Features
• Utilizes the AVR® RISC Architecture
• AVR – High-performance and Low-power RISC Architecture
•
•
•
•
•
•
•
– 120 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 20 MIPS Throughput at 20 MHz
Data and Non-volatile Program and Data Memories
– 2K Bytes of In-System Self Programmable Flash
Endurance 10,000 Write/Erase Cycles
– 128 Bytes In-System Programmable EEPROM
Endurance: 100,000 Write/Erase Cycles
– 128 Bytes Internal SRAM
– Programming Lock for Flash Program and EEPROM Data Security
Peripheral Features
– One 8-bit Timer/Counter with Separate Prescaler and Compare Mode
– One 16-bit Timer/Counter with Separate Prescaler, Compare and Capture Modes
– Four PWM Channels
– On-chip Analog Comparator
– Programmable Watchdog Timer with On-chip Oscillator
– USI – Universal Serial Interface
– Full Duplex USART
Special Microcontroller Features
– debugWIRE On-chip Debugging
– In-System Programmable via SPI Port
– External and Internal Interrupt Sources
– Low-power Idle, Power-down, and Standby Modes
– Enhanced Power-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated Oscillator
I/O and Packages
– 18 Programmable I/O Lines
– 20-pin PDIP, 20-pin SOIC, and 32-pin MLF
Operating Voltages
– 1.8 - 5.5V (ATtiny2313V)
– 2.7 - 5.5V (ATtiny2313)
Speed Grades
– ATtiny2313V: 0 - 4 MHz @ 1.8 - 5.5V, 0 - 10 MHz @ 2.7 - 5.5V
– ATtiny2313: 0 - 10 MHz @ 2.7 - 5.5V, 0 - 20 MHz @ 4.5 - 5.5V
Typical Power Consumption
– Active Mode
1 MHz, 1.8V: 230 µA
32 kHz, 1.8V: 20 µA (including oscillator)
– Power-down Mode
< 0.1 µA at 1.8V
8-bit
Microcontroller
with 2K Bytes
In-System
Programmable
Flash
ATtiny2313/V
Preliminary
Rev. 2543F–AVR–08/04
Pin Configurations
Figure 1. Pinout ATtiny2313
PDIP/SOIC
(RESET/dW)PA2
(RXD)PD0
(TXD)PD1
(XTAL2)PA1
(XTAL1)PA0
(CKOUT/XCK/INT0)PD2
(INT1)PD3
(T0)PD4
(OC0B/T1)PD5
GND
Overview
2
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
VCC
PB7(UCSK/SCK/PCINT7)
PB6(MISO/DO/PCINT6)
PB5(MOSI/DI/SDA/PCINT5)
PB4(OC1B/PCINT4)
PB3(OC1A/PCINT3)
PB2(OC0A/PCINT2)
PB1(AIN1/PCINT1)
PB0(AIN0/PCINT0)
PD6(ICP)
The ATtiny2313 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 ATtiny2313 achieves throughputs approaching 1 MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Block Diagram
Figure 2. Block Diagram
XTAL1
XTAL2
PA0 - PA2
PORTA DRIVERS
VCC
DATA DIR.
REG. PORTA
DATA REGISTER
PORTA
8-BIT DATA BUS
INTERNAL
CALIBRATED
OSCILLATOR
INTERNAL
OSCILLATOR
OSCILLATOR
WATCHDOG
TIMER
TIMING AND
CONTROL
GND
PROGRAM
COUNTER
STACK
POINTER
PROGRAM
FLASH
SRAM
MCU CONTROL
REGISTER
ON-CHIP
DEBUGGER
MCU STATUS
REGISTER
INSTRUCTION
REGISTER
GENERAL
PURPOSE
REGISTER
RESET
TIMER/
COUNTERS
INTERRUPT
UNIT
INSTRUCTION
DECODER
EEPROM
CONTROL
LINES
ALU
USI
STATUS
REGISTER
ANALOG
COMPARATOR
PROGRAMMING
LOGIC
SPI
DATA REGISTER
PORTB
USART
DATA DIR.
REG. PORTB
DATA REGISTER
PORTD
DATA DIR.
REG. PORTD
PORTB DRIVERS
PORTD DRIVERS
PB0 - PB7
PD0 - PD6
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The AVR core combines a rich instruction set with 32 general purpose working registers.
All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing
two independent registers to be accessed in one single instruction executed in one clock
cycle. The resulting architecture is more code efficient while achieving throughputs up to
ten times faster than conventional CISC microcontrollers.
The ATtiny2313 provides the following features: 2K bytes of In-System Programmable
Flash, 128 bytes EEPROM, 128 bytes SRAM, 18 general purpose I/O lines, 32 general
purpose working registers, a single-wire Interface for On-chip Debugging, two flexible
Timer/Counters with compare modes, internal and external interrupts, a serial programmable USART, Universal Serial Interface with Start Condition Detector, a programmable
Watchdog Timer with internal Oscillator, and three software selectable power saving
modes. The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, and
interrupt system to continue functioning. The Power-down mode saves the register contents but freezes the Oscillator, disabling all other chip functions until the next interrupt
or hardware reset. In Standby mode, the crystal/resonator Oscillator is running while the
rest of the device is sleeping. This allows very fast start-up combined with low-power
consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology.
The On-chip ISP Flash allows the program memory to be reprogrammed In-System
through an SPI serial interface, or by a conventional non-volatile memory programmer.
By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip, the Atmel ATtiny2313 is a powerful microcontroller that provides a highly
flexible and cost effective solution to many embedded control applications.
The ATtiny2313 AVR is supported with a full suite of program and system development
tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators, and Evaluation kits.
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2543F–AVR–08/04
ATtiny2313/V
Pin Descriptions
VCC
Digital supply voltage.
GND
Ground.
Port A (PA2..PA0)
Port A is a 3-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 also serves the functions of various special features of the ATtiny2313 as listed
on page 52.
Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port B output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port B pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port B also serves the functions of various special features of the ATtiny2313 as listed
on page 52.
Port D (PD6..PD0)
Port D is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port D output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port D pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port D also serves the functions of various special features of the ATtiny2313 as listed
on page 55.
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in Table
15 on page 33. Shorter pulses are not guaranteed to generate a reset. The Reset Input
is an alternate function for PA2 and dW.
XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
XTAL1 is an alternate function for PA0.
XTAL2
Output from the inverting Oscillator amplifier. XTAL2 is an alternate function for PA1.
About Code
Examples
This documentation contains simple code examples that briefly show how to use various
parts of the device. These code examples assume that the part specific header file is
included before compilation. Be aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please
confirm with the C compiler documentation for more details.
Disclaimer
Typical values contained in this data sheet 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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2543F–AVR–08/04
AVR CPU Core
Introduction
This section discusses the AVR core architecture in general. The main function of the
CPU core is to ensure correct program execution. The CPU must therefore be able to
access memories, perform calculations, control peripherals, and handle interrupts.
Architectural Overview
Figure 3. 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
SPI
Unit
Watchdog
Timer
ALU
Analog
Comparator
I/O Module1
Data
SRAM
I/O Module 2
I/O Module n
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture
– with separate memories and buses for program and data. Instructions in the program
memory are executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept
enables instructions to be executed in every clock cycle. The program memory is InSystem Reprogrammable Flash memory.
The fast-access Register File contains 32 x 8-bit general purpose working registers with
a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU)
operation. In a typical ALU operation, two operands are output from the Register File,
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ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
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,
able to directly address the whole address space. Most AVR instructions have a single
16-bit word format. Every program memory address contains a 16- or 32-bit instruction.
During interrupts and subroutine calls, the return address Program Counter (PC) is
stored on the Stack. The Stack is effectively allocated in the general data SRAM, and
consequently the Stack size is only limited by the total SRAM size and the usage of the
SRAM. All user programs must initialize the SP in the Reset routine (before subroutines
or interrupts are executed). The Stack Pointer (SP) is read/write accessible in the I/O
space. The data SRAM can easily be accessed through the five different addressing
modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional
Global Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt
Vector in the Interrupt Vector table. The interrupts have priority in accordance with their
Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control
Registers, 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.
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.
Status Register
The Status Register contains information about the result of the most recently executed
arithmetic instruction. This information can be used for altering program flow in order to
perform conditional operations. Note that the Status Register is updated after all ALU
operations, as specified in the Instruction Set Reference. This will in many cases
remove the need for using the dedicated compare instructions, resulting in faster and
more compact code.
The Status Register is not automatically stored when entering an interrupt routine and
restored when returning from an interrupt. This must be handled by software.
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2543F–AVR–08/04
The AVR Status Register – SREG – is defined as:
Bit
7
6
5
4
3
2
1
0
I
T
H
S
V
N
Z
C
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SREG
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global
Interrupt Enable 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 Ibit 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.
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 shows the structure of the 32 general purpose working registers in the CPU.
8
ATtiny2313/V
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ATtiny2313/V
Figure 4. 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, 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.
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 5.
Figure 5. The X-, Y-, and Z-registers
15
X-register
XH
7
XL
0
R27 (0x1B)
15
Y-register
YH
7
YL
0
0
7
0
R28 (0x1C)
15
ZH
7
0
R31 (0x1F)
0
R26 (0x1A)
R29 (0x1D)
Z-register
0
7
ZL
7
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).
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Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for
storing return addresses after interrupts and subroutine calls. The Stack Pointer Register always points to the top of the Stack. Note that the Stack is implemented as growing
from higher memory locations to lower memory locations. This implies that a Stack
PUSH command decreases the Stack Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt Stacks are located. This Stack space in the data SRAM must be defined by the
program before any subroutine calls are executed or interrupts are enabled. The Stack
Pointer must be set to point above 0x60. The Stack Pointer is decremented by one
when data is pushed onto the Stack with the PUSH instruction, and it is decremented by
two when the return address is pushed onto the Stack with subroutine call or interrupt.
The Stack Pointer is incremented by one when data is popped from the Stack with the
POP instruction, and it is incremented by two when data is popped from the Stack with
return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is implementation dependent. Note that the data space in some
implementations of the AVR architecture is so small that only SPL is needed. In this
case, the SPH Register will not be present.
Bit
Read/Write
Initial Value
Instruction Execution
Timing
15
14
13
12
11
10
9
–
–
–
–
–
–
–
8
–
SPH
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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 6 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 6. 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 7 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.
10
ATtiny2313/V
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ATtiny2313/V
Figure 7. Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
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 43.
The list also determines the priority levels of the different interrupts. The lower the
address the higher is the priority level. RESET has the highest priority, and next is INT0
– the External Interrupt Request 0. Refer to “Interrupts” on page 43 for more information.
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 simulta-
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neously 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 */
__disable_interrupt();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
When using the SEI instruction to enable interrupts, the instruction following SEI will be
executed before any pending interrupts, as shown in this example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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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ATtiny2313/V
AVR ATtiny2313
Memories
This section describes the different memories in the ATtiny2313. The AVR architecture
has two main memory spaces, the Data Memory and the Program Memory space. In
addition, the ATtiny2313 features an EEPROM Memory for data storage. All three memory spaces are linear and regular.
In-System
Reprogrammable Flash
Program Memory
The ATtiny2313 contains 2K bytes 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 1K x 16.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The
ATtiny2313 Program Counter (PC) is 10 bits wide, thus addressing the 1K program
memory locations. “Memory Programming” on page 157 contains a detailed description
on Flash data serial downloading using the SPI pins.
Constant tables can be allocated within the entire program memory address space (see
the LPM – Load Program Memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 10.
Figure 8. Program Memory Map
Program Memory
0x0000
0x03FF
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SRAM Data Memory
Figure 9 shows how the ATtiny2313 SRAM Memory is organized.
The lower 224 data memory locations address both the Register File, the I/O memory,
Extended I/O memory, and the internal data SRAM. The first 32 locations address the
Register File, the next 64 location the standard I/O memory, and the next 128 locations
address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In
the Register File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base
address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and postincrement, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 128 bytes of internal data SRAM in the ATtiny2313 are all accessible through all these addressing
modes. The Register File is described in “General Purpose Register File” on page 8.
Figure 9. Data Memory Map
Data Memory
32 Registers
64 I/O Registers
0x0000 - 0x001F
0x0020 - 0x005F
0x0060
Internal SRAM
(128 x 8)
0x00DF
Data Memory Access Times
14
This section describes the general access timing concepts for internal memory access.
The internal data SRAM access is performed in two clkCPU cycles as described in Figure
10.
ATtiny2313/V
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ATtiny2313/V
Figure 10. On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Address valid
Compute Address
Write
Data
WR
Read
Data
RD
Memory Access Instruction
Next Instruction
EEPROM Data Memory
The ATtiny2313 contains 128 bytes of data EEPROM memory. It is organized as a separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM
and the CPU is described in the following, specifying the EEPROM Address Registers,
the EEPROM Data Register, and the EEPROM Control Register. For a detailed description of Serial data downloading to the EEPROM, see page 171.
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 1. A self-timing function, however, lets the user software detect when the next byte can be written. If the user code
contains instructions that write the EEPROM, some precautions must be taken. In
heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This
causes the device for some period of time to run at a voltage lower than specified as
minimum for the clock frequency used. See “Preventing EEPROM Corruption” on page
19. for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the EEPROM Control Register 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.
The EEPROM Address
Register
Bit
7
6
5
4
3
2
1
0
–
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
X
X
X
X
X
X
X
EEAR
• Bit 7 – Res: Reserved Bit
This bit is reserved in the ATtiny2313 and will always read as zero.
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2543F–AVR–08/04
• Bits 6..0 – EEAR6..0: EEPROM Address
The EEPROM Address Register – EEAR specify the EEPROM address in the 128 bytes
EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 127.
The initial value of EEAR is undefined. A proper value must be written before the
EEPROM may be accessed.
The EEPROM Data Register –
EEDR
Bit
7
6
5
4
3
2
1
0
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EEDR
• 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.
The EEPROM Control Register
– EECR
Bit
7
6
5
4
3
2
1
0
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
X
X
0
0
X
0
EECR
• Bits 7..6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313 and will always read as zero.
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bits setting defines which programming action that
will be triggered when writing EEPE. It is possible to program data in one atomic operation (erase the old value and program the new value) or to split the Erase and Write
operations in two different operations. The Programming times for the different modes
are shown in Table 1. While EEPE is set, any write to EEPMn will be ignored. During
reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming.
Table 1. EEPROM Mode Bits
EEPM1
EEPM0
Programming
Time
0
0
3.4 ms
Erase and Write in one operation (Atomic Operation)
0
1
1.8 ms
Erase Only
1
0
1.8 ms
Write Only
1
1
–
Operation
Reserved for future use
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set.
Writing EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a
constant interrupt when Non-volatile memory is ready for programming.
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ATtiny2313/V
• 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.
Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the
EEPROM, the user must write the address into the EEAR Register and data into EEDR
Register. If the EEPMn bits are zero, writing EEPE (within four cycles after EEMPE is
written) will trigger the erase/write operation. Both the erase and write cycle are done in
one operation and the total programming time is given in Table 1. The EEPE bit remains
set until the erase and write operations are completed. While the device is busy with
programming, it is not possible to do any other EEPROM operations.
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-consuming operations (typically after Power-up).
Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the EEPE (within four cycles after EEMPE is written) will trigger the erase operation
only (programming time is given in Table 1). The EEPE bit remains set until the erase
operation completes. While the device is busy programming, it is not possible to do any
other EEPROM operations.
Write
To write a location, the user must write the address into EEAR and the data into EEDR.
If the EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written)
will trigger the write operation only (programming time is given in Table 1). The EEPE bit
remains set until the write operation completes. If the location to be written has not been
erased before write, the data that is stored must be considered as lost. While the device
is busy with programming, it is not possible to do any other EEPROM operations.
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The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator frequency is within the requirements described in “Oscillator Calibration Register –
OSCCAL” on page 25.
The following code examples show one assembly and one C function for writing to 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 up address (r17) in address register
out EEAR, r17
; Write data (r16) to data register
out EEDR,r16
; 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 uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address and data registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
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ATtiny2313/V
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ATtiny2313/V
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,EEWE
rjmp EEPROM_read
; Set up address (r17) in address register
out EEAR, 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 uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
Preventing EEPROM
Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the EEPROM to operate properly. These issues are the
same as for board level systems using EEPROM, and the same design solutions should
be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too
low. First, a regular write sequence to the EEPROM requires a minimum voltage to
operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the
supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design
recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD). If the detection
level of the internal BOD does not match the needed detection level, an external low
VCC reset Protection circuit can be used. If a reset occurs while a write operation is in
progress, the write operation will be completed provided that the power supply voltage is
sufficient.
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I/O Memory
The I/O space definition of the ATtiny2313 is shown in “Register Summary” on page
209.
All ATtiny2313 I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between
the 32 general purpose working registers and the I/O space. I/O Registers within the
address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and
SBIC instructions. Refer to the instruction set section for more details. When using the
I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used.
When addressing I/O Registers as data space using LD and ST instructions, 0x20 must
be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the status flags are cleared by writing a logical one to them. Note that, unlike
most other AVRs, the CBI and SBI instructions will only operate on the specified bit, and
can therefore be used on registers containing such status flags. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
General Purpose I/O Registers The ATtiny2313 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 bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
General Purpose I/O Register
2 – GPIOR2
Bit
7
6
5
4
3
2
1
MSB
General Purpose I/O Register
1 – GPIOR1
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
7
6
5
4
3
2
1
Bit
MSB
General Purpose I/O Register
0 – GPIOR0
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
7
6
5
4
3
2
1
Bit
GPIOR2
0
LSB
MSB
20
0
LSB
GPIOR1
0
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GPIOR0
ATtiny2313/V
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ATtiny2313/V
System Clock and
Clock Options
Clock Systems and their
Distribution
Figure 11 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 29. The clock systems
are detailed below.
Figure 11. Clock Distribution
General I/O
Modules
clkI/O
CPU Core
AVR Clock
Control Unit
RAM
Flash and
EEPROM
clkCPU
clkFLASH
Reset Logic
Source clock
Watchdog Timer
Watchdog clock
Clock
Multiplexer
Watchdog
Oscillator
External Clock
Crystal
Oscillator
Calibrated RC
Oscillator
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR
core. Examples of such modules are the General Purpose Register File, the Status Register and the data memory holding the Stack Pointer. Halting the CPU clock inhibits the
core from performing general operations and calculations.
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, and
USART. 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. Also note that start condition detection in the USI
module is carried out asynchronously when clkI/O is halted, enabling USI start condition
detection in all sleep modes.
Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually
active simultaneously with the CPU clock.
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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 2. Device Clocking Select(1)
Device Clocking Option
CKSEL3..0
External Clock
0000
Calibrated Internal RC Oscillator 4MHz
0010
Calibrated internal RC Oscillator 8MHz
0100
Watchdog Oscillator 128kHz
0110
External Crystal/Ceramic Resonator
1000 - 1111
Reserved
Note:
0001/0011/0101/0111
1. For all fuses “1” means unprogrammed while “0” means programmed.
The various choices for each clocking option is given in the following sections. When the
CPU wakes up from Power-down, the selected clock source is used to time the start-up,
ensuring stable Oscillator operation before instruction execution starts. When the CPU
starts from reset, there is 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 3. The frequency of the Watchdog Oscillator is voltage
dependent as shown in “ATtiny2313 Typical Characteristics” on page 179.
Table 3. Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V)
Typ Time-out (VCC = 3.0V)
Number of Cycles
4.1 ms
4.3 ms
4K (4,096)
65 ms
69 ms
64K (65,536)
Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed.
The default clock source setting is the Internal RC Oscillator with longest start-up time
and an initial system clock prescaling of 8. This default setting ensures that all users can
make their desired clock source setting using an In-System or Parallel programmer.
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an On-chip Oscillator, as shown in Figure 12 on page 23. Either
a quartz crystal or a ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value
of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial guidelines for
choosing capacitors for use with crystals are given in Table 4 on page 23. For ceramic
resonators, the capacitor values given by the manufacturer should be used.
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ATtiny2313/V
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ATtiny2313/V
Figure 12. Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in
Table 4.
Table 4. Crystal Oscillator Operating Modes
CKSEL3..1
Frequency Range(1) (MHz)
Recommended Range for Capacitors C1
and C2 for Use with Crystals (pF)
100(2)
0.4 - 0.9
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 -
12 - 22
Notes:
1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown
in Table 5.
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2543F–AVR–08/04
Table 5. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
(1)
Additional Delay
from Reset
(VCC = 5.0V)
Recommended Usage
0
00
258 CK
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
258 CK(1)
14CK + 65 ms
Ceramic resonator,
slowly rising power
0
10
1K CK(2)
14CK
Ceramic resonator,
BOD enabled
0
11
1K CK(2)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K CK(2)
14CK + 65 ms
Ceramic resonator,
slowly rising power
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
11
16K CK
14CK + 65 ms
Crystal Oscillator,
slowly rising power
1
1
1
Notes:
Calibrated Internal RC
Oscillator
SUT1..0
Start-up Time from
Power-down and
Power-save
1. These options should only be used when not operating close to the maximum frequency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
The calibrated internal RC Oscillator provides a fixed 8.0 MHz clock. The frequency is
nominal value at 3V and 25°C. If 8 MHz frequency exceeds the specification of the
device (depends on VCC), the CKDIV8 Fuse must be programmed in order to divide the
internal frequency by 8 during start-up. The device is shipped with the CKDIV8 Fuse
programmed. This clock may be selected as the system clock by programming the
CKSEL Fuses as shown in Table 6. If selected, it will operate with no external components. During reset, hardware loads the calibration byte into the OSCCAL Register and
thereby automatically calibrates the RC Oscillator. At 3V and 25°C, this calibration gives
a frequency within ± 10% of the nominal frequency. Using calibration methods as
described in application notes available at www.atmel.com/avr it is possible to achieve ±
2% accuracy at any given VCC and Temperature. When this Oscillator is used as the
chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the
Reset Time-out. For more information on the pre-programmed calibration value, see the
section “Calibration Byte” on page 159.
Table 6. Internal Calibrated RC Oscillator Operating Modes
Note:
24
CKSEL3..0
Nominal Frequency
0010 - 0011
4.0 MHz(1)
0100 - 0101
8.0 MHz
1. The device is shipped with this option selected.
ATtiny2313/V
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ATtiny2313/V
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 7.
Table 7. Start-up times for the internal calibrated RC Oscillator clock selection
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
10(1)
6 CK
14CK + 65 ms
Slowly rising power
11
Note:
Oscillator Calibration Register
– OSCCAL
Recommended Usage
BOD enabled
Reserved
1. The device is shipped with this option selected.
Bit
Read/Write
Initial Value
7
6
5
4
3
2
1
0
–
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
OSCCAL
Device Specific Calibration Value
• Bits 6..0 – CAL6..0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the internal Oscillator to remove process variations from the Oscillator frequency. This is done automatically during Chip
Reset. When OSCCAL is zero, the lowest available frequency is chosen. Writing nonzero values to this register will increase the frequency of the internal Oscillator. Writing
0x7F to the register gives the highest available frequency. The calibrated Oscillator is
used to time EEPROM and Flash access. If EEPROM or Flash is written, do not calibrate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash
write may fail. Note that the Oscillator is intended for calibration to 8.0/4.0 MHz. Tuning
to other values is not guaranteed, as indicated in Table 8.
Avoid changing the calibration value in large steps when calibrating the Calibrated Internal RC Oscillator to ensure stable operation of the MCU. A variation in frequency of
more than 2% from one cycle to the next can lead to unpredictable behavior. Changes in
OSCCAL should not exceed 0x20 for each calibration.
Table 8. Internal RC Oscillator Frequency Range.
OSCCAL Value
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
0x00
50%
100%
0x3F
75%
150%
0x7F
100%
200%
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2543F–AVR–08/04
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in
Figure 13. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 13. External Clock Drive Configuration
NC
XTAL2
EXTERNAL
CLOCK
SIGNAL
XTAL1
GND
When this clock source is selected, start-up times are determined by the SUT Fuses as
shown in Table 10.
Table 9. Crystal Oscillator Clock Frequency
CKSEL3..0
Frequency Range
0000 - 0001
0 - 16 MHz
Table 10. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
10
6 CK
14CK + 65 ms
Slowly rising power
11
Recommended Usage
BOD enabled
Reserved
When applying an external clock, it is required to avoid sudden changes in the applied
clock frequency to ensure stable operation of the MCU. A variation in frequency of more
than 2% from one clock cycle to the next can lead to unpredictable 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.
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ATtiny2313/V
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ATtiny2313/V
128 kHz Internal
Oscillator
The 128 kHz Internal Oscillator is a low power Oscillator providing a clock of 128 kHz.
The frequency is nominal at 3 V and 25°C. This clock may be selected as the system
clock by programming the CKSEL Fuses to “0110 - 0111”.
When this clock source is selected, start-up times are determined by the SUT Fuses as
shown in Table 11.
Table 11. Start-up Times for the 128 kHz Internal Oscillator
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset
00
6 CK
14CK
01
6 CK
14CK + 4 ms
Fast rising power
10
6 CK
14CK + 64 ms
Slowly rising power
11
Clock Prescale Register –
CLKPR
Bit
Recommended Usage
BOD enabled
Reserved
7
6
5
4
3
2
1
0
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
CLKPR
See Bit Description
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The
CLKPCE bit is only updated when the other bits in CLKPR are simultaneously written to
zero. CLKPCE is cleared by hardware four cycles after it is written or when 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 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 12.
To avoid unintentional changes of clock frequency, a special write procedure must be
followed to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits
in CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to
CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits
are reset to “0011”, giving a division factor of 8 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 selected clock source has a higher
27
2543F–AVR–08/04
frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed.
Table 12. Clock Prescaler Select
28
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
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Power Management
and Sleep Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby
saving power. The AVR provides various sleep modes allowing the user to tailor the
power consumption to the application’s requirements.
To enter any of the three sleep modes, the SE bit in SMCR must be written to logic one
and a SLEEP instruction must be executed. The SM1 and SM0 bits in the MCUCR Register select which sleep mode (Idle, Power-down, or Standby) will be activated by the
SLEEP instruction. See Table 13 for a summary. If an enabled interrupt occurs while the
MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles in
addition to the start-up time, executes the interrupt routine, and resumes execution from
the instruction following SLEEP. The contents of the register file and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode, the
MCU wakes up and executes from the Reset Vector.
Figure 11 on page 21 presents the different clock systems in the ATtiny2313, and their
distribution. The figure is helpful in selecting an appropriate sleep mode.
MCU Control Register –
MCUCR
The Sleep Mode Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
PUD
SM1
SE
SM0
ISC11
ISC10
ISC01
ISC00
Read/Write
R
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 6, 4 – SM1..0: Sleep Mode Select Bits 1 and 0
These bits select between the five available sleep modes as shown in Table 13.
Table 13. Sleep Mode Select
Note:
SM1
SM0
Sleep Mode
0
0
Idle
0
1
Power-down
1
1
Power-down
1
0
Standby
1. Standby mode is only recommended for use with external crystals or resonators.
• 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.
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 the UART, Analog Comparator, ADC, USI,
Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep
mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as
internal ones like the Timer Overflow and UART Transmit Complete interrupts. If wakeup from the Analog Comparator interrupt is not required, the Analog Comparator can be
powered down by setting the ACD bit in the Analog Comparator Control and Status
Register – ACSR. This will reduce power consumption in Idle mode.
29
2543F–AVR–08/04
Power-down Mode
When the SM1..0 bits are written to 01 or 11, the SLEEP instruction makes the MCU
enter Power-down mode. In this mode, the external Oscillator is stopped, while the
external interrupts, the USI start condition detection, and the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, USI
start condition interrupt, an external level interrupt on INT0, or a pin change interrupt can
wake up the MCU. This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the
changed level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 58 for details.
When waking up from Power-down mode, there is a delay from the wake-up condition
occurs until the wake-up becomes effective. This allows the clock to restart and become
stable after having been stopped. The wake-up period is defined by the same CKSEL
Fuses that define the Reset Time-out period, as described in “Clock Sources” on page
22.
Standby Mode
When the SM1..0 bits are 10 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.
INT0, INT1 and
Pin Change
USI Start
Condition
SPM/EEPROM
Ready
Other I/O
X
X
X
X
X
X
X(2)
X
X(2)
X
Power-down
Standby(1)
Notes:
Wake-up Sources
Enabled
clkIO
Idle
Oscillators
clkCPU
Sleep Mode
Active Clock Domains
clkFLASH
Table 14. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
X
1. Only recommended with external crystal or resonator selected as clock source.
2. For INT0, only level interrupt.
Minimizing Power
Consumption
There are several issues to consider when trying to minimize the power consumption in
an AVR controlled system. In general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as possible of the device’s
functions are operating. All functions not needed should be disabled. In particular, the
following modules may need special consideration when trying to achieve the lowest
possible power consumption.
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. In
other sleep modes, the Analog Comparator is automatically disabled. However, if the
Analog Comparator is set up to use the Internal Voltage Reference as input, the Analog
Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep mode. Refer to “Analog Comparator” on
page 148 for details on how to configure the Analog Comparator.
30
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned
off. If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in
all sleep modes, and hence, always consume power. In the deeper sleep modes, this
will contribute significantly to the total current consumption. Refer to “Brown-out Detection” on page 34 for details on how to configure the Brown-out Detector.
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection or the Analog Comparator. If these modules are disabled as described in the
sections above, the internal voltage reference will be disabled and it will not be consuming power. When turned on again, the user must allow the reference to start up before
the output is used. If the reference is kept on in sleep mode, the output can be used
immediately. Refer to “Internal Voltage Reference” on page 37 for details on the start-up
time.
Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off.
If the Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence,
always consume power. In the deeper sleep modes, this will contribute significantly to
the total current consumption. Refer to “Interrupts” on page 43 for details on how to configure the Watchdog Timer.
Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power.
The most important is then to ensure that no pins drive resistive loads. In sleep modes
where the I/O clock (clkI/O) is stopped, the input buffers of the device will be disabled.
This ensures that no power is consumed by the input logic when not needed. In some
cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 49 for
details on which pins are enabled. If the input buffer is enabled and the input signal is
left floating or have 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 Registers (DIDR). Refer to “Digital Input Disable Register – DIDR” on page 149.
31
2543F–AVR–08/04
System Control and
Reset
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 an
RJMP – Relative Jump – instruction to the reset handling routine. If the program never
enables an interrupt source, the Interrupt Vectors are not used, and regular program
code can be placed at these locations. The circuit diagram in Figure 14 shows the reset
logic. Table 15 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source
goes active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the
internal reset. This allows the power to reach a stable level before normal operation
starts. The time-out period of the delay counter is defined by the user through the SUT
and CKSEL Fuses. The different selections for the delay period are presented in “Clock
Sources” on page 22.
Reset Sources
The ATtiny2313 has four sources of reset:
•
Power-on Reset. The MCU is reset when the supply voltage is below the Power-on
Reset threshold (VPOT).
•
External Reset. The MCU is reset when a low level is present on the RESET pin for
longer than the minimum pulse length.
•
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires, the
Watchdog is enabled, and Watchdog Interrupt is disabled.
•
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.
Figure 14. 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]
32
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table 15. Reset Characteristics
Symbol
Condition
Min(1)
Typ(1)
Max(1)
Units
Power-on Reset
Threshold Voltage
(rising)
TA = -40 - 85°C
1.2
V
Power-on Reset
Threshold Voltage
(falling)(2)
TA = -40 - 85°C
1.1
V
VRST
RESET Pin Threshold
Voltage
VCC = 1.8 - 5.5V
tRST
Minimum pulse width
on RESET Pin
VCC = 1.8 - 5.5V
VPOT
Notes:
Power-on Reset
Parameter
0.1 VCC
0.9 VCC
V
2.5
µs
1. Values are guidelines only. Actual values are TBD.
2. The Power-on Reset will not work unless the supply voltage has been below VPOT
(falling)
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level is defined in Table 15. 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 15. MCU Start-up, RESET Tied to VCC
VCC
RESET
TIME-OUT
VPOT
VRST
tTOUT
INTERNAL
RESET
33
2543F–AVR–08/04
Figure 16. MCU Start-up, RESET Extended Externally
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than the minimum pulse width (see Table 15) 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 17. External Reset During Operation
CC
Brown-out Detection
ATtiny2313 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.
Table 16. BODLEVEL Fuse Coding(1)
BODLEVEL 2..0 Fuses
34
Min VBOT
Typ VBOT
Max VBOT
111
BOD Disabled
110
1.8
101
2.7
100
4.3
Units
V
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table 16. BODLEVEL Fuse Coding(1)
BODLEVEL 2..0 Fuses
Min VBOT
Typ VBOT
Max VBOT
Units
011
010
Reserved
001
000
Note:
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.
The test is performed using BODLEVEL = 110 for ATtiny2313V and
BODLEVEL = 101 for ATtiny2313L.
Table 17. Brown-out Characteristics
Symbol
Parameter
Min
Typ
Max
Units
VHYST
Brown-out Detector Hysteresis
50
mV
tBOD
Min Pulse Width on Brown-out Reset
2
ns
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOTin Figure 18), the Brown-out Reset is immediately activated. When VCC increases above
the trigger level (VBOT+ in Figure 18), 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 Table 15.
Figure 18. Brown-out Reset During Operation
VCC
VBOT-
VBOT+
RESET
TIME-OUT
tTOUT
INTERNAL
RESET
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2543F–AVR–08/04
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out period
tTOUT. Refer to page 43 for details on operation of the Watchdog Timer.
Figure 19. Watchdog Reset During Operation
CC
CK
MCU Status Register –
MCUSR
The MCU Status Register provides information on which reset source caused an MCU
reset.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
MCUSR
See Bit Description
• 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.
36
ATtiny2313/V
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ATtiny2313/V
Internal Voltage
Reference
ATtiny2313 features an internal bandgap reference. This reference is used for Brownout Detection, and it can be used as an input to the Analog Comparator.
Voltage Reference Enable
Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used.
The start-up time is given in Table 18. To save power, the reference is not always turned
on. The reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting
the ACBG bit in ACSR).
Thus, when the BOD is not enabled, after setting the ACBG bit, the user must always
allow the reference to start up before the output from the Analog Comparator is used. To
reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering Power-down mode.
Table 18. Internal Voltage Reference Characteristics(1)
Symbol
VBG
tBG
IBG
Note:
Parameter
Condition
Min
Typ
Max
Units
Bandgap reference voltage
VCC = 2.7V,
TA = 25°C
1.0
1.1
1.2
V
Bandgap reference start-up time
VCC = 2.7V,
TA = 25°C
40
70
µs
Bandgap reference current
consumption
VCC = 2.7V,
TA = 25°C
15
µA
1. Values are guidelines only. Actual values are TBD.
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2543F–AVR–08/04
Watchdog Timer
ATtiny2313 has an Enhanced Watchdog Timer (WDT). The main features are:
• Clocked from separate On-chip Oscillator
• 3 Operating modes
– Interrupt
– System Reset
– Interrupt and System Reset
• Selectable Time-out period from 16ms to 8s
• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
128kHz
OSCILLATOR
WATCHDOG
RESET
WDE
OSC/2K
OSC/4K
OSC/8K
OSC/16K
OSC/32K
OSC/64K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K
Figure 20. Watchdog Timer
WDP0
WDP1
WDP2
WDP3
MCU RESET
WDIF
WDIE
INTERRUPT
The Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 kHz
oscillator. The WDT gives an interrupt or a system reset when the counter reaches a
given time-out value. In normal operation mode, it is required that the system uses the
WDR - Watchdog Timer Reset - instruction to restart the counter before the time-out
value is reached. If the system doesn't restart the counter, an interrupt or system reset
will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can
be used to wake the device from sleep-modes, and also as a general system timer. One
example is to limit the maximum time allowed for certain operations, giving an interrupt
when the operation has run longer than expected. In System Reset mode, the WDT
gives a reset when the timer expires. This is typically used to prevent system hang-up in
case of runaway code. The third mode, Interrupt and System Reset mode, combines the
other two modes by first giving an interrupt and then switch to System Reset mode. This
mode will for instance allow a safe shutdown by saving critical parameters before a system reset.
The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer
to System Reset mode. With the fuse programmed the System Reset mode bit (WDE)
and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively.
To further ensure program security, alterations to the Watchdog set-up must follow
timed sequences. The sequence for clearing WDE and changing time-out configuration
is as follows:
1. In the same operation, write a logic one to the Watchdog change enable bit
(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, write the WDE and Watchdog prescaler bits
(WDP) as desired, but with the WDCE bit cleared. This must be done in one
operation.
38
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
The following code example shows one assembly and one C function for turning off the
Watchdog Timer. The example assumes that interrupts are controlled (e.g. by disabling
interrupts globally) so that no interrupts will occur during the execution of these
functions.
Assembly Code Example(1)
WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
in
r16, MCUSR
andi
r16, (0xff & (0<<WDRF))
out
MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional time-out
in
r16, WDTCSR
ori
r16, (1<<WDCE) | (1<<WDE)
out
WDTCSR, r16
; Turn off WDT
ldi
r16, (0<<WDE)
out
WDTCSR, r16
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_off(void)
{
__disable_interrupt();
__watchdog_reset();
/* Clear WDRF in MCUSR */
MCUSR &= ~(1<<WDRF);
/* Write logical one to WDCE and WDE */
/* Keep old prescaler setting to prevent unintentional time-out
*/
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
}
Note:
1. The example code assumes that the part specific header file is included.
Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or
brown-out condition, the device will be reset and the Watchdog Timer will stay enabled.
If the code is not set up to handle the Watchdog, this might lead to an eternal loop of
time-out resets. To avoid this situation, the application software should always clear the
39
2543F–AVR–08/04
Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.
The following code example shows one assembly and one C function for changing the
time-out value of the Watchdog Timer.
Assembly Code Example(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
in
r16, WDTCSR
ori
r16, (1<<WDCE) | (1<<WDE)
out
WDTCSR, r16
; --
Got four cycles to set the new values from here -
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi
r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
out
WDTCSR, r16
; --
Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed
equence */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR
= (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Note:
1. The example code assumes that the part specific header file is included.
Note: The Watchdog Timer should be reset before any change of the WDP bits, since a
change in the WDP bits can result in a time-out when switching to a shorter time-out
period.
40
ATtiny2313/V
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ATtiny2313/V
Watchdog Timer Control
Register - WDTCSR
Bit
7
6
5
4
3
2
1
0
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
0
0
0
WDTCSR
• Bit 7 - WDIF: Watchdog 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 Interrupt Enable
When this bit is written to one and the I-bit in the Status Register is set, the Watchdog
Interrupt is enabled. If WDE is cleared in combination with this setting, the Watchdog
Timer is in Interrupt Mode, and the corresponding interrupt is executed if time-out in the
Watchdog Timer occurs.
If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. The first
time-out in the Watchdog Timer will set WDIF. Executing the corresponding interrupt
vector will clear WDIE and WDIF automatically by hardware (the Watchdog goes to System Reset Mode). This is useful for keeping the Watchdog Timer security while using
the interrupt. To stay in Interrupt and System Reset Mode, WDIE must be set after each
interrupt. This should however not be done within the interrupt service routine itself, as
this might compromise the safety-function of the Watchdog System Reset mode. If the
interrupt is not executed before the next time-out, a System Reset will be applied.
Table 19. Watchdog Timer Configuration
WDTON
WDE
WDIE
Mode
Action on Time-out
0
0
0
Stopped
None
0
0
1
Interrupt Mode
Interrupt
0
1
0
System Reset Mode
Reset
0
1
1
Interrupt and System
Reset Mode
Interrupt, then go to
System Reset Mode
1
x
x
System Reset Mode
Reset
• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the
WDE bit, and/or change the prescaler bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when
WDRF is set. To clear WDE, WDRF must be cleared first. This feature ensures multiple
resets during conditions causing failure, and a safe start-up after the failure.
• Bit 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 running. The different prescaling values and their corresponding time-out periods are
shown in Table 20 on page 42.
41
2543F–AVR–08/04
Table 20. Watchdog Timer Prescale Select
WDP3
WDP2
WDP1
WDP0
Number of WDT Oscillator
Cycles
Typical Time-out at
VCC = 5.0V
0
0
0
0
2K (2048) cycles
16 ms
0
0
0
1
4K (4096) cycles
32 ms
0
0
1
0
8K (8192) cycles
64 ms
0
0
1
1
16K (16384) cycles
0.125 s
0
1
0
0
32K (32768) cycles
0.25 s
0
1
0
1
64K (65536) cycles
0.5 s
0
1
1
0
128K (131072) cycles
1.0 s
0
1
1
1
256K (262144) cycles
2.0 s
1
0
0
0
512K (524288) cycles
4.0 s
1
0
0
1
1024K (1048576) cycles
8.0 s
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
Reserved
42
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Interrupts
Interrupt Vectors in
ATtiny2313
This section describes the specifics of the interrupt handling as performed in
ATtiny2313. For a general explanation of the AVR interrupt handling, refer to “Reset and
Interrupt Handling” on page 11.
Table 21. Reset and Interrupt Vectors
Vector
No.
Program
Address
Source
Interrupt Definition
1
0x0000
RESET
External Pin, Power-on Reset, Brown-out Reset,
and Watchdog Reset
2
0x0001
INT0
External Interrupt Request 0
3
0x0002
INT1
External Interrupt Request 1
4
0x0003
TIMER1 CAPT
Timer/Counter1 Capture Event
5
0x0004
TIMER1 COMPA
Timer/Counter1 Compare Match A
6
0x0005
TIMER1 OVF
Timer/Counter1 Overflow
7
0x0006
TIMER0 OVF
Timer/Counter0 Overflow
8
0x0007
USART0, RX
USART0, Rx Complete
9
0x0008
USART0, UDRE
USART0 Data Register Empty
10
0x0009
USART0, TX
USART0, Tx Complete
11
0x000A
ANALOG COMP
Analog Comparator
12
0x000B
PCINT
Pin Change Interrupt
13
0x000C
TIMER1 COMPB
Timer/Counter1 Compare Match B
14
0x000D
TIMER0 COMPA
Timer/Counter0 Compare Match A
15
0x000E
TIMER0 COMPB
Timer/Counter0 Compare Match B
16
0x000F
USI START
USI Start Condition
17
0x0010
USI OVERFLOW
USI Overflow
18
0x0011
EE READY
EEPROM Ready
19
0x0012
WDT OVERFLOW
Watchdog Timer Overflow
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2543F–AVR–08/04
The most typical and general program setup for the Reset and Interrupt Vector
Addresses in ATtiny2313 is:
Address Labels Code
Comments
0x0000
rjmp
RESET
; Reset Handler
0x0001
rjmp
INT0
; External Interrupt0 Handler
0x0002
rjmp
INT1
; External Interrupt1 Handler
0x0003
rjmp
TIM1_CAPT
; Timer1 Capture Handler
0x0004
rjmp
TIM1_COMPA
; Timer1 CompareA Handler
0x0005
rjmp
TIM1_OVF
; Timer1 Overflow Handler
0x0006
rjmp
TIM0_OVF
; Timer0 Overflow Handler
0x0007
rjmp
USART0_RXC
; USART0 RX Complete Handler
0x0008
rjmp
USART0_DRE
; USART0,UDR Empty Handler
0x0009
rjmp
USART0_TXC
; USART0 TX Complete Handler
0x000A
rjmp
ANA_COMP
; Analog Comparator Handler
0x000B
rjmp
PCINT
; Pin Change Interrupt
0x000C
rjmp
TIMER1_COMPB
; Timer1 Compare B Handler
0x000D
rjmp
TIMER0_COMPA
; Timer0 Compare A Handler
0x000E
rjmp
TIMER0_COMPB
; Timer0 Compare B Handler
0x000F
rjmp
USI_START
; USI Start Handler
0x0010
rjmp
USI_OVERFLOW
; USI Overflow Handler
0x0011
rjmp
EE_READY
; EEPROM Ready Handler
0x0012
rjmp
WDT_OVERFLOW
; Watchdog Overflow Handler
;
0x0013
RESET: ldi
0x0014
RAM
out
0x0015
sei
0x0016
<instr>
...
44
...
...
r16, low(RAMEND); Main program start
SPL,r16
Set Stack Pointer to top of
; Enable interrupts
xxx
...
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
I/O-Ports
Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital
I/O ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The
same applies when changing drive value (if configured as output) or enabling/disabling
of pull-up resistors (if configured as input). Each output buffer 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 21. Refer to “Electrical Characteristics” on page
176 for a complete list of parameters.
Figure 21. I/O Pin Equivalent Schematic
Rpu
Logic
Pxn
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case
“x” represents the numbering letter for the port, and a lower case “n” represents the bit
number. However, when using the register or bit defines in a program, the precise form
must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally
as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description for I/O-Ports” on page 57.
Three I/O memory address locations are allocated for each port, one each for the Data
Register – PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The
Port Input Pins I/O location is read only, while the Data Register and the Data Direction
Register are read/write. However, writing a logic one to a bit in the PINx Register, will
result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up
Disable – PUD bit in MCUCR disables the pull-up function for all pins in all ports when
set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on
page 46. 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 50. Refer to the individual module sections for a
full description of the alternate functions.
45
2543F–AVR–08/04
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.
Ports as General Digital
I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 22 shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 22. General Digital I/O(1)
PUD
Q
D
DDxn
Q CLR
WDx
RESET
1
Q
Pxn
D
0
PORTxn
Q CLR
WPx
DATA BUS
RDx
RESET
WRx
SLEEP
RRx
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD:
SLEEP:
clkI/O:
Note:
Configuring the Pin
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
WDx:
RDx:
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.
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in
“Register Description for I/O-Ports” on page 57, the DDxn bits are accessed at the
DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at
the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written
logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up
resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic
zero or the pin has to be configured as an output pin. The port pins are tri-stated when
reset condition becomes active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is
driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).
46
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
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.
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} = 0b11) as an intermediate step.
Table 22 summarizes the control signals for the pin value.
Table 22. Port Pin Configurations
Reading the Pin Value
DDxn
PORTxn
PUD (in
MCUCR2)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled
low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output Low (Sink)
1
1
X
Output
No
Output High (Source)
Comment
Independent of the setting of Data Direction bit DDxn, the port pin can be read through
the PINxn Register bit. As shown in Figure 22, 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
23 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 23. 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
47
2543F–AVR–08/04
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 24. 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 1 system clock
period.
Figure 24. 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
48
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and
define the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The
resulting pin values are read back again, but as previously discussed, a nop instruction
is included to be able to read back the value recently assigned to some of the pins.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi
r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out
PORTB,r16
out
DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
Note:
Digital Input Enable and Sleep
Modes
1. For the assembly program, two temporary registers are used to minimize the time
from pull-ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set,
defining bit 2 and 3 as low and redefining bits 0 and 1 as strong high drivers.
As shown in Figure 22, the digital input signal can be clamped to ground at the input of
the Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep
Controller in Power-down mode, and Standby mode to avoid high power consumption if
some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP is active also for these pins. SLEEP is also
overridden by various other alternate functions as described in “Alternate Port Functions” on page 50.
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.
49
2543F–AVR–08/04
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure
25 shows how the port pin control signals from the simplified Figure 22 can be overridden by alternate functions. The overriding signals may not be present in all port pins, but
the figure serves as a generic description applicable to all port pins in the AVR microcontroller family.
Figure 25. Alternate Port Functions(1)
PUOExn
PUOVxn
1
PUD
0
DDOExn
DDOVxn
1
D
Q
DDxn
0
Q CLR
WDx
PVOExn
RESET
RDx
1
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
DATA BUS
PVOVxn
WPx
DIEOVxn
RESET
WRx
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
Q
D
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
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.
Table 23 summarizes the function of the overriding signals. The pin and port indexes
from Figure 25 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
50
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table 23. 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 bi-directionally.
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.
51
2543F–AVR–08/04
MCU Control Register –
MCUCR
Bit
7
6
5
4
3
2
1
0
PUD
SM1
SE
SM0
ISC11
ISC10
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 – 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 46 for more details about this feature.
Alternate Functions of Port A
The Port A pins with alternate functions are as shown in Table 5.
Table 24. Port A Pins Alternate Functions
Port Pin
Alternate Functions of Port B
Alternate Function
PA2
RESET, dW
PA1
XTAL2
PA0
XTAL1
The Port B pins with alternate functions are shown in Table 25.
Table 25. Port B Pins Alternate Functions
Port Pin
Alternate Functions
PB7
USCK/SCL/PCINT7
PB6
DO/PCINT6
PB5
DI/SDA/PCINT5
PB4
OC1B/PCINT4
PB3
OC1A/PCINT3
PB2
OC0A/PCINT2
PB1
AIN1/PCINT1
PB0
AIN0/PCINT0
The alternate pin configuration is as follows:
• USCK/SCL/PCINT7 - Port B, Bit 7
USCK: Three-wire mode Universal Serial Interface Clock.
SCL: Two-wire mode Serial Clock for USI Two-wire mode.
PCINT7: Pin Change Interrupt source 7. The PB7 pin can serve as an external interrupt
source.
• DO/PCINT6 - Port B, Bit 6
DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output overrides PORTB6 value and it is driven to the port when data direction bit DDB6 is
set (one). However the PORTB6 bit still controls the pull-up enabling pull-up, if direction
is input and PORTB6 is set (one).
PCINT6: Pin Change Interrupt Source 6. The PB6 pin can serve as an external interrupt
source.
• DI/SDA/PCINT5 - Port B, Bit 5
52
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
DI: Three-wire mode Universal Serial Interface Data input. Three-wire mode does not
override normal port functions, so pin must be configured as an input. SDA: Two-wire
mode Serial Interface Data.
PCINT5: Pin Change Interrupt Source 5. The PB5 pin can serve as an external interrupt
source.
• OC1B/PCINT4 – Port B, Bit 4
OC1B: Output Compare Match B output: The PB4 pin can serve as an external output
for the Timer/Counter1 Output Compare B. The pin has to be configured as an output
(DDB6 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM
mode timer function.
PCINT4: Pin Change Interrupt Source 4. The PB4 pin can serve as an external interrupt
source.
• OC1A/PCINT3 – Port B, Bit 3
OC1A: Output Compare Match A output: The PB3 pin can serve as an external output
for the Timer/Counter1 Output Compare A. The pin has to be configured as an output
(DDB3 set (one)) to serve this function. The OC1A pin is also the output pin for the PWM
mode timer function.
PCINT3: Pin Change Interrupt Source 3: The PB3 pin can serve as an external interrupt
source.
• OC0A/PCINT2 – Port B, Bit 2
OC0A: Output Compare Match A output. The PB2 pin can serve as an external output
for the Timer/Counter0 Output Compare A. The 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.
PCINT2: Pin Change Interrupt Source 2. The PB2 pin can serve as an external interrupt
source.
• AIN1/PCINT1 – Port B, Bit 1
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.
PCINT1: Pin Change Interrupt Source 1. The PB1 pin can serve as an external interrupt
source.
• AIN0/PCINT0 – Port B, Bit 0
AIN0: Analog Comparator Positive input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of
the Analog Comparator.
PCINT0: Pin Change Interrupt Source 0. The PB0 pin can serve as an external interrupt
source.
Table 26 and Table 27 relate the alternate functions of Port B to the overriding signals
shown in Figure 25 on page 50. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute
the MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE
INPUT.
53
2543F–AVR–08/04
Table 26. Overriding Signals for Alternate Functions in PB7..PB4
Signal
Name
PB7/USCK/
SCL/PCINT7
PB6/DO/PCINT6
PB5/SDA/
DI/PCINT5
PB4/OC1B/
PCINT4
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
USI_TWO_WIRE
0
USI_TWO_WIRE
0
DDOV
(USI_SCL_HOLD
+ PORTB7)•DDB7
0
(SDA + PORTB5)•
DDRB5
0
PVOE
USI_TWO_WIRE
• DDRB7
USI_THREE_WIRE
USI_TWO_WIRE
• DDRB5
OC1B_PVOE
PVOV
0
DO
0
0OC1B_PVOV
PTOE
USI_PTOE
0
0
0
DIEOE
(PCINT7•PCIE)
+USISIE
(PCINT6•PCIE)
(PCINT5•PCIE) +
USISIE
(PCINT4•PCIE)
DIEOV
1
1
1
1
DI
PCINT7 INPUT
USCK INPUT SCL
INPUT
PCINT6 INPUT
PCINT5 INPUT
SDA INPUT
DI INPUT
PCINT4 INPUT
AIO
–
–
–
–
Table 27. Overriding Signals for Alternate Functions in PB3..PB0
54
Signal
Name
PB3/OC1A/
PCINT3
PB2/OC0A/
PCINT2
PB1/AIN1/
PCINT1
PB0/AIN0/
PCINT0
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
OC1A_PVOE
OC0A_PVOE
0
0
PVOV
OC1A_PVOV
OC0A_PVOV
0
0
PTOE
0
0
0
0
DIEOE
(PCINT3 • PCIE)
(PCINT2 • PCIE)
(PCINT1 • PCIE)
(PCINT0 • PCIE)
DIEOV
1
1
1
1
DI
PCINT7 INPUT
PCINT6 INPUT
PCINT5 INPUT
PCINT4 INPUT
AIO
–
–
AIN1
AIN0
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Alternate Functions of Port D
The Port D pins with alternate functions are shown in Table 28.
Table 28. Port D Pins Alternate Functions
Port Pin
Alternate Function
PD6
ICP
PD5
OC0B/T1
PD4
T0
PD3
INT1
PD2
INT0/XCK/CKOUT
PD1
TXD
PD0
RXD
The alternate pin configuration is as follows:
• ICP – Port D, Bit 6
ICP: Timer/Counter1 Input Capture Pin. The PD6 pin can act as an Input Capture pin for
Timer/Counter1
• OC1B/T1 – Port D, Bit 5
OC0B: Output Compare Match B output: The PD5 pin can serve as an external output
for the Timer/Counter0 Output Compare B. The pin has to be configured as an output
(DDB5 set (one)) to serve this function. The OC0B pin is also the output pin for the PWM
mode timer function.
T1: Timer/Counter1 External Counter Clock input is enabled by setting (one) the bits
CS02 and CS01 in the Timer/Counter1 Control Register (TCCR1).
• T0 – Port D, Bit 4
T0: Timer/Counter0 External Counter Clock input is enabled by setting (one) the bits
CS02 and CS01 in the Timer/Counter0 Control Register (TCCR0).
• INT1 – Port D, Bit 3
INT0: External Interrupt Source 0. The PD3 pin can serve as an external interrupt
source to the MCU.
• INT0/XCK/CKOUT – Port D, Bit 2
INT1: External Interrupt Source 1. The PD2 pin can serve as en external interrupt
source to the MCU.
XCK: USART Transfer Clock used only by Synchronous Transfer mode.
CKOUT: System Clock Output
• TXD – Port D, Bit 1
TXD: UART Data Transmitter.
• RXD – Port D, Bit 0
RXD: UART Data Receiver.
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2543F–AVR–08/04
Table 29 and Table 30 relates the alternate functions of Port D to the overriding signals
shown in Figure 25 on page 50.
Table 29. Overriding Signals for Alternate Functions PD7..PD4
Signal
Name
PD6/ICP
PD5/OC1B/T1
PD4/T0
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
0
0
DDOV
0
0
0
PVOE
0
OC1B_PVOE
0
PVOV
0
OC1B_PVOV
0
PTOE
0
0
0
DIEOE
ICP ENABLE
T1 ENABLE
T0 ENABLE
DIEOV
1
1
1
DI
ICP INPUT
T1 INPUT
T0 INPUT
AIO
–
–
AIN1
Table 30. Overriding Signals for Alternate Functions in PD3..PD0
56
Signal
Name
PD3/INT1
PD2/INT0/XCK/
CKOUT
PD1/TXD
PD0/RXD
PUOE
0
0
TXD_OE
RXD_OE
PUOV
0
0
0
PORTD0 • PUD
DDOE
0
0
TXD_OE
RXD_EN
DDOV
0
0
1
0
PVOE
0
XCKO_PVOE
TXD_OE
0
PVOV
0
XCKO_PVOV
TXD_PVOV
0
PTOE
0
0
0
0
DIEOE
INT1 ENABLE
INT0 ENABLE/
XCK INPUT
ENABLE
0
0
DIEOV
1
1
0
0
DI
INT1 INPUT
INT0 INPUT/
XCK INPUT
–
RXD INPUT
AIO
–
–
–
–
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Register Description for I/O-Ports
Port A Data Register – PORTA
Bit
Port A Data Direction Register
– DDRA
Port A Input Pins Address –
PINA
7
6
5
4
3
2
1
0
–
–
–
–
–
PORTA2
PORTA1
PORTA0
Read/Write
R
R
R
R
R
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
–
–
–
–
–
DDA2
DDA1
DDA0
Read/Write
R
R
R
R
R
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
–
–
–
–
–
PINA2
PINA1
PINA0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTA
DDRA
PINA
Port B Data Register – PORTB
Bit
Port B Data Direction Register
– DDRB
Port B Input Pins Address –
PINB
7
6
5
4
3
2
1
0
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
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
PORTB
DDRB
PINB
Port D Data Register – PORTD
Bit
Port D Data Direction Register
– DDRD
Port D Input Pins Address –
PIND
7
6
5
4
3
2
1
0
–
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
–
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
–
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
Read/Write
R
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
PORTD
DDRD
PIND
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2543F–AVR–08/04
External Interrupts
The External Interrupts are triggered by the INT0 pin, INT1 pin or any of the PCINT7..0
pins. Observe that, if enabled, the interrupts will trigger even if the INT0, INT1or
PCINT7..0 pins are configured as outputs. This feature provides a way of generating a
software interrupt. The pin change interrupt PCI1 will trigger if any enabled PCINT7..8
pin toggles. Pin change interrupts PCI0 will trigger if any enabled PCINT7..0 pin toggles.
The PCMSK1 and PCMSK0 Registers control which pins contribute to the pin change
interrupts. Pin change interrupts on PCINT7..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 and INT1 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 External Interrupt Control Register
A – EICRA. When the INT0 or INT1 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 and INT1 requires the presence of an I/O clock,
described in “Clock Systems and their Distribution” on page 21. Low level interrupt on
INT0 and INT1 is detected asynchronously. This implies that this interrupt can be used
for waking the part from sleep modes other than Idle mode. The I/O clock is halted in all
sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the
required level must be held long enough for the MCU to complete the wake-up to trigger
the level interrupt. If the level disappears before the end of the Start-up Time, the MCU
will still wake up, but no interrupt will be generated. The start-up time is defined by the
SUT and CKSEL Fuses as described in “System Clock and Clock Options” on page 21.
MCU Control Register –
MCUCR
The External Interrupt Control Register A contains control bits for interrupt sense
control.
Bit
7
6
5
4
3
2
1
0
PUD
SM1
SE
SMD
ISC11
ISC10
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 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The External Interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the
corresponding interrupt mask are set. The level and edges on the external INT1 pin that
activate the interrupt are defined in Table 32. The value on the INT1 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 31. Interrupt 0 Sense Control
ISC11
ISC10
Description
0
0
The low level of INT1 generates an interrupt request.
0
1
Any logical change on INT1 generates an interrupt request.
1
0
The falling edge of INT1 generates an interrupt request.
1
1
The rising edge of INT1 generates an interrupt request.
• Bit 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
58
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
activate the interrupt are defined in Table 32. 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 32. Interrupt 0 Sense Control
General Interrupt Mask
Register – GIMSK
ISC01
ISC00
0
0
The low level of INT0 generates an interrupt request.
0
1
Any logical change on INT0 generates an interrupt request.
1
0
The falling edge of INT0 generates an interrupt request.
1
1
The rising edge of INT0 generates an interrupt request.
Bit
Description
7
6
5
4
3
2
1
INT1
INT0
PCIE
–
–
–
–
0
–
Read/Write
R/W
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIMSK
• Bit 7 – INT1: External Interrupt Request 1 Enable
When the INT1 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 Control1 bits 1/0 (ISC11 and
ISC10) in the MCU Control Register – MCUCR – define whether the external interrupt is
activated on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin
will cause an interrupt request even if INT1 is configured as an output. The corresponding interrupt of External Interrupt Request 1 is executed from the INT1 Interrupt Vector.
• Bit 6 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and
ISC00) in the MCU Control Register – MCUCR – define whether the external interrupt is
activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin
will cause an interrupt request even if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt Vector.
• Bit 5 – PCIE: Pin Change Interrupt Enable
When the PCIE bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
pin change interrupt 1 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 PCI Interrupt Vector. PCINT7..0 pins are enabled individually by the PCMSK
Register.
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2543F–AVR–08/04
External Interrupt Flag
Register – EIFR
Bit
7
6
5
4
3
2
1
INTF1
INTF0
PCIF
–
–
–
–
0
–
Read/Write
R/W
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
EIFR
• Bit 7 – INTF1: External Interrupt Flag 1
When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1
becomes set (one). If the I-bit in SREG and the INT1 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 INT1 is configured as a level interrupt.
• 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 – PCIF: Pin Change Interrupt Flag
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 PCIE bit in GIMSK are set (one), the MCU will
jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine
is executed. Alternatively, the flag can be cleared by writing a logical one to it.
Pin Change Mask Register –
PCMSK
Bit
7
6
5
4
3
2
1
0
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
PCMSK
• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 15..8
Each PCINT7..0-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is set and the PCIE 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.
60
ATtiny2313/V
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ATtiny2313/V
8-bit Timer/Counter0
with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent
Output Compare Units, and with PWM support. It allows accurate program execution
timing (event management) and wave generation. The main features are:
• Two Independent Output Compare Units
• Double Buffered Output Compare Registers
• Clear Timer on Compare Match (Auto Reload)
• Glitch Free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 26. For the
actual placement of I/O pins, refer to “Pinout ATtiny2313” on page 2. CPU accessible
I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O
Register and bit locations are listed in the “8-bit Timer/Counter Register Description” on
page 72.
Figure 26. 8-bit Timer/Counter Block Diagram
Count
Clear
Direction
TOVn
(Int.Req.)
Control Logic
clkTn
Clock Select
Edge
Detector
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCnA
DATA BUS
OCRnA
Fixed
TOP
Value
Waveform
Generation
=
OCnB
OCRnB
TCCRnA
Registers
OCnB
(Int.Req.)
TCCRnB
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are
8-bit registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR). All interrupts are individually masked
with the Timer Interrupt Mask Register (TIMSK). TIFR and TIMSK are not shown in the
figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock
source on the T0 pin. The Clock Select logic block controls which clock source and edge
the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is
inactive when no clock source is selected. The output from the Clock Select logic is
referred to as the timer clock (clkT0).
The double buffered Output Compare Registers (OCR0A and OCR0B) is compared with
the Timer/Counter value at all times. The result of the compare can be used by the
Waveform Generator to generate a PWM or variable frequency output on the Output
61
2543F–AVR–08/04
Compare pins (OC0A and OC0B). See “Output Compare Unit” on page 63. for details.
The Compare Match event will also set the Compare Flag (OCF0A or OCF0B) which
can be used to generate an Output Compare interrupt request.
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 33 are also used extensively throughout the document.
Table 33. Definitions
BOTTOM
The counter reaches the BOTTOM when it becomes 0x00.
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP
The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR0A Register. The
assignment is dependent on the mode of operation.
Timer/Counter Clock
Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock
source is selected by the Clock Select logic which is controlled by the Clock Select
(CS02:0) bits located in the Timer/Counter Control Register (TCCR0B). For details on
clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on
page 79.
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.
Figure 27 shows a block diagram of the counter and its surroundings.
Figure 27. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
count
TCNTn
clear
Control Logic
clkTn
Edge
Detector
Tn
direction
( From Prescaler )
bottom
top
Signal description (internal signals):
62
count
Increment or decrement TCNT0 by 1.
direction
Select between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT0 in the following.
top
Signalize that TCNT0 has reached maximum value.
bottom
Signalize that TCNT0 has reached minimum value (zero).
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
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 93.
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.
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 93).
Figure 28 shows a block diagram of the Output Compare unit.
Figure 28. 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
63
2543F–AVR–08/04
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.
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be
forced by writing a one to the Force Output Compare (FOC0x) bit. Forcing Compare
Match will not set the OCF0x Flag or reload/clear the timer, but the OC0x pin will be
updated as if a real Compare Match had occurred (the COM0x1:0 bits settings define
whether the OC0x pin is set, cleared or toggled).
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.
Using the Output Compare
Unit
Since writing TCNT0 in any mode of operation will block all Compare Matches for one
timer clock cycle, there are risks involved when changing TCNT0 when using the Output
Compare Unit, independently of whether the Timer/Counter is running or not. If the
value written to TCNT0 equals the OCR0x value, the Compare Match will be missed,
resulting in incorrect waveform generation. Similarly, do not write the TCNT0 value
equal to BOTTOM when the counter is down-counting.
The setup of the OC0x should be performed before setting the Data Direction Register
for the port pin to output. The easiest way of setting the OC0x value is to use the Force
Output Compare (FOC0x) strobe bits in Normal mode. The OC0x Registers keep their
values even when changing between Waveform Generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare
value. Changing the COM0x1:0 bits will take effect immediately.
Compare Match Output
Unit
64
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 29
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”.
ATtiny2313/V
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ATtiny2313/V
Figure 29. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCn
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC0x) from the
Waveform Generator if either of the COM0x1:0 bits are set. However, the OC0x pin
direction (input or output) is still controlled by the Data Direction Register (DDR) for the
port pin. The Data Direction Register bit for the OC0x pin (DDR_OC0x) must be set as
output before the OC0x value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0x state before
the output is enabled. Note that some COM0x1:0 bit settings are reserved for certain
modes of operation. See “8-bit Timer/Counter Register Description” on page 72.
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 Figure 28 on page 63. For fast PWM
mode, refer to Table 26 on page 54, and for phase correct PWM refer to Table 27 on
page 54.
A change of the COM0x1:0 bits state will have effect at the first Compare Match after
the bits are written. For non-PWM modes, the action can be forced to have immediate
effect by using the FOC0x strobe bits.
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare
pins, is defined by the combination of the Waveform Generation mode (WGM02:0) and
Compare Output mode (COM0x1:0) bits. The Compare Output mode bits do not affect
the counting sequence, while the Waveform Generation mode bits do. The COM0x1:0
bits control whether the PWM output generated should be inverted or not (inverted or
non-inverted PWM). For non-PWM modes the COM0x1:0 bits control whether the output should be set, cleared, or toggled at a Compare Match (See “Compare Match
Output Unit” on page 64.).
For detailed timing information refer to Figure 33, Figure 34, Figure 35 and Figure 36 in
“Timer/Counter Timing Diagrams” on page 70.
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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.
Clear Timer on Compare
Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used
to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for
the counter, hence also its resolution. This mode allows greater control of the Compare
Match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 30. The counter value
(TCNT0) increases until a Compare Match occurs between TCNT0 and OCR0A, and
then counter (TCNT0) is cleared.
Figure 30. 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 maxi-
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ATtiny2313/V
mum frequency of fOC0 = 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.
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 non-inverting Compare Output mode, the Output Compare (OC0x) is
cleared on the Compare Match between TCNT0 and OCR0x, and set at BOTTOM. In
inverting Compare Output mode, the output is set on Compare Match and cleared at
BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM
mode can be twice as high as the phase correct PWM mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited for power regulation,
rectification, and DAC applications. High frequency allows physically small sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP
value. The counter is then cleared at the following timer clock cycle. The timing diagram
for the fast PWM mode is shown in Figure 29. The TCNT0 value is in the timing diagram
shown as a histogram for illustrating the single-slope operation. The diagram includes
non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0
slopes represent Compare Matches between OCR0x and TCNT0.
Figure 31. 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
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inverted PWM output can be generated by setting the COM0x1:0 to three: Setting the
COM0A1:0 bits to one allows 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 26 on page
54). The actual OC0x value will only be visible on the port pin if the data direction for the
port pin is set as output. The PWM waveform is generated by setting (or clearing) the
OC0x Register at the Compare Match between OCR0x and TCNT0, and clearing (or
setting) the OC0x Register at the timer clock cycle the counter is cleared (changes from
TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating
a PWM waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM,
the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A
equal to MAX will result in a constantly high or low output (depending on the polarity of
the output set by the COM0A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved
by setting OC0x to toggle its logical level on each Compare Match (COM0x1:0 = 1). The
waveform generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is
set to zero. This feature is similar to the OC0A toggle in CTC mode, except the double
buffer feature of the Output Compare unit is enabled in the fast PWM mode.
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 non-inverting 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 down-counting. 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 32. The TCNT0 value is in the timing diagram shown as
a histogram for illustrating the dual-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x and TCNT0.
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ATtiny2313/V
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ATtiny2313/V
Figure 32. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCn
(COMnx1:0 = 2)
OCn
(COMnx1:0 = 3)
Period
1
2
3
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The Interrupt Flag can be used to generate an interrupt each time the counter
reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on
the OC0x pins. Setting the COM0x1:0 bits to two will produce a non-inverted PWM. An
inverted PWM output can be generated by setting the COM0x1:0 to three: Setting the
COM0A0 bits to one allows the OC0A pin to toggle on Compare Matches if the WGM02
bit is set. This option is not available for the OC0B pin (See Table 27 on page 54). 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 32 OCn has a transition from high to low even
though there is no Compare Match. The point of this transition is to guarantee symmetry
around BOTTOM. There are two cases that give a transition without Compare Match.
•
OCR0A changes its value from MAX, like in Figure 32. When the OCR0A value is
MAX the OCn pin value is the same as the result of a down-counting Compare
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Match. To ensure symmetry around BOTTOM the OCn value at MAX must
correspond to the result of an up-counting Compare Match.
•
Timer/Counter Timing
Diagrams
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.
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 33 contains timing data for basic Timer/Counter
operation. The figure shows the count sequence close to the MAX value in all modes
other than phase correct PWM mode.
Figure 33. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 33 shows the same timing data, but with the prescaler enabled.
Figure 34. 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 35 shows the setting of OCF0B in all modes and OCF0A in all modes except
CTC mode and PWM mode, where OCR0A is TOP.
Figure 35. 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
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ATtiny2313/V
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ATtiny2313/V
Figure 36 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast
PWM mode where OCR0A is TOP.
Figure 36. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with
Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
OCRnx
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP
OCFnx
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8-bit Timer/Counter
Register Description
Timer/Counter Control
Register A – TCCR0A
Bit
7
6
5
4
3
2
1
0
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0A
• Bits 7:6 – 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 34 shows the COM0A1:0 bit functionality when the
WGM02:0 bits are set to a normal or CTC mode (non-PWM).
Table 34. 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 35 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast
PWM mode.
Table 35. 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 TOP
1
1
Set OC0A on Compare Match, clear OC0A at TOP
Note:
72
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case,
the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 67 for more details.
ATtiny2313/V
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ATtiny2313/V
Table 36 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to
phase correct PWM mode.
Table 36. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.
1
1
Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case,
the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page 68 for more details.
• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
These bits control the Output Compare pin (OC0B) behavior. If one or both of the
COM0B1:0 bits are set, the OC0B output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0B pin must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the
WGM02:0 bit setting. Table 37 shows the COM0A1:0 bit functionality when the
WGM02:0 bits are set to a normal or CTC mode (non-PWM).
Table 37. 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
Table 38 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast
PWM mode.
Table 38. 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 TOP
1
1
Set OC0B on Compare Match, clear OC0B at TOP
Note:
Description
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case,
the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 67 for more details.
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Table 39 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to
phase correct PWM mode.
Table 39. 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 68 for more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313 and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B Register, these bits control the
counting sequence of the counter, the source for maximum (TOP) counter value, and
what type of waveform generation to be used, see Table 40. 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 93).
Table 40. Waveform Generation Mode Bit Description
TOP
Update of
OCRx at
TOV Flag
Set on(1)(2)
Mode
WGM2
WGM1
WGM0
0
0
0
0
Normal
0xFF
Immediate
MAX
1
0
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
2
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
TOP
MAX
4
1
0
0
Reserved
–
–
–
5
1
0
1
PWM, Phase
Correct
OCRA
TOP
BOTTOM
6
1
1
0
Reserved
–
–
–
7
1
1
1
Fast PWM
OCRA
TOP
TOP
Notes:
74
Timer/Counter
Mode of
Operation
1. MAX
= 0xFF
2. BOTTOM = 0x00
ATtiny2313/V
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ATtiny2313/V
Timer/Counter Control
Register B – TCCR0B
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
Read/Write
W
W
R
R
R/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.
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 ATtiny2313 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR0A” on page 72.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
See Table 41 on page 76.
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2543F–AVR–08/04
Table 41. 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.
Timer/Counter Register –
TCNT0
Bit
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to
the Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes)
the Compare Match on the following timer clock. Modifying the counter (TCNT0) while
the counter is running, introduces a risk of missing a Compare Match between TCNT0
and the OCR0x Registers.
Output Compare Register A –
OCR0A
Bit
7
6
5
4
3
2
1
0
OCR0A[7:0]
OCR0A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
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.
Output Compare Register B –
OCR0B
Bit
7
6
5
4
3
2
1
0
OCR0B[7:0]
OCR0B
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register B contains an 8-bit value that is continuously compared
with the counter value (TCNT0). A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the OC0B pin.
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ATtiny2313/V
Timer/Counter Interrupt Mask
Register – TIMSK
Bit
7
6
5
4
3
2
1
0
TOIE1
OCIE1A
OCIE1B
–
ICIE1
OCIE0B
TOIE0
OCIE0A
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
TIMSK
• Bit 4 – Res: Reserved Bit
This bit is reserved bit in the ATtiny2313 and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter0 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 – TIFR.
• Bit 1 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if
an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR.
• Bit 0 – 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 – TIFR.
Timer/Counter Interrupt Flag
Register – TIFR
Bit
7
6
5
4
3
2
1
0
TOV1
OCF1A
OCF1B
–
ICF1
OCF0B
TOV0
OCF0A
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
TIFR
• Bit 4 – Res: Reserved Bit
This bit is reserved bit in the ATtiny2313 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 the flag. When the I-bit in SREG, OCIE0B
(Timer/Counter Compare B Match Interrupt Enable), and OCF0B are set, the
Timer/Counter Compare Match Interrupt is executed.
• Bit 1 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by
hardware when executing the corresponding interrupt handling vector. Alternatively,
TOV0 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0
(Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set, the Timer/Counter0
Overflow interrupt is executed.
The setting of this flag is dependent of the WGM02:0 bit setting. Refer to Table 40,
“Waveform Generation Mode Bit Description” on page 74.
• Bit 0 – OCF0A: Output Compare Flag 0 A
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The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and
the data in OCR0A – Output Compare Register0 A. 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.
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Timer/Counter0 and
Timer/Counter1
Prescalers
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the
Timer/Counters can have different prescaler settings. The description below applies to
both Timer/Counter1 and Timer/Counter0.
Internal Clock Source
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.
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of
the Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. Since the
prescaler is not affected by the Timer/Counter’s clock select, the state of the prescaler
will have implications for situations where a prescaled clock is used. One example of
prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 >
CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to the
first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program
execution. However, care must be taken if the other Timer/Counter that shares the
same prescaler also uses prescaling. A prescaler reset will affect the prescaler period
for all Timer/Counters it is connected to.
External Clock Source
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge
detector. Figure 37 shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector logic. The registers are clocked at the positive edge of the
internal system clock (clkI/O). The latch is transparent in the high period of the internal
system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0 = 6) edge it detects.
Figure 37. T1/T0 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system
clock cycles from an edge has been applied to the T1/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T1/T0 has been stable for
at least one system clock cycle, otherwise it is a risk that a false Timer/Counter clock
pulse is generated.
Each half period of the external clock applied must be longer than one system clock
cycle to ensure correct sampling. The external clock must be guaranteed to have less
than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since
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the edge detector uses sampling, the maximum frequency of an external clock it can
detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system clock frequency and duty cycle caused by Oscillator source (crystal,
resonator, and capacitors) tolerances, it is recommended that maximum frequency of an
external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 38. Prescaler for Timer/Counter0 and Timer/Counter1(1)
clk I/O
Clear
PSR10
T0
Synchronization
T1
Synchronization
clkT1
Note:
General Timer/Counter
Control Register – GTCCR
clkT0
1. The synchronization logic on the input pins (T1/T0) is shown in Figure 37.
Bit
7
6
5
4
3
2
1
0
—
–
–
–
–
–
—
PSR10
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bits 7..1 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313 and will always read as zero.
• Bit 0 – PSR10: Prescaler Reset Timer/Counter1 and Timer/Counter0
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This
bit is normally cleared immediately by hardware. Note that Timer/Counter1 and
Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both
timers.
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ATtiny2313/V
16-bit
Timer/Counter1
The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave generation, and signal timing measurement. The main features are:
• 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
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.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 39. For the
actual placement of I/O pins, refer to “Pinout ATtiny2313” 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 “16-bit Timer/Counter Register Description”
on page 103.
Figure 39. 16-bit Timer/Counter Block Diagram(1)
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
Note:
TCCRnB
1. Refer to Figure 1 on page 2 for Timer/Counter1 pin placement and description.
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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 16-bit registers. These procedures are described in the section “Accessing 16-bit Registers” on page 83. 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 90.. 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 148.) 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.
Definitions
The following definitions are used extensively throughout the section:
Table 42. Definitions
Compatibility
82
BOTTOM
The counter reaches the BOTTOM when it becomes 0x0000.
MAX
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
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 one of the fixed values:
0x00FF, 0x01FF, or 0x03FF, or to the value stored in the OCR1A or ICR1 Register. The assignment is dependent of the mode of operation.
The 16-bit Timer/Counter has been updated and improved from previous versions of the
16-bit AVR Timer/Counter. 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.
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ATtiny2313/V
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:
•
FOC1A and FOC1B are added to TCCR1A.
•
WGM13 is added to TCCR1B.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some
special cases.
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 16-bit 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(1)
...
; 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(1)
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
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.
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ATtiny2313/V
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(1)
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
C Code Example(1)
unsigned int TIM16_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
__disable_interrupt();
/* Read TCNT1 into i */
i = TCNT1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
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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(1)
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
C Code Example(1)
void TIM16_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
__disable_interrupt();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to
be written to TCNT1.
Reusing the Temporary High
Byte Register
86
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.
ATtiny2313/V
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ATtiny2313/V
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/Counter0 and Timer/Counter1 Prescalers” on
page 79.
Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional
counter unit. Figure 40 shows a block diagram of the counter and its surroundings.
Figure 40. 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
Signal description (internal signals):
Count
Increment or decrement TCNT1 by 1.
Direction
Select between increment and decrement.
Clear
Clear TCNT1 (set all bits to zero).
clkT1
Timer/Counter clock.
TOP
Signalize that TCNT1 has reached maximum value.
BOTTOM
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
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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 93.
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.
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, dutycycle, 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 41. 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.
Figure 41. 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.
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ATtiny2313/V
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 83.
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 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 37 on page 79). 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.
Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme.
The noise canceler input is monitored over four samples, and all four must be equal for
changing the output that in turn is used by the edge detector.
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 additional four system clock cycles of delay from a change applied to the input, to
the update of the ICR1 Register. The noise canceler uses the system clock and is therefore not affected by the prescaler.
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).
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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 (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 (See
“Modes of Operation” on page 93.)
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 42 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 42. 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
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(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 Register 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 83.
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 (FOC1x) 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).
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.
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 (FOC1x) 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.
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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 43 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”.
Figure 43. Compare Match Output Unit, Schematic
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. Refer
to Table 43, Table 44 and Table 45 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 “16-bit Timer/Counter Register Description” on page 103.
The COM1x1:0 bits have no effect on the Input Capture unit.
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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 43 on page 103. For fast
PWM mode refer to Table 44 on page 103, and for phase correct and phase and frequency correct PWM refer to Table 45 on page 104.
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 FOC1x strobe bits.
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 (See “Compare Match Output
Unit” on page 92.)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 101.
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.
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 44 on page 94. 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 44. 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 fOC1A = 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.
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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 set on the compare match between TCNT1 and OCR1x, and
cleared at TOP. In inverting Compare Output mode output is cleared on compare match
and set at TOP. 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 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 45. 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 45. 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.
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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 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 43
on page 103). 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 fOC1A = 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.
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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 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 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.
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:
( TOP + 1 )R PCPWM = log
---------------------------------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 46. 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 46. 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
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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 46 illustrates, 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
44 on page 103). 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.
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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 dualslope 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 46 and Figure 47).
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 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 47.
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 47. 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
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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 47 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.
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 45 on page 104). 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 non-inverted PWM mode. For inverted PWM the output will have the
opposite logic values.
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ATtiny2313/V
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 48 shows a timing
diagram for the setting of OCF1x.
Figure 48. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 49 shows the same timing data, but with the prescaler enabled.
Figure 49. Timer/Counter Timing Diagram, Setting of OCF1x, 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 50 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.
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Figure 50. 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 51 shows the same timing data, but with the prescaler enabled.
Figure 51. 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)
102
Old OCRnx Value
New OCRnx Value
ATtiny2313/V
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ATtiny2313/V
16-bit Timer/Counter
Register Description
Timer/Counter1 Control
Register A – TCCR1A
Bit
7
6
5
4
3
2
1
0
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 43 shows the COM1x1:0 bit functionality
when the WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 43. 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 44 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the
fast PWM mode.
Table 44. 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 TOP
1
1
Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at TOP
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 TOP.
See “Fast PWM Mode” on page 95. for more details.
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Table 45 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 45. Compare Output Mode, Phase Correct and Phase and 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. See “Phase Correct PWM Mode” on page 97. for more details.
• 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 46. 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. (See
“Modes of Operation” on page 93.).
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Table 46. Waveform Generation Mode Bit Description(1)
Mode
WGM13
WGM12
(CTC1)
WGM11
(PWM11)
WGM10
(PWM10)
Timer/Counter Mode of
Operation
TOP
Update of
OCR1x at
TOV1 Flag
Set on
0
0
0
0
0
Normal
0xFFFF
Immediate
MAX
1
0
0
0
1
PWM, Phase Correct, 8-bit
0x00FF
TOP
BOTTOM
2
0
0
1
0
PWM, Phase Correct, 9-bit
0x01FF
TOP
BOTTOM
3
0
0
1
1
PWM, Phase Correct, 10-bit
0x03FF
TOP
BOTTOM
4
0
1
0
0
CTC
OCR1A
Immediate
MAX
5
0
1
0
1
Fast PWM, 8-bit
0x00FF
TOP
TOP
6
0
1
1
0
Fast PWM, 9-bit
0x01FF
TOP
TOP
7
0
1
1
1
Fast PWM, 10-bit
0x03FF
TOP
TOP
8
1
0
0
0
PWM, Phase and Frequency
Correct
ICR1
BOTTOM
BOTTOM
9
1
0
0
1
PWM, Phase and Frequency
Correct
OCR1A
BOTTOM
BOTTOM
10
1
0
1
0
PWM, Phase Correct
ICR1
TOP
BOTTOM
11
1
0
1
1
PWM, Phase Correct
OCR1A
TOP
BOTTOM
12
1
1
0
0
CTC
ICR1
Immediate
MAX
13
1
1
0
1
(Reserved)
–
–
–
14
1
1
1
0
Fast PWM
ICR1
TOP
TOP
15
1
1
1
1
Fast PWM
OCR1A
TOP
TOP
Note:
1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
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Timer/Counter1 Control
Register B – TCCR1B
Bit
7
6
5
4
3
2
1
0
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.
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 48 and Figure 49.
Table 47. 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.
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ATtiny2313/V
Timer/Counter1 Control
Register C – TCCR1C
Bit
7
6
5
4
3
2
1
0
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 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.
Timer/Counter1 – TCNT1H
and TCNT1L
Bit
7
6
5
4
3
2
1
0
TCNT1[15:8]
TCNT1H
TCNT1[7:0]
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 83.
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.
Output Compare Register 1 A
– OCR1AH and OCR1AL
Bit
7
6
5
4
3
2
1
0
OCR1A[15:8]
OCR1AH
OCR1A[7:0]
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
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Output Compare Register 1 B
- OCR1BH and OCR1BL
Bit
7
6
5
4
3
2
1
0
OCR1B[15:8]
OCR1BH
OCR1B[7:0]
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 16-bit registers. See “Accessing 16-bit Registers” on page 83.
Input Capture Register 1 –
ICR1H and ICR1L
Bit
7
6
5
4
3
2
1
0
ICR1[15:8]
ICR1H
ICR1[7:0]
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. See “Accessing 16-bit Registers” on page 83.
Timer/Counter Interrupt Mask
Register – TIMSK
Bit
7
6
5
4
3
2
1
0
TOIE1
OCIE1A
OCIE1B
–
ICIE1
OCIE0B
TOIE0
OCIE0A
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
TIMSK
• Bit 7 – 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 43.) is executed when the TOV1 flag, located
in TIFR, is set.
• Bit 6 – 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 43.) is executed when the
OCF1A flag, located in TIFR, is set.
• Bit 5 – 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 43.) is executed when the
OCF1B flag, located in TIFR, is set.
• Bit 3 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
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ATtiny2313/V
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ATtiny2313/V
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Input Capture interrupt is enabled. The
corresponding Interrupt Vector (See “Interrupts” on page 43.) is executed when the
ICF1 flag, located in TIFR, is set.
Timer/Counter Interrupt Flag
Register – TIFR
Bit
7
6
5
4
3
2
1
0
TOV1
OCF1A
OCF1B
–
ICF1
OCF0B
TOV0
OCF0A
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
TIFR
• Bit 7 – 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. Refer to Table 46 on page 105
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.
• Bit 6 – 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 (FOC1A) 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 5 – 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 (FOC1B) 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 3 – 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.
109
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USART
The Universal Synchronous and Asynchronous serial Receiver and Transmitter
(USART) is a highly flexible serial communication device. The main features are:
• Full Duplex Operation (Independent Serial Receive and Transmit Registers)
• Asynchronous or Synchronous Operation
• Master or Slave Clocked Synchronous Operation
• High Resolution Baud Rate Generator
• Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
• Odd or Even Parity Generation and Parity Check Supported by Hardware
• Data OverRun Detection
• Framing Error Detection
• Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
• Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete
• Multi-processor Communication Mode
• Double Speed Asynchronous Communication Mode
Overview
A simplified block diagram of the USART Transmitter is shown in Figure 52. CPU accessible I/O Registers and I/O pins are shown in bold.
Figure 52. USART Block Diagram(1)
Clock Generator
UBRR[H:L]
OSC
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCK
Transmitter
TX
CONTROL
UDR (Transmit)
DATA BUS
PARITY
GENERATOR
110
TxD
Receiver
UCSRA
Note:
PIN
CONTROL
TRANSMIT SHIFT REGISTER
CLOCK
RECOVERY
RX
CONTROL
RECEIVE SHIFT REGISTER
DATA
RECOVERY
PIN
CONTROL
UDR (Receive)
PARITY
CHECKER
UCSRB
RxD
UCSRC
1. Refer to Figure 1 on page 2, Table 29 on page 56, and Table 26 on page 54 for
USART pin placement.
ATtiny2313/V
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ATtiny2313/V
The dashed boxes in the block diagram separate the three main parts of the USART
(listed from the top): Clock Generator, Transmitter and Receiver. Control registers are
shared by all units. The Clock Generation logic consists of synchronization logic for
external clock input used by synchronous slave operation, and the baud rate generator.
The XCK (Transfer Clock) pin is only used by synchronous transfer mode. The Transmitter consists of a single write buffer, a serial Shift Register, Parity Generator and
Control logic for handling different serial frame formats. The write buffer allows a continuous transfer of data without any delay between frames. The Receiver is the most
complex part of the USART module due to its clock and data recovery units. The recovery units are used for asynchronous data reception. In addition to the recovery units, the
Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDR). The Receiver supports the same frame formats as the Transmitter, and can detect Frame Error, Data OverRun and Parity Errors.
AVR USART vs. AVR UART –
Compatibility
The USART is fully compatible with the AVR UART regarding:
•
Bit locations inside all USART Registers.
•
Baud Rate Generation.
•
Transmitter Operation.
•
Transmit Buffer Functionality.
•
Receiver Operation.
However, the receive buffering has two improvements that will affect the compatibility in
some special cases:
•
A second Buffer Register has been added. The two Buffer Registers operate as a
circular FIFO buffer. Therefore the UDR must only be read once for each incoming
data! More important is the fact that the error flags (FE and DOR) and the ninth data
bit (RXB8) are buffered with the data in the receive buffer. Therefore the status bits
must always be read before the UDR Register is read. Otherwise the error status
will be lost since the buffer state is lost.
•
The Receiver Shift Register can now act as a third buffer level. This is done by
allowing the received data to remain in the serial Shift Register (see Figure 52) if the
Buffer Registers are full, until a new start bit is detected. The USART is therefore
more resistant to Data OverRun (DOR) error conditions.
The following control bits have changed name, but have same functionality and register
location:
Clock Generation
•
CHR9 is changed to UCSZ2.
•
OR is changed to DOR.
The Clock Generation logic generates the base clock for the Transmitter and Receiver.
The USART supports four modes of clock operation: Normal asynchronous, Double
Speed asynchronous, Master synchronous and Slave synchronous mode. The UMSEL
bit in USART Control and Status Register C (UCSRC) selects between asynchronous
and synchronous operation. Double Speed (asynchronous mode only) is controlled by
the U2X found in the UCSRA Register. When using synchronous mode (UMSEL = 1),
the Data Direction Register for the XCK pin (DDR_XCK) controls whether the clock
source is internal (Master mode) or external (Slave mode). The XCK pin is only active
when using synchronous mode.
Figure 53 shows a block diagram of the clock generation logic.
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Figure 53. Clock Generation Logic, Block Diagram
UBRR
U2X
fosc
Prescaling
Down-Counter
UBRR+1
/2
/4
/2
0
1
0
OSC
DDR_XCK
xcki
XCK
Pin
Sync
Register
Edge
Detector
xcko
DDR_XCK
1
0
UMSEL
1
UCPOL
txclk
1
0
rxclk
Signal description:
Internal Clock Generation –
The Baud Rate Generator
txclk
Transmitter clock (Internal Signal).
rxclk
Receiver base clock (Internal Signal).
xcki
Input from XCK pin (internal Signal). Used for synchronous slave operation.
xcko
Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
fosc
XTAL pin frequency (System Clock).
Internal clock generation is used for the asynchronous and the synchronous master
modes of operation. The description in this section refers to Figure 53.
The USART Baud Rate Register (UBRR) and the down-counter connected to it function
as a programmable prescaler or baud rate generator. The down-counter, running at system clock (fosc), is loaded with the UBRR value each time the counter has counted down
to zero or when the UBRRL Register is written. A clock is generated each time the
counter reaches zero. This clock is the baud rate generator clock output (=
fosc/(UBRR+1)). The Transmitter divides the baud rate generator clock output by 2, 8 or
16 depending on mode. The baud rate generator output is used directly by the
Receiver’s clock and data recovery units. However, the recovery units use a state
machine that uses 2, 8 or 16 states depending on mode set by the state of the UMSEL,
U2X and DDR_XCK bits.
Table 48 contains equations for calculating the baud rate (in bits per second) and for
calculating the UBRR value for each mode of operation using an internally generated
clock source.
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Table 48. Equations for Calculating Baud Rate Register Setting
Equation for Calculating
Baud Rate(1)
Equation for Calculating
UBRR Value
Asynchronous Normal
mode (U2X = 0)
f OSC
BAUD = -------------------------------------16 ( UBRR + 1 )
f OSC
UBRR = -----------------------–1
16BAUD
Asynchronous Double
Speed mode (U2X = 1)
f OSC
BAUD = ---------------------------------8 ( UBRR + 1 )
f OSC
UBRR = -------------------–1
8BAUD
Synchronous Master
mode
f OSC
BAUD = ---------------------------------2 ( UBRR + 1 )
f OSC
UBRR = -------------------–1
2BAUD
Operating Mode
Note:
1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD Baud rate (in bits per second, bps)
fOSC
System Oscillator clock frequency
UBRR Contents of the UBRRH and UBRRL Registers, (0-4095)
Some examples of UBRR values for some system clock frequencies are found in Table
56 (see page 133).
Double Speed Operation
(U2X)
The transfer rate can be doubled by setting the U2X bit in UCSRA. Setting this bit only
has effect for the asynchronous operation. Set this bit to zero when using synchronous
operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively
doubling the transfer rate for asynchronous communication. Note however that the
Receiver will in this case only use half the number of samples (reduced from 16 to 8) for
data sampling and clock recovery, and therefore a more accurate baud rate setting and
system clock are required when this mode is used. For the Transmitter, there are no
downsides.
External Clock
External clocking is used by the synchronous slave modes of operation. The description
in this section refers to Figure 53 for details.
External clock input from the XCK pin is sampled by a synchronization register to minimize the chance of meta-stability. The output from the synchronization register must
then pass through an edge detector before it can be used by the Transmitter and
Receiver. This process introduces a two CPU clock period delay and therefore the maximum external XCK clock frequency is limited by the following equation:
f OSC
f XCK < ----------4
Note that fosc depends on the stability of the system clock source. It is therefore recommended to add some margin to avoid possible loss of data due to frequency variations.
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Synchronous Clock Operation When synchronous mode is used (UMSEL = 1), the XCK pin will be used as either clock
input (Slave) or clock output (Master). The dependency between the clock edges and
data sampling or data change is the same. The basic principle is that data input (on
RxD) is sampled at the opposite XCK clock edge of the edge the data output (TxD) is
changed.
Figure 54. Synchronous Mode XCK Timing.
UCPOL = 1
XCK
RxD / TxD
Sample
UCPOL = 0
XCK
RxD / TxD
Sample
The UCPOL bit UCRSC selects which XCK clock edge is used for data sampling and
which is used for data change. As Figure 54 shows, when UCPOL is zero the data will
be changed at rising XCK edge and sampled at falling XCK edge. If UCPOL is set, the
data will be changed at falling XCK edge and sampled at rising XCK edge.
Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start
and stop bits), and optionally a parity bit for error checking. The USART accepts all 30
combinations of the following as valid frame formats:
•
1 start bit
•
5, 6, 7, 8, or 9 data bits
•
no, even or odd parity bit
•
1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next
data bits, up to a total of nine, are succeeding, ending with the most significant bit. If
enabled, the parity bit is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can be directly followed by a new frame, or the
communication line can be set to an idle (high) state. Figure 55 illustrates the possible
combinations of the frame formats. Bits inside brackets are optional.
Figure 55. Frame Formats
FRAME
(IDLE)
114
St
0
1
2
3
4
St
Start bit, always low.
(n)
Data bits (0 to 8).
P
Parity bit. Can be odd or even.
[5]
[6]
[7]
[8]
[P]
Sp1 [Sp2]
(St / IDLE)
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Sp
Stop bit, always high.
IDLE
No transfers on the communication line (RxD or TxD). An IDLE line must be
high.
The frame format used by the USART is set by the UCSZ2:0, UPM1:0 and USBS bits in
UCSRB and UCSRC. The Receiver and Transmitter use the same setting. Note that
changing the setting of any of these bits will corrupt all ongoing communication for both
the Receiver and Transmitter.
The USART Character SiZe (UCSZ2:0) bits select the number of data bits in the frame.
The USART Parity mode (UPM1:0) bits enable and set the type of parity bit. The selection between one or two stop bits is done by the USART Stop Bit Select (USBS) bit. The
Receiver ignores the second stop bit. An FE (Frame Error) will therefore only be
detected in the cases where the first stop bit is zero.
Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is
used, the result of the exclusive or is inverted. The relation between the parity bit and
data bits is as follows:
P even = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 0
P odd = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 1
Peven
Parity bit using even parity
Podd
Parity bit using odd parity
dn
Data bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial
frame.
USART Initialization
The USART has to be initialized before any communication can take place. The initialization process normally consists of setting the baud rate, setting frame format and
enabling the Transmitter or the Receiver depending on the usage. For interrupt driven
USART operation, the Global Interrupt Flag should be cleared (and interrupts globally
disabled) when doing the initialization.
Before doing a re-initialization with changed baud rate or frame format, be sure that
there are no ongoing transmissions during the period the registers are changed. The
TXC flag can be used to check that the Transmitter has completed all transfers, and the
RXC flag can be used to check that there are no unread data in the receive buffer. Note
that the TXC flag must be cleared before each transmission (before UDR is written) if it
is used for this purpose.
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The following simple USART initialization code examples show one assembly and one
C function that are equal in functionality. The examples assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format. The baud rate is
given as a function parameter. For the assembly code, the baud rate parameter is
assumed to be stored in the r17:r16 Registers.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out
UBRRH, r17
out
UBRRL, r16
; Enable receiver and transmitter
ldi
r16, (1<<RXEN)|(1<<TXEN)
out
UCSRB,r16
; Set frame format: 8data, 2stop bit
ldi
r16, (1<<USBS)|(3<<UCSZ0)
out
UCSRC,r16
ret
C Code Example(1)
void USART_Init( unsigned int baud )
{
/* Set baud rate */
UBRRH = (unsigned char)(baud>>8);
UBRRL = (unsigned char)baud;
/* Enable receiver and transmitter */
UCSRB = (1<<RXEN)|(1<<TXEN);
/* Set frame format: 8data, 2stop bit */
UCSRC = (1<<USBS)|(3<<UCSZ0);
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
More advanced initialization routines can be made that include frame format as parameters, disable interrupts and so on. However, many applications use a fixed setting of the
baud and control registers, and for these types of applications the initialization code can
be placed directly in the main routine, or be combined with initialization code for other
I/O modules.
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Data Transmission – The
USART Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the
UCSRB Register. When the Transmitter is enabled, the normal port operation of the
TxD pin is overridden by the USART and given the function as the Transmitter’s serial
output. The baud rate, mode of operation and frame format must be set up once before
doing any transmissions. If synchronous operation is used, the clock on the XCK pin will
be overridden and used as transmission clock.
Sending Frames with 5 to 8
Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The CPU can load the transmit buffer by writing to the UDR I/O location. The
buffered data in the transmit buffer will be moved to the Shift Register when the Shift
Register is ready to send a new frame. The Shift Register is loaded with new data if it is
in idle state (no ongoing transmission) or immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is loaded with new data, it will transfer
one complete frame at the rate given by the Baud Register, U2X bit or by XCK depending on mode of operation.
The following code examples show a simple USART transmit function based on polling
of the Data Register Empty (UDRE) flag. When using frames with less than eight bits,
the most significant bits written to the UDR are ignored. The USART has to be initialized
before the function can be used. For the assembly code, the data to be sent is assumed
to be stored in Register R16
Assembly Code Example(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out
UDR,r16
ret
C Code Example(1)
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE)) )
;
/* Put data into buffer, sends the data */
UDR = data;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The function simply waits for the transmit buffer to be empty by checking the UDRE flag,
before loading it with new data to be transmitted. If the Data Register Empty interrupt is
utilized, the interrupt routine writes the data into the buffer.
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Sending Frames with 9 Data
Bit
If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8 bit in
UCSRB before the low byte of the character is written to UDR. The following code
examples show a transmit function that handles 9-bit characters. For the assembly
code, the data to be sent is assumed to be stored in registers R17:R16.
Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi
UCSRB,TXB8
sbrc r17,0
sbi
UCSRB,TXB8
; Put LSB data (r16) into buffer, sends the data
out
UDR,r16
ret
C Code Example(1)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) )
;
/* Copy 9th bit to TXB8 */
UCSRB &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSRB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDR = data;
}
Notes:
1. These transmit functions are written to be general functions. They can be optimized if
the contents of the UCSRB is static. For example, only the TXB8 bit of the UCSRB
Register is used after initialization.
2. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The ninth bit can be used for indicating an address frame when using multi processor
communication mode or for other protocol handling as for example synchronization.
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Transmitter Flags and
Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register
Empty (UDRE) and Transmit Complete (TXC). Both flags can be used for generating
interrupts.
The Data Register Empty (UDRE) flag indicates whether the transmit buffer is ready to
receive new data. This bit is set when the transmit buffer is empty, and cleared when the
transmit buffer contains data to be transmitted that has not yet been moved into the Shift
Register. For compatibility with future devices, always write this bit to zero when writing
the UCSRA Register.
When the Data Register Empty Interrupt Enable (UDRIE) bit in UCSRB is written to one,
the USART Data Register Empty Interrupt will be executed as long as UDRE is set (provided that global interrupts are enabled). UDRE is cleared by writing UDR. When
interrupt-driven data transmission is used, the Data Register Empty interrupt routine
must either write new data to UDR in order to clear UDRE or disable the Data Register
Empty interrupt, otherwise a new interrupt will occur once the interrupt routine
terminates.
The Transmit Complete (TXC) flag bit is set one when the entire frame in the Transmit
Shift Register has been shifted out and there are no new data currently present in the
transmit buffer. The TXC flag bit is automatically cleared when a transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location. The TXC flag is
useful in half-duplex communication interfaces (like the RS-485 standard), where a
transmitting application must enter receive mode and free the communication bus
immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIE) bit in UCSRB is set, the USART
Transmit Complete Interrupt will be executed when the TXC flag becomes set (provided
that global interrupts are enabled). When the transmit complete interrupt is used, the
interrupt handling routine does not have to clear the TXC flag, this is done automatically
when the interrupt is executed.
Parity Generator
The Parity Generator calculates the parity bit for the serial frame data. When parity bit is
enabled (UPM1 = 1), the transmitter control logic inserts the parity bit between the last
data bit and the first stop bit of the frame that is sent.
Disabling the Transmitter
The disabling of the Transmitter (setting the TXEN to zero) will not become effective
until ongoing and pending transmissions are completed, i.e., when the Transmit Shift
Register and Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter will no longer override the TxD pin.
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Data Reception – The
USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXEN) bit in the
UCSRB Register to one. When the Receiver is enabled, the normal pin operation of the
RxD pin is overridden by the USART and given the function as the Receiver’s serial
input. The baud rate, mode of operation and frame format must be set up once before
any serial reception can be done. If synchronous operation is used, the clock on the
XCK pin will be used as transfer clock.
Receiving Frames with 5 to 8
Data Bits
The Receiver starts data reception when it detects a valid start bit. Each bit that follows
the start bit will be sampled at the baud rate or XCK clock, and shifted into the Receive
Shift Register until the first stop bit of a frame is received. A second stop bit will be
ignored by the Receiver. When the first stop bit is received, i.e., a complete serial frame
is present in the Receive Shift Register, the contents of the Shift Register will be moved
into the receive buffer. The receive buffer can then be read by reading the UDR I/O
location.
The following code example shows a simple USART receive function based on polling
of the Receive Complete (RXC) flag. When using frames with less than eight bits the
most significant bits of the data read from the UDR will be masked to zero. The USART
has to be initialized before the function can be used.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSRA, RXC
rjmp USART_Receive
; Get and return received data from buffer
in
r16, UDR
ret
C Code Example(1)
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSRA & (1<<RXC)) )
;
/* Get and return received data from buffer */
return UDR;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The function simply waits for data to be present in the receive buffer by checking the
RXC flag, before reading the buffer and returning the value.
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Receiving Frames with 9 Data
Bits
If 9-bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8 bit in
UCSRB before reading the low bits from the UDR. This rule applies to the FE, DOR and
UPE Status Flags as well. Read status from UCSRA, then data from UDR. Reading the
UDR I/O location will change the state of the receive buffer FIFO and consequently the
TXB8, FE, DOR and UPE bits, which all are stored in the FIFO, will change.
The following code example shows a simple USART receive function that handles both
nine bit characters and the status bits.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSRA, RXC
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
in
r18, UCSRA
in
r17, UCSRB
in
r16, UDR
; If error, return -1
andi r18,(1<<FE)|(1<<DOR)|(1<<UPE)
breq USART_ReceiveNoError
ldi
r17, HIGH(-1)
ldi
r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr
r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSRA & (1<<RXC)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSRA;
resh = UCSRB;
resl = UDR;
/* If error, return -1 */
if ( status & (1<<FE)|(1<<DOR)|(1<<UPE) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
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Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The receive function example reads all the I/O Registers into the Register File before
any computation is done. This gives an optimal receive buffer utilization since the buffer
location read will be free to accept new data as early as possible.
Receive Compete Flag and
Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) flag indicates if there are unread data present in the
receive buffer. This flag is one when unread data exist in the receive buffer, and zero
when the receive buffer is empty (i.e., does not contain any unread data). If the Receiver
is disabled (RXEN = 0), the receive buffer will be flushed and consequently the RXC bit
will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRB is set, the USART
Receive Complete interrupt will be executed as long as the RXC flag is set (provided
that global interrupts are enabled). When interrupt-driven data reception is used, the
receive complete routine must read the received data from UDR in order to clear the
RXC flag, otherwise a new interrupt will occur once the interrupt routine terminates.
Receiver Error Flags
The USART Receiver has three error flags: Frame Error (FE), Data OverRun (DOR) and
Parity Error (UPE). All can be accessed by reading UCSRA. Common for the error flags
is that they are located in the receive buffer together with the frame for which they indicate the error status. Due to the buffering of the error flags, the UCSRA must be read
before the receive buffer (UDR), since reading the UDR I/O location changes the buffer
read location. Another equality for the error flags is that they can not be altered by software doing a write to the flag location. However, all flags must be set to zero when the
UCSRA is written for upward compatibility of future USART implementations. None of
the error flags can generate interrupts.
The Frame Error (FE) flag indicates the state of the first stop bit of the next readable
frame stored in the receive buffer. The FE flag is zero when the stop bit was correctly
read (as one), and the FE flag will be one when the stop bit was incorrect (zero). This
flag can be used for detecting out-of-sync conditions, detecting break conditions and
protocol handling. The FE flag is not affected by the setting of the USBS bit in UCSRC
since the Receiver ignores all, except for the first, stop bits. For compatibility with future
devices, always set this bit to zero when writing to UCSRA.
The Data OverRun (DOR) flag indicates data loss due to a receiver buffer full condition.
A Data OverRun occurs when the receive buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a new start bit is detected. If the DOR
flag is set there was one or more serial frame lost between the frame last read from
UDR, and the next frame read from UDR. For compatibility with future devices, always
write this bit to zero when writing to UCSRA. The DOR flag is cleared when the frame
received was successfully moved from the Shift Register to the receive buffer.
The Parity Error (UPE) Flag indicates that the next frame in the receive buffer had a Parity Error when received. If Parity Check is not enabled the UPE bit will always be read
zero. For compatibility with future devices, always set this bit to zero when writing to
UCSRA. For more details see “Parity Bit Calculation” on page 115 and “Parity Checker”
on page 123.
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Parity Checker
The Parity Checker is active when the high USART Parity mode (UPM1) bit is set. Type
of Parity Check to be performed (odd or even) is selected by the UPM0 bit. When
enabled, the Parity Checker calculates the parity of the data bits in incoming frames and
compares the result with the parity bit from the serial frame. The result of the check is
stored in the receive buffer together with the received data and stop bits. The Parity
Error (UPE) flag can then be read by software to check if the frame had a Parity Error.
The UPE bit is set if the next character that can be read from the receive buffer had a
Parity Error when received and the Parity Checking was enabled at that point (UPM1 =
1). This bit is valid until the receive buffer (UDR) is read.
Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from
ongoing receptions will therefore be lost. When disabled (i.e., the RXEN is set to zero)
the Receiver will no longer override the normal function of the RxD port pin. The
Receiver buffer FIFO will be flushed when the Receiver is disabled. Remaining data in
the buffer will be lost
Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer
will be emptied of its contents. Unread data will be lost. If the buffer has to be flushed
during normal operation, due to for instance an error condition, read the UDR I/O location until the RXC flag is cleared. The following code example shows how to flush the
receive buffer.
Assembly Code Example(1)
USART_Flush:
sbis UCSRA, RXC
ret
in
r16, UDR
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSRA & (1<<RXC) ) dummy = UDR;
}
Note:
Asynchronous Data
Reception
1. The example code assumes that the part specific header file is included.
For I/O Registers located in 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 “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The USART includes a clock recovery and a data recovery unit for handling asynchronous data reception. The clock recovery logic is used for synchronizing the internally
generated baud rate clock to the incoming asynchronous serial frames at the RxD pin.
The data recovery logic samples and low pass filters each incoming bit, thereby improving the noise immunity of the Receiver. The asynchronous reception operational range
depends on the accuracy of the internal baud rate clock, the rate of the incoming
frames, and the frame size in number of bits.
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Asynchronous Clock
Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 56 illustrates the sampling process of the start bit of an incoming frame. The sample
rate is 16 times the baud rate for Normal mode, and eight times the baud rate for Double
Speed mode. The horizontal arrows illustrate the synchronization variation due to the
sampling process. Note the larger time variation when using the Double Speed mode
(U2X = 1) of operation. Samples denoted zero are samples done when the RxD line is
idle (i.e., no communication activity).
Figure 56. Start Bit Sampling
RxD
IDLE
START
BIT 0
Sample
(U2X = 0)
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
Sample
(U2X = 1)
0
1
2
3
4
5
6
7
8
1
2
When the clock recovery logic detects a high (idle) to low (start) transition on the RxD
line, the start bit detection sequence is initiated. Let sample 1 denote the first zero-sample as shown in the figure. The clock recovery logic then uses samples 8, 9, and 10 for
Normal mode, and samples 4, 5, and 6 for Double Speed mode (indicated with sample
numbers inside boxes on the figure), to decide if a valid start bit is received. If two or
more of these three samples have logical high levels (the majority wins), the start bit is
rejected as a noise spike and the Receiver starts looking for the next high to low-transition. If however, a valid start bit is detected, the clock recovery logic is synchronized and
the data recovery can begin. The synchronization process is repeated for each start bit.
Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin.
The data recovery unit uses a state machine that has 16 states for each bit in Normal
mode and eight states for each bit in Double Speed mode. Figure 57 shows the sampling of the data bits and the parity bit. Each of the samples is given a number that is
equal to the state of the recovery unit.
Figure 57. Sampling of Data and Parity Bit
RxD
BIT n
Sample
(U2X = 0)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
Sample
(U2X = 1)
1
2
3
4
5
6
7
8
1
The decision of the logic level of the received bit is taken by doing a majority voting of
the logic value to the three samples in the center of the received bit. The center samples
are emphasized on the figure by having the sample number inside boxes. The majority
voting process is done as follows: If two or all three samples have high levels, the
received bit is registered to be a logic 1. If two or all three samples have low levels, the
received bit is registered to be a logic 0. This majority voting process acts as a low pass
filter for the incoming signal on the RxD pin. The recovery process is then repeated until
a complete frame is received. Including the first stop bit. Note that the Receiver only
uses the first stop bit of a frame.
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Figure 58 shows the sampling of the stop bit and the earliest possible beginning of the
start bit of the next frame.
Figure 58. Stop Bit Sampling and Next Start Bit Sampling
RxD
STOP 1
(A)
(B)
(C)
Sample
(U2X = 0)
1
2
3
4
5
6
7
8
9
10
0/1
0/1
0/1
Sample
(U2X = 1)
1
2
3
4
5
6
0/1
The same majority voting is done to the stop bit as done for the other bits in the frame. If
the stop bit is registered to have a logic 0 value, the Frame Error (FE) flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after
the last of the bits used for majority voting. For Normal Speed mode, the first low level
sample can be at point marked (A) in Figure 58. For Double Speed mode the first low
level must be delayed to (B). (C) marks a stop bit of full length. The early start bit detection influences the operational range of the Receiver.
Asynchronous Operational
Range
The operational range of the Receiver is dependent on the mismatch between the
received bit rate and the internally generated baud rate. If the Transmitter is sending
frames at too fast or too slow bit rates, or the internally generated baud rate of the
Receiver does not have a similar (see Table 49) base frequency, the Receiver will not
be able to synchronize the frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and
internal receiver baud rate.
( D + 1 )S
R slow = -----------------------------------------S – 1 + D ⋅ S + SF
( D + 2 )S
R fast = ----------------------------------( D + 1 )S + S M
D
Sum of character size and parity size (D = 5 to 10 bit)
S
Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
SF
First sample number used for majority voting. SF = 8 for normal speed and SF = 4
for Double Speed mode.
SM
Middle sample number used for majority voting. SM = 9 for normal speed and
SM = 5 for Double Speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
Table 49 and Table 50 list the maximum receiver baud rate error that can be tolerated.
Note that Normal Speed mode has higher toleration of baud rate variations.
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Table 49. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode
(U2X = 0)
D
# (Data+Parity Bit)
Rslow (%)
Rfast (%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
93.20
106.67
+6.67/-6.8
± 3.0
6
94.12
105.79
+5.79/-5.88
± 2.5
7
94.81
105.11
+5.11/-5.19
± 2.0
8
95.36
104.58
+4.58/-4.54
± 2.0
9
95.81
104.14
+4.14/-4.19
± 1.5
10
96.17
103.78
+3.78/-3.83
± 1.5
Table 50. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2X = 1)
D
# (Data+Parity Bit)
Rslow (%)
Rfast (%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
94.12
105.66
+5.66/-5.88
± 2.5
6
94.92
104.92
+4.92/-5.08
± 2.0
7
95.52
104,35
+4.35/-4.48
± 1.5
8
96.00
103.90
+3.90/-4.00
± 1.5
9
96.39
103.53
+3.53/-3.61
± 1.5
10
96.70
103.23
+3.23/-3.30
± 1.0
The recommendations of the maximum receiver baud rate error was made under the
assumption that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The Receiver’s system
clock (XTAL) will always have some minor instability over the supply voltage range and
the temperature range. When using a crystal to generate the system clock, this is rarely
a problem, but for a resonator the system clock may differ more than 2% depending of
the resonators tolerance. The second source for the error is more controllable. The baud
rate generator can not always do an exact division of the system frequency to get the
baud rate wanted. In this case an UBRR value that gives an acceptable low error can be
used if possible.
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Multi-processor
Communication Mode
Setting the Multi-processor Communication mode (MPCM) bit in UCSRA enables a filtering function of incoming frames received by the USART Receiver. Frames that do not
contain address information will be ignored and not put into the receive buffer. This
effectively reduces the number of incoming frames that has to be handled by the CPU,
in a system with multiple MCUs that communicate via the same serial bus. The Transmitter is unaffected by the MPCM setting, but has to be used differently when it is a part
of a system utilizing the Multi-processor Communication mode.
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop
bit indicates if the frame contains data or address information. If the Receiver is set up
for frames with nine data bits, then the ninth bit (RXB8) is used for identifying address
and data frames. When the frame type bit (the first stop or the ninth bit) is one, the frame
contains an address. When the frame type bit is zero the frame is a data frame.
The Multi-processor Communication mode enables several slave MCUs to receive data
from a master MCU. This is done by first decoding an address frame to find out which
MCU has been addressed. If a particular slave MCU has been addressed, it will receive
the following data frames as normal, while the other slave MCUs will ignore the received
frames until another address frame is received.
Using MPCM
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZ =
7). The ninth bit (TXB8) must be set when an address frame (TXB8 = 1) or cleared when
a data frame (TXB = 0) is being transmitted. The slave MCUs must in this case be set to
use a 9-bit character frame format.
The following procedure should be used to exchange data in Multi-processor Communication mode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCM in UCSRA
is set).
2. The Master MCU sends an address frame, and all slaves receive and read this
frame. In the Slave MCUs, the RXC flag in UCSRA will be set as normal.
3. Each Slave MCU reads the UDR Register and determines if it has been
selected. If so, it clears the MPCM bit in UCSRA, otherwise it waits for the next
address byte and keeps the MPCM setting.
4. The addressed MCU will receive all data frames until a new address frame is
received. The other Slave MCUs, which still have the MPCM bit set, will ignore
the data frames.
5. When the last data frame is received by the addressed MCU, the addressed
MCU sets the MPCM bit and waits for a new address frame from master. The
process then repeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the
Receiver must change between using n and n+1 character frame formats. This makes
full-duplex operation difficult since the Transmitter and Receiver uses the same character size setting. If 5- to 8-bit character frames are used, the Transmitter must be set to
use two stop bit (USBS = 1) since the first stop bit is used for indicating the frame type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCM bit.
The MPCM bit shares the same I/O location as the TXC flag and this might accidentally
be cleared when using SBI or CBI instructions.
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USART Register
Description
USART I/O Data Register –
UDR
Bit
7
6
5
4
3
2
1
0
RXB[7:0]
UDR (Read)
TXB[7:0]
UDR (Write)
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 USART Transmit Data Buffer Register and USART Receive Data Buffer Registers
share the same I/O address referred to as USART Data Register or UDR. The Transmit
Data Buffer Register (TXB) will be the destination for data written to the UDR Register
location. Reading the UDR Register location will return the contents of the Receive Data
Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter
and set to zero by the Receiver.
The transmit buffer can only be written when the UDRE flag in the UCSRA Register is
set. Data written to UDR when the UDRE flag is not set, will be ignored by the USART
Transmitter. When data is written to the transmit buffer, and the Transmitter is enabled,
the Transmitter will load the data into the Transmit Shift Register when the Shift Register
is empty. Then the data will be serially transmitted on the TxD pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever
the receive buffer is accessed. Due to this behavior of the receive buffer, do not use
Read-Modify-Write instructions (SBI and CBI) on this location. Be careful when using bit
test instructions (SBIC and SBIS), since these also will change the state of the FIFO.
USART Control and Status
Register A – UCSRA
Bit
7
6
5
4
3
2
1
0
RXC
TXC
UDRE
FE
DOR
UPE
U2X
MPCM
Read/Write
R
R/W
R
R
R
R
R/W
R/W
Initial Value
0
0
1
0
0
0
0
0
UCSRA
• Bit 7 – RXC: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the
receive buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive buffer will be flushed and consequently the RXC bit will become zero.
The RXC flag can be used to generate a Receive Complete interrupt (see description of
the RXCIE bit).
• Bit 6 – TXC: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted
out and there are no new data currently present in the transmit buffer (UDR). The TXC
flag bit is automatically cleared when a transmit complete interrupt is executed, or it can
be cleared by writing a one to its bit location. The TXC flag can generate a Transmit
Complete interrupt (see description of the TXCIE bit).
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• Bit 5 – UDRE: USART Data Register Empty
The UDRE flag indicates if the transmit buffer (UDR) is ready to receive new data. If
UDRE is one, the buffer is empty, and therefore ready to be written. The UDRE flag can
generate a Data Register Empty interrupt (see description of the UDRIE bit).
UDRE is set after a reset to indicate that the Transmitter is ready.
• Bit 4 – FE: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when
received. I.e., when the first stop bit of the next character in the receive buffer is zero.
This bit is valid until the receive buffer (UDR) is read. The FE bit is zero when the stop
bit of received data is one. Always set this bit to zero when writing to UCSRA.
• Bit 3 – DOR: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the
receive buffer is full (two characters), it is a new character waiting in the Receive Shift
Register, and a new start bit is detected. This bit is valid until the receive buffer (UDR) is
read. Always set this bit to zero when writing to UCSRA.
• Bit 2 – UPE: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received
and the Parity Checking was enabled at that point (UPM1 = 1). This bit is valid until the
receive buffer (UDR) is read. Always set this bit to zero when writing to UCSRA.
• Bit 1 – U2X: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using
synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for asynchronous communication.
• Bit 0 – MPCM: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCM bit is written to one, all the incoming frames received by the USART Receiver that do not contain
address information will be ignored. The Transmitter is unaffected by the MPCM setting.
For more detailed information see “Multi-processor Communication Mode” on page 127.
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USART Control and Status
Register B – UCSRB
Bit
7
6
5
4
3
2
1
0
RXCIE
TXCIE
UDRIE
RXEN
TXEN
UCSZ2
RXB8
TXB8
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
R/W
Initial Value
0
0
0
0
0
0
0
0
UCSRB
• Bit 7 – RXCIE: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXC flag. A USART Receive Complete
interrupt will be generated only if the RXCIE bit is written to one, the Global Interrupt
Flag in SREG is written to one and the RXC bit in UCSRA is set.
• Bit 6 – TXCIE: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXC flag. A USART Transmit Complete
interrupt will be generated only if the TXCIE bit is written to one, the Global Interrupt
Flag in SREG is written to one and the TXC bit in UCSRA is set.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDRE flag. A Data Register Empty interrupt will be generated only if the UDRIE bit is written to one, the Global Interrupt Flag in
SREG is written to one and the UDRE bit in UCSRA is set.
• Bit 4 – RXEN: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal
port operation for the RxD pin when enabled. Disabling the Receiver will flush the
receive buffer invalidating the FE, DOR, and UPE Flags.
• Bit 3 – TXEN: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port operation for the TxD pin when enabled. The disabling of the Transmitter
(writing TXEN to zero) will not become effective until ongoing and pending transmissions are completed, i.e., when the Transmit Shift Register and Transmit Buffer Register
do not contain data to be transmitted. When disabled, the Transmitter will no longer
override the TxD port.
• Bit 2 – UCSZ2: Character Size
The UCSZ2 bits combined with the UCSZ1:0 bit in UCSRC sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8: Receive Data Bit 8
RXB8 is the ninth data bit of the received character when operating with serial frames
with nine data bits. Must be read before reading the low bits from UDR.
• Bit 0 – TXB8: Transmit Data Bit 8
TXB8 is the ninth data bit in the character to be transmitted when operating with serial
frames with nine data bits. Must be written before writing the low bits to UDR.
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USART Control and Status
Register C – UCSRC
Bit
7
6
5
4
3
2
1
0
–
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
1
1
0
UCSRC
• Bit 6 – UMSEL: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
Table 51. UMSEL Bit Settings
UMSEL
Mode
0
Asynchronous Operation
1
Synchronous Operation
• Bit 5:4 – UPM1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter will automatically generate and send the parity of the transmitted data bits within
each frame. The Receiver will generate a parity value for the incoming data and compare it to the UPM0 setting. If a mismatch is detected, the UPE Flag in UCSRA will be
set.
Table 52. UPM Bits Settings
UPM1
UPM0
Parity Mode
0
0
Disabled
0
1
Reserved
1
0
Enabled, Even Parity
1
1
Enabled, Odd Parity
• Bit 3 – USBS: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver
ignores this setting.
Table 53. USBS Bit Settings
USBS
Stop Bit(s)
0
1-bit
1
2-bit
• Bit 2:1 – UCSZ1:0: Character Size
The UCSZ1:0 bits combined with the UCSZ2 bit in UCSRB sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use. See Table 54 on page
132.
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Table 54. UCSZ Bits Settings
UCSZ2
UCSZ1
UCSZ0
Character Size
0
0
0
5-bit
0
0
1
6-bit
0
1
0
7-bit
0
1
1
8-bit
1
0
0
Reserved
1
0
1
Reserved
1
1
0
Reserved
1
1
1
9-bit
• Bit 0 – UCPOL: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous
mode is used. The UCPOL bit sets the relationship between data output change and
data input sample, and the synchronous clock (XCK).
Table 55. UCPOL Bit Settings
Transmitted Data Changed (Output of
TxD Pin)
Received Data Sampled (Input on
RxD Pin)
0
Rising XCK Edge
Falling XCK Edge
1
Falling XCK Edge
Rising XCK Edge
UCPOL
USART Baud Rate Registers –
UBRRL and UBRRH
Bit
15
14
13
12
–
–
–
–
11
10
9
8
UBRR[11:8]
UBRRH
UBRR[7:0]
7
Read/Write
Initial Value
6
5
UBRRL
4
3
2
1
0
R
R
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit
must be written to zero when UBRRH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the
four most significant bits, and the UBRRL contains the eight least significant bits of the
USART baud rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate is changed. Writing UBRRL will trigger an immediate update of
the baud rate prescaler.
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Examples of Baud Rate
Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for
asynchronous operation can be generated by using the UBRR settings in Table 56.
UBRR values which yield an actual baud rate differing less than 0.5% from the target
baud rate, are bold in the table. Higher error ratings are acceptable, but the Receiver will
have less noise resistance when the error ratings are high, especially for large serial
frames (see “Asynchronous Operational Range” on page 125). The error values are calculated using the following equation:
BaudRate Closest Match
- – 1⎞⎠ • 100%
Error[%] = ⎛⎝ ------------------------------------------------------BaudRate
Table 56. Examples of UBRR Settings for Commonly Used Oscillator Frequencies
fosc = 1.0000 MHz
fosc = 1.8432 MHz
fosc = 2.0000 MHz
Baud
Rate
(bps)
UBRR
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
51
0.2%
103
0.2%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
25
0.2%
51
0.2%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
12
0.2%
25
0.2%
14.4k
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
19.2k
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
28.8k
1
8.5%
3
8.5%
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
38.4k
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
57.6k
0
8.5%
1
8.5%
1
0.0%
3
0.0%
1
8.5%
3
8.5%
76.8k
–
–
1
-18.6%
1
-25.0%
2
0.0%
1
-18.6%
2
8.5%
115.2k
–
–
0
8.5%
0
0.0%
1
0.0%
0
8.5%
1
8.5%
230.4k
–
–
–
–
–
–
0
0.0%
–
–
–
–
250k
–
–
–
–
–
–
–
–
–
–
0
0.0%
Max.
1.
U2X = 0
(1)
U2X = 1
Error
UBRR
62.5 kbps
U2X = 0
Error
125 kbps
UBRR
U2X = 1
Error
115.2 kbps
UBRR
U2X = 0
Error
230.4 kbps
UBRR
U2X = 1
Error
125 kbps
UBRR
Error
250 kbps
UBRR = 0, Error = 0.0%
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Table 57. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 3.6864 MHz
fosc = 4.0000 MHz
fosc = 7.3728 MHz
Baud
Rate
(bps)
UBRR
2400
95
0.0%
191
0.0%
103
0.2%
207
0.2%
191
0.0%
383
0.0%
4800
47
0.0%
95
0.0%
51
0.2%
103
0.2%
95
0.0%
191
0.0%
9600
23
0.0%
47
0.0%
25
0.2%
51
0.2%
47
0.0%
95
0.0%
14.4k
15
0.0%
31
0.0%
16
2.1%
34
-0.8%
31
0.0%
63
0.0%
19.2k
11
0.0%
23
0.0%
12
0.2%
25
0.2%
23
0.0%
47
0.0%
28.8k
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
15
0.0%
31
0.0%
38.4k
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
57.6k
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
76.8k
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
115.2k
1
0.0%
3
0.0%
1
8.5%
3
8.5%
3
0.0%
7
0.0%
230.4k
0
0.0%
1
0.0%
0
8.5%
1
8.5%
1
0.0%
3
0.0%
250k
0
-7.8%
1
-7.8%
0
0.0%
1
0.0%
1
-7.8%
3
-7.8%
0.5M
–
–
0
-7.8%
–
–
0
0.0%
0
-7.8%
1
-7.8%
–
–
–
–
–
–
–
–
–
–
0
-7.8%
1M
Max.
1.
134
(1)
U2X = 0
U2X = 1
Error
UBRR
230.4 kbps
U2X = 0
Error
460.8 kbps
UBRR
U2X = 1
Error
250 kbps
UBRR
U2X = 0
Error
0.5 Mbps
UBRR
U2X = 1
Error
460.8 kbps
UBRR
Error
921.6 kbps
UBRR = 0, Error = 0.0%
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table 58. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 11.0592 MHz
fosc = 8.0000 MHz
fosc = 14.7456 MHz
Baud
Rate
(bps)
UBRR
2400
207
0.2%
416
-0.1%
287
0.0%
575
0.0%
383
0.0%
767
0.0%
4800
103
0.2%
207
0.2%
143
0.0%
287
0.0%
191
0.0%
383
0.0%
9600
51
0.2%
103
0.2%
71
0.0%
143
0.0%
95
0.0%
191
0.0%
14.4k
34
-0.8%
68
0.6%
47
0.0%
95
0.0%
63
0.0%
127
0.0%
19.2k
25
0.2%
51
0.2%
35
0.0%
71
0.0%
47
0.0%
95
0.0%
28.8k
16
2.1%
34
-0.8%
23
0.0%
47
0.0%
31
0.0%
63
0.0%
38.4k
12
0.2%
25
0.2%
17
0.0%
35
0.0%
23
0.0%
47
0.0%
57.6k
8
-3.5%
16
2.1%
11
0.0%
23
0.0%
15
0.0%
31
0.0%
76.8k
6
-7.0%
12
0.2%
8
0.0%
17
0.0%
11
0.0%
23
0.0%
115.2k
3
8.5%
8
-3.5%
5
0.0%
11
0.0%
7
0.0%
15
0.0%
230.4k
1
8.5%
3
8.5%
2
0.0%
5
0.0%
3
0.0%
7
0.0%
250k
1
0.0%
3
0.0%
2
-7.8%
5
-7.8%
3
-7.8%
6
5.3%
0.5M
0
0.0%
1
0.0%
–
–
2
-7.8%
1
-7.8%
3
-7.8%
–
–
0
0.0%
–
–
–
–
0
-7.8%
1
-7.8%
U2X = 0
1M
Max.
1.
(1)
U2X = 1
Error
UBRR
0.5 Mbps
Error
1 Mbps
U2X = 0
UBRR
U2X = 1
Error
691.2 kbps
UBRR
U2X = 0
Error
1.3824 Mbps
UBRR
Error
921.6 kbps
U2X = 1
UBRR
Error
1.8432 Mbps
UBRR = 0, Error = 0.0%
135
2543F–AVR–08/04
Table 59.
Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 16.0000 MHz
Baud Rate
(bps)
UBRR
U2X = 1
Error
UBRR
Error
2400
416
-0.1%
832
0.0%
4800
207
0.2%
416
-0.1%
9600
103
0.2%
207
0.2%
14.4k
68
0.6%
138
-0.1%
19.2k
51
0.2%
103
0.2%
28.8k
34
-0.8%
68
0.6%
38.4k
25
0.2%
51
0.2%
57.6k
16
2.1%
34
-0.8%
76.8k
12
0.2%
25
0.2%
115.2k
8
-3.5%
16
2.1%
230.4k
3
8.5%
8
-3.5%
250k
3
0.0%
7
0.0%
0.5M
1
0.0%
3
0.0%
0
0.0%
1
0.0%
1M
Max.
1.
136
U2X = 0
(1)
1 Mbps
2 Mbps
UBRR = 0, Error = 0.0%
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Universal Serial
Interface – USI
The Universal Serial Interface, or USI, provides the basic hardware resources needed
for serial communication. Combined with a minimum of control software, the USI allows
significantly higher transfer rates and uses less code space than solutions based on
software only. Interrupts are included to minimize the processor load. The main features
of the USI are:
• Two-wire Synchronous Data Transfer (Master or Slave, fSCLmax = fCK/16)
• Three-wire Synchronous Data Transfer (Master, fSCKmax = fCK/2, Slave fSCKmax = fCK/4)
• Data Received Interrupt
• Wake-up from Idle Mode
• In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
• Two-wire Start Condition Detector with Interrupt Capability
Overview
A simplified block diagram of the USI is shown on Figure 59. For the actual placement of
I/O pins, refer to “Pinout ATtiny2313” on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit
locations are listed in the “USI Register Descriptions” on page 143.
Figure 59. Universal Serial Interface, Block Diagram
USIPF
1
0
4-bit Counter
USIDC
USIOIF
USISIF
(Output only)
DI/SDA
(Input/Open Drain)
USCK/SCL
(Input/Open Drain)
3
2
USIDR
DATA BUS
DO
Bit0
Bit7
D Q
LE
TIM0 COMP
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 Shift Register is directly accessible via the data bus and contains the incoming
and outgoing data. The register has no buffering so the data must be read as quickly as
possible to ensure that no data is lost. The most significant bit is connected to one of two
output pins depending of the wire mode configuration. A transparent latch is inserted
between the serial register output and output pin, which delays the change of data output to the opposite clock edge of the data input sampling. The serial input is always
sampled from the Data Input (DI) pin independent of the configuration.
The 4-bit counter can be both read and written via the data bus, and can generate an
overflow interrupt. Both the serial register and the counter are clocked simultaneously
by the same clock source. This allows the counter to count the number of bits received
or transmitted and generate an interrupt when the transfer is complete. Note that when
an external clock source is selected the counter counts both clock edges. In this case
the counter counts the number of edges, and not the number of bits. The clock can be
selected from three different sources: The USCK pin, Timer0 overflow, or from software.
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2543F–AVR–08/04
The Two-wire clock control unit can generate an interrupt when a start condition is
detected on the Two-wire bus. It can also generate wait states by holding the clock pin
low after a start condition is detected, or after the counter overflows.
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 60. 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 60 shows two USI units operating in Three-wire mode, one as Master and one as
Slave. The two Shift Registers are interconnected in such way that after eight USCK
clocks, the data in each register are interchanged. The same clock also increments the
USI’s 4-bit counter. The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be
used to determine when a transfer is completed. The clock is generated by the Master
device software by toggling the USCK pin via the PORT Register or by writing a one to
the USITC bit in USICR.
Figure 61. Three-wire Mode, Timing Diagram
CYCLE
( Reference )
1
2
3
4
5
6
7
8
USCK
USCK
DO
MSB
DI
MSB
A
138
B
C
D
6
5
4
3
2
1
LSB
6
5
4
3
2
1
LSB
E
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
The Three-wire mode timing is shown in Figure 61. At the top of the figure is a USCK
cycle reference. One bit is shifted into the USI Shift Register (USIDR) for each of these
cycles. The USCK timing is shown for both external clock modes. In External Clock
mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (data register is shifted by one) at negative edges. External Clock mode 1 (USICS0 = 1) uses the
opposite edges versus mode 0, i.e., samples data at negative and changes the output at
positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 61.), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on
the protocol used, enables its output driver (mark A and B). The output is set up
by writing the data to be transmitted to the Serial Data Register. Enabling of the
output is done by setting the corresponding bit in the port Data Direction Register. Note that point A and B does not have any specific order, but both must be at
least one half USCK cycle before point C where the data is sampled. This must
be done to ensure that the data setup requirement is satisfied. The 4-bit counter
is reset to zero.
2. The Master generates a clock pulse by software toggling the USCK line twice (C
and D). The bit value on the slave and master’s data input (DI) pin is sampled by
the USI on the first edge (C), and the data output is changed on the opposite
edge (D). The 4-bit counter will count both edges.
3. Step 2. is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that the transfer is completed. The data bytes transferred must now be
processed before a new transfer can be initiated. The overflow interrupt will wake
up the processor if it is set to Idle mode. Depending of the protocol used the
slave device can now set its output to high impedance.
SPI Master Operation
Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
out
USIDR,r16
ldi
r16,(1<<USIOIF)
out
USISR,r16
ldi
r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
out
USICR,r16
sbis
USISR,USIOIF
rjmp
SPITransfer_loop
in
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example
assumes that the DO and USCK pins are enabled as output in the DDRE Register. The
value stored in register r16 prior to the function is called is transferred to the Slave
device, and when the transfer is completed the data received from the Slave is stored
back into the r16 Register.
The second and third instructions clears the USI Counter Overflow Flag and the USI
counter value. The fourth and fifth instruction set Three-wire mode, positive edge Shift
Register clock, count at USITC strobe, and toggle USCK. The loop is repeated 16 times.
139
2543F–AVR–08/04
The following code demonstrates how to use the USI module as a SPI Master with maximum speed (fsck = fck/2):
SPITransfer_Fast:
out
USIDR,r16
ldi
r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi
r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
out
USICR,r16 ; MSB
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16
out
USICR,r17
out
USICR,r16 ; LSB
out
USICR,r17
in
r16,USIDR
ret
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi
r16,(1<<USIWM0)|(1<<USICS1)
out
USICR,r16
...
SlaveSPITransfer:
out
USIDR,r16
ldi
r16,(1<<USIOIF)
out
USISR,r16
SlaveSPITransfer_loop:
sbis
USISR,USIOIF
rjmp
SlaveSPITransfer_loop
in
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example
assumes that the DO is configured as output and USCK pin is configured as input in the
DDR Register. The value stored in register r16 prior to the function is called is trans-
140
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
ferred to the master device, and when the transfer is completed the data received from
the Master is stored back into the r16 Register.
Note that the first two instructions is for initialization only and needs only to be executed
once.These instructions sets Three-wire mode and positive edge Shift Register clock.
The loop is repeated until the USI Counter Overflow Flag is set.
Two-wire Mode
The USI Two-wire mode does not incorporate slew rate limiting on outputs and input
noise filtering. Pin names used by this mode are SCL and SDA.
Figure 62. Two-wire Mode Operation, Simplified Diagram
VCC
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
HOLD
SCL
Two-wire Clock
Control Unit
SLAVE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
PORTxn
MASTER
Figure 62 shows two USI units operating in Two-wire mode, one as Master and one as
Slave. It is only the physical layer that is shown since the system operation is highly
dependent of the communication scheme used. The main differences between the Master and Slave operation at this level, is the serial clock generation which is always done
by the Master, and only the Slave uses the clock control unit. Clock generation must be
implemented in software, but the shift operation is done automatically by both devices.
Note that only clocking on negative edge for shifting data is of practical use in this mode.
The slave can insert wait states at start or end of transfer by forcing the SCL clock low.
This means that the Master must always check if the SCL line was actually released
after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate
that the transfer is completed. The clock is generated by the master by toggling the
USCK pin via the PORT Register.
The data direction is not given by the physical layer. A protocol, like the one used by the
TWI-bus, must be implemented to control the data flow.
141
2543F–AVR–08/04
Figure 63. 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
P
E
F
Referring to the timing diagram (Figure 63.), a bus transfer involves the following steps:
1. The a start condition is generated by the Master by forcing the SDA low line while
the SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of
the Shift Register, or by setting the corresponding bit in the PORT Register to
zero. Note that the Data Direction Register bit must be set to one for the output to
be enabled. The slave device’s start detector logic (Figure 64.) detects the start
condition and sets the USISIF flag. The flag can generate an interrupt if
necessary.
2. In addition, the start detector will hold the SCL line low after the Master has
forced an negative edge on this line (B). This allows the Slave to wake up from
sleep or complete its other tasks before setting up the Shift Register to receive
the address. This is done by clearing the start condition flag and reset the
counter.
3. The Master set the first bit to be transferred and releases the SCL line (C). The
Slave samples the data and shift it into the serial register at the positive edge of
the SCL clock.
4. After eight bits are transferred containing slave address and data direction (read
or write), the Slave counter overflows and the SCL line is forced low (D). If the
slave is not the one the Master has addressed, it releases the SCL line and waits
for a new start condition.
5. If the Slave is addressed it holds the SDA line low during the acknowledgment
cycle before holding the SCL line low again (i.e., the Counter Register must be
set to 14 before releasing SCL at (D)). Depending of the R/W bit the Master or
Slave enables its output. If the bit is set, a master read operation is in progress
(i.e., the slave drives the SDA line) The slave can hold the SCL line low after the
acknowledge (E).
6. Multiple bytes can now be transmitted, all in same direction, until a stop condition
is given by the Master (F). Or a new start condition is given.
If the Slave is not able to receive more data it does not acknowledge the data byte it has
last received. When the Master does a read operation it must terminate the operation by
force the acknowledge bit low after the last byte transmitted.
Figure 64. Start Condition Detector, Logic Diagram
USISIF
D Q
D Q
CLR
CLR
SDA
CLOCK
HOLD
SCL
Write( USISIF)
142
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Start Condition Detector
The start condition detector is shown in Figure 64. 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 working asynchronously and can therefore wake up the
processor from the Power-down sleep mode. However, the protocol used might have
restrictions on the SCL hold time. Therefore, when using this feature in this case the
Oscillator start-up time set by the CKSEL Fuses (see “Clock Systems and their Distribution” on page 21) must also be taken into the consideration.
Alternative USI Usage
When the USI unit is not used for serial communication, it can be set up to do alternative
tasks due to its flexible design.
Half-duplex Asynchronous
Data Transfer
By utilizing the Shift Register in Three-wire mode, it is possible to implement a more
compact and higher performance UART than by software only.
4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note
that if the counter is clocked externally, both clock edges will generate an increment.
12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
Edge Triggered External
Interrupt
By setting the counter to maximum value (F) it can function as an additional external
interrupt. The overflow flag and interrupt enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock
strobe.
USI Register
Descriptions
USI Data Register – USIDR
Bit
7
6
5
4
3
2
1
MSB
0
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USIDR
The USI uses no buffering of the serial register, i.e., when accessing the Data Register
(USIDR) the serial register is accessed directly. If a serial clock occurs at the same cycle
the register is written, the register will contain the value written and no shift is performed.
A (left) shift operation is performed depending of the USICS1..0 bits setting. The shift
operation can be controlled by an external clock edge, by a Timer/Counter0 overflow, or
directly by software using the USICLK strobe bit. Note that even when no wire mode is
selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the external clock
input (USCK/SCL) can still be used by the Shift Register.
The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the Data Register. The output latch is open
(transparent) during the first half of a serial clock cycle when an external clock source is
selected (USICS1 = 1), and constantly open when an internal clock source is used
(USICS1 = 0). The output will be changed immediately when a new MSB written as long
as the latch is open. The latch ensures that data input is sampled and data output is
changed on opposite clock edges.
143
2543F–AVR–08/04
Note that the corresponding Data Direction Register to the pin must be set to one for
enabling data output from the Shift Register.
USI Status Register – USISR
Bit
7
6
5
4
3
2
1
0
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
Read/Write
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USISR
The Status Register contains interrupt flags, line status flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When Two-wire mode is selected, the USISIF flag is set (to one) when a start condition
is detected. When output disable mode or Three-wire mode is selected and (USICSx =
0b11 & USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the SCK pin sets
the flag.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the
Global Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one
to the USISIF bit. Clearing this bit will release the start detection hold of USCL in Twowire mode.
A start condition interrupt will wake-up the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to
0). An interrupt will be generated when the flag is set while the USIOIE bit in USICR and
the Global Interrupt Enable Flag are set. The flag will only be cleared if a one is written
to the USIOIF bit. Clearing this bit will release the counter overflow hold of SCL in Twowire mode.
A counter overflow interrupt will wake-up the processor from Idle sleep mode.
• Bit 5 – USIPF: Stop Condition Flag
When Two-wire mode is selected, the USIPF flag is set (one) when a stop condition is
detected. The flag is cleared by writing a one to this bit. Note that this is not an interrupt
flag. This signal is useful when implementing Two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the Shift Register differs from the physical pin value.
The flag is only valid when Two-wire mode is used. This signal is useful when implementing Two-wire bus master arbitration.
• Bits 3..0 – USICNT3..0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be
read or written by the CPU.
The 4-bit counter increments by one for each clock generated either by the external
clock edge detector, by a Timer/Counter0 overflow, or by software using USICLK or
USITC strobe bits. The clock source depends of the setting of the USICS1..0 bits. For
external clock operation a special feature is added that allows the clock to be generated
by writing to the USITC strobe bit. This feature is enabled by write a one to the USICLK
bit while setting an external clock source (USICS1 = 1).
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) are can still be used by the counter.
144
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
USI Control Register – USICR
Bit
7
6
5
4
3
2
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
W
W
Initial Value
0
0
0
0
0
0
0
0
USICR
The Control Register includes interrupt enable control, wire mode setting, Clock Select
setting, and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending
interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will
immediately be executed.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when the USIOIE and the Global Interrupt Enable Flag is set to one, this will
immediately be executed.
• Bit 5..4 – USIWM1..0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the
outputs are affected by these bits. Data and clock inputs are not affected by the mode
selected and will always have the same function. The counter and Shift Register can
therefore be clocked externally, and data input sampled, even when outputs are
disabled. The relations between USIWM1..0 and the USI operation is summarized in
Table 60 on page 146.
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Table 60. Relations between USIWM1..0 and the USI Operation
USIWM1
USIWM0
0
0
Outputs, clock hold, and start detector disabled. Port pins operates as
normal.
0
1
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORT
Register in this mode. However, the corresponding DDR bit still
controls the data direction. When the port pin is set as input the pins
pull-up is controlled by the PORT bit.
The Data Input (DI) and Serial Clock (USCK) pins do not affect the
normal port operation. When operating as master, clock pulses are
software generated by toggling the PORT Register, while the data
direction is set to output. The USITC bit in the USICR Register can be
used for this purpose.
1
0
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).
The Serial Data (SDA) and the Serial Clock (SCL) pins are bidirectional and uses open-collector output drives. The output drivers
are enabled by setting the corresponding bit for SDA and SCL in the
DDR Register.
When the output driver is enabled for the SDA pin, the output driver will
force the line SDA low if the output of the Shift Register or the
corresponding bit in the PORT Register is zero. Otherwise the SDA
line will not be driven (i.e., it is released). When the SCL pin output
driver is enabled the SCL line will be forced low if the corresponding bit
in the PORT Register is zero, or by the start detector. Otherwise the
SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition
and the output is enabled. Clearing the start condition flag (USISIF)
releases the line. The SDA and SCL pin inputs is not affected by
enabling this mode. Pull-ups on the SDA and SCL port pin are
disabled in Two-wire mode.
1
1
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the Two-wire mode described above, except
that the SCL line is also held low when a counter overflow occurs, and
is held low until the Timer Overflow Flag (USIOIF) is cleared.
Note:
146
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.
ATtiny2313/V
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ATtiny2313/V
• Bit 3..2 – USICS1..0: Clock Source Select
These bits set the clock source for the Shift Register and counter. The data output latch
ensures that the output is changed at the opposite edge of the sampling of the data
input (DI/SDA) when using external clock source (USCK/SCL). When software strobe or
Timer0 overflow clock option is selected, the output latch is transparent and therefore
the output is changed immediately. Clearing the USICS1..0 bits enables software strobe
option. When using this option, writing a one to the USICLK bit clocks both the Shift
Register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no
longer used as a strobe, but selects between external clocking and software clocking by
the USITC strobe bit.
Table 61 shows the relationship between the USICS1..0 and USICLK setting and clock
source used for the Shift Register and the 4-bit counter.
Table 61. Relations between the USICS1..0 and USICLK Setting
Shift Register Clock
Source
4-bit Counter Clock
Source
0
No Clock
No Clock
0
1
Software clock strobe
(USICLK)
Software clock strobe
(USICLK)
0
1
X
Timer/Counter0 overflow
Timer/Counter0 overflow
1
0
0
External, positive edge
External, both edges
1
1
0
External, negative edge
External, both edges
1
0
1
External, positive edge
Software clock strobe
(USITC)
1
1
1
External, negative edge
Software clock strobe
(USITC)
USICS1
USICS0
USICLK
0
0
0
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the Shift Register to shift one step and the
counter to increment by one, provided that the USICS1..0 bits are set to zero and by
doing so the software clock strobe option is selected. The output will change immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value
shifted into the Shift Register is sampled the previous instruction cycle. The bit will be
read as zero.
When an external clock source is selected (USICS1 = 1), the USICLK function is
changed from a clock strobe to a Clock Select Register. Setting the USICLK bit in this
case will select the USITC strobe bit as clock source for the 4-bit counter (see Table 61).
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from
1 to 0. The toggling is independent of the setting in the Data Direction Register, but if the
PORT value is to be shown on the pin the DDRE4 must be set as output (to one). This
feature allows easy clock generation when implementing master devices. The bit will be
read as zero.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to
one, writing to the USITC strobe bit will directly clock the 4-bit counter. This allows an
early detection of when the transfer is done when operating as a master device.
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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’s
output can be set to trigger the Timer/Counter1 Input Capture function. In addition, 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 65.
Figure 65. Analog Comparator Block Diagram
BANDGAP
REFERENCE
ACBG
Analog Comparator Control
and Status Register – ACSR
Bit
7
6
5
4
3
2
1
0
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 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. See “Internal Voltage Reference” on page 37.
• 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
148
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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 between the Analog Comparator and the input capture
function exists. To make the comparator trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask Register (TIMSK) 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 62.
Table 62. 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.
Digital Input Disable Register
– DIDR
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
AIN1D
AIN0D
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR
• Bit 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled.
The corresponding PIN Register bit will always read as zero when this bit is set. When
an analog signal is applied to the AIN1/0 pin and the digital input from this pin is not
needed, this bit should be written logic one to reduce power consumption in the digital
input buffer.
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debugWIRE On-chip
Debug System
Features
•
•
•
•
•
•
•
•
•
•
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.
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.
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
Figure 66. The debugWIRE Setup
1.8 - 5.5V
VCC
dW
dW(RESET)
GND
Figure 66 shows the schematic of a target MCU, with debugWIRE enabled, and the
emulator connector. The system clock is not affected by debugWIRE and will always be
the clock source selected by the CKSEL Fuses.
When designing a system where debugWIRE will be used, the following observations
must be made for correct operation:
150
•
Pull-Up resistor on the dW/(RESET) line must be larger than 10k. However, the pullup resistor is optional.
•
Connecting the RESET pin directly to VCC will not work.
ATtiny2313/V
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ATtiny2313/V
Software Break Points
•
Capacitors inserted on the RESET pin must be disconnected when using
debugWire.
•
All external reset sources must be disconnected.
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 Flash Data retention. Devices used for debugging purposes should not be shipped to end customers.
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.
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.
debugWIRE Related
Register in I/O Memory
debugWire Data Register –
DWDR
The following section describes the registers used with the debugWire.
Bit
7
6
5
4
3
2
1
0
DWDR[7:0]
DWDR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The DWDR Register provides a communication channel from the running program in
the MCU to the debugger. This register is only accessible by the debugWIRE and can
therefore not be used as a general purpose register in the normal operations.
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Self-Programming
the Flash
The device provides a Self-Programming mechanism for downloading and uploading
program code by the MCU itself. The Self-Programming can use any available data
interface and associated protocol to read code and write (program) that code into the
Program memory.
The Program memory is updated in a page by page fashion. Before programming a
page with the data stored in the temporary page buffer, the page must be erased. The
temporary page buffer is filled one word at a time using SPM and the buffer can be filled
either before the Page Erase command or between a Page Erase and a Page Write
operation:
Alternative 1, fill the buffer before a Page Erase
•
Fill temporary page buffer
•
Perform a Page Erase
•
Perform a Page Write
Alternative 2, fill the buffer after Page Erase
•
Perform a Page Erase
•
Fill temporary page buffer
•
Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for
example in the temporary page buffer) before the erase, and then be re-written. When
using alternative 1, the Boot Loader provides an effective Read-Modify-Write feature
which allows the user software to first read the page, do the necessary changes, and
then write back the modified data. If alternative 2 is used, it is not possible to read the
old data while loading since the page is already 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.
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.
•
Filling the Temporary Buffer
(Page Loading)
The CPU is halted during the Page Erase operation.
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing
SPMCSR. The content of PCWORD in the Z-register is used to address the data in the
temporary buffer. The temporary buffer will auto-erase after a Page Write operation or
by writing the CTPB bit in SPMCSR. It is also erased after a system reset. Note that it is
not possible to write more than one time to each address without erasing the temporary
buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded
will be lost.
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.
•
152
The CPU is halted during the Page Write operation.
ATtiny2313/V
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ATtiny2313/V
Addressing the Flash
During SelfProgramming
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 69 on page 159), 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 67. 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 67. Addressing the Flash During SPM(1)
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:
1. The different variables used in Figure 67 are listed in Table 69 on page 159.
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Store Program Memory
Control and Status Register –
SPMCSR
The Store Program Memory Control and Status Register contains the control bits
needed to control the Program memory operations.
Bit
7
6
5
4
3
2
1
0
–
–
–
CTPB
RFLB
PGWRT
PGERS
SELFPRGEN
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPMCSR
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313 and always read as zero.
• Bit 4 – CTPB: Clear Temporary Page Buffer
If the CTPB bit is written while filling the temporary page buffer, the temporary page
buffer will be cleared and the data will be lost.
• Bit 3 – RFLB: Read Fuse and Lock Bits
An LPM instruction within three cycles after RFLB and SELFPRGEN 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 SELFPRGEN, 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 SELFPRGEN, 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 – SELFPRGEN: Self Programming Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one
together with either CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction
will have a special meaning, see description above. If only SELFPRGEN 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 SELFPRGEN 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 SELFPRGEN bit
remains high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the
lower five bits will have no effect.
154
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ATtiny2313/V
EEPROM Write Prevents
Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash.
Reading the Fuses and Lock bits from software will also be prevented during the
EEPROM write operation. It is recommended that the user checks the status bit (EEWE)
in the EECR Register and verifies that the bit is cleared before writing to the SPMCSR
Register.
Reading the Fuse and Lock
Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits,
load the Z-pointer with 0x0001 and set the RFLB and SELFPRGEN bits in SPMCSR.
When an LPM instruction is executed within three CPU cycles after the RFLB and
SELFPRGEN bits are set in SPMCSR, the value of the Lock bits will be loaded in the
destination register. The RFLB and SELFPRGEN bits will auto-clear upon completion of
reading the Lock bits or if no LPM instruction is executed within three CPU cycles or no
SPM instruction is executed within four CPU cycles. When RFLB and SELFPRGEN are
cleared, LPM will work as described in the Instruction set Manual.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
–
–
–
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for
reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and
set the RFLB and SELFPRGEN bits in SPMCSR. When an LPM instruction is executed
within three cycles after the RFLB and SELFPRGEN bits are set in the SPMCSR, the
value of the Fuse Low byte (FLB) will be loaded in the destination register as shown
below. Refer to Table 68 on page 159 for a detailed description and mapping of the
Fuse Low byte.
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM
instruction is executed within three cycles after the RFLB and SELFPRGEN bits are set
in the SPMCSR, the value of the Fuse High byte (FHB) will be loaded in the destination
register as shown below. Refer to Table XXX on page xxx for detailed description and
mapping of the Fuse High byte.
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that
are unprogrammed, will be read as one.
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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.
Programming Time for Flash
when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 63 shows the typical
programming time for Flash accesses from the CPU.
Table 63. SPM Programming Time
156
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
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Memory
Programming
Program And Data
Memory Lock Bits
The ATtiny2313 provides two Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 65. The Lock bits can
only be erased to “1” with the Chip Erase command.
Table 64. Lock Bit Byte(1)
Lock Bit Byte
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
4
–
1 (unprogrammed)
3
–
1 (unprogrammed)
2
–
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
Note:
Bit No
1. “1” means unprogrammed, “0” means programmed
Table 65. Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
LB2
LB1
1
1
1
No memory lock features enabled.
0
Further programming of the Flash and EEPROM is
disabled in Parallel and Serial Programming mode. The
Fuse bits are locked in both Serial and Parallel
Programming mode.(1)
0
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming
mode. The Boot Lock bits and Fuse bits are locked in both
Serial and Parallel Programming mode.(1)
2
3
Notes:
1
0
1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
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Fuse Bits
The ATtiny2313 has three Fuse bytes. Table 67 and Table 68 describe briefly the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the
fuses are read as logical zero, “0”, if they are programmed.
Table 66. Fuse Extended Byte
Fuse Extended
Byte
SELFPRGEN
Bit
No
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
4
–
1 (unprogrammed)
3
–
1 (unprogrammed)
2
–
1 (unprogrammed)
1
–
1 (unprogrammed)
0
Self Programming Enable
1 (unprogrammed)
Description
Default Value
Table 67. Fuse High Byte
Fuse High Byte
Bit
No
(3)
7
debugWIRE Enable
1 (unprogrammed)
EESAVE
6
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed, EEPROM
not preserved)
SPIEN(1)
5
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
DWEN
WDTON(2)
4
Watchdog Timer always on
1 (unprogrammed)
(4)
BODLEVEL2
3
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL1(4)
2
Brown-out Detector trigger level
1 (unprogrammed)
(4)
BODLEVEL0
1
Brown-out Detector trigger level
1 (unprogrammed)
(5)
0
External Reset disable
1 (unprogrammed)
RSTDISBL
Note:
1. The SPIEN Fuse is not accessible in serial programming mode.
2. See “Watchdog Timer Control Register - WDTCSR” on page 41 for details.
3. Never ship a product with the DWEN Fuse programmed regardless of the setting of
Lock bits. A programmed DWEN Fuse enables some parts of the clock system to be
running in all sleep modes. This may increase the power consumption.
4. See Table 16 on page 34 for BODLEVEL Fuse decoding.
5. See “Alternate Functions of Port A” on page 52 for description of RSTDISBL Fuse.
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Table 68. Fuse Low Byte
Fuse Low Byte
Bit No
Description
Default Value
CKDIV8
7
Divide clock by 8
0 (programmed)
CKOUT
6
Output Clock on CKOUT pin
1 (unprogrammed)
SUT1
5
Select start-up time
1 (unprogrammed)(1)
SUT0
4
Select start-up time
0 (programmed)(1)
CKSEL3
3
Select Clock source
0 (programmed)(2)
CKSEL2
2
Select Clock source
0 (programmed)(2)
CKSEL1
1
Select Clock source
1 (unprogrammed)(2)
CKSEL0
0
Select Clock source
0 (programmed)(2)
Note:
1. The default value of SUT1..0 results in maximum start-up time for the default clock
source. See Table 15 on page 33 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are
locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the
Lock bits.
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of
the fuse values will have no effect until the part leaves Programming mode. This does
not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses
are also latched on Power-up in Normal mode.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device.
This code can be read in both serial and parallel mode, also when the device is locked.
The three bytes reside in a separate address space.
For the ATtiny2313 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x91 (indicates 2KB Flash memory).
3. 0x002: 0x0A (indicates ATtiny2313 device when 0x001 is 0x91).
Calibration Byte
The ATtiny2313 stores two different calibration values for the internal RC Oscillator.
These bytes resides in the high byte of address 0x0000 and 0x0001 in the signature
address space for 4 and 8 MHz respectively. During reset, the 4 MHz value is automatically written to the “Oscillator Calibration Register – OSCCAL” on page 25, to ensure
correct frequency of the calibrated RC Oscillator.
Page Size
Table 69. No. of Words in a Page and No. of Pages in the Flash
Flash Size
1K words (2K bytes)
Page Size
PCWORD
No. of Pages
PCPAGE
PCMSB
16 words
PC[3:0]
64
PC[9:4]
9
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Table 70. No. of Words in a Page and No. of Pages in the EEPROM
EEPROM Size
Page Size
PCWORD
No. of Pages
PCPAGE
EEAMSB
128 bytes
4 bytes
EEA[1:0]
32
EEA[6:2]
6
Parallel Programming
Parameters, Pin
Mapping, and
Commands
This section describes how to parallel program and verify Flash Program memory,
EEPROM Data memory, Memory Lock bits, and Fuse bits in the ATtiny2313. Pulses are
assumed to be at least 250 ns unless otherwise noted.
Signal Names
In this section, some pins of the ATtiny2313 are referenced by signal names describing
their functionality during parallel programming, see Figure 68 and Table 71. Pins not
described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in Table 73.
When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 74.
Figure 68. Parallel Programming
+5V
RDY/BSY
PD1
OE
PD2
WR
PD3
BS1/PAGEL
PD4
XA0
PD5
XA1/BS2
PD6
+12 V
VCC
PB7 - PB0
DATA I/O
RESET
XTAL1
GND
Table 71. Pin Name Mapping
160
Signal Name
in
Programming
Mode
Pin
Name
I/O
Function
RDY/BSY
PD1
O
0: Device is busy programming, 1: Device is ready for
new command.
OE
PD2
I
Output Enable (Active low).
WR
PD3
I
Write Pulse (Active low).
BS1/PAGEL
PD4
I
Byte Select 1 (“0” selects low byte, “1” selects high
byte).
Program Memory and EEPROM Data Page Load.
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Table 71. Pin Name Mapping (Continued)
Signal Name
in
Programming
Mode
Pin
Name
I/O
XA0
PD5
I
XTAL Action Bit 0
XA1/BS2
PD6
I
XTAL Action Bit 1.
Byte Select 2 (“0” selects low byte, “1” selects 2’nd high
byte).
DATA I/O
PB7-0
I/O
Function
Bi-directional Data bus (Output when OE is low).
Table 72. Pin Values Used to Enter Programming Mode
Pin
Symbol
Value
XA1
Prog_enable[3]
0
XA0
Prog_enable[2]
0
BS1
Prog_enable[1]
0
WR
Prog_enable[0]
0
Table 73. XA1 and XA0 Coding
XA1
XA0
Action when XTAL1 is Pulsed
0
0
Load Flash or EEPROM Address (High or low address byte
determined by BS1).
0
1
Load Data (High or Low data byte for Flash determined by BS1).
1
0
Load Command
1
1
No Action, Idle
Table 74. Command Byte Bit Coding
Command Byte
Command Executed
1000 0000
Chip Erase
0100 0000
Write Fuse bits
0010 0000
Write Lock bits
0001 0000
Write Flash
0001 0001
Write EEPROM
0000 1000
Read Signature Bytes and Calibration byte
0000 0100
Read Fuse and Lock bits
0000 0010
Read Flash
0000 0011
Read EEPROM
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Serial Programming Pin
Mapping
Table 75. Pin Mapping Serial Programming
Symbol
Pins
I/O
Description
MOSI
PB5
I
Serial Data in
MISO
PB6
O
Serial Data out
SCK
PB7
I
Serial Clock
Parallel Programming
Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 72 on page 161 to “0000” and wait at
least 100 ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns
after +12V has been applied to RESET, will cause the device to fail entering programming mode.
5. Wait at least 50 µs before sending a new command.
Note:
If the RESET pin is disabled by programming the RSTDISBL Fuse, it may not be possible
to follow the proposed algorithm above. The same may apply when External Crystal or
External RC configuration is selected because it is not possible to apply qualified XTAL1
pulses. In such cases, the following algorithm should be followed:
1. Set Prog_enable pins listed in Table 72 on page 161 to “0000”.
2. Apply 4.5 - 5.5V between VCC and GND simultanously as 11.5 - 12.5V is applied
to RESET.
3. Wait 100 ns.
4. Re-program the fuses to ensure that External Clock is selected as clock source
(CKSEL3:0 = 0b0000) and RESET pin is activated (RSTDISBL unprogrammed).
If Lock bits are programmed, a Chip Erase command must be executed before
changing the fuses.
5. Exit Programming mode by power the device down or by bringing RESET pin to
0b0.
Entering Programming mode with the original algorithm, as described above.
Considerations for Efficient
Programming
Chip Erase
162
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.
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
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are not changed. A Chip Erase must be performed before the Flash and/or EEPROM
are reprogrammed.
Note:
1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is
programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
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Programming the Flash
The Flash is organized in pages, see Table 69 on page 159. When programming the
Flash, the program data is latched into a page buffer. This allows one page of program
data to be programmed simultaneously. The following procedure describes how to program the entire Flash memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 70 for signal waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is
loaded.
While the lower bits in the address are mapped to words within the page, the higher bits
address the pages within the FLASH. This is illustrated in Figure 69 on page 165. Note
that if less than eight bits are required to address words in the page (pagesize < 256),
the most significant bit(s) in the address low byte are used to address the page when
performing a Page Write.
G. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of data.
RDY/BSY goes low.
2. Wait until RDY/BSY goes high (See Figure 70 for signal waveforms).
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I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.
Figure 69. Addressing the Flash Which is Organized in Pages(1)
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
PCWORD[PAGEMSB:0]:
00
INSTRUCTION WORD
01
02
PAGEEND
Note:
1. PCPAGE and PCWORD are listed in Table 69 on page 159.
Figure 70. Programming the Flash Waveforms(1)
F
DATA
A
B
0x10
ADDR. LOW
C
DATA LOW
D
E
DATA HIGH
XX
B
ADDR. LOW
C
D
DATA LOW
DATA HIGH
E
XX
G
ADDR. HIGH
H
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
Note:
1. “XX” is don’t care. The letters refer to the programming description above.
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Programming the EEPROM
The EEPROM is organized in pages, see Table 70 on page 160. When programming
the EEPROM, the program data is latched into a page buffer. This allows one page of
data to be programmed simultaneously. The programming algorithm for the EEPROM
data memory is as follows (refer to “Programming the Flash” on page 164 for details on
Command, Address and Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page.
RDY/BSY goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure
71 for signal waveforms).
Figure 71. Programming the EEPROM Waveforms
K
DATA
A
G
0x11
ADDR. HIGH
B
ADDR. LOW
C
DATA
E
XX
B
ADDR. LOW
C
DATA
E
L
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the
Flash” on page 164 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
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Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the
Flash” on page 164 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at
DATA.
5. Set OE to “1”.
Programming the Fuse Low
Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming
the Flash” on page 164 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
Programming the Fuse High
Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming
the Flash” on page 164 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
Programming the Extended
Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the Flash” on page 164 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse
bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 72. Programming the FUSES Waveforms
Write Fuse Low byte
DATA
A
C
0x40
DATA
XX
Write Fuse high byte
A
C
0x40
DATA
XX
Write Extended Fuse byte
A
C
0x40
DATA
XX
XA1
XA0
BS1
BS2
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
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Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” on page 164 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed (LB1 and LB2 is programmed), it is not possible to program the Boot
Lock bits by any External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
Reading the Fuse and Lock
Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming
the Flash” on page 164 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can
now be read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can
now be read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the Extended Fuse bits
can now be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be
read at DATA (“0” means programmed).
6. Set OE to “1”.
Figure 73. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
0
Fuse Low Byte
0
Extended Fuse Byte
1
DATA
BS2
0
Lock Bits
1
Fuse High Byte
1
BS1
BS2
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the
Flash” on page 164 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected Signature byte can now be read at
DATA.
4. Set OE to “1”.
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Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the
Flash” on page 164 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Parallel Programming
Characteristics
Figure 74. Parallel Programming Timing, Including some General Timing
Requirements
tXLWL
tXHXL
XTAL1
tDVXH
tXLDX
Data & Contol
(DATA, XA0/1, BS1, BS2)
tPLBX t BVWL
tBVPH
PAGEL
tWLBX
tPHPL
tWLWH
WR
tPLWL
WLRL
RDY/BSY
tWLRH
Figure 75. Parallel Programming Timing, Loading Sequence with Timing
Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA LOAD DATA
(HIGH BYTE)
LOAD DATA
(LOW BYTE)
t XLXH
tXLPH
LOAD ADDRESS
(LOW BYTE)
tPLXH
XTAL1
BS1
PAGEL
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
1. The timing requirements shown in Figure 74 (i.e., tDVXH, tXHXL, and tXLDX) also apply
to loading operation.
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Figure 76. Parallel Programming Timing, Reading Sequence (within the Same Page)
with Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
tXLOL
XTAL1
tBVDV
BS1
tOLDV
OE
tOHDZ
DATA
ADDR0 (Low Byte)
ADDR1 (Low Byte)
DATA (High Byte)
DATA (Low Byte)
XA0
XA1
Note:
1. The timing requirements shown in Figure 74 (i.e., tDVXH, tXHXL, and tXLDX) also apply
to reading operation.
Table 76. Parallel Programming Characteristics, VCC = 5V ± 10%
170
Symbol
Parameter
Min
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXLXH
XTAL1 Low to XTAL1 High
200
ns
tXHXL
XTAL1 Pulse Width High
150
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
0
ns
tXLPH
XTAL1 Low to PAGEL high
0
ns
tPLXH
PAGEL low to XTAL1 high
150
ns
tBVPH
BS1 Valid before PAGEL High
67
ns
tPHPL
PAGEL Pulse Width High
150
ns
tPLBX
BS1 Hold after PAGEL Low
67
ns
tWLBX
BS2/1 Hold after WR Low
67
ns
tPLWL
PAGEL Low to WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tWLWH
WR Pulse Width Low
150
ns
tWLRL
WR Low to RDY/BSY Low
tWLRH
WR Low to RDY/BSY High(1)
(2)
tWLRH_CE
WR Low to RDY/BSY High for Chip Erase
tXLOL
XTAL1 Low to OE Low
Typ
Max
Units
12.5
V
250
µA
0
1
µs
3.7
4.5
ms
7.5
9
ms
0
ns
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ATtiny2313/V
Table 76. Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
Symbol
Parameter
tBVDV
BS1 Valid to DATA valid
tOLDV
tOHDZ
Notes:
Serial Downloading
Min
Max
Units
250
ns
OE Low to DATA Valid
250
ns
OE High to DATA Tri-stated
250
ns
0
Typ
1.
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock
bits commands.
2. tWLRH_CE is valid for the Chip Erase command.
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI
bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI
(input) and MISO (output). After RESET is set low, the Programming Enable instruction
needs to be executed first before program/erase operations can be executed. NOTE, in
Table 75 on page 162, the pin mapping for SPI programming is listed. Not all parts use
the SPI pins dedicated for the internal SPI interface.
Figure 77. Serial Programming and Verify(1)
+1.8 - 5.5V
VCC
MOSI
MISO
SCK
XTAL1
RESET
GND
Notes:
1. If the device is clocked by the internal Oscillator, it is no need to connect a clock
source to the XTAL1 pin.
2. VCC - 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8 - 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the Serial mode ONLY) and there is no need to first execute the
Chip Erase instruction. The Chip Erase operation turns the content of every memory
location in both the Program and EEPROM arrays into 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
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Serial Programming
Algorithm
When writing serial data to the ATtiny2313, data is clocked on the rising edge of SCK.
When reading data from the ATtiny2313, data is clocked on the falling edge of SCK. See
Figure 78, Figure 79 and Table 79 for timing details.
To program and verify the ATtiny2313 in the serial programming mode, the following
sequence is recommended (See four byte instruction formats in Table 78 on page 173):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In
some systems, the programmer can not guarantee that SCK is held low during
power-up. In this case, RESET must be given a positive pulse of at least two
CPU clock cycles duration after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of
synchronization. When in sync. the second byte (0x53), will echo back when
issuing the third byte of the Programming Enable instruction. Whether the echo
is correct or not, all four bytes of the instruction must be transmitted. If the 0x53
did not echo back, give RESET a positive pulse and issue a new Programming
Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one
byte at a time by supplying the 4 LSB of the address and data together with the
Load Program Memory Page instruction. To ensure correct loading of the page,
the data low byte must be loaded before data high byte is applied for a given
address. The Program Memory Page is stored by loading the Write Program
Memory Page instruction with the 6 MSB of the address. If polling (RDY/BSY) is
not used, the user must wait at least tWD_FLASH before issuing the next page. (See
Table 77 on page 173.) 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 77 on page 173.) 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 5 MSB of the address. When using EEPROM page access only byte locations loaded with the Load EEPROM Memory Page instruction is altered. The
remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used
must wait at least tWD_EEPROM before issuing the next page (See Table 77 on
page 173). 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.
172
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table 77. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol
Minimum Wait Delay
tWD_FLASH
4.5 ms
tWD_EEPROM
4.0 ms
tWD_ERASE
4.0 ms
tWD_FUSE
4.5 ms
Figure 78. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
Table 78. Serial Programming Instruction Set
Instruction Format
Instruction
Byte 1
Byte 2
Byte 3
Byte4
Operation
Programming Enable
1010 1100
0101 0011
xxxx xxxx
xxxx xxxx
Enable Serial Programming after
RESET goes low.
Chip Erase
1010 1100
100x xxxx
xxxx xxxx
xxxx xxxx
Chip Erase EEPROM and Flash.
Read Program Memory
0010 H000
0000 00aa
bbbb bbbb
oooo oooo
Read H (high or low) data o from
Program memory at word address a:b.
Load Program Memory Page
0100 H000
000x xxxx
xxxx bbbb
iiii iiii
Write H (high or low) data i to Program
Memory page at word address b. Data
low byte must be loaded before Data
high byte is applied within the same
address.
Write Program Memory Page
0100 1100
0000 00aa
bbbb xxxx
xxxx xxxx
Write Program Memory Page at
address a:b.
Read EEPROM Memory
1010 0000
000x xxxx
xbbb bbbb
oooo oooo
Read data o from EEPROM memory at
address b.
Write EEPROM Memory
1100 0000
000x xxxx
xbbb bbbb
iiii iiii
Write data i to EEPROM memory at
address b.
Load EEPROM Memory
Page (page access)
1100 0001
0000 0000
0000 00bb
iiii iiii
Load data i to EEPROM memory page
buffer. After data is loaded, program
EEPROM page.
Write EEPROM Memory
Page (page access)
1100 0010
00xx xxxx
xbbb bb00
xxxx xxxx
Write EEPROM page at address b.
173
2543F–AVR–08/04
Table 78. Serial Programming Instruction Set
Instruction Format
Instruction
Byte 1
Byte 2
Byte 3
Byte4
Read Lock bits
0101 1000
0000 0000
xxxx xxxx
xxoo oooo
Read Lock bits. “0” = programmed, “1”
= unprogrammed. See Table 64 on
page 157 for details.
Write Lock bits
1010 1100
111x xxxx
xxxx xxxx
11ii iiii
Write Lock bits. Set bits = “0” to
program Lock bits. See Table 64 on
page 157 for details.
Read Signature Byte
0011 0000
000x xxxx
xxxx xxbb
oooo oooo
Read Signature Byte o at address b.
Write Fuse bits
1010 1100
1010 0000
xxxx xxxx
iiii iiii
Set bits = “0” to program, “1” to
unprogram.
Write Fuse High bits
1010 1100
1010 1000
xxxx xxxx
iiii iiii
Set bits = “0” to program, “1” to
unprogram.
Write Extended Fuse Bits
1010 1100
1010 0100
xxxx xxxx
xxxx xxxi
Set bits = “0” to program, “1” to
unprogram.
Read Fuse bits
0101 0000
0000 0000
xxxx xxxx
oooo oooo
Read Fuse bits. “0” = programmed, “1”
= unprogrammed.
Read Fuse High bits
0101 1000
0000 1000
xxxx xxxx
oooo oooo
Read Fuse High bits. “0” = programmed, “1” = unprogrammed.
Read Extended Fuse Bits
0101 0000
0000 1000
xxxx xxxx
oooo oooo
Read Extended Fuse bits. “0” = programmed, “1” = unprogrammed.
Read Calibration Byte
0011 1000
000x xxxx
0000 000b
oooo oooo
Read Calibration Byte at address b.
Poll RDY/BSY
1111 0000
0000 0000
xxxx xxxx
xxxx xxxo
If o = “1”, a programming operation is
still busy. Wait until this bit returns to
“0” before applying another command.
Note:
174
Operation
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Serial Programming
Characteristics
Figure 79. Serial Programming Timing
MOSI
tSHOX
tOVSH
SCK
tSLSH
tSHSL
MISO
tSLIV
Table 79. Serial Programming Characteristics, TA = -40°C to 85°C, VCC = 2.7V - 5.5V
(Unless Otherwise Noted)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (ATtiny2313L)
Oscillator Period (ATtiny2313L)
tCLCL
Min
Typ
0
Max
Units
8
MHz
125
ns
Oscillator Frequency (ATtiny2313, VCC = 4.5V 5.5V)
0
tCLCL
Oscillator Period (ATtiny2313, VCC = 4.5V 5.5V)
67
ns
tSHSL
SCK Pulse Width High
2 tCLCL*
ns
tSLSH
SCK Pulse Width Low
2 tCLCL*
ns
tOVSH
MOSI Setup to SCK High
tCLCL
ns
tSHOX
MOSI Hold after SCK High
2 tCLCL
ns
tSLIV
SCK Low to MISO Valid
1/tCLCL
Note:
TBD
16
TBD
TBD
MHz
ns
1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz
175
2543F–AVR–08/04
Electrical Characteristics
Absolute Maximum Ratings*
Operating Temperature.................................. -55°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA
DC Characteristics
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)(1)
Symbol
Parameter
VIL
Input Low Voltage
VIH
Input High-voltage
VIH2
Input High-voltage
Condition
(4)
Min.
Typ.
Max.
Units
-0.5
0.2VCC
V
Except RESET pin
0.6VCC(3)
VCC +0.5
V
RESET pin
0.9VCC(3)
VCC +0.5
V
0.7
0.5
V
V
VOL
Output Low Voltage
(Port B)
VOH
Output High-voltage(5)
(Port B)
IOH = -10 mA, VCC = 5V
IOH = -5 mA, VCC = 3V
IIL
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin low
(absolute value)
1
µA
IIH
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin high
(absolute value)
1
µA
RRST
Reset Pull-up Resistor
30
60
kΩ
Rpu
I/O Pin Pull-up Resistor
20
50
kΩ
Active 1MHz, VCC = 2V
0.35
mA
Active 4MHz, VCC = 3V
2
mA
Active 8MHz, VCC = 5V
6
mA
Power Supply Current
ICC
Power-down mode
Notes:
176
IOL = 10 mA, VCC = 5V
IOL = 5 mA, VCC = 3V
4.2
2.5
V
V
Idle 1MHz, VCC = 2V
0.08
0.2
mA
Idle 4MHz, VCC = 3V
0.41
1
mA
Idle 8MHz, VCC = 5V
1.6
3
mA
WDT enabled, VCC = 3V
<3
6
µA
WDT disabled, VCC = 3V
< 0.5
2
µA
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. “Max” means the highest value where the pin is guaranteed to be read as low.
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 60 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
5. Although each I/O port can source more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 60 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
External Clock Drive
Waveforms
Figure 80. External Clock Drive Waveforms
V IH1
V IL1
External Clock Drive
Table 80. External Clock Drive (Estimated Values)
VCC = 1.8 - 5.5V
VCC = 4.5 - 5.5V
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Max.
Units
1/tCLCL
Oscillator
Frequency
0
1
0
8
0
16
MHz
tCLCL
Clock Period
1000
125
62.5
ns
tCHCX
High Time
400
50
25
ns
tCLCX
Low Time
400
50
25
ns
tCLCH
Rise Time
2.0
1.6
0.5
µs
tCHCL
Fall Time
2.0
1.6
0.5
µs
2
2
2
%
∆tCLCL
Change in
period from one
clock cycle to
the next
177
2543F–AVR–08/04
Maximum Speed vs. VCC
Maximum frequency is dependent on VCC. As shown in Figure 81 and Figure 82, the
Maximum Frequency vs. VCC curve is linear between 1.8V < VCC < 2.7V and between
2.7V < VCC < 4.5V.
Figure 81. Maximum Frequency vs. VCC, ATtiny2313V
10 MHz
Safe Operating Area
4 MHz
1.8V
2.7V
5.5V
Figure 82. Maximum Frequency vs. VCC, ATtiny2313
20 MHz
10 MHz
Safe Operating Area
2.7V
178
4.5V
5.5V
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
ATtiny2313 Typical
Characteristics
The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins
configured as inputs and with internal pull-ups enabled. A sine wave generator with railto-rail output is used as clock source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage,
operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and
ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as
CL*VCC*f where CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog
Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.
Values are estimates. All values are subject to change.
Active Supply Current
Figure 83. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY
0.1 - 1.0 MHz
1.2
5.5 V
1
5.0 V
ICC (mA)
0.8
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)
179
2543F–AVR–08/04
Figure 84. Active Supply Current vs. Frequency (1 - 20 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
14
5.5 V
12
5.0 V
ICC (mA)
10
4.5 V
8
6
4.0 V
3.3 V
2.7 V
4
2
1.8 V
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
Figure 85. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
9
85 ˚C
25 ˚C
-40 ˚C
8
7
ICC (mA)
6
5
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
180
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 86. Active Supply Current vs. VCC (Internal RC Oscillator, 4 MHz)
ACTIVE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 4 MHz
6
-40 °C
85 °C
25 °C
5
Icc (mA)
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Figure 87. Active Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
ACTIVE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 1 MHz
1.8
85 °C
25 °C
-40 °C
1.6
1.4
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)
181
2543F–AVR–08/04
Figure 88. Active Supply Current vs. VCC (Internal RC Oscillator, 0.5 MHz)
ACTIVE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 0.5 MHz
1.2
1
85 °C
25 °C
-40 °C
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 89. 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
6
Vcc (V)
182
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Idle Supply Current
Figure 90. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
0.25
5.5 V
0.2
5.0 V
I cc (m A)
4.5 V
0.15
4.0 V
3.3 V
0.1
2.7 V
1.8 V
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 91. Idle Supply Current vs. Frequency (1 - 20 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
5
4.5
5.5 V
4
5.0 V
3.5
4.5 V
I cc (mA)
3
2.5
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)
183
2543F–AVR–08/04
Figure 92. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 8 MHz
3
85 °C
25 °C
-40 °C
2.5
Icc (mA)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Figure 93. Idle Supply Current vs. VCC (Internal RC Oscillator, 4 MHz)
IDLE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 4 MHz
1.6
85 °C
25 °C
-40 °C
1.4
1.2
Icc (mA)
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)
184
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 94. Idle Supply Current vs. VCC (Internal RC Oscillator, 1 MHz)
IDLE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 1 MHz
0.5
85 °C
25 °C
-40 °C
0.4
Icc (mA)
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Figure 95. Idle Supply Current vs. VCC (Internal RC Oscillator, 0.5 MHz)
IDLE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 0.5 MHz
0.3
85 °C
25 °C
-40 °C
0.25
Icc (mA)
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)
185
2543F–AVR–08/04
Figure 96. Idle Supply Current vs. VCC (Internal RC Oscillator, 128 KHz)
IDLE SUPPLY CURRENT vs. Vcc
INTERNAL RC OSCILLATOR, 128 KHz
0.035
-40 °C
25 °C
85 °C
0.03
I cc (m A)
0.025
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)
Power-down Supply Current
Figure 97. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. Vcc
WATCHDOG TIMER DISABLED
1.5
85 °C
1.25
I cc (uA)
1
-40 °C
0.75
25 °C
0.5
0.25
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
186
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 98. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. Vcc
WATCHDOG TIMER ENABLED
20
85 °C
18
25 °C
-40 °C
16
14
Icc (uA)
12
10
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Standby Supply Current
Figure 99. Standby Supply Current vs. VCC
STANDBY SUPPLY CURRENT vs. Vcc
0.08
2MHz Res
2MHz Xtal
0.07
0.06
455KHz Res
1MHz Res
I cc (m A)
0.05
0.04
0.03
0.02
0.01
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
187
2543F–AVR–08/04
Pin Pull-up
Figure 100. 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
85 °C
25 °C
120
-40 °C
I OP (uA )
100
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOP (V)
Figure 101. 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
25 °C
85 °C
70
-40 °C
60
IOP (uA)
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VOP (V)
188
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 102. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 5V
120
25 °C
-40 °C
100
85 °C
IRESET (uA)
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VRESET(V)
Figure 103. 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
25 °C
-40 °C
50
85 °C
IRESET (uA)
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VRESET (V)
189
2543F–AVR–08/04
Pin Driver Strength
Figure 104. I/O Pin Source Current vs. Output Voltage (VCC = 5V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
90
80
85 °C
70
60
-40 °C
IOH (mA)
25 °C
50
40
30
20
10
0
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
5
VOH (V)
Figure 105. I/O Pin Source Current vs. Output Voltage (VCC = 2.7V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
35
30
25
-40 °C
25 °C
IOH (mA)
85 °C
20
15
10
5
0
0.5
1
1.5
2
2.5
3
VOH (V)
190
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 106. I/O Pin Source Current vs. Output Voltage (VCC = 1.8V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
9
-40 °C
25 °C 8
85 °C
7
IOH (mA)
6
5
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOH (V)
Figure 107. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
100
-40 °C
90
80
25 °C
70
85 °C
IOL (mA)
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
191
2543F–AVR–08/04
Figure 108. I/O Pin Sink Current vs. Output Voltage (VCC = 2.7V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
40
35
-40 °C
30
25 °C
IOL (mA)
25
85 °C
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
Figure 109. I/O Pin Sink Current vs. Output Voltage (VCC = 1.8V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
14
12
-40 °C
10
25 °C
IOL (mA)
85 °C
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
VOL (V)
192
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 110. Reset I/O Pin Source Current vs. Output Voltage (VCC = 5V)
RESET I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
16
-40 °C
14
12
Current (mA)
25 °C
10
8
85 °C
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOH (V)
Figure 111. Reset I/O Pin Source Current vs. Output Voltage (VCC = 2.7V)
RESET I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
4.5
4
-40 °C
3.5
25 °C
Current (m A)
3
2.5
85 °C
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
193
2543F–AVR–08/04
Figure 112. Reset I/O Pin Source Current vs. Output Voltage (VCC = 1.8V)
RESET I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
1.4
-40 °C
1.2
25 °C
Current (mA)
1
0.8
85 °C
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOH (V)
Figure 113. Reset I/O Pin Sink Current vs. Output Voltage (VCC = 5V)
RESET I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
16
-40 °C
Current (mA)
14
12
25 °C
10
85 °C
8
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOL (V)
194
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 114. Reset I/O Pin Sink Current vs. Output Voltage (VCC = 2.7V)
RESET I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
4.5
-40 °C
Current (mA)
4
3.5
25 °C
3
85 °C
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOL (V)
Figure 115. Reset I/O Pin Sink Current vs. Output Voltage (VCC = 1.8V)
RESET I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
1.4
-40 °C
1.2
25 °C
85 °C
Current (mA)
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
VOL (V)
195
2543F–AVR–08/04
Pin Thresholds and
Hysteresis
Figure 116. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as “1”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. Vcc
VIH, IO PIN READ AS '1'
3
85 °C
-40 °C
25 °C
2.5
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 117. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as “0”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. Vcc
VIL, IO PIN READ AS '0'
3
85 °C
25 °C
-40 °C
2.5
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
196
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 118. Reset I/O Input Threshold Voltage vs. VCC (VIH,Reset Pin Read as “1”)
RESET I/O PIN INPUT THRESHOLD VOLTAGE vs. Vcc
VIH, IO PIN READ AS '1'
3
85 °C
25 °C
-40 °C
2.5
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
Figure 119. Reset I/O Input Threshold Voltage vs. VCC (VIL,Reset Pin Read as “0”)
RESET I/O PIN INPUT THRESHOLD VOLTAGE vs. Vcc
VIL, IO PIN READ AS '0'
2.5
85°C
25°C
-40°C
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
197
2543F–AVR–08/04
Figure 120. Reset I/O Input Pin Hysteresis vs. VCC
RESET I/O INPUT PIN HYSTERESIS vs. Vcc
1
0.9
Input Hysteresis (V)
0.8
-40 °C
0.7
0.6
25 °C
0.5
85 °C
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)
Figure 121. Reset Input Threshold Voltage vs. VCC (VIH,Reset Pin Read as “1”)
RESET INPUT THRESHOLD VOLTAGE vs. Vcc
VIH, IO PIN READ AS '1'
2.5
Threshold (V)
2
1.5
-40 °C
25 °C
85 °C
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
198
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 122. Reset Input Threshold Voltage vs. VCC (VIL,Reset Pin Read as “0”)
RESET INPUT THRESHOLD VOLTAGE vs. Vcc
VIL, IO PIN READ AS '0'
2.5
Threshold (V)
2
1.5
1
85 °C
25 °C
-40 °C
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
5
5.5
Vcc (V)
Figure 123. Reset Input Pin Hysteresis vs. VCC
RESET INPUT PIN HYSTERESIS vs. Vcc
0.7
-40 °C
0.6
Input Hysteresis (V)
0.5
25 °C
0.4
85 °C
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
Vcc (V)
199
2543F–AVR–08/04
BOD Thresholds and Analog
Comparator Offset
Figure 124. BOD Thresholds vs. Temperature (BOD Level is 4.3V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 4.3V
4.45
Rising Vcc
Thres hol d (V )
4.4
4.35
Falling Vcc
4.3
4.25
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
80
90
Temperature (C)
Figure 125. BOD Thresholds vs. Temperature (BOD Level is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 2.7V
2.85
Rising Vcc
Threshold (V)
2.8
2.75
Falling Vcc
2.7
2.65
-40
-30
-20
-10
0
10
20
30
40
50
60
70
Temperature (C)
200
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 126. BOD Thresholds vs. Temperature (BOD Level is 1.8V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 1.8V
1.88
1.86
Threshold (V)
Rising Vcc
1.84
1.82
Falling Vcc
1.8
1.78
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
Temperature (C)
Internal Oscillator Speed
Figure 127. Watchdog Oscillator Frequency vs. VCC
WATCHDOG OSCILLATOR FREQUENCY vs. VCC
0.104
0.103
0.102
-40 °C
F RC (M Hz )
0.101
0.1
25 °C
0.099
0.098
0.097
0.096
85 °C
0.095
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
201
2543F–AVR–08/04
Figure 128. Watchdog Oscillator Frequency vs. Temperature
WATCHDOG OSCILLATOR FREQUENCY vs. TEMPERATURE
0.105
0.104
0.103
F RC (MHz)
0.102
0.101
0.1
1.8 V
0.099
2.7 V
0.098
3.3 V
0.097
4.0 V
5.5 V
5.0 V
4.5 V
0.096
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
Figure 129. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
8.4
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
8.3
F RC (MHz )
8.2
8.1
8
7.9
7.8
7.7
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
202
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 130. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. Vcc
8.4
8.3
85 °C
FRC (MHz)
8.2
8.1
25 °C
8
-40 °C
7.9
7.8
7.7
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 131. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
14
25 °C
12
FRC (MHz)
10
8
6
4
2
0
0
16
32
48
64
80
96
112
128
OSCCAL VALUE
203
2543F–AVR–08/04
Figure 132. Calibrated 4 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
4.2
5.5 V
5.0 V
3.3 V
1.8 V
4.15
FRC (MHz)
4.1
4.05
4
3.95
3.9
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
Figure 133. Calibrated 4 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. Vcc
4.2
4.15
85 °C
FRC (MHz)
4.1
4.05
25 °C
4
-40 °C
3.95
3.9
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
204
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Figure 134. Calibrated 4 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 4MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
7
25 °C
6
F RC (MHz )
5
4
3
2
1
0
0
8
16
24
32
40
48
56
64
72
80
88
96
104
112 120
128
OSCCAL VALUE
Current Consumption of
Peripheral Units
Figure 135. Brownout Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs. Vcc
30
-40 °C
85 °C
25 °C
25
Icc (uA)
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Vcc (V)
205
2543F–AVR–08/04
Figure 136. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. Vcc
70
-40 °C
60
25 °C
85 °C
Icc (uA)
50
40
30
20
10
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
5
5.5
Vcc (V)
Figure 137. Programming Current vs. VCC
PROGRAMMING CURRENT vs. Vcc
4.5
4
3.5
-40 °C
Icc (mA)
3
2.5
25 °C
2
1.5
85 °C
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
Vcc (V)
206
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Current Consumption in
Reset and Reset Pulsewidth
Figure 138. 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
4.5 V
Icc (mA)
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 139. 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
2.5
5.5 V
5.0 V
2
4.5 V
Icc (mA)
1.5
4.0 V
3.3 V
1
2.7 V
0.5
0
0
2
4
6
8
10
12
14
16
18
20
Frequency (MHz)
207
2543F–AVR–08/04
Figure 140. 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
Vcc (V)
208
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
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
7
0x3E (0x5E)
Reserved
–
–
–
–
–
–
–
–
0x3D (0x5D)
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
0x3C (0x5C)
OCR0B
0x3B (0x5B)
GIMSK
INT1
INT0
PCIE
–
–
–
–
–
0x3A (0x5A)
EIFR
INTF1
INTF0
PCIF
–
–
–
–
–
60
0x39 (0x59)
TIMSK
TOIE1
OCIE1A
OCIE1B
–
ICIE1
OCIE0B
TOIE0
OCIE0A
77, 108
0x38 (0x58)
TIFR
TOV1
–
ICF1
OCF0B
TOV0
OCF0A
77
SPMCSR
–
OCF1A
–
OCF1B
0x37 (0x57)
–
CTPB
RFLB
PGWRT
PGERS
SELFPRGEN
154
PUD
SM1
SE
SM0
ISC11
ISC10
ISC01
ISC00
52
0x36 (0x56)
OCR0A
0x35 (0x55)
MCUCR
Timer/Counter0 – Compare Register B
10
76
Timer/Counter0 – Compare Register A
59
76
0x34 (0x54)
MCUSR
–
–
–
–
WDRF
BORF
EXTRF
PORF
36
0x33 (0x53)
TCCR0B
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
75
–
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
25
0x32 (0x52)
TCNT0
0x31 (0x51)
OSCCAL
Timer/Counter0 (8-bit)
76
0x30 (0x50)
TCCR0A
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
72
0x2F (0x4F)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1BO
–
–
WGM11
WGM10
103
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
106
0x2E (0x4E)
TCCR1B
0x2D (0x4D)
TCNT1H
Timer/Counter1 – Counter Register High Byte
0x2C (0x4C)
TCNT1L
Timer/Counter1 – Counter Register Low Byte
107
0x2B (0x4B)
OCR1AH
Timer/Counter1 – Compare Register A High Byte
107
107
107
0x2A (0x4A)
OCR1AL
Timer/Counter1 – Compare Register A Low Byte
0x29 (0x49)
OCR1BH
Timer/Counter1 – Compare Register B High Byte
108
0x28 (0x48)
OCR1BL
Timer/Counter1 – Compare Register B Low Byte
108
0x27 (0x47)
Reserved
–
–
–
–
–
–
–
–
0x26 (0x46)
CLKPR
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
0x25 (0x45)
ICR1H
Timer/Counter1 - Input Capture Register High Byte
27
108
0x24 (0x44)
ICR1L
0x23 (0x43)
GTCCR
–
–
–
Timer/Counter1 - Input Capture Register Low Byte
–
–
–
–
PSR10
108
80
0x22 (ox42)
TCCR1C
FOC1A
FOC1B
–
–
–
–
–
–
107
0x21 (0x41)
WDTCSR
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
41
0x20 (0x40)
PCMSK
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
60
0x1F (0x3F)
Reserved
–
–
–
–
–
–
–
–
–
0x1E (0x3E)
EEAR
0x1D (0x3D)
EEDR
EEPROM Address Register
15
0x1C (0x3C)
EECR
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
16
0x1B (0x3B)
PORTA
–
–
–
–
–
PORTR2
PORTA1
PORTA0
57
0x1A (0x3A)
DDRA
–
–
–
–
–
DDA2
DDA1
DDA0
57
0x19 (0x39)
PINA
–
–
–
–
–
PINA2
PINA1
PINA0
57
0x18 (0x38)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
57
0x17 (0x37)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
57
0x16 (0x36)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
0x15 (0x35)
GPIOR2
General Purpose I/O Register 2
20
0x14 (0x34)
GPIOR1
General Purpose I/O Register 1
20
0x13 (0x33)
GPIOR0
General Purpose I/O Register 0
0x12 (0x32)
PORTD
–
0x11 (0x31)
DDRD
–
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
57
0x10 (0x30)
PIND
–
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
57
EEPROM Data Register
PORTD6
PORTD5
PORTD4
PORTD3
16
57
20
PORTD2
PORTD1
PORTD0
USI Data Register
57
0x0F (0x2F)
USIDR
0x0E (0x2E)
USISR
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
143
144
0x0D (0x2D)
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
145
UPE
U2X
MPCM
128
UCSZ2
RXB8
TXB8
130
148
0x0C (0x2C)
UDR
0x0B (0x2B)
UCSRA
RXC
TXC
UDRE
UART Data Register (8-bit)
FE
0x0A (0x2A)
UCSRB
RXCIE
TXCIE
UDRIE
RXEN
0x09 (0x29)
UBRRL
0x08 (0x28)
ACSR
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
DOR
TXEN
UBRRH[7:0]
128
132
0x07 (0x27)
Reserved
–
–
–
–
–
–
–
–
0x06 (0x26)
Reserved
–
–
–
–
–
–
–
–
0x05 (0x25)
Reserved
–
–
–
–
–
–
–
–
0x04 (0x24)
Reserved
–
–
–
–
–
–
–
–
0x03 (0x23)
UCSRC
–
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
0x02 (0x22)
UBRRH
–
–
–
–
0x01 (0x21)
DIDR
–
–
–
–
–
–
AIN1D
AIN0D
0x00 (0x20)
Reserved
–
–
–
–
–
–
–
–
UBRRH[11:8]
131
132
149
209
2543F–AVR–08/04
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 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.
4. 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.
210
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Instruction Set Summary
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD
Rd, Rr
Add two Registers
Rd ← Rd + Rr
Z,C,N,V,H
ADC
Rd, Rr
Add with Carry two Registers
Rd ← Rd + Rr + C
Z,C,N,V,H
1
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
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
3
ICALL
Indirect Call to (Z)
PC ← Z
None
RET
Subroutine Return
PC ← STACK
None
4
RETI
Interrupt Return
PC ← STACK
I
4
CPSE
Rd,Rr
Compare, Skip if Equal
if (Rd = Rr) PC ← PC + 2 or 3
None
CP
Rd,Rr
Compare
Rd − Rr
Z, N,V,C,H
1
CPC
Rd,Rr
Compare with Carry
Rd − Rr − C
Z, N,V,C,H
1
CPI
Rd,K
Compare Register with Immediate
Rd − K
Z, N,V,C,H
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ← PC + 2 or 3
None
1/2/3
1/2/3
1
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC ← PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b)=0) PC ← PC + 2 or 3
None
1/2/3
SBIS
P, b
Skip if Bit in I/O Register is Set
if (P(b)=1) PC ← PC + 2 or 3
None
1/2/3
BRBS
s, k
Branch if Status Flag Set
if (SREG(s) = 1) then PC←PC+k + 1
None
1/2
BRBC
s, k
Branch if Status Flag Cleared
if (SREG(s) = 0) then PC←PC+k + 1
None
1/2
BREQ
k
Branch if Equal
if (Z = 1) then PC ← PC + k + 1
None
1/2
BRNE
k
Branch if Not Equal
if (Z = 0) then PC ← PC + k + 1
None
1/2
BRCS
k
Branch if Carry Set
if (C = 1) then PC ← PC + k + 1
None
1/2
BRCC
k
Branch if Carry Cleared
if (C = 0) then PC ← PC + k + 1
None
1/2
BRSH
k
Branch if Same or Higher
if (C = 0) then PC ← PC + k + 1
None
1/2
BRLO
k
Branch if Lower
if (C = 1) then PC ← PC + k + 1
None
1/2
BRMI
k
Branch if Minus
if (N = 1) then PC ← PC + k + 1
None
1/2
BRPL
k
Branch if Plus
if (N = 0) then PC ← PC + k + 1
None
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V= 0) then PC ← PC + k + 1
None
1/2
BRLT
k
Branch if Less Than Zero, Signed
if (N ⊕ V= 1) then PC ← PC + k + 1
None
1/2
BRHS
k
Branch if Half Carry Flag Set
if (H = 1) then PC ← PC + k + 1
None
1/2
BRHC
k
Branch if Half Carry Flag Cleared
if (H = 0) then PC ← PC + k + 1
None
1/2
BRTS
k
Branch if T Flag Set
if (T = 1) then PC ← PC + k + 1
None
1/2
BRTC
k
Branch if T Flag Cleared
if (T = 0) then PC ← PC + k + 1
None
1/2
BRVS
k
Branch if Overflow Flag is Set
if (V = 1) then PC ← PC + k + 1
None
1/2
BRVC
k
Branch if Overflow Flag is Cleared
if (V = 0) then PC ← PC + k + 1
None
1/2
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ← PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ← PC + k + 1
None
1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI
P,b
Set Bit in I/O Register
I/O(P,b) ← 1
None
2
CBI
P,b
Clear Bit in I/O Register
I/O(P,b) ← 0
None
2
LSL
Rd
Logical Shift Left
Rd(n+1) ← Rd(n), Rd(0) ← 0
Z,C,N,V
1
LSR
Rd
Logical Shift Right
Rd(n) ← Rd(n+1), Rd(7) ← 0
Z,C,N,V
1
ROL
Rd
Rotate Left Through Carry
Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7)
Z,C,N,V
1
211
2543F–AVR–08/04
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ROR
Rd
Rotate Right Through Carry
Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0)
Z,C,N,V
1
ASR
Rd
Arithmetic Shift Right
Rd(n) ← Rd(n+1), n=0..6
Z,C,N,V
1
SWAP
Rd
Swap Nibbles
Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0)
None
1
BSET
s
Flag Set
SREG(s) ← 1
SREG(s)
1
BCLR
s
Flag Clear
SREG(s) ← 0
SREG(s)
1
BST
Rr, b
Bit Store from Register to T
T ← Rr(b)
T
1
BLD
Rd, b
Bit load from T to Register
Rd(b) ← T
None
1
SEC
Set Carry
C←1
C
1
CLC
Clear Carry
C←0
C
1
SEN
Set Negative Flag
N←1
N
1
CLN
Clear Negative Flag
N←0
N
1
SEZ
Set Zero Flag
Z←1
Z
1
CLZ
Clear Zero Flag
Z←0
Z
1
SEI
Global Interrupt Enable
I←1
I
1
CLI
Global Interrupt Disable
I←0
I
1
SES
Set Signed Test Flag
S←1
S
1
CLS
Clear Signed Test Flag
S←0
S
1
SEV
Set Twos Complement Overflow.
V←1
V
1
CLV
Clear Twos Complement Overflow
V←0
V
1
SET
Set T in SREG
T←1
T
1
CLT
Clear T in SREG
T←0
T
1
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
H←1
H←0
H
H
1
1
Rd ← Rr
Rd+1:Rd ← Rr+1:Rr
None
1
None
1
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
MOVW
Rd, Rr
Copy Register Word
LDI
Rd, K
Load Immediate
Rd ← K
None
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ← X - 1, Rd ← (X)
None
LD
Rd, Y
Load Indirect
Rd ← (Y)
None
2
LD
Rd, Y+
Load Indirect and Post-Inc.
Rd ← (Y), Y ← Y + 1
None
2
LD
Rd, - Y
Load Indirect and Pre-Dec.
Y ← Y - 1, Rd ← (Y)
None
2
LDD
Rd,Y+q
Load Indirect with Displacement
Rd ← (Y + q)
None
2
LD
Rd, Z
Load Indirect
Rd ← (Z)
None
2
LD
Rd, Z+
Load Indirect and Post-Inc.
Rd ← (Z), Z ← Z+1
None
2
LD
Rd, -Z
Load Indirect and Pre-Dec.
Z ← Z - 1, Rd ← (Z)
None
2
LDD
Rd, Z+q
Load Indirect with Displacement
Rd ← (Z + q)
None
2
LDS
Rd, k
Load Direct from SRAM
Rd ← (k)
None
2
ST
X, Rr
Store Indirect
(X) ← Rr
None
2
ST
X+, Rr
Store Indirect and Post-Inc.
(X) ← Rr, X ← X + 1
None
2
ST
- X, Rr
Store Indirect and Pre-Dec.
X ← X - 1, (X) ← Rr
None
2
ST
Y, Rr
Store Indirect
(Y) ← Rr
None
2
ST
Y+, Rr
Store Indirect and Post-Inc.
(Y) ← Rr, Y ← Y + 1
None
2
ST
- Y, Rr
Store Indirect and Pre-Dec.
Y ← Y - 1, (Y) ← Rr
None
2
STD
Y+q,Rr
Store Indirect with Displacement
(Y + q) ← Rr
None
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
2
ST
Z+, Rr
Store Indirect and Post-Inc.
(Z) ← Rr, Z ← Z + 1
None
2
ST
-Z, Rr
Store Indirect and Pre-Dec.
Z ← Z - 1, (Z) ← Rr
None
2
STD
Z+q,Rr
Store Indirect with Displacement
(Z + q) ← Rr
None
2
STS
k, Rr
Store Direct to SRAM
(k) ← Rr
None
2
Load Program Memory
R0 ← (Z)
None
3
LPM
LPM
Rd, Z
Load Program Memory
Rd ← (Z)
None
3
LPM
Rd, Z+
Load Program Memory and Post-Inc
Rd ← (Z), Z ← Z+1
None
3
Store Program Memory
(Z) ← R1:R0
None
-
IN
Rd, P
In Port
Rd ← P
None
1
OUT
P, Rr
Out Port
P ← Rr
None
1
PUSH
Rr
Push Register on Stack
STACK ← Rr
None
2
POP
Rd
Pop Register from Stack
Rd ← STACK
None
2
SPM
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
212
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Ordering Information
Speed (MHz)
10(3)
20(3)
Note:
Ordering Code
Package(1)
Operation Range
1.8 - 5.5V
ATtiny2313V-10PI
ATtiny2313V-10PJ(2)
ATtiny2313V-10SI
ATtiny2313V-10SJ(2)
20P3
20P3
20S
20S
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATtiny2313-20PI
ATtiny2313-20PJ(2)
ATtiny2313-20SI
ATtiny2313-20SJ(2)
20P3
20P3
20S
20S
Industrial
(-40°C to 85°C)
Power Supply
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative.
3. See Figure 81 on page 178 and Figure 82 on page 178.
Package Type
20P3
20-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)
20S
20-lead, 0.300" Wide, Plastic Gull Wing Small Outline (SOIC)
213
2543F–AVR–08/04
Packaging Information
20P3
D
PIN
1
E1
A
SEATING PLANE
A1
L
B
B1
e
E
COMMON DIMENSIONS
(Unit of Measure = mm)
C
eC
eB
Notes:
1. This package conforms to JEDEC reference MS-001, Variation AD.
2. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25 mm (0.010").
SYMBOL
MIN
NOM
MAX
A
–
–
5.334
A1
0.381
–
–
D
25.493
–
25.984
E
7.620
–
8.255
E1
6.096
–
7.112
B
0.356
–
0.559
B1
1.270
–
1.551
L
2.921
–
3.810
C
0.203
–
0.356
eB
–
–
10.922
eC
0.000
–
1.524
e
NOTE
Note 2
Note 2
2.540 TYP
1/12/04
R
214
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20P3, 20-lead (0.300"/7.62 mm Wide) Plastic Dual
Inline Package (PDIP)
DRAWING NO.
20P3
REV.
C
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
20S
C
1
L
E H
N
A1
Top View
End View
COMMON DIMENSIONS
(Unit of Measure = inches)
e
SYMBOL
b
A
D
Side View
MIN
NOM
MAX
NOTE
A
0.0926
0.1043
A1
0.0040
0.0118
b
0.0130
0.0200
C
0.0091
0.0125
D
0.4961
0.5118
1
2
E
0.2914
0.2992
H
0.3940
0.4190
L
0.0160
0.050
e
4
3
0.050 BSC
Notes: 1. This drawing is for general information only; refer to JEDEC Drawing MS-013, Variation AC for additional information.
2. Dimension "D" does not include mold Flash, protrusions or gate burrs. Mold Flash, protrusions and gate burrs shall not exceed
0.15 mm (0.006") per side.
3. Dimension "E" does not include inter-lead Flash or protrusion. Inter-lead Flash and protrusions shall not exceed 0.25 mm
(0.010") per side.
4. "L" is the length of the terminal for soldering to a substrate.
5. The lead width "b", as measured 0.36 mm (0.014") or greater above the seating plane, shall not exceed a maximum value of 0.61 mm
1/9/02
(0.024") per side.
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20S2, 20-lead, 0.300" Wide Body, Plastic Gull
Wing Small Outline Package (SOIC)
DRAWING NO.
20S2
REV.
A
215
2543F–AVR–08/04
Errata
The revision in this section refers to the revision of the ATtiny2313 device.
ATtiny2313 Rev B
• Wrong values read after Erase Only operation
• Parallel Programming does not work
• Watchdog Timer Interrupt disabled
1. Wrong values read after Erase Only operation
At supply voltages below 2.7 V, an EEPROM location that is erased by the Erase
Only operation may read as programmed (0x00).
Problem Fix/Workaround
If it is necessary to read an EEPROM location after Erase Only, use an Atomic Write
operation with 0xFF as data in order to erase a location. In any case, the Write Only
operation can be used as intended. Thus no special considerations are needed as
long as the erased location is not read before it is programmed.
2. Parallel Programming does not work
Parallel Programming is not functioning correctly. Because of this, reprogramming
of the device is impossible if one of the following modes are selected:
–
In-System Programming disabled (SPIEN unprogrammed)
–
Reset Disabled (RSTDISBL programmed)
Problem Fix/Workaround
Serial Programming is still working correctly. By avoiding the two modes above, the
device can be reprogrammed serially.
3. Watchdog Timer Interrupt disabled
If the watchdog timer interrupt flag is not cleared before a new timeout occurs, the
watchdog will be disabled, and the interrupt flag will automatically be cleared. This is
only applicable in interrupt only mode. If the Watchdog is configured to reset the
device in the watchdog time-out following an interrupt, the device works correctly.
Problem fix / Workaround
Make sure there is enough time to always service the first timeout event before a
new watchdog timeout occurs. This is done by selecting a long enough time-out
period.
ATtiny2313 Rev A
216
Revision A has not been sampled.
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Datasheet Change
Log for ATtiny2313
Changes from Rev.
2514E-04/04 to Rev.
2514F-08/04
Please note that the referring page numbers in this section are referred to this document. The referring revision in this section are referring to the document revision.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Changes from Rev.
2514D-03/04 to Rev.
2514E-04/04
1.
2.
3.
4.
5.
Changes from Rev.
2514C-12/03 to Rev.
2514D-03/04
1.
2.
3.
4.
5.
6.
7.
8.
9.
Changes from Rev.
2514B-09/03 to Rev.
2514C-12/03
1.
Updated “Features” on page 1.
Updated “Alternate Functions of Port B” on page 52.
Updated “Calibration Byte” on page 159.
Moved Table 69 on page 159 and Table 70 on page 160 to “Page Size”
on page 159.
Updated “Enter Programming Mode” on page 162.
Updated “Serial Programming Algorithm” on page 172.
Updated Table 78 on page 173.
Updated “DC Characteristics” on page 176.
Updated “ATtiny2313 Typical Characteristics” on page 179.
Changed occurences of PCINT15 to PCINT7, EEMWE to EEMPE and
EEWE to EEPE in the document.
Speed Grades changed
- 12MHz to 10MHz
- 24MHz to 20MHz
Updated Figure 1 on page 2.
Updated “Ordering Information” on page 213.
Updated “Maximum Speed vs. VCC” on page 178.
Updated “ATtiny2313 Typical Characteristics” on page 179.
Updated Table 2 on page 22.
Replaced “Watchdog Timer” on page 38.
Added “Maximum Speed vs. VCC” on page 178.
“Serial Programming Algorithm” on page 172 updated.
Changed mA to µA in preliminary Figure 135 on page 205.
“Ordering Information” on page 213 updated.
MLF package option removed
Package drawing “20P3” on page 214 updated.
Updated C-code examples.
Renamed instances of SPMEN to SELFPRGEN, Self Programming
Enable.
Updated “Calibrated Internal RC Oscillator” on page 24.
217
2543F–AVR–08/04
Changes from Rev.
2514A-09/03 to Rev.
2514B-09/03
1.
2.
3.
4.
5.
6.
7.
8.
9.
218
Fixed typo from UART to USART and updated Speed Grades and Power
Consumption Estimates in “Features” on page 1.
Updated “Pin Configurations” on page 2.
Updated Table 15 on page 33 and Table 80 on page 177.
Updated item 5 in “Serial Programming Algorithm” on page 172.
Updated “Electrical Characteristics” on page 176.
Updated Figure 81 on page 178 and added Figure 82 on page 178.
Changed SFIOR to GTCCR in “Register Summary” on page 209.
Updated “Ordering Information” on page 213.
Added new errata in “Errata” on page 216.
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Table of Contents
Features................................................................................................ 1
Pin Configurations............................................................................... 2
Overview............................................................................................... 2
Block Diagram ...................................................................................................... 3
Pin Descriptions.................................................................................................... 5
About Code Examples......................................................................... 5
Disclaimer............................................................................................. 5
AVR CPU Core ..................................................................................... 6
Introduction ........................................................................................................... 6
Architectural Overview.......................................................................................... 6
ALU – Arithmetic Logic Unit.................................................................................. 7
Status Register ..................................................................................................... 7
General Purpose Register File ............................................................................. 8
Stack Pointer ...................................................................................................... 10
Instruction Execution Timing............................................................................... 10
Reset and Interrupt Handling.............................................................................. 11
AVR ATtiny2313 Memories ............................................................... 13
In-System Reprogrammable Flash Program Memory ........................................
SRAM Data Memory...........................................................................................
EEPROM Data Memory......................................................................................
I/O Memory .........................................................................................................
13
14
15
20
System Clock and Clock Options .................................................... 21
Clock Systems and their Distribution ..................................................................
Clock Sources.....................................................................................................
Default Clock Source ..........................................................................................
Crystal Oscillator.................................................................................................
Calibrated Internal RC Oscillator ........................................................................
External Clock.....................................................................................................
128 kHz Internal Oscillator..................................................................................
21
22
22
22
24
26
27
Power Management and Sleep Modes............................................. 29
Idle Mode ............................................................................................................
Power-down Mode..............................................................................................
Standby Mode.....................................................................................................
Minimizing Power Consumption .........................................................................
29
30
30
30
System Control and Reset ................................................................ 32
Internal Voltage Reference ................................................................................. 37
Watchdog Timer ................................................................................................. 38
i
2543F–AVR–08/04
Interrupts ............................................................................................ 43
Interrupt Vectors in ATtiny2313 .......................................................................... 43
I/O-Ports.............................................................................................. 45
Introduction .........................................................................................................
Ports as General Digital I/O ................................................................................
Alternate Port Functions .....................................................................................
Register Description for I/O-Ports.......................................................................
45
46
50
57
External Interrupts............................................................................. 58
8-bit Timer/Counter0 with PWM........................................................ 61
Overview.............................................................................................................
Timer/Counter Clock Sources.............................................................................
Counter Unit........................................................................................................
Output Compare Unit..........................................................................................
Compare Match Output Unit ...............................................................................
Modes of Operation ............................................................................................
Timer/Counter Timing Diagrams.........................................................................
8-bit Timer/Counter Register Description ...........................................................
61
62
62
63
64
65
70
72
Timer/Counter0 and Timer/Counter1 Prescalers ............................ 79
16-bit Timer/Counter1........................................................................ 81
Overview............................................................................................................. 81
Accessing 16-bit Registers ................................................................................. 83
Timer/Counter Clock Sources............................................................................. 87
Counter Unit........................................................................................................ 87
Input Capture Unit............................................................................................... 88
Output Compare Units ........................................................................................ 90
Compare Match Output Unit ............................................................................... 92
Modes of Operation ............................................................................................ 93
Timer/Counter Timing Diagrams....................................................................... 101
16-bit Timer/Counter Register Description ....................................................... 103
USART .............................................................................................. 110
Overview...........................................................................................................
Clock Generation ..............................................................................................
Frame Formats .................................................................................................
USART Initialization..........................................................................................
Data Transmission – The USART Transmitter .................................................
Data Reception – The USART Receiver ..........................................................
Asynchronous Data Reception .........................................................................
Multi-processor Communication Mode .............................................................
USART Register Description ............................................................................
Examples of Baud Rate Setting........................................................................
ii
110
111
114
115
117
120
123
127
128
133
ATtiny2313/V
2543F–AVR–08/04
ATtiny2313/V
Universal Serial Interface – USI...................................................... 137
Overview...........................................................................................................
Functional Descriptions ....................................................................................
Alternative USI Usage ......................................................................................
USI Register Descriptions.................................................................................
137
138
143
143
Analog Comparator ......................................................................... 148
debugWIRE On-chip Debug System .............................................. 150
Features............................................................................................................
Overview...........................................................................................................
Physical Interface .............................................................................................
Software Break Points ......................................................................................
Limitations of debugWIRE ................................................................................
debugWIRE Related Register in I/O Memory ...................................................
150
150
150
151
151
151
Self-Programming the Flash........................................................... 152
Addressing the Flash During Self-Programming .............................................. 153
Memory Programming..................................................................... 157
Program And Data Memory Lock Bits ..............................................................
Fuse Bits...........................................................................................................
Signature Bytes ................................................................................................
Calibration Byte ................................................................................................
Page Size .........................................................................................................
Parallel Programming Parameters, Pin Mapping, and Commands ..................
Serial Programming Pin Mapping .....................................................................
Parallel Programming .......................................................................................
Serial Downloading...........................................................................................
157
158
159
159
159
160
162
162
171
Electrical Characteristics................................................................ 176
Absolute Maximum Ratings*............................................................................. 176
DC Characteristics............................................................................................ 176
External Clock Drive Waveforms ...................................................................... 177
External Clock Drive ......................................................................................... 177
Maximum Speed vs. VCC ........................................................................................................................ 178
ATtiny2313 Typical Characteristics ............................................... 179
Register Summary ........................................................................... 209
Instruction Set Summary ................................................................ 211
Ordering Information....................................................................... 213
Packaging Information .................................................................... 214
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2543F–AVR–08/04
20P3 ................................................................................................................. 214
20S ................................................................................................................... 215
Errata ................................................................................................ 216
ATtiny2313 Rev B............................................................................................. 216
ATtiny2313 Rev A............................................................................................. 216
Datasheet Change Log for ATtiny2313.......................................... 217
Changes from Rev. 2514E-04/04 to Rev. 2514F-08/04 ...................................
Changes from Rev. 2514D-03/04 to Rev. 2514E-04/04 ...................................
Changes from Rev. 2514C-12/03 to Rev. 2514D-03/04...................................
Changes from Rev. 2514B-09/03 to Rev. 2514C-12/03 ...................................
Changes from Rev. 2514A-09/03 to Rev. 2514B-09/03 ...................................
217
217
217
217
218
Table of Contents ................................................................................. i
iv
ATtiny2313/V
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