/45/85 memories.
22.1
Program And Data Memory Lock Bits
The ATtiny25/45/85 provides two Lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional security listed in Table 22-2. The Lock bits can only be
erased to “1” with the Chip Erase command.
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Program memory can be read out via the debugWIRE interface when the DWEN fuse is programmed, even if the Lock Bits are set. Thus, when Lock Bit security is required, should always
debugWIRE be disabled by clearing the DWEN fuse.
Table 22-1.
Lock Bit Byte(1)
Lock Bit Byte
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
4
–
1 (unprogrammed)
3
–
1 (unprogrammed)
2
–
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
Note:
Bit No
1. “1” means unprogrammed, “0” means programmed
Table 22-2.
Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
LB2
LB1
1
1
1
No memory lock features enabled.
0
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.
0
Further programming and verification 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.
2
1
3
Notes:
0
1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
22.2
Fuse Bytes
The ATtiny25/45/85 has three Fuse bytes. Table 22-4, Table 22-5 and Table61 describe briefly
the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the
fuses are read as logical zero, “0”, if they are programmed.
Table 22-3.
Fuse Extended Byte
Fuse High Byte
140
Bit No
Description
Default Value
7
-
1 (unprogrammed)
6
-
1 (unprogrammed)
5
-
1 (unprogrammed)
4
-
1 (unprogrammed)
3
-
1 (unprogrammed)
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Fuse Extended Byte
Table 22-3.
Fuse High Byte
SELFPRGEN
Table 22-4.
Description
Default Value
2
-
1 (unprogrammed)
1
-
1 (unprogrammed)
0
Self-Programming Enable
1 (unprogrammed)
Fuse High Byte
Fuse High Byte
RSTDISBL
Bit No
(1)
Bit No
Description
Default Value
7
External Reset disable
1 (unprogrammed)
(2)
DWEN
6
DebugWIRE Enable
1 (unprogrammed)
SPIEN(3)
6
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
WDTON(4)
4
Watchdog Timer always on
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed, EEPROM
not preserved)
BODLEVEL2(5)
2
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL1
(5)
1
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL0
(5)
0
Brown-out Detector trigger level
1 (unprogrammed)
Notes:
1. See “Alternate Functions of Port B” on page 54 for description of RSTDISBL and DWEN
Fuses.
2. DWEN must be unprogrammed when Lock Bit security is required. See “Program And Data
Memory Lock Bits” on page 139.
3. The SPIEN Fuse is not accessible in SPI Programming mode.
4. See “Watchdog Timer Control Register – WDTCR” on page 41 for details.
5. See Table 8-2 on page 38 for BODLEVEL Fuse decoding.
6. When programming the RSTDISBL Fuse, High-voltage Serial programming has to be used to
change fuses to perform further programming.
Table 22-5.
Fuse Low Byte
Fuse Low Byte
Bit No
Description
Default Value
CKDIV8(1)
7
Divide clock by 8
0 (unprogrammed)
(2)
6
Clock Output Enable
1 (unprogrammed)
SUT1
5
Select start-up time
1 (unprogrammed)(3)
SUT0
4
Select start-up time
0 (programmed)(3)
CKSEL3
3
Select Clock source
0 (programmed)(4)
CKSEL2
2
Select Clock source
0 (programmed)(4)
CKSEL1
1
Select Clock source
1 (unprogrammed)(4)
CKSEL0
0
Select Clock source
0 (programmed)(4)
CKOUT
Notes:
1. See “System Clock Prescaler” on page 29 for details.
2. The CKOUT Fuse allows the system clock to be output on PORTB4. See “Clock Output
Buffer” on page 30 for details.
3. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 6-7 on page 26 for details.
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4. The default setting of CKSEL1..0 results in internal RC Oscillator @ 8.0 MHz. See Table 6-6
on page 26 for details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if
Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits.
22.2.1
22.3
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the
fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and High-voltage Programming mode, also when the device is
locked. The three bytes reside in a separate address space.
22.3.1
ATtiny25 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x91 (indicates 2 KB Flash memory).
3. 0x002: 0x08 (indicates ATtiny25 device when 0x001 is 0x91).
22.3.2
ATtiny45 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x92 (indicates 4 KB Flash memory).
3. 0x002: 0x06 (indicates ATtiny45 device when 0x001 is 0x92).
22.3.3
ATtiny85 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8 KB Flash memory).
3. 0x002: 0x0B (indicates ATtiny85 device when 0x001 is 0x93).
22.4
Calibration Byte
Signature area of the ATtiny25/45/85 has one byte of calibration data for the internal RC Oscillator. This byte resides in the high byte of address 0x000. During reset, this byte is automatically
written into the OSCCAL Register to ensure correct frequency of the calibrated RC Oscillator.
22.5
Page Size
Table 22-6.
Device
142
No. of Words in a Page and No. of Pages in the Flash
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
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Table 22-7.
No. of Words in a Page and No. of Pages in the EEPROM
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
Device
22.6
Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while
RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the Programming Enable instruction needs to be executed first
before program/erase operations can be executed. NOTE, in Table 22-8 on page 143, the pin
mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal
SPI interface.
Figure 22-1. Serial Programming and Verify(1)
+1.8 - 5.5V
VCC
MOSI
MISO
SCK
RESET
GND
Notes:
1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
CLKI pin.
Table 22-8.
Pin Mapping Serial Programming
Symbol
Pins
I/O
Description
MOSI
PB0
I
Serial Data in
MISO
PB1
O
Serial Data out
SCK
PB2
I
Serial Clock
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:
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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
22.6.1
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 22-2 and Figure 22-3 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 22-10):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization. When in sync. the second byte (0x53), will echo back when issuing the
third byte of the Programming Enable instruction. Whether the echo is correct or not, all
four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give
RESET a positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at
a time by supplying the 5 LSB of the address and data together with the Load Program
memory Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program memory
Page is stored by loading the Write Program memory Page instruction with the 6 MSB
of the address. If polling (RDY/BSY) is not used, the user must wait at least tWD_FLASH
before issuing the next page. (See Table 22-9.) Accessing the serial programming
interface before the Flash write operation completes can result in incorrect
programming.
5. A: The EEPROM array is programmed one byte at a time by supplying the address and
data together with the appropriate Write instruction. An EEPROM memory location is
first automatically erased before new data is written. If polling (RDY/BSY) is not used,
the user must wait at least tWD_EEPROM before issuing the next byte. (See Table 22-9.) In
a chip erased device, no 0xFFs in the data file(s) need to be programmed.
B: The EEPROM array is programmed one page at a time. The Memory page is loaded
one byte at a time by supplying the 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 EEPROM
Memory Page instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used must wait at least tWD_EEPROM before issuing the
next page (See Table 22-7). In a chip erased device, no 0xFF in the data file(s) need to
be programmed.
6. Any memory location can be verified by using the Read instruction which returns the
content at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal
operation.
144
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ATtiny25/45/85 Auto
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
Table 22-9.
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
4.0 ms
tWD_FUSE
4.5 ms
Figure 22-2. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
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Table 22-10. Serial Programming Instruction Set
Instruction Format
Instruction
Byte 1
Byte 2
Byte 3
Byte4
Operation
Programming Enable
1010
1100
0101
0011
xxxx
xxxx
xxxx
xxxx
Enable Serial Programming
after RESET goes low.
Chip Erase
1010
1100
100x
xxxx
xxxx
xxxx
xxxx
xxxx
Chip Erase EEPROM and
Flash.
0010
H000
0000
000a
bbbb
bbbb
oooo
oooo
Read H (high or low) data o
from Program memory at
word address a:b.
0100
H000
000x
xxxx
xxxb
bbbb
iiii
iiii
Write H (high or low) data i to
Program memory page at
word address b. Data low
byte must be loaded before
Data high byte is applied
within the same address.
Write Program
Memory Page
0100
1100
0000
000a
bbxx
xxxx
xxxx
xxxx
Write Program memory Page
at address a:b.
Read EEPROM
Memory
1010
0000
000x
xxxx
xxbb
bbbb
oooo
oooo
Read data o from EEPROM
memory at address b.
Write EEPROM
Memory
1100
0000
000x
xxxx
xxbb
bbbb
iiii
iiii
Write data i to EEPROM
memory at address b.
Load EEPROM
Memory Page (page
access)
1100
0001
0000
0000
0000
00bb
iiii
iiii
Load data i to EEPROM
memory page buffer. After
data is loaded, program
EEPROM page.
Write EEPROM
Memory Page (page
access)
1100
0010
00xx
xxxx
xxbb
bb00
xxxx
xxxx
0101
1000
0000
0000
xxxx
xxxx
xxoo
oooo
Read Lock bits. “0” =
programmed, “1” =
unprogrammed. See Table
22-1 on page 140 for details.
1010
1100
111x
xxxx
xxxx
xxxx
11ii
iiii
Write Lock bits. Set bits = “0”
to program Lock bits. See
Table 22-1 on page 140 for
details.
0011
0000
000x
xxxx
xxxx
xxbb
oooo
oooo
Read Signature Byte o at
address b.
Write Fuse bits
1010
1100
1010
0000
xxxx
xxxx
iiii
iiii
Set bits = “0” to program, “1”
to unprogram. See Table 225 on page 141 for details.
Write Fuse High bits
1010
1100
1010
1000
xxxx
xxxx
iiii
iiii
Set bits = “0” to program, “1”
to unprogram. See Table 224 on page 141 for details.
1010
1100
1010
0100
xxxx
xxxx
xxxx
xxxi
Set bits = “0” to program, “1”
to unprogram. See Table 223 on page 140 for details.
Read Program
Memory
Load Program
Memory Page
Read Lock bits
Write Lock bits
Read Signature Byte
Write Extended Fuse
Bits
146
Write EEPROM page at
address b.
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Table 22-10. Serial Programming Instruction Set
Instruction Format
Instruction
Read Fuse bits
Read Fuse High bits
Read Extended Fuse
Bits
Read Calibration Byte
Byte 1
Byte 2
Byte 3
Byte4
Operation
0101
0000
0000
0000
xxxx
xxxx
oooo
oooo
Read Fuse bits. “0” =
programmed, “1” =
unprogrammed. See Table
22-5 on page 141 for details.
0101
1000
0000
1000
xxxx
xxxx
oooo
oooo
Read Fuse High bits. “0” =
pro-grammed, “1” =
unprogrammed. See Table
22-4 on page 141 for details.
0101
0000
0000
1000
xxxx
xxxx
oooo
oooo
Read Extended Fuse bits. “0”
= pro-grammed, “1” =
unprogrammed. See Table
22-3 on page 140 for details.
0011
1000
000x
xxxx
0000
0000
oooo
oooo
Read Calibration Byte
1111
0000
0000
0000
xxxx
xxxx
xxxx
xxxo
If o = “1”, a programming
operation is still busy. Wait
until this bit returns to “0”
before applying another
command.
Poll RDY/BSY
Note:
22.6.2
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Serial Programming Characteristics
Figure 22-3. Serial Programming Timing
MOSI
tSHOX
tOVSH
SCK
tSLSH
tSHSL
MISO
tSLIV
Table 22-11. Serial Programming Characteristics, TA = -40°C to 125°C, VCC = 2.7 - 5.5V
(Unless Otherwise Noted)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (ATtiny25/45/85V)
tCLCL
1/tCLCL
tCLCL
Oscillator Period (ATtiny25/45/85V)
Oscillator Frequency (ATtiny25/45/85L, VCC = 2.7 5.5V)
Oscillator Period (ATtiny25/45/85L, VCC = 2.7 5.5V)
Min
0
Typ
Max
Units
4
MHz
250
0
100
ns
10
MHz
ns
147
7598D–AVR–02/07
Table 22-11. Serial Programming Characteristics, TA = -40°C to 125°C, VCC = 2.7 - 5.5V
(Unless Otherwise Noted)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (ATtiny25/45/85, VCC = 4.5V 5.5V)
0
tCLCL
Oscillator Period (ATtiny25/45/85, 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
Note:
22.7
Min
Typ
15
Max
Units
20
MHz
ns
1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
High-voltage Serial Programming
This section describes how to program and verify Flash Program memory, EEPROM Data memory, Lock bits and Fuse bits in the ATtiny25/45/85.
Figure 22-4. High-voltage Serial Programming
CC
Table 22-12. 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)
The minimum period for the Serial Clock Input (SCI) during High-voltage Serial Programming is
220 ns.
148
ATtiny25/45/85 Auto
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ATtiny25/45/85 Auto
Table 22-13. Pin Values Used to Enter Programming Mode
22.8
Pin
Symbol
Value
SDI
Prog_enable[0]
0
SII
Prog_enable[1]
0
SDO
Prog_enable[2]
0
High-voltage Serial Programming Algorithm
To program and verify the ATtiny25/45/85 in the High-voltage Serial Programming mode, the following sequence is recommended (See instruction formats in Table 22-15):
22.8.1
Enter High-voltage Serial Programming Mode
The following algorithm puts the device in High-voltage Serial Programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET pin to “0” and toggle SCI at least six times.
3. Set the Prog_enable pins listed in Table 22-13 to “000” and wait at least 100 ns.
4. Apply VHVRST - 5.5V to RESET. Keep the Prog_enable pins unchanged for at least
tHVRST after the High-voltage has been applied to ensure the Prog_enable signature
has been latched.
5. Shortly after latching the Prog_enable signature, the device will activly output data on
the Prog_enable[2]/SDO pin, and the resulting drive contention may increase the
power consumption. To minimize this drive contention, release the Prog_enable[2] pin
after tHVRST has elapsed.
6. Wait at least 50 µs before giving any serial instructions on SDI/SII.
Table 22-14. High-voltage Reset Characteristics
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
Supply Voltage
22.8.2
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 needs only be loaded once when writing or reading multiple memory
locations.
• Skip writing the data value 0xFF that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
• 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.
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22.8.3
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 reprogrammed.
Note:
1. The EEPROM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
1. Load command “Chip Erase” (see Table 22-15).
2. Wait after Instr. 3 until SDO goes high for the “Chip Erase” cycle to finish.
3. Load Command “No Operation”.
22.8.4
Programming the Flash
The Flash is organized in pages, see Table 22-10 on page 146. When programming the Flash,
the program data is latched into a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes how to program the entire Flash
memory:
1. Load Command “Write Flash” (see Table 22-15).
2. Load Flash Page Buffer.
3. Load Flash High Address and Program Page. Wait after Instr. 3 until SDO goes high
for 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 22-6, Figure 22-7 and Table 22-16 for details.
Figure 22-5. Addressing the Flash which is Organized in Pages
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
150
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ATtiny25/45/85 Auto
Figure 22-6. High-voltage Serial Programming Waveforms
SDI
PB0
MSB
LSB
SII
PB1
MSB
LSB
MSB
SDO
PB2
SCI
PB3
22.8.5
0
LSB
1
2
3
4
5
6
7
8
9
10
Programming the EEPROM
The EEPROM is organized in pages, see Table 22-11 on page 147. When programming the
EEPROM, the data is latched into a page buffer. This allows one page of data to be programmed simultaneously. The programming algorithm for the EEPROM Data memory is as
follows (refer to Table 22-15):
1. Load Command “Write EEPROM”.
2. Load EEPROM Page Buffer.
3. Program EEPROM Page. Wait after Instr. 2 until SDO goes high for the “Page Programming” 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”.
22.8.6
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to Table 22-15):
1. Load Command "Read Flash".
2. Read Flash Low and High Bytes. The contents at the selected address are available at
serial output SDO.
22.8.7
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Table 22-15):
1. Load Command “Read EEPROM”.
2. Read EEPROM Byte. The contents at the selected address are available at serial output SDO.
22.8.8
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 22-15.
22.8.9
Reading the Signature Bytes and Calibration Byte
The algorithms for reading the Signature bytes and Calibration byte are shown in Table 22-15.
22.8.10
Power-off sequence
Set SCI to “0”. Set RESET to “1”. Turn VCC power off.
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Table 22-15. High-voltage Serial Programming Instruction Set for ATtiny25/45/85
Instruction Format
Instruction
Chip Erase
Load “Write
Flash”
Command
Instr.1/5
Instr.2/6
Instr.3
SD
I
0_1000_0000_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0110_0100_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0001_0000_00
SII
0_0100_1100_00
SD
O
x_xxxx_xxxx_xx
SD
I
SII
Load Flash
Page Buffer
Load Flash
High Address
and Program
Page
Load “Read
Flash”
Command
Read Flash
Low and High
Bytes
Load “Write
EEPROM”
Command
152
SD
O
0_ bbbb_bbbb
_00
0_0000_1100_00
x_xxxx_xxxx_xx
SD
I
0_0000_0000_00
SII
0_0111_1100_00
SD
O
x_xxxx_xxxx_xx
0_dddd_dddd_00
0_0000_0000_00
0_0010_1100_00
0_0011_1100_00
0_0111_1101_00
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
0_0000_0000_00
0_0000_0000_00
0_0001_1100_00
0_0110_0100_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
0_0100_1100_00
SD
O
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. See Note 1.
Enter Flash Read mode.
SD
I
0_bbbb_bbbb_00
0_0000_000a_00
0_0000_0000_00
0_0000_0000_00
SII
0_0000_1100_00
0_0001_1100_00
0_0110_1000_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqqx_xx
SD
I
0_0000_0000_00
0_0000_0000_00
SII
0_0111_1000_00
0_0111_1100_00
SD
O
x_xxxx_xxxx_xx
p_pppp_pppx_xx
SD
I
0_0001_0001_00
SII
0_0100_1100_00
SD
O
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.
See Note 1.
Instr 5.
0_0000_000a_00
0_0000_0010_00
Wait after Instr.3 until SDO goes
high for the Chip Erase cycle to
finish.
0_eeee_eeee_00
SII
SII
Operation Remarks
Enter Flash Programming code.
SD
I
SD
I
Instr.4
Repeat Instr. 1, 3 - 6 for each
new address. Repeat Instr. 2 for
a new 256 byte page.
Instr 5 - 6.
Enter EEPROM Programming
mode.
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Table 22-15. High-voltage Serial Programming Instruction Set for ATtiny25/45/85 (Continued)
Instruction Format
Instruction
Load
EEPROM
Page Buffer
Program
EEPROM
Page
Write
EEPROM
Byte
Load “Read
EEPROM”
Command
Read
EEPROM
Byte
Write Fuse
Low Bits
Write Fuse
High Bits
Write Lock
Bits
Read Fuse
Low Bits
Instr.1/5
Instr.2/6
Instr.3
Instr.4
SD
I
0_00bb_bbbb_00
0_eeee_eeee_00
0_0000_0000_00
0_0000_0000_00
SII
0_0000_1100_00
0_0010_1100_00
0_0110_1101_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0000_0000_00
0_0000_0000_00
SII
0_0110_0100_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_00bb_bbbb_00
0_eeee_eeee_00
0_0000_0000_00
0_0000_0000_00
SII
0_0000_1100_00
0_0010_1100_00
0_0110_1101_00
0_0110_0100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0000_0000_00
SII
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
SD
I
0_0000_0011_00
SII
0_0100_1100_00
SD
O
x_xxxx_xxxx_xx
Operation Remarks
Repeat Instr. 1 - 4 until the entire
page buffer is filled or until all
data within the page is filled. See
Note 2.
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.
Repeat Instr. 1 - 5 for each new
address. Wait after Instr. 5 until
SDO goes high. See Note 3.
Instr. 5
Enter EEPROM Read mode.
SD
I
0_bbbb_bbbb_00
0_aaaa_aaaa_00
0_0000_0000_00
0_0000_0000_00
SII
0_0000_1100_00
0_0001_1100_00
0_0110_1000_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqq0_00
SD
I
0_0100_0100_00
0_A987_6543_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0010_1100_00
0_0110_0100_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0100_0000_00
0_000F_EDCB_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0010_1100_00
0_0111_0100_00
0_0111_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0010_0000_00
0_0000_0021_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0010_1100_00
0_0110_0100_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SD
I
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0110_1000_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
A_9876_543x_xx
Repeat Instr. 1, 3 - 4 for each
new address. Repeat Instr. 2 for
a new 256 byte page.
Wait after Instr. 4 until SDO goes
high. Write A - 3 = “0” to program
the Fuse bit.
Wait after Instr. 4 until SDO goes
high. Write F - B = “0” to program
the Fuse bit.
Wait after Instr. 4 until SDO goes
high. Write 2 - 1 = “0” to program
the Lock Bit.
Reading A - 3 = “0” means the
Fuse bit is programmed.
153
7598D–AVR–02/07
Table 22-15. High-voltage Serial Programming Instruction Set for ATtiny25/45/85 (Continued)
Instruction Format
Instruction
Read Fuse
High Bits
Read Lock
Bits
Read
Signature
Bytes
Read
Calibration
Byte
Load “No
Operation”
Command
Instr.1/5
Instr.2/6
Instr.3
SD
I
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0111_1010_00
0_0111_1110_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxFE_DCBx_xx
SD
I
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0111_1000_00
0_0111_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_x21x_xx
SD
I
0_0000_1000_00
0_0000_00bb_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0000_1100_00
0_0110_1000_00
0_0110_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqqx_xx
SD
I
0_0000_1000_00
0_0000_0000_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0000_1100_00
0_0111_1000_00
0_0111_1100_00
SD
O
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
p_pppp_pppx_xx
SD
I
0_0000_0000_00
SII
0_0100_1100_00
SD
O
x_xxxx_xxxx_xx
Instr.4
Operation Remarks
Reading F - B = “0” means the
Fuse bit is programmed.
Reading 2, 1 = “0” means the
Lock bit is programmed.
Repeats Instr 2 4 for each
signature byte address.
Note:
a = address high bits, b = address low bits, d = data in high bits, e = data in low bits, p = data out high bits, q = data out low bits,
x = don’t care, 1 = Lock Bit1, 2 = Lock Bit2, 3 = CKSEL0 Fuse, 4 = CKSEL1 Fuse, 5 = SUT0 Fuse, 6 = SUT1 Fuse, 7 = CKDIV8,
Fuse, 8 = WDTON Fuse, 9 = EESAVE Fuse, A = SPIEN Fuse, B = RSTDISBL Fuse, C = BODLEVEL0 Fuse, D= BODLEVEL1
Fuse, E = MONEN Fuse, F = SPMEN Fuse
Notes:
1. For page sizes less than 256 words, parts of the address (bbbb_bbbb) will be parts of the page address.
2. For page sizes less than 256 bytes, parts of the address (bbbb_bbbb) will be parts of the page address.
3. The EEPROM is written page-wise. But only the bytes that are loaded 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.
154
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
22.9
High-voltage Serial Programming Characteristics
Figure 22-7. High-voltage Serial Programming Timing
CC
CK
Table 22-16. High-voltage Serial Programming Characteristics TA = 25°C ± 10%, VCC = 5.0V ±
10% (Unless otherwise noted)
Symbol
Parameter
Min
tSHSL
SCI (PB3) Pulse Width High
110
ns
tSLSH
SCI (PB3) Pulse Width Low
110
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
Wait after Instr. 3 for Write Fuse Bits
2.5
ms
tWLWH_PFB
Typ
Max
Units
155
7598D–AVR–02/07
23. Electrical Characteristics
23.1
Absolute Maximum Ratings*
Operating Temperature.................................. -40°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-1.0V to VCC+0.5V
Voltage on RESET with respect to Ground......-1.0V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA
DC Characteristics TA = -40°C to 125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1) .
Symbol
Parameter
Condition
Min.
VIL
Input Low Voltage
Except RESET and XTAL
pins
VIL1
Input Low Voltage
VIL2
Max.
Units
-0.5
0.3VCC
V
XTAL pin
-0.5
0.1VCC
V
Input Low Voltage
RESET pin
-0.5
0.1VCC
V
VIH
Input High-voltage
Except RESET and XTAL
pins
0.6VCC(3)
VCC +0.5
V
VIH1
Input High-voltage
XTAL pin
0.9VCC(3)
VCC +0.5
V
VIH2
Input High-voltage
RESET pin
0.9VCC(3)
VCC +0.5
V
VOL
Output Low Voltage(4)
(Port B) except PB5
IOL = 8 mA, VCC = 5V
IOL = 5 mA, VCC = 3V
0.6
0.5
V
V
VOH
Output High-voltage(5)
(Port B) except PB5
IOH = -8 mA, VCC = 5V
IOH = -5 mA, VCC = 3V
VOL1
Output Low Voltage(4)
PB5
IOL = 1 mA
VOH1
Output High-voltage(5)
PB5
IOH = -200µA, VCC = 5V
IIL
Input Leakage
Current I/O Pin except
RESET
Vcc = 5.5V, pin low
(absolute value)
1
µA
IIH
Input Leakage
Current I/O Pin except
RESET
Vcc = 5.5V, pin high
(absolute value)
1
µA
RRST
Reset Pull-up Resistor
30
60
kΩ
Rpu
I/O Pin Pull-up Resistor
20
50
kΩ
156
Typ.
4.1
2.3
V
V
0.6
3.2
V
V
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
DC Characteristics TA = -40°C to 125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1) .
Symbol
Parameter
Condition
Power Supply Current
ICC
Power-down mode
Notes:
Min.
Typ.
Max.
Units
Active 4MHz, VCC = 3V
1.25
2
mA
Active 8MHz, VCC = 5V
5
10
mA
Active 16MHz, VCC = 5V
10
15
mA
Idle 4MHz, VCC = 3V
0.4
0.5
mA
Idle 8MHz, VCC = 5V
1.2
2
mA
Idle 16MHz, VCC = 5V
2.5
5
mA
WDT enabled, VCC = 3V
5
30
µA
WDT disabled, VCC = 3V
2
24
µA
WDT enabled, VCC = 5V
9
50
µA
WDT disabled, VCC = 5V
3
36
µA
1. All DC Characteristics contained in this data sheet result from actual silicon characterization.
2. “Max” means the highest value where the pin is guaranteed to be read as low.
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (8 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 60 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
5. Although each I/O port can source more than the test conditions (8 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 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.
23.2
External Clock Drive Waveforms
Figure 23-1. External Clock Drive Waveforms
V IH1
V IL1
157
7598D–AVR–02/07
23.3
External Clock Drive
Table 23-1.
External Clock Drive(1). PRELIMINARY
VCC = 2.7 - 5.5V
Notes:
VCC = 4.5 5.5V
Symbol
Parameter
Min.
Max.
Min.
Max.
Units
1/tCLCL
Clock Frequency
0
8
0
16
MHz
tCLCL
Clock Period
100
50
ns
tCHCX
High Time
40
20
ns
tCLCX
Low Time
40
20
ns
tCLCH
Rise Time
1.6
0.5
µs
tCHCL
Fall Time
1.6
0.5
µs
∆tCLCL
Change in period from one clock cycle to
the next
2
2
%
1. All DC Characteristics contained in this data sheet result from actual silicon characterization.
Figure 23-2. Maximum Frequency vs. VCC
16 MHz
8 MHz
Safe Operating
Area
2.7V
158
4.5V
5.5V
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
23.4
ADC Characteristics – Preliminary Data
ADC Characteristics, Single Ended Channels. -40°C - 125°C. (1). PRELIMINARY
Table 23-2.
Symbol
Parameter
Resolution
Single Ended Conversion
Max(1)
Units
10
Bits
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
3
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
Noise Reduction Mode
1.5
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
Noise Reduction Mode
2.5
LSB
Integral Non-linearity (INL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
1
LSB
Differential Non-linearity (DNL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
0.5
LSB
Gain Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2.5
LSB
Offset Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
1.5
LSB
Conversion Time
Free Running Conversion
Analog Supply Voltage
Input Voltage
13
260
µs
50
1000
kHz
VCC - 0.3(2)
VCC + 0.3(3)
V
GND
VREF-50mV
V
Input Bandwidth
VINT
Internal Voltage Reference
RAIN
Analog Input Resistance
Note:
Typ(1)
2
Clock Frequency
VIN
Min(1)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
Absolute accuracy (Including
INL, DNL, quantization error,
gain and offset error)
AVCC
Condition
38.5
1.0
1.1
100
kHz
1.2
V
MΩ
1. All DC Characteristics contained in this data sheet result from actual silicon characterization.
2. Minimum for AVCC is 2.7V.
3. Maximum for AVCC is 5.5V.
159
7598D–AVR–02/07
23.5
Calibrated RC Oscillator Accuracy
Table 23-3.
Calibration Accuracy of Internal RC Oscillator
Factory
Calibration
User Calibration
Frequency
Vcc
Temperature
Calibration
Accuracy
8.0 MHz
3V
25°C
±1%
7.3 - 8.1 MHz
2.7V - 5.5V
-40°C - +125°C
±14%
24. Typical Characteristics
The data contained in this section is extracted from actual silicon characterization and should be
treated as indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. A sine wave generator with railtorail output is used as clock
source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f
where CL = load capacitance, VCC = operating voltage and f = average switching frequency of
I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.
160
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
24.1
Active Supply Current
Figure 24-1. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE S UP P LY CURRENT vs . LOW FREQUENCY
0.1 - 1.0 MHz
0.040
5.5 V
0.035
5.0 V
0.030
4.5 V
4.0 V
ICC (mA)
0.025
0.020
3.3 V
2.7 V
0.015
1.8 V
0.010
0.005
0.000
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 24-2. Active Supply Current vs. Frequency (1 - 20 MHz)
ACTIVE S UP P LY CURRENT vs . FREQUENCY
1 - 20MHz
14
5.5 V
12
5.0 V
ICC (mA)
10
4.5 V
8
4.0 V
6
3.3 V
4
2.7 V
2
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
161
7598D–AVR–02/07
Figure 24-3. Active Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
ACTIVE S UP P LY CURRENT vs . VC C
INTERNAL RC OSCILLATOR, 128 KHz
0.25
125
85
25
-40
ICC(mA)
0.2
˚C
˚C
˚C
˚C
0.15
0.1
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-4. Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
ACTIVE S UP P LY CURRENT vs . VC C
INTERNAL RC OSCILLATOR, 1 MHz
1.8
1.6
125
85
25
-40
1.4
ICC (mA)
1.2
˚C
˚C
˚C
˚C
1
0.8
0.6
0.4
0.2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
162
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-5. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE S UP P LY CURRENT vs . V
CC
INTERNAL RC OSCILLATOR, 8 MHz
8
7
125
85
25
-40
ICC (mA)
6
˚C
˚C
˚C
˚C
5
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
24.2
Idle Supply Current
Figure 24-6. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
IDLE S UP P LY CURRENT vs . LOW FREQUENCY
0.1 - 1.0 MHz
0.25
5.5 V
0.2
5.0 V
Idle (mA)
4.5 V
4.0 V
0.15
3.3 V
2.7 V
0.1
1.8 V
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
163
7598D–AVR–02/07
Figure 24-7. Idle Supply Current vs. Frequency (1 - 20 MHz)
IDLE S UP P LY CURRENT vs . FREQUENCY
1 - 20MHz
Idle (mA)
4
3.5
5.5 V
3
5.0 V
2.5
4.5 V
2
4.0 V
1.5
3.3 V
1
2.7 V
0.5
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 24-8. Idle Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
IDLE S UP P LY CURRENT vs . VC C
INTERNAL RC OSCILLATOR, 128 KHz
0.25
125
85
25
-40
0.2
˚C
˚C
˚C
˚C
ICC
0.15
0.1
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
164
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-9. Idle Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
IDLE S UP P LY CURRENT vs . VC C
INTERNAL RC OSCILLATOR, 1 MHz
0.6
0.5
Idle (mA)
0.4
125
85
25
-40
˚C
˚C
˚C
˚C
125
85
25
-40
˚C
˚C
˚C
˚C
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-10. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE S UP P LY CURRENT vs . VC C
INTERNAL RC OSCILLATOR, 8 MHz
2
1.8
Idle (mA)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
24.2.1
Using the Power Reduction Register
The tables and formulas below can be 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
165
7598D–AVR–02/07
are controlled by the Power Reduction Register. See “Power Reduction Register” on page 33 for
details.
Table 24-1.
Additional Current Consumption for the different I/O modules (absolute values)
PRR bit
Typical numbers
VCC = 2V, F = 1MHz
VCC = 3V, F = 4MHz
VCC = 5V, F = 8MHz
PRTIM1
43 uA
270 uA
1090 uA
PRTIM0
5.0 uA
28 uA
116 uA
PRUSI
4.0 uA
25 uA
102 uA
PRADC
13 uA
84 uA
351 uA
Table 24-2.
Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external
clock
(see Figure 24-1 and Figure 24-2)
Additional Current consumption
compared to Idle with external clock
(see Figure 24-6 and Figure 24-7)
PRTIM1
17.3%
68.4 %
PRTIM0
1.8 %
7.3 %
PRUSI
1.6 %
6.4 %
PRADC
5.4 %
21.4 %
It is possible to calculate the typical current consumption based on the numbers from Table 2 for
other VCC and frequency settings than listed in Table 1.
24.2.1.1
Example 1
Calculate the expected current consumption in idle mode with USI, TIMER0, and ADC enabled
at VCC = 2.0V and F = 1MHz. From Table 24-2, third column, we see that we need to add 6.4%
for the USI, 7.3% for the TIMER0 module, and 21.4% for the ADC module. Reading from Figure
24-9, we find that the idle current consumption is ~0,25mA at VCC = 3.0V and F = 1MHz. The
total current consumption in idle mode with USI, TIMER0, and ADC enabled, gives:
I CC total ≈ ( 0.25 )mA • ( 1 + 0.064 + 0.073 + 0.214 ) ≈ 0.337mA
166
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
24.3
Power-Down Supply Current
Figure 24-11. Power-Down Supply Current vs. VCC (Watchdog Timer Disabled)
P OWER-DOWN S UP P LY CURRENT vs . VC C
WATCHDOG TIMER DISABLED
4
125 ˚C
3.5
3
ICC (uA)
2.5
2
1.5
1
85 ˚C
0.5
-40 ˚C
25 ˚C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-12. Power-Down Supply Current vs. VCC (Watchdog Timer Enabled)
P OWER-DOWN S UP P LY CURRENT vs . VC C
WATCHDOG TIMER ENABLED
12
10
125 ˚C
-40 ˚C
25 ˚C
85 ˚C
ICC (uA)
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
167
7598D–AVR–02/07
24.4
Pin Pull-up
Figure 24-13. I/O Pin Pull-Up Resistor Current vs. Input Voltage (VCC = 1.8V)
I/O P IN P ULL-UP RES IS TOR CURRENT vs . INP UT VOLTAGE
Vcc = 1.8V
60
50
IOP (uA)
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
-40
25
85
2 125
˚C
˚C
˚C
˚C
V OP (V)
Figure 24-14. I/O Pin Pull-Up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O P IN P ULL-UP RES IS TOR CURRENT vs . INP UT VOLTAGE
Vcc = 2.7V
90
80
70
IOP (uA)
60
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
125
85
25
3 -40
˚C
˚C
˚C
˚C
V OP (V)
168
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-15. I/O Pin Pull-Up Resistor Current vs. Input Voltage (VCC = 5.0V)
I/O P IN P ULL-UP RES IS TOR CURRENT vs . INP UT VOLTAGE
Vcc = 5.0V
160
140
120
IOP (uA)
100
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
125 ˚C
85 ˚C
25 ˚C
5 -40 ˚C
V OP (V)
Figure 24-16. Reset Pull-Up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
RES ET P ULL-UP RES IS TOR CURRENT vs . RES ET P IN VOLTAGE
Vcc = 1.8V
40
35
IRE S E T (uA)
30
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
125
85
25
2 -40
˚C
˚C
˚C
˚C
V RES ET (V)
169
7598D–AVR–02/07
Figure 24-17. Reset Pull-Up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
RES ET P ULL-UP RES IS TOR CURRENT vs . RES ET P IN VOLTAGE
Vcc = 2.7V
70
60
IRE S E T (uA)
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
125
85
25
-40
˚C
˚C
˚C
˚C
V RES ET (V)
Figure 24-18. Reset Pull-Up Resistor Current vs. Reset Pin Voltage (VCC = 5.0V)
RES ET P ULL-UP RES IS TOR CURRENT vs . RES ET P IN VOLTAGE
Vcc = 5.0V
140
120
IRE S E T (uA)
100
80
60
40
20
0
0
1
2
3
4
5
125
85
25
6
-40
˚C
˚C
˚C
˚C
V RES ET (V)
170
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
24.5
Pin Driver Strength
Figure 24-19. I/O Pin Source Current vs. Output Voltage (VCC = 1.8V)
I/O P IN S INK CURRENT vs . OUTP UT VOLTAGE
V CC = 1.8V
12
-40 ˚C
10
25 ˚C
85 ˚C
125 ˚C
IOL (mA)
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
V OL (V)
Figure 24-20. I/O Pin Source Current vs. Output Voltage (VCC = 3V)
I/O P IN OUTP UT VOLTAGE vs . S INK CURRENT
Vc c = 3.0V
1.2
125
1
85
V OL (V)
0.8
25
0.6
-40
0.4
0.2
0
0
5
10
15
20
25
IOL (V)
171
7598D–AVR–02/07
Figure 24-21. I/O Pin Source Current vs. Output Voltage (VCC = 5V)
I/O P IN OUTP UT VOLTAGE vs . S INK CURRENT
Vc c = 5.0V
0.7
125
0.6
V OL (V)
85
0.5
25
0.4
-40
0.3
0.2
0.1
0
0
5
10
15
20
25
IOL (V)
Figure 24-22. I/O Pin Sink Current vs. Output Voltage (VCC = 1.8V)
I/O P IN S OURCE CURRENT vs . OUTP UT VOLTAGE
V CC = 1.8V
9
8
25 ˚C
7
IOH (mA)
6
-40 ˚C
85 ˚C
5
125 ˚C
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
V OH (V)
172
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-23. I/O Pin Sink Current vs. Output Voltage (VCC = 3V)
I/O P IN OUTP UT VOLTAGE vs . S OURCE CURRENT
Vc c = 3V
3.5
3
V OH (V
2.5
-40
25
85
125
2
1.5
1
0.5
0
0
5
10
15
20
25
IOH (mA)
Figure 24-24. I/O Pin Sink Current vs. Output Voltage (VCC = 5.0V)
I/O P IN OUTP UT VOLTAGE vs . S OURCE CURRENT
Vc c = 5.0V
5.1
5
4.9
V OH (V)
4.8
4.7
4.6
-40
4.5
25
85
125
4.4
4.3
0
5
10
15
20
25
IOH (mA)
173
7598D–AVR–02/07
24.6
Pin Thresholds and Hysteresis
Figure 24-25. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read As '1')
I/O P IN INP UT THRES HOLD VOLTAGE vs . V
CC
VIH, IO PIN READ AS '1'
-40
25
85
125
3
2.5
˚C
˚C
˚C
˚C
Thre s hold
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-26. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read As '0')
I/O P IN INP UT THRES HOLD VOLTAGE vs . VC C
VIL, IO PIN READ AS '0'
125
85
25
-40
2.5
˚C
˚C
˚C
˚C
Thre s hold
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
174
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-27. I/O Pin Input Hysteresis vs. VCC
I/O P IN INP UT HYS TERES IS
0.8
0.7
Thre s hold
0.6
0.5
0.4
-40
25
85
125
0.3
0.2
˚C
˚C
˚C
˚C
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-28. Reset Input Threshold Voltage vs. VCC (VIH, Reset Pin Read As '1')
RES ET INP UT THRES HOLD VOLTAGE vs . V C C
VIH, IO PIN READ AS '1'
125
85
25
-40
2.5
˚C
˚C
˚C
˚C
Thre s hold
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
175
7598D–AVR–02/07
Figure 24-29. Reset Input Threshold Voltage vs. VCC (VIL, Reset Pin Read As '0')
RES ET INP UT THRES HOLD VOLTAGE vs . CVC
VIL, IO PIN READ AS '0'
125
85
25
-40
˚C
˚C
˚C
˚C
125
85
25
5.5 -40
˚C
˚C
˚C
˚C
2.5
Thre s hold
2
1.5
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-30. Reset Input Pin Hysteresis vs. VCC
RES ET INP UT THRES HOLD VOLTAGE vs . CC
V
VIH, IO PIN READ AS '1'
0.25
Thre s hold
0.2
0.15
0.1
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
V CC (V)
176
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
24.7
BOD Thresholds and Analog Comparator Offset
Figure 24-31. BOD Thresholds vs. Temperature (BODLEVEL Is 4.3V)
BOD THRES HOLDS vs . TEMP ERATURE
BODLEVEL = 4.3V
4.4
4.35
Ris ing
Thre s hold (V)
4.3
Falling
4.25
4.2
4.15
4.1
4.05
4
-50 -40 -30 -20 -10
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140
Temperature (C)
Figure 24-32. BOD Thresholds vs. Temperature (BODLEVEL Is 2.7V)
BOD THRES HOLDS vs . TEMP ERATURE
BODLEVEL = 2.7V
2.8
Ris ing
Thre s hold (V)
2.75
2.7
Falling
2.65
2.6
2.55
2.5
-50 -40 -30 -20 -10
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140
Te mpe ra ture (C)
177
7598D–AVR–02/07
Figure 24-33. BOD Thresholds vs. Temperature (BODLEVEL Is 1.8V)
BOD THRES HOLDS vs . TEMP ERATURE
BODLEVEL at 1.8V
1.9
1.85
Thre s hold (V)
Ris ing Vcc
1.8
Falling Vcc
1.75
1.7
1.65
1.6
-50 -40 -30 -20 -10
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140
Temperature (C)
24.8
Internal Oscillator Speed
Figure 24-34. Watchdog Oscillator Frequency vs. VCC)
WATCHDOC OS CILLATOR FREQUENCY vs . V CC
0.118
0.116
-40 ˚C
0.114
25 ˚C
FRC (MHz )
0.112
0.11
0.108
85 ˚C
0.106
0.104
125 ˚C
0.102
0.1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
178
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-35. Watchdog Oscillator Frequency vs. Temperature
WATCHDOG OS CILLATOR FREQUENCY vs . TEMP ERATURE
0.118
0.116
0.114
FRC (MHz )
0.112
0.11
0.108
1.8 V
0.106
2.7
3.6
4.0
5.5
0.104
0.102
0.1
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
V
V
V
V
100 110 120
Temperature
Figure 24-36. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8MHz RC OS CILLATOR FREQUENCY vs . TEMP ERATURE
8.4
5.0 V
3.0 V
8.3
8.2
FRC (MHz )
8.1
8
7.9
7.8
7.7
7.6
7.5
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
179
7598D–AVR–02/07
Figure 24-37. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8MHz RC OS CILLATOR FREQUENCY vs . OP ERATING VOLTAGE
8.4
125 ˚C
8.3
85 ˚C
8.2
FRC (MHz )
8.1
25 ˚C
8
7.9
7.8
-40 ˚C
7.7
7.6
7.5
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-38. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 8MHz RC OS CILLATOR FREQUENCY vs . OS CCAL VALUE
14
125
85
25
-40
12
˚C
˚C
˚C
˚C
FRC (MHz )
10
8
6
4
2
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL (X1)
180
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
24.9
Current Consumption of Peripheral Units
Figure 24-39. Brownout Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs . CVC
35
125
85
25
-40
30
ICC (uA)
25
˚C
˚C
˚C
˚C
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-40. Analog Comparator Current vs. VCC
ANALOG COMP ARATOR CURRENT vs . V
CC
AREF = AVcc
350
150 ˚C
300
125 ˚C
85 ˚C
ICC (uA)
250
200
25 ˚C
150
100
50
-40 ˚C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
V CC (V)
181
7598D–AVR–02/07
24.10 Current Consumption in Reset and Reset Pulse width
Figure 24-41. Reset Supply Current vs. VCC (0.1 - 1.0 MHz, Excluding Current through the
Reset Pull-up)
RES ET S UP P LY CURRENT vs . CVC
0.1 - 1.0 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
0.14
5.5 V
0.12
5.0 V
ICC (mA)
0.1
4.5 V
4.0 V
0.08
3.3 V
0.06
2.7 V
0.04
1.8 V
0.02
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 24-42. Reset Supply Current vs. VCC (1 - 24 MHz, Excluding Current through the Reset
Pull-up)
RES ET S UP P LY CURRENT vs . V C C
1 - 20 MHz , EXCLUDING CURRENT THROUGH THE RESET PULLUP
2.5
5.5 V
5.0 V
2
ICC (mA)
4.5 V
1.5
4.0 V
1
3.3 V
0.5
2.7 V
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
182
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-43. Reset Pulse Width vs. VCC
MINIMUM RES ET P ULS E WIDTH vs . VC C
2500
Puls e width (ns )
2000
1500
1000
125
85
25
-40
500
˚C
˚C
˚C
˚C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
24.11 Analog to Digital Converter
Figure 24-44. Analog to Digital Converter Differential mode OFFSET vs. VCC
Analog to Digital Converter - OFFS ET
Diffe re ntia l Inputs , Vc c = 4V, Vre f = 4V
2
1.5
1
0.5
Diff x1
0
-0.5
-1
-1.5
Diff x20
-2
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
Te mpe ra ture
183
7598D–AVR–02/07
Figure 24-45. Analog to Digital Converter Single Endded mode OFFSET vs. VCC
Analog to Digital Converter - OFFS ET
Single Ended, Vcc = 4V, Vref = 4V
2.5
2
LSB
1.5
1
0.5
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
Figure 24-46. Analog to Digital Converter Differential mode GAIN vs. VCC
Analog to Digital Converter - GAIN
Differential Inputs , Vcc = 5V, Vref = 4V
-1
-1.2
-1.4
-1.6
Diff x20
LSB
-1.8
-2
-2.2
-2.4
-2.6
Diff x1
-2.8
-3
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
184
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-47. Analog to Digital Converter Single Endded mode GAIN vs. VCC
Analog to Digital Converter - GAIN
Single Ended, Vcc = 4V, Vref = 4V
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
-0.5
LSB
-1
-1.5
-2
-2.5
Temperature
Figure 24-48. Analog to Digital Converter Differential mode DNL vs. VCC
Analog to Digital Converter - Differential Non Linearity DNL
Differential Inputs , Vcc = 4V, Vref = 4V
1.2
Diff x20
1
LSB
0.8
0.6
0.4
Diff x1
0.2
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
185
7598D–AVR–02/07
Figure 24-49. Analog to Digital Converter Single Endded mode DNL vs. VCC
Analog to Digital Converter - Differential Non Linearity DNL
Single Ended, Vcc = 4V, Vref = 4V
0.57
0.56
0.55
0.54
LSB
0.53
0.52
0.51
0.5
0.49
0.48
0.47
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
Figure 24-50. Analog to Digital Converter differential mode INL vs. VCC
Analog to Digital Converter - Integral Non Linearity INL
Differential Inputs , Vcc = 4V, Vref = 4V
1.8
1.6
Diff x20
1.4
LSB
1.2
1
0.8
0.6
Diff x1
0.4
0.2
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
186
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Figure 24-51. Analog to Digital Converter Single Endded mode INL vs. VCC
Analog to Digital Converter - Integral Non Linearity INL
Single Ended, Vcc = 4V, Vref = 4V
0.72
0.7
LSB
0.68
0.66
0.64
0.62
0.6
0.58
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100 110 120
Temperature
187
7598D–AVR–02/07
25. Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x3F
SREG
I
T
H
S
V
N
Z
C
page 7
0x3E
SPH
–
–
–
–
–
–
–
SP8
page 10
0x3D
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
page 10
0x3C
Reserved
188
Page
–
0x3B
GIMSK
–
INT0
PCIE
–
–
–
–
–
page 59
0x3A
GIFR
–
INTF0
PCIF
–
–
–
–
–
page 59
0x39
TIMSK
–
OCIE1A
OCIE1B
OCIE0A
OCIE0B
TOIE1
TOIE0
–
page 76
0x38
TIFR
–
OCF1A
OCF1B
OCF0A
OCF0B
TOV1
TOV0
–
page 76
0x37
SPMCSR
–
–
–
CTPB
RFLB
PGWRT
PGERS
SPMEN
page 137
0x36
Reserved
0x35
MCUCR
–
PUD
SE
SM1
SM0
–
ISC01
ISC00
page 31, page 53, page 58
0x34
MCUSR
–
–
–
–
WDRF
BORF
EXTRF
PORF
page 39,
0x33
TCCR0B
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
page 74
0x32
TCNT0
Timer/Counter0
0x31
OSCCAL
Oscillator Calibration Register
0x30
TCCR1
–
CTC1
PWM1A
COM1A1
COM1A0
CS13
page 75
page 27
CS12
CS11
CS10
page 82, page 94
0x2F
TCNT1
Timer/Counter1
page 84, page 95
0x2E
OCR1A
Timer/Counter1 Output Compare Register A
page 85, page 96
0x2D
OCR1C
Timer/Counter1 Output Compare Register C
0x2C
GTCCR
TSM
PWM1B
COM1B1
COM0A1
COM0A0
COM0B1
COM1B0
FOC1B
page 85, page 96
FOC1A
0x2B
OCR1B
0x2A
TCCR0A
0x29
OCR0A
Timer/Counter0 – Output Compare Register A
0x28
OCR0B
Timer/Counter0 – Output Compare Register B
0x27
PLLCSR
SM
0x26
CLKPR
CLKPCE
–
0x25
DT1A
DT1AH3
DT1AH2
0x24
DT1B
DT1BH3
DT1BH2
0x23
DTPS1
-
-
0x22
DWDR
0x21
WDTCR
WDTIF
0x20
PRR
–
0x1F
EEARH
0x1E
EEARL
0x1D
EEDR
0x1C
EECR
0x1B
Reserved
–
0x1A
Reserved
–
0x19
Reserved
0x18
PORTB
–
–
PORTB5
0x17
DDRB
–
–
0x16
PINB
–
0x15
PCMSK
0x14
DIDR0
PSR1
PSR0
WGM01
WGM00
Timer/Counter1 Output Compare Register B
–
–
COM0B0
page 85
–
EEAR7
EEAR6
page 71
page 75
page 76
–
–
PCKE
PLLE
PLOCK
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
page 29
DT1AH1
DT1AH0
DT1AL3
DT1AL2
DT1AL1
DT1AL0
page 102
DT1BH1
DT1BH0
DT1BL3
DT1BL2
DT1BL1
DT1BL0
page 102
-
-
-
-
DTPS11
DTPS10
page 101
WDE
WDP2
WDP1
WDP0
page 41
PRTIM1
PRTIM0
PRUSI
PRADC
page 33
EEAR8
page 15
page 16
DWDR[7:0]
WDTIE
page 78, page 83, page 95
WDP3
EEAR5
WDCE
EEAR4
page 87, page 97
page 135
EEAR3
EEAR2
EEAR1
EEAR0
EERIE
EEMWE
EEWE
EERE
page 16
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
page 58
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
page 58
–
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
page 58
–
–
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
page 60
–
–
ADC0D
ADC2D
ADC3D
ADC1D
EIN1D
AIN0D
page 117, page 133
EEPROM Data Register
–
–
EEPM1
EEPM0
page 16
–
0x13
GPIOR2
General Purpose I/O Register 2
0x12
GPIOR1
General Purpose I/O Register 1
0x11
GPIOR0
General Purpose I/O Register 0
0x10
USIBR
USI Buffer Register
0x0F
USIDR
USI Data Register
0x0E
USISR
USICIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
page 111
0x0D
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
page 112
0x0C
Reserved
–
0x0B
Reserved
–
0x0A
Reserved
–
0x09
Reserved
0x08
ACSR
ACD
ACBG
ACO
ACI
ACIE
–
ACIS1
ACIS0
page 115
0x07
ADMUX
REFS1
REFS0
ADLAR
REFS2
MUX3
MUX2
MUX1
MUX0
page 128
0x06
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
page 130
0x05
ADCH
ADC Data Register High Byte
0x04
ADCL
ADC Data Register Low Byte
0x03
ADCSRB
0x02
Reserved
–
0x01
Reserved
–
0x00
Reserved
–
page 110
page 110
–
BIN
ACME
IPR
–
–
page 131
page 131
ADTS2
ADTS1
ADTS0
page 115, page 132
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
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.
189
7598D–AVR–02/07
26. 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
ADC
Rd, Rr
Add with Carry two Registers
Rd ← Rd + Rr + C
Z,C,N,V,H
1
1
ADIW
Rdl,K
Add Immediate to Word
Rdh:Rdl ← Rdh:Rdl + K
Z,C,N,V,S
2
SUB
Rd, Rr
Subtract two Registers
Rd ← Rd - Rr
Z,C,N,V,H
1
SUBI
Rd, K
Subtract Constant from Register
Rd ← Rd - K
Z,C,N,V,H
1
SBC
Rd, Rr
Subtract with Carry two Registers
Rd ← Rd - Rr - C
Z,C,N,V,H
1
SBCI
Rd, K
Subtract with Carry Constant from Reg.
Rd ← Rd - K - C
Z,C,N,V,H
1
SBIW
Rdl,K
Subtract Immediate from Word
Rdh:Rdl ← Rdh:Rdl - K
Z,C,N,V,S
2
AND
Rd, Rr
Logical AND Registers
Rd ← Rd • Rr
Z,N,V
1
ANDI
Rd, K
Logical AND Register and Constant
Rd ← Rd • K
Z,N,V
1
OR
Rd, Rr
Logical OR Registers
Rd ← Rd v Rr
Z,N,V
1
ORI
Rd, K
Logical OR Register and Constant
Rd ← Rd v K
Z,N,V
1
EOR
Rd, Rr
Exclusive OR Registers
Rd ← Rd ⊕ Rr
Z,N,V
1
COM
Rd
One’s Complement
Rd ← 0xFF − Rd
Z,C,N,V
1
NEG
Rd
Two’s Complement
Rd ← 0x00 − Rd
Z,C,N,V,H
1
1
SBR
Rd,K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
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
Indirect Jump to (Z)
PC ← Z
None
2
Relative Subroutine Call
PC ← PC + k + 1
None
3
ICALL
Indirect Call to (Z)
PC ← Z
None
3
RET
Subroutine Return
PC ← STACK
None
4
RETI
Interrupt Return
PC ← STACK
I
Compare, Skip if Equal
if (Rd = Rr) PC ← PC + 2 or 3
None
IJMP
RCALL
CPSE
k
Rd,Rr
4
1/2/3
CP
Rd,Rr
Compare
Rd − Rr
Z, N,V,C,H
CPC
Rd,Rr
Compare with Carry
Rd − Rr − C
Z, N,V,C,H
1
1
CPI
Rd,K
Compare Register with Immediate
Rd − K
Z, N,V,C,H
1
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ← PC + 2 or 3
None
1/2/3
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC ← PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b)=0) PC ← PC + 2 or 3
None
1/2/3
SBIS
P, b
Skip if Bit in I/O Register is Set
if (P(b)=1) PC ← PC + 2 or 3
None
1/2/3
BRBS
s, k
Branch if Status Flag Set
if (SREG(s) = 1) then PC←PC+k + 1
None
1/2
BRBC
s, k
Branch if Status Flag Cleared
if (SREG(s) = 0) then PC←PC+k + 1
None
1/2
BREQ
k
Branch if Equal
if (Z = 1) then PC ← PC + k + 1
None
1/2
BRNE
k
Branch if Not Equal
if (Z = 0) then PC ← PC + k + 1
None
1/2
BRCS
k
Branch if Carry Set
if (C = 1) then PC ← PC + k + 1
None
1/2
BRCC
k
Branch if Carry Cleared
if (C = 0) then PC ← PC + k + 1
None
1/2
BRSH
k
Branch if Same or Higher
if (C = 0) then PC ← PC + k + 1
None
1/2
BRLO
k
Branch if Lower
if (C = 1) then PC ← PC + k + 1
None
1/2
BRMI
k
Branch if Minus
if (N = 1) then PC ← PC + k + 1
None
1/2
BRPL
k
Branch if Plus
if (N = 0) then PC ← PC + k + 1
None
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V= 0) then PC ← PC + k + 1
None
1/2
BRLT
k
Branch if Less Than Zero, Signed
if (N ⊕ V= 1) then PC ← PC + k + 1
None
1/2
BRHS
k
Branch if Half Carry Flag Set
if (H = 1) then PC ← PC + k + 1
None
1/2
BRHC
k
Branch if Half Carry Flag Cleared
if (H = 0) then PC ← PC + k + 1
None
1/2
BRTS
k
Branch if T Flag Set
if (T = 1) then PC ← PC + k + 1
None
1/2
BRTC
k
Branch if T Flag Cleared
if (T = 0) then PC ← PC + k + 1
None
1/2
BRVS
k
Branch if Overflow Flag is Set
if (V = 1) then PC ← PC + k + 1
None
1/2
BRVC
k
Branch if Overflow Flag is Cleared
if (V = 0) then PC ← PC + k + 1
None
1/2
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ← PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ← PC + k + 1
None
1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI
P,b
Set Bit in I/O Register
I/O(P,b) ← 1
None
2
CBI
P,b
Clear Bit in I/O Register
I/O(P,b) ← 0
None
2
LSL
Rd
Logical Shift Left
Rd(n+1) ← Rd(n), Rd(0) ← 0
Z,C,N,V
1
LSR
Rd
Logical Shift Right
Rd(n) ← Rd(n+1), Rd(7) ← 0
Z,C,N,V
1
ROL
Rd
Rotate Left Through Carry
Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7)
Z,C,N,V
1
190
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ROR
Rd
Rotate Right Through Carry
Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0)
Z,C,N,V
1
ASR
Rd
Arithmetic Shift Right
Rd(n) ← Rd(n+1), n=0..6
Z,C,N,V
1
SWAP
Rd
Swap Nibbles
Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0)
None
1
BSET
s
Flag Set
SREG(s) ← 1
SREG(s)
1
BCLR
s
Flag Clear
SREG(s) ← 0
SREG(s)
1
BST
Rr, b
Bit Store from Register to T
T ← Rr(b)
T
1
BLD
Rd, b
Bit load from T to Register
Rd(b) ← T
None
1
SEC
Set Carry
C←1
C
1
CLC
Clear Carry
C←0
C
1
SEN
Set Negative Flag
N←1
N
1
CLN
Clear Negative Flag
N←0
N
1
SEZ
Set Zero Flag
Z←1
Z
1
CLZ
Clear Zero Flag
Z←0
Z
1
SEI
Global Interrupt Enable
I←1
I
1
CLI
Global Interrupt Disable
I←0
I
1
SES
Set Signed Test Flag
S←1
S
1
CLS
Clear Signed Test Flag
S←0
S
1
SEV
Set Twos Complement Overflow.
V←1
V
1
CLV
Clear Twos Complement Overflow
V←0
V
1
SET
Set T in SREG
T←1
T
1
CLT
Clear T in SREG
T←0
T
1
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
H←1
H←0
H
H
1
None
1
None
1
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
MOVW
Rd, Rr
Copy Register Word
Rd ← Rr
Rd+1:Rd ← Rr+1:Rr
LDI
Rd, K
Load Immediate
Rd ← K
None
1
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ← X - 1, Rd ← (X)
None
2
LD
Rd, Y
Load Indirect
Rd ← (Y)
None
2
LD
Rd, Y+
Load Indirect and Post-Inc.
Rd ← (Y), Y ← Y + 1
None
2
LD
Rd, - Y
Load Indirect and Pre-Dec.
Y ← Y - 1, Rd ← (Y)
None
2
LDD
Rd,Y+q
Load Indirect with Displacement
Rd ← (Y + q)
None
2
LD
Rd, Z
Load Indirect
Rd ← (Z)
None
2
LD
Rd, Z+
Load Indirect and Post-Inc.
Rd ← (Z), Z ← Z+1
None
2
LD
Rd, -Z
Load Indirect and Pre-Dec.
Z ← Z - 1, Rd ← (Z)
None
2
LDD
Rd, Z+q
Load Indirect with Displacement
Rd ← (Z + q)
None
2
LDS
Rd, k
Load Direct from SRAM
Rd ← (k)
None
2
ST
X, Rr
Store Indirect
(X) ← Rr
None
2
ST
X+, Rr
Store Indirect and Post-Inc.
(X) ← Rr, X ← X + 1
None
2
ST
- X, Rr
Store Indirect and Pre-Dec.
X ← X - 1, (X) ← Rr
None
2
ST
Y, Rr
Store Indirect
(Y) ← Rr
None
2
ST
Y+, Rr
Store Indirect and Post-Inc.
(Y) ← Rr, Y ← Y + 1
None
2
ST
- Y, Rr
Store Indirect and Pre-Dec.
Y ← Y - 1, (Y) ← Rr
None
2
STD
Y+q,Rr
Store Indirect with Displacement
(Y + q) ← Rr
None
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
2
ST
Z+, Rr
Store Indirect and Post-Inc.
(Z) ← Rr, Z ← Z + 1
None
2
ST
-Z, Rr
Store Indirect and Pre-Dec.
Z ← Z - 1, (Z) ← Rr
None
2
STD
Z+q,Rr
Store Indirect with Displacement
(Z + q) ← Rr
None
2
STS
k, Rr
Store Direct to SRAM
(k) ← Rr
None
2
Load Program Memory
R0 ← (Z)
None
3
LPM
LPM
Rd, Z
Load Program Memory
Rd ← (Z)
None
3
LPM
Rd, Z+
Load Program Memory and Post-Inc
Rd ← (Z), Z ← Z+1
None
3
SPM
Store Program Memory
(z) ← R1:R0
None
IN
Rd, P
In Port
Rd ← P
None
1
OUT
P, Rr
Out Port
P ← Rr
None
1
PUSH
Rr
Push Register on Stack
STACK ← Rr
None
2
POP
Rd
Pop Register from Stack
Rd ← STACK
None
2
MCU CONTROL INSTRUCTIONS
NOP
No Operation
None
1
SLEEP
Sleep
(see specific descr. for Sleep function)
None
1
WDR
BREAK
Watchdog Reset
Break
(see specific descr. for WDR/Timer)
For On-chip Debug Only
None
None
1
N/A
191
7598D–AVR–02/07
27. Ordering Information
Power Supply
Notes:
Speed (MHz)
Ordering Code
Package
Operation Range
2.7 - 5.5V
8 - 16
(3)
ATtiny25/45/85-15SZ
ATtiny25/45/85-15ST
ATtiny25/45/85-15ST1
T5
Automotive (-40°C to 125°C)
Automotive (-40°C to +85°C)
Automotive (-40°C to +105°C)
2.7 - 5.5V
8 - 16(3)
ATtiny25/45/85-15MZ
ATtiny25/45/85-15MT
ATtiny25/45/85-15MT1
PC
Automotive (-40°C to 125°C)
Automotive (-40°C to +85°C)
Automotive (-40°C to +105°C)
1. Green and ROHS packaging
2. Tape and Reel with Dry-pack delivery.
3. For Speed vs. VCC,see Figure 23-2 on page 158.
Package Type
T5
8-lead, 0.208
PC
20-lead, QFN
192
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
28. Packaging Information
28.1
T5
193
7598D–AVR–02/07
28.2
194
PC
ATtiny25/45/85 Auto
7598D–AVR–02/07
ATtiny25/45/85 Auto
29. Document Revision History
29.1
Rev. 7598D - 02/07
1. Clarification of Power On Reset Specifications table, Table 8-1 on page 37.
2. Errata list updated.
3. Added QFN packages.
29.2
Rev. 7598C - 09/06
1. Correction of package codification and drawings.
29.3
Rev. 7598B - 08/06
1. Clarification of several TBD values
2. Addition of the Power On Reset specification
3. DC characteristics Limits completed after corner run characterization
4. Typical Characteristic curves produced
29.4
Changes from
Rev. 2535A-09/01 to
Rev. 7598A-04/06
1. Automotive grade created:
Features:
- Change voltage and temperature range (2.7V - 5.5V), (-40°C, +125°C)
- Adapt Stand-by current to automotive temperature range
Packages:
- PDIP removed
- Ordering info limited to Automotive versions (green only, dry pack)
DC & AC parameters
- Only PRELIMINARY values are produced.
Typical Characteristics removed.
195
7598D–AVR–02/07
30. Errata
The revision letter in this section refers to the revision of the ATtiny25/45/85 device.
30.1
ATtiny25
Rev. E
1. No known errata. Flash security improvements.
30.2
ATtiny45
Rev. G
1. No known errata. Flash security improvements.
30.3
ATtiny85
Rev. C
1. No known errata. Flash security improvements.
196
ATtiny25/45/85 Auto
7598D–AVR–02/07
Auto
Features ..................................................................................................... 1
1
Pin Configurations ................................................................................... 2
2
Overview ................................................................................................... 2
2.1 Block Diagram ........................................................................................................3
2.2 Automotive Quality Grade ......................................................................................4
2.3 Pin Descriptions .....................................................................................................5
3
About Code Examples ............................................................................. 5
4
AVR CPU Core .......................................................................................... 5
4.1 Introduction .............................................................................................................5
4.2 Architectural Overview ...........................................................................................6
4.3 ALU – Arithmetic Logic Unit ...................................................................................7
4.4 Status Register .......................................................................................................7
4.5 General Purpose Register File ...............................................................................9
4.6 Stack Pointer ........................................................................................................10
4.7 Instruction Execution Timing ................................................................................10
4.8 Reset and Interrupt Handling ...............................................................................11
5
AVR ATtiny25/45/85 Memories ............................................................. 13
5.1 In-System Re-programmable Flash Program Memory .........................................13
5.2 SRAM Data Memory ............................................................................................14
5.3 EEPROM Data Memory .......................................................................................15
5.4 I/O Memory ...........................................................................................................21
6
System Clock and Clock Options ......................................................... 21
6.1 Clock Systems and their Distribution ....................................................................21
6.2 Clock Sources ......................................................................................................23
6.3 Default Clock Source ............................................................................................24
6.4 Crystal Oscillator ..................................................................................................24
6.5 Low-frequency Crystal Oscillator ..........................................................................25
6.6 Calibrated Internal RC Oscillator ..........................................................................26
6.7 External Clock ......................................................................................................27
6.8 128 kHz Internal Oscillator ...................................................................................28
6.9 Clock Output Buffer ..............................................................................................29
6.10 System Clock Prescaler .....................................................................................29
7
Power Management and Sleep Modes ................................................. 31
7.1 Idle Mode ..............................................................................................................32
i
7598D–AVR–02/07
7.2 ADC Noise Reduction Mode ................................................................................32
7.3 Power-down Mode ...............................................................................................32
7.4 Power Reduction Register ....................................................................................33
7.5 Minimizing Power Consumption ...........................................................................34
8
System Control and Reset .................................................................... 35
8.1 Internal Voltage Reference ...................................................................................40
8.2 Watchdog Timer ...................................................................................................40
8.3 Timed Sequences for Changing the Configuration of the Watchdog Timer .........44
9
Interrupts ................................................................................................ 45
9.1 Interrupt Vectors in ATtiny25/45/85 ......................................................................45
10 I/O Ports .................................................................................................. 46
10.1 Introduction .........................................................................................................46
10.2 Ports as General Digital I/O ................................................................................47
10.3 Alternate Port Functions .....................................................................................52
10.4 Register Description for I/O-Ports .......................................................................57
11 External Interrupts ................................................................................. 58
12 8-bit Timer/Counter0 with PWM ............................................................ 60
12.1 Overview ............................................................................................................60
12.2 Timer/Counter Clock Sources ............................................................................62
12.3 Counter Unit .......................................................................................................62
12.4 Output Compare Unit .........................................................................................63
12.5 Compare Match Output Unit ...............................................................................64
12.6 Modes of Operation ............................................................................................65
12.7 Timer/Counter Timing Diagrams ........................................................................70
12.8 8-bit Timer/Counter Register Description ...........................................................71
13 Timer/Counter Prescaler ....................................................................... 77
14 8-bit Timer/Counter1 .............................................................................. 79
14.1 Timer/Counter1 ..................................................................................................80
15 8-bit Timer/Counter1 in ATtiny15 Mode ............................................... 90
15.1 Timer/Counter1 Prescaler ..................................................................................91
15.2 Timer/Counter1 ..................................................................................................91
16 Dead Time Generator ........................................................................... 100
17 Universal Serial Interface – USI .......................................................... 103
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17.1 Overview ..........................................................................................................103
17.2 Functional Descriptions ....................................................................................104
17.3 Alternative USI Usage ......................................................................................109
17.4 USI Register Descriptions ................................................................................110
18 Analog Comparator ............................................................................. 114
18.1 Analog Comparator Multiplexed Input ..............................................................116
19 Analog to Digital Converter ................................................................ 117
19.1 Features ...........................................................................................................117
19.2 Operation ..........................................................................................................118
19.3 Starting a Conversion .......................................................................................119
19.4 Prescaling and Conversion Timing ...................................................................120
19.5 Changing Channel or Reference Selection ......................................................122
19.6 ADC Noise Canceler ........................................................................................123
19.7 ADC Conversion Result ...................................................................................126
20 debugWIRE On-chip Debug System .................................................. 133
20.1 Features ...........................................................................................................133
20.2 Overview ..........................................................................................................133
20.3 Physical Interface .............................................................................................134
20.4 Software Break Points ......................................................................................134
20.5 Limitations of debugWIRE ................................................................................135
20.6 debugWIRE Related Register in I/O Memory ...................................................135
21 Self-Programming the Flash ............................................................... 135
21.1 Addressing the Flash During Self-Programming ..............................................136
22 Memory Programming ......................................................................... 139
22.1 Program And Data Memory Lock Bits ..............................................................139
22.2 Fuse Bytes .......................................................................................................140
22.3 Signature Bytes ................................................................................................142
22.4 Calibration Byte ................................................................................................142
22.5 Page Size .........................................................................................................142
22.6 Serial Downloading ..........................................................................................143
22.7 High-voltage Serial Programming .....................................................................148
22.8 High-voltage Serial Programming Algorithm ....................................................149
22.9 High-voltage Serial Programming Characteristics ............................................155
23 Electrical Characteristics .................................................................... 156
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23.1 Absolute Maximum Ratings* ............................................................................156
23.2 External Clock Drive Waveforms ......................................................................157
23.3 External Clock Drive .........................................................................................158
23.4 ADC Characteristics – Preliminary Data ...........................................................159
23.5 Calibrated RC Oscillator Accuracy ...................................................................160
24 Typical Characteristics ........................................................................ 160
24.1 Active Supply Current .......................................................................................161
24.2 Idle Supply Current ...........................................................................................163
24.3 Power-Down Supply Current ............................................................................167
24.4 Pin Pull-up ........................................................................................................168
24.5 Pin Driver Strength ...........................................................................................171
24.6 Pin Thresholds and Hysteresis .........................................................................174
24.7 BOD Thresholds and Analog Comparator Offset .............................................177
24.8 Internal Oscillator Speed ..................................................................................178
24.9 Current Consumption of Peripheral Units .........................................................181
24.10 Current Consumption in Reset and Reset Pulse width ..................................182
24.11 Analog to Digital Converter ............................................................................183
25 Register Summary ............................................................................... 188
26 Instruction Set Summary .................................................................... 190
27 Ordering Information ........................................................................... 192
28 Packaging Information ........................................................................ 193
28.1 T5 .....................................................................................................................193
28.2 PC ....................................................................................................................194
29 Document Revision History ................................................................ 195
29.1 Rev. 7598D - 02/07 ..........................................................................................195
29.2 Rev. 7598C - 09/06 ..........................................................................................195
29.3 Rev. 7598B - 08/06 ..........................................................................................195
29.4 Changes from Rev. 2535A-09/01 to Rev. 7598A-04/06......................................195
30 Errata ..................................................................................................... 196
30.1 ATtiny25 Rev. E ...............................................................................................196
30.2 ATtiny45 Rev. G ...............................................................................................196
30.3 ATtiny85 Rev. C ...............................................................................................196
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