ATMEL ATtiny24V-10SSU 8-bit microcontroller with 2/4/8k bytes in-system programmable flash Datasheet

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 Bytes of In-System Programmable Program Memory Flash
• Endurance: 10,000 Write/Erase Cycles
– 128/256/512 Bytes of In-System Programmable EEPROM
• Endurance: 100,000 Write/Erase Cycles
– 128/256/512 Bytes of Internal SRAM
– Data retention: 20 years at 85°C / 100 years at 25°C
– Programming Lock for Self-Programming Flash & EEPROM Data Security
Peripheral Features
– One 8-Bit and One 16-Bit Timer/Counter with Two PWM Channels, Each
– 10-bit ADC
• 8 Single-Ended Channels
• 12 Differential ADC Channel Pairs with Programmable Gain (1x / 20x)
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-Chip Analog Comparator
– Universal Serial Interface
Special Microcontroller Features
– debugWIRE On-chip Debug System
– In-System Programmable via SPI Port
– Internal and External Interrupt Sources: Pin Change Interrupt on 12 Pins
– Low Power Idle, ADC Noise Reduction, Standby and Power-Down Modes
– Enhanced Power-on Reset Circuit
– Programmable Brown-Out Detection Circuit
– Internal Calibrated Oscillator
– On-Chip Temperature Sensor
I/O and Packages
– Available in 20-Pin QFN/MLF & 14-Pin SOIC and PDIP
– Twelve Programmable I/O Lines
Operating Voltage:
– 1.8 – 5.5V for ATtiny24V/44V/84V
– 2.7 – 5.5V for ATtiny24/44/84
Speed Grade
– ATtiny24V/44V/84V
• 0 – 4 MHz @ 1.8 – 5.5V
• 0 – 10 MHz @ 2.7 – 5.5V
– ATtiny24/44/84
• 0 – 10 MHz @ 2.7 – 5.5V
• 0 – 20 MHz @ 4.5 – 5.5V
Industrial Temperature Range: -40°C to +85°C
Low Power Consumption
– Active Mode (1 MHz System Clock): 300 µA @ 1.8V
– Power-Down Mode: 0.1 µA @ 1.8V
8-bit
Microcontroller
with 2/4/8K
Bytes In-System
Programmable
Flash
ATtiny24/44/84
Preliminary
ATtiny24/44 not
recommended for
new designs. Use:
ATtiny24A
ATtiny44A
Rev. 8006H–AVR–10/09
1. Pin Configurations
Figure 1-1.
Pinout ATtiny24/44/84
PDIP/SOIC
VCC
(PCINT8/XTAL1/CLKI) PB0
(PCINT9/XTAL2) PB1
(PCINT11/RESET/dW) PB3
(PCINT10/INT0/OC0A/CKOUT) PB2
(PCINT7/ICP/OC0B/ADC7) PA7
(PCINT6/OC1A/SDA/MOSI/DI/ADC6) PA6
1
2
3
4
5
6
7
14
13
12
11
10
9
8
GND
PA0 (ADC0/AREF/PCINT0)
PA1 (ADC1/AIN0/PCINT1)
PA2 (ADC2/AIN1/PCINT2)
PA3 (ADC3/T0/PCINT3)
PA4 (ADC4/USCK/SCL/T1/PCINT4)
PA5 (ADC5/DO/MISO/OC1B/PCINT5)
NOTE
Bottom pad should be
soldered to ground.
DNC: Do Not Connect
1.1
1.1.1
15
14
13
12
11
6
7
8
9
10
1
2
3
4
5
Pin 16: PA6 (PCINT6/OC1A/SDA/MOSI/DI/ADC6)
Pin 20: PA5 (ADC5/DO/MISO/OC1B/PCINT5)
PA7 (PCINT7/ICP/OC0B/ADC7)
PB2 (PCINT10/INT0/OC0A/CKOUT)
PB3 (PCINT11/RESET/dW)
PB1 (PCINT9/XTAL2)
PB0 (PCINT8/XTAL1/CLKI)
DNC
DNC
GND
VCC
DNC
(ADC4/USCK/SCL/T1/PCINT4) PA4
(ADC3/T0/PCINT3) PA3
(ADC2/AIN1/PCINT2) PA2
(ADC1/AIN0/PCINT1) PA1
(ADC0/AREF/PCINT0) PA0
20
19
18
17
16
PA5
DNC
DNC
DNC
PA6
QFN/MLF
Pin Descriptions
VCC
Supply voltage.
1.1.2
GND
Ground.
1.1.3
2
Port B (PB3...PB0)
Port B is a 4-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 except PB3 which has the RESET capability. To use pin PB3 as an I/O pin, instead of
RESET pin, program (‘0’) RSTDISBL fuse. 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.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Port B also serves the functions of various special features of the ATtiny24/44/84 as listed in
Section 10.2 “Alternate Port Functions” on page 58.
1.1.4
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 and provided the reset pin has not been disabled. The minimum pulse length is given in Table 20-4 on page 177. Shorter pulses are not guaranteed to
generate a reset.
The reset pin can also be used as a (weak) I/O pin.
1.1.5
Port A (PA7...PA0)
Port A is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port A output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port A pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port A has alternate functions as analog inputs for the ADC, analog comparator, timer/counter,
SPI and pin change interrupt as described in “Alternate Port Functions” on page 58.
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2. Overview
ATtiny24/44/84 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 ATtiny24/44/84
achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize
power consumption versus processing speed.
Figure 2-1.
Block Diagram
VCC
8-BIT DATABUS
INTERNAL
OSCILLATOR
INTERNAL
CALIBRATED
OSCILLATOR
TIMING AND
CONTROL
GND
PROGRAM
COUNTER
STACK
POINTER
WATCHDOG
TIMER
PROGRAM
FLASH
SRAM
MCU CONTROL
REGISTER
INSTRUCTION
REGISTER
MCU STATUS
REGISTER
GENERAL
PURPOSE
REGISTERS
TIMER/
COUNTER0
X
Y
Z
INSTRUCTION
DECODER
TIMER/
COUNTER1
CONTROL
LINES
ALU
STATUS
REGISTER
INTERRUPT
UNIT
ANALOG
COMPARATOR
+
-
PROGRAMMING
LOGIC
EEPROM
ISP INTERFACE
DATA REGISTER
PORT A
DATA DIR.
REG.PORT A
PORT A DRIVERS
PA7-PA0
ADC
OSCILLATORS
DATA REGISTER
PORT B
DATA DIR.
REG.PORT B
PORT B DRIVERS
PB3-PB0
The AVR core combines a rich instruction set with 32 general purpose working registers. All 32
registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
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.
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ATtiny24/44/84
The ATtiny24/44/84 provides the following features: 2/4/8K byte of In-System Programmable
Flash, 128/256/512 bytes EEPROM, 128/256/512 bytes SRAM, 12 general purpose I/O lines, 32
general purpose working registers, an 8-bit Timer/Counter with two PWM channels, a 16-bit
timer/counter with two PWM channels, Internal and External Interrupts, a 8-channel 10-bit ADC,
programmable gain stage (1x, 20x) for 12 differential ADC channel pairs, a programmable
Watchdog Timer with internal oscillator, internal calibrated oscillator, and four software selectable power saving modes. Idle mode stops the CPU while allowing the SRAM, Timer/Counter,
ADC, Analog Comparator, and Interrupt system to continue functioning. ADC Noise Reduction
mode minimizes switching noise during ADC conversions by stopping the CPU and all I/O modules except the ADC. In Power-down mode registers keep their contents and all chip functions
are disbaled until the next interrupt or hardware reset. In Standby mode, the crystal/resonator
oscillator is running while the rest of the device is sleeping, allowing very fast start-up combined
with low power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The onchip 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 ATtiny24/44/84 AVR is supported with a full suite of program and system development tools
including: C Compilers, Macro Assemblers, Program Debugger/Simulators and Evaluation kits.
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3. About
3.1
Resources
A comprehensive set of drivers, application notes, data sheets and descriptions on development
tools are available for download at http://www.atmel.com/avr.
3.2
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.
For I/O Registers located in the extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically, this
means “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. Note that not all
AVR devices include an extended I/O map.
3.3
Data Retention
Reliability Qualification results show that the projected data retention failure rate is much less
than 1 PPM over 20 years at 85°C or 100 years at 25°C.
3.4
Disclaimer
Typical values contained in this datasheet are based on simulations and characterization of
other AVR microcontrollers manufactured on the same process technology. Min and Max values
will be available after the device is characterized.
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ATtiny24/44/84
4. CPU Core
This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
4.1
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
Timer/Counter 0
Data
SRAM
Timer/Counter 1
Universal
Serial Interface
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.
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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.
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, capable of
directly addressing the whole address space. Most AVR instructions have a single 16-bit word
format but 32-bit wide instructions also exist. The actual instruction set varies, as some devices
only implement a part of the instruction set.
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.
4.2
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.
4.3
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.
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ATtiny24/44/84
The Status Register is neither automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt. This must be handled by software.
4.3.1
SREG – AVR Status Register
Bit
7
6
5
4
3
2
1
0
0x3F (0x5F)
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
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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4.4
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 below 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.
4.4.1
10
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 below.
ATtiny24/44/84
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ATtiny24/44/84
Figure 4-3.
The X-, Y-, and Z-registers
15
X-register
XH
XL
7
0
R27 (0x1B)
YH
YL
7
0
R29 (0x1D)
Z-register
0
R26 (0x1A)
15
Y-register
0
7
0
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).
4.5
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.
4.5.1
SPH and SPL — Stack Pointer Register
Bit
15
14
13
12
11
10
9
8
0x3E (0x5E)
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
0x3D (0x5D)
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
Initial Value
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
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4.6
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.
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
4.7
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 48. The list also
determines the priority levels of the different interrupts. The lower the address the higher is the
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ATtiny24/44/84
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
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, EEMPE
; start EEPROM write
sbi EECR, EEPE
out SREG, r16
; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
Note:
See “Code Examples” on page 6.
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When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in the following 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) */
Note:
4.7.1
See “Code Examples” on page 6.
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.
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ATtiny24/44/84
5. Memories
This section describes the different memories in the ATtiny24/44/84. The AVR architecture has
two main memory spaces, the Data memory and the Program memory space. In addition, the
ATtiny24/44/84 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 ATtiny24/44/84 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
1024/2048/4096 x 16.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny24/44/84
Program Counter (PC) is 10/11/12 bits wide, thus addressing the 1024/2048/4096 Program
memory locations. “Memory Programming” on page 159 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 instructions LPM – Load Program Memory and SPM – Store Program Memory).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 12.
Figure 5-1.
Program Memory Map
Program Memory
0x0000
0x03FF/0x07FF/0xFFF
5.2
SRAM Data Memory
Figure 5-2 on page 16 shows how the ATtiny24/44/84 SRAM Memory is organized.
The lower 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.
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8006H–AVR–10/09
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 ATtiny24/44/84 are all accessible through all these addressing modes.
The Register File is described in “General Purpose Register File” on page 10.
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
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 illustrated in Figure 5-3.
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 ATtiny24/44/84 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 “Serial Programming” on page 163.
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ATtiny24/44/84
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ATtiny24/44/84
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 on page 22. 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 19 for details on how to avoid
problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
See “Atomic Byte Programming” on page 17 and “Split Byte Programming” on page 17 for
details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
5.3.2
Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the
user must write the address into register EEAR and data into register EEDR. If the EEPMn bits
are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the erase/write
operation. Both the erase and write cycle are done in one operation and the total programming
time is given in Table 5-1 on page 22. 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.
5.3.3
Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if
the system requires short access time for some limited period of time (typically if the power 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).
5.3.4
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 5-1 on page 22). The EEPE bit remains set until the erase operation
completes. While the device is busy programming, it is not possible to do any other EEPROM
operations.
5.3.5
Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the
EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger
the write operation only (programming time is given in Table 5-1 on page 22). 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.
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8006H–AVR–10/09
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator frequency is within the requirements described in “OSCCAL – Oscillator Calibration Register” on
page 30.
5.3.6
Program Examples
The following code examples show one assembly and one C function for erase, write, or atomic
write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling
interrupts globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR, EEPE
rjmp EEPROM_write
; Set Programming mode
ldi
r16, (0<<EEPM1)|(0<<EEPM0)
out
EECR, r16
; Set up address (r18:r17) in address registers
out EEARH, r18
out EEARL, r17
; Write data (r19) to data register
out EEDR, r19
; Write logical one to EEMPE
sbi EECR, EEMPE
; Start eeprom write by setting EEPE
sbi EECR, EEPE
ret
C Code Example
void EEPROM_write(unsigned int ucAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set Programming mode */
EECR = (0<<EEPM1)|(0<<EEPM0)
/* Set up address and data registers */
EEAR = ucAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
Note:
18
See “Code Examples” on page 6.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
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 (r18:r17) in address registers
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR, EERE
; Read data from data register
in
r16, EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
Note:
5.3.7
See “Code Examples” on page 6.
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
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8006H–AVR–10/09
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.
5.4
I/O Memory
The I/O space definition of the ATtiny24/44/84 is shown in “Register Summary” on page 213.
All ATtiny24/44/84 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. See 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 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.
5.4.1
5.5
5.5.1
General Purpose I/O Registers
The ATtiny24/44/84 contains three General Purpose I/O Registers. These registers can be used
for storing any information, and they are particularly useful for storing global variables and status
flags. General Purpose I/O Registers within the address range 0x00 - 0x1F are directly bitaccessible using the SBI, CBI, SBIS, and SBIC instructions.
Register Description
EEARH – EEPROM Address Register
Bit
7
6
5
4
3
2
1
0
0x1F (0x3F)
–
–
–
–
–
–
–
EEAR8
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
X/0
EEARH
• Bits 7..1 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bit 0 – EEAR8: EEPROM Address
This is the most significant EEPROM address bit of ATtiny84. In devices with less EEPROM, i.e.
ATtiny24/ATtiny44, this bit is reserved and will always read zero. The initial value of the
EEPROM Address Register (EEAR) is undefined and a proper value must therefore be written
before the EEPROM is accessed.
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ATtiny24/44/84
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ATtiny24/44/84
5.5.2
EEARL – EEPROM Address Register
Bit
7
6
5
4
3
2
1
0
0x1E (0x3E)
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
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
EEARL
• Bit 7 – EEAR7: EEPROM Address
This is the most significant EEPROM address bit of ATtiny44. In devices with less EEPROM, i.e.
ATtiny24, this bit is reserved and will always read zero. The initial value of the EEPROM
Address Register (EEAR) is undefined and a proper value must therefore be written before the
EEPROM is accessed.
• Bits 6..0 – EEAR6..0: EEPROM Address
These are the (low) bits of the EEPROM Address Register. The EEPROM data bytes are
addressed linearly in the range 0...128/256/512. The initial value of EEAR is undefined and a
proper value must be therefore be written before the EEPROM may be accessed.
5.5.3
EEDR – EEPROM Data Register
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
0
0
0
0
0
0
0
0
0x1D (0x3D)
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.
5.5.4
EECR – EEPROM Control Register
Bit
7
6
5
4
3
2
1
0
0x1C (0x3C)
–
–
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 ATtiny24/44/84. 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 ATtiny24/44/84 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
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8006H–AVR–10/09
old value and program the new value) or to split the Erase and Write operations in two different
operations. The Programming times for the different modes are shown in Table 5-1.
Table 5-1.
EEPROM Programming Mode Bits and Programming Times
EEPM1
EEPM0
Programming Time
Operation
0
0
3.4 ms
Erase and Write in one operation (Atomic Operation)
0
1
1.8 ms
Erase Only
1
0
1.8 ms
Write Only
1
1
–
Reserved for future use
When EEPE is set any write to EEPMn will be ignored. During reset, the EEPMn bits will be
reset to 0b00 unless the EEPROM is busy programming.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a constant 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.
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ATtiny24/44/84
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ATtiny24/44/84
5.5.5
GPIOR2 – General Purpose I/O Register 2
Bit
5.5.6
6
5
4
3
2
1
0
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
5
4
3
2
1
GPIOR2
GPIOR1 – General Purpose I/O Register 1
Bit
5.5.7
7
0x15 (0x35)
7
6
0
0x14 (0x34)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
5
4
3
2
1
GPIOR1
GPIOR0 – General Purpose I/O Register 0
Bit
7
6
0
0x13 (0x33)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GPIOR0
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6. Clock System
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 33.
Figure 6-1.
Clock Distribution
General I/O
Modules
ADC
clkI/O
CPU Core
RAM
Flash and
EEPROM
clkCPU
AVR Clock
Control Unit
clkADC
clkFLASH
Reset Logic
Watchdog Timer
Source clock
Watchdog clock
System Clock
Prescaler
Clock
Multiplexer
External Clock
6.1
Calibrated
Crystal RC
Oscillator
Watchdog
Oscillator
Low-Frequency
Crystal Oscillator
Calibrated RC
Oscillator
Clock Subsystems
The clock subsystems are detailed in the sections below.
6.1.1
24
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.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
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.
6.2
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
CKSEL3:0(1)
Device Clocking Option
External Clock (see page 26)
0000
Reserved
0001
Calibrated Internal 8 MHz Oscillator (see page 26)
0010
Reserved
0011
Internal 128 kHz Oscillator (see page 27)
0100
Reserved
0101
Low-Frequency Crystal Oscillator (see page 28)
0110
Reserved
0111
Crystal Oscillator / Ceramic Resonator (see page 28)
Note:
1000-1111
1. For all fuses “1” means unprogrammed and “0” means programmed.
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down the selected clock source is used to time the start-up, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts from reset,
there is 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 6-2.
Table 6-2.
Number of Watchdog Oscillator Cycles
Typ Time-out
Number of Cycles
4 ms
512
64 ms
8K (8,192)
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8006H–AVR–10/09
6.2.1
External Clock
To drive the device from an external clock source, CLKI should be driven as shown in Figure 6-2
on page 26. To run the device on an external clock, the CKSEL Fuses must be programmed to
“0000”.
Figure 6-2.
External Clock Drive Configuration
EXTERNAL
CLOCK
SIGNAL
CLKI
GND
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-3.
Table 6-3.
Start-up Times for the External Clock Selection
SUT1..0
Start-up Time
from Power-down
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
When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. See “System Clock Prescaler” on page 30
for details.
6.2.2
Calibrated Internal 8 MHz Oscillator
By default, the Internal Oscillator provides an approximate 8 MHz clock. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the user. See Table 20-2
on page 176 and “Internal Oscillator Speed” on page 205 for more details. The device is shipped
with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 30 for more details.
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 6-4. If selected, it will operate with no external components. During reset, hardware loads
the pre-programmed calibration value into the OSCCAL Register and thereby automatically cal-
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ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 20-2 on page 176.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 30, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of this calibration is shown as User calibration in Table 20-2 on page 176.
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 162.
Table 6-4.
Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
0010
Note:
Nominal Frequency
(1)
8.0 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 6-5..
Table 6-5.
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(2)
01
6 CK
14CK + 4 ms
Fast rising power
6 CK
14CK + 64 ms
Slowly rising power
10
(1)
11
Note:
Recommended Usage
BOD enabled
Reserved
1. The device is shipped with this option selected.
2. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
ensure programming mode can be entered.
6.2.3
Internal 128 kHz Oscillator
The 128 kHz internal oscillator is a low power oscillator providing a clock of 128 kHz. The frequency depends on supply voltage, temperature and batch variations. This clock may be
selected as the system clock by programming the CKSEL Fuses to “0100”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-6.
Table 6-6.
Start-up Times for the 128 kHz Internal Oscillator
SUT1..0
Start-up Time
from Power-down
Additional Delay
from Reset
00
6 CK
14CK(1)
01
6 CK
14CK + 4 ms
Fast rising power
10
6 CK
14CK + 64 ms
Slowly rising power
11
Note:
Recommended
Usage
BOD enabled
Reserved
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
ensure programming mode can be entered.
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8006H–AVR–10/09
6.2.4
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. To find suitable capacitors please consult the manufacturer’s datasheet.
For this oscillator start-up times can be set with the SUT fuses, as shown in Table 6-7.
Table 6-7.
Start-up Times for the Low-Frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time
from Power Down
Additional Delay
from Reset
00
1K CK(1)
4 ms
Fast rising power or BOD enabled
01
(1)
1K CK
64 ms
Slowly rising power
10
32K CK
64 ms
Stable frequency at start-up
11
Notes:
Reserved
1. These options should be used only if frequency stability at start-up is not important.
Table 6-8.
6.2.5
Recommended usage
Capacitance for the Low-Frequency Crystal Oscillator
Device
32 kHz Osc.
Type
Cap
(Xtal1/Tosc1)
Cap
(Xtal2/Tosc2)
ATtiny24/44/88
System Osc.
16 pF
6 pF
Crystal Oscillator / Ceramic Resonator
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.
Figure 6-3.
Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
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 6-9 below. For ceramic resonators, the capacitor values
given by the manufacturer should be used.
28
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ATtiny24/44/84
Table 6-9.
Crystal Oscillator Operating Modes
CKSEL3..1
Frequency Range (MHz)
Recommended C1 and C2 Value (pF)
0.4 - 0.9
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 -
12 - 22
100
Notes:
(1)
1. This option should not be used with crystals, only with ceramic resonators.
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by fuses CKSEL3..1 as shown in Table 6-9.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
6-10.
Table 6-10.
Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
SUT1..0
Start-up Time from
Power-down(1)
Additional Delay
from Reset
0
00
258 CK(2)
14CK + 4 ms
Ceramic resonator,
fast rising power
0
01
258 CK(2)
14CK + 64 ms
Ceramic resonator,
slowly rising power
0
10
1K CK(3)
14CK
Ceramic resonator,
BOD enabled
0
11
1K CK(3)
14CK + 4 ms
Ceramic resonator,
fast rising power
1
00
1K CK(3)
14CK + 64 ms
Ceramic resonator,
slowly rising power
1
01
16K CK
14CK
Crystal Oscillator,
BOD enabled
1
10
16K CK
14CK + 4 ms
Crystal Oscillator,
fast rising power
1
11
16K CK
14CK + 64 ms
Crystal Oscillator,
slowly rising power
Notes:
Recommended Usage
1. When the BOD has been disabled by software, the wake-up time from sleep mode will be
approximately 60µs to ensure that the BOD is working correctly before the MCU continues
executing code.
2. 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.
3. 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.
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8006H–AVR–10/09
6.2.6
Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is therefore the Internal Oscillator running at 8.0 MHz with longest start-up
time and an initial system clock prescaling of 8, resulting in 1.0 MHz system clock. This default
setting ensures that all users can make their desired clock source setting using an in-system or
high-voltage programmer.
For low-voltage devices (ATtiny24V/44V/84V) it should be noted that unprogramming the
CKDIV8 fuse may result in overclocking. At low voltages (below 2.7V) the devices are rated for
maximum 4 MHz operation (see Section 20.3 on page 175), but routing the clock signal from the
internal oscillator directly to the system clock line will run the device at 8 MHz.
6.3
System Clock Prescaler
The ATtiny24/44/84 system clock can be divided by setting the “CLKPR – Clock Prescale Register” on page 31. 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 6-11 on page 32.
6.3.1
Switching Time
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither the
clock frequency corresponding to the previous setting, nor the clock frequency corresponding to
the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
6.4
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 that the normal
operation of the 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.
6.5
6.5.1
Register Description
OSCCAL – Oscillator Calibration Register
Bit
7
6
5
4
3
2
1
0
0x31 (0x51)
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
OSCCAL
Device Specific Calibration Value
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
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ATtiny24/44/84
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the Factory calibrated frequency as
specified in Table 20-2 on page 176. The application software can write this register to change
the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 202 on page 176. Calibration outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two 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. See “Calibrated 8 MHz RC Oscillator Frequency vs, OSCCAL Value” on page 207 for typical frequencies.
To ensure stable operation of the MCU the calibration value should be changed in small. 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.
6.5.2
CLKPR – Clock Prescale Register
Bit
7
6
5
4
3
2
1
0
0x26 (0x46)
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 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 6-11 on page 32.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
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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 6-11.
32
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
ATtiny24/44/84
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ATtiny24/44/84
7. Power Management and Sleep Modes
The high performance and industry leading code efficiency makes the AVR microcontrollers an
ideal choise for low power applications. In addition, sleep modes enable the application to shut
down unused modules in the MCU, thereby saving power. The AVR provides various sleep
modes allowing the user to tailor the power consumption to the application’s requirements.
7.1
Sleep Modes
Figure 6-1 on page 24 presents the different clock systems and their distribution in
ATtiny24/44/84. The figure is helpful in selecting an appropriate sleep mode. Table 7-1 shows
the different sleep modes and their wake up sources.
Table 7-1.
Active Clock Domains and Wake-up Sources in Different Sleep Modes
clkADC
Main Clock
Source Enabled
INT0 and
Pin Change
SPM/EEPROM
Ready Interrupt
ADC
Interrupt
Other I/O
Watchdog
Interrupt
Wake-up Sources
X
X
X
X
X
X
X
X
ADC Noise Reduction
Power-down
Stand-by
Note:
Oscillators
clkIO
Idle
clkFLASH
Sleep Mode
clkCPU
Active Clock Domains
X
X
X
(1)
X
X
X
X(1)
X
(1)
X
X
1. For INT0, only level interrupt.
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM1..0 bits in the MCUCR Register select which
sleep mode (Idle, ADC Noise Reduction, Standby or Power-down) will be activated by the
SLEEP instruction. See Table 7-2 on page 37 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.
Note that if a level triggered interrupt is used for wake-up the changed level must be held for
some time to wake up the MCU (and for the MCU to enter the interrupt service routine). See
“External Interrupts” on page 49 for details.
7.1.1
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,
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the Analog Comparator can be powered down by setting the ACD bit in “ACSR – Analog Comparator Control and Status Register” on page 130. This will reduce power consumption in Idle
mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
7.1.2
ADC Noise Reduction Mode
When the 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.
7.1.3
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.
7.1.4
Standby Mode
When the SM1..0 bits are 11 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down
with the exception that the Oscillator is kept running. From Standby mode, the device wakes up
in six clock cycles.
7.2
Software BOD Disable
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 19-4 on page
160), the BOD is actively monitoring the supply voltage during a sleep period. In some devices it
is possible to save power by disabling the BOD by software in Power-Down and Stand-By sleep
modes. The sleep mode power consumption will then be at the same level as when BOD is globally disabled by fuses.
If BOD is disabled by software, the BOD function is turned off immediately after entering the
sleep mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe
operation in case the VCC level has dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately
60µs to ensure that the BOD is working correctly before the MCU continues executing code.
BOD disable is controlled by the BODS (BOD Sleep) bit of MCU Control Register, see “MCUCR
– MCU Control Register” on page 36. Writing this bit to one turns off BOD in Power-Down and
Stand-By, while writing a zero keeps the BOD active. The default setting is zero, i.e. BOD active.
Writing to the BODS bit is controlled by a timed sequence and an enable bit, see “MCUCR –
MCU Control Register” on page 36.
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ATtiny24/44/84
7.2.1
Limitations
BOD disable functionality has been implemented in the following devices, only:
• ATtiny24, revision E, and newer
• ATtiny44, revision D, and newer
• ATtiny84, revision B, and newer
Revisions are marked on the device package and can be located as follows:
• Bottom side of packages 14P3 and 14S1
• Top side of package 20M1
7.3
Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 37, provides a method to reduce power consumption by stopping the clock to individual peripherals.
The current state of the peripheral is frozen and the I/O registers can 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. See “Supply Current
of I/O Modules” on page 185 for examples.
7.4
Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as 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.
7.4.1
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. See “Analog to Digital Converter” on page 132 for
details on ADC operation.
7.4.2
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. See “Analog Comparator” on page 129 for details on how to configure the Analog Comparator.
35
8006H–AVR–10/09
7.4.3
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. See “Brown-out Detection” on page 41 and “Software BOD Disable” on page 34 for details on how to configure the Brown-out Detector.
7.4.4
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are 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. See “Internal Voltage
Reference” on page 42 for details on the start-up time.
7.4.5
Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be 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. See “Watchdog Timer” on page 42 for details on how to configure the Watchdog Timer.
7.4.6
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
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. See the section “Digital Input Enable and Sleep Modes” on page 58 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). See
“DIDR0 – Digital Input Disable Register 0” on page 150 for details.
7.5
7.5.1
Register Description
MCUCR – MCU Control Register
The MCU Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
BODS
PUD
SE
SM1
SM0
BODSE
ISC01
ISC00
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
MCUCR
• Bit 7 – BODS: BOD Sleep
BOD disable functionality is available in some devices, only. See “Limitations” on page 35.
In order to disable BOD during sleep (see Table 7-1 on page 33) the BODS bit must be written to
logic one. This is controlled by a timed sequence and the enable bit, BODSE in MCUCR. First,
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ATtiny24/44/84
both BODS and BODSE must be set to one. Second, within four clock cycles, BODS must be
set to one and BODSE must be set to zero. The BODS bit is active three clock cycles after it is
set. A sleep instruction must be executed while BODS is active in order to turn off the BOD for
the actual sleep mode. The BODS bit is automatically cleared after three clock cycles.
In devices where Sleeping BOD has not been implemented this bit is unused and will always
read zero.
• Bit 5 – SE: Sleep Enable
The SE bit must be written to 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 7-2.
Table 7-2.
Note:
Sleep Mode Select
SM1
SM0
Sleep Mode
0
0
Idle
0
1
ADC Noise Reduction
1
0
Power-down
1
1
Standby(1)
1. Only recommended with external crystal or resonator selected as clock source
• Bit 2 – BODSE: BOD Sleep Enable
BOD disable functionality is available in some devices, only. See “Limitations” on page 35.
The BODSE bit enables setting of BODS control bit, as explained on BODS bit description. BOD
disable is controlled by a timed sequence.
This bit is unused in devices where software BOD disable has not been implemented and will
read as zero in those devices.
7.5.2
PRR – Power Reduction Register
The Power Reduction Register provides a method to reduce power consumption by allowing
peripheral clock signals to be disabled.
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 and will always read 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.
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8006H–AVR–10/09
• 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
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.
The analog comparator cannot be used when the ADC is shut down.
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8. System Control and Reset
8.1
Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a RJMP – Relative
Jump – instruction to the reset handling routine. If the program never enables an 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. Electrical parameters of the
reset circuitry are given in Table 20-4 on page 177.
Figure 8-1.
Reset Logic
DATA BUS
PORF
BORF
EXTRF
WDRF
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
Brown-out
Reset Circuit
BODLEVEL [2..0]
Pull-up Resistor
SPIKE
FILTER
Watchdog
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
SUT[1:0]
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 25.
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8.2
Reset Sources
The ATtiny24/44/84 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 when RESET function is enabled.
• 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.
8.2.1
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in “System and Reset Characteristics” on page 177. 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.
VCC
RESET
MCU Start-up, RESET Tied to VCC
VPOT
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
Figure 8-3.
VCC
RESET
TIME-OUT
MCU Start-up, RESET Extended Externally
VPOT
VRST
tTOUT
INTERNAL
RESET
40
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
8.2.2
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 “System and Reset Characteristics” on page 177) 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.
Figure 8-4.
External Reset During Operation
CC
8.2.3
Brown-out Detection
ATtiny24/44/84 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 VBOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
8-5 on page 41), the Brown-out Reset is immediately activated. When VCC increases above the
trigger level (VBOT+ in Figure 8-5 on page 41), the delay counter starts the MCU after the Timeout period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD given in “System and Reset Characteristics” on page 177.
Figure 8-5.
Brown-out Reset During Operation
VCC
VBOT-
VBOT+
RESET
TIME-OUT
tTOUT
INTERNAL
RESET
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8006H–AVR–10/09
8.2.4
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. See
“Watchdog Timer” on page 42 for details on operation of the Watchdog Timer.
Figure 8-6.
Watchdog Reset During Operation
CC
CK
8.3
Internal Voltage Reference
ATtiny24/44/84 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. The bandgap
voltage varies with supply voltage and temperature.
8.3.1
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 “System and Reset Characteristics” on page 177. 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 internal 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.
8.4
Watchdog Timer
The Watchdog Timer is clocked from an On-chip Oscillator which runs at 128 kHz. By controlling
the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table
8-3 on page 47. 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 ATtiny24/44/84 resets and executes from the Reset Vector. For timing details on the Watchdog Reset, refer to Table 8-3 on page 47.
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ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
The Wathdog Timer can also be configured to generate an interrupt instead of a reset. This can
be very helpful when using the Watchdog to wake-up from Power-down.
To prevent 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 8-1 See “Timed
Sequences for Changing the Configuration of the Watchdog Timer” on page 43 for details.
Table 8-1.
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
WDP0
WDP1
WDP2
WDP3
OSC/512K
OSC/1024K
OSC/256K
OSC/64K
OSC/128K
OSC/8K
OSC/4K
OSC/2K
WATCHDOG
RESET
OSC/32K
WATCHDOG
PRESCALER
128 kHz
OSCILLATOR
OSC/16K
Figure 8-7.
MUX
WDE
MCU RESET
8.4.1
8.4.1.1
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.
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.
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8006H–AVR–10/09
8.4.1.2
Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
always is set, the WDE must be written to one to start the timed sequence.
2. Within the next four clock cycles, in the same operation, write the WDP bits as desired,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
8.4.2
Code Example
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
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, WDTCSR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCSR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCSR, r16
ret
C Code Example
void WDT_off(void)
{
_WDR();
/* Clear WDRF in MCUSR */
MCUSR = 0x00
/* Write logical one to WDCE and WDE */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
}
Note:
44
See “Code Examples” on page 6.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
8.5
8.5.1
Register Description
MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU Reset.
Bit
7
6
5
4
3
2
1
0
0x34 (0x54)
–
–
–
–
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 ATtiny24/44/84 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.
• 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.
8.5.2
WDTCSR – Watchdog Timer Control and Status Register
Bit
7
6
5
4
3
2
1
0
0x21 (0x41)
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
WDTCSR
• 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,
45
8006H–AVR–10/09
the next time-out will generate a reset. To avoid the Watchdog Reset, WDIE must be set after
each interrupt.
Table 8-2.
Watchdog Timer Configuration
WDE
WDIE
Watchdog Timer State
Action on Time-out
0
0
Stopped
None
0
1
Running
Interrupt
1
0
Running
Reset
1
1
Running
Interrupt
• 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. See 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 43.
• 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 43.
In safety level 1, WDE is overridden by WDRF in MCUSR. See “MCUSR – MCU Status Register” on page 45 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:
46
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.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
• Bits 5, 2..0 – WDP3..0: Watchdog Timer Prescaler 3, 2, 1, and 0
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 8-3.
Table 8-3.
Watchdog Timer Prescale Select
WDP3
WDP2
WDP1
WDP0
Number of WDT Oscillator
Cycles
Typical Time-out at
VCC = 5.0V
0
0
0
0
2K 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
Note:
Reserved(1)
1. If selected, one of the valid settings below 0b1010 will be used.
47
8006H–AVR–10/09
9. Interrupts
This section describes the specifics of the interrupt handling as performed in ATtiny24/44/84.
For a general explanation of the AVR interrupt handling, see “Reset and Interrupt Handling” on
page 12.
9.1
Interrupt Vectors
The interrupt vectors of ATtiny24/44/84 are described in Table 9-1 below.
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
PCINT1
Pin Change Interrupt Request 1
5
0x0004
WDT
Watchdog Time-out
6
0x0005
TIM1_CAPT
Timer/Counter1 Capture Event
7
0x0006
TIM1_COMPA
Timer/Counter1 Compare Match A
8
0x0007
TIM1_COMPB
Timer/Counter1 Compare Match B
9
0x0008
TIM1_OVF
Timer/Counter1 Overflow
10
0x0009
TIM0_COMPA
Timer/Counter0 Compare Match A
11
0x000A
TIM0_COMPB
Timer/Counter0 Compare Match B
12
0x000B
TIM0_OVF
Timer/Counter0 Overflow
13
0x000C
ANA_COMP
Analog Comparator
14
0x000D
ADC
ADC Conversion Complete
15
0x000E
EE_RDY
EEPROM Ready
16
0x000F
USI_STR
USI START
17
0x0010
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 setup for Reset and Interrupt Vector Addresses in ATtiny24/44/84
is shown in the program example below.
48
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Address Labels Code
Comments
0x0000
rjmp
RESET
; Reset Handler
0x0001
rjmp
INT0
; IRQ0 Handler
0x0002
rjmp
PCINT0
; PCINT0 Handler
0x0003
rjmp
PCINT1
; PCINT1 Handler
0x0004
rjmp
WDT
; Watchdog Interrupt Handler
0x0005
rjmp
TIM1_CAPT
; Timer1 Capture Handler
0x0006
rjmp
TIM1_COMPA
; Timer1 Compare A Handler
0x0007
rjmp
TIM1_COMPB
; Timer1 Compare B Handler
0x0008
rjmp
TIM1_OVF
; Timer1 Overflow Handler
0x0009
rjmp
TIM0_COMPA
; Timer0 Compare A Handler
0x000A
rjmp
TIM0_COMPB
; Timer0 Compare B Handler
0x000B
rjmp
TIM0_OVF
; Timer0 Overflow Handler
0x000C
rjmp
ANA_COMP
; Analog Comparator Handler
0x000D
rjmp
ADC
; ADC Conversion Handler
0x000E
rjmp
EE_RDY
; EEPROM Ready Handler
0x000F
rjmp
USI_STR
; USI STart Handler
0x0010
rjmp
USI_OVF
; USI Overflow Handler
;
9.2
0x0011
RESET: ldi
0x0012
out
SPH,r16
r16, high(RAMEND); Main program start
0x0013
ldi
r16, low(RAMEND)
0x0014
out
SPL,r16
0x0015
sei
0x0016
<instr>
...
...
; Set Stack Pointer to top of RAM
; Enable interrupts
External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT11..0 pins. Observe
that, if enabled, the interrupts will trigger even if the INT0 or PCINT11..0 pins are configured as
outputs. This feature provides a way of generating a software interrupt. Pin change 0 interrupts
PCI0 will trigger if any enabled PCINT7..0 pin toggles. Pin change 1 interrupts PCI1 will trigger if
any enabled PCINT11..8 pin toggles. The PCMSK0 and PCMSK1 Registers control which pins
contribute to the pin change interrupts. Pin change interrupts on PCINT11..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, as described in “Clock Sources” on page 25.
9.2.1
Low Level Interrupt
A low level interrupt on INT0 is detected asynchronously. This means that the interrupt source
can be used for waking the part also from sleep modes other than Idle (the I/O clock is halted in
all sleep modes except Idle).
49
8006H–AVR–10/09
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 “Clock System” on page 24.
If the low level on the interrupt pin is removed before the device has woken up then program
execution will not be diverted to the interrupt service routine but continue from the instruction following the SLEEP command.
9.2.2
Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in Figure 9-1.
Figure 9-1.
Timing of pin change interrupts
pin_lat
PCINT(0)
LE
clk
D
pcint_in_(0)
Q
pin_sync
PCINT(0) in PCMSK(x)
0
pcint_syn
pcint_setflag
PCIF
x
clk
clk
PCINT(0)
pin_lat
pin_sync
pcint_in_(0)
pcint_syn
pcint_setflag
PCIF
50
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
9.3
9.3.1
Register Description
MCUCR – MCU Control Register
The External Interrupt Control Register A contains control bits for interrupt sense control.
Bit
7
6
5
4
3
2
1
0
0x35 (0x55)
BODS
PUD
SE
SM1
SM0
BODSE
ISC01
ISC00
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
MCUCR
• Bits 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt are defined in Table 9-2. 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 9-2.
9.3.2
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.
GIMSK – General Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0x3B (0x5B)
–
INT0
PCIE1
PCIE0
–
–
–
0
–
Read/Write
R
R/W
R/W
R/w
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIMSK
• Bits 7, 3..0 – Res: Reserved Bits
These bits are reserved 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 Control bits (ISC01 and ISC00) in the External
Interrupt Control Register A (EICRA) 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 – PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 1 is enabled. Any change on any enabled PCINT11..8 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1
Interrupt Vector. PCINT11..8 pins are enabled individually by the PCMSK1 Register.
51
8006H–AVR–10/09
• Bit 4– PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 0 is enabled. Any change on any enabled PCINT7..0 pin will cause an interrupt.
The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0 Interrupt Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
9.3.3
GIFR – General Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0x3A (0x5A
–
INTF0
PCIF1
PCIF0
–
–
–
0
–
Read/Write
R
R/W
R/W
R/W
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIFR
• Bits 7, 3..0 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bit 6 – INTF0: External Interrupt Flag 0
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 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT11..8 pin triggers an interrupt request, PCIF1 becomes set
(one). If the I-bit in SREG and the PCIE1 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.
• Bit 4– PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF becomes set
(one). If the I-bit in SREG and the PCIE0 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.
9.3.4
PCMSK1 – Pin Change Mask Register 1
Bit
7
6
5
4
3
2
1
0
0x20 (0x40)
–
–
–
–
PCINT11
PCINT10
PCINT9
PCINT8
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCMSK1
• Bits 7, 4– Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 3..0 – PCINT11..8: Pin Change Enable Mask 11..8
Each PCINT11..8 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT11..8 is set and the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT11..8 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.
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ATtiny24/44/84
9.3.5
PCMSK0 – Pin Change Mask Register 0
Bit
7
6
5
4
3
2
1
0
0x12 (0x32)
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
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
PCMSK0
• Bits 7..0 – PCINT7..0: Pin Change Enable Mask 7..0
Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT7..0 is set and the PCIE0 bit in GIMSK is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding I/O pin
is disabled.
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8006H–AVR–10/09
10. I/O Ports
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 on page 54. See “Electrical Characteristics” on page 174 for a complete list of parameters.
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” on page 67.
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
55. 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 58. 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.
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10.1
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.
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
WPx
RRx
SLEEP
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD:
SLEEP:
clkI/O:
Note:
10.1.1
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” on page 67, 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).
55
8006H–AVR–10/09
10.1.2
Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port.
10.1.3
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.
10.1.4
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 on page 55, 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
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ATtiny24/44/84
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 on page 57. 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
0xFF
t pd
The following code example shows how to set port A 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.
Assembly Code Example
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16,(1<<PA4)|(1<<PA1)|(1<<PA0)
ldi
r17,(1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0)
out
PORTA,r16
out
DDRA,r17
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINA
...
Note:
Two temporary registers are used to minimize the time from pull-ups are set on pins 0, 1 and 4,
until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as
strong high drivers.
57
8006H–AVR–10/09
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTA = (1<<PA4)|(1<<PA1)|(1<<PA0);
DDRA = (1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINA;
...
Note:
10.1.5
See “Code Examples” on page 6.
Digital Input Enable and Sleep Modes
As shown in Figure 10-2 on page 55, 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 and Standby modes 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 58.
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.
10.1.6
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.
10.2
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. In Figure 10-5
below is shown how the port pin control signals from the simplified Figure 10-2 on page 55 can
be overridden by alternate functions.
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ATtiny24/44/84
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
DIEOVxn
RESET
WRx
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
D
RPx
Q
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
Note:
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
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.
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.
59
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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.
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ATtiny24/44/84
10.2.1
Alternate Functions of Port A
The Port A pins with alternate function are shown in Table 10-3.
Table 10-3.
Port A Pins Alternate Functions
Port Pin
Alternate Function
PA0
ADC0: ADC Input Channel 0
AREF: External Analog Reference
PCINT0: Pin Change Interrupt 0, Source 0
PA1
ADC1: ADC Input Channel 1
AIN0:
Analog Comparator, Positive Input
PCINT1:Pin Change Interrupt 0, Source 1
PA2
ADC2: ADC Input Channel 2
AIN1:
Analog Comparator, Negative Input
PCINT2: Pin Change Interrupt 0, Source 2
PA3
ADC3: ADC Input Channel 3
T0:
Timer/Counter0 Clock Source.
PCINT3: Pin Change Interrupt 0, Source 3
ADC4:
PA4
ADC Input Channel 4
USCK: USI Clock (Three Wire Mode)
SCL : USI Clock (Two Wire Mode)
T1:
Timer/Counter1 Clock Source
PCINT4: Pin Change Interrupt 0, Source 4
PA5
ADC5: ADC Input Channel 5
DO:
USI Data Output (Three Wire Mode)
MISO: SPI Master Data Input / Slave Data Output
OC1B: Timer/Counter1 Compare Match B Output
PCINT5: Pin Change Interrupt 0, Source 5
PA6
ADC6: ADC Input Channel 6
DI:
USI Data Input (Three Wire Mode)
SDA:
USI Data Input (Two Wire Mode)
MOSI: SPI Master Data Output / Slave Data Input
OC1A: Timer/Counter1 Compare Match A Output
PCINT6: Pin Change Interrupt 0, Source 6
PA7
ADC7: ADC Input Channel 7
OC0B: Timer/Counter0 Compare Match B Output
ICP1:
Timer/Counter1 Input Capture Pin
PCINT7: Pin Change Interrupt 0, Source 7
• Port A, Bit 0 – ADC0/AREF/PCINT0
• ADC0: Analog to Digital Converter, Channel 0.
• AREF: External Analog Reference for ADC. Pullup and output driver are disabled on PA0
when the pin is used as an external reference or Internal Voltage Reference with external
capacitor at the AREF pin by setting (one) the bit REFS0 in the ADC Multiplexer Selection
Register (ADMUX).
• PCINT0: Pin Change Interrupt source 0. The PA0 pin can serve as an external interrupt
source for pin change interrupt 0.
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8006H–AVR–10/09
• Port A, Bit 1 – ADC1/AIN0/PCINT1
• ADC1: Analog to Digital Converter, Channel 1.
• AIN0: Analog Comparator Positive Input. Configure the port pin as input with the internal pullup switched off to avoid the digital port function from interfering with the function of the
Analog Comparator.
• PCINT1: Pin Change Interrupt source 1. The PA1 pin can serve as an external interrupt
source for pin change interrupt 0.
• Port A, Bit 2 – ADC2/AIN1/PCINT2
• ADC2: Analog to Digital Converter, Channel 2.
• 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.
• PCINT2: Pin Change Interrupt source 2. The PA2 pin can serve as an external interrupt
source for pin change interrupt 0.
• Port A, Bit 3 – ADC3/T0/PCINT3
• ADC3: Analog to Digital Converter, Channel 3.
• T0: Timer/Counter0 counter source.
• PCINT3: Pin Change Interrupt source 3. The PA3 pin can serve as an external interrupt
source for pin change interrupt 0.
• Port A, Bit 4 – ADC4/USCK/SCL/T1/PCINT4
• ADC4: Analog to Digital Converter, Channel 4.
• USCK: Three-wire mode Universal Serial Interface Clock.
• SCL: Two-wire mode Serial Clock for USI Two-wire mode.
• T1: Timer/Counter1 counter source.
• PCINT4: Pin Change Interrupt source 4. The PA4 pin can serve as an external interrupt
source for pin change interrupt 0.
• Port A, Bit 5 – ADC5/DO/MISO/OC1B/PCINT5
• ADC5: Analog to Digital Converter, Channel 5.
• DO: Data Output in USI Three-wire mode. Data output (DO) overrides PORTA5 value and it
is driven to the port when the data direction bit DDA5 is set (one). However the PORTA5 bit
still controls the pullup, enabling pullup if direction is input and PORTA5 is set(one).
• 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 DDA5. When the SPI is
enabled as a Slave, the data direction of this pin is controlled by DDA5. When the pin is
forced by the SPI to be an input, the pull-up can still be controlled by the PORTA5 bit.
• OC1B: Output Compare Match output: The PA5 pin can serve as an external output for the
Timer/Counter1 Compare Match B. The PA5 pin has to be configured as an output (DDA5 set
(one)) to serve this function. The OC1B pin is also the output pin for the PWM mode timer
function.
• PCINT5: Pin Change Interrupt source 5. The PA5 pin can serve as an external interrupt
source for pin change interrupt 0.
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ATtiny24/44/84
• Port A, Bit 6 – ADC6/DI/SDA/MOSI/OC1A/PCINT6
• ADC6: Analog to Digital Converter, Channel 6.
• SDA: Two-wire mode Serial Interface Data.
• 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.
• MOSI: 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 DDA6. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDA6. When the pin is
forced by the SPI to be an input, the pull-up can still be controlled by the PORTA6 bit.
• OC1A, Output Compare Match output: The PA6 pin can serve as an external output for the
Timer/Counter1 Compare Match A. The pin has to be configured as an output (DDA6 set
(one)) to serve this function. This is also the output pin for the PWM mode timer function.
• PCINT6: Pin Change Interrupt source 6. The PA6 pin can serve as an external interrupt
source for pin change interrupt 0.
• Port A, Bit 7 – ADC7/OC0B/ICP1/PCINT7
• ADC7: Analog to Digital Converter, Channel 7.
• OC0B, Output Compare Match output: The PA7 pin can serve as an external output for the
Timer/Counter0 Compare Match B. The pin has to be configured as an output (DDA7 set
(one)) to serve this function. This is also the output pin for the PWM mode timer function.
• ICP1, Input Capture Pin: The PA7 pin can act as an Input Capture Pin for Timer/Counter1.
• PCINT7: Pin Change Interrupt source 7. The PA7 pin can serve as an external interrupt
source for pin change interrupt 0.
Table 10-4 and Table 10-6 relate the alternate functions of Port A to the overriding signals
shown in Figure 10-5 on page 59.
Table 10-4.
Overriding Signals for Alternate Functions in PA7..PA5
Signal
Name
PA7/ADC7/OC0B/ICP1/
PCINT7
PA6/ADC6/DI/SDA/MOSI/
OC1A/ PCINT6
PA5/ADC5/MISO/DO/
OC1B/ PCINT5
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
USIWM1
0
DDOV
0
(SDA + PORTA6) • DDA6
0
PVOE
OC0B enable
(USIWM1 • DDA6) +
OC1A enable
(USIWM1 • USIWM0) + OC1B
enable
PVOV
OC0B
( USIWM1• DDA6) • OC1A
USIWM1 • USIWM0 • DO +
(USIWM1 + USIWM0) • OC1B
PTOE
0
0
0
DIEOE
PCINT7 • PCIE0 + ADC7D
USISIE + (PCINT6 •
PCIE0) + ADC6D
PCINT5 • PCIE + ADC5D
DIEOV
PCINT7 • PCIE0
USISIE + PCINT7 • PCIE0
PCINT5 • PCIE
DI
PCINT7/ICP1 Input
DI/SDA/PCINT6 Input
PCINT5 Input
AIO
ADC7 Input
ADC6 Input
ADC5 Input
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8006H–AVR–10/09
Table 10-5.
Signal
Name
PA4/ADC4/USCK/SCL/T1/
PCINT4
PA3/ADC3/T0/PCINT3
PA2/ADC2/AIN1/PCINT2
PUOE
0
0
0
PUOV
0
0
0
DDOE
USIWM1
0
0
DDOV
USI_SCL_HOLD +
PORTA4) • DDA4
0
0
PVOE
USIWM1 • DDA4
0
0
PVOV
0
0
0
PTOE
USI_PTOE
0
0
DIEOE
USISIE +
(PCINT4 • PCIE0) + ADC4D
(PCINT3 • PCIE0) + ADC3D
PCINT2 • PCIE + ADC2D
DIEOV
USISIE +
(PCINT4 • PCIE0)
PCINT3 • PCIE0
PCINT3 • PCIE0
DI
USCK/SCL/T1/PCINT4 input
PCINT1 Input
PCINT0 Input
AIO
ADC4 Input
ADC3 Input
ADC2/Analog Comparator
Negative Input
Table 10-6.
64
Overriding Signals for Alternate Functions in PA4..PA2
Overriding Signals for Alternate Functions in PA1..PA0
Signal
Name
PA1/ADC1/AIN0/PCINT1
PA0/ADC0/AREF/PCINT0
PUOE
0
RESET •
(REFS1 • REFS0 + REFS1 • REFS0)
PUOV
0
0
DDOE
0
RESET •
(REFS1 • REFS0 + REFS1 • REFS0)
DDOV
0
0
PVOE
0
RESET •
(REFS1 • REFS0 + REFS1 • REFS0)
PVOV
0
0
PTOE
0
0
DIEOE
PCINT1 • PCIE0 + ADC1D
PCINT0 • PCIE0 + ADC0D
DIEOV
PCINT1 • PCIE0
PCINT0 • PCIE0
DI
PCINT1 Input
PCINT0 Input
AIO
ADC1/Analog Comparator Positive Input
ADC1 Input
Analog reference
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
10.2.2
Alternate Functions of Port B
The Port B pins with alternate function are shown in Table 10-7.
Table 10-7.
Port B Pins Alternate Functions
Port Pin
Alternate Function
PB0
XTAL1: Crystal Oscillator Input
PCINT8: Pin Change Interrupt 1, Source 8
CLKI:
External Clock Input
PB1
XTAL2: Crystal Oscillator Output
PCINT9: Pin Change Interrupt 1, Source 9
PB2
INT0:
External Interrupt 0 Input
OC0A: Timer/Counter0 Compare Match A output
CKOUT: System Clock Output
PCINT10:Pin Change Interrupt 1, Source 10
PB3
RESET: Reset pin
dW:
debugWire I/O
PCINT11:Pin Change Interrupt 1, Source 11.
• Port B, Bit 0 – XTAL1/PCINT8
• 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.
When using internal calibratable RC Oscillator as a chip clock source, PB0 serves as an
ordinary I/O pin.
• PCINT8: Pin Change Interrupt source 8. The PB0 pin can serve as an external interrupt
source for pin change interrupt 1.
• CLKI: Clock Input from an external clock source, see “External Clock” on page 26.
• Port B, Bit 1 – XTAL2/PCINT9
• 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, PB1 serves as an ordinary I/O pin.
• PCINT9: Pin Change Interrupt source 9. The PB1 pin can serve as an external interrupt
source for pin change interrupt 1.
• Port B, Bit 2 – INT0/OC0A/CKOUT/PCINT10
• INT0: External Interrupt Request 0.
• OC0A: Output Compare Match output: The PB2 pin can serve as an external output for the
Timer/Counter0 Compare Match A. The PB2 pin has to be configured as an output (DDB2
set (one)) to serve this function. The OC0A pin is also the output pin for the PWM mode timer
function.
• CKOUT - System Clock Output: The system clock can be output on the PB2 pin. The system
clock will be output if the CKOUT Fuse is programmed, regardless of the PORTB2 and DDB2
settings. It will also be output during reset.
• PCINT10: Pin Change Interrupt source 10. The PB2 pin can serve as an external interrupt
source for pin change interrupt 1.
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• Port B, Bit 3 – RESET/dW/PCINT11
• 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.
• PCINT11: Pin Change Interrupt source 11. The PB3 pin can serve as an external interrupt
source for pin change interrupt 1.
Table 10-8 on page 66 and Table 10-9 on page 67 relate the alternate functions of Port B to the
overriding signals shown in Figure 10-5 on page 59.
Table 10-8.
Signal
Name
Overriding Signals for Alternate Functions in PB3..PB2
PB3/RESET/dW/
PCINT11
PUOE
RSTDISBL
PUOV
1
(1)
PB2/INT0/OC0A/CKOUT/PCINT10
(2)
+ DEBUGWIRE_ENABLE
CKOUT
0
(1)
(2)
DDOE
RSTDISBL
DDOV
DEBUGWIRE_ENABLE(2) • debugWire
Transmit
1
PVOE
RSTDISBL(1) + DEBUGWIRE_ENABLE(2)
CKOUT + OC0A enable
PVOV
0
CKOUT • System Clock + CKOUT • OC0A
PTOE
0
+ DEBUGWIRE_ENABLE
CKOUT
0
(1)
(2)
DIEOE
RSTDISBL + DEBUGWIRE_ENABLE
PCINT11 • PCIE1
DIEOV
DEBUGWIRE_ENABLE(2) + (RSTDISBL(1) •
PCINT11 • PCIE1)
PCINT10 • PCIE1 + INT0
DI
dW/PCINT11 Input
INT0/PCINT10 Input
+
PCINT10 • PCIE1 + INT0
AIO
66
1.
RSTDISBL is 1 when the Fuse is “0” (Programmed).
2.
DebugWIRE is enabled wheb DWEN Fuse is programmed and Lock bits are unprogrammed.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Table 10-9.
Signal
Name
Overriding Signals for Alternate Functions in PB1..PB0
PB1/XTAL2/PCINT9
PB0/XTAL1/PCINT8
(1)
EXT_CLOCK (2) + EXT_OSC(1)
PUOE
EXT_OSC
PUOV
0
0
DDOE
EXT_OSC(1)
EXT_CLOCK(2) + EXT_OSC(1)
DDOV
0
0
PVOE
EXT_OSC
PVOV
0
PTOE
0
(1)
EXT_CLOCK(2) + EXT_OSC(1)
0
0
(1)
10.3
10.3.1
DIEOE
EXT_OSC +
PCINT9 • PCIE1
EXT_CLOCK(2) + EXT_OSC(1) +
(PCINT8 • PCIE1)
DIEOV
EXT_OSC(1) • PCINT9 • PCIE1
( EXT_CLOCK(2) • PWR_DOWN ) +
(EXT_CLOCK(2) • EXT_OSC(1) • PCINT8 • PCIE1)
DI
PCINT9 Input
CLOCK/PCINT8 Input
AIO
XTAL2
XTAL1
1.
EXT_OSC = crystal oscillator or low frequency crystal oscillator is selected as system clock.
2.
EXT_CLOCK = external clock is selected as system clock.
Register Description
MCUCR – MCU Control Register
Bit
7
6
5
4
3
2
1
0
BODS
PUD
SE
SM1
SM0
BODSE
ISC01
ISC00
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
R
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• 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 55 for more details about this feature.
10.3.2
PORTA – Port A Data Register
Bit
10.3.3
7
6
5
4
3
2
1
0
0x1B (0x3B)
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PORTA
DDRA – Port A Data Direction Register
Bit
7
6
5
4
3
2
1
0
0x1A (0x3A)
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DDRB
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8006H–AVR–10/09
10.3.4
PINA – Port A Input Pins
Bit
10.3.5
10.3.6
10.3.7
68
7
6
5
4
3
2
1
0
0x19 (0x39)
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PINB
PORTB – Port B Data Register
Bit
7
6
5
4
3
2
1
0
0x18 (0x38)
–
–
–
–
PORTB3
PORTB2
PORTB1
PORTB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PORTB
DDRB – Port B Data Direction Register
Bit
7
6
5
4
3
2
1
0
0x17 (0x37)
–
–
–
–
DDB3
DDB2
DDB1
DDB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x16 (0x36)
–
–
–
–
PINB3
PINB2
PINB1
PINB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
N/A
N/A
N/A
N/A
DDRB
PINB – Port B Input Pins
PINB
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
11. 8-bit Timer/Counter0 with PWM
11.1
Features
•
•
•
•
•
•
•
11.2
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
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.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 11-1 on page 69. For
the actual placement of I/O pins, refer to Figure 1-1 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 “Register Description” on page 80.
Figure 11-1. 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
OCnB
(Int.Req.)
Waveform
Generation
=
OCnB
OCRnB
TCCRnA
TCCRnB
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8006H–AVR–10/09
11.2.1
Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in Figure 11-1) signals are all visible in the
Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK0). TIFR0 and TIMSK0 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 71 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.
11.2.2
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.
The definitions in Table 11-1 are also used extensively throughout the document.
Table 11-1.
11.3
Definitions
Constant
Description
BOTTOM
The counter reaches BOTTOM when it becomes 0x00
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the
value stored in the OCR0A Register. The assignment depends on the mode of operation
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 115.
11.4
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
11-2 on page 71 shows a block diagram of the counter and its surroundings.
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ATtiny24/44/84
Figure 11-2. 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
direction
clear
clkTn
top
bottom
Increment or decrement TCNT0 by 1.
Select between increment and decrement.
Clear TCNT0 (set all bits to zero).
Timer/Counter clock, referred to as clkT0 in the following.
Signalize that TCNT0 has reached maximum value.
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
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 74.
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.
11.5
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers
(OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a
match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock
cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output
Compare interrupt. 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 74.
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Figure 11-3 shows a block diagram of the Output Compare unit.
Figure 11-3. 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.
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.
11.5.1
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (0x) 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).
11.5.2
Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any Compare Match that occur in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.
11.5.3
Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all Compare Matches for one timer
clock cycle, there are risks involved when changing TCNT0 when using the Output Compare
Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT0
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ATtiny24/44/84
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 (0x) 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.
11.6
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 11-4 on page 73 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”.
Figure 11-4. 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.
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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 “Register Description” on page 80
11.6.1
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 11-2 on page 80. For fast PWM mode, refer to Table 11-3 on
page 81, and for phase correct PWM refer to Table 11-4 on page 81.
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 0x
strobe bits.
11.7
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (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 “Modes of Operation” on page 74).
For detailed timing information refer to Figure 11-8 on page 79, Figure 11-9 on page 79, Figure
11-10 on page 79 and Figure 11-11 on page 80 in “Timer/Counter Timing Diagrams” on page
78.
11.7.1
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.
11.7.2
74
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.
ATtiny24/44/84
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ATtiny24/44/84
The timing diagram for the CTC mode is shown in Figure 11-5 on page 75. The counter value
(TCNT0) increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.
Figure 11-5. 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
the pin is set to output. The waveform generated will have a maximum frequency of 0 = 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.
11.7.3
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
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8006H–AVR–10/09
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 11-6 on page 76. The TCNT0 value is in the timing diagram
shown as a histogram for illustrating the single-slope operation. The diagram includes noninverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x and TCNT0.
Figure 11-6. 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.
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 11-3 on page 81). 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
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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 0 = 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.
11.7.4
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 11-7 on page 77. The TCNT0 value is in the timing diagram shown as a histogram for
illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches
between OCR0x and TCNT0.
Figure 11-7. 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
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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 11-4 on page 81). 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 11-7 on page 77 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 11-7 on page 77. When the OCR0A value
is MAX the OCn pin value is the same as the result of a down-counting Compare Match. To
ensure symmetry around BOTTOM the OCn value at MAX must correspond to the result of
an up-counting Compare Match.
• The timer starts counting from a 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.
11.8
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set. Figure 11-8 on page 79 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.
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Figure 11-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 11-9 on page 79 shows the same timing data, but with the prescaler enabled.
Figure 11-9. 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 11-10 on page 79 shows the setting of OCF0B in all modes and OCF0A in all modes
except CTC mode and PWM mode, where OCR0A is TOP.
Figure 11-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 11-11 on page 80 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode
and fast PWM mode where OCR0A is TOP.
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Figure 11-11. 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
BOTTOM + 1
TOP
OCRnx
OCFnx
11.9
11.9.1
Register Description
TCCR0A – Timer/Counter Control Register A
Bit
7
6
5
4
3
2
1
0
0x30 (0x50)
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 – COM0A1:0: 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.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM02:0 bit setting. Table 11-2 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 11-2.
Compare Output Mode, non-PWM Mode
COM0A1
COM0A0
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 11-3 shows COM0A1:0 bit functionality when WGM01:0 bits are set to fast PWM mode.
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Table 11-3.
Compare Output Mode, Fast 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
Set OC0A at BOTTOM (non-inverting mode)
1
1
Set OC0A on Compare Match
Clear OC0A at BOTTOM (inverting mode)
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 BOTTOM. See “Fast PWM Mode” on
page 75 for more details.
Table 11-4 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 11-4.
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 77 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.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the
WGM02:0 bit setting. Table 11-5 shows the COM0B1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 11-5.
Compare Output Mode, non-PWM Mode
COM0B1
COM0B0
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
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Table 11-6 shows COM0B1:0 bit functionality when WGM02:0 bits are set to fast PWM mode.
Table 11-6.
Compare Output Mode, Fast PWM Mode(1)
COM0B1
COM0B0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match, set OC0B at BOTTOM
(non-inverting mode)
1
1
Set OC0B on Compare Match, clear OC0B at BOTTOM
(inverting mode)
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 BOTTOM. See “Fast PWM Mode” on
page 75 for more details.
Table 11-7 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 11-7.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1
COM0B0
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 77 for more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved and will always read 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 11-8. Modes of operation supported by the Timer/Counter
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 74).
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Table 11-8.
Timer/Counter
Mode of Operation
TOP
Update of
OCRx at
TOV Flag
Set on(1)
0
Normal
0xFF
Immediate
MAX
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
BOTTOM
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
BOTTOM
TOP
Mode
WGM02
WGM01
WGM00
0
0
0
1
0
2
Note:
11.9.2
Waveform Generation Mode Bit Description
1. MAX
= 0xFF
BOTTOM = 0x00
TCCR0B – Timer/Counter Control Register B
Bit
7
6
5
4
3
2
1
0
0x33 (0x53)
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
Read/Write
W
W
R
R
R/W
R/W
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
strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the
forced compare.
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A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits in the ATtiny24/44/84 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “TCCR0A – Timer/Counter Control Register A” on page 80.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 11-9.
Clock Select Bit Description
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.
11.9.3
TCNT0 – Timer/Counter Register
Bit
7
6
5
0x32 (0x52)
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.
11.9.4
OCR0A – Output Compare Register A
Bit
7
6
5
0x36 (0x56)
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
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.
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11.9.5
OCR0B – Output Compare Register B
Bit
7
6
5
0x3C (0x5C)
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.
11.9.6
TIMSK0 – Timer/Counter 0 Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0
0x39 (0x59)
–
–
–
–
–
OCIE0B
OCIE0A
TOIE0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the ATtiny24/44/84 and will always read as zero.
• Bit 2– 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 1– 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 0– 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.
11.9.7
TIFR0 – Timer/Counter 0 Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x38 (0x58)
–
–
–
–
–
OCF0B
OCF0A
TOV0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the ATtiny24/44/84 and will always read as zero.
• Bit 2– 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
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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– OCF0A: Output Compare Flag 0 A
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare 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 0– 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. See Table 11-8 on page 83 and
“Waveform Generation Mode Bit Description” on page 83.
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12. 16-bit Timer/Counter1
12.1
Features
•
•
•
•
•
•
•
•
•
•
•
12.2
True 16-bit Design (i.e., Allows 16-bit PWM)
Two independent Output Compare Units
Double Buffered Output Compare Registers
One Input Capture Unit
Input Capture Noise Canceler
Clear Timer on Compare Match (Auto Reload)
Glitch-free, Phase Correct Pulse Width Modulator (PWM)
Variable PWM Period
Frequency Generator
External Event Counter
Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1)
Overview
The 16-bit Timer/Counter unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 12-1 on page 87. For
actual placement of I/O pins, refer to “Pinout ATtiny24/44/84” 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 “Register Description” on page 108.
Figure 12-1. 16-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
OCnB
(Int.Req.)
Fixed
TOP
Values
Waveform
Generation
=
OCRnB
OCnB
( From Analog
Comparator Ouput )
ICFn (Int.Req.)
Edge
Detector
ICRn
Noise
Canceler
ICPn
TCCRnA
TCCRnB
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Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit
channel. However, when using the register or bit defines in a program, the precise form must be
used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
12.2.1
Registers
The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture Register (ICR1) are all 16-bit registers. Special procedures must be followed when accessing the 16bit registers. These procedures are described in the section “Accessing 16-bit Registers” on
page 105. The Timer/Counter Control Registers (TCCR1A/B) are 8-bit registers and have no
CPU access restrictions. Interrupt requests (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 T1 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 (clkT1).
The double buffered Output Compare Registers (OCR1A/B) are compared with the Timer/Counter value at all time. The result of the compare can be used by the Waveform Generator to
generate a PWM or variable frequency output on the Output Compare pin (OC1A/B). See “Output Compare Units” on page 92. The compare match event will also set the Compare Match
Flag (OCF1A/B) which can be used to generate an Output Compare interrupt request.
The Input Capture Register can capture the Timer/Counter value at a given external (edge triggered) event on either the Input Capture pin (ICP1) or on the Analog Comparator pins (See
“Analog Comparator” on page 129). The Input Capture unit includes a digital filtering unit (Noise
Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined
by either the OCR1A Register, the ICR1 Register, or by a set of fixed values. When using
OCR1A as TOP value in a PWM mode, the OCR1A Register can not be used for generating a
PWM output. However, the TOP value will in this case be double buffered allowing the TOP
value to be changed in run time. If a fixed TOP value is required, the ICR1 Register can be used
as an alternative, freeing the OCR1A to be used as PWM output.
12.2.2
Definitions
The following definitions are used extensively throughout the section:
Table 12-1.
88
Definitions
Constant
Description
BOTTOM
The counter reaches BOTTOM when it becomes 0x00
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the
value stored in the OCR0A Register. The assignment depends on the mode of operation
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12.2.3
Compatibility
The 16-bit Timer/Counter has been updated and improved from previous versions of 16-bit AVR
Timer/Counters. This 16-bit Timer/Counter is fully compatible with the earlier version regarding:
• All 16-bit Timer/Counter related I/O Register address locations, including Timer Interrupt
Registers.
• Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt Registers.
• Interrupt Vectors.
The following control bits have changed name, but have same functionality and register location:
• PWM10 is changed to WGM10.
• PWM11 is changed to WGM11.
• CTC1 is changed to WGM12.
The following bits are added to the 16-bit Timer/Counter Control Registers:
• 1A and 1B are added to TCCR1A.
• WGM13 is added to TCCR1B.
The 16-bit Timer/Counter has improvements that will affect backward compatibility in some special cases.
12.3
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 (CS12:0) bits
located in the Timer/Counter control Register B (TCCR1B). For details on clock sources and
prescaler, see “Timer/Counter Prescaler” on page 115.
12.4
Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.
Figure 12-2 on page 89 shows a block diagram of the counter and its surroundings.
Figure 12-2. Counter Unit Block Diagram
DATA BUS
(8-bit)
TOVn
(Int.Req.)
TEMP (8-bit)
Clock Select
Count
TCNTnH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
Clear
Direction
Control Logic
clkTn
Edge
Detector
Tn
( From Prescaler )
TOP
BOTTOM
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Signal description (internal signals):
Count
Direction
Clear
clkT1
TOP
BOTTOM
Increment or decrement TCNT1 by 1.
Select between increment and decrement.
Clear TCNT1 (set all bits to zero).
Timer/Counter clock.
Signalize that TCNT1 has reached maximum value.
Signalize that TCNT1 has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) containing the upper eight bits of the counter, and Counter Low (TCNT1L) containing the lower eight
bits. The TCNT1H Register can only be indirectly accessed by the CPU. When the CPU does an
access to the TCNT1H I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNT1H value when the TCNT1L is read, and
TCNT1H is updated with the temporary register value when TCNT1L is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNT1 Register when the
counter is counting that will give unpredictable results. The special cases are described in the
sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT1). The clkT1 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS12:0). When no clock source is selected (CS12:0 = 0) the
timer is stopped. However, the TCNT1 value can be accessed by the CPU, independent of
whether clkT1 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 Waveform Generation mode bits
(WGM13:0) located in the Timer/Counter Control Registers A and B (TCCR1A and TCCR1B).
There are close connections between how the counter behaves (counts) and how waveforms
are generated on the Output Compare outputs OC1x. For more details about advanced counting
sequences and waveform generation, see “Modes of Operation” on page 96.
The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected by
the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt.
12.5
Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events and give
them a time-stamp indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICP1 pin or alternatively, via the analog-comparator unit. The
time-stamps can then be used to calculate frequency, duty-cycle, and other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 12-3 on page 91. The
elements of the block diagram that are not directly a part of the Input Capture unit are gray
shaded. The small “n” in register and bit names indicates the Timer/Counter number.
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Figure 12-3. Input Capture Unit Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
ICRnH (8-bit)
WRITE
ICRnL (8-bit)
TCNTnH (8-bit)
ICRn (16-bit Register)
ACO*
Analog
Comparator
ACIC*
TCNTnL (8-bit)
TCNTn (16-bit Counter)
ICNC
ICES
Noise
Canceler
Edge
Detector
ICFn (Int.Req.)
ICPn
When a change of the logic level (an event) occurs on the Input Capture pin (ICP1), alternatively
on the Analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter
(TCNT1) is written to the Input Capture Register (ICR1). The Input Capture Flag (ICF1) is set at
the same system clock as the TCNT1 value is copied into ICR1 Register. If enabled (ICIE1 = 1),
the Input Capture Flag generates an Input Capture interrupt. The ICF1 flag is automatically
cleared when the interrupt is executed. Alternatively the ICF1 flag can be cleared by software by
writing a logical one to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICR1) is done by first reading the low
byte (ICR1L) and then the high byte (ICR1H). When the low byte is read the high byte is copied
into the high byte temporary register (TEMP). When the CPU reads the ICR1H I/O location it will
access the TEMP Register.
The ICR1 Register can only be written when using a Waveform Generation mode that utilizes
the ICR1 Register for defining the counter’s TOP value. In these cases the Waveform Generation mode (WGM13:0) bits must be set before the TOP value can be written to the ICR1
Register. When writing the ICR1 Register the high byte must be written to the ICR1H I/O location
before the low byte is written to ICR1L.
For more information on how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 105.
12.5.1
Input Capture Trigger Source
The main trigger source for the Input Capture unit is the Input Capture pin (ICP1).
Timer/Counter1 can alternatively use the Analog Comparator output as trigger source for the
Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog
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Comparator Input Capture (ACIC) bit in the Analog Comparator Control and Status Register
(ACSR). Be aware that changing trigger source can trigger a capture. The Input Capture Flag
must therefore be cleared after the change.
Both the Input Capture pin (ICP1) and the Analog Comparator output (ACO) inputs are sampled
using the same technique as for the T1 pin (Figure 13-1 on page 115). The edge detector is also
identical. However, when the noise canceler is enabled, additional logic is inserted before the
edge detector, which increases the delay by four system clock cycles. Note that the input of the
noise canceler and edge detector is always enabled unless the Timer/Counter is set in a Waveform Generation mode that uses ICR1 to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP1 pin.
12.5.2
Noise Canceler
The noise canceler uses a simple digital filtering technique to improve noise immunity. Consecutive samples are monitored in a pipeline four units deep. The signal going to the edge detecter is
allowed to change only when all four samples are equal.
The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNC1) bit in
Timer/Counter Control Register B (TCCR1B). When enabled, the noise canceler introduces an
additional delay of four system clock cycles to a change applied to the input and before ICR1 is
updated.
The noise canceler uses the system clock directly and is therefore not affected by the prescaler.
12.5.3
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICR1 Register before the next event occurs, the ICR1 will be
overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICR1 Register should be read as early in the interrupt handler routine as possible. Even though the Input Capture interrupt has relatively high
priority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.
Using the Input Capture unit in any mode of operation when the TOP value (resolution) is
actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICR1
Register has been read. After a change of the edge, the Input Capture Flag (ICF1) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICF1 flag is not required (if an interrupt handler is used).
12.6
Output Compare Units
The 16-bit comparator continuously compares TCNT1 with the Output Compare Register
(OCR1x). If TCNT equals OCR1x the comparator signals a match. A match will set the Output
Compare Flag (OCF1x) at the next timer clock cycle. If enabled (OCIE1x = 1), the Output Compare Flag generates an Output Compare interrupt. The OCF1x flag is automatically cleared
when the interrupt is executed. Alternatively the OCF1x 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 Waveform Generation mode
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(WGM13:0) bits and Compare Output mode (COM1x1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (“Modes of Operation” on page 96).
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value (i.e.,
counter resolution). In addition to the counter resolution, the TOP value defines the period time
for waveforms generated by the Waveform Generator.
Figure 12-4 on page 93 shows a block diagram of the Output Compare unit. The small “n” in the
register and bit names indicates the device number (n = 1 for Timer/Counter 1), and the “x” indicates Output Compare unit (A/B). The elements of the block diagram that are not directly a part
of the Output Compare unit are gray shaded.
Figure 12-4. Output Compare Unit, Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
OCRnxH Buf. (8-bit)
OCRnxL Buf. (8-bit)
TCNTnH (8-bit)
OCRnx Buffer (16-bit Register)
OCRnxH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
OCRnxL (8-bit)
OCRnx (16-bit Register)
= (16-bit Comparator )
OCFnx (Int.Req.)
TOP
BOTTOM
Waveform Generator
WGMn3:0
OCnx
COMnx1:0
The OCR1x Register is double buffered when using any of the twelve 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 OCR1x Compare Register 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.
The OCR1x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR1x Buffer Register, and if double buffering is disabled the CPU will access the OCR1x directly. The content of the OCR1x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as when
accessing other 16-bit registers. Writing the OCR1x Registers must be done via the TEMP Reg-
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ister since the compare of all 16 bits is done continuously. The high byte (OCR1xH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
updated by the value written. Then when the low byte (OCR1xL) is written to the lower eight bits,
the high byte will be copied into the upper 8-bits of either the OCR1x buffer or OCR1x Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 105.
12.6.1
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 (1x) bit. Forcing compare match will not set the
OCF1x flag or reload/clear the timer, but the OC1x pin will be updated as if a real compare
match had occurred (the COM11:0 bits settings define whether the OC1x pin is set, cleared or
toggled).
12.6.2
Compare Match Blocking by TCNT1 Write
All CPU writes to the TCNT1 Register will block any compare match that occurs in the next timer
clock cycle, even when the timer is stopped. This feature allows OCR1x to be initialized to the
same value as TCNT1 without triggering an interrupt when the Timer/Counter clock is enabled.
12.6.3
Using the Output Compare Unit
Since writing TCNT1 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT1 when using any of the Output Compare
channels, independent of whether the Timer/Counter is running or not. If the value written to
TCNT1 equals the OCR1x value, the compare match will be missed, resulting in incorrect waveform generation. Do not write the TCNT1 equal to TOP in PWM modes with variable TOP
values. The compare match for the TOP will be ignored and the counter will continue to 0xFFFF.
Similarly, do not write the TCNT1 value equal to BOTTOM when the counter is downcounting.
The setup of the OC1x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC1x value is to use the Force Output Compare (1x) strobe bits in Normal mode. The OC1x Register keeps its value even when changing
between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare value.
Changing the COM1x1:0 bits will take effect immediately.
12.7
Compare Match Output Unit
The Compare Output Mode (COM1x1:0) bits have two functions. The Waveform Generator uses
the COM1x1:0 bits for defining the Output Compare (OC1x) state at the next compare match.
Secondly the COM1x1:0 bits control the OC1x pin output source. Figure 12-5 on page 95 shows
a simplified schematic of the logic affected by the COM1x1:0 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 COM1x1:0 bits are shown. When referring to
the OC1x state, the reference is for the internal OC1x Register, not the OC1x pin. If a system
reset occur, the OC1x Register is reset to “0”.
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Figure 12-5. Compare Match Output Unit, Schematic (non-PWM Mode)
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC1x) from the Waveform
Generator if either of the COM1x1:0 bits are set. However, the OC1x 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 OC1x pin (DDR_OC1x) must be set as output before the OC1x value is visible on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. See Table 12-2 on page 109, Table 12-3 on page 109
and Table 12-4 on page 109 for details.
The design of the Output Compare pin logic allows initialization of the OC1x state before the output is enabled. Note that some COM1x1:0 bit settings are reserved for certain modes of
operation. See “Register Description” on page 108
The COM1x1:0 bits have no effect on the Input Capture unit.
12.7.1
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM1x1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COM1x1:0 = 0 tells the Waveform Generator that no action on the
OC1x Register is to be performed on the next compare match. For compare output actions in the
non-PWM modes refer to Table 12-2 on page 109. For fast PWM mode refer to Table 12-3 on
page 109, and for phase correct and phase and frequency correct PWM refer to Table 12-4 on
page 109.
A change of the COM1x1:0 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 1x
strobe bits.
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12.8
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 (WGM13:0) and Compare Output
mode (COM1x1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM1x1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM1x1:0 bits control whether the output should be set, cleared or toggle at a compare
match (“Compare Match Output Unit” on page 94)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 103.
12.8.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM13:0 = 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 16-bit value (MAX = 0xFFFF) and then restarts from the
BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOV1) will be set in
the same timer clock cycle as the TCNT1 becomes zero. The TOV1 flag in this case behaves
like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow
interrupt that automatically clears the TOV1 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 Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval
between events are too long, the timer overflow interrupt or the prescaler must be used to
extend the resolution for the capture unit.
The Output Compare units 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.
12.8.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1 Register
are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNT1) matches either the OCR1A (WGM13:0 = 4) or the ICR1 (WGM13:0 =
12). The OCR1A or ICR1 define 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 12-6 on page 97. The counter value
(TCNT1) increases until a compare match occurs with either OCR1A or ICR1, and then counter
(TCNT1) is cleared.
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Figure 12-6. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnA
(Toggle)
Period
(COMnA1:0 = 1)
1
2
3
4
An interrupt can be generated at each time the counter value reaches the TOP value by either
using the OCF1A or ICF1 flag according to the register used to define the TOP value. If the interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However,
changing the 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 OCR1A or ICR1 is lower than the current value of TCNT1, the
counter will miss the compare match. The counter will then have to count to its maximum value
(0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. In many
cases this feature is not desirable. An alternative will then be to use the fast PWM mode using
OCR1A for defining TOP (WGM13:0 = 15) since the OCR1A then will be double buffered.
For generating a waveform output in CTC mode, the OC1A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM1A1:0 = 1). The OC1A value will not be visible on the port pin unless the data direction for
the pin is set to output (DDR_OC1A = 1). The waveform generated will have a maximum frequency of 1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The waveform frequency is defined
by the following equation:
f clk_I/O
f OCnA = --------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnA )
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV1 flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
12.8.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM13:0 = 5, 6, 7, 14, or 15) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is cleared
on the compare match between TCNT1 and OCR1x, and set at BOTTOM. In inverting Compare
Output mode 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 and phase and frequency correct PWM modes that use dual-slope operation. This high
frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
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applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or
OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can be
calculated by using the following equation:
log ( TOP + 1 )
R FPWM = ----------------------------------log ( 2 )
In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in ICR1 (WGM13:0 =
14), or the value in OCR1A (WGM13:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in Figure 12-7 on page 98. The
figure shows fast PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 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
TCNT1 slopes represent compare matches between OCR1x and TCNT1. The OC1x interrupt
flag will be set when a compare match occurs.
Figure 12-7. Fast PWM Mode, Timing Diagram
OCRnx/TOP Update and
TOVn Interrupt Flag Set and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
8
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. In addition
the OC1A or ICF1 flag is set at the same timer clock cycle as TOV1 is set when either OCR1A or
ICR1 is used for defining the TOP value. If one of the interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCR1x Registers are written.
The procedure for updating ICR1 differs from updating OCR1A when used for defining the TOP
value. The ICR1 Register is not double buffered. This means that if ICR1 is changed to a low
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value when the counter is running with none or a low prescaler value, there is a risk that the new
ICR1 value written is lower than the current value of TCNT1. The result will then be that the
counter will miss the compare match at the TOP value. The counter will then have to count to the
MAX value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
The OCR1A Register however, is double buffered. This feature allows the OCR1A I/O location
to be written anytime. When the OCR1A I/O location is written the value written will be put into
the OCR1A Buffer Register. The OCR1A Compare Register will then be updated with the value
in the Buffer Register at the next timer clock cycle the TCNT1 matches TOP. The update is done
at the same timer clock cycle as the TCNT1 is cleared and the TOV1 flag is set.
Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using
ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However,
if the base PWM frequency is actively changed (by changing the TOP value), using the OCR1A
as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins.
Setting the COM1x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM1x1:0 to three (see Table 12-3 on page 109). The actual
OC1x value will only be visible on the port pin if the data direction for the port pin is set as output
(DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at
the compare match between OCR1x and TCNT1, and clearing (or setting) the OC1x 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 ⋅ ( 1 + TOP )
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR1x is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCR1x equal to TOP
will result in a constant high or low output (depending on the polarity of the output set by the
COM1x1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC1A to toggle its logical level on each compare match (COM1A1:0 = 1). The waveform
generated will have a maximum frequency of 1A = fclk_I/O/2 when OCR1A is set to zero (0x0000).
This feature is similar to the OC1A toggle in CTC mode, except the double buffer feature of the
Output Compare unit is enabled in the fast PWM mode.
12.8.4
Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGM13:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a dualslope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from
TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is
cleared on the compare match between TCNT1 and OCR1x 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.
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The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined
by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to
0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can be calculated by using the following equation:
log ( TOP + 1 )
R PCPWM = ----------------------------------log ( 2 )
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1
(WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 12-8 on page
100. The figure shows phase correct PWM mode when OCR1A or ICR1 is used to define TOP.
The TCNT1 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 TCNT1 slopes represent compare matches between OCR1x and TCNT1. The
OC1x interrupt flag will be set when a compare match occurs.
Figure 12-8. Phase Correct PWM Mode, Timing Diagram
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM. When
either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 flag is set accordingly at the same timer clock cycle as the OCR1x Registers are updated with the double buffer
value (at TOP). The interrupt flags can be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
Note that when using fixed TOP values, the unused bits are masked to zero when any of the
OCR1x Registers are written. As the third period shown in Figure 12-8 on page 100 illustrates,
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changing the TOP actively while the Timer/Counter is running in the phase correct mode can
result in an unsymmetrical output. The reason for this can be found in the time of update of the
OCR1x Register. Since the OCR1x update occurs at TOP, the PWM period starts and ends at
TOP. This implies that the length of the falling slope is determined by the previous TOP value,
while the length of the rising slope is determined by the new TOP value. When these two values
differ the two slopes of the period will differ in length. The difference in length gives the unsymmetrical result on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct
mode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COM1x1:0 to three (See Table 12-4 on page 109).
The actual OC1x value will only be visible on the port pin if the data direction for the port pin is
set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x
Register at the compare match between OCR1x and TCNT1 when the counter increments, and
clearing (or setting) the OC1x Register at compare match between OCR1x and TCNT1 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 = --------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
12.8.5
Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM
mode (WGM13:0 = 8 or 9) provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the
Output Compare (OC1x) is cleared on the compare match between TCNT1 and OCR1x while
upcounting, and set on the compare match while downcounting. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCR1x Register is updated by the OCR1x Buffer Register, (see Figure 128 on page 100 and Figure 12-9 on page 102).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either
ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and
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the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can
be calculated using the following equation:
log ( TOP + 1 )
R PFCPWM = ----------------------------------log ( 2 )
In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICR1 (WGM13:0 = 8), or the value in OCR1A (WGM13:0 = 9). The
counter has then reached the TOP and changes the count direction. The TCNT1 value will be
equal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency
correct PWM mode is shown on Figure 12-9 on page 102. The figure shows phase and frequency correct PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 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 TCNT1
slopes represent compare matches between OCR1x and TCNT1. The OC1x interrupt flag will be
set when a compare match occurs.
Figure 12-9. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/TOP Updateand
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set at the same timer clock cycle as the OCR1x
Registers are updated with the double buffer value (at BOTTOM). When either OCR1A or ICR1
is used for defining the TOP value, the OC1A or ICF1 flag set when TCNT1 has reached TOP.
The interrupt flags can then be used to generate an interrupt each time the counter reaches the
TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
As Figure 12-9 on page 102 shows the output generated is, in contrast to the phase correct
mode, symmetrical in all periods. Since the OCR1x Registers are updated at BOTTOM, the
length of the rising and the falling slopes will always be equal. This gives symmetrical output
pulses and is therefore frequency correct.
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Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using
ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However,
if the base PWM frequency is actively changed by changing the TOP value, using the OCR1A as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and
an inverted PWM output can be generated by setting the COM1x1:0 to three (See Table 12-4 on
page 109). The actual OC1x value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing)
the OC1x Register at the compare match between OCR1x and TCNT1 when the counter increments, and clearing (or setting) the OC1x Register at compare match between OCR1x and
TCNT1 when the counter decrements. The PWM frequency for the output when using phase
and frequency correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPFCPWM = --------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represents special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be set to high for noninverted PWM mode. For inverted PWM the output will have the opposite logic values.
12.9
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT1) is therefore shown as a
clock enable signal in the following figures. The figures include information on when interrupt
flags are set, and when the OCR1x Register is updated with the OCR1x buffer value (only for
modes utilizing double buffering). Figure 12-10 shows a timing diagram for the setting of OCF1x.
Figure 12-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 12-11 on page 104 shows the same timing data, but with the prescaler enabled.
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Figure 12-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 12-12 on page 104 shows the count sequence close to TOP in various modes. When
using phase and frequency correct PWM mode the OCR1x Register is updated at BOTTOM.
The timing diagrams will be the same, but TOP should be replaced by BOTTOM, TOP-1 by
BOTTOM+1 and so on. The same renaming applies for modes that set the TOV1 flag at
BOTTOM.
Figure 12-12. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
Figure 12-13 on page 105 shows the same timing data, but with the prescaler enabled.
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Figure 12-13. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICF n (if used
as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
12.10 Accessing 16-bit Registers
The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR CPU via
the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations.
Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16-bit
access. The same temporary register is shared between all 16-bit registers within each 16-bit
timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a
16-bit register is written by the CPU, the high byte stored in the temporary register, and the low
byte written are both copied into the 16-bit register in the same clock cycle. When the low byte of
a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the temporary register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR1A/B 16bit registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
The following code examples show how to access the 16-bit timer registers assuming that no
interrupts updates the temporary register. The same principle can be used directly for accessing
the OCR1A/B and ICR1 Registers. Note that when using “C”, the compiler handles the 16-bit
access.
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Assembly Code Examples
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
C Code Examples
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
Note:
See “Code Examples” on page 6.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit timer registers,
then the result of the access outside the interrupt will be corrupted. Therefore, when both the
main code and the interrupt code update the temporary register, the main code must disable the
interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 Register contents.
Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Assembly Code Example
TIM16_ReadTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
; Restore global interrupt flag
out SREG,r18
ret
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C Code Example
unsigned int TIM16_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT1 into i */
i = TCNT1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
See “Code Examples” on page 6.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
The following code examples show how to do an atomic write of the TCNT1 Register contents.
Writing any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Assembly Code Example
TIM16_WriteTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TCNT1H,r17
out TCNT1L,r16
; Restore global interrupt flag
out SREG,r18
ret
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C Code Example
void TIM16_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
See “Code Examples” on page 6.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1.
12.10.1
Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.
12.11 Register Description
12.11.1
TCCR1A – Timer/Counter1 Control Register A
Bit
7
6
5
4
3
2
1
0
0x2F (0x4F)
COM1A1
COM1A0
COM1B1
COM1B0
–
–
WGM11
WGM10
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
TCCR1A
• Bit 7:6 – COM1A1:0: Compare Output Mode for Channel A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Channel B
The COM1A1:0 and COM1B1:0 control the Output Compare pins (OC1A and OC1B respectively) behavior. If one or both of the COM1A1:0 bits are written to one, the OC1A output
overrides the normal port functionality of the I/O pin it is connected to. If one or both of the
COM1B1:0 bit are written to one, the OC1B 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 OC1A or OC1B pin must be set in order to enable the output driver.
When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is dependent of the WGM13:0 bits setting. Table 12-2 on page 109 shows the COM1x1:0 bit functionality
when the WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
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Table 12-2.
Compare Output Mode, non-PWM
COM1A1/COM1B1
COM1A0/COM1B0
Description
0
0
Normal port operation, OC1A/OC1B disconnected.
0
1
Toggle OC1A/OC1B on Compare Match.
1
0
Clear OC1A/OC1B on Compare Match (Set output to
low level).
1
1
Set OC1A/OC1B on Compare Match (Set output to
high level).
Table 12-3 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast
PWM mode.
Table 12-3.
Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1
COM1A0/COM1B0
0
0
Normal port operation, OC1A/OC1B disconnected.
0
1
WGM13=0: Normal port operation, OC1A/OC1B
disconnected.
WGM13=1: Toggle OC1A on Compare Match, OC1B
reserved.
1
0
Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at BOTTOM (non-inverting mode)
1
1
Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at BOTTOM (inverting mode)
Note:
Description
1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In
this case the compare match is ignored, but the set or clear is done at BOTTOM. “Fast PWM
Mode” on page 97 for more details.
Table 12-4 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the phase
correct or the phase and frequency correct, PWM mode.
Table 12-4.
Compare Output Mode, Phase Correct and Phase & Frequency Correct PWM(1)
COM1A1/COM1B1
COM1A0/COM1B0
0
0
Normal port operation, OC1A/OC1B disconnected.
0
1
WGM13=0: Normal port operation, OC1A/OC1B
disconnected.
WGM13=1: Toggle OC1A on Compare Match, OC1B
reserved.
1
0
Clear OC1A/OC1B on Compare Match when upcounting. Set OC1A/OC1B on Compare Match when
downcounting.
1
1
Set OC1A/OC1B on Compare Match when upcounting. Clear OC1A/OC1B on Compare Match
when downcounting.
Note:
Description
1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set.
“Phase Correct PWM Mode” on page 99 for more details.
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• Bit 1:0 – WGM11:0: Waveform Generation Mode
Combined with the WGM13:2 bits found in the TCCR1B 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 12-5 on page 110. Modes of operation supported by the
Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode,
and three types of Pulse Width Modulation (PWM) modes. (“Modes of Operation” on page 96).
Table 12-5.
12.11.2
Waveform Generation Modes
Mode
WGM
13:10
Mode of
Operation
TOP
Update of
OCR1x at
TOV1 Flag
Set on
0
0000
Normal
0xFFFF
Immediate
MAX
1
0001
PWM, Phase Correct, 8-bit
0x00FF
TOP
BOTTOM
2
0010
PWM, Phase Correct, 9-bit
0x01FF
TOP
BOTTOM
3
0011
PWM, Phase Correct, 10-bit
0x03FF
TOP
BOTTOM
4
0100
CTC (Clear Timer on Compare)
OCR1A
Immediate
MAX
5
0101
Fast PWM, 8-bit
0x00FF
TOP
TOP
6
0110
Fast PWM, 9-bit
0x01FF
TOP
TOP
7
0111
Fast PWM, 10-bit
0x03FF
TOP
TOP
8
1000
PWM, Phase & Freq. Correct
ICR1
BOTTOM
BOTTOM
9
1001
PWM, Phase & Freq. Correct
OCR1A
BOTTOM
BOTTOM
10
1010
PWM, Phase Correct
ICR1
TOP
BOTTOM
11
1011
PWM, Phase Correct
OCR1A
TOP
BOTTOM
12
1100
CTC (Clear Timer on Compare)
ICR1
Immediate
MAX
13
1101
(Reserved)
–
–
–
14
1110
Fast PWM
ICR1
TOP
TOP
15
1111
Fast PWM
OCR1A
TOP
TOP
TCCR1B – Timer/Counter1 Control Register B
Bit
7
6
5
4
3
2
1
0
0x2E (0x4E)
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR1B
• Bit 7 – ICNC1: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is
activated, the input from the Input Capture pin (ICP1) is filtered. The filter function requires four
successive equal valued samples of the ICP1 pin for changing its output. The Input Capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICES1: Input Capture Edge Select
This bit selects which edge on the Input Capture pin (ICP1) that is used to trigger a capture
event. When the ICES1 bit is written to zero, a falling (negative) edge is used as trigger, and
when the ICES1 bit is written to one, a rising (positive) edge will trigger the capture.
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When a capture is triggered according to the ICES1 setting, the counter value is copied into the
Input Capture Register (ICR1). The event will also set the Input Capture Flag (ICF1), and this
can be used to cause an Input Capture Interrupt, if this interrupt is enabled.
When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in the
TCCR1A and the TCCR1B Register), the ICP1 is disconnected and consequently the Input Capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCR1B is written.
• Bit 4:3 – WGM13:2: Waveform Generation Mode
See TCCR1A Register description.
• Bit 2:0 – CS12:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure
12-10 and Figure 12-11.
Table 12-6.
Clock Select Bit Description
CS12
CS11
CS10
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clkI/O/1 (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 T1 pin. Clock on falling edge.
1
1
1
External clock source on T1 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
12.11.3
TCCR1C – Timer/Counter1 Control Register C
Bit
7
6
5
4
3
2
1
0
0x22 (0x42)
FOC1A
FOC1B
–
–
–
–
–
–
Read/Write
W
W
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
TCCR1C
• Bit 7 – FOC1A: Force Output Compare for Channel A
• Bit 6 – FOC1B: Force Output Compare for Channel B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM mode.
However, for ensuring compatibility with future devices, these bits must be set to zero when
TCCR1A is written when operating in a PWM mode. When writing a logical one to the
FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform Generation unit.
The OC1A/OC1B output is changed according to its COM1x1:0 bits setting. Note that the
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FOC1A/FOC1B bits are implemented as strobes. Therefore it is the value present in the
COM1x1:0 bits that determine the effect of the forced compare.
A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in Clear Timer
on Compare match (CTC) mode using OCR1A as TOP.
The FOC1A/FOC1B bits are always read as zero.
• Bit 5..0 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when the register is written.
12.11.4
TCNT1H and TCNT1L – Timer/Counter1
Bit
7
6
5
4
3
0x2D (0x4D)
TCNT1[15:8]
0x2C (0x4C)
TCNT1[7:0]
2
1
0
TCNT1H
TCNT1L
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 two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct
access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To
ensure that both the high and low bytes are read and written simultaneously when the CPU
accesses these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit
Registers” on page 105.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match between TCNT1 and one of the OCR1x Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock
for all compare units.
12.11.5
OCR1AH and OCR1AL – Output Compare Register 1 A
Bit
12.11.6
7
6
5
4
3
0x2B (0x4B)
OCR1A[15:8]
0x2A (0x4A)
OCR1A[7:0]
2
1
0
OCR1AH
OCR1AL
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
4
3
2
1
0
OCR1BH and OCR1BL – Output Compare Register 1 B
Bit
7
6
5
0x29 (0x49)
OCR1B[15:8]
0x28 (0x48)
OCR1B[7:0]
OCR1BH
OCR1BL
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 Registers contain a 16-bit value that is continuously compared with the
counter value (TCNT1). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC1x pin.
The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are
written simultaneously when the CPU writes to these registers, the access is performed using an
8-bit temporary high byte register (TEMP). This temporary register is shared by all the other 16bit registers. See “Accessing 16-bit Registers” on page 105.
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12.11.7
ICR1H and ICR1L – Input Capture Register 1
Bit
7
6
5
4
3
0x25 (0x45)
ICR1[15:8]
0x24 (0x44)
ICR1[7:0]
2
1
0
ICR1H
ICR1L
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 Input Capture is updated with the counter (TCNT1) value each time an event occurs on the
ICP1 pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture
can be used for defining the counter TOP value.
The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit
temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit
registers. “Accessing 16-bit Registers” on page 105.
12.11.8
TIMSK1 – Timer/Counter Interrupt Mask Register 1
Bit
7
6
5
4
3
2
1
0
0x0C (0x2C)
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK1
• Bit 7,6,4,3 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when the register is written.
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Countern Input Capture interrupt is enabled. The
corresponding Interrupt Vector (See “Interrupts” on page 66.) is executed when the
ICF1 Flag, located in TIFR1, is set.
• Bit 2– OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare B Match interrupt is enabled. The corresponding
Interrupt Vector (see “Interrupts” on page 48) is executed when the OCF1B flag, located in
TIFR1, is set.
• Bit 1– OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare A Match interrupt is enabled. The corresponding
Interrupt Vector (see “Interrupts” on page 48) is executed when the OCF1A flag, located in
TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Overflow interrupt is enabled. The corresponding Interrupt Vector
(see “Interrupts” on page 48) is executed when the TOV1 flag, located in TIFR1, is set.
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12.11.9
TIFR1 – Timer/Counter Interrupt Flag Register 1
Bit
0x0B (0x2B)
7
–
6
–
5
ICF1
4
–
3
–
2
1
OCF1B
OCF1A
0
TOV1
TIFR1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
• Bit 7,6,4,3 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when the register is written.
• Bit 5– ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register
(ICR1) is set by the WGM13:0 to be used as the TOP value, the ICF1 flag is set when the counter reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF1 can be cleared by writing a logic one to its bit location.
• Bit 2– OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register B (OCR1B).
Note that a Forced Output Compare (1B) strobe will not set the OCF1B flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is executed. Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
• Bit 1– OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register A (OCR1A).
Note that a Forced Output Compare (1A) strobe will not set the OCF1A flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is executed. Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 0– TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGM13:0 bits setting. In Normal and CTC modes,
the TOV1 flag is set when the timer overflows. See Table 12-5 on page 110 for the TOV1 flag
behavior when using another WGM13:0 bit setting.
TOV1 is automatically cleared when the Timer/Counter1 Overflow Interrupt Vector is executed.
Alternatively, TOV1 can be cleared by writing a logic one to its bit location.
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13. Timer/Counter Prescaler
Timer/Counter0 and Timer/Counter1 share the same prescaler module, but the Timer/Counters
can have different prescaler settings. The description below applies to both Timer/Counters. Tn
is used as a general name, n = 0, 1.
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.
13.1
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/CounterCounter, and it is shared by the Timer/Counter Tn. 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 (CSn2:0 = 2, 3, 4, or 5). 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).
The Prescaler Reset can be used for synchronizing the Timer/Counter to program execution.
13.2
External Clock Source
An external clock source applied to the Tn pin can be used as Timer/Counter clock (clkTn). The
Tn 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 Tn 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.
Figure 13-1. T0 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The edge detector generates one clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0
= 6) edge it detects. 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 Tn pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn 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 fre-
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quency (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:
13.3
13.3.1
1. The synchronization logic on the input pins (T0) is shown in Figure 13-1 on page 115.
Register Description
GTCCR – General Timer/Counter Control Register
Bit
7
6
5
4
3
2
1
0
0x23 (0x43)
TSM
–
–
–
–
–
–
PSR10
Read/Write
R/W
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• 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 PSR10 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 PSR10 bit is cleared by
hardware, and the Timer/Counter start counting.
• Bit 0 – PSR10: Prescaler 0 Reset Timer/Counter n
When this bit is one, the Timer/Countern prescaler will be Reset. This bit is normally cleared
immediately by hardware, except if the TSM bit is set.
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14. USI – Universal Serial Interface
14.1
Features
•
•
•
•
•
•
14.2
Two-wire Synchronous Data Transfer (Master or Slave)
Three-wire Synchronous Data Transfer (Master or Slave)
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
The Universal Serial Interface (USI), provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rates and uses less code space than solutions based on software only. Interrupts
are included to minimize the processor load.
A simplified block diagram of the USI is shown in Figure 14-1 For actual placement of I/O pins
refer to “Pinout ATtiny24/44/84” on page 2. Device-specific I/O Register and bit locations are
listed in the “Register Descriptions” on page 124.
Figure 14-1. 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]
Two-wire Clock
Control Unit
USISR
USITC
USICLK
USICS0
USICS1
USIWM0
USIWM1
USISIE
USIOIE
2
USICR
The 8-bit USI Data Register (USIDR) contains the incoming and outgoing data. It is directly
accessible via the data bus but a copy of the contents is also placed in the USI Buffer Register
(USIBR) where it can be retrieved later. If reading the USI Data Register directly, the register
must be read as quickly as possible to ensure that no data is lost.
The most significant bit of the USI Data Register is connected to one of two output pins (depending on the mode configuration, see “USICR – USI Control Register” on page 126). There is a
transparent latch between the output of the USI Data Register and the output pin, which delays
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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 it can generate an overflow
interrupt. Both the USI Data 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. This means the counter registers the number of
clock edges and not the number of data bits. The clock can be selected from three different
sources: The USCK pin, Timer/Counter0 Compare Match or from software.
The two-wire clock control unit can be configured to generate an interrupt when a start condition
has been detected on the two-wire bus. It can also be set to generate wait states by holding the
clock pin low after a start condition is detected, or after the counter overflows.
14.3
14.3.1
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 14-2. 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 14-2 shows two USI units operating in three-wire mode, one as Master and one as Slave.
The two USI Data Registers are interconnected in such way that after eight USCK clocks, the
data in each register has been 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 PORTA register or by writing a one to bit USITC bit in USICR.
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Figure 14-3. Three-wire Mode, Timing Diagram
CYCLE
( Reference )
1
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 14-3 At the top of the figure is a USCK cycle reference. One bit is shifted into the USI Data Register (USIDR) for each of these cycles. The
USCK timing is shown for both external clock modes. In external clock mode 0 (USICS0 = 0), DI
is sampled at positive edges, and DO is changed (USI Data Register is shifted by one) at negative edges. In external clock mode 1 (USICS0 = 1) the opposite edges with respect to mode 0
are used. In other words, data is sampled at negative and output is changed at positive edges.
The USI clock modes corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 14-3), a bus transfer involves the following steps:
1. The slave and master devices set up their data outputs and, depending on the protocol
used, enable their output drivers (mark A and B). The output is set up by writing the
data to be transmitted to the USI Data Register. The output is enabled by setting the
corresponding bit in the Data Direction Register of Port A. Note that there is not a preferred order of points A and B in the figure, but both must be at least one half USCK
cycle before point C, where the data is sampled. This is in order to ensure that the data
setup requirement is satisfied. The 4-bit counter is reset to zero.
2. The master software generates a clock pulse by toggling the USCK line twice (C and
D). The bit values on the data input (DI) pins are sampled by the USI on the first edge
(C), and the data output is changed on the opposite edge (D). The 4-bit counter will
count both edges.
3. Step 2. is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that
the transfer has been completed. If USI Buffer Registers are not used the data bytes
that have been 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 on the protocol used the slave device can now set its output to high
impedance.
14.3.2
SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
out
USIDR,r16
ldi
r16,(1<<USIOIF)
out
USISR,r16
ldi
r17,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
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SPITransfer_loop:
out
USICR,r17
in
r16, USISR
sbrs
r16, USIOIF
rjmp
SPITransfer_loop
in
r16,USIDR
ret
The code is size optimized using only eight instructions (plus return). The code example
assumes that the DO and USCK pins have been enabled as outputs in DDRA. 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 register r16.
The second and third instructions clear the USI Counter Overflow Flag and the USI counter
value. The fourth and fifth instructions set three-wire mode, positive edge clock, count at USITC
strobe, and toggle USCK. The loop is repeated 16 times.
The following code demonstrates how to use the USI as an SPI master with maximum speed
(fSCK = fCK/2):
SPITransfer_Fast:
out
USIDR,r16
ldi
r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi
r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
out
USICR,r16 ; MSB
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16 ; LSB
out
USICR,r17
in
r16,USIDR
ret
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14.3.3
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi
r16,(1<<USIWM0)|(1<<USICS1)
out
USICR,r16
...
SlaveSPITransfer:
out
USIDR,r16
ldi
r16,(1<<USIOIF)
out
USISR,r16
SlaveSPITransfer_loop:
in
r16, USISR
sbrs
r16, USIOIF
rjmp
SlaveSPITransfer_loop
in
r16,USIDR
ret
The code is size optimized using only eight instructions (plus return). The code example
assumes that the DO and USCK pins have been enabled as outputs in DDRA. 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 register r16.
Note that the first two instructions are for initialization, only, and need only be executed once.
These instructions set three-wire mode and positive edge clock. The loop is repeated until the
USI Counter Overflow Flag is set.
14.3.4
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 without input noise filtering. Pin names used in this mode are SCL and SDA.
Figure 14-4 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. Only the slave uses
the clock control unit.
Clock generation must be implemented in software, but the shift operation is done automatically
in both devices. Note that clocking only on negative edges for shifting data is of practical use in
this mode. The slave can insert wait states at start or end of transfer by forcing the SCL clock
low. This means that the master must always check if the SCL line was actually released after it
has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate that the
transfer is completed. The clock is generated by the master by toggling the USCK pin via the
PORTA register.
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Figure 14-4. 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
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 14-5. 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 14-5), a bus transfer involves the following steps:
1. The start condition is generated by the master by forcing the SDA low line while keeping the SCL line high (A). SDA can be forced low either by writing a zero to bit 7 of the
USI Data Register, or by setting the corresponding bit in the PORTA register to zero.
Note that the Data Direction Register bit must be set to one for the output to be
enabled. The start detector logic of the slave device (see Figure 14-6 on page 123)
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 a
negative edge on this line (B). This allows the slave to wake up from sleep or complete
other tasks before setting up the USI Data Register to receive the address. This is done
by clearing the start condition flag and resetting the counter.
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3. The master set the first bit to be transferred and releases the SCL line (C). The slave
samples the data and shifts it into the USI Data Register at the positive edge of the SCL
clock.
4. After eight bits containing slave address and data direction (read or write) have been
transferred, the slave counter overflows and the SCL line is forced low (D). If the slave
is not the one the master has addressed, it releases the SCL line and waits for a new
start condition.
5. When the slave is addressed, it holds the SDA line low during the acknowledgment
cycle before holding the SCL line low again (i.e., the USI Counter Register must be set
to 14 before releasing SCL at (D)). Depending on the R/W bit the master or slave
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 forcing the
acknowledge bit low after the last byte transmitted.
14.3.5
Start Condition Detector
The start condition detector is shown in Figure 14-6. The SDA line is delayed (in the range of 50
to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is only enabled
in two-wire mode.
Figure 14-6. Start Condition Detector, Logic Diagram
USISIF
D Q
D Q
CLR
CLR
SDA
CLOCK
HOLD
SCL
Write( USISIF)
The start condition detector works asynchronously and can therefore wake up the processor
from power-down sleep mode. However, the protocol used might have restrictions on the SCL
hold time. Therefore, when using this feature the oscillator start-up time (set by CKSEL fuses,
see “Clock Sources” on page 25) must also be taken into consideration. Refer to the description
of the USISIF bit on page 125 for further details.
14.3.6
Clock speed considerations
Maximum frequency for SCL and SCK is fCK / 2. This is also the maximum data transmit and
receive rate in both two- and three-wire mode. In two-wire slave mode the Two-wire Clock Control Unit will hold the SCL low until the slave is ready to receive more data. This may reduce the
actual data rate in two-wire mode.
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14.4
Alternative USI Usage
The flexible design of the USI allows it to be used for other tasks when serial communication is
not needed. Below are some examples.
14.4.1
Half-Duplex Asynchronous Data Transfer
Using the USI Data Register in three-wire mode it is possible to implement a more compact and
higher performance UART than by software, only.
14.4.2
4-Bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the
counter is clocked externally, both clock edges will increment the counter value.
14.4.3
12-Bit Timer/Counter
Combining the 4-bit USI counter with one of the 8-bit timer/counters creates a 12-bit counter.
14.4.4
Edge Triggered External Interrupt
By setting the counter to maximum value (F) it can function as an additional external interrupt.
The Overflow Flag and Interrupt Enable bit are then used for the external interrupt. This feature
is selected by the USICS1 bit.
14.4.5
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.
14.5
14.5.1
Register Descriptions
USIDR – USI Data Register
Bit
7
6
5
4
3
2
1
0
0x0F (0x2F)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USIDR
The USI Data Register can be accessed directly but a copy of the data can also be found in the
USI Buffer Register.
Depending on the USICS1:0 bits of the USI Control Register a (left) shift operation may be performed. The shift operation can be synchronised to an external clock edge, to a Timer/Counter0
Compare Match, or directly to software via the USICLK bit. If a serial clock occurs at the same
cycle the register is written, the register will contain the value written and no shift is performed.
Note that even 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 USI Data Register.
The output pin (DO or SDA, depending on the wire mode) is connected via the output latch to
the most significant bit (bit 7) of the USI Data Register. The output latch ensures that data input
is sampled and data output is changed on opposite clock edges. The latch is open (transparent)
during the first half of a serial clock cycle when an external clock source is selected (USICS1 =
1) and constantly open when an internal clock source is used (USICS1 = 0). The output will be
changed immediately when a new MSB is written as long as the latch is open.
Note that the Data Direction Register bit corresponding to the output pin must be set to one in
order to enable data output from the USI Data Register.
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14.5.2
USIBR – USI Data Buffer
Bit
7
6
5
4
3
2
1
0
0x10 (0x30)
MSB
LSB
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
USIBR
Instead of reading data from the USI Data Register the USI Buffer Register can be used. This
makes controlling the USI less time critical and gives the CPU more time to handle other program tasks. USI flags as set similarly as when reading the USIDR register.
The content of the USI Data Register is loaded to the USI Buffer Register when the transfer has
been completed.
14.5.3
USISR – USI Status Register
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
0x0D (0x2D)
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 has
been detected. When three-wire mode or output disable mode has been selected any edge on
the SCK pin will set the flag.
If USISIE bit in USICR and the Global Interrupt Enable Flag are set, an interrupt will be generated when this flag is set. The flag will only be cleared by writing a logical one to the USISIF bit.
Clearing this bit will release the start detection hold of USCL in two-wire mode.
A start condition interrupt will wakeup the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). If the
USIOIE bit in USICR and the Global Interrupt Enable Flag are set an interrupt will also be generated when the flag is 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 has been
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 USI Data 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.
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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 on the setting of the USICS1:0 bits.
For external clock operation a special feature is added that allows the clock to be generated by
writing to the USITC strobe bit. This feature is enabled by choosing an external clock source
(USICS1 = 1) and writing a one to the USICLK bit.
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) can still be used by the counter.
14.5.4
USICR – USI Control Register
Bit
7
6
5
4
3
2
1
0
0x0D (0x2D)
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 USI Control Register includes bits for interrupt enable, setting the wire mode, selecting the
clock and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the start condition detector interrupt. If there is a pending interrupt
and USISIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed
immediately. Refer to the USISIF bit description on page 125 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the counter overflow interrupt. If there is a pending interrupt and
USIOIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed immediately. Refer to the USIOIF bit description on page 125 for further details.
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used, as shown in Table 14-1 on page 127.
Basically, only the function of the outputs are affected by these bits. Data and clock inputs are
not affected by the mode selected and will always have the same function. The counter and USI
Data Register can therefore be clocked externally and data input sampled, even when outputs
are disabled.
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Table 14-1.
Relationship between USIWM1:0 and USI Operation
USIWM1
USIWM0
0
0
Outputs, clock hold, and start detector disabled.
Port pins operate as normal.
1
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORTA
register. However, the corresponding DDRA bit still controls the data direction.
When the port pin is set as input the pin pull-up is controlled by the PORTA 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 PORTA 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
use open-collector output drives. The output drivers are enabled by setting the
corresponding bit for SDA and SCL in the DDRA 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 USI Data Register or the corresponding bit in
the PORTA 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 PORTA register is zero, or by the start
detector. Otherwise the SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition and the
output is enabled. Clearing the Start Condition Flag (USISIF) releases the line.
The SDA and SCL pin inputs is not affected by enabling this mode. Pull-ups on
the SDA and SCL port pin are disabled in Two-wire mode.
1
Two-wire mode. Uses SDA and SCL pins.
Same operation as in two-wire mode above, except that the SCL line is also
held low when a counter overflow occurs, and until the Counter Overflow Flag
(USIOIF) is cleared.
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 USI Data Register and counter. The data output latch
ensures that the output is changed at the opposite edge of the sampling of the data input
(DI/SDA) when using external clock source (USCK/SCL). When software strobe or
Timer/Counter0 Compare Match clock option is selected, the output latch is transparent and
therefore the output is changed immediately.
Clearing the USICS1:0 bits enables software strobe option. When using this option, writing a
one to the USICLK bit clocks both the USI Data Register and the counter. For external clock
source (USICS1 = 1), 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 14-2 shows the relationship between the USICS1:0 and USICLK setting and clock source
used for the USI Data Register and the 4-bit counter.
Table 14-2.
Relationship between the USICS1:0 and USICLK Setting
USICS1
USICS0
USICLK
Clock Source
4-bit Counter Clock Source
0
0
0
No Clock
No Clock
0
0
1
Software clock strobe (USICLK)
Software clock strobe (USICLK)
0
1
X
Timer/Counter0 Compare Match
Timer/Counter0 Compare Match
1
0
0
External, positive edge
External, both edges
1
1
0
External, negative edge
External, both edges
1
0
1
External, 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 USI Data Register to shift one step and the counter
to increment by one, provided that the software clock strobe option has been selected by writing
USICS1:0 bits to zero. The output will change immediately when the clock strobe is executed,
i.e., during the same instruction cycle. The value shifted into the USI Data Register is sampled
the previous instruction cycle.
When an external clock source is selected (USICS1 = 1), the USICLK function is changed from
a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the
USITC strobe bit as clock source for the 4-bit counter (see Table 14-2).
The bit will be read as zero.
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0.
The toggling is independent of the setting in the Data Direction Register, but if the PORT value is
to be shown on the pin the corresponding DDR pin must be set as output (to one). This feature
allows easy clock generation when implementing master devices.
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.
The bit will read as zero.
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15. 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 15-1.
Figure 15-1. Analog Comparator Block Diagram
BANDGAP
REFERENCE
ACBG
ACME
ADEN
ACIC
To T/C1 Capture
Trigger MUX
ADC MULTIPLEXER
OUTPUT (1)
Notes:
1. See Table 15-1 on page 129.
See Figure 1-1 on page 2 and Table 10-9 on page 67 for Analog Comparator pin placement.
15.1
Analog Comparator Multiplexed Input
When the Analog to Digital Converter (ADC) is configurated as single ended input channel, it is
possible to select any of the ADC7..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
15-1. If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the analog
comparator.
Table 15-1.
Analog Comparator Multiplexed Input
ACME
ADEN
MUX4..0
Analog Comparator Negative Input
0
X
XXXXX
AIN1
1
1
XXXXX
AIN1
1
0
00000
ADC0
1
0
00001
ADC1
1
0
00010
ADC2
1
0
00011
ADC3
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Table 15-1.
15.2
15.2.1
Analog Comparator Multiplexed Input (Continued)
ACME
ADEN
MUX4..0
Analog Comparator Negative Input
1
0
00100
ADC4
1
0
00101
ADC5
1
0
00110
ADC6
1
0
00111
ADC7
Register Description
ACSR – Analog Comparator Control and Status Register
Bit
7
6
5
4
3
2
1
0
0x08 (0x28)
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
Read/Write
R/W
R/W
R
R/W
R/W
R/W
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, a fixed, internal bandgap reference voltage replaces the positive input to the
Analog Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog
Comparator.
• 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 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to the
input capture front-end logic, making the comparator utilize the noise canceler and edge select
features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection
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between the Analog Comparator and the input capture function exists. To make the comparator
trigger the Timer/Counter1 Input Capture inter-rupt, the ICIE1 bit in the Timer Interrupt Mask
Register (TIMSK1) must be set.
• 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 15-2.
Table 15-2.
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.
15.2.2
ADCSRB – ADC Control and Status Register B
Bit
7
6
5
4
3
2
1
0
0x03 (0x23)
BIN
ACME
–
ADLAR
–
ADTS2
ADTS1
ADTS0
Read/Write
R/W
R/W
R
R/W
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 129.
15.2.3
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
0x01 (0x21)
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
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 2, 1– ADC2D, ADC1D: ADC 2/1 Digital input buffer 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.
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16. Analog to Digital Converter
16.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
16.2
10-bit Resolution
1.0 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
13µs Conversion Time
15 kSPS at Maximum Resolution
Eight Multiplexed Single Ended Input Channels
Twelve Differential Input Channels with Selectable Gain (1x, 20x)
Temperature Sensor Input Channel
Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
1.1V ADC Reference Voltage
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
Unipolar / Bipolar Input Mode
Input Polarity Reversal Mode
Overview
The ATtiny24/44/84 features a 10-bit successive approximation ADC. The ADC is connected to
8-pin port A for external sources. In addition to external sources internal temperature sensor can
be measured by ADC. Analog Multiplexer allows eight single-ended channels or 12 differential
channels from Port A. The programmable gain stage provides ampification steps 0 dB (1x) and
26 dB (20x) for 12 differential ADC channels.
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 16-1
on page 133.
Internal reference voltage of nominally 1.1V is provided On-chip. Alternatively, VCC can be used
as reference voltage for single ended channels. There is also an option to use an external voltage reference and turn-off the internal voltage reference.
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Figure 16-1. Analog to Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
INTERRUPT
FLAGS
ADTS2...ADTS0
AREF
VCC
INTERNAL
REFERENCE
1.1V
TRIGGER
SELECT
ADC[9:0]
ADPS1
ADPS0
ADPS2
ADIF
ADSC
ADATE
ADEN
ADLAR
MUX4...MUX0
0
ADC DATA REGISTER
(ADCH/ADCL)
MUX DECODER
CHANNEL SELECTION
REFS1..REFS0
BIN
15
ADC CTRL. & STATUS A
REGISTER (ADCSRA)
ADC MULTIPLEXER
SELECT (ADMUX)
PRESCALER
START
GAIN SELECTION
ADC CTRL. & STATUS B
REGISTER (ADCSRB)
ADIE
ADIF
8-BIT DATA BUS
CONVERSION LOGIC
TEMPERATURE
SENSOR
SAMPLE & HOLD
COMPARATOR
10-BIT DAC
ADC8
AGND
+
SINGLE ENDED / DIFFERENTIAL SELECTION
ADC7
ADC MULTIPLEXER
OUTPUT
ADC6
ADC5
POS.
INPUT
MUX
ADC4
+
-
ADC3
GAIN
AMPLIFIER
ADC2
ADC1
ADC0
NEG.
INPUT
MUX
16.3
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 reference
voltage.The voltage reference for the ADC may be selected by writing to the REFS1..0 bits in
ADMUX. The VCC supply, the AREF pin or an internal 1.1V voltage reference may be selected
as the ADC voltage reference.
The analog input channel and differential gain are selected by writing to the MUX5..0 bits in
ADMUX. Any of the eight ADC input pins ADC7..0 can be selected as single ended inputs to the
ADC. For differential measurements all analog inputs next to each other can be selected as a
input pair. Every input is also possible to measure with ADC3. These pairs of differential inputs
are measured by ADC trough the differential gain amplifier.
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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 MUX0 bit 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.
The offset of the differential channels can be measure by selecting the same input for both negative and positive input. Offset calibration can be done for ADC0, ADC3 and ADC7. When ADC0
or ADC3 or ADC7 is selected as both the positive and negative input to the differential gain
amplifier , 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 LSB.
The on-chip temperature sensor is selected by writing the code “100010” to the MUX5..0 bits in
ADMUX register.
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 ADCSRB.
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.
16.4
Starting a Conversion
A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC.
This bit stays high as long as the conversion is in progress and 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 16-2. 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.
16.5
Prescaling and Conversion Timing
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. It is
not recommended to use a higher input clock frequency than 1 MHz.
Figure 16-3. 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
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The ADC module contains a prescaler, as illustrated in Figure 16-3 on page 135, which generates an acceptable ADC clock frequency from any CPU frequency above 100 kHz. The
prescaling is set by the ADPS bits in ADCSRA. The prescaler starts counting from the moment
the ADC is switched on by setting the ADEN bit in ADCSRA. The prescaler keeps 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,
as shown in Figure 16-4 below.
Figure 16-4. 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
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock cycles after the start of an 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.
Figure 16-5. ADC Timing Diagram, Single Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
3
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
MUX and REFS
Update
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Conversion
Complete
MUX and REFS
Update
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When Auto Triggering is used, the prescaler is reset when the trigger event occurs, as shown in
Figure 16-6 below. 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.
Figure 16-6. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
1
Cycle Number
2
3
4
5
6
7
8
Next Conversion
10
9
11
12
13
1
2
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Prescaler
Reset
Sample &
Hold
Prescaler
Reset
Conversion
Complete
MUX and REFS
Update
In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. See Figure 16-7.
Figure 16-7. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
12
13
Next Conversion
14
1
2
3
4
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Conversion
Complete
Sample & Hold
MUX and REFS
Update
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For a summary of conversion times, see Table 16-1.
Table 16-1.
ADC Conversion Time
Condition
Sample & Hold (Cycles from
Start of Conversion)
First conversion
13.5
25
Normal conversions
1.5
13
2
13.5
2.5
14
Auto Triggered conversions
Free Running conversion
16.6
Conversion Time (Cycles)
Changing Channel or Reference Selection
The MUX5:0 and REFS1:0 bits in the ADMUX Register are single buffered through a temporary
register to which the CPU has random access. This ensures that the channels and reference
selection only takes place at a safe point during the conversion. The channel and reference
selection is continuously updated until a conversion is started. Once the conversion starts, the
channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in
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 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:
• When ADATE or ADEN is cleared.
• During conversion, minimum one ADC clock cycle after the trigger event.
• 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.
16.6.1
ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the 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
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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.
16.6.2
16.7
ADC Voltage Reference
The reference voltage 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 reference, or external AREF pin. The first ADC conversion result
after switching reference voltage 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. This reduces
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:
• 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.
• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the
CPU has been halted.
• If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake
up the CPU and execute the ADC Conversion Complete interrupt 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 automatically be 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.
16.8
Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 16-8 on page 140. 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 10kΩ 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, which can vary widely. With slowly varying signals the user is recommended to
use sources with low impedance, only, 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.
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Figure 16-8. Analog Input Circuitry
IIH
ADCn
1..100 kohm
CS/H = 14 pF
IIL
VCC/2
Note:
16.9
The capacitor in the figure depicts the total capacitance, including the sample/hold capacitor and
any stray or parasitic capacitance inside the device. The value given is worst case.
Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. When conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
• Keep analog signal paths as short as possible.
• Make sure analog tracks run over the analog ground plane.
• Keep analog tracks well away from high-speed switching digital tracks.
• If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.
• Place bypass capacitors as close to VCC and GND pins as possible.
Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as
described in Section 16.7 on page 139. This is especially the case when system clock frequency
is above 1 MHz, or when the ADC is used for reading the internal temperature sensor, as
described in Section 16.12 on page 144. A good system design with properly placed, external
bypass capacitors does reduce the need for using ADC Noise Reduction Mode
16.10 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and V REF in 2 n steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior, as follows:
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• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Ideal value: 0 LSB.
Figure 16-9. 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 16-10. 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 16-11. 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 16-12. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
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• 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.
16.11 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversio as there are three types of conversions: single ended conversion, unipolar differential
conversion and bipolar differential conversion.
16.11.1
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 16-3 on page 145 and Table 16-4 on page 146). 0x000 represents analog ground, and
0x3FF represents the selected reference voltage minus one LSB. The result is presented in onesided form, from 0x3FF to 0x000.
16.11.2
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. The voltage of the positive pin must always be larger
than the voltage of the negative pin or otherwise the voltage difference is saturated to zero. The
result is presented in one-sided form, from 0x000 (0d) through 0x3FF (+1023d). The GAIN is
either 1x or 20x.
16.11.3
Bipolar Differential Conversion
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 0x1FF (+511d). The GAIN is either 1x or 20x. Note that if the user wants
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to perform a quick polarity check of the result, 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.
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.
16.12 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC8 channel. Selecting the ADC8 channel by writing the MUX5:0 bits in ADMUX
register to “100010” enables the temperature sensor. The internal 1.1V reference must also be
selected for the ADC 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 16-2
The sensitivity is approximately 1 LSB / °C and the accuracy depends on the method of user calibration. Typically, the measurement accuracy after a single temperature calibration is ±10°C,
assuming calibration at room temperature. Better accuracies are achieved by using two
temperature points for calibration.
Table 16-2.
Temperature
ADC
Temperature vs. Sensor Output Voltage (Typical Case)
-40°C
+25°C
+85°C
230 LSB
300 LSB
370 LSB
The values described in Table 16-2 are typical values. However, due to 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 sofware calibration can be done using the formula:
T = k * [(ADCH << 8) | ADCL] + TOS
where ADCH and ADCL are the ADC data registers, k is the fixed slope coefficient and TOS is the
temperature sensor offset. Typically, k is very close to 1.0 and in single-point calibration the
coefficient may be omitted. Where higher accuracy is required the slope coefficient should be
evaluated based on measurements at two temperatures.
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16.13 Register Description
16.13.1
ADMUX – ADC Multiplexer Selection Register
Bit
7
6
5
4
3
2
1
0
0x07 (0x27)
REFS1
REFS0
MUX5
MUX4
MUX3
MUX2
MUX1
MUX0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADMUX
• Bit 7:6 – REFS1:REFS0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 16-3.
Table 16-3.
Voltage Reference Selections for ADC
REFS1
REFS0
Voltage Reference Selection
0
0
VCC used as analog reference, disconnected from PA0 (AREF)
0
1
External voltage reference at PA0 (AREF) pin, internal reference turned off
1
0
Internal 1.1V voltage reference
1
1
Reserved
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). Also note, that when these bits are changed,
the next conversion will take 25 ADC clock cycles.
Special care should be taken when changing differential channels. Once a differential channel
has been selected the input stage may take a while to stabilize. It is therefore recommended to
force the ADC to perform a long conversion when changing multiplexer or voltage reference settings. This can be done by first turning off the ADC, then changing reference settings and then
turn on the ADC. Alternatively, the first conversion results after changing reference settings
should be discarded.
It is not recommended to use an external AREF higher than (VCC - 1V) for channels with differential gain, as this will affect ADC accuracy.
Internal voltage reference options may not be used if an external voltage is being applied to the
AREF pin.
• Bits 5:0 – MUX5:0: 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, gain selection is also made with these bits. Selections on Table 16-4 on
page 146 show values for single endid channels and where the differential channels as well as
the offset calibration selections are located. Selecting the single-ended channel ADC8 enables
the temperature measurement. See Table 16-4 on page 146 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).
Special care should be taken when changing differential channels. Once a differential channel
has been selected the input stage may take a while to stabilize. It is therefore recommended to
force the ADC to perform a long conversion when changing multiplexer settings. This can be
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done by first turning off the ADC, then changing multiplexer settings and then turn on the ADC.
Alternatively, the first conversion results after changing multiplexer settings should be discarded.
Table 16-4.
Single-Ended Input channel Selections.
Single Ended Input
MUX5:0
ADC0 (PA0)
000000
ADC1 (PA1)
000001
ADC2 (PA2)
000010
ADC3 (PA3)
000011
ADC4 (PA4)
000100
ADC5 (PA5)
000101
ADC6 (PA6)
000110
ADC7 (PA7)
000111
Reserved for differential channels(1)
001000 - 011111
0V (AGND)
100000
1.1V (I Ref)
100001
ADC8
(2)
100010
Reserved for offset calibration(3)
100011 - 100111
Reserved for reversal differential channels
Notes:
(1)
101000 - 111111
1. See Table 16-5 for details.
2. See “Temperature Measurement” on page 144.
3. For offset calibration, only. See Table 16-5 on page 146 and “Operation” on page 133.
See Table 16-5 for details of selections of differential input channel selections as well as selections of offset calibration channels. MUX0 bit works as a gain selection bit for differential
channels. When MUX0 is cleared (‘0’) 1x gain is selected and when it is set (‘1’) 20x gain is
selected. For normal differential channel pairs MUX5 bit work as a polarity reversal bit. Toggling
of the MUX5 bit exhanges the positive and negative channel other way a round.
Table 16-5.
Differential Input channel Selections.
MUX5:0
Positive Differential Input
Negative Differential Input
Gain 1x
Gain 20x
(1)
N/A
100011
ADC1 (PA1)
001000
001001
ADC3 (PA3)
001010
001011
ADC0 (PA0)
101000
101001
ADC2 (PA2)
001100
001101
ADC3 (PA3)
001110
001111
ADC1 (PA1)
101100
101101
ADC3 (PA3)
010000
010001
ADC0 (PA0)
ADC0 (PA0)
ADC1 (PA1)
ADC2 (PA2)
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Table 16-5.
Differential Input channel Selections. (Continued)
MUX5:0
Positive Differential Input
Negative Differential Input
Gain 1x
Gain 20x
ADC0 (PA0)
101010
101011
ADC1 (PA1)
101110
101111
ADC2 (PA2)
110000
110001
ADC3 (PA3)(1)
100100
100101
ADC4 (PA4
010010
010011
ADC5 (PA5)
010100
010101
ADC6 (PA6)
010110
010111
ADC7 (PA7)
011000
011001
ADC3 (PA3)
110010
110011
ADC5 (PA5)
011010
011011
ADC3 (PA3)
110100
110101
ADC4 (PA4)
111010
111011
ADC6 (PA6)
011100
011101
ADC3 (PA3)
110110
110111
ADC5 (PA5)
111100
111101
ADC7 (PA7)
011110
011111
ADC3 (PA3)
111000
111001
ADC6 (PA6)
111110
111111
ADC7 (PA7)(1)
100110
100111
ADC3 (PA3)
ADC4 (PA4)
ADC5 (PA5)
ADC6 (PA6)
ADC7 (PA7)
1.
For offset calibration, only. See “Operation” on page 133.
For offset calibration purpose the offset of the certain differential channels can be measure by
selecting the same input for both negative and positive input. This calibration can be done for
ADC0, ADC3 and ADC7. “Operation” on page 133 describes offset calibration in a more detailed
level.
16.13.2
ADCSRA – ADC Control and Status Register A
Bit
7
6
5
4
3
2
1
0
0x06 (0x26)
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
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8006H–AVR–10/09
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
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 instruction is 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 16-6.
148
ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
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ATtiny24/44/84
16.13.3
16.13.3.1
ADCL and ADCH – ADC Data Register
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
0x05 (0x25)
–
–
–
–
–
–
ADC9
ADC8
ADCH
0x04 (0x24)
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
7
6
5
4
3
2
1
0
Read/Write
Initial Value
16.13.3.2
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
15
14
13
12
11
10
9
8
0x05 (0x25)
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
0x04 (0x24)
ADC1
ADC0
–
–
–
–
–
–
ADCL
7
6
5
4
3
2
1
0
Read/Write
Initial Value
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.
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 ADCSRB, 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 143.
16.13.4
ADCSRB – ADC Control and Status Register B
Bit
7
6
5
4
3
2
1
0
0x03 (0x23)
BIN
ACME
–
ADLAR
–
ADTS2
ADTS1
ADTS0
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
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.
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• Bit 6 – ACME: Analog Comparator Multiplexer Enable
See “ADCSRB – ADC Control and Status Register B” on page 131.
• Bit 5 – Res: Reserved Bit
This is a reserved bit in ATtiny24/44/84. For compatibility with future devices always write this bit
to zero.
• Bit 4 – 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 the description of this bit, see “ADCL and ADCH – ADC Data Register” on
page 149.
• Bit 3 – Res: Reserved Bit
This bit is reserved bit in the ATtiny24/44/84 and will always read as what was wrote there.
• 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
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 16-7.
16.13.5
ADC Auto Trigger Source Selections
ADTS2
ADTS1
ADTS0
Trigger Source
0
0
0
Free Running mode
0
0
1
Analog Comparator
0
1
0
External Interrupt Request 0
0
1
1
Timer/Counter0 Compare Match A
1
0
0
Timer/Counter0 Overflow
1
0
1
Timer/Counter1 Compare Match B
1
1
0
Timer/Counter1 Overflow
1
1
1
Timer/Counter1 Capture Event
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
0x01 (0x21)
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
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 7..0 – ADC7D..ADC0D: ADC7..0 Digital Input Disable
When a 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 ADC7..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.
150
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ATtiny24/44/84
17. debugWIRE On-chip Debug System
17.1
Features
•
•
•
•
•
•
•
•
•
•
17.2
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.
17.3
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 17-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.
Figure 17-1. The debugWIRE Setup
1.8 - 5.5V
VCC
dW
dW(RESET)
GND
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8006H–AVR–10/09
When designing a system where debugWIRE will be used, the following must be observed:
• Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 kΩ. However, the
pull-up resistor is 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.
17.4
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.
17.5
Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is
enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken while
accessing some of the I/O Registers via the debugger (AVR Studio). See the debugWIRE documentation for detailed description of the limitations.
The debugWIRE interface is asynchronous, which means that the debugger needs to synchronize to the system clock. If the system clock is changed by software (e.g. by writing CLKPS bits)
communication via debugWIRE may fail. Also, clock frequencies below 100 kHz may cause
communication problems.
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.
17.6
Register Description
The following section describes the registers used with the debugWire.
17.6.1
DWDR – debugWire Data Register
Bit
7
6
5
0x27 (0x47)
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.
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ATtiny24/44/84
18. 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 SPM
instruction is disabled by default but it can be enabled by programming the SELFPRGEN fuse
(to “0”).
The Program memory is updated in a page by page fashion. Before programming a page with
the data stored in 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
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.
18.1
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.
Note:
18.2
The CPU is halted during the Page Erase operation.
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.
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8006H–AVR–10/09
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
18.3
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.
Note:
18.4
The CPU is halted during the Page Write operation.
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 19-8 on page 162), 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 19-1 on page 163. 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.
Figure 18-1. Addressing the Flash During SPM
BIT
15
ZPCMSB
ZPAGEMSB
Z - REGISTER
1 0
0
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
154
The variables used in Figure 18-1 are listed in Table 19-8 on page 162.
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ATtiny24/44/84
18.5
EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
18.6
Reading Lock, Fuse and Signature Data from Software
It is possible for firmware to read device fuse and lock bits. In addition, firmware can also read
data from the device signature imprint table (see page 161).
Note:
18.6.1
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are unprogrammed, will be read as one.
Reading Lock Bits from Firmware
Lock bit values are returned in the destination register after an LPM instruction has been issued
within three CPU cycles after RFLB and SELFPRGEN bits have been set in SPMCSR. The
RFLB and SELFPRGEN bits automatically clear upon completion of reading the lock bits, or if no
LPM instruction is executed within three CPU cycles, or if no SPM instruction is executed within
four CPU cycles. When RFLB and SELFPRGEN are cleared LPM functions normally.
To read the lock bits, follow the below procedure:
1. Load the Z-pointer with 0x0001.
2. Set RFLB and SELFPRGEN bits in SPMCSR.
3. Issue an LPM instruction within three clock cycles.
4. Read the lock bits from the LPM destination register.
If successful, the contents of the destination register are as follows.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
–
–
–
LB2
LB1
See section “Program And Data Memory Lock Bits” on page 159 for more information.
18.6.2
Reading Fuse Bits from Firmware
The algorithm for reading fuse bytes is similar to the one described above for reading lock bits,
only the addresses are different. To read the Fuse Low Byte (FLB), follow the below procedure:
1. Load the Z-pointer with 0x0000.
2. Set RFLB and SELFPRGEN bits in SPMCSR.
3. Issue an LPM instruction within three clock cycles.
4. Read the FLB from the LPM destination register.
If successful, the contents of the destination register are as follows.
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Refer to Table 19-5 on page 161 for a detailed description and mapping of the Fuse Low Byte.
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8006H–AVR–10/09
To read the Fuse High Byte (FHB), simply replace the address in the Z-pointer with 0x0003 and
repeat the procedure above. If successful, the contents of the destination register are as follows.
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
Refer to Table 19-4 on page 160 for detailed description and mapping of the Fuse High Byte.
To read the Fuse Extended Byte (FEB), replace the address in the Z-pointer with 0x0002 and
repeat the previous procedure. If successful, the contents of the destination register are as
follows.
Bit
7
6
5
4
3
2
1
0
Rd
FEB7
FEB6
FEB5
FEB4
FEB3
FEB2
FEB1
FEB0
Refer to Table 19-3 on page 160 for detailed description and mapping of the Fuse Extended
Byte.
18.6.3
Reading Device Signature Imprint Table from Firmware
To read the contents of the device signature imprint table, follow the below procedure:
1. Load the Z-pointer with the table index.
2. Set RSIG and SPMEN bits in SPMCSR.
3. Issue an LPM instruction within three clock cycles.
4. Wait three clock cycles for SPMEN bits to be cleared.
5. Read table data from the LPM destination register.
The RSIG and SPMEN bits will auto-clear after three CPU cycles. When RSIG and SPMEN are
cleared, LPM will work as described in the “AVR Instruction Set” description.
See program example below.
Assembly Code Example
DSIT_read:
; Uses Z-pointer as table index
ldi
ZH, 0
ldi
ZL, 1
; Preload SPMCSR bits into R16, then write to SPMCSR
ldi
r16, (1<<RSIG)|(1<<SPMEN)
out SPMCSR, r16
; Issue LPM. Table data will be returned into r17
lpm r17, Z
ret
Note:
156
See “Code Examples” on page 6.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
If successful, the contents of the destination register are as described in section “Device Signature Imprint Table” on page 161.
18.7
Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and 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.
18.8
Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 18-1 shows the typical programming time for Flash accesses from the CPU.
Table 18-1.
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
Note:
18.9
18.9.1
SPM Programming Time(1)
1. The min and max programming times is per individual operation.
Register Description
SPMCSR – Store Program Memory Control and Status Register
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
0x37 (0x57)
–
–
RSIG
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..6 – Res: Reserved Bits
These bits are reserved and always read as zero.
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8006H–AVR–10/09
• Bit 5 – RSIG: Read Device Signature Imprint Table
Issuing an LPM instruction within three cycles after RSIG and SPMEN bits have been set in
SPMCSR will return the selected data (depending on Z-pointer value) from the device signature
imprint table into the destination register. See “Device Signature Imprint Table” on page 161 for
details.
• 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 155 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
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 set to one together with
RSIG, CTPB, RFLB, PGWRT or PGERS, the following LPM/SPM instruction will have a special
meaning, as described elsewhere.
If only SPMEN is written, the following SPM instruction will store the value in 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.
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19. Memory Programming
This section describes the different methods for programming ATtiny24/44/84 memories.
19.1
Program And Data Memory Lock Bits
The ATtiny24/44/84 provides two lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional security listed in Table 19-2. The lock bits can only be
erased to “1” with the Chip Erase command.
The device has no separate boot loader section. The SPM instruction is enabled for the whole
Flash, if the SELFPROGEN fuse is programmed (“0”), otherwise it is disabled.
Program memory can be read out via the debugWIRE interface when the DWEN fuse is programmed, even if lock bits are set. Thus, when lock bit security is required, debugWIRE should
always be disabled by clearing the DWEN fuse.
Table 19-1.
Lock Bit Byte
Lock Bit
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” means unprogrammed, “0” means programmed.
Table 19-2.
Lock Bit Protection Modes.
Memory Lock Bits (1)
(2)
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
3
Notes:
1
0
1. Program fuse bits before programming LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Lock bits can also be read by device firmware. See section “Reading Lock, Fuse and Signature
Data from Software” on page 155.
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19.2
Fuse Bytes
The ATtiny24/44/84 have three fuse bytes. Table 19-3, Table 19-4 and Table 19-5 briefly
describe 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 19-3.
Fuse Extended Byte
Fuse Extended Byte
Bit No
SELFPRGEN (1)
Notes:
Description
Default Value
7
-
1 (unprogrammed)
6
-
1 (unprogrammed)
5
-
1 (unprogrammed)
4
-
1 (unprogrammed)
3
-
1 (unprogrammed)
2
-
1 (unprogrammed)
1
-
1 (unprogrammed)
0
Self-Programming Enable
1 (unprogrammed)
1. Enables SPM instruction. See “Self-Programming the Flash” on page 153.
Table 19-4.
Fuse High Byte
Fuse High Byte
Description
Default Value
7
External Reset disable
1 (unprogrammed)
DWEN (2)
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)
(5)
1
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL0 (5)
0
Brown-out Detector trigger level
1 (unprogrammed)
RSTDISBL
(1)
BODLEVEL1
Notes:
Bit No
1. See “Alternate Functions of Port B” on page 65 for description of RSTDISBL and DWEN
Fuses. After programming the RSTDISBL fuse, high-voltage serial programming must be used
to change fuses and allow further programming.
2. DWEN must be unprogrammed when Lock Bit security is required. See “Program And Data
Memory Lock Bits” on page 159.
3. The SPIEN Fuse is not accessible in SPI programming mode.
4. Programming this fues will disable the Watchdog Timer Interrupt. See “WDT Configuration as
a Function of the Fuse Settings of WDTON” on page 43 for details.
5. See Table 20-7 on page 179 for BODLEVEL Fuse decoding.
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Table 19-5.
Fuse Low Byte
Fuse Low Byte
(1)
CKOUT (2)
CKDIV8
SUT1
(3)
SUT0
(3)
Bit No
Description
Default Value
7
Divide clock by 8
0 (programmed)
6
Clock Output Enable
1 (unprogrammed)
5
Select start-up time
1 (unprogrammed)
4
Select start-up time
0 (programmed)
(4)
3
Select Clock source
0 (programmed)
CKSEL2 (4)
2
Select Clock source
0 (programmed)
CKSEL1 (4)
1
Select Clock source
1 (unprogrammed)
(4)
0
Select Clock source
0 (programmed)
CKSEL3
CKSEL0
Notes:
1. See “System Clock Prescaler” on page 30 for details.
2. Allows system clock to be output on pin. See “Clock Output Buffer” on page 30 for details.
3. The default value results in maximum start-up time for the default clock source. See Table 6-5
on page 27 for details.
4. The default setting results in internal RC Oscillator @ 8.0 MHz. See Table 6-4 on page 27 for
details.
Note that fuse bits are locked if Lock Bit 1 (LB1) is programmed. Fuse bits should be programmed before lock bits. The status of fuse bits is not affected by chip erase.
Fuse bits can also be read by device firmware. See section “Reading Lock, Fuse and Signature
Data from Software” on page 155.
19.2.1
19.3
Latching of Fuses
Fuse values are latched when the device enters programming mode and changes to fuse values
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. Fuses are also latched on power-up.
Device Signature Imprint Table
The device signature imprint table is a dedicated memory area used for storing miscellaneous
device information, such as the device signature and oscillator calibaration data. Most of this
memory segment is reserved for internal use, as outlined in Table 19-6.
Table 19-6.
Contents of Device Signature Imprint Table.
Address
High Byte
0x00
Signature byte 0 (1)
0x01
Calibration data for internal oscillator (2)
0x02
Signature byte 1 (1)
0x03
Reserved for internal use
0x04
Signature byte 2 (1)
0x05 ... 0x2A
Reserved for internal use
Notes:
1. See section “Signature Bytes” for more information.
2. See section “Calibration Byte” for more information.
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19.3.1
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and High-voltage Programming mode, also when the device is
locked.
Signature bytes can also be read by the device firmware. See section “Reading Lock, Fuse and
Signature Data from Software” on page 155.
The three signature bytes reside in a separate address space called the device signature imprint
table. The signature data for ATtiny24/44/84 is given in Table 19-7.
Table 19-7.
Device Signature Bytes
Part
19.3.2
Signature Byte 0
Signature Byte 1
Signature Byte 0
ATtiny24
0x1E
0x91
0x0B
ATtiny44
0x1E
0x92
0x07
ATtiny84
0x1E
0x93
0x0C
Calibration Byte
The device signature imprint table of ATtiny24/44/84 contains one byte of calibration data for the
internal oscillator, as shown in Table 19-6 on page 161. During reset, this byte is automatically
written into the OSCCAL register to ensure correct frequency of the calibrated oscillator.
Calibration bytes can also be read by the device firmware. See section “Reading Lock, Fuse and
Signature Data from Software” on page 155.
19.4
Page Size
Table 19-8.
Device
Flash Size
Page Size
PCWORD
No. of Pages
PCPAGE
PCMSB
ATtiny24
1K words
(2K bytes)
16 words
PC[3:0]
64
PC[9:4]
9
ATtiny44
2K words
(4K bytes)
32 words
PC[4:0]
64
PC[10:5]
10
ATtiny84
4K words
(8K bytes)
32 words
PC[4:0]
128
PC[11:5]
11
Table 19-9.
Device
162
No. of Words in a Page and No. of Pages in the Flash
No. of Words in a Page and No. of Pages in the EEPROM
EEPROM Size
Page Size
PCWORD
No. of Pages
PCPAGE
EEAMSB
ATtiny24
128 bytes
4 bytes
EEA[1:0]
32
EEA[6:2]
6
ATtiny44
256 bytes
4 bytes
EEA[1:0]
64
EEA[7:2]
7
ATtiny84
512 bytes
4 bytes
EEA[1:0]
128
EEA[8:2]
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19.5
Serial Programming
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). See Figure 19-1 below.
Figure 19-1. Serial Programming and Verify
+1.8 - 5.5V
VCC
MOSI
MISO
SCK
RESET
GND
Note:
If clocked by internal oscillator there is no need to connect a clock source to the CLKI pin.
After RESET is set low, the Programming Enable instruction needs to be executed first before
program/erase operations can be executed.
Table 19-10. Pin Mapping Serial Programming
Note:
Symbol
Pins
I/O
Description
MOSI
PA6
I
Serial Data in
MISO
PA5
O
Serial Data out
SCK
PA4
I
Serial Clock
In Table 19-10 above, the pin mapping for SPI programming is listed. Not all devices use the SPI
pins dedicated for the internal SPI interface.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
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instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
• Low:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
• High:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
19.5.1
Serial Programming Algorithm
When writing serial data to the ATtiny24/44/84, data is clocked on the rising edge of SCK. When
reading, data is clocked on the falling edge of SCK. See Figure 20-4 and Figure 20-5 for timing
details.
To program and verify the ATtiny24/44/84 in the Serial Programming mode, the following
sequence is recommended (see four byte instruction formats in Table 19-12):
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 after SCK has been set to '0'. The duration
of the pulse must be at least tRST (the minimum pulse width on RESET pin, see Table
20-4 on page 177) plus two CPU clock cycles.
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 3 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 19-11 on page 165.) 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 19-11 on
page 165.) 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 4 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
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next page (See Table 19-11 on page 165). 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.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
Table 19-11. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
19.5.2
Symbol
Minimum Wait Delay
tWD_FLASH
4.5 ms
tWD_EEPROM
4.0 ms
tWD_ERASE
4.0 ms
tWD_FUSE
4.5 ms
Serial Programming Instruction set
The instruction set is described in Table 19-12 and Figure 19-2 on page 166.
Table 19-12. Serial Programming Instruction Set
Instruction Format
(1)
Byte 1
Byte 2
Byte 3
Byte4
Programming Enable
$AC
$53
$00
$00
Chip Erase (Program Memory/EEPROM)
$AC
$80
$00
$00
Poll RDY/BSY
$F0
$00
$00
data byte out
Load Extended Address byte
$4D
$00
Extended adr
$00
Load Program Memory Page, High byte
$48
adr MSB
adr LSB
high data byte in
Load Program Memory Page, Low byte
$40
adr MSB
adr LSB
low data byte in
Load EEPROM Memory Page (page access)
$C1
$00
adr LSB
data byte in
Read Program Memory, High byte
$28
adr MSB
adr LSB
high data byte out
Read Program Memory, Low byte
$20
adr MSB
adr LSB
low data byte out
Read EEPROM Memory
$A0
$00
adr LSB
data byte out
Read Lock bits
$58
$00
$00
data byte out
Read Signature Byte
$30
$00
adr LSB
data byte out
Read Fuse bits
$50
$00
$00
data byte out
Read Fuse High bits
$58
$08
$00
data byte out
Read Extended Fuse Bits
$50
$08
$00
data byte out
Read Calibration Byte
$38
$00
$00
data byte out
Instruction/Operation
Load Instructions
Read Instructions
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Table 19-12. Serial Programming Instruction Set (Continued)
Instruction Format
(1)
Instruction/Operation
Byte 1
Byte 2
Byte 3
Byte4
Write Program Memory Page
$4C
adr MSB
adr LSB
$00
Write EEPROM Memory
$C0
$00
adr LSB
data byte in
Write EEPROM Memory Page (page access)
$C2
$00
adr LSB
$00
Write Lock bits
$AC
$E0
$00
data byte in
Write Fuse bits
$AC
$A0
$00
data byte in
Write Fuse High bits
$AC
$A8
$00
data byte in
Write Extended Fuse Bits
$AC
$A4
$00
data byte in
Write Instructions
Notes:
(6)
1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (‘1’) .
5. Refer to the correspondig section for Fuse and Lock bits, Calibration and Signature bytes and Page size.
6. Instructions accessing program memory use a word address. This address may be random within the page range.
7. See http://www.atmel.com/avr for Application Notes regarding programming and programmers.
Figure 19-2. Serial Programming Instruction example
Serial Programming Instruction
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Byte 1
Byte 2
Adr MSB
A
Byte 3
Write Program Memory Page/
Write EEPROM Memory Page
Byte 1
Byte 4
Byte 2
Adr LSB
Bit 15 B
Adr MSB
Bit 15 B
0
Byte 3
Byte 4
Adrr LSB
B
0
Page Buffer
Page Offset
Page 0
Page 1
Page 2
Page Number
Page N-1
Program Memory/
EEPROM Memory
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ATtiny24/44/84
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until
this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 19-2 on page
166.
19.6
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 ATtiny24/44/84.
Figure 19-3. High-voltage Serial Programming
+11.5 - 12.5V
SCI
+4.5 - 5.5V
PB3 (RESET)
VCC
PB0
PA4
SDO
PA2:0
PA5
SII
GND
PA6
SDI
Table 19-13. Pin Name Mapping
Signal Name in High-voltage
Serial Programming Mode
Pin Name
SDI
PA6
I
Serial Data Input
SII
PA5
I
Serial Instruction Input
SDO
PA4
O
Serial Data Output
SCI
PB0
I
Serial Clock Input (min. 220ns period)
I/O
Function
The minimum period for the Serial Clock Input (SCI) during High-voltage Serial Programming is
220 ns.
Table 19-14. Pin Values Used to Enter Programming Mode
Pin
Symbol
Value
PA0
Prog_enable[0]
0
PA1
Prog_enable[1]
0
PA2
Prog_enable[2]
0
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19.7
High-Voltage Serial Programming Algorithm
To program and verify the ATtiny24/44/84 in the High-voltage Serial Programming mode, the following sequence is recommended (See instruction formats in Table 19-16 on page 171):
19.7.1
Enter High-voltage Serial Programming Mode
The following algorithm puts the device in High-voltage Serial Programming mode:
1. Set Prog_enable pins listed in Table 19-14 on page 167 to “000”, RESET pin and VCC
to 0V.
2. Apply 4.5 - 5.5V between VCC and GND. Ensure that VCC reaches at least 1.8V within
the next 20 µs.
3. Wait 20 - 60 µs, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 µs after the High-voltage has
been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin after tHVRST has elapsed.
6. Wait at least 300 µs before giving any serial instructions on SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
If the rise time of the VCC is unable to fulfill the requirements listed above, the following alternative algorithm can be used:
1. Set Prog_enable pins listed in Table 19-14 on page 167 to “000”, RESET pin and VCC
to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Monitor VCC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 µs after the High-voltage has
been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO
pin.
6. Wait until VCC actually reaches 4.5 - 5.5V before giving any serial instructions on
SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
Table 19-15. 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
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19.7.2
Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command 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.
19.7.3
Chip Erase
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the Program memory has been completely erased. The Fuse bits are not
changed. A Chip Erase must be performed before the Flash and/or EEPROM are reprogrammed.
1. Load command “Chip Erase” (see Table 19-16 on page 171).
2. Wait after Instr. 3 until SDO goes high for the “Chip Erase” cycle to finish.
3. Load Command “No Operation”.
Note:
19.7.4
1. The EEPROM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Programming the Flash
The Flash is organized in pages, see “Page Size” on page 162. 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 19-16 on page 171).
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 ATtiny24/44/84, data is clocked on the rising edge of
the serial clock, see Figure 20-6 on page 184, Figure 19-3 on page 167 and Table 20-13 on
page 184 for details.
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Figure 19-4. Addressing the Flash which is Organized in Pages
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
Figure 19-5. High-voltage Serial Programming Waveforms
SDI
PB0
MSB
LSB
SII
PB1
MSB
LSB
SDO
PB2
SCI
PB3
19.7.5
MSB
0
LSB
1
2
3
4
5
6
7
8
9
10
Programming the EEPROM
The EEPROM is organized in pages, see Table 20-12 on page 183. 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 19-16 on page 171):
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”.
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19.7.6
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to Table 19-16 on page 171):
1. Load Command "Read Flash".
2. Read Flash Low and High Bytes. The contents at the selected address are available at
serial output SDO.
19.7.7
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Table 19-16 on page
171):
1. Load Command “Read EEPROM”.
2. Read EEPROM Byte. The contents at the selected address are available at serial output SDO.
19.7.8
Programming and Reading the Fuse and Lock Bits
The algorithms for programming and reading the Fuse Low/High bits and Lock bits are shown in
Table 19-16 on page 171.
19.7.9
Reading the Signature Bytes and Calibration Byte
The algorithms for reading the Signature bytes and Calibration byte are shown in Table 19-16 on
page 171.
19.7.10
Power-off sequence
Set SCI to “0”. Set RESET to “1”. Turn VCC power off.
Table 19-16. High-voltage Serial Programming Instruction Set for ATtiny24/44/84
Instruction Format
Instruction
Chip Erase
Load “Write
Flash”
Command
Load Flash
Page Buffer
Load Flash
High Address
and Program
Page
Instr.1/5
Instr.2/6
Instr.3/7
Instr.4
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_0001_0000_00
SII
0_0100_1100_00
SDO
x_xxxx_xxxx_xx
SDI
0_ bbbb_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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_dddd_dddd_00
0_0000_0000_00
0_0000_0000_00
SII
0_0011_1100_00
0_0111_1101_00
0_0111_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
Operation Remarks
Wait after Instr.3 until SDO
goes high for the Chip Erase
cycle to finish.
Enter Flash Programming code.
SDI
0_0000_000a_00
0_0000_0000_00
0_0000_0000_00
SII
0_0001_1100_00
0_0110_0100_00
0_0110_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
Repeat after Instr. 1 - 7until the
entire page buffer is filled or
until all data within the page is
filled. See Note 1.
Instr 5-7.
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.
171
8006H–AVR–10/09
Table 19-16. High-voltage Serial Programming Instruction Set for ATtiny24/44/84 (Continued)
Instruction Format
Instruction
Instr.1/5
Instr.2/6
Instr.3/7
Instr.4
SDI
0_0000_0010_00
SII
0_0100_1100_00
SDO
x_xxxx_xxxx_xx
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqqx_xx
SDI
0_0000_0000_00
0_0000_0000_00
SII
0_0111_1000_00
0_0111_1100_00
SDO
x_xxxx_xxxx_xx
p_pppp_pppx_xx
SDI
0_0001_0001_00
SII
0_0100_1100_00
SDO
x_xxxx_xxxx_xx
SDI
0_bbbb_bbbb_00
0_aaaa_aaaa_00
SII
0_0000_1100_00
0_0001_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_0000_0000_00
SII
0_0110_1100_00
SDO
x_xxxx_xxxx_xx
SDI
0_0000_0000_00
0_0000_0000_00
SII
0_0110_0100_00
0_0110_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_bbbb_bbbb_00
0_aaaa_aaaa_00
0_eeee_eeee_00
0_0000_0000_00
SII
0_0000_1100_00
0_0001_1100_00
0_0010_1100_00
0_0110_1101_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_0000_0000_00
0_0000_0000_00
SII
0_0110_0100_00
0_0110_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
Load “Read
EEPROM”
Command
SDI
0_0000_0011_00
SII
0_0100_1100_00
SDO
x_xxxx_xxxx_xx
Read
EEPROM
Byte
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqq0_00
SDI
0_0100_0000_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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
0_0100_0000_00
0_IHGF_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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
Load “Read
Flash”
Command
Read Flash
Low and High
Bytes
Load “Write
EEPROM”
Command
Load
EEPROM
Page Buffer
Program
EEPROM
Page
Write
EEPROM
Byte
Write Fuse
Low Bits
Write Fuse
High Bits
Write Fuse
Extended Bits
172
Enter Flash Read mode.
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.
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
Repeat Instr. 1 - 5 until the
entire page buffer is filled or
until all data within the page is
filled. 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 - 6 for each new
address. Wait after Instr. 6 until
SDO goes high. See Note 3.
Instr. 5-6
Enter EEPROM Read mode.
SDI
0_0100_0000_00
0_0000_000J_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0010_1100_00
0_0110_0110_00
0_0110_1110_00
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDO
Operation Remarks
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 J = “0” to
program the Fuse bit.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Table 19-16. High-voltage Serial Programming Instruction Set for ATtiny24/44/84 (Continued)
Instruction Format
Instruction
Write Lock
Bits
Read Fuse
Low Bits
Read Fuse
High Bits
Instr.1/5
Instr.2/6
Instr.3/7
Instr.4
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
A_9876_543x_xx
SDI
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0111_1010_00
0_0111_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
I_HGFE_DCBx_xx
Reading F - B = “0” means the
Fuse bit is programmed.
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0110_1010_00
0_0110_1110_00
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxJx_xx
SDI
0_0000_0100_00
0_0000_0000_00
0_0000_0000_00
SII
0_0100_1100_00
0_0111_1000_00
0_0110_1100_00
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_x21x_xx
Read
Signature
Bytes
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
q_qqqq_qqqx_xx
Read
Calibration
Byte
SDI
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
SDO
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
x_xxxx_xxxx_xx
p_pppp_pppx_xx
Load “No
Operation”
Command
SDI
0_0000_0000_00
SII
0_0100_1100_00
SDO
x_xxxx_xxxx_xx
Read Lock
Bits
SDO
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.
SDI
Read Fuse
Extended Bits
Operation Remarks
Reading J = “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 = CKSEL2 Fuse, 6 = CKSEL3 Fuse, 7 =
SUT0 Fuse, 8 = SUT1 Fuse, 9 = CKDIV8 Fuse, A = CKOUT Fuse, B = BODLEVEL0 Fuse, C = BODLEVEL1 Fuse, D=
BODLEVEL2 Fuse, E = EESAVE Fuse, F = WDTON Fuse, G = SPIEN Fuse, H = DWEN Fuse, I = RSTDISBL Fuse
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.
173
8006H–AVR–10/09
20. Electrical Characteristics
20.1
Absolute Maximum Ratings*
Operating Temperature.................................. -55°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA
20.2
DC Characteristics
Table 20-1.
DC Characteristics. TA = -40°C to +85°C
Max (1)
Units
-0.5
0.2VCC
0.3VCC
V
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC +0.5(3)
V
Input High-voltage
RESET pin
VCC = 1.8V to 5.5V
0.9VCC(2)
VCC +0.5(3)
V
VOL
Output Low Voltage(4)
Except RESET pin(6)
IOL = 10 mA, VCC = 5V
IOL = 5 mA, VCC = 3V
0.6
0.5
V
V
VOH
Output High-voltage(5)
Except RESET pin(6)
IOH = -10 mA, VCC = 5V
IOH = -5 mA, VCC = 3V
ILIL
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin low
(absolute value)
<0.05
1
µA
ILIH
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin high
(absolute value)
<0.05
1
µA
RRST
Reset Pull-up Resistor
Vcc = 5.5V, input low
30
60
kΩ
RPU
I/O Pin Pull-up Resistor
Vcc = 5.5V, input low
20
50
kΩ
Symbol
Parameter
Condition
VIL
Input Low Voltage
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
VIH
Input High-voltage
Except RESET pin
VIH1
174
Min (1)
Typ (1)
4.3
2.5
V
V
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Table 20-1.
Symbol
DC Characteristics. TA = -40°C to +85°C (Continued)
Parameter
Power Supply Current
ICC
Power-down mode
Notes:
Typ (1)
Max (1)
Units
Active 1MHz, VCC = 2V
0.33
0.8
mA
Active 4MHz, VCC = 3V
1.6
2.5
mA
Active 8MHz, VCC = 5V
5
9
mA
Idle 1MHz, VCC = 2V
0.11
0.4
mA
Idle 4MHz, VCC = 3V
0.4
1.0
mA
Idle 8MHz, VCC = 5V
1.5
3.5
mA
WDT enabled, VCC = 3V
4.5
10
µA
WDT disabled, VCC = 3V
0.15
2
µA
Condition
Min (1)
1. All DC Characteristics contained in this data sheet are based on simulation and characterization of other AVR microcontrollers manufactured in the same process technology. These values are preliminary values representing design targets, and
will be updated after characterization of actual silicon.
2. “Min” means the lowest value where the pin is guaranteed to be read as high.
3. “Max” means the highest value where the pin is guaranteed to be read as low.
4. Although each I/O port can sink more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the sum of all IOL (for all ports) should not exceed 60 mA. If IOL exceeds the test conditions, 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 (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the sum of all IOH (for all ports) should not exceed 60 mA. If IOH exceeds the test condition, VOH
may exceed the related specification. Pins are not guaranteed to source current greater than the listed test condition.
6. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence,
has a weak drive strength as compared to regular I/O pins. See Figure 21-24, Figure 21-25, Figure 21-26, and Figure 21-27
(starting on page 198).
20.3
Speed Grades
The maximum operating frequency of the device depends on VCC. As shown in Figure 20-1 and
Figure 20-2, the maximum frequency vs. VCC relationship is linear between 1.8V < VCC < 2.7V
and between 2.7V < VCC < 4.5V.
Figure 20-1. Maximum Frequency vs. VCC (ATtiny24V/44V/84V)
10 MHz
Safe Operating Area
4 MHz
1.8V
2.7V
5.5V
175
8006H–AVR–10/09
Figure 20-2. Maximum Frequency vs. VCC (ATtiny24/44/84)
20 MHz
10 MHz
Safe Operating Area
2.7V
20.4
20.4.1
4.5V
5.5V
Clock Characteristics
Accuracy of Calibrated Internal RC Oscillator
It is possible to manually calibrate the internal oscillator to be more accurate than default factory
calibration. Note that the oscillator frequency depends on temperature and voltage. Voltage and
temperature characteristics can be found in Figure 21-40 on page 206 and Figure 21-41 on
page 206.
Table 20-2.
Calibration
Method
Factory
Calibration
User
Calibration
Calibration Accuracy of Internal RC Oscillator
Target Frequency
VCC
Temperature
Accuracy at given voltage
& temperature(1)
8.0 MHz
3V
25°C
±10%
Fixed frequency within:
7.3 – 8.1 MHz
Fixed voltage within:
1.8V – 5.5V(2)
2.7V – 5.5V(3)
Fixed temperature
within:
-40°C – 85°C
±1%
Notes:
1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
2. Voltage range for ATtiny24V/44V/84V.
3. Voltage range for ATtiny24/44/84.
176
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
20.4.2
External Clock Drive
Figure 20-3. External Clock Drive Waveform
V IH1
V IL1
Table 20-3.
External Clock Drive Characteristics
VCC = 1.8 - 5.5V
VCC = 2.7 - 5.5V
VCC = 4.5 - 5.5V
Symbol
Parameter
1/tCLCL
Clock Frequency
tCLCL
Clock Period
250
100
50
ns
tCHCX
High Time
100
40
20
ns
tCLCX
Low Time
100
40
20
ns
tCLCH
Rise Time
2.0
1.6
0.5
μs
tCHCL
Fall Time
2.0
1.6
0.5
μs
ΔtCLCL
Change in period from one clock cycle to the next
2
2
2
%
20.5
Min.
Max.
Min.
Max.
Min.
Max.
Units
0
4
0
10
0
20
MHz
System and Reset Characteristics
Table 20-4.
Symbol
Reset, Brown-out, and Internal Voltage Characteristics
Parameter
VRST
RESET Pin Threshold Voltage
tRST
Minimum pulse width on RESET
Pin
VHYST
Condition
Min(1)
Typ(1)
0.2 VCC
Max(1)
Units
0.9VCC
V
2000
700
400
ns
Brown-out Detector Hysteresis
50
mV
tBOD
Min Pulse Width on
Brown-out Reset
2
µs
VBG
Internal bandgap reference
voltage
VCC = 5V
TA = 25°C
tBG
Internal bandgap reference
start-up time
IBG
Internal bandgap reference
current consumption
Note:
VCC = 1.8V
VCC = 3V
VCC = 5V
1.0
1.1
1.2
V
VCC = 5V
TA = 25°C
40
70
µs
VCC = 5V
TA = 25°C
15
µA
1. Values are guidelines, only
177
8006H–AVR–10/09
Two versions of power-on reset have been implemented, as follows.
20.5.1
Standard Power-On Reset
This implementation of power-on reset existed in early versions of ATtiny24/44/84. The table
below describes the characteristics of this power-on reset and it is valid for the following devices,
only:
• ATtiny24, revision D, and older
• ATtiny44, revision C, and older
• ATtiny84, revision A
Note:
Revisions are marked on the package (packages 14P3 and 14S1: bottom, package 20M1: top)
Table 20-5.
Symbol
Characteristics of Standard Power-On Reset. TA = -40 - 85°C
Parameter
Release threshold of power-on reset (2)
VPOR
VPOA
Activation threshold of power-on reset
SRON
Power-on slope rate
Note:
(3)
Min(1)
Typ(1)
Max(1)
Units
0.7
1.0
1.4
V
0.05
0.9
1.3
V
4.5
V/ms
0.01
1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is rising
3. The power-on reset will not work unless the supply voltage has been below VPOA
20.5.2
Enhanced Power-On Reset
This implementation of power-on reset exists in newer versions of ATtiny24/44/84. The table
below describes the characteristics of this power-on reset and it is valid for the following devices,
only:
• ATtiny24, revision E, and newer
• ATtiny44, revision D, and newer
• ATtiny84, revision B, and newer
Table 20-6.
Symbol
Characteristics of Enhanced Power-On Reset. TA = -40 - 85°C
Parameter
Release threshold of power-on reset
VPOR
(2)
VPOA
Activation threshold of power-on reset
SRON
Power-On Slope Rate
Note:
(3)
Min(1)
Typ(1)
Max(1)
Units
1.1
1.4
1.6
V
0.6
1.3
1.6
V
0.01
V/ms
1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is rising
3. The Power-on Reset will not work unless the supply voltage has been below VPOA
178
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
20.5.3
Brown-Out Detection
Table 20-7.
VBOT vs. BODLEVEL Fuse Coding
BODLEVEL [2..0] Fuses
Min(1)
111
20.6
Max(1)
110
1.7
1.8
2.0
101
2.5
2.7
2.9
100
4.1
4.3
4.5
Reserved
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.
Analog Comparator Characteristics, TA = -40°C - 85°C
Symbol
Parameter
Condition
VAIO
Input Offset Voltage
VCC = 5V, VIN = VCC / 2
ILAC
Input Leakage Current
VCC = 5V, VIN = VCC / 2
Analog Propagation Delay
(from saturation to slight overdrive)
VCC = 2.7V
750
VCC = 4.0V
500
Analog Propagation Delay
(large step change)
VCC = 2.7V
100
VCC = 4.0V
75
Digital Propagation Delay
VCC = 1.8V - 5.5
1
tAPD
Note:
V
Analog Comparator Characteristics
Table 20-8.
tDPD
Units
BOD Disabled
0XX
Note:
Typ(1)
Min
Typ
Max
Units
< 10
40
mV
50
nA
-50
ns
2
CLK
All parameters are based on simulation results and they are not tested in production
179
8006H–AVR–10/09
20.7
ADC Characteristics – Preliminary Data
Table 20-9.
Symbol
ADC Characteristics, Single Ended Channels. T = -40°C - 85°C
Parameter
Condition
Min(1)
Typ(1)
Resolution
Units
10
Bits
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2.0
TBD
LSB
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
2.5
TBD
LSB
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
Noise Reduction Mode
1.5
TBD
LSB
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
Noise Reduction Mode
2.0
TBD
LSB
Integral Non-Linearity (INL)
(Accuracy after Offset and
Gain Calibration)
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
1.0
TBD
LSB
Differential Non-linearity
(DNL)
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
0.5
TBD
LSB
Gain Error
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2.0
TBD
LSB
Offset Error
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
1.5
TBD
LSB
Conversion Time
Free Running Conversion
14
280
µs
50
1000
kHz
GND
VREF
V
Absolute accuracy
(Including INL, DNL, and
Quantization, Gain and Offset
Errors)
Clock Frequency
VIN
Max(1)
Input Voltage
Input Bandwidth
38.4
kHz
AREF
External Voltage Reference
2.0
VINT
Internal Voltage Reference
1.0
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
ADC Conversion Output
Note:
180
0
1.1
VCC
V
1.2
V
1023
LSB
1. Values are preliminary.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Table 20-10. ADC Characteristics, Differential Channels (Unipolar Mode), TA = -40°C to 85°C
Symbol
Parameter
Max(1)
Units
Gain = 1x
10
Bits
Gain = 20x
10
Bits
Condition
Min(1)
Typ(1)
Resolution
Absolute accuracy
(Including INL, DNL, and Quantization, Gain
and Offset Errors)
Integral Non-Linearity (INL)
(Accuracy after Offset and Gain Calibration)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
10.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
20.0
TBD
LSB
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
4.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
10.0
TBD
LSB
Gain = 1x
10.0
TBD
LSB
Gain = 20x
15.0
TBD
LSB
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
3.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
4.0
TBD
LSB
70
280
µs
50
200
kHz
GND
VCC
V
VREF/Gain
V
Gain Error
Offset Error
Conversion Time
Clock Frequency
VIN
Input Voltage
VDIFF
Input Differential Voltage
Free Running Conversion
Input Bandwidth
4
kHz
AREF
External Reference Voltage
2.0
VINT
Internal Voltage Reference
1.0
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
ADC Conversion Output
Note:
0
1.1
VCC - 1.0
V
1.2
V
1023
LSB
1. Values are preliminary.
181
8006H–AVR–10/09
Table 20-11. ADC Characteristics, Differential Channels (Bipolar Mode), TA = -40°C to 85°C
Symbol
Parameter
Max(1)
Units
Gain = 1x
10
Bits
Gain = 20x
10
Bits
Condition
Min(1)
Typ(1)
Resolution
Absolute accuracy
(Including INL, DNL, and Quantization, Gain
and Offset Errors)
Integral Non-Linearity (INL)
(Accuracy after Offset and Gain Calibration)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
8.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
8.0
TBD
LSB
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
4.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
5.0
TBD
LSB
Gain = 1x
4.0
TBD
LSB
Gain = 20x
5.0
TBD
LSB
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
3.0
TBD
LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200 kHz
4.0
TBD
LSB
70
280
µs
50
200
kHz
GND
VCC
V
VREF/Gain
V
Gain Error
Offset Error
Conversion Time
Clock Frequency
VIN
Input Voltage
VDIFF
Input Differential Voltage
Free Running Conversion
Input Bandwidth
4
kHz
AREF
External Reference Voltage
2.0
VINT
Internal Voltage Reference
1.0
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
ADC Conversion Output
Note:
182
-512
1.1
VCC - 1.0
V
1.2
V
511
LSB
1. Values are preliminary.
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
20.8
Serial Programming Characteristics
Figure 20-4. Serial Programming Timing
MOSI
SCK
tSLSH
tSHOX
tOVSH
tSHSL
MISO
Figure 20-5. Serial Programming Waveform
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
Table 20-12. Serial Programming Characteristics, TA = -40°C to 85°C, VCC = 1.8 - 5.5V (Unless
Otherwise Noted)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (ATtiny24/44/84V)
Min
0
Oscillator Period (ATtiny24/44/84V)
tCLCL
Oscillator Freq. (ATtiny24/44/84, VCC = 4.5V - 5.5V)
0
tCLCL
Oscillator Period (ATtiny24/44/84, VCC = 4.5V - 5.5V)
50
SCK Pulse Width High
tSLSH
SCK Pulse Width Low
tOVSH
MOSI Setup to SCK High
tSHOX
MOSI Hold after SCK High
Note:
Max
Units
4
MHz
250
1/tCLCL
tSHSL
Typ
2
ns
20
MHz
ns
tCLCL(1)
ns
(1)
ns
2 tCLCL
tCLCL
ns
2 tCLCL
ns
1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
183
8006H–AVR–10/09
20.9
High-Voltage Serial Programming Characteristics
Figure 20-6. High-voltage Serial Programming Timing
SDI (PA6), SII (PA5)
tIVSH
SCI (PB0)
tSLSH
tSHIX
tSHSL
SDO (PA4)
tSHOV
Table 20-13. High-voltage Serial Programming Characteristics
TA = 25°C, VCC = 5V (Unless otherwise noted)
Symbol
Parameter
Min
tSHSL
SCI (PB0) Pulse Width High
125
ns
tSLSH
SCI (PB0) Pulse Width Low
125
ns
tIVSH
SDI (PA6), SII (PB1) Valid to SCI (PB0) High
50
ns
tSHIX
SDI (PA6), SII (PB1) Hold after SCI (PB0) High
50
ns
tSHOV
SCI (PB0) High to SDO (PA4) Valid
16
ns
Wait after Instr. 3 for Write Fuse Bits
2.5
ms
tWLWH_PFB
184
Typ
Max
Units
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
21. Typical Characteristics
The data contained in this section is largely based on simulations and characterization of similar
devices in the same process and design methods. Thus, the data should be treated as indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing.
During characterisation devices are operated at frequencies higher than test limits but they are
not guaranteed to function properly at frequencies higher than the ordering code indicates.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. 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.
A sine wave generator with rail-to-rail output is used as clock source but current consumption in
Power-Down mode is independent of clock selection. 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.
The current drawn from pins with a capacitive load may be estimated (for one pin) as follows:
I CP ≈ V CC × C L × f SW
where VCC = operating voltage, CL = load capacitance and fSW = average switching frequency of
I/O pin.
21.1
Supply Current of I/O Modules
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
is controlled by the Power Reduction Register. See “Power Reduction Register” on page 35 for
details.
Table 21-1.
Additional Current Consumption for the different I/O modules (absolute values)
Typical numbers
PRR bit
VCC = 2V, f = 1MHz
VCC = 3V, f = 4MHz
VCC = 5V, f = 8MHz
PRTIM1
5.1 uA
31.0 uA
118.2 uA
PRTIM0
6.6 uA
40.0 uA
153.0 uA
PRUSI
3.7 uA
23.1 uA
92.2 uA
PRADC
29.6 uA
88.3 uA
333.3 uA
Table 21-2 below can be used for calculating typical current consumption for other supply voltages and frequencies than those mentioned in the Table 21-1 above.
185
8006H–AVR–10/09
Table 21-2.
Additional Current Consumption (percentage) in Active and Idle mode
Current consumption additional to
active mode with external clock
(see Figure 21-1 and Figure 21-2)
PRR bit
21.1.1
Current consumption additional to
idle mode with external clock
(see Figure 21-6 and Figure 21-7)
PRTIM1
1.8 %
8.0 %
PRTIM0
2.3 %
10.4 %
PRUSI
1.4 %
6.1 %
PRADC
6.7 %
28.8 %
Example
Calculate the expected current consumption in idle mode with USI, TIMER0, and ADC enabled
at VCC = 2.0V and f = 1MHz. From Table 21-2 on page 186, third column, we see that we need to
add 6.1% for the USI, 10.4% for TIMER0, and 28.8% for the ADC. Reading from Figure 21-6 on
page 189, we find that current consumption in idle mode at 2V and 1MHz is about 0.04mA. The
total current consumption in idle mode with USI, TIMER0, and ADC enabled is therefore:
I CCTOT ≈ 0.04mA × ( 1 + 0.061 + 0.104 + 0.288 ) ≈ 0.06mA
21.2
Active Supply Current
Figure 21-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY
(PRR=0xFF)
1.2
1
5.5 V
5.0 V
0.8
ICC (mA)
4.5 V
4.0 V
0.6
3.3 V
0.4
2.7 V
1.8 V
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
186
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-2. Active Supply Current vs. frequency (1 - 20 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
(PRR=0xFF)
14
5.5 V
12
5.0 V
ICC (mA)
10
4.5 V
8
6
4.0 V
4
3.3 V
2.7 V
2
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 21-3. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. SUPPLY VOLTAGE
INTERNAL RC OSCILLATOR, 8 MHz
6
25 °C
5
-40 °C
85 °C
ICC (mA)
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
187
8006H–AVR–10/09
Figure 21-4. Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 1 MHz
1.2
85 °C
25 °C
-40 °C
1
ICC (mA)
0.8
0.6
0.4
0.2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-5. Active Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 128 KHz
0.14
-40 °C
25 °C
85 °C
0.12
ICC (mA)
0.1
0.08
0.06
0.04
0.02
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
188
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
21.3
Idle Supply Current
Figure 21-6. Idle Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
IDLE SUPPLY CURRENT vs. LOW FREQUENCY
(PRR=0xFF)
ICC (mA)
0.18
0.16
5.5 V
0.14
5.0 V
0.12
4.5 V
0.1
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 21-7. Idle Supply Current vs. Frequency (1 - 20 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
(PRR=0xFF)
5
4.5
4
ICC (mA)
3.5
5.5 V
3
5.0 V
2.5
4.5 V
2
1.5
4.0 V
3.3 V
2.7 V
1
0.5
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
189
8006H–AVR–10/09
Figure 21-8. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
2
1.8
1.6
85 °C
1.4
25 °C
-40 °C
ICC (mA)
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
VCC (V)
Figure 21-9. Idle Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 1 MHz
0.35
85 °C
0.3
25 °C
-40 °C
ICC (mA)
0.25
0.2
0.15
0.1
0.05
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
190
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-10. Idle Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 128 KHz
0.03
-40 °C
25 °C
0.025
85 °C
ICC (mA)
0.02
0.015
0.01
0.005
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
21.4
Power-down Supply Current
Figure 21-11. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER DISABLED
0.7
85 °C
0.6
ICC (uA)
0.5
0.4
0.3
0.2
25 °C
0.1
-40 °C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
191
8006H–AVR–10/09
Figure 21-12. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER ENABLED
10
9
-40 °C
8
25 °C
85 °C
7
ICC (uA)
6
5
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
21.5
Standby Supply Current
Figure 21-13. Standby Supply Current vs. VCC (4 MHz External Crystal, Watchdog Timer
Disabled)
STANDBY SUPPLY CURRENT vs. VCC
4 MHz EXTERNAL CRYSTAL, WATCHDOG TIMER DISABLED
I CC (mA)
0.14
0.12
85 ˚C
0.1
25 ˚C
0.08
-40 ˚C
0.06
0.04
0.02
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
192
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
21.6
Pin Pull-up
Figure 21-14. I/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
VCC = 1.8V
50
45
40
IOP (uA)
35
30
25
20
15
10
25 ˚C
5
85 ˚C
-40 ˚C
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOP (V)
Figure 21-15. I/O Pin Pull-up Resistor Current vs. input Voltage (VCC = 2.7V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
VCC = 2.7V
80
70
60
IOP (uA)
50
40
30
20
25 ˚C
10
85 ˚C
-40 ˚C
0
0
0.5
1
1.5
2
2.5
3
VOP (V)
193
8006H–AVR–10/09
Figure 21-16. I/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
VCC = 5V
160
140
120
IOP (uA)
100
80
60
40
25 ˚C
20
85 ˚C
-40 ˚C
0
0
1
2
3
4
5
6
VOP (V)
Figure 21-17. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
VCC = 1.8V
40
35
I RESET (uA)
30
25
20
15
10
25 ˚C
5
-40 ˚C
85 ˚C
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VRESET (V)
194
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-18. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
VCC = 2.7V
60
50
I RESET(uA)
40
30
20
25 ˚C
10
-40 ˚C
85 ˚C
0
0
0.5
1
1.5
2
2.5
3
VRESET (V)
Figure 21-19. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
VCC = 5V
120
100
I RESET (uA)
80
60
40
25 ˚C
20
-40 ˚C
85 ˚C
0
0
1
2
3
4
5
6
VRESET(V)
195
8006H–AVR–10/09
21.7
Pin Driver Strength
Figure 21-20. I/O Pin Output Voltage vs. Sink Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 3V
1
0.9
85 ˚C
0.8
VOL (V)
0.7
25 ˚C
0.6
-40 ˚C
0.5
0.4
0.3
0.2
0.1
0
0
5
10
15
20
25
IOL (mA)
Figure 21-21. I/O pin Output Voltage vs. Sink Current (VCC = 5V)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 5V
0.7
0.6
85 ˚C
VOL (V)
0.5
25 ˚C
0.4
-40 ˚C
0.3
0.2
0.1
0
0
5
10
15
20
25
IOL (mA)
196
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-22. I/O Pin Output Voltage vs. Source Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 3V
3.5
3
VOH (V)
2.5
-40 ˚C
25 ˚C
85 ˚C
2
1.5
1
0.5
0
0
5
10
15
20
25
IOH (mA)
Figure 21-23. I/O Pin output Voltage vs. Source Current (VCC = 5V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 5V
5.1
5
4.9
VOH (V)
4.8
4.7
4.6
-40 ˚C
4.5
25 ˚C
85 ˚C
4.4
4.3
0
5
10
15
20
25
IOH (mA)
197
8006H–AVR–10/09
Figure 21-24. Reset Pin Output Voltage vs. Sink Current (VCC = 3V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 3V
1.5
85 °C
VOL (V)
1
0 °C
-45 °C
0.5
0
0
0.5
1
1.5
2
2.5
3
IOL (mA)
Figure 21-25. Reset Pin Output Voltage vs. Sink Current (VCC = 5V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
VCC = 5V
1
0.8
VOL (V)
0.6
85 °C
0.4
0 °C
-45 °C
0.2
0
0
0.5
1
1.5
2
2.5
3
IOL (mA)
198
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-26. Reset Pin Output Voltage vs. Source Current (VCC = 3V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 3V
3.5
3
VOH (V)
2.5
2
1.5
-45 °C
25 °C
85 °C
1
0.5
0
0
0.5
1
1.5
2
IOH (mA)
Figure 21-27. Reset Pin Output Voltage vs. Source Current (VCC = 5V)
RESET AS I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
VCC = 5V
5
4.5
VOH (V)
4
3.5
3
-45 °C
25 °C
85 °C
2.5
0
0.5
1
1.5
2
IOH (mA)
199
8006H–AVR–10/09
21.8
Pin Threshold and Hysteresis
Figure 21-28. I/O Pin Input Threshold Voltage vs. VCC (VIH, IO Pin Read as ‘1’)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
3.5
85 ˚C
25 ˚C
-40 ˚C
Threshold (V)
3
2.5
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-29. I/O Pin Input threshold Voltage vs. VCC (VIL, IO Pin Read as ‘0’)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIL, IO PIN READ AS '0'
2.5
85 ˚C
25 ˚C
Threshold (V)
2
-40 ˚C
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
200
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-30. I/O Pin Input Hysteresis vs. VCC
I/O PIN INPUT HYSTERESIS vs. VCC
0.6
Input Hysteresis (V)
0.5
85 °C
-40 °C
0.4
25 °C
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-31. Reset Input Threshold Voltage vs. VCC (VIH, I/O Pin Threshold as ‘1’)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
2.5
-40 ˚C
25 ˚C
2
Threshold (V)
85 ˚C
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
201
8006H–AVR–10/09
Figure 21-32. Reset Input Threshold Voltage vs. VCC (VIL, I/O pin Read as ‘0’)
RESET INPUT THRESHOLD VOLTAGE vs. V CC
VIL, IO PIN READ AS '0'
2.5
85 ˚C
25 ˚C
2
Threshold (V)
-40 ˚C
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-33. Reset Pin Input Hysteresis vs. VCC
RESET PIN INPUT HYSTERESIS vs. VCC
0.8
Input Hysteresis (V)
0.7
0.6
0.5
0.4
0.3
0.2
-40 °C
25 °C
85 °C
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
202
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-34. Reset Pin Input Hysteresis vs. VCC (Reset Pin Used as I/O)
RESET PIN AS I/O, INPUT HYSTERESIS vs. VCC
VIL, I/O PIN READ AS "0"
1
0.9
0.8
Input Hysteresis (mV)
-40 °C
0.7
25 °C
0.6
85 °C
0.5
0.4
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
21.9
BOD Threshold and Analog Comparator Offset
Figure 21-35. BOD Threshold vs. Temperature (BODLEVEL is 4.3V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL is 4.3V
4.34
4.32
Rising Vcc
Threshold (V)
4.3
4.28
4.26
4.24
4.22
Falling Vcc
4.2
4.18
4.16
4.14
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
203
8006H–AVR–10/09
Figure 21-36. BOD Threshold vs, Temperature (BODLEVEL is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL is 2.7V
2.75
Rising Vcc
2.74
2.73
Threshold (V)
2.72
2.71
2.7
2.69
2.68
2.67
Falling Vcc
2.66
2.65
2.64
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
Figure 21-37. BOD Threshold vs. Temperature (BODLEVEL is 1.8V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL is 1.8V
1.82
Rising Vcc
1.815
Threshold (V)
1.81
1.805
1.8
1.795
1.79
Falling Vcc
1.785
1.78
1.775
1.77
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
204
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
21.10 Internal Oscillator Speed
Figure 21-38. Watchdog Oscillator Frequency vs. VCC
WATCHDOG OSCILLATOR FREQUENCY vs. OPERATING VOLTAGE
110
109
108
Frequency (kHz)
107
-40 °C
106
105
25 °C
104
103
102
101
85 °C
100
99
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-39. Watchdog Oscillator Frequency vs. Temperature
WATCHDOG OSCILLATOR FREQUENCY vs. TEMPERATURE
110
109
108
Frequency (kHz)
107
106
105
104
1.8 V
103
2.7 V
102
3.3 V
101
4.0 V
5.5 V
100
-60
-40
-20
0
20
40
60
80
100
Temperature
205
8006H–AVR–10/09
Figure 21-40. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8.0MHz RC OSCILLATOR FREQUENCY vs. OPERATING VOLTAGE
9
85 °C
8
25 °C
-40 °C
Frequency (MHz)
7
6
5
4
3
2
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-41. Calibrated 8 MHz RC oscillator Frequency vs. Temperature
CALIBRATED 8.0MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
8.3
5.0 V
8.2
3.0 V
Frequency (MHz)
8.1
8
7.9
7.8
7.7
7.6
-60
-40
-20
0
20
40
60
80
100
Temperature
206
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-42. Calibrated 8 MHz RC Oscillator Frequency vs, OSCCAL Value
CALIBRATED 8 MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
16
FRC (MHz)
85 ˚C
14
25 ˚C
12
-40 ˚C
10
8
6
4
2
0
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL (X1)
21.11 Current Consumption of Peripheral Units
Figure 21-43. ADC Current vs. VCC
ADC CURRENT vs. VCC
4.0 MHz FREQUENCY
700
600
ICC (uA)
500
400
300
200
100
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
207
8006H–AVR–10/09
Figure 21-44. AREF External Reference Current vs. VCC
AREF EXTERNAL REFERENCE CURRENT vs. VCC
180
25 ˚C
150
ICC (uA)
120
90
60
30
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC (V)
Figure 21-45. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. VCC
140
120
ICC (uA)
100
25 ˚C
80
60
40
20
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC (V)
208
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-46. Programming Current vs. VCC (ATtiny24)
PROGRAMMING CURRENT vs. VCC
ATtiny24
8000
7000
25 °C
6000
ICC (uA)
5000
4000
3000
2000
1000
0
1.5
2.5
3.5
4.5
5.5
VCC (V)
Figure 21-47. Programming Current vs. VCC (ATtiny44)
PROGRAMMING CURRENT vs. VCC
ATtiny44
9000
8000
25 °C
7000
ICC (uA)
6000
5000
4000
3000
2000
1000
0
1.5
2.5
3.5
4.5
5.5
VCC (V)
209
8006H–AVR–10/09
Figure 21-48. Programming Current vs. VCC (ATtiny84)
PROGRAMMING CURRENT vs. VCC
ATtiny84
16000
25 °C
14000
12000
ICC (uA)
10000
8000
6000
4000
2000
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 21-49. Brownout Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs. VCC
45
40
35
ICC (uA)
30
85 ˚C
25 ˚C
-40 ˚C
25
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
210
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
Figure 21-50. Watchdog Timer Current vs. VCC
WATCHDOG TIMER CURRENT vs. VCC
10
9
-40 ˚C
85 ˚C
8
ICC (uA)
7
25 ˚C
6
5
4
3
2
1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC (V)
21.12 Current Consumption in Reset and Reset Pulsewidth
Figure 21-51. Reset Supply Current vs. VCC (0.1 - 1.0 MHz, excluding Current Through the
Reset Pull-up)
RESET SUPPLY CURRENT vs. VCC
0.1 - 1.0 MHz,EXCLUDING CURRENT THROUGH THE RESET PULLUP
0.14
5.5 V
0.12
5.0 V
ICC (mA)
0.1
4.5 V
0.08
4.0 V
0.06
3.3 V
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)
211
8006H–AVR–10/09
Figure 21-52. Reset Supply Current vs. VCC (1 - 20 MHz, Excluding Current Through the Reset
Pull-up)
RESET SUPPLY CURRENT vs. VCC
1 - 20 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
3
2.5
5.5 V
5.0 V
4.5 V
ICC (mA)
2
1.5
1
4.0V
3.3V
2.7V
0.5
1.8V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 21-53. Minimum Reset Pulse Width vs. VCC
MINIMUM RESET PULSE WIDTH vs. VCC
2500
Pulsewidth (ns)
2000
1500
1000
500
85 ˚C
25 ˚C
-40 ˚C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
VCC (V)
212
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
22. Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x3F (0x5F)
SREG
I
T
H
S
V
N
Z
C
Page 8
–
–
–
–
SP9
SP8
Page 11
SP1
SP0
0x3E (0x5E)
SPH
–
–
0x3D (0x5D)
SPL
SP7
SP6
0x3C (0x5C)
OCR0B
0x3B (0x5B)
GIMSK
–
INT0
PCIE1
PCIE0
–
–
–
–
Page 51
0x3A (0x5A
GIFR
–
INTF0
PCIF1
PCIF0
–
–
–
–
Page 52
0x39 (0x59)
TIMSK0
–
–
–
–
–
OCIE0B
OCIE0A
TOIE0
Page 85
0x38 (0x58)
TIFR0
–
–
–
–
OCF0B
OCF0A
TOV0
Page 85
0x37 (0x57)
SPMCSR
RSIG
CTPB
RFLB
PGWRT
Timer/Counter0 – Output Compare Register A
PGERS
SPMEN
Page 157
0x36 (0x56)
OCR0A
0x35 (0x55)
MCUCR
SP5
SP4
SP3
SP2
Timer/Counter0 – Output Compare Register B
–
–
BODS
PUD
SE
SM1
Page 11
Page 85
Page 84
SM0
BODSE
ISC01
ISC00
Pages 36, 51, and 67
0x34 (0x54)
MCUSR
–
–
–
–
WDRF
BORF
EXTRF
PORF
Page 45
0x33 (0x53)
TCCR0B
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
Page 83
0x32 (0x52)
TCNT0
0x31 (0x51)
OSCCAL
CAL2
CAL1
CAL0
Page 30
Timer/Counter0
CAL7
CAL6
CAL5
CAL4
CAL3
Page 84
0x30 (0x50)
TCCR0A
COM0A1
COM0A0
COM0B1
COM0B0
–
WGM01
WGM00
Page 80
0x2F (0x4F)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1B0
–
WGM11
WGM10
Page 108
ICNC1
ICES1
–
WGM13
WGM12
CS11
CS10
Page 110
0x2E (0x4E)
TCCR1B
0x2D (0x4D)
TCNT1H
Timer/Counter1 – Counter Register High Byte
CS12
Page 112
0x2C (0x4C)
TCNT1L
Timer/Counter1 – Counter Register Low Byte
Page 112
0x2B (0x4B)
OCR1AH
Timer/Counter1 – Compare Register A High Byte
Page 112
0x2A (0x4A)
OCR1AL
Timer/Counter1 – Compare Register A Low Byte
Page 112
0x29 (0x49)
OCR1BH
Timer/Counter1 – Compare Register B High Byte
Page 112
0x28 (0x48)
OCR1BL
Timer/Counter1 – Compare Register B Low Byte
Page 112
0x27 (0x47)
DWDR
DWDR[7:0]
Page 152
0x26 (0x46)
CLKPR
0x25 (0x45)
ICR1H
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Timer/Counter1 - Input Capture Register High Byte
Page 31
Page 113
0x24 (0x44)
ICR1L
0x23 (0x43)
GTCCR
TSM
–
Timer/Counter1 - Input Capture Register Low Byte
–
–
–
–
–
PSR10
Page 113
Page 116
0x22 (0x42)
TCCR1C
FOC1A
FOC1B
–
–
–
–
–
–
Page 111
0x21 (0x41)
WDTCSR
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
Page 45
0x20 (0x40)
PCMSK1
–
–
–
–
PCINT11
PCINT10
PCINT9
PCINT8
Page 52
0x1F (0x3F)
EEARH
–
–
–
–
–
–
–
EEAR8
Page 20
0x1E (0x3E)
EEARL
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
0x1D (0x3D)
EEDR
EEPROM Data Register
Page 21
Page 21
0x1C (0x3C)
EECR
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
Page 21
0x1B (0x3B)
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
Page 67
0x1A (0x3A)
DDRA
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
Page 67
0x19 (0x39)
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Page 68
0x18 (0x38)
PORTB
–
–
–
–
PORTB3
PORTB2
PORTB1
PORTB0
Page 68
0x17 (0x37)
DDRB
–
–
–
–
DDB3
DDB2
DDB1
DDB0
Page 68
0x16 (0x36)
PINB
–
–
–
–
PINB3
PINB2
PINB1
PINB0
Page 68
0x15 (0x35)
GPIOR2
General Purpose I/O Register 2
Page 23
0x14 (0x34)
GPIOR1
General Purpose I/O Register 1
Page 23
0x13 (0x33)
GPIOR0
General Purpose I/O Register 0
0x12 (0x32)
PCMSK0
0x11 (0x31))
Reserved
–
0x10 (0x30)
USIBR
USI Buffer Register
Page 125
0x0F (0x2F)
USIDR
USI Data Register
Page 124
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
Page 23
PCINT2
PCINT1
PCINT0
Page 53
0x0E (0x2E)
USISR
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
Page 125
0x0D (0x2D)
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
Page 126
0x0C (0x2C)
TIMSK1
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
Page 113
0x0B (0x2B)
TIFR1
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
Page 114
0x0A (0x2A)
Reserved
0x09 (0x29)
Reserved
0x08 (0x28)
ACSR
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
Page 130
0x07 (0x27)
ADMUX
REFS1
REFS0
MUX5
MUX4
MUX3
MUX2
MUX1
MUX0
Page 145
0x06 (0x26)
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
0x05 (0x25)
ADCH
0x04 (0x24)
ADCL
0x03 (0x23)
ADCSRB
0x02 (0x22)
Reserved
0x01 (0x21)
0x00 (0x20)
–
–
ADC Data Register High Byte
ADC Data Register Low Byte
BIN
ACME
–
ADLAR
DIDR0
ADC7D
ADC6D
ADC5D
ADC4D
PRR
–
–
–
–
–
Page 147
Page 149
Page 149
ADTS2
ADTS1
ADTS0
Page 131, Page 149
ADC3D
ADC2D
PRTIM1
PRTIM0
ADC1D
ADC0D
Page 131, Page 150
PRUSI
PRADC
Page 37
–
213
8006H–AVR–10/09
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.
214
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
23. Instruction Set Summary
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD
Rd, Rr
Add two Registers
Rd ← Rd + Rr
Z,C,N,V,H
1
ADC
Rd, Rr
Add with Carry two Registers
Rd ← Rd + Rr + C
Z,C,N,V,H
1
ADIW
Rdl,K
Add Immediate to Word
Rdh:Rdl ← Rdh:Rdl + K
Z,C,N,V,S
2
SUB
Rd, Rr
Subtract two Registers
Rd ← Rd - Rr
Z,C,N,V,H
1
SUBI
Rd, K
Subtract Constant from Register
Rd ← Rd - K
Z,C,N,V,H
1
SBC
Rd, Rr
Subtract with Carry two Registers
Rd ← Rd - Rr - C
Z,C,N,V,H
1
SBCI
Rd, K
Subtract with Carry Constant from Reg.
Rd ← Rd - K - C
Z,C,N,V,H
1
SBIW
Rdl,K
Subtract Immediate from Word
Rdh:Rdl ← Rdh:Rdl - K
Z,C,N,V,S
2
AND
Rd, Rr
Logical AND Registers
Rd ← Rd • Rr
Z,N,V
1
ANDI
Rd, K
Logical AND Register and Constant
Rd ← Rd • K
Z,N,V
1
OR
Rd, Rr
Logical OR 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
SBR
Rd,K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
1
CBR
Rd,K
Clear Bit(s) in Register
Rd ← Rd • (0xFF - K)
Z,N,V
1
INC
Rd
Increment
Rd ← Rd + 1
Z,N,V
1
DEC
Rd
Decrement
Rd ← Rd − 1
Z,N,V
1
TST
Rd
Test for Zero or Minus
Rd ← Rd • Rd
Z,N,V
1
CLR
Rd
Clear Register
Rd ← Rd ⊕ Rd
Z,N,V
1
SER
Rd
Set Register
Rd ← 0xFF
None
1
2
BRANCH INSTRUCTIONS
RJMP
k
IJMP
RCALL
k
Relative Jump
PC ← PC + k + 1
None
Indirect Jump to (Z)
PC ← Z
None
2
Relative Subroutine Call
PC ← PC + k + 1
None
3
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
CPSE
Rd,Rr
4
1/2/3
CP
Rd,Rr
Compare
Rd − Rr
Z, N,V,C,H
1
CPC
Rd,Rr
Compare with Carry
Rd − Rr − C
Z, N,V,C,H
1
CPI
Rd,K
Compare Register with Immediate
Rd − K
Z, N,V,C,H
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ← PC + 2 or 3
None
1
1/2/3
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC ← PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b)=0) PC ← PC + 2 or 3
None
1/2/3
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
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
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V= 0) then PC ← PC + k + 1
None
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
2
BIT AND BIT-TEST INSTRUCTIONS
SBI
P,b
Set Bit in I/O Register
I/O(P,b) ← 1
None
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
215
8006H–AVR–10/09
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
ASR
Rd
Arithmetic Shift Right
Rd(n) ← Rd(n+1), n=0..6
Z,C,N,V
1
1
SWAP
Rd
Swap Nibbles
Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0)
None
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
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
1
Rd, Rr
Copy Register Word
Rd ← Rr
Rd+1:Rd ← Rr+1:Rr
None
MOVW
None
1
LDI
Rd, K
Load Immediate
Rd ← K
None
1
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ← X - 1, Rd ← (X)
None
2
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
2
ST
Y+, Rr
Store Indirect and Post-Inc.
(Y) ← Rr, Y ← Y + 1
None
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
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
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
Load Program Memory
Rd ← (Z)
None
3
3
LPM
LPM
Rd, Z
LPM
Rd, Z+
SPM
Load Program Memory and Post-Inc
Rd ← (Z), Z ← Z+1
None
Store Program Memory
(z) ← R1:R0
None
IN
Rd, P
In Port
Rd ← P
None
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
1
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
216
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
24. Ordering Information
24.1
ATtiny24
Speed (MHz)
10
20
Notes:
Power Supply
Ordering Code(1)
Package(2)
1.8 - 5.5V
ATtiny24V-10SSU
ATtiny24V-10PU
ATtiny24V-10MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATtiny24-20SSU
ATtiny24-20PU
ATtiny24-20MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also
Halide free and fully Green.
Package Type
14S1
14-lead, 0.150" Wide Body, Plastic Gull Wing Small Outline Package (SOIC)
14P3
14-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
20M1
20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
217
8006H–AVR–10/09
24.2
ATtiny44
Speed (MHz)
Power Supply
Ordering Code(1)
Package(2)
10
1.8 - 5.5V
ATtiny44V-10SSU
ATtiny44V-10PU
ATtiny44V-10MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
20
2.7 - 5.5V
ATtiny44-20SSU
ATtiny44-20PU
ATtiny44-20MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
Notes:
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also
Halide free and fully Green.
Package Type
14S1
14-lead, 0.150" Wide Body, Plastic Gull Wing Small Outline Package (SOIC)
14P3
14-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
20M1
20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
218
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
24.3
ATtiny84
Speed (MHz)
Power Supply
Ordering Code(1)
Package(2)
10
1.8 - 5.5V
ATtiny84V-10SSU
ATtiny84V-10PU
ATtiny84V-10MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
20
2.7 - 5.5V
ATtiny84-20SSU
ATtiny84-20PU
ATtiny84-20MU
14S1
14P3
20M1
Industrial
(-40°C to 85°C)
Notes:
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also
Halide free and fully Green.
Package Type
14S1
14-lead, 0.150" Wide Body, Plastic Gull Wing Small Outline Package (SOIC)
14P3
14-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
20M1
20-pad, 4 x 4 x 0.8 mm Body, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
219
8006H–AVR–10/09
25. Packaging Information
25.1
20M1
D
1
Pin 1 ID
2
SIDE VIEW
E
3
TOP VIEW
A2
D2
A1
A
0.08
1
2
Pin #1
Notch
(0.20 R)
3
COMMON DIMENSIONS
(Unit of Measure = mm)
E2
b
L
e
BOTTOM VIEW
SYMBOL
MIN
A
0.70
0.75
0.80
A1
–
0.01
0.05
A2
b
D
D2
E2
L
MAX
NOTE
0.23
0.30
4.00 BSC
2.45
2.60
2.75
4.00 BSC
2.45
e
Reference JEDEC Standard MO-220, Fig. 1 (SAW Singulation) WGGD-5.
NOM
0.20 REF
0.18
E
Note:
C
2.60
2.75
0.50 BSC
0.35
0.40
0.55
10/27/04
R
220
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20M1, 20-pad, 4 x 4 x 0.8 mm Body, Lead Pitch 0.50 mm,
2.6 mm Exposed Pad, Micro Lead Frame Package (MLF)
DRAWING NO.
20M1
REV.
A
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
25.2
14P3
D
PIN
1
E1
A
SEATING PLANE
A1
L
B
B1
e
E
COMMON DIMENSIONS
(Unit of Measure = mm)
C
eC
eB
Notes:
1. This package conforms to JEDEC reference MS-001, Variation AA.
2. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25 mm (0.010").
MIN
NOM
MAX
A
–
–
5.334
A1
0.381
–
–
D
18.669
–
19.685
E
7.620
–
8.255
E1
6.096
–
7.112
B
0.356
–
0.559
B1
1.143
–
1.778
L
2.921
–
3.810
C
0.203
–
0.356
eB
–
–
10.922
eC
0.000
–
1.524
SYMBOL
e
NOTE
Note 2
Note 2
2.540 TYP
11/02/05
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
14P3, 14-lead (0.300"/7.62 mm Wide) Plastic Dual
Inline Package (PDIP)
DRAWING NO.
14P3
REV.
A
221
8006H–AVR–10/09
25.3
14S1
1
E
H
E
N
L
Top View
End View
e
COMMON DIMENSIONS
(Unit of Measure = mm/inches)
b
SYMBOL
A1
A
D
Side View
NOM
MAX
–
1.75/0.0688
NOTE
1.35/0.0532
A1
0.1/.0040
–
0.25/0.0098
b
0.33/0.0130
–
0.5/0.0200 5
D
8.55/0.3367
–
8.74/0.3444
2
E
3.8/0.1497
–
3.99/0.1574
3
H
5.8/0.2284
–
6.19/0.2440
L
0.41/0.0160
–
1.27/0.0500
e
Notes:
MIN
A
4
1.27/0.050 BSC
1. This drawing is for general information only; refer to JEDEC Drawing MS-012, Variation AB for additional information.
2. Dimension D does not include mold Flash, protrusions or gate burrs. Mold Flash, protrusion and gate burrs shall not
exceed 0.15 mm (0.006") per side.
3. Dimension E does not include inter-lead Flash or protrusion. Inter-lead flash and protrusions shall not exceed 0.25 mm
(0.010") per side.
4. L is the length of the terminal for soldering to a substrate.
5. The lead width B, as measured 0.36 mm (0.014") or greater above the seating plane, shall not exceed a maximum value
of 0.61 mm (0.024") per side.
2/5/02
TITLE
R
222
2325 Orchard Parkway
San Jose, CA 95131
DRAWING NO.
14S1, 14-lead, 0.150" Wide Body, Plastic Gull
Wing Small Outline Package (SOIC)
14S1
REV.
A
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
26. Errata
The revision letters in this section refer to the revision of the corresponding ATtiny24/44/84
device.
26.1
26.1.1
ATtiny24
Rev. D – E
No known errata.
26.1.2
Rev. C
• Reading EEPROM when system clock frequency is below 900 kHz may not work
1. Reading EEPROM when system clock frequency is below 900 kHz may not work
Reading data from the EEPROM at system clock frequency below 900 kHz may result in
wrong data read.
Problem Fix/Work around
Avoid using the EEPROM at clock frequency below 900 kHz.
26.1.3
Rev. B
• EEPROM read from application code does not work in Lock Bit Mode 3
• Reading EEPROM when system clock frequency is below 900 kHz may not work
1. EEPROM read from application code does not work in Lock Bit Mode 3
When the Memory Lock Bits LB2 and LB1 are programmed to mode 3, EEPROM read does
not work from the application code.
Problem Fix/Work around
Do not set Lock Bit Protection Mode 3 when the application code needs to read from
EEPROM.
2. Reading EEPROM when system clock frequency is below 900 kHz may not work
Reading data from the EEPROM at system clock frequency below 900 kHz may result in
wrong data read.
Problem Fix/Work around
Avoid using the EEPROM at clock frequency below 900 kHz.
26.1.4
Rev. A
Not sampled.
223
8006H–AVR–10/09
26.2
26.2.1
ATtiny44
Rev. B – D
No known errata.
26.2.2
Rev. A
• Reading EEPROM when system clock frequency is below 900 kHz may not work
1. Reading EEPROM when system clock frequency is below 900 kHz may not work
Reading data from the EEPROM at system clock frequency below 900 kHz may result in
wrong data read.
Problem Fix/Work around
Avoid using the EEPROM at clock frequency below 900 kHz.
224
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
26.3
26.3.1
ATtiny84
Rev. A – B
No known errata.
225
8006H–AVR–10/09
27. Datasheet Revision History
27.1
Rev H. 10/09
1. Updated document template. Re-arranged some sections.
2. Updated “Low-Frequency Crystal Oscillator” with the Table 6-8 on page 28
3. Updated Tables:
– “Active Clock Domains and Wake-up Sources in Different Sleep Modes” on page 33
– “DC Characteristics” on page 174
– “Register Summary” on page 213
4. Updated Register Description:
– “ADMUX – ADC Multiplexer Selection Register” on page 145
5. Signature Imprint Reading Instructions updated in “Reading Device Signature Imprint
Table from Firmware” on page 156.
6. Updated Section:
– Step 1. on page 164
7. Added Table:
– “Analog Comparator Characteristics” on page 179
8. Updated Figure:
– “Active Supply Current vs. frequency (1 - 20 MHz)” on page 187
9. Updated Figure 21-30 on page 201 and Figure 21-33 on page 202 under “Pin Threshold and Hysteresis”.
10. Changed ATtiny24/44 device status to “Not Recommended for New Designs. Use:
ATtiny24A/44A”.
27.2
Rev G. 01/08
1. Updated sections:
– “Features” on page 1
– “RESET” on page 3
– “Overview” on page 4
– “About” on page 6
– “SPH and SPL — Stack Pointer Register” on page 11
– “Atomic Byte Programming” on page 17
– “Write” on page 17
– “Clock Sources” on page 25
– “Default Clock Source” on page 30
– “Sleep Modes” on page 33
– “Software BOD Disable” on page 34
– “External Interrupts” on page 49
– “USIBR – USI Data Buffer” on page 125
– “USIDR – USI Data Register” on page 124
– “DIDR0 – Digital Input Disable Register 0” on page 131
– “Features” on page 132
226
ATtiny24/44/84
8006H–AVR–10/09
ATtiny24/44/84
– “Prescaling and Conversion Timing” on page 135
– “Temperature Measurement” on page 144
– “ADMUX – ADC Multiplexer Selection Register” on page 145
– “Limitations of debugWIRE” on page 152
– “Reading Lock, Fuse and Signature Data from Software” on page 155
– “Device Signature Imprint Table” on page 161
– “Enter High-voltage Serial Programming Mode” on page 168
– “Absolute Maximum Ratings*” on page 174
– “DC Characteristics” on page 174
– “Speed Grades” on page 175
– “Clock Characteristics” on page 176
– “Accuracy of Calibrated Internal RC Oscillator” on page 176
– “System and Reset Characteristics” on page 177
– “Supply Current of I/O Modules” on page 185
– “ATtiny24” on page 223
– “ATtiny44” on page 224
– “ATtiny84” on page 225
2. Updated bit definitions in sections:
– “MCUCR – MCU Control Register” on page 36
– “MCUCR – MCU Control Register” on page 51
– “MCUCR – MCU Control Register” on page 67
– “PINA – Port A Input Pins” on page 68
– “SPMCSR – Store Program Memory Control and Status Register” on page 157
– “Register Summary” on page 213
3. Updated Figures:
– “Reset Logic” on page 39
– “Watchdog Reset During Operation” on page 42
– “Compare Match Output Unit, Schematic (non-PWM Mode)” on page 95
– “Analog to Digital Converter Block Schematic” on page 133
– “ADC Timing Diagram, Free Running Conversion” on page 137
– “Analog Input Circuitry” on page 140
– “High-voltage Serial Programming” on page 167
– “Serial Programming Timing” on page 183
– “High-voltage Serial Programming Timing” on page 184
– “Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz)” on page 186
– “Active Supply Current vs. frequency (1 - 20 MHz)” on page 187
– “Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)” on page 187
– “Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)” on page 188
– “Active Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)” on page 188
– “Idle Supply Current vs. Low Frequency (0.1 - 1.0 MHz)” on page 189
– “Idle Supply Current vs. Frequency (1 - 20 MHz)” on page 189
227
8006H–AVR–10/09
– “Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)” on page 190
– “Idle Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)” on page 190
– “Idle Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)” on page 191
– “Power-down Supply Current vs. VCC (Watchdog Timer Disabled)” on page 191
– “Power-down Supply Current vs. VCC (Watchdog Timer Enabled)” on page 192
– “Reset Pin Input Hysteresis vs. VCC” on page 202
– “Reset Pin Input Hysteresis vs. VCC (Reset Pin Used as I/O)” on page 203
– “Watchdog Oscillator Frequency vs. VCC” on page 205
– “Watchdog Oscillator Frequency vs. Temperature” on page 205
– “Calibrated 8 MHz RC Oscillator Frequency vs. VCC” on page 206
– “Calibrated 8 MHz RC oscillator Frequency vs. Temperature” on page 206
– “ADC Current vs. VCC” on page 207
– “Programming Current vs. VCC (ATtiny24)” on page 209
– “Programming Current vs. VCC (ATtiny44)” on page 209
– “Programming Current vs. VCC (ATtiny84)” on page 210
4. Added Figures:
– “Reset Pin Output Voltage vs. Sink Current (VCC = 3V)” on page 198
– “Reset Pin Output Voltage vs. Sink Current (VCC = 5V)” on page 198
– “Reset Pin Output Voltage vs. Source Current (VCC = 3V)” on page 199
– “Reset Pin Output Voltage vs. Source Current (VCC = 5V)” on page 199
5. Updated Tables:
– “Device Clocking Options Select” on page 25
– “Start-up Times for the Crystal Oscillator Clock Selection” on page 29
– “Start-up Times for the Internal Calibrated RC Oscillator Clock Selection” on page 27
– “Start-up Times for the External Clock Selection” on page 26
– “Start-up Times for the 128 kHz Internal Oscillator” on page 27
– “Active Clock Domains and Wake-up Sources in Different Sleep Modes” on page 33
– “Watchdog Timer Prescale Select” on page 47
– “Reset and Interrupt Vectors” on page 48
– “Overriding Signals for Alternate Functions in PA7..PA5” on page 63
– “Overriding Signals for Alternate Functions in PA4..PA2” on page 64
– “Overriding Signals for Alternate Functions in PA1..PA0” on page 64
– “Port B Pins Alternate Functions” on page 65
– “Overriding Signals for Alternate Functions in PB3..PB2” on page 66
– “Overriding Signals for Alternate Functions in PB1..PB0” on page 67
– “Waveform Generation Modes” on page 110
– “ADC Conversion Time” on page 138
– “Temperature vs. Sensor Output Voltage (Typical Case)” on page 144
– “DC Characteristics. TA = -40°C to +85°C” on page 174
– “Calibration Accuracy of Internal RC Oscillator” on page 176
– “Reset, Brown-out, and Internal Voltage Characteristics” on page 177
228
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– “VBOT vs. BODLEVEL Fuse Coding” on page 179
– “ADC Characteristics, Single Ended Channels. T = -40°C - 85°C” on page 180
– “ADC Characteristics, Differential Channels (Bipolar Mode), TA = -40°C to 85°C” on
page 182
– “Serial Programming Characteristics, TA = -40°C to 85°C, VCC = 1.8 - 5.5V (Unless
Otherwise Noted)” on page 183
– “High-voltage Serial Programming Characteristics TA = 25°C, VCC = 5V (Unless
otherwise noted)” on page 184
6. Updated code examples in sections:
– “Write” on page 17
– “SPI Master Operation Example” on page 119
7. Updated “Ordering Information” in:
– “ATtiny84” on page 219
27.3
Rev F. 02/07
1.
2.
3.
4.
5.
6.
7.
8.
9.
27.4
Updated Figure 1-1 on page 2, Figure 8-7 on page 43, Figure 20-6 on page 184.
Updated Table 9-1 on page 48, Table 10-7 on page 65, Table 11-2 on page 80, Table
11-3 on page 81, Table 11-5 on page 81, Table 11-6 on page 82, Table 11-7 on page
82, Table 11-8 on page 83, Table 20-11 on page 182, Table 20-13 on page 184.
Updated table references in “TCCR0A – Timer/Counter Control Register A” on page 80.
Updated Port B, Bit 0 functions in “Alternate Functions of Port B” on page 65.
Updated WDTCR bit name to WDTCSR in assembly code examples.
Updated bit5 name in “TIFR1 – Timer/Counter Interrupt Flag Register 1” on page 114.
Updated bit5 in “TIFR1 – Timer/Counter Interrupt Flag Register 1” on page 114.
Updated “SPI Master Operation Example” on page 119.
Updated step 5 in “Enter High-voltage Serial Programming Mode” on page 168.
Rev E. 09/06
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
All characterization data moved to “Electrical Characteristics” on page 174.
All Register Descriptions gathered up in separate sections at the end of each chapter.
Updated “System Control and Reset” on page 39.
Updated Table 11-3 on page 81, Table 11-6 on page 82, Table 11-8 on page 83, Table
12-3 on page 109 and Table 12-5 on page 110.
Updated “Fast PWM Mode” on page 97.
Updated Figure 12-7 on page 98 and Figure 16-1 on page 133.
Updated “Analog Comparator Multiplexed Input” on page 129.
Added note in Table 19-12 on page 165.
Updated “Electrical Characteristics” on page 174.
Updated “Typical Characteristics” on page 185.
229
8006H–AVR–10/09
27.5
27.6
27.7
Rev D. 08/06
1.
2.
3.
4.
5.
6.
Updated “Calibrated Internal 8 MHz Oscillator” on page 26.
Updated “OSCCAL – Oscillator Calibration Register” on page 30.
Added Table 20-2 on page 176.
Updated code examples in “SPI Master Operation Example” on page 119.
Updated code examples in “SPI Slave Operation Example” on page 121.
Updated “Signature Bytes” on page 162.
1.
2.
3.
4.
Updated Features in “USI – Universal Serial Interface” on page 117.
Added “Clock speed considerations” on page 123.
Updated Bit description in “ADMUX – ADC Multiplexer Selection Register” on page 145.
Added note to Table 18-1 on page 157.
1.
2.
3.
Updated “Default Clock Source” on page 30
Updated “Power Reduction Register” on page 35.
Updated Table 20-4 on page 177, Table 9-4 on page 42, Table 16-3 on page 145,
Table 19-5 on page 161, Table 19-12 on page 165, Table 19-16 on page 171, Table 2011 on page 182.
Updated Features in “Analog to Digital Converter” on page 132.
Updated Operation in “Analog to Digital Converter” on page 132.
Updated “Temperature Measurement” on page 144.
Updated DC Characteristics in “Electrical Characteristics” on page 174.
Updated “Typical Characteristics” on page 185.
Updated “Errata” on page 223.
Rev C. 07/06
Rev B. 05/06
4.
5.
6.
7.
8.
9.
27.8
Rev A. 12/05
Initial revision.
230
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ATtiny24/44/84
Table of Contents
Features ..................................................................................................... 1
1
Pin Configurations ................................................................................... 2
1.1
Pin Descriptions .................................................................................................2
2
Overview ................................................................................................... 4
3
About ......................................................................................................... 6
4
5
6
7
3.1
Resources .........................................................................................................6
3.2
Code Examples .................................................................................................6
3.3
Data Retention ...................................................................................................6
3.4
Disclaimer ..........................................................................................................6
CPU Core .................................................................................................. 7
4.1
Architectural Overview .......................................................................................7
4.2
ALU – Arithmetic Logic Unit ...............................................................................8
4.3
Status Register ..................................................................................................8
4.4
General Purpose Register File ........................................................................10
4.5
Stack Pointer ...................................................................................................11
4.6
Instruction Execution Timing ...........................................................................12
4.7
Reset and Interrupt Handling ...........................................................................12
Memories ................................................................................................ 15
5.1
In-System Re-programmable Flash Program Memory ....................................15
5.2
SRAM Data Memory ........................................................................................15
5.3
EEPROM Data Memory ..................................................................................16
5.4
I/O Memory ......................................................................................................20
5.5
Register Description ........................................................................................20
Clock System ......................................................................................... 24
6.1
Clock Subsystems ...........................................................................................24
6.2
Clock Sources .................................................................................................25
6.3
System Clock Prescaler ..................................................................................30
6.4
Clock Output Buffer .........................................................................................30
6.5
Register Description ........................................................................................30
Power Management and Sleep Modes ................................................. 33
7.1
Sleep Modes ....................................................................................................33
7.2
Software BOD Disable .....................................................................................34
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8
9
7.3
Power Reduction Register ...............................................................................35
7.4
Minimizing Power Consumption ......................................................................35
7.5
Register Description ........................................................................................36
System Control and Reset .................................................................... 39
8.1
Resetting the AVR ...........................................................................................39
8.2
Reset Sources .................................................................................................40
8.3
Internal Voltage Reference ..............................................................................42
8.4
Watchdog Timer ..............................................................................................42
8.5
Register Description ........................................................................................45
Interrupts ................................................................................................ 48
9.1
Interrupt Vectors ..............................................................................................48
9.2
External Interrupts ...........................................................................................49
9.3
Register Description ........................................................................................51
10 I/O Ports .................................................................................................. 54
10.1
Ports as General Digital I/O .............................................................................55
10.2
Alternate Port Functions ..................................................................................58
10.3
Register Description ........................................................................................67
11 8-bit Timer/Counter0 with PWM ............................................................ 69
11.1
Features ..........................................................................................................69
11.2
Overview ..........................................................................................................69
11.3
Clock Sources .................................................................................................70
11.4
Counter Unit ....................................................................................................70
11.5
Output Compare Unit .......................................................................................71
11.6
Compare Match Output Unit ............................................................................73
11.7
Modes of Operation .........................................................................................74
11.8
Timer/Counter Timing Diagrams .....................................................................78
11.9
Register Description ........................................................................................80
12 16-bit Timer/Counter1 ............................................................................ 87
ii
12.1
Features ..........................................................................................................87
12.2
Overview ..........................................................................................................87
12.3
Timer/Counter Clock Sources .........................................................................89
12.4
Counter Unit ....................................................................................................89
12.5
Input Capture Unit ...........................................................................................90
12.6
Output Compare Units .....................................................................................92
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12.7
Compare Match Output Unit ............................................................................94
12.8
Modes of Operation .........................................................................................96
12.9
Timer/Counter Timing Diagrams ...................................................................103
12.10
Accessing 16-bit Registers ............................................................................105
12.11
Register Description ......................................................................................108
13 Timer/Counter Prescaler ..................................................................... 115
13.1
Prescaler Reset .............................................................................................115
13.2
External Clock Source ...................................................................................115
13.3
Register Description ......................................................................................116
14 USI – Universal Serial Interface .......................................................... 117
14.1
Features ........................................................................................................117
14.2
Overview ........................................................................................................117
14.3
Functional Descriptions .................................................................................118
14.4
Alternative USI Usage ...................................................................................124
14.5
Register Descriptions ....................................................................................124
15 Analog Comparator ............................................................................. 129
15.1
Analog Comparator Multiplexed Input ...........................................................129
15.2
Register Description ......................................................................................130
16 Analog to Digital Converter ................................................................ 132
16.1
Features ........................................................................................................132
16.2
Overview ........................................................................................................132
16.3
Operation .......................................................................................................133
16.4
Starting a Conversion ....................................................................................134
16.5
Prescaling and Conversion Timing ................................................................135
16.6
Changing Channel or Reference Selection ...................................................138
16.7
ADC Noise Canceler .....................................................................................139
16.8
Analog Input Circuitry ....................................................................................139
16.9
Noise Canceling Techniques .........................................................................140
16.10
ADC Accuracy Definitions .............................................................................140
16.11
ADC Conversion Result .................................................................................143
16.12
Temperature Measurement ...........................................................................144
16.13
Register Description ......................................................................................145
17 debugWIRE On-chip Debug System .................................................. 151
17.1
Features ........................................................................................................151
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17.2
Overview ........................................................................................................151
17.3
Physical Interface ..........................................................................................151
17.4
Software Break Points ...................................................................................152
17.5
Limitations of debugWIRE .............................................................................152
17.6
Register Description ......................................................................................152
18 Self-Programming the Flash ............................................................... 153
18.1
Performing Page Erase by SPM ....................................................................153
18.2
Filling the Temporary Buffer (Page Loading) .................................................153
18.3
Performing a Page Write ...............................................................................154
18.4
Addressing the Flash During Self-Programming ...........................................154
18.5
EEPROM Write Prevents Writing to SPMCSR ..............................................155
18.6
Reading Lock, Fuse and Signature Data from Software ...............................155
18.7
Preventing Flash Corruption ..........................................................................157
18.8
Programming Time for Flash when Using SPM ............................................157
18.9
Register Description ......................................................................................157
19 Memory Programming ......................................................................... 159
19.1
Program And Data Memory Lock Bits ...........................................................159
19.2
Fuse Bytes .....................................................................................................160
19.3
Device Signature Imprint Table .....................................................................161
19.4
Page Size ......................................................................................................162
19.5
Serial Programming .......................................................................................163
19.6
High-voltage Serial Programming ..................................................................167
19.7
High-Voltage Serial Programming Algorithm .................................................168
20 Electrical Characteristics .................................................................... 174
20.1
Absolute Maximum Ratings* .........................................................................174
20.2
DC Characteristics .........................................................................................174
20.3
Speed Grades ...............................................................................................175
20.4
Clock Characteristics .....................................................................................176
20.5
System and Reset Characteristics ................................................................177
20.6
Analog Comparator Characteristics ...............................................................179
20.7
ADC Characteristics – Preliminary Data ........................................................180
20.8
Serial Programming Characteristics ..............................................................183
20.9
High-Voltage Serial Programming Characteristics ........................................184
21 Typical Characteristics ........................................................................ 185
21.1
iv
Supply Current of I/O Modules ......................................................................185
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21.2
Active Supply Current ....................................................................................186
21.3
Idle Supply Current ........................................................................................189
21.4
Power-down Supply Current ..........................................................................191
21.5
Standby Supply Current ................................................................................192
21.6
Pin Pull-up .....................................................................................................193
21.7
Pin Driver Strength ........................................................................................196
21.8
Pin Threshold and Hysteresis ........................................................................200
21.9
BOD Threshold and Analog Comparator Offset ............................................203
21.10
Internal Oscillator Speed ...............................................................................205
21.11
Current Consumption of Peripheral Units ......................................................207
21.12
Current Consumption in Reset and Reset Pulsewidth ..................................211
22 Register Summary ............................................................................... 213
23 Instruction Set Summary .................................................................... 215
24 Ordering Information ........................................................................... 217
24.1
ATtiny24 ........................................................................................................217
24.2
ATtiny44 ........................................................................................................218
24.3
ATtiny84 ........................................................................................................219
25 Packaging Information ........................................................................ 220
25.1
20M1 ..............................................................................................................220
25.2
14P3 ..............................................................................................................221
25.3
14S1 ..............................................................................................................222
26 Errata ..................................................................................................... 223
26.1
ATtiny24 ........................................................................................................223
26.2
ATtiny44 ........................................................................................................224
26.3
ATtiny84 ........................................................................................................225
27 Datasheet Revision History ................................................................ 226
27.1
Rev H. 09/09 ..................................................................................................226
27.2
Rev G. 01/08 .................................................................................................226
27.3
Rev F. 02/07 ..................................................................................................229
27.4
Rev E. 09/06 ..................................................................................................229
27.5
Rev D. 08/06 ..................................................................................................229
27.6
Rev C. 07/06 ..................................................................................................230
27.7
Rev B. 05/06 ..................................................................................................230
27.8
Rev A. 12/05 ..................................................................................................230
v
8006H–AVR–10/09
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8006H–AVR–10/09