ATMEL ATTINY167-15XZ

Features
• High Performance, Low Power AVR® 8-Bit Microcontroller
• Advanced RISC Architecture
•
•
•
•
•
•
– 123 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
Non-volatile Program and Data Memories
– 8K/16K Byte of In-System Programmable (ISP) Program Memory Flash
Endurance: 10,000 Write/Erase Cycles
– 512 Bytes In-System Programmable EEPROM
Endurance: 100,000 Write/Erase Cycles
– 512 Bytes Internal SRAM
– Programming Lock for Self-Programming Flash Program and EEPROM Data
Security
– Low size LIN/UART Software In-System Programmable
Peripheral Features
– LIN 2.1 and 1.3 Controller or 8-Bit UART
– 8-bit Asynchronous Timer/Counter0:
. 10-bit Clock Prescaler
. 1 Output Compare or 8-bit PWM Channel
– 16-bit Synchronous Timer/Counter1:
. 10-bit Clock Prescaler
. External Event Counter
. 2 Output Compares Units or 16-bit PWM Channels each Driving up to 4 Ouput
Pins
– Master/Slave SPI Serial Interface,
– Universal Serial Interface (USI) with Start Condition Detector (Master/Slave SPI,
TWI, ...)
– 10-bit ADC:
. 11 Single Ended Channels
. 8 Differential ADC Channel Pairs with Programmable Gain (8x or 20x)
– On-chip Analog Comparator with Selectable Voltage Reference
– 100µA ±10% Current Source (LIN Node Identification)
– On-chip Temperature Sensor
– Programmable Watchdog Timer with Separate On-chip Oscillator
Special Microcontroller Features
– Dynamic Clock Switching (External/Internal RC/Watchdog Clock) for Power
Control, EMC Reduction
– DebugWIRE On-chip Debug (OCD) System
– Hardware In-System Programmable (ISP) via SPI Port
– External and Internal Interrupt Sources
– Interrupt and Wake-up on Pin Change
– Low Power Idle, ADC Noise Reduction, and Power-down Modes
– Enhanced Power-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated RC Oscillator 8MHz
– 4-16 MHz and 32 KHz Crystal/Ceramic Resonator Oscillators
I/O and Packages
– 16 Programmable I/O Lines
– 20-pin SOIC, 32-pad QFN and 20-pin TSSOP
Operating Voltage:
– 2.7 - 5.5V for ATtiny87/167
Speed Grade:
– 0 - 8 MHz @ 2.7 - 5.5V (Automotive Temp. Range: -40°C to +125°C)
– 0 - 16 MHz @ 4.5 - 5.5V (Automotive Temp. Range: -40°C to +125°C)
8-bit
Microcontroller
with 8K/16K
Bytes In-System
Programmable
Flash and LIN
Controller
ATtiny87
ATtiny167
Automotive
7728D–AVR–07/09
1. Description
1.1
Comparison Between ATtiny87 and ATtiny167
ATtiny87 and ATtiny167 are hardware and software compatible. They differ only in memory
sizes as shown in Table 1-1.
Table 1-1.
1.2
Memory Size Summary
Device
Flash
EEPROM
SRAM
Interrupt Vector size
ATtiny167
16K Bytes
512 Bytes
512 Bytes
2-instruction-words / vector
ATtiny87
8K Bytes
512 Bytes
512 Bytes
2-instruction-words / vector
Part Description
The ATtiny87/167 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 ATtiny87/167
achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize
power consumption versus processing speed.
The AVR core combines a rich instruction set with 32 general purpose working registers. All
the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The
resulting architecture is more code efficient while achieving throughputs up to ten times faster
than conventional CISC microcontrollers.
The ATtiny87/167 provides the following features: 8K/16K byte of In-System Programmable
Flash, 512 bytes EEPROM, 512 bytes SRAM, 16 general purpose I/O lines, 32 general purpose working registers, one 8-bit Timer/Counter with compare modes, one 8-bit high speed
Timer/Counter, Universal Serial Interface, a LIN controller, Internal and External Interrupts, a
11-channel, 10-bit ADC, a programmable Watchdog Timer with internal Oscillator, and three
software selectable power saving modes. The Idle mode stops the CPU while allowing the
SRAM, Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. The Power-down mode saves the register contents, disabling all chip functions until the
next Interrupt or Hardware Reset. The ADC Noise Reduction mode stops the CPU and all I/O
modules except ADC, to minimize switching noise during ADC conversions.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip ISP Flash allows the Program memory to be re-programmed In-System through an
SPI serial interface, by a conventional non-volatile memory programmer or by an On-chip boot
code running on the AVR core. The Boot program can use any interface to download the application program in the Flash memory. By combining an 8-bit RISC CPU with In-System
Self-Programmable Flash on a monolithic chip, the Atmel ATtiny87/167 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control
applications.
The ATtiny87/167 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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ATtiny87/ATtiny167
1.3
Automotive Quality Grade
The ATtiny87/167 have been developed and manufactured according to the most stringent
requirements of the international standard ISO-TS-16949. This data sheet contains limit values extracted from the results of extensive characterization (temperature and voltage). The
quality and reliability of the ATtiny87/167 have been verified during regular product qualification as per AEC-Q100 grade 1.
As indicated in the ordering information paragraph, this document refers only to grade 1 products, for grade 0 products refer to appendix A.
Table 1-2.
1.4
Temperature Grade Identification for Automotive Products
Temperature
Temperature
Identifier
-40°C / +125°C
Z
Grade 1
-40°C / +150°C
D
Grade 0
Comments
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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7728D–AVR–07/09
Block Diagram
Block Diagram
GND
Figure 1-1.
VCC
1.5
Watchdog
Timer
Watchdog
Oscillator
Oscillator
Circuits /
Clock
Generation
Power
Supervision
POR / BOD &
RESET
debugWIRE
Flash
SRAM
PROGRAM
LOGIC
CPU
EEPROM
AVCC
AGND
Timer/Counter-0
A/D Conv.
Analog Comp.
Internal
Voltage
References
DATABUS
Timer/Counter-1
SPI & USI
2
11
PORT B (8)
PORT A (8)
LIN / UART
RESET
XTAL[1;2]
PB[0..7]
4
PA[0..7]
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Pin Configuration
Pinout ATtiny87/167 - SOIC20 & TSSOP20
(RXLIN / RXD / ADC0 / PCINT0) PA0
(TXLIN / TXD / ADC1 / PCINT1) PA1
(MISO / DO / OC0A / ADC2 / PCINT2) PA2
(INT1 / ISRC / ADC3 / PCINT3) PA3
AVCC
AGND
(MOSI / SDA / DI / ICP1 / ADC4 / PCINT4) PA4
(SCK / SCL / USCK / T1 / ADC5 / PCINT5) PA5
(SS / AIN0 / ADC6 / PCINT6) PA6
(AREF / XREF / AIN1 / ADC7 / PCINT7) PA7
Pinout ATtiny87/167 - QFN32
26
25
27
28
1
24
2
23
3
22
32-lead
4
5
21
20
top view
6
19
18
7
8
nc
nc
nc
GND
VCC
PB4 (PCINT12 / OC1AW / XTAL1 / CLKI)
PB5 (PCINT13 / ADC8 / OC1BW / XTAL2 / CLKO)
nc
16
15
14
13
11
(MOSI / SDA / DI / ICP1 / ADC4 / PCINT4) PA4
(SCK / SCL / USCK / T1 / ADC5 / PCINT5) PA5
(SS / AIN0 / ADC6 / PCINT6) PA6
(AREF / XREF / AIN1 / ADC7 / PCINT7) PA7
nc
(dW / RESET / OC1BX / ADC10 / PCINT15) PB7
(INT0 / OC1AX / ADC9 / PCINT14 ) PB6
nc
12
17
9
nc
nc
(INT1 / ISRC / ADC3 / PCINT3) PA3
AVCC
AGND
nc
nc
nc
29
32
INDEX CORNER
30
nc
PA2 (PCINT2 / ADC2 / OC0A / DO / MISO)
PA1 (PCINT1 / ADC1 / TXD / TXLIN)
PA0 (PCINT0 / ADC0 / RXD / RXLIN)
PB0 (PCINT8 / OC1AU / DI / SDA)
PB1 (PCINT9 / OC1BU / DO)
PB2 (PCINT10 / OC1AV / USCK / SCL)
PB3 (PCINT11 / OC1BV)
Figure 1-3.
PB0 (PCINT8 / OC1AU / DI / SDA)
PB1 (PCINT9 / OC1BU / DO)
PB2 (PCINT10 / OC1AV / USCK / SCL)
PB3 (PCINT11 / OC1BV)
GND
VCC
PB4 (PCINT12 / OC1AW / XTAL1 / CLKI)
PB5 (PCINT13 / ADC8 / OC1BW / XTAL2 / CLKO)
PB6 (PCINT14 / ADC9 / OC1AX / INT0)
PB7 (PCINT15 / ADC10 / OC1BX / RESET / dW)
1
20
2
19
18
3
4 20-pin 17
5
16
6
top 15
7 view 14
8
13
9
12
10
11
31
Figure 1-2.
10
1.6
Bottom pad should be
soldered to ground
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7728D–AVR–07/09
1.7
1.7.1
Pin Description
Vcc
Supply voltage.
1.7.2
GND
Ground.
1.7.3
AVcc
Analog supply voltage.
1.7.4
AGND
Analog ground.
1.7.5
Port A (PA7..PA0)
Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit).
The Port A output buffers have symmetrical drive characteristics with both high sink and
source capability. As inputs, Port A pins that are externally pulled low will source current if the
pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Port A also serves the functions of various special features of the ATtiny87/167 as listed on
Section 9.3.3 “Alternate Functions of Port A” on page 76.
1.7.6
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 ATtiny87/167 as listed on
Section 9.3.4 “Alternate Functions of Port B” on page 81.
1.8
Resources
A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
1.9
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.
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ATtiny87/ATtiny167
2. AVR CPU Core
2.1
Overview
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.
Figure 2-1.
Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Program
Counter
Status
and Control
Interrupt
Unit
32 x 8
General
Purpose
Registrers
Instruction
Register
Instruction
Decoder
Indirect Addressing
A.D.C.
Direct Addressing
Control Lines
Watchdog
Timer
ALU
Analog
Comparator
I/O Module1
Data
SRAM
I/O Module 2
I/O Module n
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the Program memory are
executed with a single level pipelining. While one instruction is being executed, the next
instruction is pre-fetched from the Program memory. This concept enables instructions to be
executed in every clock cycle. The Program memory is In-System Reprogrammable Flash
memory. The fast-access Register File contains 32 x 8-bit general purpose working registers
with a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU)
operation. In a typical ALU operation, two operands are output from the Register File, the
operation is executed, and the result is stored back in the Register File – in one clock cycle.
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7728D–AVR–07/09
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, SPI, and other I/O functions. The I/O memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F.
2.2
ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are
divided into three main categories – arithmetic, logical, and bit-functions. Some implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned
multiplication and fractional format. See the “Instruction Set” section for a detailed description.
2.3
Status Register
The Status Register contains information about the result of the most recently executed arithmetic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using
the dedicated compare instructions, resulting in faster and more compact code.
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.
8
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
2.3.1
SREG – AVR Status Register
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 I-bit can also be set and
cleared by the application with the SEI and CLI instructions, as described in the instruction set
reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit from a register in the Register File can be copied into T by
the BST instruction, and a bit in T can be copied into a bit in a register in the Register File by
the BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry is useful in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
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7728D–AVR–07/09
2.4
General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by
the Register File:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 2-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 2-2.
AVR CPU General Purpose Working Registers
7
0
Addr.
R0
0x00
R1
0x01
R2
0x02
…
R13
0x0D
General
R14
0x0E
Purpose
R15
0x0F
Working
R16
0x10
Registers
R17
0x11
…
R26
0x1A
X-register Low Byte
R27
0x1B
X-register High Byte
R28
0x1C
Y-register Low Byte
R29
0x1D
Y-register High Byte
R30
0x1E
Z-register Low Byte
R31
0x1F
Z-register High Byte
Most of the instructions operating on the Register File have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 2-2, each register is also assigned a Data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
2.4.1
10
The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These
registers are 16-bit address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described in Figure 2-3 on page 11.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 2-3.
The X-, Y-, and Z-registers
15
X-register
XH
XL
7
0
R27 (0x1B)
YH
YL
7
0
R29 (0x1D)
Z-register
0
R26 (0x1A)
15
Y-register
0
7
0
7
0
R28 (0x1C)
15
ZH
7
0
ZL
0
7
R31 (0x1F)
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).
2.5
Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always
points to the top of the Stack. Note that the Stack is implemented as growing from higher
memory locations to lower memory locations. This implies that a Stack PUSH command
decreases the Stack Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program
before any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be
set to point above 0x60. The Stack Pointer is decremented by one when data is pushed onto
the Stack with the PUSH instruction, and it is decremented by two when the return address is
pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is incremented by
one when data is popped from the Stack with the POP instruction, and it is incremented by two
when data is popped from the Stack with return from subroutine RET or return from interrupt
RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH
Register will not be present
2.5.1
SPH and SPL – Stack Pointer Register
Bit
Read/Write
Initial Value
15
14
13
12
11
10
9
8
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
ISRAM end (See Table 3-1 on page 15)
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7728D–AVR–07/09
2.6
Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for
the chip. No internal clock division is used.
Figure 2-4 shows the parallel instruction fetches and instruction executions enabled by the
Harvard architecture and the fast access Register File concept. This is the basic pipelining
concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions
per cost, functions per clocks, and functions per power-unit.
Figure 2-4.
The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 2-5 shows the internal timing concept for the Register File. In a single clock cycle an
ALU operation using two register operands is executed, and the result is stored back to the
destination register.
Figure 2-5.
Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
2.7
Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate Program Vector in the Program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt Enable bit in the Status Register in order to enable the interrupt.
The lowest addresses in the Program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in Section 7. “Interrupts” on page 59.
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.
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ATtiny87/ATtiny167
2.7.1
Interrupt behavior
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All
enabled interrupts can then interrupt the current interrupt routine. The I-bit is automatically set
when a Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt
Vector in order to execute the interrupt handling routine, and hardware clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit
position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt
enable bit is cleared, the Interrupt Flag will be set and remembered until the interrupt is
enabled, or the flag is cleared by software. Similarly, if one or more interrupt conditions occur
while the Global Interrupt Enable bit is cleared, the corresponding Interrupt Flag(s) will be set
and remembered until the Global Interrupt Enable bit is set, and will then be executed by order
of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before
the interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute
one more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine,
nor restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously
with the CLI instruction. The following example shows how this can be used to avoid interrupts
during the timed EEPROM write sequence.
Assembly Code Example
in
cli
r16, SREG
; store SREG value
; disable interrupts during timed sequence
sbi
EECR, EEMPE
sbi
EECR, EEPE
out
SREG, r16
; start EEPROM write
; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
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7728D–AVR–07/09
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in this example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep
; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI();
/* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
2.7.2
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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ATtiny87/ATtiny167
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ATtiny87/ATtiny167
3. AVR Memories
This section describes the different memories in the ATtiny87/167. The AVR architecture has
two main memory spaces, the Data memory and the Program memory space. In addition, the
ATtiny87/167 features an EEPROM Memory for data storage. All three memory spaces are
linear and regular.
Table 3-1.
Memory Mapping.
Memory
Flash
32 Registers
I/O
Registers
Ext I/O
Registers
Internal
SRAM
EEPROM
Notes:
Mnemonic
ATtiny87
ATtiny167
Size
Flash size
8 K bytes
16 K bytes
Start Address
-
0x0000
0x1FFF(1)
0x0FFF(2)
0x3FFF(1)
0x1FFF(2)
End Address
Flash end
Size
-
32 bytes
Start Address
-
0x0000
End Address
-
0x001F
Size
-
64 bytes
Start Address
-
0x0020
End Address
-
0x005F
Size
-
160 bytes
Start Address
-
0x0060
End Address
-
0x00FF
Size
ISRAM size
512 bytes
Start Address
ISRAM start
0x0100
End Address
ISRAM end
0x02FF
Size
E2 size
512 bytes
Start Address
-
0x0000
End Address
E2 end
0x01FF
1. Byte address.
2. Word (16-bit) address.
3.1
In-System Re-programmable Flash Program Memory
The ATtiny87/167 contains On-chip In-System Reprogrammable Flash memory for program
storage (see “Flash size” in Table 3-1 on page 15). Since all AVR instructions are 16 or 32 bits
wide, the Flash is organized as 16 bits wide. ATtiny87/167 does not have separate Boot
Loader and Application Program sections, and the SPM instruction can be executed from the
entire Flash. See SELFPRGEN description in Section 20.2.1 “Store Program Memory Control
and Status Register – SPMCSR” on page 219 for more details.
The Flash memory has an endurance of at least 10,000 write/erase cycles in automotive
range. The ATtiny87/167 Program Counter (PC) address the program memory locations. Section 21. “Memory Programming” on page 225 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).
15
7728D–AVR–07/09
Timing diagrams for instruction fetch and execution are presented in Section 2.6 “Instruction
Execution Timing” on page 12.
Figure 3-1.
Program Memory Map
Program Memory
0x0000
Flash end
3.2
SRAM Data Memory
Figure 3-2 shows how the ATtiny87/167 SRAM Memory is organized.
The ATtiny87/167 is a complex microcontroller with more peripheral units than can be supported within the 64 locations reserved in the Opcode for the IN and OUT instructions. For the
Extended I/O space in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be
used.
The 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, then 160 locations of Extended I/O memory, and the
next locations address the internal data SRAM (see “ISRAM size” in Table 3-1 on page 15).
The five different addressing modes for the Data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register
File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address
given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers and
the internal data SRAM in the ATtiny87/167 are all accessible through all these addressing
modes. The Register File is described in “General Purpose Register File” on page 10.
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ATtiny87/ATtiny167
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ATtiny87/ATtiny167
Figure 3-2.
Data Memory Map
Data Memory
32 Registers
64 I/O Registers
160 Ext I/O Reg.
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
ISRAM start
Internal SRAM
(ISRAM size)
ISRAM end
3.2.1
Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figure 3-3.
Figure 3-3.
On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Compute Address
Address valid
Write
Data
WR
Read
Data
RD
Memory Access Instruction
3.3
Next Instruction
EEPROM Data Memory
The ATtiny87/167 contains EEPROM memory (see “E2 size” in Table 3-1 on page 15). 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 in automotive range. 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.
Section 21. “Memory Programming” on page 225 contains a detailed description on EEPROM
programming in SPI or Parallel Programming mode.
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7728D–AVR–07/09
3.3.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access times for the EEPROM are given in Table 3-2. A self-timing function, however, lets the user software detect when the next byte can be written. If the user code contains
instructions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, Vcc is likely to rise or fall slowly on Power-up/down. This causes the device for some
period of time to run at a voltage lower than specified as minimum for the clock frequency
used. See “Preventing EEPROM Corruption” on page 20 for details on how to avoid problems
in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to “Atomic Byte Programming” on page 18 and “Split Byte Programming” on page 18 for
details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction
is executed. When the EEPROM is written, the CPU is halted for two clock cycles before the
next instruction is executed.
3.3.2
Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM,
the user must write the address into the EEARL Register and data into EEDR Register. If the
EEPMn bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the
erase/write operation. Both the erase and write cycle are done in one operation and the total
programming time is given in Table 1. The EEPE bit remains set until the erase and write
operations are completed. While the device is busy with programming, it is not possible to do
any other EEPROM operations.
3.3.3
Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if
the system requires short access time for some limited period of time (typically if the power
supply voltage falls). In order to take advantage of this method, it is required that the locations
to be written have been erased before the write operation. But since the erase and write operations are split, it is possible to do the erase operations when the system allows doing
time-critical operations (typically after Power-up).
3.3.4
Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the
EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (programming time is given in Table 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.
3.3.5
Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the
EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger
the write operation only (programming time is given in Table 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.
18
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator frequency is within the requirements described in “OSCCAL – Oscillator Calibration Register” on
page 37.
The following code examples show one assembly and one C function for erase, write, or
atomic write of the EEPROM. The examples assume that interrupts are controlled (e.g., by
disabling interrupts globally) so that no interrupts will occur during execution of these
functions.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic
EECR,EEPE
rjmp
EEPROM_write
; Set Programming mode
ldi
r16, (0<<EEPM1)|(0<<EEPM0)
out
EECR, r16
; Set up address (r18:r17) in address register
out
EEARH, r18
out
EEARL, r17
; Write data (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 char ucAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set Programming mode */
EECR = (0<<EEPM1)|(0<<EEPM0);
/* Set up address and data registers */
EEAR = ucAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
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7728D–AVR–07/09
The next code examples show assembly and C functions for reading the EEPROM. The
examples assume that interrupts are controlled so that no interrupts will occur during execution of these functions.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic
EECR,EEPE
rjmp
EEPROM_read
; Set up address (r18:r17) in address register
out
EEARH, r18
out
EEARL, r17
; Start eeprom read by writing EERE
sbi
EECR,EERE
; Read data from data register
in
r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned char ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
3.3.6
Preventing EEPROM Corruption
During periods of low Vcc, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low.
First, a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too
low.
EEPROM data corruption can easily be avoided by following this design recommendation:
20
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
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.
3.4
I/O Memory
The I/O space definition of the ATtiny87/167 is shown in Section 25. “Register Summary” on
page 268.
All ATtiny87/167 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. The ATtiny87/167 is a
complex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from
0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
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.
3.4.1
General Purpose I/O Registers
The ATtiny87/167 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.
The General Purpose I/O Registers within the address range 0x00 - 0x1F are directly
bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
3.5
3.5.1
Register Description
EEARH and EEARL – EEPROM Address Register
Bit
Bit
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
EEAR8
EEARH
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
EEARL
7
6
5
4
3
2
1
0
Read/Write
R
R
R
R
R
R
R
R/W
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
X
Initial Value
X
X
X
X
X
X
X
X
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7728D–AVR–07/09
• Bit 7:1 – Reserved Bits
These bits are reserved for future use and will always read as 0 in ATtiny87/167.
• Bits 8:0 – EEAR8:0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL – specifies the high EEPROM
address in the EEPROM space (see “E2 size” in Table 3-1 on page 15). The EEPROM data
bytes are addressed linearly between 0 and “E2 size”. The initial value of EEAR is undefined.
A proper value must be written before the EEPROM may be accessed.
Note:
3.5.2
For information only - ATtiny47: EEAR8 exists as register bit but it is not used for addressing.
EEDR – EEPROM Data Register
Bit
7
6
5
4
3
2
1
0
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
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.
3.5.3
EECR – EEPROM Control Register
Bit
7
6
5
4
3
2
1
0
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
X
X
0
0
X
0
EECR
• Bit 7,6 – Res: Reserved Bits
These bits are reserved for future use and will always read as 0 in ATtiny87/167. After reading,
mask out these bits. For compatibility with future AVR devices, always write these bits to 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 3-2. 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 3-2.
22
EEPROM Mode Bits
Typical
Programming Time Operation
EEPM1
EEPM0
0
0
3.4 ms
Erase and Write in one operation (Atomic Operation)
0
1
1.8 ms
Erase Only
1
0
1.8 ms
Write Only
1
1
–
Reserved for future use
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a constant
interrupt when Non-volatile memory is ready for programming.
• Bit 2 – EEMPE: EEPROM Master Program Enable
The EEMPE bit determines whether writing EEPE to one will have effect or not.
When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the
selected address. If EEMPE is zero, setting EEPE will have no effect. When EEMPE has been
written to one by software, hardware clears the bit to zero after four clock cycles.
• Bit 1 – EEPE: EEPROM Program Enable
The EEPROM Program Enable Signal EEPE is the programming enable signal to the
EEPROM. When EEPE is written, the EEPROM will be programmed according to the EEPMn
bits setting. The EEMPE bit must be written to one before a logical one is written to EEPE, otherwise no EEPROM write takes place. When the write access time has elapsed, the EEPE bit
is cleared by hardware. When EEPE has been set, the CPU is halted for two cycles before the
next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the
correct address is set up in the EEAR Register, the EERE bit must be written to one to trigger
the EEPROM read. The EEPROM read access takes one instruction, and the requested data
is available immediately. When the EEPROM is read, the CPU is halted for four cycles before
the next instruction is executed. The user should poll the EEPE bit before starting the read
operation. If a write operation is in progress, it is neither possible to read the EEPROM, nor to
change the EEAR Register.
3.5.4
General Purpose I/O Register 2 – GPIOR2
Bit
3.5.5
7
6
5
4
3
2
1
0
GPIOR27
GPIOR26
GPIOR25
GPIOR24
GPIOR23
GPIOR22
GPIOR21
GPIOR20
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
General Purpose I/O Register 1 – GPIOR1
Bit
3.5.6
GPIOR2
7
6
5
4
3
2
1
0
GPIOR17
GPIOR16
GPIOR15
GPIOR14
GPIOR13
GPIOR12
GPIOR11
GPIOR10
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
GPIOR1
General Purpose I/O Register 0 – GPIOR0
Bit
7
6
5
4
3
2
1
0
GPIOR07
GPIOR06
GPIOR05
GPIOR04
GPIOR03
GPIOR02
GPIOR01
GPIOR00
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GPIOR0
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7728D–AVR–07/09
4. System Clock and Clock Options
The ATtiny87/167 provides a large number of clock sources. They can be divided into two categories: internal and external. Some external clock sources can be shared with the
asynchronous timer. After reset, the clock source is determined by the CKSEL Fuses. Once
the device is running, software clock switching is possible to any other clock sources.
Hardware controls are provided for clock switching management but some specific procedures must be observed. Clock switching should be performed with caution as some settings
could result in the device having an incorrect configuration.
4.1
Clock Systems and their Distribution
Figure 4-1 presents the principal clock systems in the AVR and their distribution. All of the
clocks may not need to be active at any given time. In order to reduce power consumption, the
clocks to modules not being used can be halted by using different sleep modes or by using
features of the dynamic clock switch circuit (See “Power Management and Sleep Modes” on
page 42 and “Dynamic Clock Switch” on page 31). The clock systems are detailed below.
Figure 4-1.
Clock Distribution
Asynchronous
Timer/Counter0
General I/O
Modules
ADC
CPU Core
RAM
Flash and
EEPROM
clkADC
clkI/O
clkCPU
AVR Clock
Control Unit
clkASY
clkFLASH
Reset Logic
Source Clock
Watchdog Timer
Watchdog Clock
Prescaler
Clock Switch
Multiplexer
Watchdog
Oscillator
CKOUT
Fuse
External Clock
Low-frequency
Crystal Oscillator
PB4 / XTAL1 / CLKI
24
Calibrated RC
Oscillator
Crystal
Oscillator
PB5 / XTAL2 / CLKO
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
4.1.1
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with the AVR core operation. 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.
4.1.2
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like synchronous Timer/Counter. The
I/O clock is also used by the External Interrupt module, but note that some external interrupts
are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O
clock is halted.
4.1.3
Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually active
simultaneously with the CPU clock.
4.1.4
Asynchronous Timer Clock – clkASY
The asynchronous timer clock allows the asynchronous Timer/Counter to be clocked directly
from an external clock or an external low frequency crystal. The dedicated clock domain
allows using this Timer/Counter as a real-time counter even when the device is in sleep mode.
4.1.5
ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O
clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC
conversion results.
4.2
Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits (default) or
by the CLKSELR register (dynamic clock switch circuit) as shown below. The clock from the
selected source is input to the AVR clock generator, and routed to the appropriate modules.
Table 4-1.
Device Clocking Options Select(1) vs. PB4 and PB5 Functionality
CKSEL3..0 (2)
CSEL3..0 (3)
PB4
PB5
External Clock
0000 b
CLKI
CLKO - I/O
Calibrated Internal RC Oscillator 8.0 MHz
0010 b
I/O
CLKO - I/O
Watchdog Oscillator 128 kHz
0011 b
I/O
CLKO - I/O
External Low-frequency Oscillator
01xx b
XTAL1
XTAL2
External Crystal/Ceramic Resonator (0.4 - 0.9 MHz)
100x b
XTAL1
XTAL2
External Crystal/Ceramic Resonator (0.9 - 3.0 MHz)
101x b
XTAL1
XTAL2
External Crystal/Ceramic Resonator (3.0 - 8.0 MHz)
110x b
XTAL1
XTAL2
External Crystal/Ceramic Resonator (8.0 - 16.0
MHz)
111x b
XTAL1
XTAL2
Device Clocking Option
Notes:
1. For all fuses “1” means unprogrammed while “0” means programmed.
2. Flash Fuse bits.
3. CLKSELR register bits.
25
7728D–AVR–07/09
The various choices for each clocking option are given in the following sections.
When the CPU wakes up from Power-down or Power-save, or when a new clock source is
enabled by the dynamic clock switch circuit, 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 sequence. The number of WDT Oscillator cycles used for each
time-out is shown in Table 4-2.
Table 4-2.
4.2.1
Number of Watchdog Oscillator Cycles
Typ. Time-out (Vcc = 5.0V)
Typ. Time-out (Vcc = 5.0V)
Number of Cycles
4.1 ms
4.3 ms
512
65 ms
69 ms
8K (8,192)
Default Clock Source
At reset, the CKSEL and SUT fuse settings are copied into the CLKSELR register. The device
will then use the clock source and the start-up timings defined by the CLKSELR bits
(CSEL3..0 and CSUT1:0).
The device is shipped with CKSEL Fuses = 0010 b, SUT Fuses = 10 b, and CKDIV8 Fuse programmed. The default clock source setting is therefore the Internal RC Oscillator running at 8
MHz with the longest start-up time and an initial system clock divided by 8. This default setting
ensures that all users can make their desired clock source setting using an In-System or
High-voltage Programmer. This set-up must be taken into account when using ISP tools.
4.2.2
Calibrated Internal RC Oscillator
By default, the Internal RC Oscillator provides an approximate 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be accurately calibrated by the user. See Table
22-1 on page 245 and Section 24.7 “Internal Oscillator Speed” on page 265 for more details.
If selected, it can operate without external components. At reset, hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby automatically configuring
the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in Table
22-1 on page 245.
By adjusting the OSCCAL register in software, see “OSCCAL – Oscillator Calibration Register” on page 37, it is possible to get a higher calibration accuracy than by using the factory
calibration. The accuracy of this calibration is shown as User calibration in Table 22-1 on page
245.
The Watchdog Oscillator will still be used for the Watchdog Timer and for the Reset Time-out
even when this Oscillator is used as the device clock. For more information on the pre-programmed calibration value, see the section “Calibration Byte” on page 228.
26
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Table 4-3.
Notes:
Internal Calibrated RC Oscillator Operating Modes(1)
Frequency Range(2) (MHz)
CKSEL3..0(3)(4)
CSEL3..0(5)
7.6 - 8.4
0010
1. If 8 MHz frequency exceeds the specification of the device (depends on Vcc), the CKDIV8
fuse can be programmed in order to divide the internal frequency by 8.
2. The frequency ranges are guideline values.
3. The device is shipped with this CKSEL = “0010”.
4. Flash Fuse bits.
5. CLKSELR register bits.
When this Oscillator is selected, start-up times are determined by the SUT Fuses or by CSUT
field as shown in Table 4-4.
Table 4-4.
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0(1)
CSUT1..0(2)
Start-up Time from
Power-down/save
Additional Delay from
Reset (Vcc = 5.0V)
00(3)
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
6 CK
14CK + 65 ms
Slowly rising power
(4)
10
11
Notes:
Recommended Usage
BOD enabled
Reserved
1. Flash Fuse bits
2. CLKSELR register bits
3. This setting is only available if RSTDISBL fuse is not set
4. The device is shipped with this option selected.
4.2.3
128 KHz Internal Oscillator
The 128 KHz internal Oscillator is a low power Oscillator providing a clock of 128 KHz. The
frequency is nominal at 3V and 25°C. This clock may be selected as the system clock by programming CKSEL Fuses or CSEL field as shown in Table 4-1 on page 25.
When this clock source is selected, start-up times are determined by the SUT Fuses or by
CSUT field as shown in Table 4-5.
Table 4-5.
Start-up Times for the 128 kHz Internal Oscillator
SUT1..0(1)
CSUT1..0(2)
Start-up Time from
Power-down/save
Additional Delay
from Reset (Vcc = 5.0V)
00(3)
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
10
6 CK
14CK + 65 ms
Slowly rising power
11
Notes:
Recommended Usage
BOD enabled
Reserved
1. Flash Fuse bits
2. CLKSELR register bits
3. This setting is only available if RSTDISBL fuse is not set
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4.2.4
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be
configured for use as an On-chip Oscillator, as shown in Figure 4-2. 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 4-6. For ceramic resonators, the capacitor values given
by the manufacturer should be used.
Figure 4-2.
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 CKSEL3..1 fuses or by CSEL3..1 field as shown in
Table 4-6.
Table 4-6.
Crystal Oscillator Operating Modes
(1)
CKSEL3..1
CSEL3..1(2)
Frequency Range (MHz)
Recommended Range for Capacitors
C1 and C2 for Use with Crystals (pF)
100(3)
0.4 - 0.9
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 - 16.0
12 - 22
Notes:
1. Flash Fuse bits.
2. CLKSELR register bits.
3. This option should not be used with crystals, only with ceramic resonators.
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The CKSEL0 Fuse together with the SUT1..0 Fuses or CSEL0 together with CSUT1..0 field
select the start-up times as shown in Table 4-7.
Table 4-7.
Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0(1)
CSEL0(2)
SUT1..0(1)
CSUT1..0(2)
Start-up Time from
Power-down/save
Additional Delay
from Reset
(Vcc = 5.0V)
0
00
258 CK(3)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
258 CK(3)
14CK + 65 ms
Ceramic resonator, slowly
rising power
0
10(5)
1K (1024) CK(4)
14CK
Ceramic resonator, BOD
enabled
0
11
1K (1024)CK(4)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K (1024)CK(4)
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01(5)
16K (16384) CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K (16384) CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K (16384) CK
14CK + 65 ms
Crystal Oscillator, slowly
rising power
Notes:
Recommended Usage
1. Flash Fuse bits.
2. CLKSELR register bits.
3. 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.
4. 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.
5. This setting is only available if RSTDISBL fuse is not set.
4.2.5
Low-frequency Crystal Oscillator
To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by setting CKSEL fuses or CSEL field as shown in Table 4-1 on
page 25. The crystal should be connected as shown in Figure 4-3. Refer to the 32.768 kHz
Crystal Oscillator Application Note for details on oscillator operation and how to choose appropriate values for C1 and C2.
The 32.768 kHz watch crystal oscillator can be used by the asynchronous timer if the
(high-frequency) Crystal Oscillator is not running or if the External Clock is not enabed (See
”Enable/Disable Clock Source” on page 32.). The asynchronous timer is then able to start
itself this low-frequency crystal oscillator.
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Figure 4-3.
Low-frequency Crystal Oscillator Connections
C1=12-22 pF
XTAL2
32.768 KHz
XTAL1
C2=12-22 pF
GND
12-22 pF capacitors may be necessary if parasitic
impedance (pads, wires & PCB) is very low.
When this oscillator is selected, start-up times are determined by the SUT fuses or by CSUT
field as shown in Table 4-8.
Table 4-8.
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
(1)
SUT1..0
CSUT1..0(2)
Start-up Time from
Power-down/save
Additional Delay from
Reset (Vcc = 5.0V)
00
1K (1024) CK(3)
4.1 ms
Fast rising power or BOD enabled
01
1K (1024) CK(3)
65 ms
Slowly rising power
10
32K (32768) CK
65 ms
Stable frequency at start-up
11
Notes:
Recommended usage
Reserved
1. Flash Fuse bits.
2. CLKSELR register bits.
3. These options should only be used if frequency stability at start-up is not important for the
application.
4.2.6
External Clock
To drive the device from this external clock source, CLKI should be driven as shown in Figure
4-4. To run the device on an external clock, the CKSEL Fuses or CSEL field must be programmed as shown in Table 4-1 on page 25.
Figure 4-4.
External Clock Drive Configuration
~
External
Clock
Signal
(XTAL2)
(CLKO)
CLKI
(XTAL1)
GND
When this clock source is selected, start-up times are determined by the SUT Fuses or CSUT
field as shown in Table 4-9.
This external clock can be used by the asynchronous timer if the high or low frequency Crystal
Oscillator is not running (See ”Enable/Disable Clock Source” on page 32.). The asynchronous
timer is then able to enable this input.
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Table 4-9.
Start-up Times for the External Clock Selection
(1)
SUT1..0
CSUT1..0(2)
Start-up Time from
Power-down/save
Additional Delay from Reset
(Vcc = 5.0V)
00
6 CK
14CK (+ 4.1 ms(3))
01
6 CK
14CK + 4.1 ms
Fast rising power
10
6 CK
14CK + 65 ms
Slowly rising power
11
Notes:
Recommended Usage
BOD enabled
Reserved
1. Flash Fuse bits.
2. CLKSELR register bits.
3. Additional delay (+ 4ms) available if RSTDISBL fuse is set.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on
page 37 for details.
4.2.7
4.3
4.3.1
Clock Output Buffer
If not using a crystal oscillator, the device can output the system clock on the CLKO pin. To
enable the output, the CKOUT Fuse or COUT bit of CLKSELR register has to be programmed.
This option is useful when the device clock is needed to drive other circuits on the system.
Note that the clock will not be output during reset and the normal operation of I/O pin will be
overridden when the fuses are programmed. If the System Clock Prescaler is used, it is the
divided system clock that is output.
Dynamic Clock Switch
Features
The ATtiny87/167 provides a powerful dynamic clock switch circuit that allows users to turn on
and off clocks of the device on the fly. The built-in de-glitching circuitry allows clocks to be
enabled or disabled asynchronously. This enables efficient power management schemes to
be implemented easily and quickly. In a safety application, the dynamic clock switch circuit
allows continuous monitoring of the external clock permitting a fallback scheme in case of
clock failure.
The control of the dynamic clock switch circuit must be supervised by software. This operation
is facilitated by the following features:
• Safe commands, to avoid unintentional commands, a special write procedure must be
followed to change the CLKCSR register bits (See “CLKPR – Clock Prescaler Register” on
page 38.):
• Exclusive action, the actions are controlled by a decoding table (commands) written to the
CLKCSR register. This ensures that only one command operation can be launched at any
time. The main actions of the decoding table are:
– ‘Disable Clock Source’,
– ‘Enable Clock Source’,
– ‘Request Clock Availability’,
– ‘Clock Source Switching’,
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7728D–AVR–07/09
– ‘Recover System Clock Source’,
– ‘Enable Watchdog in Automatic Reload Mode’.
• Command status return. The ‘Request Clock Availability ’ command returns status via the
CLKRDY bit in the CLKCSR register. The ‘Recover System Clock Source ’ command
returns a code of the current clock source in the CLKSELR register. This information is
used in the supervisory software routines as shown in Section 4.3.7 on page 33.
4.3.2
CLKSELR Register
4.3.2.1
Fuses Substitution
At reset, bits of the Low Fuse Byte are copied into the CLKSELR register. The content of this
register can subsequently be user modified to overwrite the default values from the Low Fuse
Byte. CKSEL3..0, SUT1..0 and CKOUT fuses correspond respectively to CSEL3..0, CSUT1:0
and ~(COUT) bits of the CLKSELR register as shown in Figure 4-5 on page 32.
4.3.2.2
Source Selection
The available codes of clock source are given in Table 4-1 on page 25.
Fuses substitution and Clock Source Selection
CLKSELR
SEL-0
CKSEL[3..0]
CSEL[3..0]
CSUT[1..0]
COUT
Default
CLKSEL[3..0]
SUT[1..0]
CKOUT
Reset
R/W Reg.
Register:
Fuse Low Byte
Internal
Data Bus
Fuse:
( )
SCLKRq *
SEL
Decoder
Figure 4-5.
SEL-1
SEL-2
SEL-n
Selected
Configuration
SUT[1..0]
CKOUT
( )
SCLKRq * : Command of Clock Control & Status Register
SEL
Encoder
EN-0
EN-1
EN-2
Clock
Switch
Current
Configuration
EN-n
The CLKSELR register contains the CSEL, CSUT and COUT values which will be used by the
‘Enable/Disable Clock Source’, ‘Request for Clock Availability’ or ‘Clock Source Switching’
commands.
4.3.2.3
4.3.3
32
Source Recovering
The ‘Recover System Clock Source’ command updates the CKSEL field of CLKSELR register
(See “System Clock Source Recovering” on page 33.).
Enable/Disable Clock Source
The ‘Enable Clock Source’ command selects and enables a clock source configured by the
settings in the CLKSELR register. CSEL3..0 will select the clock source and CSUT1:0 will
select the start-up time (just as CKSEL and SUT fuse bits do). To be sure that a clock source
is operating, the ‘Request for Clock Availability ’ command must be executed after the ‘Enable
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
Clock Source’ command. This will indicate via the CLKRDY bit in the CLKCSR register that a
valid clock source is available and operational.
The ‘Disable Clock Source’ command disables the clock source indicated by the settings of
CLKSELR register (only CSEL3..0). If the clock source indicated is currently the one that is
used to drive the system clock, the command is not executed.
Because the selected configuration is latched at clock source level, it is possible to enable
many clock sources at a given time (ex: the internal RC oscillator for system clock + an oscillator with external crystal). The user (code) is responsible of this management.
4.3.4
COUT Command
The ‘CKOUT ’ command allows to drive the CLKO pin. Refer to Section 4.2.7 “Clock Output
Buffer” on page 31 for using.
4.3.5
Clock Availability
‘Request for Clock Availability’ command enables a hardware oscillation cycle counter driven
by the selected source clock, CSEL3..0. The count limit value is determined by the settings of
CSUT1..0. The clock is declared ready (CLKRDY = 1) when the count limit value is reached.
The CLKRDY flag is reset when the count starts. Once set, this flag remains unchanged until a
new count is commanded. To perform this checking, the CKSEL and CSUT fields should not
be changed while the operation is running.
Note that once the new clock source is selected (‘Enable Clock Source’ command), the count
procedure is automatically started. The user (code) should wait for the setting of the CLKRDY
flag in CLKSCR register before using a newly selected clock.
At any time, the user (code) can ask for the availability of a clock source. The user (code) can
request it by writing the ‘Request for Clock Availability ’ command in the CLKSCR register. A
full polling of the status of clock sources can thus be done.
4.3.6
System Clock Source Recovering
The ‘Recover System Clock Source’ command returns the current clock source used to drive
the system clock as per Table 4-1 on page 25. The CKSEL field of CLKSELR register is then
updated with this returned value. There is no information on the SUT used or status on
CKOUT.
4.3.7
Clock Switching
To drive the system clock, the user can switch from the current clock source to any other of the
following ones (one of them being the current clock source):
1. Calibrated internal RC oscillator 8.0 MHz,
2. Internal watchdog oscillator 128 kHz,
3. External clock,
4. External low-frequency oscillator,
5. External Crystal/Ceramic Resonator.
The clock switching is performed by a sequence of commands. First, the user (code) must
make sure that the new clock source is operating. Then the ‘Clock Source Switching’ command can be issued. Once this command has been successfully completed using the
‘Recover System Clock Source’ command, the user (code) may stop the previous clock
source.
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It is strongly recommended to run this sequence only once the interrupts have been disabled.
The user (code) is responsible for the correct implementation of the clock switching sequence.
Here is a “light” C-code that describes such a sequence of commands.
C Code Example
void ClockSwiching (unsigned char clk_number, unsigned char sut) {
#define
#define
#define
#define
CLOCK_RECOVER
CLOCK_ENABLE
CLOCK_SWITCH
CLOCK_DISABLE
0x05
0x02
0x04
0x01
unsigned char previous_clk, temp;
// Disable interrupts
temp = SREG; asm ("cli");
// Save the current system clock source
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_RECOVER;
previous_clk = CLKSELR & 0x0F;
// Enable the new clock source
CLKSELR = ((sut << 4 ) & 0x30) | (clk_number & 0x0F);
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_ENABLE;
// Wait for clock validity
while ((CLKCSR & (1 << CLKRDY)) == 0);
// Switch clock source
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_SWITCH;
// Wait for effective switching
while (1){
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_RECOVER;
if ((CLKSELR & 0x0F) == (clk_number & 0x0F)) break;
}
// Shut down unneeded clock source
if (previous_clk != (clk_number & 0x0F)) {
CLKSELR = previous_clk;
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_DISABLE;
}
// Re-enable interrupts
SREG = temp;
}
Warning:
In the ATtiny87/167, only one among the three external clock sources can be enabled at a
given time. Moreover, the enables of the external clock and of the external low-frequency
oscillator are shared with the asynchronous timer.
4.3.8
34
Clock Monitoring
A safe system needs to monitor its clock sources. Two domains need to be monitored:
- Clock sources for peripherals,
- Clocks sources for system clock generation.
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
In the first domain, the user (code) can easily check the validity of the clock(s) (See “COUT
Command” on page 33.).
In the second domain, the lack of a clock results in the code not running. Thus, the presence
of the system clock needs to be monitored by hardware.
Using the on-chip watchdog allows this monitoring. Normally, the watchdog reloading is performed only if the code reaches some specific software labels, reaching these labels proves
that the system clock is running. Otherwise the watchdog reset is enabled. This behavior can
be considered as a clock monitoring.
If the standard watchdog functionality is not desired, the ATtiny87/167 watchdog permits the
system clock to be monitored without having to resort to the complexity of a full software
watchdog handler. The solution proposed in the ATtiny87/167 is to automate the watchdog
reloading with only one command, at the beginning of the session.
So, to monitor the system clock, the user will have two options:
1. Using the standard watchdog features (software reload),
2. Or using the automatic reloading (hardware reload).
The two options are exclusive.
Note:
Warning:
These two options make sense ONLY if the clock source at RESET is an INTERNAL SOURCE.
The fuse settings determine this operation.
Figure 4-6.
Watchdog Timer with Automatic Reloading.
WD
Interrupt
WatchDog Clock
WatchDog
WD
Reset
Reload
WDIE
WDE
WDTCSR
WDIF
Register:
WDP[3..0]
0
Automatic
Reloading
Mode
1
Enable
Checker
System CLK
Internal Bus
The ‘Enable Watchdog in Automatic Reload Mode’ command has priority over the standard
watchdog enabling. In this mode, only the reset function of the watchdog is enabled (no more
watchdog interrupt). The WDP3..0 bits of the WDTCSR register always determine the watchdog timer prescaling.
As the watchdog will not be active before executing the ‘Enable Watchdog in Automatic
Reload Mode’ command, it is recommended to activate this command before switching to an
external clock source (See note on page 35).
Notes:
1. ONLY the reset (watchdog reset included) disables this function. The Watchdog System
Reset Flag (WDRF bit of MCUSR register) can be used to monitor the reset cause.
2. ONLY clock frequencies greater than or equal to (4 * WatchDog Clock Frequency) can be
monitored.
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Here is a “light” C-code of a clock switching function using automatic clock monitoring.
C Code Example
void ClockSwiching (unsigned char clk_number, unsigned char sut) {
CLOCK_RECOVER
CLOCK_ENABLE
CLOCK_SWITCH
CLOCK_DISABLE
WD_ARL_ENABLE
0x05
0x02
0x04
0x01
0x06
#define WD_2048CYCLES
0x07
#define
#define
#define
#define
#define
unsigned char previous_clk, temp;
// Disable interrupts
temp = SREG; asm ("cli");
// Save the current system clock source
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_RECOVER;
previous_clk = CLKSELR & 0x0F;
// Enable the new clock source
CLKSELR = ((sut << 4 ) & 0x30) | (clk_number & 0x0F);
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_ENABLE;
// Wait for clock validity
while ((CLKCSR & (1 << CLKRDY)) == 0);
// Enable the watchdog in automatic reload mode
WDTCSR = (1 << WDCE) | (1 << WDE);
WDTCSR = (1 << WDE ) | WD_2048CYCLES;
CLKCSR = 1 << CLKCCE;
CLKCSR = WD_ARL_ENABLE;
// Switch clock source
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_SWITCH;
// Wait for effective switching
while (1){
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_RECOVER;
if ((CLKSELR & 0x0F) == (clk_number & 0x0F)) break;
}
// Shut down unneeded clock source
if (previous_clk != (clk_number & 0x0F)) {
CLKSELR = previous_clk;
CLKCSR = 1 << CLKCCE;
CLKCSR = CLOCK_DISABLE;
}
// Re-enable interrupts
SREG = temp;
}
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ATtiny87/ATtiny167
4.4
4.4.1
System Clock Prescaler
Features
The ATtiny87/167 system clock can be divided by setting the Clock Prescaler Register –
CLKPR. This feature can be used to decrease power consumption when the requirement for
processing power is low. This can be used with all clock source options, and it will affect the
clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH
are divided by a factor as shown in Table 4-10 on page 39.
4.4.2
Switching Time
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither
the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before
the new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1
is the previous clock period, and T2 is the period corresponding to the new prescaler setting.
4.5
4.5.1
Register Description
OSCCAL – Oscillator Calibration Register
Bit
Read/Write
Initial Value
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
OSCCAL
Device Specific Calibration Value
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator frequency of 8.0 MHz at
25°C. The application software can write this register to change the oscillator frequency. The
oscillator can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ± 2% accuracy.
Calibration outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to
more than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in
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7728D–AVR–07/09
the range. Incrementing CAL6..0 by 1 will give a frequency increment of less than 2% in the
frequency range 7.3 - 8.1 MHz.
4.5.2
CLKPR – Clock Prescaler Register
Bit
7
6
5
4
3
2
1
0
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
CLKPR
See Bit Description
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the other bits in CLKPR are simultaneously written to zero.
CLKPCE is cleared by hardware four cycles after it is written or when the CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out
period, nor clear the CLKPCE bit.
• Bits 6:4 – Res: Reserved Bits
These bits are reserved bits in the ATtiny87/167 and will always read as zero.
• Bits 3:0 – CLKPS3:0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As the divider divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given
in Table 4-10.
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 in order not to disturb the
procedure.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to
“0011”, giving a division factor of eight at start up. This feature should be used if the selected
clock source has a higher frequency than the maximum frequency of the device at the present
operating conditions. Note that any value can be written to the CLKPS bits regardless of the
CKDIV8 Fuse setting. The Application software must ensure that a sufficient division factor is
chosen if the selected clock source has a higher frequency than the maximum frequency of
the device at the present operating conditions. The device is shipped with the CKDIV8 Fuse
programmed.
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Table 4-10.
4.5.3
Clock Prescaler Select
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Clock Division Factor
0
0
0
0
1
0
0
0
1
2
0
0
1
0
4
0
0
1
1
8
0
1
0
0
16
0
1
0
1
32
0
1
1
0
64
0
1
1
1
128
1
0
0
0
256
1
0
0
1
Reserved
1
0
1
0
Reserved
1
0
1
1
Reserved
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
CLKCSR – Clock Control & Status Register
Bit
7
6
5
4
3
2
1
0
CLKCCE
–
–
CLKRDY
CLKC3
CLKC2
CLKC1
CLKC0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
CLKCSR
• Bit 7 – CLKCCE: Clock Control Change Enable
The CLKCCE bit must be written to logic one to enable change of the CLKCSR bits. The
CLKCCE bit is only updated when the other bits in CLKCSR are simultaneously written to
zero. CLKCCE is cleared by hardware four cycles after it is written or when the CLKCSR bits
are written. Rewriting the CLKCCE bit within this time-out period does neither extend the
time-out period, nor clear the CLKCCE bit.
• Bits 6:5 – Res: Reserved Bits
These bits are reserved bits in the ATtiny87/167 and will always read as zero.
• Bits 4 – CLKRDY: Clock Ready Flag
This flag is the output of the ‘Clock Availability ’ logic.
This flag is cleared by the ‘Request for Clock Availability’ command or ‘Enable Clock Source’
command being entered.
It is set when ‘Clock Availability’ logic confirms that the (selected) clock is running and is stable. The delay from the request and the flag setting is not fixed, it depends on the clock
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start-up time, the clock frequency and, of course, if the clock is alive. The user’s code has to
differentiate between ‘no_clock_signal’ and ‘clock_signal_not_yet_available’ condition.
• Bits 3:0 – CLKC3:0: Clock Control Bits 3 - 0
These bits define the command to provide to the ‘Clock Switch’ module. The special write procedure must be followed to change the CLKC3..0 bits (See ”Bit 7 – CLKCCE: Clock Control
Change Enable” on page 39.).
1. Write the Clock Control Change Enable (CLKCCE) bit to one and all other bits in
CLKCSR to zero.
2. Within 4 cycles, write the desired value to CLKCSR register while clearing CLKCCE
bit.
Interrupts should be disabled when setting CLKCSR register in order not to disturb the
procedure.
Table 4-11.
Clock command list.
Clock Command
4.5.4
CLKC3..0
No command
0000 b
Disable clock source
0001 b
Enable clock source
0010 b
Request for clock availability
0011 b
Clock source switch
0100 b
Recover system clock source code
0101 b
Enable watchdog in automatic reload mode
0110 b
CKOUT command
0111 b
No command
1xxx b
CLKSELR - Clock Selection Register
Bit
7
6
5
4
3
2
1
0
-
COUT
CSUT1
CSUT0
CSEL3
CSEL2
CSEL1
CSEL0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
~ (CKOUT)
fuse
SUT1..0
fuses
CLKSELR
CKSEL3..0
fuses
• Bit 7– Res: Reserved Bit
This bit is reserved bit in the ATtiny87/167 and will always read as zero.
• Bit 6 – COUT: Clock Out
The COUT bit is initialized with ~(CKOUT) Fuse bit.
The COUT bit is only used in case of ‘CKOUT’ command. Refer to Section 4.2.7 “Clock Output
Buffer” on page 31 for using.
In case of ‘Recover System Clock Source’ command, COUT it is not affected (no recovering of
this setting).
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• Bits 5:4 – CSUT1:0: Clock Start-up Time
CSUT bits are initialized with the values of SUT Fuse bits.
In case of ‘Enable/Disable Clock Source’ command, CSUT field provides the code of the clock
start-up time. Refer to subdivisions of Section 4.2 “Clock Sources” on page 25 for code of
clock start-up times.
In case of ‘Recover System Clock Source’ command, CSUT field is not affected (no recovering of SUT code).
• Bits 3:0 – CSEL3:0: Clock Source Select
CSEL bits are initialized with the values of CKSEL Fuse bits.
In case of ‘Enable/Disable Clock Source’, ‘Request for Clock Availability’ or ‘Clock Source
Switch’ command, CSEL field provides the code of the clock source. Refer to Table 4-1 on
page 25 and subdivisions of Section 4.2 “Clock Sources” on page 25 for clock source codes.
In case of ‘Recover System Clock Source’ command, CSEL field contains the code of the
clock source used to drive the Clock Control Unit as described in Figure 4-1 on page 24.
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5. 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.
When enabled, the Brown-out Detector (BOD) actively monitors the power supply voltage during the sleep periods. To further save power, it is possible to disable the BOD in some sleep
modes. See “BOD Disable” on page 43 for more details.
5.1
Sleep Modes
Figure 4-1 on page 24 presents the different clock systems in the ATtiny87/167, and their distribution. The figure is helpful in selecting an appropriate sleep mode. Table 5-1 shows the
different sleep modes, their wake up sources and BOD disable ability.
Active Clock Domains and Wake-up Sources in the Different Sleep Modes
clkASY
Main Clock
Source Enabled
Timer0 Osc.
Enable
INT1, INT0 and
Pin Change
SPM/EEPROM
Ready
ADC
WDT
USI Start Condition
Timer0
Other I/O
Wake-up Sources
clkADC
ADC Noise
Reduction
Oscillators
clkIO
Idle
clkFLASH
Sleep Mode
clkCPU
Active Clock Domains
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X(1)
X
X
X
X
X
Power-down
X(1)
X
X
Power-Save
(1)
X
X
Note:
X
X
X
Software
BOD Disable
Table 5-1.
X
X
X
1. For INT1 and INT0, only level interrupt.
To enter any of the four 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 SMCR Register select
which sleep mode (Idle, ADC Noise Reduction, Power-down, or Power-save) will be activated
by the SLEEP instruction. See Table 5-2 on page 47 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.
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5.2
BOD Disable
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses, Table 21-3 on page
226, the BOD is actively monitoring the power supply voltage during a sleep period. To save
power, it is possible to disable the BOD by software for some of the sleep modes, see Table
5-1. The sleep mode power consumption will then be at the same level as when BOD is globally disabled by fuses. If BOD is disabled in software, the BOD function is turned off
immediately after entering the sleep mode. Upon wake-up from sleep, BOD is automatically
enabled again. This ensures safe operation in case the Vcc level has dropped during the sleep
period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately
60 µs to ensure that the BOD is working correctly before the MCU continues executing code.
BOD disable is controlled by BODS bit (BOD Sleep) in the control register MCUCR, see
“MCUCR – MCU Control Register” on page 47. Setting it to one turns off the BOD in relevant
sleep modes, while a zero in this bit keeps BOD active. Default setting keeps BOD active, i.e.
BODS is cleared to zero.
Writing to the BODS bit is controlled by a timed sequence and an enable bit, see “MCUCR –
MCU Control Register” on page 47.
5.3
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 SPI, Analog Comparator, ADC, USI start condition,
Asynchronous Timer/Counter, Watchdog, and the interrupt system to continue operating. This
sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the SPI interrupts. If wake-up from the Analog Comparator interrupt is not required,
the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If
the ADC is enabled, a conversion starts automatically when this mode is entered.
5.4
ADC Noise Reduction Mode
When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC
Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the
USI start condition, the asynchronous Timer/Counter and the Watchdog to continue operating
(if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the
other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements.
If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart from
the ADC Conversion Complete interrupt, only an External Reset, a Watchdog System Reset, a
Watchdog Interrupt, a Brown-out Reset, a USI start condition interrupt, an asynchronous
Timer/Counter interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT0
or INT1 or a pin change interrupt can wake up the MCU from ADC Noise Reduction mode.
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5.5
Power-down Mode
When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter
Power-down mode. In this mode, the external Oscillator is stopped, while the external interrupts, the USI start condition, and the Watchdog continue operating (if enabled). Only an
External Reset, a Watchdog System Reset, a Watchdog Interrupt, a Brown-out Reset, the USI
start condition interrupt, an external level interrupt on INT0 or INT1, 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 Section 8. “External
Interrupts” on page 62 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 Section 4.2 “Clock Sources” on page 25.
5.6
Power-save Mode
When the SM1..0 bits are written to 11, the SLEEP instruction makes the MCU enter
Power-save mode. This mode is identical to Power-down, with one exception:
If Timer/Counter0 is clocked asynchronously, i.e., the AS0 bit in ASSR is set, Timer/Counter0
will run during sleep. The device can wake up from either Timer Overflow or Output Compare
event from Timer/Counter0 if the corresponding Timer/Counter0 interrupt enable bits are set in
TIMSK0, and the global interrupt enable bit in SREG is set.
If the Asynchronous Timer is NOT clocked asynchronously, Power-down mode is recommended instead of Power-save mode because the contents of the registers in the
asynchronous timer should be considered undefined after wake-up in Power-save mode if
AS0 is 0.
This sleep mode basically halts all clocks except clkASY, allowing operation only of asynchronous modules, including Timer/Counter0 if clocked asynchronously.
5.7
Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 47,
provides a method to stop the clock to individual peripherals to reduce power consumption.
The current state of the peripheral is frozen and the I/O registers can not be read or written.
Resources used by the peripheral when stopping the clock will remain occupied, hence the
peripheral should in most cases be disabled before stopping the clock. Waking up a module,
which is done by clearing the bit in PRR, puts the module in the same state as before
shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.
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5.8
Minimizing Power Consumption
There are several possibilities 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.
5.8.1
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to Section 17. “ADC – Analog to Digital Converter” on page 191 for details on ADC operation.
5.8.2
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC Noise Reduction mode, the Analog Comparator should be disabled. In 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 Section 18. “AnaComp - Analog Comparator” on page
211 for details on how to configure the Analog Comparator.
5.8.3
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 Section 6.1.5 “Brown-out Detection” on
page 51 for details on how to configure the Brown-out Detector.
5.8.4
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power.
When turned on again, the user must allow the reference to start up before the output is used.
If the reference is kept on in sleep mode, the output can be used immediately. Refer to Section
6.2 “Internal Voltage Reference” on page 53 for details on the start-up time.
Output the internal voltage reference is not needed in the deeper sleep modes. This module
should be turned off to reduce significantly to the total current consumption. Refer to “AMISCR
– Analog Miscellaneous Control Register” on page 190 for details on how to disable the internal voltage reference output.
5.8.5
Internal Current Source
The Internal Current Source is not needed in the deeper sleep modes. This module should be
turned off to reduce significantly to the total current consumption. Refer to “AMISCR – Analog
Miscellaneous Control Register” on page 190 for details on how to disable the Internal Current
Source.
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5.8.6
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 Section 6.3 “Watchdog Timer” on page 53 for details on how to configure
the Watchdog Timer.
5.8.7
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 both
the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device will
be disabled. This ensures that no power is consumed by the input logic when not needed. In
some cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section Section 9.2.6 “Digital Input Enable and Sleep Modes” on page
72 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 (DIDR1 and
DIDR0). Refer to Section 17.11.6 “DIDR1 – Digital Input Disable Register 1” on page 210 and
Section 17.11.5 “DIDR0 – Digital Input Disable Register 0” on page 209 for details.
5.8.8
5.9
5.9.1
On-chip Debug System
If the On-chip debug system is enabled by the DWEN Fuse and the chip enters sleep mode,
the main clock source is enabled and hence always consumes power. In the deeper sleep
modes, this will contribute significantly to the total current consumption.
Register Description
SMCR – Sleep Mode Control Register
The Sleep Mode Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
SM1
SM0
SE
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SMCR
• Bits 7..3 Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
• Bits 2..1 – SM1..0: Sleep Mode Select Bits 1, and 0
These bits select between the four available sleep modes as shown in Table 5-2.
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Table 5-2.
Sleep Mode Select
SM1
SM0
Sleep Mode
0
0
Idle
0
1
ADC Noise Reduction
1
0
Power-down
1
1
Power-save
• Bit 0 – 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.
5.9.2
MCUCR – MCU Control Register
Bit
7
6
5
4
3
2
1
0
–
BODS
BODSE
PUD
–
–
–
–
Read/Write
R
R/W
R/W
R/W
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 6 – BODS: BOD Sleep
The BODS bit must be written to logic one in order to turn off BOD during sleep, see Table 5-1
on page 42. Writing to the BODS bit is controlled by a timed sequence and an enable bit,
BODSE in MCUCR. To disable BOD in relevant sleep modes, both BODS and BODSE must
first be set to one. Then, to set the BODS bit, BODS must be set to one and BODSE must be
set to zero within four clock cycles.
The BODS bit is active three clock cycles after it is set. A sleep instruction must be executed
while BODS is active in order to turn off the BOD for the actual sleep mode. The BODS bit is
automatically cleared after three clock cycles.
• Bit 5 – BODSE: BOD Sleep Enable
BODSE enables setting of BODS control bit, as explained in BODS bit description. BOD disable is controlled by a timed sequence.
5.9.3
PRR – Power Reduction Register
Bit
7
6
5
4
3
2
1
0
–
–
PRLIN
PRSPI
PRTIM1
PRTIM0
PRUSI
PRADC
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PRR
• Bit 7 - Res: Reserved bit
This bit is reserved in ATtiny87/167 and will always read as zero.
• Bit 6 - Res: Reserved bit
This bit is reserved in ATtiny87/167 and will always read as zero.
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• Bit5 - PRLIN: Power Reduction LIN / UART controller
Writing a logic one to this bit shuts down the LIN by stopping the clock to the module. When
waking up the LIN again, the LIN should be re initialized to ensure proper operation.
• Bit 4 - PRSPI: Power Reduction Serial Peripheral Interface
If using debugWIRE On-chip Debug System, this bit should not be written to one.
Writing a logic one to this bit shuts down the Serial Peripheral Interface by stopping the clock
to the module. When waking up the SPI again, the SPI should be re initialized to ensure
proper operation.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the
Timer/Counter1 is enabled, operation will continue like before the shutdown.
• Bit 2 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module in synchronous mode
(AS0 is 0). When the Timer/Counter0 is enabled, operation will continue like before the
shutdown.
• Bit 1 - PRUSI: Power Reduction USI
Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When
waking up the USI again, the USI should be re-initialized to ensure proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut
down. The analog comparator cannot use the ADC input MUX when the ADC is shut down.
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6. System Control and Reset
6.1
6.1.1
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 6-1 shows the reset circuit. Tables in Section 22.5
“RESET Characteristics” on page 246 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 Section 4.2 “Clock
Sources” on page 25.
6.1.2
Reset Sources
The ATtiny87/167 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 System Reset. The MCU is reset when the Watchdog Timer period expires and
the Watchdog System Reset mode is enabled.
• Brown-out Reset. The MCU is reset when the supply voltage Vcc is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
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7728D–AVR–07/09
Figure 6-1.
Reset Circuit
DATA BUS
PORF
BORF
EXTRF
WDRF
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
Brown-out
Reset Circuit
BODLEVEL [2..0]
Pull-up Resistor
RSTDISBL
Spike
Filter
Watchdog
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
SUT[1:0]
6.1.3
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection
level is defined in Table 22-4 on page 246. 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 6-2.
MCU Start-up, RESET Tied to Vcc
VCCRR
VCC
VPORMAX
VPOT
VPORMIN
TIME-OUT
tTOUT
INTERNAL
RESET
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Figure 6-3.
MCU Start-up, RESET Extended Externally
VCCRR
VCC
VPOR
RESET
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
6.1.4
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 22-3 on page 246) 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. The External Reset can be disabled
by the RSTDISBL fuse, see Table 21-4 on page 226.
Figure 6-4.
External Reset During Operation
CC
6.1.5
Brown-out Detection
ATtiny87/167 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 (See ”BODLEVEL Fuse Coding” on page 247.). The trigger
level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the detection level should be interpreted as VBOT+ = VBOT + VHYST / 2 and VBOT– = VBOT - VHYST / 2.
When the BOD is enabled, and Vcc decreases to a value below the trigger level (VBOT– in Figure 6-5), the Brown-out Reset is immediately activated. When Vcc increases above the trigger
level (VBOT+ in Figure 6-5), the delay counter starts the MCU after the Time-out period tTOUT
has expired.
The BOD circuit will only detect a drop in Vcc if the voltage stays below the trigger level for longer than tBOD given in Table 22-6 on page 247.
51
7728D–AVR–07/09
Figure 6-5.
Brown-out Reset During Operation
VCC
VBOT+
VBOT-
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
6.1.6
Watchdog System 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 53 for details on operation of the Watchdog Timer.
Figure 6-6.
Watchdog System Reset During Operation
CC
CK
6.1.7
MCU Status Register – MCUSR
The MCU Status Register provides information on which reset source caused an MCU reset.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
MCUSR
See Bit Description
• Bit 7..4 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
• Bit 3 – WDRF: Watchdog System Reset Flag
This bit is set if a Watchdog System 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.
52
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
• 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.
6.2
Internal Voltage Reference
ATtiny87/167 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator or the ADC.
6.2.1
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 22-7 on page 247. 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] Fuses).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACIRS bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACIRS bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
ADC is used. To reduce power consumption in Power-down mode or in Power-save, the user
can avoid the three conditions above to ensure that the reference is turned off before entering
in these power reduction modes.
6.3
Watchdog Timer
ATtiny87/167 has an Enhanced Watchdog Timer (WDT). The main features are:
• Clocked from separate On-chip Oscillator
• 4 Operating modes
– Interrupt
– System Reset
– Interrupt and System Reset
– Clock Monitoring
• Selectable Time-out period from 16ms to 8s
• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
6.3.1
Watchdog Timer Behavior
The Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 KHz
oscillator.
53
7728D–AVR–07/09
Figure 6-7.
Watchdog Timer
WATCHDOG
PRESCALER
OSC / 2K
OSC / 4K
OSC / 8K
OSC / 16K
OSC / 32K
OSC / 64K
OSC / 128K
OSC / 256K
OSC / 512K
OSC / 1024K
~128 KHz
OSCILLATOR
WATCHDOG
RESET
WDP0
WDP1
WDP2
WDP3
CLOCK
MONITORING
WDE
MCU
RESET
WDIF
INTERRUPT
WDIE
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.
54
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
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
lds r16, WDTCR
ori
r16, (1<<WDCE) | (1<<WDE)
sts WDTCR, r16
; Turn off WDT
ldi
r16, (0<<WDE)
sts WDTCR, 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 */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
__enable_interrupt();
}
Note:
1. See ”About Code Examples” on page 6.
Note that 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 Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialization routine, even if the
Watchdog is not in use.
55
7728D–AVR–07/09
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
lds r16, WDTCR
ori
r16, (1<<WDCE) | (1<<WDE)
sts WDTCR, 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)
sts WDTCR, 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 sequence */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCR
= (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Notes:
1. See ”About Code Examples” on page 6.
2. 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.
6.3.2
56
Clock monitoring
The Watchdog Timer can be used to detect a loss of system clock. This configuration is driven
by the dynamic clock switch circuit. Please refer to Section 4.3.8 “Clock Monitoring” on page
34 for more information.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
6.3.3
Watchdog Timer Control Register - WDTCR
Bit
7
6
5
4
3
2
1
0
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
0
0
0
WDTCR
• Bit 7 - WDIF: Watchdog 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.
If the Watchdog Timer is used as clock monitor (c.f. Section • “Bits 3:0 – CLKC3:0: Clock Control Bits 3 - 0” on page 40), the System Reset Mode is enabled and the Interrupt Mode is
automatically disabled.
Table 6-1.
Watchdog Timer Configuration
Clock
Monitor
WDTON
WDE
x
0
0
0
Stopped
None
(1)
(1)
(1)
System Reset Mode
Reset
On
Off
Note:
y
y
WDIE Mode
y
Action on Time-out
0
0
1
Interrupt Mode
Interrupt
0
1
0
System Reset Mode
Reset
Interrupt, then go to System
Reset Mode
Reset
0
1
1
Interrupt and System Reset
Mode
1
x
x
System Reset Mode
1. At least one of these three enables (WDTON, WDE & WDIE) equal to 1.
• 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.
57
7728D–AVR–07/09
• 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 6-2 on page 58.
Table 6-2.
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
58
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
7. Interrupts
This section describes the specifics of the interrupt handling as performed in ATtiny87/167.
For a general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling” on page 12.
7.1
Interrupt Vectors in ATtiny87/167
Table 7-1.
Reset and Interrupt Vectors in ATtiny87/167
Program Address
Vector
Nb.
ATtiny87
ATtiny167
Source
Interrupt Definition
1
0x0000
0x0000
RESET
External Pin, Power-on Reset, Brown-out Reset and
Watchdog System Reset
2
0x0001
0x0002
INT0
External Interrupt Request 0
3
0x0002
0x0004
INT1
External Interrupt Request 1
4
0x0003
0x0006
PCINT0
Pin Change Interrupt Request 0
5
0x0004
0x0008
PCINT1
Pin Change Interrupt Request 1
6
0x0005
0x000A
WDT
Watchdog Time-out Interrupt
7
0x0006
0x000C
TIMER1 CAPT
Timer/Counter1 Capture Event
8
0x0007
0x000E
TIMER1 COMPA
Timer/Counter1 Compare Match A
9
0x0008
0x0010
TIMER1 COMPB
Timer/Coutner1 Compare Match B
10
0x0009
0x0012
TIMER1 OVF
Timer/Counter1 Overflow
11
0x000A
0x0014
TIMER0 COMPA
Timer/Counter0 Compare Match A
12
0x000B
0x0016
TIMER0 OVF
Timer/Counter0 Overflow
13
0x000C
0x0018
LIN TC
LIN/UART Transfer Complete
14
0x000D
0x001A
LIN ERR
LIN/UART Error
15
0x000E
0x001C
SPI, STC
SPI Serial Transfer Complete
16
0x000F
0x001E
ADC
ADC Conversion Complete
17
0x0010
0x0020
EE READY
EEPROM Ready
18
0x0011
0x0022
ANALOG COMP
Analog Comparator
19
0x0012
0x0024
USI START
USI Start Condition Detection
20
0x0013
0x0026
USI OVF
USI Counter Overflow
59
7728D–AVR–07/09
7.2
Program Setup in ATtiny87
The most typical and general program setup for the Reset and Interrupt Vector Addresses in
ATtiny87 is (2-byte step - using “rjmp” instruction):
Address(Note:)Label Code
0x0000
rjmp
RESET
; Reset Handler
0x0001
rjmp
INT0addr
; IRQ0 Handler
0x0002
rjmp
INT1addr
; IRQ1 Handler
0x0003
rjmp
PCINT0addr
; PCINT0 Handler
0x0004
rjmp
PCINT1addr
; PCINT1 Handler
0x0005
rjmp
WDTaddr
; Watchdog Timer Handler
0x0006
rjmp
ICP1addr
; Timer1 Capture Handler
0x0007
rjmp
OC1Aaddr
; Timer1 Compare A Handler
0x0008
rjmp
OC1Baddr
; Timer1 Compare B Handler
0x0009
rjmp
OVF1addr
; Timer1 Overflow Handler
0x000A
rjmp
OC0Aaddr
; Timer0 Compare A Handler
0x000B
rjmp
OVF0addr
; Timer0 Overflow Handler
0x000C
rjmp
LINTCaddr
; LIN Transfer Complete Handler
0x000D
rjmp
LINERRaddr
; LIN Error Handler
0x000E
rjmp
SPIaddr
; SPI Transfer Complete Handler
0x000F
rjmp
ADCCaddr
; ADC Conversion Complete Handler
0x0010
rjmp
ERDYaddr
; EEPROM Ready Handler
0x0011
rjmp
ACIaddr
; Analog Comparator Handler
0x0012
rjmp
USISTARTaddr
; USI Start Condition Handler
0x0013
rjmp
USIOVFaddr
; USI Overflow Handler
0x0014 RESET:
ldi
r16, high(RAMEND); Main program start
0x0015
out
SPH,r16
0x0016
ldi
r16, low(RAMEND)
0x0017
out
SPL,r16
0x0018
sei
0x0019
...
Note:
60
Comments
; Enable interrupts
<instr>
...
...
; Set Stack Pointer to top of RAM
xxx
...
16-bit address
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
7.3
Program Setup in ATtiny167
The most typical and general program setup for the Reset and Interrupt Vector Addresses in
ATtiny167 is (4-byte step - using “jmp” instruction):
Address(Note:)Label Code
Comments
0x0000
jmp
RESET
; Reset Handler
0x0002
jmp
INT0addr
; IRQ0 Handler
0x0004
jmp
INT1addr
; IRQ1 Handler
0x0006
jmp
PCINT0addr
; PCINT0 Handler
0x0008
jmp
PCINT1addr
; PCINT1 Handler
0x000A
jmp
WDTaddr
; Watchdog Timer Handler
0x000C
jmp
ICP1addr
; Timer1 Capture Handler
0x000E
jmp
OC1Aaddr
; Timer1 Compare A Handler
0x0010
jmp
OC1Baddr
; Timer1 Compare B Handler
0x0012
jmp
OVF1addr
; Timer1 Overflow Handler
0x0014
jmp
OC0Aaddr
; Timer0 Compare A Handler
0x0016
jmp
OVF0addr
; Timer0 Overflow Handler
0x0018
jmp
LINTCaddr
; LIN Transfer Complete Handler
0x001A
jmp
LINERRaddr
; LIN Error Handler
0x001C
jmp
SPIaddr
; SPI Transfer Complete Handler
0x001E
jmp
ADCCaddr
; ADC Conversion Complete Handler
0x0020
jmp
ERDYaddr
; EEPROM Ready Handler
0x0022
jmp
ACIaddr
; Analog Comparator Handler
0x0024
jmp
USISTARTaddr
; USI Start Condition Handler
0x0026
jmp
USIOVFaddr
; USI Overflow Handler
0x0028 RESET:
ldi
r16, high(RAMEND); Main program start
0x0029
out
SPH,r16
0x002A
ldi
r16, low(RAMEND)
0x002B
out
SPL,r16
0x002C
sei
0x002D
...
Note:
; Enable interrupts
<instr>
...
...
; Set Stack Pointer to top of RAM
xxx
...
16-bit address
61
7728D–AVR–07/09
8. External Interrupts
8.1
Overview
The External Interrupts are triggered by the INT1..0 pins or any of the PCINT15..0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT1..0 or PCINT15..0 pins are
configured as outputs. This feature provides a way of generating a software interrupt.
The pin change interrupt PCINT1 will trigger if any enabled PCINT15..8 pin toggles. The pin
change interrupt PCINT0 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 PCINT15..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 INT1..0 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 INT1..0 interrupts are enabled and are configured as level triggered, the interrupts will trigger as long as the pin is held low. The recognition of falling or rising edge interrupts on INT1..0
requires the presence of an I/O clock, described in “Clock Systems and their Distribution” on
page 24. Low level interrupts and the edge interrupt on INT1..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 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 or Power-save,
the required level must be held long enough for the MCU to complete the wake-up to trigger
the level interrupt. If the level disappears before the end of the Start-up Time, the MCU will still
wake up, but no interrupt will be generated. The start-up time is defined by the SUT and
CKSEL Fuses as described in “Clock Systems and their Distribution” on page 24.
8.2
Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in Figure 8-1.
Figure 8-1.
Timing of pin change interrupts
0
PCINT[i]
pin
D
Q
pin_lat
D
Q
pin_sync
LE
PCINT[i] bit
(of PCMSKn)
clk
pcint_sync
pcint_in[i]
D
Q
pcint_set/flag
D
Q
D
Q
PCIFn
(interrupt flag)
7
clk
clk
PCINT[i] pin
pin_lat
pin_sync
pcint_in[i]
pcint_syn
pcint_set/flag
PCIFn
62
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
8.3
8.3.1
External Interrupts Register Description
External Interrupt Control Register A – EICRA
The External Interrupt Control Register A contains control bits for interrupt sense control.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
ISC11
ISC10
ISC01
ISC00
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EICRA
• Bit 7..4 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
• 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 8-1. 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.
• 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 activate the
interrupt are defined in Table 8-1. The value on the INT0 pin is sampled before detecting
edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will
generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level
interrupt is selected, the low level must be held until the completion of the currently executing
instruction to generate an interrupt.
Table 8-1.
8.3.2
Interrupt Sense Control
ISCn1
ISCn0
Description
0
0
The low level of INTn generates an interrupt request.
0
1
Any logical change on INTn generates an interrupt request.
1
0
The falling edge of INTn generates an interrupt request.
1
1
The rising edge of INTn generates an interrupt request.
External Interrupt Mask Register – EIMSK
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
INT1
INT0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EIMSK
• Bit 7, 2 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
63
7728D–AVR–07/09
• Bit 1 – 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 External Interrupt Control Register A (EICRA) 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 0 – 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 External Interrupt Control Register A (EICRA) define whether the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause
an interrupt request even if INT0 is configured as an output. The corresponding interrupt of
External Interrupt Request 0 is executed from the INT0 Interrupt Vector.
8.3.3
External Interrupt Flag Register – EIFR
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
INTF1
INTF0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EIFR
• Bit 7, 2 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
• Bit 1 – 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 EIMSK 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 0 – 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 EIMSK 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.
8.3.4
Pin Change Interrupt Control Register – PCICR
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
PCIE1
PCIE0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCICR
• Bit 7, 2 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
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• Bit 1 - PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 1 is enabled. Any change on any enabled PCINT15..8 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1
Interrupt Vector. PCINT15..8 pins are enabled individually by the PCMSK1 Register.
• Bit 0 - PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 0 is enabled. Any change on any enabled PCINT7..0 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0
Interrupt Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
8.3.5
Pin Change Interrupt Flag Register – PCIFR
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
PCIF1
PCIF0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCIFR
• Bit 7, 2 – Res: Reserved Bits
These bits are unused bits in the ATtiny87/167, and will always read as zero.
• Bit 1 - PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT15..8 pin triggers an interrupt request, PCIF1 becomes set
(one). If the I-bit in SREG and the PCIE1 bit in PCICR are set (one), the MCU will jump to the
corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 0 - PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0 becomes set
(one). If the I-bit in SREG and the PCIE0 bit in PCICR 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.
8.3.6
Pin Change Mask Register 1 – PCMSK1
Bit
7
6
5
4
3
2
1
0
PCINT15
PCINT14
PCINT13
PCINT12
PCINT11
PCINT10
PCINT9
PCINT8
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
PCMSK1
• Bit 7..0 – PCINT15..8: Pin Change Enable Mask 15..8
Each PCINT15..8-bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT15..8 is set and the PCIE1 bit in EIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT15..8 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.
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8.3.7
Pin Change Mask Register 0 – PCMSK0
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
PCMSK0
• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 7..0
Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT7..0 is set and the PCIE0 bit in EIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.
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9. I/O-Ports
9.1
Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O
ports. This means that the direction of one port pin can be changed without unintentionally
changing the direction of any other pin with the SBI and CBI instructions. The same applies
when changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if
configured as input). Each output buffer has symmetrical drive characteristics with both high
sink and source capability. The pin driver is strong enough to drive LED displays directly. All
port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both Vcc and Ground as indicated in Figure 9-1.
Refer to “Electrical Characteristics” on page 243 for a complete list of parameters.
Figure 9-1.
I/O Pin Equivalent Schematic
Rpu
Pxn
Logic
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 86.
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 or PUDx in PORTCR 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
68. 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 72. Refer to the individual module sections for a full description of the
alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the port as general digital I/O.
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9.2
Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 9-2 shows a functional description of one I/O-port pin, here generically called Pxn.
Figure 9-2.
General Digital I/O(Note:)
PUD
Q
D
DDxn
Q CLR
WDx
RESET
1
D
0
PORTxn
Q CLR
WPx
RESET
DATA BUS
Q
Pxn
RDx
WRx
SLEEP
RRx
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD: PULLUP DISABLE
SLEEP: SLEEP CONTROL
clkI/O : I/O CLOCK
Note:
9.2.1
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register Description for I/O Ports” on page 86, 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).
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9.2.2
Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of
DDRxn. Note that the SBI assembler instruction can be used to toggle one single bit in a port.
9.2.3
Break-Before-Make Switching
In the Break-Before-Make mode when switching the DDRxn bit from input to output an immediate tri-state period lasting one system clock cycle is introduced as indicated in Figure 9-3.
For example, if the system clock is 4 MHz and the DDRxn is written to make an output, the
immediate tri-state period of 250 ns is introduced, before the value of PORTxn is seen on the
port pin. To avoid glitches it is recommended that the maximum DDRxn toggle frequency is
two system clock cycles. The Break-Before-Make is a port-wise mode and it is activated by the
port-wise BBMx enable bits. For further information about the BBMx bits, see “Port Control
Register – PORTCR” on page 75. When switching the DDRxn bit from output to input there is
no immediate tri-state period introduced.
Figure 9-3.
Break Before Make, switching between input and output
YSTEM CLOCK
R 16
0x02
R 17
0x01
NSTRUCTIONS
out DDRx, r16
PORTx
DDRx
nop
out DDRx, r17
0x55
0x01
0x02
Px0
0x01
tri-state
immediate tri-state cycle
Px1
tri-state
tri-state
immediate tri-state cycle
9.2.4
Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0, 0) and output high
({DDxn, PORTxn} = 1, 1), an intermediate state with either pull-up enabled
{DDxn, PORTxn} = 0, 1) or output low ({DDxn, PORTxn} = 1, 0) 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 or the PUDx bit in PORTCR Register can be set to disable all pull-ups in the
port.
Switching between input with pull-up and output low generates the same problem. The user
m u s t u s e e it h e r t h e tr i - s t a t e ( { D D x n , P O R T x n } = 0 , 0 ) o r th e o u t p u t h i g h s t a t e
({DDxn, PORTxn} = 1, 1) as an intermediate step.
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Table 9-1 summarizes the control signals for the pin value.
Table 9-1.
DDxn
PORTxn
PUD
(in MCUCR) (1)
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)
Note:
9.2.5
Port Pin Configurations
Comment
1. Or port-wise PUDx bit in PORTCR register.
Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 9-2, the PINxn Register bit and the preceding latch
constitute a synchronizer. This is needed to avoid metastability if the physical pin changes
value near the edge of the internal clock, but it also introduces a delay. Figure 9-4 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 9-4.
Synchronization when Reading an Externally Applied Pin value
SYSTEM CLK
INSTRUCTIONS
XXX
XXX
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd, max
t pd, min
Consider the clock period starting shortly after the first falling edge of the system clock. The
latch is closed when the clock is low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH” signal. The signal value is latched when the
system clock goes low. It is clocked into the PINxn Register at the succeeding positive clock
edge. As indicated by the two arrows tpd,max and tpd,min, a single 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 9-5. 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.
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Figure 9-5.
Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
0xFF
out PORTx, r16
nop
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd
The following code example shows how to set port 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:
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.
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9.2.6
Digital Input Enable and Sleep Modes
As shown in Figure 9-2, the digital input signal can be clamped to ground at the input of the
Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down or Power-save 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 72.
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.
9.2.7
Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level.
Even though most of the digital inputs are disabled in the deep sleep modes as described
above, floating inputs should be avoided to reduce current consumption in all other modes
where the digital inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal
pull-up. In this case, the pull-up will be disabled during reset. If low power consumption during
reset is important, it is recommended to use an external pull-up or pull-down. Connecting
unused pins directly to Vcc or GND is not recommended, since this may cause excessive currents if the pin is accidentally configured as an output.
9.3
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 9-6
shows how the port pin control signals from the simplified Figure 9-2 can be overridden by
alternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
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Figure 9-6.
Alternate Port Functions(1)
PUOExn
1
PUOVxn
PUD
0
DDOExn
DDOVxn
1
Q D
DDxn
0
Q CLR
PVOExn
WDx
RESET
RDx
1
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
WPx
1
0
DIEOVxn
RESET
DATA BUS
PVOVxn
WRx
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
Q
D
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn: Pxn PULL-UP OVERRIDE ENABLE
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
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
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE
Note:
PUD: PULLUP DISABLE
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clkI/O:
DIxn:
AIOxn:
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.
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Table 9-2 summarizes the function of the overriding signals. The pin and port indexes from
Figure 9-6 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
Table 9-2.
Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
PUOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, (PUD or PDUx)} = 0, 1, 0.
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,
PUD and PUDx 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
If this signal is set and the Output Driver is enabled, the port
Port Value Override value is controlled by the PVOV signal. If PVOE is cleared, and
Enable
the Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.
PVOV
Port Value Override If PVOE is set, the port value is set to PVOV, regardless of the
Value
setting of the PORTxn Register bit.
PTOE
Port Toggle Override
If PTOE is set, the PORTxn Register bit is inverted.
Enable
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
This is the Analog Input/output to/from alternate functions. The
Analog Input/Output 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.
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9.3.1
MCU Control Register – MCUCR
Bit
7
6
5
4
3
2
1
0
–
BODS
BODSE
PUD
–
–
–
–
Read/Write
R
R/W
R/W
R/W
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 4 – 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} = 0, 1). See “Configuring the Pin” on page 68 for more details about this feature.
9.3.2
Port Control Register – PORTCR
Bit
7
6
5
4
3
2
1
0
-
-
BBMB
BBMA
-
-
PUDB
PUDA
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
PORTCR
• Bits 5, 4 – BBMx: Break-Before-Make Mode Enable
When these bits are written to one, the port-wise Break-Before-Make mode is activated. The
intermediate tri-state cycle is then inserted when writing DDRxn to make an output. For further
information, see “Break-Before-Make Switching” on page 69.
• Bits 1, 0 – PUDx: Port-Wise Pull-up Disable
When these bits are written to one, the port-wise pull-ups in the defined I/O ports are disabled
even if the DDxn and PORTxn Registers are configured to enable the pull-ups
({DDxn, PORTxn} = 0, 1). The Port-Wise Pull-up Disable bits are ORed with the global Pull-up
Disable bit (PUD) from the MCUCR register. See “Configuring the Pin” on page 68 for more
details about this feature.
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9.3.3
Alternate Functions of Port A
The Port A pins with alternate functions are shown in Table 9-3.
Table 9-3.
Port A Pins Alternate Functions
Port Pin
76
Alternate Function
PA7
PCINT7 (Pin Change Interrupt 7)
ADC7 (ADC Input Channel 7)
AIN1 (Analog Comparator Positive Input)
XREF (Internal Voltage Reference Output)
AREF (External Voltage Reference Input)
PA6
PCINT6 (Pin Change Interrupt 6)
ADC6 (ADC Input Channel 6)
AIN0 (Analog Comparator Negative Input)
SS (SPI Slave Select Input)
PA5
PCINT5 (Pin Change Interrupt 5)
ADC5 (ADC Input Channel 5)
T1 (Timer/Counter1 Clock Input)
USCK (Three-wire Mode USI Alternate Clock Input)
SCL (Two-wire Mode USI Alternate Clock Input)
SCK (SPI Master Clock)
PA4
PCINT4 (Pin Change Interrupt 4)
ADC4 (ADC Input Channel 4)
ICP1 (Timer/Counter1 Input Capture Trigger)
DI (Three-wire Mode USI Alternate Data Input)
SDA (Two-wire Mode USI Alternate Data Input / Output)
MOSI (SPI Master Output / Slave Input)
PA3
PCINT3 (Pin Change Interrupt 3)
ADC3 (ADC Input Channel 3)
ISRC (Current Source Pin)
INT1 (External Interrupt1 Input)
PA2
PCINT2 (Pin Change Interrupt 2)
ADC2 (ADC Input Channel 2)
OC0A (Output Compare and PWM Output A for Timer/Counter0)
DO (Three-wire Mode USI Alternate Data Output)
MISO (SPI Master Input / Slave Output)
PA1
PCINT1 (Pin Change Interrupt 1)
ADC1 (ADC Input Channel 1)
TXD (UART Transmit Pin)
TXLIN (LIN Transmit Pin)
PA0
PCINT0 (Pin Change Interrupt 0)
ADC0 (ADC Input Channel 0)
RXD (UART Receive Pin)
RXLIN (LIN Receive Pin)
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
The alternate pin configuration is as follows:
• PCINT7/ADC7/AIN1/XREF/AREF – Port A, Bit7
PCINT7: Pin Change Interrupt, source 7.
ADC7: Analog to Digital Converter, channel 7.
AIN1: Analog Comparator Positive Input. This pin is directly connected to the positive input
of the Analog Comparator.
XREF: Internal Voltage Reference Output. The internal voltage reference 2.56V or 1.1V is
output when XREFEN is set and if either 2.56V or 1.1V is used as reference for ADC
conversion. When XREF output is enabled, the pin port pull-up and digital output
driver are turned off.
AREF: External Voltage Reference Input for ADC. The pin port pull-up and digital output
driver are disabled when the pin is used as an external voltage reference input for
ADC or as when the pin is only used to connect a bypass capacitor for the voltage reference of the ADC.
• PCINT6/ADC6/AIN0/SS – Port A, Bit6
PCINT6: Pin Change Interrupt, source 6.
ADC6: Analog to Digital Converter, channel 6.
AIN0: Analog Comparator Negative Input. This pin is directly connected to the negative input
of the Analog Comparator.
SS: SPI Slave Select Input. When the SPI is enabled as a slave, this pin is configured as an
input regardless of the setting of DDA6. As a slave, the SPI is activated when this pin
is driven low. When the SPI is enabled as a master, the data direction of this pin is
controlled by DDA6. When the pin is forced to be an input, the pull-up can still be controlled by the PORTA6 bit.
• PCINT5/ADC5/T1/USCK/SCL/SCK – Port A, Bit5
PCINT5: Pin Change Interrupt, source 5.
ADC5: Analog to Digital Converter, channel 5.
T1: Timer/Counter1 Clock Input.
USCK: Three-wire Mode USI Clock Input.
SCL: Two-wire Mode USI Clock Input.
SCK: SPI Master Clock output, Slave Clock input pin. When the SPI is enabled as a slave,
this pin is configured as an input regardless of the setting of DDA5. When the SPI is
enabled as a master, the data direction of this pin is controlled by DDA5. When the pin
is forced to be an input, the pull-up can still be controlled by the PORTA5 bit.
• PCINT4/ADC4/ICP1/DI/SDA/MOSI – Port A, Bit 4
PCINT4: Pin Change Interrupt, source 4.
ADC4: Analog to Digital Converter, channel 4.
ICP1: Timer/Counter1 Input Capture Trigger. The PA3 pin can act as an Input Capture pin for
Timer/Counter1.
DI: Three-wire Mode USI Data Input. USI Three-wire mode does not override normal port
functions, so pin must be configure as an input for DI function.
SDA: Two-wire Mode Serial Interface (USI) Data Input / Output.
MOSI: SPI Master Output / Slave Input. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDA3. When the SPI is enabled as a
77
7728D–AVR–07/09
Master, the data direction of this pin is controlled by DDA3. When the pin is forced by
the SPI to be an input, the pull-up can still be controlled by the PORTA3 bit.
• PCINT3/ADC3/ISRC/INT1 – Port A, Bit 3
PCINT3: Pin Change Interrupt, source 3.
ADC3: Analog to Digital Converter, channel 3.
ISCR: Current Source Output pin. While current is sourced by the Current Source module,
the user can use the Analog to Digital Converter channel 4 (ADC4) to measure the pin
voltage.
INT1: External Interrupt, source 1. The PA4 pin can serve as an external interrupt source.
• PCINT2/ADC2/OC0A/DO/MISO – Port A, Bit 2
PCINT2: Pin Change Interrupt, source 2.
ADC2: Analog to Digital Converter, channel 2.
OC0A: Output Compare Match A or output PWM A for Timer/Counter0. The pin has to be
configured as an output (DDA2 set (one)) to serve these functions.
DO: Three-wire Mode USI Data Output. Three-wire mode data output overrides PORTA2
and it is driven to the port when the data direction bit DDA2 is set. PORTA2 still
enables the pull-up, if the direction is input and PORTA2 is set (one).
MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled
as a Master, this pin is configured as an input regardless of the setting of DDA2. When
the SPI is enabled as a Salve, the data direction of this pin is controlled by DDA2.
When the pin is forced to be an input, the pull-up can still be controlled by PORTA2.
• PCINT1/ADC1/TXD/TXLIN – Port A, Bit 1
PCINT1: Pin Change Interrupt, source 1.
ADC1: Analog to Digital Converter, channel 1.
TXD: UART Transmit pin. When the UART transmitter is enabled, this pin is configured as an
output regardless the value of DDA1. PORTA1 still enables the pull-up, if the direction
is input and PORTA2 is set (one).
TXLIN: LIN Transmit pin. When the LIN is enabled, this pin is configured as an output
regardless the value of DDA1. PORTA1 still enables the pull-up, if the direction is input
and PORTA2 is set (one).
• PCINT0/ADC0/RXD/RXLIN – Port A, Bit 0
PCINT0: Pin Change Interrupt, source 0.
ADC0: Analog to Digital Converter, channel 0.
RXD: UART Receive pin. When the UART receiver is enabled, this pin is configured as an
input regardless of the value of DDA0. When the pin is forced to be an input, a logical
one in PORTA0 will turn on the internal pull-up.
RXLIN: LIN Receive pin. When the LIN is enabled, this pin is configured as an input regardless of the value of DDA0. When the pin is forced to be an input, a logical one in
PORTA0 will turn on the internal pull-up.
Table 9-4 and Table 9-5 relate the alternate functions of Port A to the overriding signals shown
in Figure 9-6 on page 73.
78
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Table 9-4.
Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name
PA7/PCINT7/
ADC7/AIN1
/XREF/AREF
PA6/PCINT6/
ADC6/AIN0/SS
PA5/PCINT5/ADC5/
T1/USCK/SCL/SCK
PA4/PCINT4/ADC4/
ICP1/DI/SDA/MOSI
PUOE
0
SPE & MSTR
SPE & MSTR
SPE & MSTR
PUOV
0
PORTA6 & PUD
PORTA5 & PUD
PORTA4 & PUD
SPE & MSTR
(SPE & MSTR) |
(USI_2_WIRE & USIPOS)
(SPE & MSTR) |
(USI_2_WIRE &
USIPOS)
(USI_SCL_HOLD |
PORTA5)
& DDRA6
{ (SPE & MSTR) ?
(0) :
(USI_SHIFTOUT |
PORTA4)
& DDRA4) }
DDOE
0
DDOV
0
0
PVOE
0
0
(SPE & MSTR) |
(SPE & MSTR) |
(USI_2_WIRE & USIPOS (USI_2_WIRE & USIPOS
& DDRA5)
& DDRA4)
PVOV
0
0
{ (SPE & MSTR) ?
(SCK_OUTPUT) :
~ (USI_2_WIRE &
USIPOS
& DDRA5) }
PTOE
0
0
USI_PTOE & USIPOS
0
DIEOE
ADC7D |
(PCIE0 &
PCMSK07)
ADC6D |
(PCIE0 &
PCMSK06)
ADC5D |
(USISIE & USIPOS) |
(PCIE0 & PCMSK05)
ADC4D |
(USISIE & USIPOS) |
(PCIE0 & PCMSK04)
DIEOV
PCIE0 &
PCMSK07
PCIE0 &
PCMSK06
(USISIE & USIPOS) |
(PCIE0 & PCMSK05)
(USISIE & USIPOS) |
(PCIE0 & PCMSK04)
DI
PCINT7
PCINT6 -/- SS
PCINT5 -/- T1
-/- USCK -/- SCL -/- SCK
PCINT4 -/- ICP1
-/- DI -/- SDA -/- MOSI
AIO
ADC7 -/- AIN1 -/XREF -/- AREF
ADC6 -/- AIN0
ADC5
ADC4
{ (SPE & MSTR) ?
(MOSI_OUTPUT) :
~ (USI_2_WIRE &
USIPOS
& DDRA4) }
79
7728D–AVR–07/09
Table 9-5.
Overriding Signals for Alternate Functions in PA3..PA0
Signal PA3/PCINT3/ADC3/
Name
ISRC/INT1
PUOE
PA1/PCINT1/ADC1/
TXD/TXLIN
PA0/PCINT0/ADC0/
RXD/RXLIN
SPE & MSTR
LIN_TX_ENABLE
LIN_RX_ENABLE
PORTA0 & PUD
PUOV
PORTA3 & PUD
PORTA2 & PUD
{ (LIN_TX_ENABLE)
?
(0) : (PORTA1 & PUD)
}
DDOE
0
SPE & MSTR
LIN_TX_ENABLE
LIN_RX_ENABLE
DDOV
0
0
LIN_TX_ENABLE
0
0
(SPE & MSTR) |
(USI_2_WIRE &
USI_3_WIRE & USIPOS) |
OC0A
LIN_TX_ENABLE
0
PVOE
PVOV
80
0
PA2/PCINT2/ADC2/
OC0A/DO/MISO
0
{ (SPE & MSTR) ?
(MISO_OUTPUT) :
{ (LIN_TX_ENABLE)
( ( USI_2_WIRE &
?
USI_3_WIRE & USIPOS ) ?
(LIN_TX) : (0) }
(USI_SHIFTOUT) : (OC0A) )
}
0
0
PTOE
0
0
DIEOE
ADC3D |
INT1_ENABLE |
(PCIE0 &
PCMSK03)
0
ADC2D |
(PCIE0 & PCMSK02)
DIEOV
INT1_ENABLE |
(PCIE0 &
PCMSK03)
PCIE0 & PCMSK02
PCIE0 & PCMSK01
PCIE0 & PCMSK00
DI
PCINT3 -/- INT1
PCINT2 -/- MISO
PCINT1
PCINT0
AIO
ADC3 -/- ISRC
ADC2
ADC1
ADC0
ADC1D |
ADC0D |
(PCIE0 & PCMSK01) (PCIE0 & PCMSK00)
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
9.3.4
Alternate Functions of Port B
The Port B pins with alternate functions are shown in Table 9-6.
Table 9-6.
Port Pin
Port B Pins Alternate Functions
Alternate Functions
PB7
PCINT15 (Pin Change Interrupt 15)
ADC10 (ADC Input Channel 10)
OC1BX (Output Compare and PWM Output B-X for Timer/Counter1)
RESET (Reset input pin)
dW (debugWIRE I/O)
PB6
PCINT14 (Pin Change Interrupt 14)
ADC9 (ADC Input Channel 9)
OC1AX (Output Compare and PWM Output A-X for Timer/Counter1)
INT0 (External Interrupt0 Input)
PB5
PCINT13 (Pin Change Interrupt 13)
ADC8 (ADC Input Channel 8)
OC1BW (Output Compare and PWM Output B-W for Timer/Counter1)
XTAL2 (Chip clock Oscillator pin 2)
CLKO (System clock output)
PB4
PCINT12 (Pin Change Interrupt 12)
OC1AW (Output Compare and PWM Output A-W for Timer/Counter1)
XTAL1 (Chip clock Oscillator pin 1)
CLKI (External clock input)
PB3
PCINT11 (Pin Change Interrupt 11)
OC1BV (Output Compare and PWM Output B-V for Timer/Counter1)
PB2
PCINT10 (Pin Change Interrupt 10)
OC1AV (Output Compare and PWM Output A-V for Timer/Counter1)
USCK (Three-wire Mode USI Default Clock Input)
SCL (Two-wire Mode USI Default Clock Input)
PB1
PCINT9 (Pin Change Interrupt 9)
OC1BU (Output Compare and PWM Output B-U for Timer/Counter1)
DO (Three-wire Mode USI Default Data Output)
PB0
PCINT8 (Pin Change Interrupt 8)
OC1AU (Output Compare and PWM Output A-U for Timer/Counter1)
DI (Three-wire Mode USI Default Data Input)
SDA (Two-wire Mode USI Default Data Input / Output)
The alternate pin configuration is as follows:
• PCINT15/ADC10/OC1BX/RESET/dW – Port B, Bit 7
PCINT15: Pin Change Interrupt, source 15.
ADC10: Analog to Digital Converter, channel 10.
OC1BX: Output Compare and PWM Output B-X for Timer/Counter1. The PB7 pin has to be
configured as an output (DDB7 set (one)) to serve this function. The OC1BX pin is
also the output pin for the PWM mode timer function (c.f. OC1BX bit of TCCR1D register).
81
7728D–AVR–07/09
RESET: Reset input pin. When the RSTDISBL Fuse is programmed, this pin functions as a
normal I/O pin, and the part will have to rely on Power-on Reset and Brown-out Reset
as its reset sources. When the RSTDISBL Fuse is unprogrammed, the reset circuitry
is connected to the pin, and the pin can not be used as an I/O pin.
If PB7 is used as a reset pin, DDB7, PORTB7 and PINB7 will all read 0.
dW: When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed, 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.
• PCINT14/ADC9/OC1AX/INT0 – Port B, Bit 6
PCINT14: Pin Change Interrupt, source 14.
ADC9: Analog to Digital Converter, channel 9.
OC1AX: Output Compare and PWM Output A-X for Timer/Counter1. The PB6 pin has to be
configured as an output (DDB6 set (one)) to serve this function. The OC1AX pin is
also the output pin for the PWM mode timer function (c.f. OC1AX bit of TCCR1D register).
INT0: External Interrupt0 Input. The PB6 pin can serve as an external interrupt source.
• PCINT13/ADC8/OC1BW/XTAL2/CLKO – Port B, Bit 5
PCINT13: Pin Change Interrupt, source 13.
ADC8: Analog to Digital Converter, channel 8.
OC1BW: Output Compare and PWM Output B-W for Timer/Counter1. The PB5 pin has to be
configured as an output (DDB5 set (one)) to serve this function. The OC1BW pin is
also the output pin for the PWM mode timer function (c.f. OC1BW bit of TCCR1D register).
XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency
crystal Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
CLKO: Divided system clock output. The divided system clock can be output on the PB5 pin.
The divided system clock will be output if the CKOUT Fuse is programmed, regardless
of the PORTB5 and DDB5 settings. It will also be output during reset.
• PCINT12/OC1AW/XTAL1/CLKI – Port B, Bit 4
PCINT12: Pin Change Interrupt, source 12.
OC1AW: Output Compare and PWM Output A-W for Timer/Counter1. The PB4 pin has to be
configured as an output (DDB4 set (one)) to serve this function. The OC1AW pin is
also the output pin for the PWM mode timer function (c.f. OC1AW bit of TCCR1D register).
XTAL1: Chip clock Oscillator pin 1. Used for all chip clock sources except internal calibrated
RC Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
CLKI: External clock input. When used as a clock pin, the pin can not be used as an I/O pin.
Note:
If PB4 is used as a clock pin (XTAL1 or CLKI), DDB4, PORTB4 and PINB4 will all read 0.
• PCINT11/OC1BV – Port B, Bit 3
PCINT11: Pin Change Interrupt, source 11.
OC1BV: Output Compare and PWM Output B-V for Timer/Counter1. The PB3 pin has to be
configured as an output (DDB3 set (one)) to serve this function. The OC1BV pin is
also the output pin for the PWM mode timer function (c.f. OC1BV bit of TCCR1D register).
82
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
• PCINT10/OC1AV/USCK/SCL – Port B, Bit 2
PCINT10: Pin Change Interrupt, source 10.
OC1AV: Output Compare and PWM Output A-V for Timer/Counter1. The PB2 pin has to be
configured as an output (DDB2 set (one)) to serve this function. The OC1AV pin is
also the output pin for the PWM mode timer function (c.f. OC1AV bit of TCCR1D register).
USCK: Three-wire Mode USI Clock Input.
SCL: Two-wire Mode USI Clock Input.
• PCINT9/OC1BU/DO – Port B, Bit 1
PCINT9: Pin Change Interrupt, source 9.
OC1BU: Output Compare and PWM Output B-U for Timer/Counter1. The PB1 pin has to be
configured as an output (DDB1 set (one)) to serve this function. The OC1BU pin is
also the output pin for the PWM mode timer function (c.f. OC1BU bit of TCCR1D register).
DO: Three-wire Mode USI Data Output. Three-wire mode data output overrides PORTB1
and it is driven to the port when the data direction bit DDB1 is set. PORTB1 still
enables the pull-up, if the direction is input and PORTB1 is set (one).
• PCINT8/OC1AU/DI/SDA – Port B, Bit 0
IPCINT8: Pin Change Interrupt, source 8.
OC1AU: Output Compare and PWM Output A-U for Timer/Counter1. The PB0 pin has to be
configured as an output (DDB0 set (one)) to serve this function. The OC1AU pin is
also the output pin for the PWM mode timer function (c.f. OC1AU bit of TCCR1D register).
DI: Three-wire Mode USI Data Input. USI Three-wire mode does not override normal port
functions, so pin must be configure as an input for DI function.
SDA: Two-wire Mode Serial Interface (USI) Data Input / Output.
83
7728D–AVR–07/09
Table 9-7 and Table 9-8 relate the alternate functions of Port B to the overriding signals shown
in Figure 9-6 on page 73.
Table 9-7.
Signal
Name
84
Overriding Signals for Alternate Functions in PB7..PB4
PB7/PCINT15/ADC10
PB5/PCINT13/ADC8/
/
PB6/PCINT14/ADC9/ OC1BW/XTAL2/CLK
PB4/PCINT12/
OC1BX/RESET/dW
OC1AX/INT0
O
OC1AW/XTAL1/CLKI
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
OC1B_ENABLE &
OC1BX
OC1A_ENABLE &
OC1AX
OC1B_ENABLE &
OC1BW
OC1A_ENABLE &
OC1AW
PVOV
OC1B
OC1A
OC1B
OC1A
PTOE
0
0
0
0
DIEOE
ADC10D |
(PCIE1 & PCMSK15)
ADC9D |
INT0_ENABLE |
(PCIE1 & PCMSK14)
ADC8D |
(PCIE1 & PCMSK13)
(PCIE1 & PCMSK13)
DIEOV
PCIE1 & PCMSK15
INT0_ENABLE |
(PCIE1 & PCMSK14)
PCIE1 & PCMSK13
1
DI
PCINT15
PCINT14 -/- INT1
PCINT13
PCINT12
AIO
RESET -/- ADC10 -/-
ADC9 -/- ISRC
ADC8 -/- XTAL2
XTAL1 -/- CLKI
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Table 9-8.
Overriding Signals for Alternate Functions in PB3..PB0
Signal
Name
PB3/PCINT11/
OC1BV
PB2/PCINT10/
OC1AV/USCK/SCL
PB1/PCINT9/
OC1BU/DO
PB0/IPCINT8/
OC1AU/DI/SDA
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
(USI_2_WIRE &
USIPOS)
0
(USI_2_WIRE &
USIPOS)
DDOV
0
(USI_SCL_HOLD |
PORTB2)
& DDRB2
0
(USI_SHIFTOUT |
PORTB0) & DDRB0)
PVOE
OC1B_ENABLE
&
OC1BV
(USI_2_WIRE &
USIPOS &
DDRB2) |
(OC1A_ENABLE &
OC1AV)
(USI_2_WIRE &
USI_3_WIRE &
USIPOS) |
(OC1B_ENABLE &
OC1BU)
(USI_2_WIRE &
USIPOS &
DDRB0) |
(OC1A_ENABLE &
OC1AU)
PVOV
OC1B
{ (USI_2_WIRE &
USIPOS &
DDRB2) ?
(0) : (OC1A) }
{ (USI_2_WIRE &
USI_3_WIRE &
USIPOS) ?
(USI_SHIFTOUT) :
(OC1B) }
{ (USI_2_WIRE &
USIPOS &
DDRB0) ?
(0) : (OC1A) }
PTOE
0
USI_PTOE & USIPOS
0
0
DIEOE
PCIE1 &
PCMSK11
(USISIE & USIPOS) |
(PCIE1 & PCMSK10)
PCIE1 & PCMSK9
(USISIE & USIPOS) |
(PCIE1 & PCMSK8)
DIEOV
1
(USISIE & USIPOS) |
(PCIE1 & PCMSK10)
1
(USISIE & USIPOS) |
(PCIE1 & PCMSK8)
DI
PCINT11
PCINT10 -/- USCK -/SCL
PCINT9
PCINT8 -/- DI -/- SDA
AIO
0
0
0
0
85
7728D–AVR–07/09
9.4
9.4.1
Register Description for I/O Ports
Port A Data Register – PORTA
Bit
9.4.2
7
6
5
4
3
2
1
0
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Port A Data Direction Register – DDRA
Bit
9.4.3
7
6
5
4
3
2
1
0
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
7
6
5
4
3
2
1
0
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Read/Write
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
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
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
DDRB
Port B Input Pins Register – PINB
Bit
86
PORTB
Port B Data Direction Register – DDRB
Bit
9.4.6
PINA
Port B Data Register – PORTB
Bit
9.4.5
DDRA
Port A Input Pins Register – PINA
Bit
9.4.4
PORTA
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
PINB
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
10. 8-bit Timer/Counter0 and Asynchronous Operation
Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The main
features are:
10.1
Features
•
•
•
•
•
•
•
10.2
Single Channel Counter
Clear Timer on Compare Match (Auto Reload)
Glitch-free, Phase Correct Pulse Width Modulator (PWM)
Frequency Generator
10-bit Clock Prescaler
Overflow and Compare Match Interrupt Sources (TOV0 and OCF0A)
Allows Clocking from External Crystal (i.e. 32 kHz Watch Crystal) Independent of the I/O Clock
Overview
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. 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.
• A lower case “x” replaces the Output Compare unit channel, in this case A. However, when
using the register or bit defines in a program, the precise form must be used, i.e., OCR0A
for accessing Timer/Counter0 output compare channel A value and so on.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 10-1. For the actual
placement of I/O pins, refer to “Pin Configuration” on page 5. 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 100.
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Figure 10-1. 8-bit Timer/Counter0 Block Diagram
TCCRnx
count
TOVn
(Int.Req.)
clear
Control Logic
direction
clkTn
XTAL2
BOTTOM
TOP
Oscillator
Prescaler
XTAL1
Timer/Counter
TCNTn
=0
= 0xFF
DATA BUS
OCnx
(Int.Req.)
Waveform
Generation
=
clk I/O
OCnx
OCRnx
Synchronized Status flags
clk I/O
Synchronization Unit
clk ASY
Status flags
ASSRn
asynchronous mode
select (ASn)
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers. Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register
(TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Register
(TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked
from the XTAL1/2 pins, as detailed later in this section. The asynchronous operation is controlled by the Asynchronous Status Register (ASSR). The Clock Select logic block controls
which clock source 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 Register (OCR0A) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pin (OC0A). See ”Output
Compare Unit” on page 90. for details. The compare match event will also set the compare
flag (OCF0A) which can be used to generate an Output Compare interrupt request.
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10.2.1
Definitions
The following definitions are used extensively throughout the section:
10.3
BOTTOM
The counter reaches the BOTTOM when it becomes zero (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 synchronous or an external asynchronous
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 (TCCR0).The clock
source clkT0 is by default equal to the MCU clock, clkI/O. When the AS0 bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter Oscillator
connected to XTAL1 and XTAL2 or directly from XTAL1. For details on asynchronous operation, see “Asynchronous Status Register – ASSR” on page 103. For details on clock sources
and prescaler, see “Timer/Counter0 Prescaler” on page 100.
10.4
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 10-2 shows a block diagram of the counter and its surrounding environment.
Figure 10-2. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
XTAL2
count
TCNTn
clear
clk Tn
Control Logic
Prescaler
clk TnS
Oscillator
direction
bottom
XTAL1
top
clkI/O
Signal description (internal signals):
count
Increment or decrement TCNT0 by 1.
direction
Selects between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clkT0
Timer/Counter0 clock.
top
Signalizes that TCNT0 has reached maximum value.
bottom
Signalizes that TCNT0 has reached minimum value (zero).
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Depending on 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). 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 92.
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.
10.5
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Register
(OCR0A). Whenever TCNT0 equals OCR0A, the comparator signals a match. A match will set
the Output Compare Flag (OCF0A) at the next timer clock cycle. If enabled (OCIE0A = 1), the
Output Compare Flag generates an Output Compare interrupt. The OCF0A flag is automatically cleared when the interrupt is executed. Alternatively, the OCF0A 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 WGM01:0 bits and
Compare Output mode (COM0A1:0) 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 (“Modes of Operation” on page 92).
Figure 10-3 shows a block diagram of the Output Compare unit.
Figure 10-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator )
OCFnx (Int.Req.)
top
bottom
Waveform Generator
OCnx
FOCn
WGMn1:0
90
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The OCR0A Register is 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 OCR0A
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 OCR0A Register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has access to the OCR0A Buffer Register, and if double buffering is
disabled the CPU will access the OCR0A directly.
10.5.1
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced
by writing a one to the Force Output Compare (FOC0A) bit. Forcing compare match will not
set the OCF0A flag or reload/clear the timer, but the OC0A pin will be updated as if a real compare match had occurred (the COM0A1:0 bits settings define whether the OC0A pin is set,
cleared or toggled).
10.5.2
Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any compare match that occurs in
the next timer clock cycle, even when the timer is stopped. This feature allows OCR0A to be
initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter
clock is enabled.
10.5.3
Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one timer
clock cycle, there are risks involved when changing TCNT0 when using the Output Compare
channel, independently of whether the Timer/Counter is running or not. If the value written to
TCNT0 equals the OCR0A 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 downcounting.
The setup of the OC0A should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0A value is to use the Force Output Compare (FOC0A) strobe bit in Normal mode. The OC0A Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM0A1:0 bits are not double buffered together with the compare value.
Changing the COM0A1:0 bits will take effect immediately.
10.6
Compare Match Output Unit
The Compare Output mode (COM0A1:0) bits have two functions. The Waveform Generator
uses the COM0A1:0 bits for defining the Output Compare (OC0A) state at the next compare
match. Also, the COM0A1:0 bits control the OC0A pin output source. Figure 10-4 shows a
simplified schematic of the logic affected by the COM0A1:0 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 COM0A1:0 bits are shown. When referring
to the OC0A state, the reference is for the internal OC0A Register, not the OC0A pin.
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Figure 10-4. Compare Match Output Logic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
10.6.1
Compare Output Function
The general I/O port function is overridden by the Output Compare (OC0A) from the Waveform Generator if either of the COM0A1:0 bits are set. However, the OC0A 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 OC0A pin (DDR_OC0A) must be set as output before the OC0A
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 OC0A state before the
output is enabled. Note that some COM0A1:0 bit settings are reserved for certain modes of
operation. See ”8-bit Timer/Counter Register Description” on page 100.
10.6.2
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0A1:0 bits differently in normal, CTC, and PWM
modes. For all modes, setting the COM0A1:0 = 0 tells the Waveform Generator that no action
on the OC0A Register is to be performed on the next compare match. For compare output
actions in the non-PWM modes refer to Table 10-1 on page 101. For fast PWM mode, refer to
Table 10-2 on page 101, and for phase correct PWM refer to Table 10-3 on page 101.
A change of the COM0A1:0 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 FOC0A strobe bits.
10.7
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins,
is defined by the combination of the Waveform Generation mode (WGM01:0) and Compare
Output mode (COM0A1:0) bits. The Compare Output mode bits do not affect the counting
sequence, while the Waveform Generation mode bits do. The COM0A1:0 bits control whether
the PWM output generated should be inverted or not (inverted or non-inverted PWM). For
non-PWM modes the COM0A1:0 bits control whether the output should be set, cleared, or toggled at a compare match (See ”Compare Match Output Unit” on page 91.).
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For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 97.
10.7.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM01:0 = 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.
10.7.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM01:0 = 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 10-5. The counter value (TCNT0)
increases until a compare match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 10-5. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCnx
(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 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 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.
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For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical level on each compare match by setting the Compare Output mode bits to toggle mode
(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction
for the pin is set to output. The waveform generated will have a maximum frequency of fOC0A =
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, 32, 64, 128, 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.
10.7.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM01:0 = 3) 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 MAX then restarts from BOTTOM.
In non-inverting Compare Output mode, the Output Compare (OC0A) is cleared on the compare match between TCNT0 and OCR0A, 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 uses 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 MAX value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 10-6. The TCNT0 value is in the timing diagram shown as a
histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0A and TCNT0.
Figure 10-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
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2
3
4
5
6
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The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches MAX. 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 OC0A pin.
Setting the COM0A1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM0A1:0 to three (See Table 10-2 on page 101). The
actual OC0A 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 OC0A Register at the
compare match between OCR0A and TCNT0, and clearing (or setting) the OC0A Register at
the timer clock cycle the counter is cleared (changes from MAX 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, 32, 64, 128, 256, or 1024).
The extreme values for the OCR0A Register represent 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 OC0A to toggle its logical level on each compare match (COM0A1:0 = 1). The waveform generated will have a maximum frequency of foc0A = 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.
10.7.4
Phase Correct PWM Mode
The phase correct PWM mode (WGM01:0 = 1) 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 MAX and then from MAX to BOTTOM.
In non-inverting Compare Output mode, the Output Compare (OC0A) is cleared on the compare match between TCNT0 and OCR0A 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 is fixed to eight bits. In phase correct
PWM mode the counter is incremented until the counter value matches MAX. When the counter reaches MAX, it changes the count direction. The TCNT0 value will be equal to MAX for
one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 10-7. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the
dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The
small horizontal line marks on the TCNT0 slopes represent compare matches between
OCR0A and TCNT0.
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Figure 10-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(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
OC0A pin. Setting the COM0A1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0A1:0 to three (See Table 10-3 on page
101). The actual OC0A 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 OC0A Register at the compare match between OCR0A and TCNT0 when the counter increments, and
setting (or clearing) the OC0A Register at compare match between OCR0A 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, 32, 64, 128, 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.
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10.8
Timer/Counter Timing Diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock
(clkT0) is therefore shown as a clock enable signal. In asynchronous mode, clkI/O should be
replaced by the Timer/Counter Oscillator clock. The figures include information on when interrupt flags are set. Figure 10-8 contains timing data for basic Timer/Counter operation. The
figure shows the count sequence close to the MAX value in all modes other than phase correct
PWM mode.
Figure 10-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 10-9 shows the same timing data, but with the prescaler enabled.
Figure 10-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 10-10 shows the setting of OCF0A in all modes except CTC mode.
Figure 10-10. Timer/Counter Timing Diagram, Setting of OCF0A, 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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Figure 10-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode.
Figure 10-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with
Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP
OCRnx
OCFnx
10.9
Asynchronous Operation of Timer/Counter0
When Timer/Counter0 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter0, the timer registers TCNT0, OCR0A, and TCCR0A might be corrupted. A
safe procedure for switching clock source is:
a. Disable the Timer/Counter0 interrupts by clearing OCIE0A and TOIE0.
b.
Select clock source by setting AS0 and EXCLK as appropriate.
c.
Write new values to TCNT0, OCR0A, and TCCR0A.
d. To switch to asynchronous operation: Wait for TCN0UB, OCR0UB, and TCR0UB.
e. Clear the Timer/Counter0 interrupt flags.
f.
Enable interrupts, if needed.
• If an 32.768 kHz watch crystal is used, the CPU main clock frequency must be more than
four times the Oscillator or external clock frequency.
• When writing to one of the registers TCNT0, OCR0A, or TCCR0A, the value is transferred
to a temporary register, and latched after two positive edges on TOSC1. The user should
not write a new value before the contents of the temporary register have been transferred
to its destination. Each of the three mentioned registers have their individual temporary
register, which means that e.g. writing to TCNT0 does not disturb an OCR0A write in
progress. To detect that a transfer to the destination register has taken place, the
Asynchronous Status Register – ASSR has been implemented.
• When entering Power-save mode after having written to TCNT0, OCR0A, or TCCR0A, the
user must wait until the written register has been updated if Timer/Counter0 is used to
wake up the device. Otherwise, the MCU will enter sleep mode before the changes are
effective. This is particularly important if the Output Compare0 interrupt is used to wake up
the device, since the Output Compare function is disabled during writing to OCR0A or
TCNT0. If the write cycle is not finished, and the MCU enters sleep mode before the
OCR0UB bit returns to zero, the device will never receive a compare match interrupt, and
the MCU will not wake up.
• If Timer/Counter0 is used to wake the device up from Power-save mode, precautions must
be taken if the user wants to re-enter one of these modes: The interrupt logic needs one
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TOSC1 cycle to be reset. If the time between wake-up and re-entering sleep mode is less
than one TOSC1 cycle, the interrupt will not occur, and the device will fail to wake up. If the
user is in doubt whether the time before re-entering Power-save mode is sufficient, the
following algorithm can be used to ensure that one TOSC1 cycle has elapsed:
a. Write a value to TCCR0A, TCNT0, or OCR0A.
b.
Wait until the corresponding Update Busy flag in ASSR returns to zero.
c.
Enter Power-save or ADC Noise Reduction mode.
• When the asynchronous operation is selected, the oscillator for Timer/Counter0 is always
running, except in Power-down mode. After a Power-up Reset or wake-up from
Power-down mode, the user should be aware of the fact that this oscillator might take as
long as one second to stabilize. The user is advised to wait for at least one second before
using Timer/Counter0 after power-up or wake-up from Power-down mode. The contents of
all Timer/Counter0 Registers must be considered lost after a wake-up from Power-down
mode due to unstable clock signal upon start-up, no matter whether the oscillator is in use
or a clock signal is applied to the XTAL1 pin.
• Description of wake up from Power-save mode when the timer is clocked asynchronously:
When the interrupt condition is met, the wake up process is started on the following cycle of
the timer clock, that is, the timer is always advanced by at least one before the processor
can read the counter value. After wake-up, the MCU is halted for four cycles, it executes
the interrupt routine, and resumes execution from the instruction following SLEEP.
• Reading of the TCNT0 Register shortly after wake-up from Power-save may give an
incorrect result. Since TCNT0 is clocked on the asynchronous clock, reading TCNT0 must
be done through a register synchronized to the internal I/O clock domain (CPU main clock).
Synchronization takes place for every rising XTAL1 edge. When waking up from
Power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT0 will read as the
previous value (before entering sleep) until the next rising XTAL1 edge. The phase of the
XTAL1 clock after waking up from Power-save mode is essentially unpredictable, as it
depends on the wake-up time. The recommended procedure for reading TCNT0 is thus as
follows:
a. Write any value to either of the registers OCR0A or TCCR0A.
b.
Wait for the corresponding Update Busy Flag to be cleared.
c.
Read TCNT0.
• During asynchronous operation, the synchronization of the interrupt flags for the
asynchronous timer takes 3 processor cycles plus one timer cycle. The timer is therefore
advanced by at least one before the processor can read the timer value causing the setting
of the interrupt flag. The Output Compare pin is changed on the timer clock and is not
synchronized to the processor clock.
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10.10 Timer/Counter0 Prescaler
Figure 10-12. Prescaler for Timer/Counter0
clkTnS
clkTnS/8
1
XTAL1
1
clkTnS/1024
10-BIT T/C PRESCALER
Clear
clkTnS/256
0
clkTnS/128
0
clkTnS/64
Oscillator
clkTnS/32
clkI/O
XTAL2
ASn
EXCLK
0
PSRn
CSn0
CSn1
CSn2
TIMER/COUNTERn CLOCK SOURCE
clkTn
The clock source for Timer/Counter0 is named clkT0S. clkT0S is by default connected to the
main system I/O clock clkIO. By setting the AS0 bit in ASSR, Timer/Counter0 is asynchronously clocked from the XTAL oscillator or XTAL1 pin. This enables use of Timer/Counter0 as
a Real Time Counter (RTC).
A crystal can then be connected between the XTAL1 and XTAL2 pins to serve as an independent clock source for Timer/Counter0.
A external clock can also be used using XTAL1 as input. Setting AS0 and EXCLK enables this
configuration.
For Timer/Counter0, the possible prescaled selections are: clkT0S/8, clkT0S/32, clkT0S/64,
clk T 0S /128, clk T 0S /256, and clk T 0 S /1024. Additionally, clkT 0S as well as 0 (stop) may be
selected. Setting the PSR0 bit in GTCCR resets the prescaler. This allows the user to operate
with a predictable prescaler.
10.11 8-bit Timer/Counter Register Description
• Timer/Counter0 Control Register A – TCCR0A
Bit
7
6
5
4
3
2
1
0
COM0A1
COM0A0
–
–
–
–
WGM01
WGM00
Read/Write
R/W
R/W
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0A
• Bit 7:6 – COM0A1:0: Compare Match Output Mode A
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 OC0A
pin must be set in order to enable the output driver.
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When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM01:0 bit setting. Table 10-1 shows the COM0A1:0 bit functionality when the WGM01:0
bits are set to a normal or CTC mode (non-PWM).
Table 10-1.
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 10-2 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Table 10-2.
Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0A0
Description
0
0
0
1
1
0
Clear OC0A on Compare Match.
Set OC0A at BOTTOM (non-inverting mode).
1
1
Set OC0A on Compare Match.
Clear OC0A at BOTTOM (inverting mode).
Normal port operation, OC0A disconnected.
Note:
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
94 for more details.
Table 10-3 shows the COM01:0 bit functionality when the WGM01:0 bits are set to phase correct PWM mode.
Table 10-3.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
Description
0
0
0
1
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.
Normal port operation, OC0A disconnected.
Note:
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 95 for more details.
• Bit 5:2 – Res: Reserved Bits
These bits are reserved in the ATtiny87/167 and will always read as zero.
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• Bit 6, 3 – WGM01:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used, see Table 10-4. 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 92.).
Table 10-4.
Waveform Generation Mode Bit Description
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter
Mode of Operation
TOP
Update of
OCR0A at
TOV0 Flag
Set on(1)(2)
0
0
0
Normal
0xFF
Immediate
MAX
1
0
1
PWM, Phase Correct
0xFF
TOP
BOTTOM
2
1
0
CTC
OCR0A
Immediate
MAX
3
1
1
Fast PWM
0xFF
TOP
MAX
Notes:
1. MAX = 0xFF,
2. BOTTOM = 0x00.
10.11.1
Timer/Counter0 Control Register B – TCCR0B
Bit
7
6
5
4
3
2
1
0
FOC0A
–
–
–
–
CS02
CS01
CS00
Read/Write
W
R
R
R
R
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 6:3 – Res: Reserved Bits
These bits are reserved in the ATtiny87/167 and will always read as zero.
• Bit 2:0 – CS02:0: Clock Select
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The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Table 10-5.
Table 10-5.
10.11.2
Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clkT0S (No prescaling)
0
1
0
clkT0S/8 (From prescaler)
0
1
1
clkT0S/32 (From prescaler)
1
0
0
clkT0S/64 (From prescaler)
1
0
1
clkT0S/128 (From prescaler)
1
1
0
clkT0S/256 (From prescaler)
1
1
1
clkT0S/1024 (From prescaler)
Timer/Counter0 Register – TCNT0
Bit
7
6
5
4
3
2
1
0
TCNT07
TCNT06
TCNT05
TCNT04
TCNT03
TCNT02
TCNT01
TCNT00
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCNT0
The Timer/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
Register.
10.11.3
Output Compare Register A – OCR0A
Bit
Read/Write
Initial Value
7
OCR0A7
R/W
0
6
OCR0A6
R/W
0
5
OCR0A5
R/W
0
4
OCR0A4
R/W
0
3
OCR0A3
R/W
0
2
OCR0A2
R/W
0
1
OCR0A1
R/W
0
0
OCR0A0
R/W
0
OCR0A
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.
10.11.4
Asynchronous Status Register – ASSR
Bit
7
6
5
4
3
2
1
0
–
EXCLK
AS0
TCN0UB
OCR0AUB
–
TCR0AUB
TCR0BUB
Read/Write
R
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
ASSR
• Bit 7 – Res: Reserved Bit
This bit is reserved in the ATtiny87/167 and will always read as zero.
• Bit 6 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input
buffer is enabled and an external clock can be input on XTAL1 pin instead of an external crystal. Writing to EXCLK should be done before asynchronous operation is selected. Note that
the crystal oscillator will only run when this bit is zero.
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• Bit 5 – AS0: Asynchronous Timer/Counter0
When AS0 is written to zero, Timer/Counter0 is clocked from the I/O clock, clkI/O and the
Timer/Counter0 acts as a synchronous peripheral.
When AS0 is written to one, Timer/Counter0 is clocked from the low-frequency crystal oscillator (See ”Low-frequency Crystal Oscillator” on page 29.) or from external clock on XTAL1 pin
(See ”External Clock” on page 30.) depending on EXCLK setting. When the value of AS0 is
changed, the contents of TCNT0, OCR0A, and TCCR0A might be corrupted.
AS0 also acts as a flag: Timer/Counter0 is clocked from the low-frequency crystal or from
external clock ONLY IF the calibrated internal RC oscillator or the internal watchdog oscillator
is used to drive the system clock. After setting AS0, if the switching is available, AS0 remains
to 1, else it is forced to 0.
• Bit 4 – TCN0UB: Timer/Counter0 Update Busy
When Timer/Counter0 operates asynchronously and TCNT0 is written, this bit becomes set.
When TCNT0 has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCNT0 is ready to be updated with a new
value.
• Bit 3 – OCR0AUB: Output Compare 0 Register A Update Busy
When Timer/Counter0 operates asynchronously and OCR0A is written, this bit becomes set.
When OCR0A has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that OCR0A is ready to be updated with a new
value.
• Bit 2 – Res: Reserved Bit
This bit is reserved in the ATtiny87/167 and will always read as zero.
• Bit 1 – TCR0AUB: Timer/Counter0 Control Register A Update Busy
When Timer/Counter0 operates asynchronously and TCCR0A is written, this bit becomes set.
When TCCR0A has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCCR0A is ready to be updated with a new
value.
• Bit 0 – TCR0BUB: Timer/Counter0 Control Register B Update Busy
When Timer/Counter0 operates asynchronously and TCCR0B is written, this bit becomes set.
When TCCR0B has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCCR0B is ready to be updated with a new
value.
If a write is performed to any of the four Timer/Counter0 Registers while its update busy flag is
set, the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT0, OCR0A, TCCR0A and TCCR0B are different. When
reading TCNT0, the actual timer value is read. When reading OCR0A, TCCR0A or TCCR0B
the value in the temporary storage register is read.
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10.11.5
Timer/Counter0 Interrupt Mask Register – TIMSK0
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
OCIE0A
TOIE0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK0
• Bit 7:2 – Res: Reserved Bits
These bits are reserved in the ATtiny87/167 and will always read as zero.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one and the I-bit in the Status Register is set (one), 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/Counter0 Interrupt Flag Register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one and the I-bit in the Status Register is set (one), 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/Counter0 Interrupt Flag Register – TIFR0.
10.11.6
Timer/Counter0 Interrupt Flag Register – TIFR0
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
–
OCF0A
TOV0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR0
• Bit 7:2 – Res: Reserved Bits
These bits are reserved in the ATtiny87/167 and will always read as zero.
• Bit 1 – OCF0A: Output Compare Flag 0 A
The OCF0A bit is set (one) when a compare match occurs between the Timer/Counter0 and
the data in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A is cleared by writing a
logic one to the flag. When the I-bit in SREG, OCIE0 (Timer/Counter0 Compare match Interrupt Enable), and OCF0A are set (one), the Timer/Counter0 Compare match Interrupt is
executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The TOV0 bit is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared by
hardware when executing the corresponding interrupt handling vector. Alternatively, TOV0 is
cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0A (Timer/Counter0
Overflow Interrupt Enable), and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is
executed. In PWM mode, this bit is set when Timer/Counter0 changes counting direction at
0x00.
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10.11.7
General Timer/Counter Control Register – GTCCR
Bit
7
6
5
4
3
2
1
0
TSM
–
–
–
–
–
PSR0
PSR1
Read/Write
R/W
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bit 1 – PSR0: Prescaler Reset Timer/Counter0
When this bit is one, the Timer/Counter0 prescaler will be reset. This bit is normally cleared
immediately by hardware. If the bit is written when Timer/Counter0 is operating in asynchronous mode, the bit will remain one until the prescaler has been reset. The bit will not be
cleared by hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM:
Timer/Counter Synchronization Mode” on page 109 for a description of the Timer/Counter
Synchronization mode.
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11. Timer/Counter1 Prescaler
11.1
Overview
Most bit references in this section are written in general form. A lower case “n” replaces the
Timer/Counter number.
11.1.1
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.
11.1.2
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/Counter. Since the prescaler is not affected by the Timer/Counter’s clock select, the
state of the prescaler will have implications for situations where a prescaled clock is used. One
example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler
(6 > CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to the
first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler
divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution. 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.
11.1.3
External Clock Source
An external clock source applied to the T1 pin can be used as Timer/Counter clock (clkT1).
The T1 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 11-1 shows a
functional equivalent block diagram of the T1 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 clk T1 pulse for each positive (CSn2:0 = 7) or negative
(CSn2:0 = 6) edge it detects.
Figure 11-1. T1 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
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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 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T1 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is
generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the
system clock frequency (fExtClk < fclk_I/O/2) given a 50/50 % duty cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the
sampling frequency (Nyquist sampling theorem). However, due to variation of the system
clock frequency and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an external clock source is
less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 11-2. Prescaler for Timer/Counter1 (1)
10-BIT T/C PRESCALER
CLKI/O
CK/1024
CK/256
PSRn
CK/64
CK/8
Clear
0
Tn
Synchronization
CSn0
CSn1
CSn2
clkTn
TIMER/COUNTERn CLOCK SOURCE
Note:
108
1. The synchronization logic on the input pin (T1) is shown in Figure 11-1.
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
11.2
11.2.1
Timer/Counter1 Prescalers Register Description
General Timer/Counter Control Register – GTCCR
Bit
7
6
5
4
3
2
1
0
TSM
–
–
–
–
–
PSR0
PSR1
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode,
the value that is written to the PSR0 and PSR1 bits is kept, hence keeping the corresponding
prescaler reset signals asserted. This ensures that the corresponding Timer/Counters are
halted and can be configured to the same value without the risk of one of them advancing during configuration. When the TSM bit is written to zero, the PSR0 and PSR1 bits are cleared by
hardware, and the Timer/Counters start counting simultaneously.
• Bit 0 – PSR1: Prescaler Reset Timer/Counter1
When this bit is one, Timer/Counter1 prescaler will be reset. This bit is normally cleared immediately by hardware, except if the TSM bit is set.
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12. 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:
12.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
12.2
True 16-bit Design (i.e., Allows 16-bit PWM)
Two independent Output Compare Units
Four Controlled Output Pins per Output Compare Unit
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
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 1. 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 lower case “x” replaces the Output Compare unit channel, in this case A or B. However,
when using the register or bit defines in a program, the precise form must be used, i.e.,
OCR1A for accessing Timer/Counter1 output compare channel A value and so on.
• A lower case “i” replaces the index of the Output Compare output pin, in this case U, V, W
or X. However, when using the register or bit defines in a program, the precise form must
be used.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 12-1. For the actual
placement of I/O pins, refer to “Pin Configuration” on page 5. 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 132.
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Figure 12-1. 16-bit Timer/Counter1 Block Diagram(1)
Count
TOVn
(Int.Req.)
Clear
Direction
Control Logic
clk Tn
Clock Select
Edge
Detector
TOP
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCFnA
(Int.Req.)
Waveform
Generation
=
OCRnA
OCnAU
OCnAV
Fixed
TOP
Values
DATABUS
Tn
BOTTOM
OCnAW
OCFnB
(Int.Req.)
Waveform
Generation
=
OCRnB
OCnAX
OCnBU
OCnBV
OCnBW
OCnBX
( From Analog Comparator Ouput )
ICFn (Int.Req.)
Edge
Detector
ICRn
Noise
Canceler
ICPn
TCCRnA
Note:
12.2.1
TCCRnB
TCCRnC
1. Refer to Figure 1-2 on page 5, Table 9-6 on page 81, and Table 9-3 on page 76 for
Timer/Counter1 pin placement and description.
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 112. 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 (TIFR1). All interrupts are individually
masked with the Timer Interrupt Mask Register (TIMSK1). TIFR1 and TIMSK1 are not shown
in the figure.
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The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source
on the Tn 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 (clkTn).
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 pins See
”Output Compare Units” on page 119.. 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
”AnaComp - Analog Comparator” on page 211.). The Input Capture unit includes a digital filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be
defined by either the OCR1A Register, the ICR1 Register, or by a set of fixed values. When
using OCR1A as TOP value in a PWM mode, the OCR1A Register can not be used for generating a PWM output. However, the TOP value will in this case be double buffered allowing the
TOP value to be changed in run time. If a fixed TOP value is required, the ICR1 Register can
be used as an alternative, freeing the OCR1A to be used as PWM output.
12.2.2
Definitions
The following definitions are used extensively throughout the section:
12.3
BOTTOM
The counter reaches the BOTTOM when it becomes 0x0000.
MAX
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65,535).
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.
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.
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12.3.1
Code Examples
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.
Assembly Code Examples(1)
...
; Set TCNT1 to 0x01FF
ldi
r17,0x01
ldi
r16,0xFF
sts
TCNT1H,r17
sts
TCNT1L,r16
; Read TCNT1 into r17:r16
lds
r16,TCNT1L
lds
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.
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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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
lds
r16,TCNT1L
lds
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 */
_CLI();
/* 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.
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
sts
TCNT1H,r17
sts
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 */
_CLI();
/* 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.
The assembly code example requires that the r17:r16 register pair contains the value to be
written to TCNT1.
12.3.2
12.4
Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. However, note that the same rule of
atomic operation described previously also applies in this case.
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/Counter1 Prescaler” on page 107.
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12.5
Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter
unit. Figure 12-2 shows a block diagram of the counter and its surroundings.
Figure 12-2. Counter Unit Block Diagram
DATA BUS (8-bit)
TOVn
(Int.Req.)
TEMP (8-bit)
Clock Select
Count
TCNTnH (8-bit)
TCNTnL (8-bit)
Clear
Direction
TCNTn (16-bit Counter)
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 how waveforms
are generated on the Output Compare outputs OC1A/B. For more details about advanced
counting sequences and waveform generation, see “Modes of Operation” on page 122.
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The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected
by the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt.
12.6
Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events and
give them a time-stamp indicating time of occurrence. The external signal indicating an event,
or multiple events, can be applied via the ICP1 pin or alternatively, via the analog-comparator
unit. The time-stamps can then be used to calculate frequency, duty-cycle, and other features
of the signal applied. Alternatively the time-stamps can be used for creating a log of the
events.
The Input Capture unit is illustrated by the block diagram shown in Figure 12-3. The elements
of the block diagram that are not directly a part of the Input Capture unit are gray shaded.
Figure 12-3. Input Capture Unit Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
ICRnH (8-bit)
WRITE
ICRnL (8-bit)
TCNTnH (8-bit)
ICRn (16-bit Register)
ACIC
TCNTnL (8-bit)
TCNTn (16-bit Counter)
ICNCn
ICESn
Noise
Canceler
Edge
Detector
ICPn
ICF1n (Int.Req.)
ACO
Analog
Comparator
When a change of the logic level (an event) occurs on the Input Capture pin (ICP1), alternatively on the Analog Comparator output (ACO), and this change confirms to the setting of the
edge detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the
counter (TCNT1) is written to the Input Capture Register (ICR1). The Input Capture Flag
(ICF1) is set at the same system clock as the TCNT1 value is copied into ICR1 Register. If
enabled (ICIE1 = 1), the Input Capture Flag generates an Input Capture interrupt. The ICF1
flag is automatically cleared when the interrupt is executed. Alternatively the ICF1 flag can be
cleared by software by writing a logical one to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICR1) is done by first reading the low
byte (ICR1L) and then the high byte (ICR1H). When the low byte is read the high byte is copied into the high byte temporary register (TEMP). When the CPU reads the ICR1H I/O location
it will access the TEMP Register.
The ICR1 Register can only be written when using a Waveform Generation mode that utilizes
the ICR1 Register for defining the counter’s TOP value. In these cases the Waveform Generation mode (WGM13:0) bits must be set before the TOP value can be written to the ICR1
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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 112.
12.6.1
Input Capture Trigger Source
The main trigger source for the Input Capture unit is the Input Capture pin (ICP1). Only
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 11-1 on page 107). The edge detector
is also identical. However, when the noise canceler is enabled, additional logic is inserted
before the edge detector, which increases the delay by four system clock cycles. Note that the
input of the noise canceler and edge detector is always enabled unless the Timer/Counter is
set in a Waveform Generation mode that uses ICR1 to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP1 pin.
12.6.2
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.
12.6.3
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICR1 Register before the next event occurs, the ICR1 will
be overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICR1 Register should be read as early in the interrupt handler routine as possible. Even though the Input Capture interrupt has relatively high
priority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.
Using the Input Capture unit in any mode of operation when the TOP value (resolution) is
actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICR1
Register has been read. After a change of the edge, the Input Capture Flag (ICF1) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency
only, the clearing of the ICF1 flag is not required (if an interrupt handler is used).
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12.7
Output Compare Units
The 16-bit comparator continuously compares TCNT1 with the Output Compare Register
(OCR1A/B). If TCNT equals OCR1A/B the comparator signals a match. A match will set the
Output Compare Flag (OCF1A/B) at the next timer clock cycle. If enabled (OCIE1A/B = 1), the
Output Compare Flag generates an Output Compare interrupt. The OCF1A/B flag is automatically cleared when the interrupt is executed. Alternatively the OCF1A/B flag can be cleared by
software by writing a logical one to its I/O bit locations. 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 (COM1A/B1:0) 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 122.)
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value
(i.e., counter resolution). In addition to the counter resolution, the TOP value defines the
period time for waveforms generated by the Waveform Generator.
Figure 12-4 shows a block diagram of the Output Compare unit. The elements of the block diagram that are not directly a part of the Output Compare unit are gray shaded.
Figure 12-4. Output Compare Unit, Block Diagram
DATA BUS (8-bit)
TEMP (8-bit)
OCRnxH Buf.(8-bit)
OCRnxL Buf.(8-bit)
TCNTnH (8-bit)
OCRnx Buffer (16-bit Register)
OCRnxH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
OCRnxL (8-bit)
OCRnx (16-bit Register)
= (16-bit Comparator )
OCFnx
TOP
BOTTOM
Waveform Generator
WGMn3:0
COMnx1:0
OCnxU
(Int.Req.)
OCnxV
OCnxW
OCnxX
The OCR1A/B 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
OCR1A/B 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.
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The OCR1A/B Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR1A/B Buffer Register, and if double buffering is disabled the CPU will access the OCR1A/B directly. The content of the OCR1A/B
(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 OCR1A/B
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 OCR1A/B Registers
must be done via the TEMP Register since the compare of all 16 bits is done continuously.
The high byte (OCR1A/BH) 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
(OCR1A/BL) is written to the lower eight bits, the high byte will be copied into the upper 8-bits
of either the OCR1A/B buffer or OCR1A/B 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 112.
12.7.1
Force Output Compare
In non-PWM Waveform Generation modes, the match output of the comparator can be forced
by writing a one to the Force Output Compare (FOC1A/B) bit. Forcing compare match will not
set the OCF1A/B flag or reload/clear the timer, but the OC1A/Bi pins will be updated as if a
real compare match had occurred (the COM1A/B1:0 bits settings define whether the OC1A/Bi
pins are set, cleared or toggled - if the respective OCnxi bit is set).
12.7.2
Compare Match Blocking by TCNT1 Write
All CPU writes to the TCNT1 Register will block any compare match that occurs in the next
timer clock cycle, even when the timer is stopped. This feature allows OCR1A/B to be initialized to the same value as TCNT1 without triggering an interrupt when the Timer/Counter clock
is enabled.
12.7.3
Using the Output Compare Unit
Since writing TCNT1 in any mode of operation will block all compare matches for one timer
clock cycle, there are risks involved when changing TCNT1 when using any of the Output
Compare channels, independent of whether the Timer/Counter is running or not. If the value
written to TCNT1 equals the OCR1A/B 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 OC1A/B should be performed before setting the Data Direction Register for
the port pin to output. The easiest way of setting the OC1A/B value is to use the Force Output
Compare (FOC1A/B) strobe bits in Normal mode. The OC1A/B Register keeps its value even
when changing between Waveform Generation modes.
Be aware that the COM1A/B1:0 bits are not double buffered together with the compare value.
Changing the COM1A/B1:0 bits will take effect immediately.
12.8
Compare Match Output Unit
The Compare Output mode (COM1A/B1:0) bits have two functions. The Waveform Generator
uses the COM1A/B1:0 bits for defining the Output Compare (OC1A/B) state at the next compare match. Secondly the COM1A/B1:0 and OCnxi bits control the OC1A/Bi pin output source.
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Figure 12-6 shows a simplified schematic of the logic affected by the COM1A/B1:0 and OCnxi
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
COM1A/B1:0 and OCnxi bits are shown. When referring to the OC1A/B state, the reference is
for the internal OC1A/B Register, not the OC1A/Bi pin. If a system reset occur, the OC1A/B
Register is reset to “0”.
Figure 12-5. Compare Match Output
OC1AU(*)
1
PORTB0
0
OC1AV(*)
1
PORTB2
0
OC1AW(*)
1
OCR1A
16-bit Register
PORTB4
COM1A0
COM1A1
OCF1A
=
Count
Clear
Direction
TCNT1
16-bit Counter
OCR1B
16-bit Register
OC1AX(*)
OCF1B
COM1B0
COM1B1
1
Waveform
Generation
FOC1A
WGM10
WGM11
WGM12
WGM13
=
0
PORTB6
0
PINB0
20 PB0 / OC1AU
DDB0
PINB2
18 PB2 / OC1AV
DDB2
PINB4
14 PB4 / OC1AW
DDB4
PINB6
12 PB6 / OC1AX
DDB6
Top
Bottom
FOC1B
Waveform
Generation
OC1BU(*)
1
PORTB1
0
OC1BV(*)
1
PORTB3
0
OC1BW(*)
1
PORTB5
0
OC1BX(*)
1
(*) OC1xi: TCCR1D register bit
PORTB7
0
PINB1
19 PB1 / OC1BU
DDB1
PINB3
17 PB3 / OC1BV
DDB3
PINB5
13 PB5 / OC1BW
DDB5
PINB7
11 PB7 / OC1BX
DDB7
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Figure 12-6. Compare Match Output Logic
OCnxi
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnxi
Pin
Q
PORT
D
Q
clk I/O
DDR
12.8.1
Compare Output Function
The general I/O port function is overridden by the Output Compare (OC1A/B) from the Waveform Generator if either of the COM1A/B1:0 bits are set and if OCnxi respective bit is set in
TCCR1D register. However, the OC1A/Bi 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 OC1A/Bi
pin (DDR_OC1A/Bi) must be set as output before the OC1A/B 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 12-1, Table 12-2 and Table 12-3 for details.
The design of the Output Compare pin logic allows initialization of the OC1A/B state before the
output is enabled. Note that some COM1A/B1:0 bit settings are reserved for certain modes of
operation. See “16-bit Timer/Counter Register Description” on page 132.
The COM1A/B1:0 bits have no effect on the Input Capture unit.
12.8.2
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM1A/B1:0 bits differently in normal, CTC, and PWM
modes. For all modes, setting the COM1A/B1:0 = 0 tells the Waveform Generator that no
action on the OC1A/B Register is to be performed on the next compare match. For compare
output actions in the non-PWM modes refer to Table 12-1 on page 132. For fast PWM mode
refer to Table 12-2 on page 133, and for phase correct and phase and frequency correct PWM
refer to Table 12-3 on page 133.
A change of the COM1A/B1:0 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 FOC1A/B strobe bits.
12.9
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 (COM1A/B1:0) bits. The Compare Output mode bits do not affect the counting
sequence, while the Waveform Generation mode bits do. The COM1A/B1:0 bits control
whether the PWM output generated should be inverted or not (inverted or non-inverted PWM).
For non-PWM modes the COM1A/B1:0 bits control whether the output should be set, cleared
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or toggle at a compare match (See ”Compare Match Output Unit” on page 120.). The OCnxi
bits over control the setting of the COM1A/B1:0 bits as shown in Figure 12-6 on page 122.
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 130.
12.9.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM13:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOV1) will be set in
the same timer clock cycle as the TCNT1 becomes zero. The TOV1 flag in this case behaves
like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV1 flag, the timer resolution can be increased by
software. There are no special cases to consider in the Normal mode, a new counter value
can be written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval between events are too long, the timer overflow interrupt or the prescaler must be used to
extend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
12.9.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1 Register
are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero
when the counter value (TCNT1) matches either the OCR1A (WGM13:0 = 4) or the ICR1
(WGM13:0 = 12). The OCR1A or ICR1 define the top value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It also
simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 12-7. The counter value (TCNT1)
increases until a compare match occurs with either OCR1A or ICR1, and then counter
(TCNT1) is cleared.
Figure 12-7. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnAi
(Toggle)
Period
(COMnA1:0 = 1)
1
2
3
4
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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) and OC1Ai is set. 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.
12.9.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM13:0 = 5, 6, 7, 14, or 15) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1A/B) is set
on the compare match between TCNT1 and OCR1A/B, 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 )
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In fast PWM mode the counter is incremented until the counter value matches either one of
the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in ICR1
(WGM13:0 = 14), or the value in OCR1A (WGM13:0 = 15). The counter is then cleared at the
following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure
12-8. 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 OCR1A/B and TCNT1.
The OC1A/B interrupt flag will be set when a compare match occurs.
Figure 12-8. 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
OCnxi
(COMnx1:0 = 2)
OCnxi
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
8
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. In addition the OC1A or ICF1 flag is set at the same timer clock cycle as TOV1 is set when either
OCR1A or ICR1 is used for defining the TOP value. If one of the interrupts are enabled, the
interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the
OCR1A/B. Note that when using fixed TOP values the unused bits are masked to zero when
any of the OCR1A/B 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.
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Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using
ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed (by changing the TOP value), using the
OCR1A as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OC1A/B
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 COM1A/B1:0 to three (see Table 12-2 on page
133). The actual OC1A/B value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is generated
by setting (or clearing) the OC1A/B Register at the compare match between OCR1A/B and
TCNT1, and clearing (or setting) the OC1A/B 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 OCR1A/B Register represents special cases when generating a
PWM waveform output in the fast PWM mode. If the OCR1A/B is set equal to BOTTOM
(0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle. Setting the
OCR1A/B equal to TOP will result in a constant high or low output (depending on the polarity
of the output set by the COM1A/B1:0 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.
12.9.4
Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGM13:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a
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
(OC1A/B) is cleared on the compare match between TCNT1 and OCR1A/B 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:
log ( TOP + 1 -)
R PCPWM = ---------------------------------log ( 2 )
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In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1
(WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer
clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 12-9.
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 OCR1A/B and TCNT1.
The OC1A/B interrupt flag will be set when a compare match occurs.
Figure 12-9. 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
OCnxi
(COMnx1:0 = 2)
OCnxi
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM.
When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 flag is set
accordingly at the same timer clock cycle as the OCR1A/B 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
OCR1A/B. Note that when using fixed TOP values, the unused bits are masked to zero when
any of the OCR1A/B Registers are written. As the third period shown in Figure 12-9 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
OCR1A/B Register. Since the OCR1A/B 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.
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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
OC1A/B pins. Setting the COM1A/B1:0 bits to two will produce a non-inverted PWM and an
inverted PWM output can be generated by setting the COM1A/B1:0 to three (See Table on
page 133). The actual OC1A/B value will only be visible on the port pin if the data direction for
the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is generated by setting (or clearing) the OC1A/B Register at the compare match between OCR1A/B
and TCNT1 when the counter increments, and clearing (or setting) the OC1A/B Register at
compare match between OCR1A/B 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 OCR1A/B Register represent special cases when generating a
PWM waveform output in the phase correct PWM mode. If the OCR1A/B is set equal to BOTTOM the output will be continuously low and if set equal to TOP the output will be continuously
high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values.
12.9.5
Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct
PWM mode (WGM13:0 = 8 or 9) provides a high resolution phase and frequency correct PWM
waveform generation option. The phase and frequency correct PWM mode is, like the phase
correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from
BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output
mode, the Output Compare (OC1A/B) is cleared on the compare match between TCNT1 and
OCR1A/B while upcounting, and set on the compare match while downcounting. In inverting
Compare Output mode, the operation is inverted. The dual-slope operation gives a lower maximum operation frequency compared to the single-slope operation. However, due to the
symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCR1A/B Register is updated by the OCR1A/B Buffer Register, (see Figure 12-9 and Figure 12-10).
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 )
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In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICR1 (WGM13:0 = 8), or the value in OCR1A (WGM13:0 = 9). The
counter has then reached the TOP and changes the count direction. The TCNT1 value will be
equal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency correct PWM mode is shown on Figure 12-10. 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 OCR1A/B and TCNT1. The OC1A/B
interrupt flag will be set when a compare match occurs.
Figure 12-10. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/TOP Update and
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnxi
(COMnx1:0 = 2)
OCnxi
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set at the same timer clock cycle as the OCR1A/B
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
OCR1A/B.
As Figure 12-10 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the OCR1A/B 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.
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In phase and frequency correct PWM mode, the compare units allow generation of PWM
waveforms on the OC1A/B pins. Setting the COM1A/B1:0 bits to two will produce a
non-inverted PWM and an inverted PWM output can be generated by setting the COM1A/B1:0
to three (See Table on page 133). The actual OC1A/B value will only be visible on the port pin
if the data direction for the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The
PWM waveform is generated by setting (or clearing) the OC1A/B Register at the compare
match between OCR1A/B and TCNT1 when the counter increments, and clearing (or setting)
the OC1A/B Register at compare match between OCR1A/B 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 OCR1A/B Register represents special cases when generating a
PWM waveform output in the phase correct PWM mode. If the OCR1A/B 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.
12.10 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 OCR1A/B Register is updated with the OCR1A/B buffer value
(only for modes utilizing double buffering). Figure 12-11 shows a timing diagram for the setting
of OCF1A/B.
Figure 12-11. Timer/Counter Timing Diagram, Setting of OCF1A/B, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 12-12 shows the same timing data, but with the prescaler enabled.
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Figure 12-12. Timer/Counter Timing Diagram, Setting of OCF1A/B, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 12-13 shows the count sequence close to TOP in various modes. When using phase
and frequency correct PWM mode the OCR1A/B Register is updated at BOTTOM. The timing
diagrams will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1
and so on. The same renaming applies for modes that set the TOV1 flag at BOTTOM.
Figure 12-13. 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
TOP - 1
TOP
TOP - 1
BOTTOM + 1
TOP - 2
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
Figure 12-14 shows the same timing data, but with the prescaler enabled.
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Figure 12-14. 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
TOP - 1
TOP
TOP - 1
BOTTOM + 1
TOP - 2
TOVn(FPWM)
and ICF n (if used
as TOP)
OCRnx
Old OCRnx Value
(Update at TOP)
New OCRnx Value
12.11 16-bit Timer/Counter Register Description
12.11.1
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 (OC1Ai and OC1Bi respectively) behavior. If one or both of the COM1A1:0 bits are written to one, the OC1Ai 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 OC1Bi output overrides the normal port functionality of
the I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit and
OC1xi bit (TCCR1D) corresponding to the OC1Ai or OC1Bi pin must be set in order to enable
the output driver.
When the OC1Ai or OC1Bi is connected to the pin, the function of the COM1A/B1:0 bits is
dependent of the WGM13:0 bits setting. Table 12-1 shows the COM1A/B1:0 bit functionality
when the WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 12-1.
Compare Output Mode, non-PWM
OC1Ai
OC1Bi
COM1A1
COM1B1
COM1A0
COM1B0
0
x
x
0
0
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).
Description
Normal port operation, OC1A/OC1B disconnected.
1
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Table 12-2 shows the COM1A/B1:0 bit functionality when the WGM13:0 bits are set to the fast
PWM mode.
Table 12-2.
Compare Output Mode, Fast PWM (1)
OC1Ai
OC1Bi
COM1A1
COM1B1
COM1A0
COM1B0
0
x
x
1
0
0
Description
Normal port operation, OC1A/OC1B disconnected.
1
0
1
WGM13=0: Normal port operation, OC1A/OC1B
disconnected.
WGM13=1: Toggle OC1A on Compare Match, OC1B
reserved.
1
1
0
Clear OC1A/OC1B on Compare Match
Set OC1A/OC1B at TOP
1
1
1
Set OC1A/OC1B on Compare Match
Clear OC1A/OC1B at TOP
Note:
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 124. for more details.
Table 12-3 shows the COM1A/B1:0 bit functionality when the WGM13:0 bits are set to the
phase correct or the phase and frequency correct, PWM mode.
Table 12-3.
Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
OC1Ai
OC1Bi
COM1A1
COM1B1
COM1A0
COM1B0
0
x
x
1
0
0
Description
Normal port operation, OC1A/OC1B disconnected.
1
0
1
WGM13=0: Normal port operation, OC1A/OC1B
disconnected.
WGM13=1: Toggle OC1A on Compare Match, OC1B
reserved.
1
1
0
Clear OC1A/OC1B on Compare Match when up-counting.
Set OC1A/OC1B on Compare Match when downcounting.
1
1
1
Set OC1A/OC1B on Compare Match when up-counting.
Clear OC1A/OC1B on Compare Match when downcounting.
Note:
1. A special case occurs when OC1A/OC1B equals TOP and COM1A1/COM1B1 is set. See
“Phase Correct PWM Mode” on page 126. for more details.
• Bit 3:2 – Reserved Bits
These bits are reserved for future use.
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• Bit 1:0 – WGM11:0: Waveform Generation Mode
Combined with the WGM13:2 bits found in the TCCR1B Register, these bits control the counting sequence of the counter, the source for maximum (TOP) counter value, and what type of
waveform generation to be used, see Table 12-4. 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
122.).
Waveform Generation Mode Bit Description (1)
Table 12-4.
Mode
WGM13
WGM12
(CTC1)
WGM11
(PWM11)
WGM10
(PWM10)
Timer/Counter
Mode of Operation
TOP
Update of
OCR1A/B 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:
134
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.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
12.11.2
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 12-11 and Figure 12-12.
Table 12-5.
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.
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7728D–AVR–07/09
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
12.11.3
Timer/Counter1 Control Register C – TCCR1C
Bit
7
6
5
4
3
2
1
0
FOC1A
FOC1B
–
–
–
–
–
–
Read/Write
R/W
R/W
R/W
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 OC1nx output is changed according to its COM1A/B1:0 and OC1nx bits setting. Note that
the FOC1A/FOC1B bits are implemented as strobes. Therefore it is the value present in the
COM1A/B1:0 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.
12.11.4
Timer/Counter1 Control Register D – TCCR1D
Bit
7
6
5
4
3
2
1
0
OC1BX
OC1BW
OC1BV
OC1BU
OC1AX
OC1AW
OC1AV
OC1AU
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
TCCR1D
• Bit 7:4 – OC1Bi: Output Compare Pin Enable for Channel B
The OC1Bi bits enable the Output Compare pins of Channel B as shown in Figure 12-6 on
page 122.
• Bit 3:0 – OC1Ai: Output Compare Pin Enable for Channel A
The OC1Ai bits enable the Output Compare pins of Channel A as shown in Figure 12-6 on
page 122.
136
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
12.11.5
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 112.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a
compare match between TCNT1 and one of the OCR1A/B Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following timer
clock for all compare units.
12.11.6
Output Compare Register A – OCR1AH and OCR1AL
Bit
7
6
5
4
3
2
1
0
OCR1A[15:8]
OCR1AH
OCR1A[7:0]
12.11.7
OCR1AL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
4
3
2
1
0
Output Compare Register B – OCR1BH and OCR1BL
Bit
7
6
5
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 OC1A/B 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 112.
137
7728D–AVR–07/09
12.11.8
Input Capture Register – 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 112.
12.11.9
Timer/Counter1 Interrupt Mask Register – TIMSK1
Bit
7
6
5
4
3
2
1
0
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK1
• Bit 7..6 – Reserved Bits
These bits are reserved for future use.
• Bit 5 – ICIE1: Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See ”Interrupt Vectors in ATtiny87/167” on page 59.) is executed when the ICF1 flag,
located in TIFR1, is set.
• Bit 4..3 – Reserved Bits
These bits are reserved for future use.
• Bit 2 – OCIE1B: 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 ”Interrupt Vectors in ATtiny87/167” on page 59.) is executed when
the OCF1B flag, located in TIFR1, is set.
• Bit 1 – OCIE1A: 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 ”Interrupt Vectors in ATtiny87/167” on page 59.) is executed when
the OCF1A flag, located in TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter 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 ”Interrupt Vectors in ATtiny87/167” on page 59.) is executed when the TOV1 flag,
located in TIFR1, is set.
138
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
12.11.10 Timer/Counter1 Interrupt Flag Register – TIFR1
Bit
7
6
5
4
3
2
1
0
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR1
• Bit 7..6 – Reserved Bits
These bits are reserved for future use.
• Bit 5 – ICF1: Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register
(ICR1) is set by the WGM13:0 to be used as the TOP value, the ICF1 flag is set when the
counter reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively, ICF1 can be cleared by writing a logic one to its bit location.
• Bit 4..3 – Reserved Bits
These bits are reserved for future use.
• Bit 2 – OCF1B: 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 1 – OCF1A: 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 0 – TOV1: Timer/Counter 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 12-4 on page 134 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.
139
7728D–AVR–07/09
13. SPI - Serial Peripheral Interface
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between
the ATtiny87/167 and peripheral devices or between several AVR devices. The ATtiny87/167
SPI includes the following features:
13.1
Features
•
•
•
•
•
•
•
•
Full-duplex, Three-wire Synchronous Data Transfer
Master or Slave Operation
LSB First or MSB First Data Transfer
Seven Programmable Bit Rates
End of Transmission Interrupt Flag
Write Collision Flag Protection
Wake-up from Idle Mode
Double Speed (CK/2) Master SPI Mode
Figure 13-1. SPI Block Diagram(1)
clk IO
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128
Note:
140
1. Refer to Figure 1.6 on page 5, and Table 9-3 on page 76 for SPI pin placement.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
The interconnection between Master and Slave CPUs with SPI is shown in Figure 13-2. The
system consists of two shift Registers, and a Master clock generator. The SPI Master initiates
the communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and Slave prepare the data to be sent in their respective shift Registers, and the Master
generates the required clock pulses on the SCK line to interchange data. Data is always
shifted from Master to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In – Slave Out, MISO, line. After each data packet, the Master will
synchronize the Slave by pulling high the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing
a byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the
eight bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end
of transmission flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set,
an interrupt is requested. The Master may continue to shift the next byte by writing it into
SPDR, or signal the end of packet by pulling high the Slave Select, SS line. The last incoming
byte will be kept in the Buffer Register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as
long as the SS pin is driven high. In this state, software may update the contents of the SPI
Data Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK
pin until the SS pin is driven low. As one byte has been completely shifted, the end of transmission flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an
interrupt is requested. The Slave may continue to place new data to be sent into SPDR before
reading the incoming data. The last incoming byte will be kept in the Buffer Register for later
use.
Figure 13-2. SPI Master-slave Interconnection
SHIFT
ENABLE
The system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must
be read from the SPI Data Register before the next character has been completely shifted in.
Otherwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the frequency of the SPI clock should never exceed
fclkio/4.
141
7728D–AVR–07/09
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to Table 13-1. For more details on automatic port overrides, refer to “Alternate
Port Functions” on page 72.
Table 13-1.
Pin
SPI Pin Overrides(1)
Direction, Master SPI
Direction, Slave SPI
MOSI
User Defined
Input
MISO
Input
User Defined
SCK
User Defined
Input
SS
User Defined
Input
Note:
1. See “Alternate Functions of Port B” on page 81 for a detailed description of how to define the
direction of the user defined SPI pins.
The following code examples show how to initialize the SPI as a Master and how to perform a
simple transmission.
DDR_SPI in the examples must be replaced by the actual Data Direction Register controlling
the SPI pins. DD_MOSI, DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin PB2, replace DD_MOSI with DDB2 and
DDR_SPI with DDRB.
Assembly Code Example(1)
142
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi
r17,(1<<DD_MOSI)|(1<<DD_SCK)
out
DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi
r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out
SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out
SPDR,r16
Wait_Transmit:
; Wait for transmission complete
in
r17,SPSR
sbrs
r17,SPIF
rjmp
Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)));
}
Note:
1. The example code assumes that the part specific header file is included.
143
7728D–AVR–07/09
The following code examples show how to initialize the SPI as a Slave and how to perform a
simple reception.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi
r17,(1<<DD_MISO)
out
DDR_SPI,r17
; Enable SPI
ldi
r17,(1<<SPE)
out
SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis
SPSR,SPIF
rjmp
SPI_SlaveReceive
; Read received data and return
in
r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)));
/* Return data register */
return SPDR;
}
Note:
144
1. The example code assumes that the part specific header file is included.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
13.2
13.2.1
SS Pin Functionality
Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When SS is
held low, the SPI is activated, and MISO becomes an output if configured so by the user. All
other pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which
means that it will not receive incoming data. Note that the SPI logic will be reset once the SS
pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous
with the master clock generator. When the SS pin is driven high, the SPI slave will immediately
reset the send and receive logic, and drop any partially received data in the Shift Register.
13.2.2
Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the
direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If the SS
pin is driven low by peripheral circuitry when the SPI is configured as a Master with the SS pin
defined as an input, the SPI system interprets this as another master selecting the SPI as a
slave and starting to send data to it. To avoid bus contention, the SPI system takes the following actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result
of the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in
SREG is set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possibility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If
the MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI
Master mode.
13.2.3
SPI Control Register – SPCR
Bit
7
6
5
4
3
2
1
0
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
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
SPCR
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and if
the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
145
7728D–AVR–07/09
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be
cleared, and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable
SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is
low when idle. Refer to Figure 13-3 and Figure 13-4 for an example. The CPOL functionality is
summarized below:
Table 13-2.
CPOL Functionality
CPOL
Leading Edge
Trailing Edge
0
Rising
Falling
1
Falling
Rising
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first)
or trailing (last) edge of SCK. Refer to Figure 13-3 and Figure 13-4 for an example. The CPOL
functionality is summarized below:
Table 13-3.
CPHA Functionality
CPHA
Leading Edge
Trailing Edge
0
Sample
Setup
1
Setup
Sample
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0
have no effect on the Slave. The relationship between SCK and the clkIO frequency fclkio is
shown in the following table:
Table 13-4.
146
Relationship Between SCK and the Oscillator Frequency
SPI2X
SPR1
SPR0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
SCK Frequency
fclkio/4
fclkio/16
fclkio/64
fclkio/128
fclkio/2
fclkio/8
fclkio/32
fclkio/64
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
13.2.4
SPI Status Register – SPSR
Bit
7
6
5
4
3
2
1
0
SPIF
WCOL
–
–
–
–
–
SPI2X
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI
is in Master mode, this will also set the SPIF flag. SPIF is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL
set, and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the ATtiny87/167 and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the
SPI is in Master mode (see Table 13-4). This means that the minimum SCK period will be two
CPU clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at
fclkio/4 or lower.
The SPI interface on the ATtiny87/167 is also used for program memory and EEPROM downloading or uploading. See “Serial Downloading” on page 238 for serial programming and
verification.
13.2.5
SPI Data Register – SPDR
Bit
7
6
5
4
3
2
1
0
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
X
X
X
X
X
X
X
X
SPDR
Undefined
• Bits 7:0 - SPD7:0: SPI Data
The SPI Data Register is a read/write register used for data transfer between the Register File
and the SPI Shift Register. Writing to the register initiates data transmission. Reading the register causes the Shift Register Receive buffer to be read.
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13.3
Data Modes
There are four combinations of SCK phase and polarity with respect to serial data, which are
determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure 13-3 and Figure 13-4. Data bits are shifted out and latched in on opposite edges of the
SCK signal, ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing Table 13-2 and Table 13-3, as done below:
Table 13-5.
CPOL Functionality
Leading Edge
Trailing Edge
SPI Mode
CPOL=0, CPHA=0
Sample (Rising)
Setup (Falling)
0
CPOL=0, CPHA=1
Setup (Rising)
Sample (Falling)
1
CPOL=1, CPHA=0
Sample (Falling)
Setup (Rising)
2
CPOL=1, CPHA=1
Setup (Falling)
Sample (Rising)
3
Figure 13-3. SPI Transfer Format with CPHA = 0
SCK (CPOL = 0)
mode 0
SCK (CPOL = 1)
mode 2
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0) MSB
LSB first (DORD = 1) LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
Figure 13-4. SPI Transfer Format with CPHA = 1
SCK (CPOL = 0)
mode 1
SCK (CPOL = 1)
mode 3
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0)
LSB first (DORD = 1)
148
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
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ATtiny87/ATtiny167
14. USI – Universal Serial Interface
14.1
Features
•
•
•
•
•
•
14.2
Two-wire Synchronous Data Transfer (Master or Slave)
Three-wire Synchronous Data Transfer (Master or Slave)
Data Received Interrupt
Wakeup from Idle Mode
In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
Two-wire Start Condition Detector with Interrupt Capability
Overview
The Universal Serial Interface, 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.
A simplified block diagram of the USI is shown on Figure 14-1 For the actual placement of I/O
pins, refer to “Pin Configuration” on page 5. CPU accessible I/O Registers, including I/O bits
and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in
the “Register Descriptions” on page 156.
Figure 14-1. Universal Serial Interface, Block Diagram
Bit7
Bit0
D Q
LE
DO
(Output only)
DI/SDA
(Input/Open Drain)
USCK/SCL
(Input/Open Drain)
3
2
USIDR
1
0
TIM0 COMP
USIPF
4-bit Counter
USIDC
USISIF
USIOIF
DATA BUS
USIDB
3
2
0
1
1
0
CLOCK
HOLD
[1]
Two-wire Clock
Control Unit
USISR
USITC
USICLK
USICS0
USICS1
USIWM0
USIWM1
USISIE
USIOIE
2
USICR
The 8-bit USI Data Register 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 USI Data Register is a serial shift register and the most
significant bit that is the output of the serial shift register is connected to one of two output pins
depending of the wire mode configuration.
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A transparent latch is inserted between the USI Data 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 USI Data Register and the counter are clocked simultaneously by the same
clock source. This allows the counter to count the number of bits received or transmitted and
generate an interrupt when the transfer is complete. Note that when an external clock source
is selected the counter counts both clock edges. In this case the counter counts the number of
edges, and not the number of bits. The clock can be selected from three different sources: The
USCK pin, Timer/Counter0 Compare Match or from software.
The Two-wire clock control unit can generate an interrupt when a start condition is detected on
the Two-wire bus. It can also generate wait states by holding the clock pin low after a start
condition is detected, or after the counter overflows.
14.3
14.3.1
Functional Descriptions
Three-wire Mode
The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0 and 1,
but does not have the slave select (SS) pin functionality. However, this feature can be implemented in software if necessary. Pin names used by this mode are: DI, DO, and USCK.
Figure 14-2. Three-wire Mode Operation, Simplified Diagram
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
SLAVE
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
PORTxn
MASTER
Figure 14-2 shows two USI units operating in Three-wire mode, one as Master and one as
Slave. The two USI Data Register 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.
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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 14-3. Three-wire Mode, Timing Diagram
CYCLE
( Reference )
1
2
3
4
5
6
7
8
USCK
USCK
DO
MSB
DI
MSB
A
B
C
6
5
4
3
2
1
LSB
6
5
4
3
2
1
LSB
D
E
The Three-wire mode timing is shown in Figure 14-3 At the top of the figure is a USCK cycle
reference. One bit is shifted into the USI Data Register (USIDR) for each of these cycles. The
USCK timing is shown for both external clock modes. In External Clock mode 0 (USICS0 = 0),
DI is sampled at positive edges, and DO is changed (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 14-3), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on the
protocol used, enables its output driver (mark A and B). The output is set up by writing the data to be transmitted to the USI 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.
14.3.2
SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
ldi
r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
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sts
USICR,r16
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SPITransfer_loop
lds
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes
that the DO and USCK pins are enabled as output in the DDRA or DDRB Register. The value
stored in register r16 prior to the function is called is transferred to the Slave device, and when
the transfer is completed the data received from the Slave is stored back into the r16 Register.
The second and third instructions clears the USI Counter Overflow Flag and the USI counter
value. The fourth and fifth instruction set Three-wire mode, positive edge Shift Register clock,
count at USITC strobe, and toggle USCK. The loop is repeated 16 times.
The following code demonstrates how to use the USI module as a SPI Master with maximum
speed (fsck = fck/4):
SPITransfer_Fast:
sts
USIDR,r16
ldi
r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi
r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
sts
USICR,r16 ; MSB
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16 ; LSB
sts
USICR,r17
lds
r16,USIDR
ret
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14.3.3
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi
r16,(1<<USIWM0)|(1<<USICS1)
sts
USICR,r16
...
SlaveSPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
SlaveSPITransfer_loop:
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SlaveSPITransfer_loop
lds
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes
that the DO is configured as output and USCK pin is configured as input in the DDR Register.
The value stored in register r16 prior to the function is called is transferred to the master
device, and when the transfer is completed the data received from the Master is stored back
into the r16 Register.
Note that the first two instructions is for initialization only and needs only to be executed
once.These instructions sets Three-wire mode and positive edge USI Data Register clock.
The loop is repeated until the USI Counter Overflow Flag is set.
14.3.4
Two-wire Mode
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate
limiting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.
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Figure 14-4. Two-wire Mode Operation, Simplified Diagram
VCC
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
HOLD
SCL
Two-wire Clock
Control Unit
SLAVE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
PORTxn
MASTER
Figure 14-4 shows two USI units operating in Two-wire mode, one as Master and one as
Slave. It is only the physical layer that is shown since the system operation is highly dependent of the communication scheme used. The main differences between the Master and Slave
operation at this level, is the serial clock generation which is always done by the Master, 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.
Figure 14-5. Two-wire Mode, Typical Timing Diagram
SDA
SCL
S
A
154
B
1-7
8
9
1-8
9
1-8
9
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
C
D
E
P
F
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Referring to the timing diagram (Figure 14-5), 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 USI Data Register bit must be set to one for the output to be enabled. The slave
device’s start detector logic (Figure 14-6.) detects the start condition and sets the
USISIF Flag. The flag can generate an interrupt if necessary.
2. In addition, the start detector will hold the SCL line low after the Master has forced an
negative edge on this line (B). This allows the Slave to wake up from sleep or complete its other tasks before setting up the USI Data 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 USI Data 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 14-6. Start Condition Detector, Logic Diagram
USISIF
D Q
D Q
CLR
CLR
SDA
CLOCK
HOLD
SCL
Write( USISIF)
14.3.5
Start Condition Detector
The start condition detector is shown in Figure 14-6. The SDA line is delayed (in the range of
50 to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is only
enabled in Two-wire mode.
The start condition detector is working asynchronously and can therefore wake up the processor from the Power-down sleep mode. However, the protocol used might have restrictions on
the SCL hold time. Therefore, when using this feature in this case the Oscillator start-up time
set by the CKSEL Fuses (see “Clock Systems and their Distribution” on page 24) must also be
taken into the consideration. Refer to the USISIF bit description on page 157 for further
details.
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14.4
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.
14.4.1
Half-duplex Asynchronous Data Transfer
By utilizing the USI Data Register in Three-wire mode, it is possible to implement a more compact and higher performance UART than by software only.
14.4.2
4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the
counter is clocked externally, both clock edges will generate an increment.
14.4.3
12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
14.4.4
Edge Triggered External Interrupt
By setting the counter to maximum value (F) it can function as an additional external interrupt.
The Overflow Flag and Interrupt Enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.
14.4.5
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.
14.5
14.5.1
Register Descriptions
USIDR – USI Data Register
Bit
7
6
5
4
3
2
1
0
USID7
USID6
USID5
USID4
USID3
USID2
USID1
USID0
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
• Bits 7:0 – USID7..0: USI Data
When accessing the USI Data Register (USIDR) the Serial Register can be accessed directly.
If a serial clock occurs at the same cycle the register is written, the register will contain the
value written and no shift is performed. A (left) shift operation is performed depending of the
USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a
Timer/Counter0 Compare Match, or directly by software using the USICLK strobe bit. Note
that even when no wire mode is selected (USIWM1..0 = 0) both the external data input
(DI/SDA) and the external clock input (USCK/SCL) can still be used by the USI Data 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.
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Note that the corresponding Data Direction Register to the pin must be set to one for enabling
data output from the USI Data Register.
14.5.2
USIBR – USI Buffer Register
Bit
7
6
5
4
3
2
1
0
USIB7
USIB6
USIB5
USIB4
USIB3
USIB2
USIB1
USIB0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
USIBR
• Bits 7:0 – USID7..0: USI Buffer
The content of the Serial Register is loaded to the USI Buffer Register when the transfer is
completed, and instead of accessing the USI Data Register (the Serial Register) the USI Data
Buffer can be accessed when the CPU reads the received data. This gives the CPU time to
handle other program tasks too as the controlling of the USI is not so timing critical. The USI
flags as set same as when reading the USIDR register.
14.5.3
USISR – USI Status Register
The Status Register contains Interrupt Flags, line Status Flags and the counter value.
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
• 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 = 11b &
USICLK = 0) or (USICS = 10b & USICLK = 0), any edge on the SCK pin sets the flag.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the
Global Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one to the
USISIF bit. Clearing this bit will release the start detection hold of USCL in Two-wire mode.
A start condition interrupt will wakeup the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). An
interrupt will be generated when the flag is set while the USIOIE bit in USICR and the Global
Interrupt Enable Flag are set. The flag will only be cleared if a one is written to the USIOIF bit.
Clearing this bit will release the counter overflow hold of SCL in Two-wire mode.
A counter overflow interrupt will wakeup the processor from Idle sleep mode.
• Bit 5 – USIPF: Stop Condition Flag
When Two-wire mode is selected, the USIPF Flag is set (one) when a stop condition is
detected. The flag is cleared by writing a one to this bit. Note that this is not an Interrupt Flag.
This signal is useful when implementing Two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the USI Data Register differs from the physical pin value.
The flag is only valid when Two-wire mode is used. This signal is useful when implementing
Two-wire bus master arbitration.
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• Bits 3:0 – USICNT3..0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read
or written by the CPU.
The 4-bit counter increments by one for each clock generated either by the external clock
edge detector, by a Timer/Counter0 Compare Match, or by software using USICLK or USITC
strobe bits. The clock source depends of the setting of the USICS1..0 bits. For external clock
operation a special feature is added that allows the clock to be generated by writing to the
USITC strobe 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.
14.5.4
USICR – USI Control Register
Bit
7
6
5
4
3
2
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
W
W
Initial Value
0
0
0
0
0
0
0
0
USICR
The Control Register includes interrupt enable control, wire mode setting, Clock Select setting,
and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately
be executed. Refer to the USISIF bit description on page 157 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt
when the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be
executed. Refer to the USIOIF bit description on page 157 for further details.
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are
affected by these bits. Data and clock inputs are not affected by the mode selected and will
always have the same function. The counter and USI Data 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 14-1.
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Table 14-1.
USIWM1
0
0
1
1
Note:
Relations between USIWM1..0 and the USI Operation
USIWM0 Description
0
Outputs, clock hold, and start detector disabled. Port pins operates as normal.
1
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORT Register
in this mode. However, the corresponding DDR bit still controls the data
direction. When the port pin is set as input the pins pull-up is controlled by the
PORT bit.
The Data Input (DI) and Serial Clock (USCK) pins do not affect the normal port
operation. When operating as master, clock pulses are software generated by
toggling the PORT Register, while the data direction is set to output. The USITC
bit in the USICR Register can be used for this purpose.
0
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).
The Serial Data (SDA) and the Serial Clock (SCL) pins are bi-directional and
uses open-collector output drives. The output drivers are enabled by setting the
corresponding bit for SDA and SCL in the DDR Register.
When the output driver is enabled for the SDA pin, the output driver will force the
line SDA low if the output of the USI Data 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
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the Two-wire mode described above, except that the SCL
line is also held low when a counter overflow occurs, and is held low until the
Counter Overflow Flag (USIOIF) is cleared.
1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL) respectively to avoid confusion between the modes of operation.
• Bit 3:2 – USICS1:0: Clock Source Select
These bits set the clock source for the USI Data Register and counter. The data output latch
ensures that the output is changed at the opposite edge of the sampling of the data input
(DI/SDA) when using external clock source (USCK/SCL). When software strobe or
Timer/Counter0 Compare Match clock option is selected, the output latch is transparent and
therefore the output is changed immediately. Clearing the USICS1:0 bits enables software
strobe option. When using this option, writing a one to the USICLK bit clocks both the USI
Data Register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no
longer used as a strobe, but selects between external clocking and software clocking by the
USITC strobe bit.
Table 14-2 on page 160 shows the relationship between the USICS1..0 and USICLK setting
and clock source used for the USI Data Register and the 4-bit counter.
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Table 14-2.
Relations between the USICS1..0 and USICLK Setting
USI Data 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 Compare
Match
Timer/Counter0 Compare
Match
1
0
0
External, positive edge
External, both edges
1
1
0
External, negative edge
External, both edges
1
0
1
External, positive edge
Software clock strobe (USITC)
1
1
1
External, negative edge
Software clock strobe (USITC)
USICS1
USICS0
USICLK
0
0
0
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the USI Data Register to shift one step and the counter to increment by one, provided that the 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 USI Data 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 14-2).
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0.
The toggling is independent of the setting in the Data Direction Register, but if the PORT value
is to be shown on the pin the DDB2 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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14.5.5
USIPP – USI Pin Position
Bit
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
USIPOS
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
USIPP
• Bits 7:1 – Res: Reserved Bits
These bits are reserved bits in the ATtiny87/167 and always reads as zero.
• Bit 0 – USIPOS: USI Pin Position
Setting or clearing this bit changes the USI pin position.
Table 14-3.
USI Pin Position
USIPOS
0
1
PortB
(Default)
USI Pin Position
DI, SDA
PB0 - (PCINT8/OC1AU)
DO
PB1 - (PCINT9/OC1BU)
USCK, SCL
PB2 - (PCINT10/OC1AV)
DI, SDA
Port A
DO
(Alternate)
USCK, SCL
PA4 - (PCINT4/ADC4/ICP1/MOSI)
PA2 - (PCINT2/ADC2/OC0A/MISO)
PA5 - (PCINT5/ADC5/T1/SCK)
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15. LIN / UART - Local Interconnect Network Controller or UART
The LIN (Local Interconnect Network) is a serial communications protocol which efficiently
supports the control of mechatronics nodes in distributed automotive applications. The main
properties of the LIN bus are:
•
•
•
•
•
•
Single master with multiple slaves concept
Low cost silicon implementation based on common UART/SCI interface
Self synchronization with on-chip oscillator in slave node
Deterministic signal transmission with signal propagation time computable in advance
Low cost single-wire implementation
Speed up to 20 Kbit/s.
LIN provides a cost efficient bus communication where the bandwidth and versatility of CAN
are not required. The specification of the line driver/receiver needs to match the ISO9141
NRZ-standard.
If LIN is not required, the controller alternatively can be programmed as Universal Asynchronous serial Receiver and Transmitter (UART).
15.1
LIN Features
• Hardware Implementation of LIN 2.1 (LIN 1.3 Compatibility)
• Small, CPU Efficient and Independent Master/Slave Routines Based on “LIN Work Flow
15.2
162
•
•
•
•
•
•
•
Concept” of LIN 2.1 Specification
Automatic LIN Header Handling and Filtering of Irrelevant LIN Frames
Automatic LIN Response Handling
Extended LIN Error Detection and Signaling
Hardware Frame Time-out Detection
“Break-in-data” Support Capability
Automatic Re-synchronization to Ensure Proper Frame Integrity
Fully Flexible Extended Frames Support Capabilities
•
•
•
•
•
Full Duplex Operation (Independent Serial Receive and Transmit Processes)
Asynchronous Operation
High Resolution Baud Rate Generator
Hardware Support of 8 Data Bits, Odd/Even/No Parity Bit, 1 Stop Bit Frames
Data Over-Run and Framing Error Detection
UART Features
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
15.3
15.3.1
LIN Protocol
Master and Slave
A LIN cluster consists of one master task and several slave tasks. A master node contains the
master task as well as a slave task. All other nodes contain a slave task only.
Figure 15-1. LIN cluster with one master node and “n” slave nodes
master node
master task
slave node
1
slave node
n
slave task
slave task
slave task
LIN bus
The master task decides when and which frame shall be transferred on the bus. The slave
tasks provide the data transported by each frame. Both the master task and the slave task are
parts of the Frame handler
15.3.2
Frames
A frame consists of a header (provided by the master task) and a response (provided by a
slave task).
The header consists of a BREAK and SYNC pattern followed by a PROTECTED IDENTIFIER.
The identifier uniquely defines the purpose of the frame. The slave task appointed for providing the response associated with the identifier transmits it. The response consists of a DATA
field and a CHECKSUM field.
Figure 15-2. Master and slave tasks behavior in LIN frame
Master Task
HEADER
HEADER
RESPONSE
Slave Task 1
RESPONSE
Slave Task 2
The slave tasks waiting for the data associated with the identifier receives the response and
uses the data transported after verifying the checksum.
Figure 15-3. Structure of a LIN frame
FRAME SLOT
HEADER
BREAK
Field
Break Delimiter
SYNC
RESPONSE
Field
PROTECTED
IDENTIFIER
Field
Response Space
DATA-0
Field
DATA-n
Field
CHECKSUM
Inter-Byte Space
Field
Inter-Frame Space
Each byte field is transmitted as a serial byte, LSB first.
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15.3.3
Data Transport
Two types of data may be transported in a frame; signals or diagnostic messages.
• Signals
Signals are scalar values or byte arrays that are packed into the data field of a frame. A
signal is always present at the same position in the data field for all frames with the same
identifier.
• Diagnostic messages
Diagnostic messages are transported in frames with two reserved identifiers. The
interpretation of the data field depends on the data field itself as well as the state of the
communicating nodes.
15.3.4
Schedule Table
The master task (in the master node) transmits frame headers based on a schedule table. The
schedule table specifies the identifiers for each header and the interval between the start of a
frame and the start of the following frame. The master application may use different schedule
tables and select among them.
15.3.5
Compatibility with LIN 1.3
LIN 2.1 is a super-set of LIN 1.3.
A LIN 2.1 master node can handle clusters consisting of both LIN 1.3 slaves and/or LIN 2.1
slaves. The master will then avoid requesting the new LIN 2.1 features from a LIN 1.3 slave:
• Enhanced checksum,
• Re-configuration and diagnostics,
• Automatic baud rate detection,
• "Response error" status monitoring.
LIN 2.1 slave nodes can not operate with a LIN 1.3 master node (e.g. the LIN1.3 master does
not support the enhanced checksum).
The LIN 2.1 physical layer is backwards compatible with the LIN1.3 physical layer. But not the
other way around. The LIN 2.1 physical layer sets greater requirements, i.e. a master node
using the LIN 2.1 physical layer can operate in a LIN 1.3 cluster.
15.4
LIN / UART Controller
The LIN/UART controller is divided in three main functions:
• Tx LIN Header function,
• Rx LIN Header function,
• LIN Response function.
These functions mainly use two services:
• Rx service,
• Tx service.
Because these two services are basically UART services, the controller is also able to switch
into an UART function.
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15.4.1
LIN Overview
The LIN/UART controller is designed to match as closely as possible to the LIN software application structure. The LIN software application is developed as independent tasks, several
slave tasks and one master task (c.f. Section 15.3.4 on page 164). The ATtiny87/167 conforms to this perspective. The only link between the master task and the slave task will be at
the cross-over point where the interrupt routine is called once a new identifier is available.
Thus, in a master node, housing both master and slave task, the Tx LIN Header function will
alert the slave task of an identifier presence. In the same way, in a slave node, the Rx LIN
Header function will alert the slave task of an identifier presence.
When the slave task is warned of an identifier presence, it has first to analyze it to know what
to do with the response. Hardware flags identify the presence of one of the specific identifiers
from 60 (0x3C) up to 63 (0x3F).
For LIN communication, only four interrupts need to be managed:
• LIDOK: New LIN identifier available,
• LRXOK: LIN response received,
• LTXOK: LIN response transmitted,
• LERR: LIN Error(s).
The wake-up management can be automated using the UART wake-up capability and a node
sending a minimum of 5 low bits (0xF0) for LIN 2.1 and 8 low bits (0x80) for LIN 1.3. Pin
change interrupt on LIN wake-up signal can be also used to exit the device of one of its sleep
modes.
Extended frame identifiers 62 (0x3E) and 63 (0x3F) are reserved to allow the embedding of
user-defined message formats and future LIN formats. The byte transfer mode offered by the
UART will ensure the upwards compatibility of LIN slaves with accommodation of the LIN
protocol.
15.4.2
UART Overview
The LIN/UART controller can also function as a conventional UART. By default, the UART
operates as a full duplex controller. It has local loop back circuitry for test purposes. The UART
has the ability to buffer one character for transmit and two for receive. The receive buffer is
made of one 8-bit serial register followed by one 8-bit independent buffer register. Automatic
flag management is implemented when the application puts or gets characters, thus reducing
the software overhead. Because transmit and receive services are independent, the user can
save one device pin when one of the two services is not used. The UART has an enhanced
baud rate generator providing a maximum error of 2% whatever the clock frequency and the
targeted baud rate.
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15.4.3
LIN/UART Controller Structure
Figure 15-4. LIN/UART Controller Block Diagram
CLK IO
Finite State Machine
Prescaler
Sample /bit
RxD
FSM
BAUD_RATE
Get Byte
RX
Put Byte
TX
Frame Time-out
TxD
Synchronization
Monitoring
Data FIFO
15.4.4
BUFFER
LIN/UART Command Overview
Figure 15-5. LIN/UART Command Dependencies
Tx
Response
Tx Header
IDOK
TXOK
Rx Header
or
LIN Abort
Rx
Response
RXOK
Automatic
Return
Recommended
Way
LIN
DISABLE
UART
Possible
Way
Byte
Transfer
Rx
Byte
Full
Duplex
Tx
Byte
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Table 15-1.
LIN/UART Command List
LENA
LCMD[2]
LCMD[1]
LCMD[0]
Command
0
x
x
x
Disable peripheral
0
Rx Header - LIN Abort
LIN Withdrawal
1
Tx Header
LCMD[2..0]=000 after Tx
0
Rx Response
LCMD[2..0]=000 after Rx
1
Tx Response
LCMD[2..0]=000 after Tx
0
0
Byte transfer
1
0
Rx Byte
0
1
Tx Byte
1
1
Full duplex
0
0
1
1
1
15.4.5
Comment
no CRC, no Time out
LTXDL=LRXDL=0
(LINDLR: read only register)
Enable / Disable
Setting the LENA bit in LINCR register enables the LIN/UART controller. To disable the
LIN/UART controller, LENA bit must be written to 0. No wait states are implemented, so, the
disable command is taken into account immediately.
15.4.6
LIN Commands
Clearing the LCMD[2] bit in LINCR register enables LIN commands.
As shown in Table 15-1 on page 167, four functions controlled by the LCMD[1..0] bits of
LINCR register are available (c.f. Figure 15-5 on page 166).
15.4.6.1
Rx Header / LIN Abort Function
This function (or state) is mainly the withdrawal mode of the controller.
When the controller has to execute a master task, this state is the start point before enabling a
Tx Header command.
When the controller has only to execute slave tasks, LIN header detection/acquisition is
enabled as background function. At the end of such an acquisition (Rx Header function), automatically the appropriate flags are set, and in LIN 1.3, the LINDLR register is set with the
uncoded length value.
This state is also the start point before enabling the Tx or the Rx Response command.
A running function (i.e. Tx Header, Tx or Rx Response ) can be aborted by clearing
LCMD[1..0] bits in LINCR register (See ”Break-in-data” on page 177.). In this case, an abort
flag - LABORT - in LINERR register will be set to inform the other software tasks. No wait
states are implemented, so, the abort command is taken into account immediately.
Rx Header function is responsible for:
• The BREAK field detection,
• The hardware re-synchronization analyzing the SYNCH field,
• The reception of the PROTECTED IDENTIFIER field, the parity control and the update of
the LINDLR register in case of LIN 1.3,
• The starting of the Frame_Time_Out,
• The checking of the LIN communication integrity.
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15.4.6.2
Tx Header Function
In accordance with the LIN protocol, only the master task must enable this function. The
header is sent in the appropriate timed slots at the programmed baud rate (c.f. LINBRR & LINBTR registers).
The controller is responsible for:
• The transmission of the BREAK field - 13 dominant bits,
• The transmission of the SYNCH field - character 0x55,
• The transmission of the PROTECTED IDENTIFIER field. It is the full content of the LINIDR
register (automatic check bits included).
At the end of this transmission, the controller automatically returns to Rx Header / LIN Abort
state (i.e. LCMD[1..0] = 00) after setting the appropriate flags. This function leaves the controller in the same setting as after the Rx Header function. This means that, in LIN 1.3, the
LINDLR register is set with the uncoded length value at the end of the Tx Header function.
During this function, the controller is also responsible for:
• The starting of the Frame_Time_Out,
• The checking of the LIN communication integrity.
15.4.6.3
Rx & TX Response Functions
These functions are initiated by the slave task of a LIN node. They must be used after sending
an header (master task) or after receiving an header (considered as belonging to the slave
task). When the TX Response order is sent, the transmission begins. A Rx Response order
can be sent up to the reception of the last serial bit of the first byte (before the stop-bit).
In LIN 1.3, the header slot configures the LINDLR register. In LIN 2.1, the user must configure
the LINDLR register, either LRXDL[3..0] for Rx Response either LTXDL[3..0] for Tx Response.
When the command starts, the controller checks the LIN13 bit of the LINCR register to apply
the right rule for computing the checksum. Checksum calculation over the DATA bytes and the
PROTECTED IDENTIFIER byte is called enhanced checksum and it is used for communication with LIN 2.1 slaves. Checksum calculation over the DATA bytes only is called classic
checksum and it is used for communication with LIN 1.3 slaves. Note that identifiers 60 (0x3C)
to 63 (0x3F) shall always use classic checksum.
At the end of this reception or transmission, the controller automatically returns to Rx Header /
LIN Abort state (i.e. LCMD[1..0] = 00) after setting the appropriate flags.
If an LIN error occurs, the reception or the transmission is stopped, the appropriate flags are
set and the LIN bus is left to recessive state.
During these functions, the controller is responsible for:
• The initialization of the checksum operator,
• The transmission or the reception of ‘n’ data with the update of the checksum calculation,
• The transmission or the checking of the CHECKSUM field,
• The checking of the Frame_Time_Out,
• The checking of the LIN communication integrity.
While the controller is sending or receiving a response, BREAK and SYNCH fields can be
detected and the identifier of this new header will be recorded. Of course, specific errors on
the previous response will be maintained with this identifier reception.
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15.4.6.4
Handling Data of LIN response
A FIFO data buffer is used for data of the LIN response. After setting all parameters in the LINSEL register, repeated accesses to the LINDAT register perform data read or data write (c.f.
“Data Management” on page 179).
Note that LRXDL[3..0] and LTXDL[3..0] are not linked to the data access.
15.4.7
UART Commands
Setting the LCMD[2] bit in LINENR register enables UART commands.
Tx Byte and Rx Byte services are independent as shown in Table 15-1 on page 167.
• Byte Transfer: the UART is selected but both Rx and Tx services are disabled,
• Rx Byte: only the Rx service is enable but Tx service is disabled,
• Tx Byte: only the Tx service is enable but Rx service is disabled,
• Full Duplex: the UART is selected and both Rx and Tx services are enabled.
This combination of services is controlled by the LCMD[1..0] bits of LINENR register (c.f. Figure 15-5 on page 166).
15.4.7.1
Data Handling
The FIFO used for LIN communication is disabled during UART accesses. LRXDL[3..0] and
LTXDL[3..0] values of LINDLR register are then irrelevant. LINDAT register is then used as
data register and LINSEL register is not relevant.
15.4.7.2
Rx Service
Once this service is enabled, the user is warned of an in-coming character by the LRXOK flag
of LINSIR register. Reading LINDAT register automatically clears the flag and makes free the
second stage of the buffer. If the user considers that the in-coming character is irrelevant without reading it, he directly can clear the flag (see specific flag management described in
Section 15.6.2 on page 182).
The intrinsic structure of the Rx service offers a 2-byte buffer. The fist one is used for serial to
parallel conversion, the second one receives the result of the conversion. This second buffer
byte is reached reading LINDAT register. If the 2-byte buffer is full, a new in-coming character
will overwrite the second one already recorded. An OVRERR error in LINERR register will
then accompany this character when read.
A FERR error in LINERR register will be set in case of framing error.
15.4.7.3
Tx Service
If this service is enabled, the user sends a character by writing in LINDAT register. Automatically the LTXOK flag of LINSIR register is cleared. It will rise at the end of the serial
transmission. If no new character has to be sent, LTXOK flag can be cleared separately (see
specific flag management described in Section 15.6.2 on page 182).
There is no transmit buffering.
No error is detected by this service.
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15.5
15.5.1
LIN / UART Description
Reset
The AVR core reset logic signal also resets the LIN/UART controller. Another form of reset
exists, a software reset controlled by LSWRES bit in LINCR register. This self-reset bit performs a partial reset as shown in Table 15-2.
Table 15-2.
15.5.2
Reset of LIN/UART Registers
Register
Name
Reset Value
LSWRES Value
LIN Control Reg.
LINCR
0000 0000 b
0000 0000 b
LIN Status & Interrupt Reg.
LINSIR
0000 0000 b
0000 0000 b
LIN Enable Interrupt Reg.
LINENIR
0000 0000 b
xxxx 0000 b
LIN Error Reg.
LINERR
0000 0000 b
0000 0000 b
LIN Bit Timing Reg.
LINBTR
0010 0000 b
0010 0000 b
LIN Baud Rate Reg. Low
LINBRRL
0000 0000 b
uuuu uuuu b
LIN Baud Rate Reg. High
LINBRRH
0000 0000 b
xxxx uuuu b
LIN Data Length Reg.
LINDLR
0000 0000 b
0000 0000 b
LIN Identifier Reg.
LINIDR
1000 0000 b
1000 0000 b
LIN Data Buffer Selection
LINSEL
0000 0000 b
xxxx 0000 b
LIN Data
LINDAT
0000 0000 b
0000 0000 b
Comment
x=unknown
u=unchanged
Clock
The I/O clock signal (clki/o) also clocks the LIN/UART controller. It is its unique clock.
15.5.3
LIN Protocol Selection
LIN13 bit in LINCR register is used to select the LIN protocol:
• LIN13 = 0 (default): LIN 2.1 protocol,
• LIN13 = 1: LIN 1.3 protocol.
The controller checks the LIN13 bit in computing the checksum (enhanced checksum in
LIN2.1 / classic checksum in LIN 1.3).
This bit is irrelevant for UART commands.
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15.5.4
Configuration
Depending on the mode (LIN or UART), LCONF[1..0] bits of the LINCR register set the controller in the following configuration (Table 15-3):
Table 15-3.
Mode
LIN
UART
Configuration Table versus Mode
LCONF[1..0]
Configuration
00 b
LIN standard configuration (default)
01 b
No CRC field detection or transmission
10 b
Frame_Time_Out disable
11 b
Listening mode
00 b
8-bit data, no parity & 1 stop-bit
01 b
8-bit data, even parity & 1 stop-bit
10 b
8-bit data, odd parity & 1 stop-bit
11 b
Listening mode, 8-bit data, no parity & 1 stop-bit
The LIN configuration is independent of the programmed LIN protocol.
The listening mode connects the internal Tx LIN and the internal Rx LIN together. In this
mode, the TXLIN output pin is disabled and the RXLIN input pin is always enabled. The same
scheme is available in UART mode.
Figure 15-6. Listening Mode
internal
Tx LIN
TXLIN
LISTEN
15.5.5
internal
1
Rx LIN
0
RXLIN
Busy Signal
LBUSY bit flag in LINSIR register is the image of the BUSY signal. It is set and cleared by
hardware. It signals that the controller is busy with LIN or UART communication.
15.5.5.1
Busy Signal in LIN Mode
Figure 15-7. Busy Signal in LIN Mode
FRAME SLOT
HEADER
LIN bus
1) LBUSY
BREAK
Field
SYNC
RESPONSE
Field
PROTECTED
IDENTIFIER
Field
DATA-0
DATA-n
Field
Field
CHECKSUM
Field
Node providing the master task
2) LBUSY
Node providing a slave task
Node providing neither the master task, neither a slave task
3) LBUSY
LCMD=Tx Header
LIDOK
LCMD=Tx or Rx Response
LTXOK or LRXOK
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When the busy signal is set, some registers are locked, user writing is not allowed:
• “LIN Control Register” - LINCR - except LCMD[2..0], LENA & LSWRES,
• “LIN Baud Rate Registers” - LINBRRL & LINBRRH,
• “LIN Data Length Register” - LINDLR,
• “LIN Identifier Register” - LINIDR,
• “LIN Data Register” - LINDAT.
If the busy signal is set, the only available commands are:
• LCMD[1..0] = 00 b, the abort command is taken into account at the end of the byte,
• LENA = 0 and/or LCMD[2] = 0, the kill command is taken into account immediately,
• LSWRES = 1, the reset command is taken into account immediately.
Note that, if another command is entered during busy signal, the new command is not validated and the LOVRERR bit flag of the LINERR register is set. The on-going transfer is not
interrupted.
15.5.5.2
Busy Signal in UART Mode
During the byte transmission, the busy signal is set. This locks some registers from being
written:
• “LIN Control Register” - LINCR - except LCMD[2..0], LENA & LSWRES,
• “LIN Data Register” - LINDAT.
The busy signal is not generated during a byte reception.
15.5.6
15.5.6.1
Bit Timing
Baud rate Generator
The baud rate is defined to be the transfer rate in bits per second (bps):
• BAUD: Baud rate (in bps),
• fclki/o: System I/O clock frequency,
• LDIV[11..0]: Contents of LINBRRH & LINBRRL registers - (0-4095), the pre-scaler
receives clki/o as input clock.
• LBT[5..0]: Least significant bits of - LINBTR register- (0-63) is the number of samplings in a
LIN or UART bit (default value 32).
Equation for calculating baud rate:
BAUD = fclki/o / LBT[5..0] x (LDIV[11..0] + 1)
Equation for setting LINDIV value:
LDIV[11..0] = ( fclki/o / LBT[5..0] x BAUD ) - 1
Note that in reception a majority vote on three samplings is made.
15.5.6.2
172
Re-synchronization in LIN Mode
When waiting for Rx Header, LBT[5..0] = 32 in LINBTR register. The re-synchronization
begins when the BREAK is detected. If the BREAK size is not in the range (10.5 bits min., 28
bits max. — 13 bits nominal), the BREAK is refused. The re-synchronization is done by adjusting LBT[5..0] value to the SYNCH field of the received header (0x55). Then the PROTECTED
IDENTIFIER is sampled using the new value of LBT[5..0].
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
The re-synchronization implemented in the controller tolerates a clock deviation of ± 20% and
adjusts the baud rate in a ± 2% range.
The new LBT[5..0] value will be used up to the end of the response. Then, the LBT[5..0] will be
reset to 32 for the next header.
The LINBTR register can be used to (software) re-calibrate the clock oscillator.
The re-synchronization is not performed if the LIN node is enabled as a master.
15.5.6.3
Handling LBT[5..0]
LDISR bit of LINBTR register is used to:
• Disable the re-synchronization (for instance in the case of LIN MASTER node),
• To enable the setting of LBT[5..0] (to manually adjust the baud rate especially in the case of
UART mode). A minimum of 8 is required for LBT[5..0] due to the sampling operation.
Note that the LENA bit of LINCR register is important for this handling (see Figure 15-8 on
page 173).
Figure 15-8. Handling LBT[5..0]
Write in LINBTR register
=1
LENA ?
(LINCR bit 4)
=0
LDISR
to write
=1
=0
LBT[5..0] forced to 0x20
LDISR forced to 0
Enable re-synch. in LIN mode
15.5.7
LBT[5..0] = LBT[5..0] to write
(LBT[5..0]min=8)
LDISR forced to 1
Disable re-synch. in LIN mode
Data Length
Section 15.4.6 “LIN Commands” on page 167 describes how to set or how are automatically
set the LRXDL[3..0] or LTXDL[3..0] fields of LINDLR register before receiving or transmitting a
response.
In the case of Tx Response the LRXDL[3..0] will be used by the hardware to count the number
of bytes already successfully sent.
In the case of Rx Response the LTXDL[3..0] will be used by the hardware to count the number
of bytes already successfully received.
If an error occurs, this information is useful to the programmer to recover the LIN messages.
15.5.7.1
Data Length in LIN 2.1
• If LTXDL[3..0]=0 only the CHECKSUM will be sent,
• If LRXDL[3..0]=0 the first byte received will be interpreted as the CHECKSUM,
• If LTXDL[3..0] or LRXDL[3..0] >8, values will be forced to 8 after the command setting and
before sending or receiving of the first byte.
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15.5.7.2
Data Length in LIN 1.3
• LRXDL and LTXDL fields are both hardware updated before setting LIDOK by decoding the
data length code contained in the received PROTECTED IDENTIFIER (LRXDL = LTXDL).
• Via the above mechanism, a length of 0 or >8 is not possible.
15.5.7.3
Data Length in Rx Response
Figure 15-9. LIN2.1 - Rx Response - No error
LIDOK
LIN bus
LRXDL (*)
4
LTXDL (*)
?
LRXOK
1st Byte
2 nd Byte
3 rd Byte
4 th Byte
DATA-0
DATA-1
DATA-2
DATA-3
CHECKSUM
1
2
3
4
0
LBUSY
LCMD2..0=000b
LCMD=Rx Response
LINDLR=0x?4
(*) : LRXDL & LTXDL updated by user
• The user initializes LRXDL field before setting the Rx Response command,
• After setting the Rx Response command, LTXDL is reset by hardware,
• LRXDL field will remain unchanged during Rx (during busy signal),
• LTXDL field will count the number of received bytes (during busy signal),
• If an error occurs, Rx stops, the corresponding error flag is set and LTXDL will give the
number of received bytes without error,
• If no error occurs, LRXOK is set after the reception of the CHECKSUM, LRXDL will be
unchanged (and LTXDL = LRXDL).
15.5.7.4
Data Length in Tx Response
Figure 15-10. LIN1.3 - Tx Response - No error
LIDOK
LIN bus
LRXDL (*)
4
LTXDL (*)
4
1st Byte
2 nd Byte
3 rd Byte
4 th Byte
DATA-0
DATA-1
DATA-2
DATA-3
0
1
2
LTXOK
CHECKSUM
3
4
LBUSY
LCMD2..0=000b
LCMD=Tx Response
(*) : LRXDL & LTXDL updated by Rx Response or Tx Response task
• The user initializes LTXDL field before setting the Tx Response command,
• After setting the Tx Response command, LRXDL is reset by hardware,
• LTXDL will remain unchanged during Tx (during busy signal),
• LRXDL will count the number of transmitted bytes (during busy signal),
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ATtiny87/ATtiny167
• If an error occurs, Tx stops, the corresponding error flag is set and LRXDL will give the
number of transmitted bytes without error,
• If no error occurs, LTXOK is set after the transmission of the CHECKSUM, LTXDL will be
unchanged (and LRXDL = LTXDL).
15.5.7.5
Data Length after Error
Figure 15-11. Tx Response - Error
LIN bus
1st Byte
2 nd Byte
DATA-0
DATA-1
3 rd Byte
LERR
DATA-2
ERROR
LRXDL
4
LTXDL
4
0
1
2
LBUSY
LCMD2..0=000b
LCMD=Tx Response
Note:
15.5.7.6
Information on response (ex: error on byte) is only available at the end of the serialization/de-serialization of the byte.
Data Length in UART Mode
• The UART mode forces LRXDL and LTXDL to 0 and disables the writing in LINDLR
register,
• Note that after reset, LRXDL and LTXDL are also forced to 0.
15.5.8
xxOK Flags
There are three xxOK flags in LINSIR register:
• LIDOK: LIN IDentifier OK
It is set at the end of the header, either by the Tx Header function or by the Rx Header. In
LIN 1.3, before generating LIDOK, the controller updates the LRXDL & LTXDL fields in
LINDLR register.
It is not driven in UART mode.
• LRXOK: LIN RX response complete
It is set at the end of the response by the Rx Response function in LIN mode and once a
character is received in UART mode.
• LTXOK: LIN TX response complete
It is set at the end of the response by the Tx Response function in LIN mode and once a
character has been sent in UART mode.
These flags can generate interrupts if the corresponding enable interrupt bit is set in the LINENIR register (see Section 15.5.13 “Interrupts” on page 178).
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15.5.9
xxERR Flags
LERR bit of the LINSIR register is an logical ‘OR’ of all the bits of LINERR register (see Section 15.5.13 “Interrupts” on page 178). There are eight flags:
• LBERR = LIN Bit ERRor.
A unit that is sending a bit on the bus also monitors the bus. A LIN bit error will be flagged
when the bit value that is monitored is different from the bit value that is sent. After
detection of a LIN bit error the transmission is aborted.
• LCERR = LIN Checksum ERRor.
A LIN checksum error will be flagged if the inverted modulo-256 sum of all received data
bytes (and the protected identifier in LIN 2.1) added to the checksum does not result in
0xFF.
• LPERR = LIN Parity ERRor (identifier).
A LIN parity error in the IDENTIFIER field will be flagged if the value of the parity bits does
not match with the identifier value. (See LP[1:0] bits in Section 15.6.8 “LIN Identifier
Register - LINIDR” on page 186). A LIN slave application does not distinguish between
corrupted parity bits and a corrupted identifier. The hardware does not undertake any
correction. However, the LIN slave application has to solve this as:
- known identifier (parity bits corrupted),
- or corrupted identifier to be ignored,
- or new identifier.
• LSERR = LIN Synchronization ERRor.
A LIN synchronization error will be flagged if a slave detects the edges of the SYNCH field
outside the given tolerance.
• LFERR = LIN Framing ERRor.
A framing error will be flagged if dominant STOP bit is sampled.
Same function in UART mode.
• LTOERR = LIN Time Out ERRor.
A time-out error will be flagged if the MESSAGE frame is not fully completed within the
maximum length T Frame_Maximum by any slave task upon transmission of the SYNCH and
IDENTIFIER fields (see Section 15.5.10 “Frame Time Out” on page 177).
• LOVERR = LIN OVerrun ERRor.
Overrun error will be flagged if a new command (other than LIN Abort) is entered while
‘Busy signal’ is present.
In UART mode, an overrun error will be flagged if a received byte overwrites the byte stored
in the serial input buffer.
• LABORT
LIN abort transfer reflects a previous LIN Abort command (LCMD[2..0] = 000) while ‘Busy
signal’ is present.
After each LIN error, the LIN controller stops its previous activity and returns to its withdrawal
mode (LCMD[2..0] = 000 b) as illustrated in Figure 15-11 on page 175.
Writing 1 in LERR of LINSIR register resets LERR bit and all the bits of the LINERR register.
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ATtiny87/ATtiny167
15.5.10
Frame Time Out
According to the LIN protocol, a frame time-out error is flagged if: T Frame > T Frame_Maximum.
This feature is implemented in the LIN/UART controller.
Figure 15-12. LIN timing and frame time-out
T Frame
T Header
BREAK
SYNC
Field
T Response
PROTECTED
IDENTIFIER
Field
DATA-0
Field
DATA-n
Field
Field
CHECKSUM
Field
Nominal
T Header_Nominal
T Response_Nominal
T Frame_Nominal
=
34 x
T Bit
T Bit
T Response_Nominal
=
10 ( Number_of_Data + 1 ) x
=
T Header_Nominal
+
Maximun
T Header_Maximum
T Response_Maximum
T Frame_Maximum
15.5.11
=
=
=
before Time-out
T Header_Nominal
1.4 x T Response_Nominal
T Header_Maximum + T Response_Maximum
1.4 x
Break-in-data
According to the LIN protocol, the LIN/UART controller can detect the BREAK/SYNC field
sequence even if the break is partially superimposed with a byte of the response. When a
BREAK/SYNC field sequence happens, the transfer in progress is aborted and the processing
of the new frame starts.
• On slave node(s), an error is generated (i.e. LBERR in case of Tx Response or LFERR in
case of Rx Response). Information on data error is also available, refer to the Section
15.5.7.5.
• On master node, the user (code) is responsible for this aborting of frame. To do this, the
master task has first to abort the on-going communication (clearing LCMD bits - LIN Abort
command) and then to apply the Tx Header command. In this case, the abort error flag LABORT - is set.
On the slave node, the BREAK detection is processed with the synchronization setting available when the LIN/UART controller processed the (aborted) response. But the
re-synchronization restarts as usual. Due to a possible difference of timing reference between
the BREAK field and the rest of the frame, the time-out values can be slightly inaccurate.
15.5.12
Checksum
The last field of a frame is the checksum.
In LIN 2.1, the checksum contains the inverted eight bit sum with carry over all data bytes and
the protected identifier. This calculation is called enhanced checksum.
⎛
⎛⎛ n
⎞
⎞
⎛⎛⎛ n
⎞
⎞
⎞⎞
⎜
⎜
⎜
⎟
⎟
CHECKSUM = 255 – unsigned char ∑DATA n + PROTECTED ID. + unsigned char ⎜ ⎜ ⎜ ∑DATA n⎟ + PROTECTED ID.⎟ » 8⎟ ⎟
⎜
⎜⎜
⎟
⎟
⎜⎜⎜
⎟
⎟
⎟⎟
⎝
⎝⎝ 0
⎠
⎠
⎝⎝⎝ 0
⎠
⎠
⎠⎠
In LIN 1.3, the checksum contains the inverted eight bit sum with carry over all data bytes.
This calculation is called classic checksum.
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⎛
⎛n
⎞
⎛⎛ n
⎞
⎞⎞
⎜
⎜
⎟
CHECKSUM = 255 – unsigned char ∑DATA n + unsigned char ⎜ ⎜ ∑DATA n⎟ » 8⎟ ⎟
⎜
⎜
⎟
⎜⎜
⎟
⎟⎟
⎝
⎝0
⎠
⎝⎝ 0
⎠
⎠⎠
Frame identifiers 60 (0x3C) to 61 (0x3D) shall always use classic checksum.
15.5.13
Interrupts
As shown in Figure 15-13 on page 178, the four communication flags of the LINSIR register
are combined to drive two interrupts. Each of these flags have their respective enable interrupt
bit in LINENIR register.
(see Section 15.5.8 “xxOK Flags” on page 175 and Section 15.5.9 “xxERR Flags” on page
176).
Figure 15-13. LIN Interrupt Mapping
LINERR.7
LINERR.6
LINERR.5
LINERR.4
LINERR.3
LINERR.2
LINERR.1
LINERR.0
LABORT
LTOERR
LOVERR
LINSIR.3
LFERR
LINENIR.3
LPERR
LENERR
LCERR
LINSIR.2
LBERR
LINSIR.1
LINSIR.0
15.5.14
LINENIR.2
LENIDOK
LINENIR.1
LENTXOK
LINENIR.0
LENRXOK
LIDOK
LIN TC
LTXOK
LRXOK
Message Filtering
Message filtering based upon the whole identifier is not implemented. Only a status for frame
headers having 0x3C, 0x3D, 0x3E and 0x3F as identifier is available in the LINSIR register.
Table 15-4.
178
LIN ERR
LERR
LSERR
Frame Status
LIDST[2..0]
Frame Status
0xx b
No specific identifier
100 b
60 (0x3C) identifier
101 b
61 (0x3D) identifier
110 b
62 (0x3E) identifier
111 b
63 (0x3F) identifier
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
The LIN protocol says that a message with an identifier from 60 (0x3C) up to 63 (0x3F) uses a
classic checksum (sum over the data bytes only). Software will be responsible for switching
correctly the LIN13 bit to provide/check this expected checksum (the insertion of the ID field in
the computation of the CRC is set - or not - just after entering the Rx or Tx Response
command).
15.5.15
15.5.15.1
Data Management
LIN FIFO Data Buffer
To preserve register allocation, the LIN data buffer is seen as a FIFO (with address pointer
accessible). This FIFO is accessed via the LINDX[2..0] field of LINSEL register through the
LINDAT register.
LINDX[2..0], the data index, is the address pointer to the required data byte. The data byte can
be read or written. The data index is automatically incremented after each LINDAT access if
the LAINC (active low) bit is cleared. A roll-over is implemented, after data index=7 it is data
index=0. Otherwise, if LAINC bit is set, the data index needs to be written (updated) before
each LINDAT access.
The first byte of a LIN frame is stored at the data index=0, the second one at the data index=1,
and so on. Nevertheless, LINSEL must be initialized by the user before use.
15.5.15.2
UART Data Register
The LINDAT register is the data register (no buffering - no FIFO). In write access, LINDAT will
be for data out and in read access, LINDAT will be for data in.
In UART mode the LINSEL register is unused.
15.5.16
OCD Support
When a debugger break occurs, the state machine of the LIN/UART controller is stopped
(included frame time-out) and further communication may be corrupted.
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15.6
LIN / UART Register Description
Table 15-5.
LIN/UART Register Bits Summary
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LSWRES
LIN13
LCONF1
LCONF0
LENA
LCMD2
LCMD1
LCMD0
LINCR
0
R/W
0
LIDST2
R/W
0
LIDST1
R/W
0
LIDST0
R/W
0
LBUSY
R/W
0
LERR
R/W
0
LIDOK
R/W
0
LTXOK
R/W
LRXOK
LINSIR
0
R
0
—
R
0
—
R
0
—
R
0
—
R/Wone
LENERR
0
R/Wone
LENIDOK
0
R/Wone
LENTXOK
0
R/Wone
LENRXOK
LINENIR
0
R
0
LABORT
R
0
LTOERR
R
0
LOVERR
R
0
LFERR
R/W
0
LSERR
R/W
0
LPERR
R/W
0
LCERR
R/W
LBERR
LINERR
0
R
0
R
0
LDISR
R
0
LBT5
R
0
LBT4
R
0
LBT3
R
0
LBT2
R
0
LBT1
R
LBT0
LINBTR
0
R/W
0
LDIV7
R
1
LDIV6
R/(W)
0
LDIV5
R/(W)
0
LDIV4
R/(W)
0
LDIV3
R/(W)
0
LDIV2
R/(W)
0
LDIV1
R/(W)
LDIV0
LINBRRL
0
R/W
0
—
R/W
0
—
R/W
0
—
R/W
0
—
R/W
0
LDIV11
R/W
0
LDIV10
R/W
0
LDIV9
R/W
LDIV8
LINBRRH
0
R
0
LTXDL3
R
0
LTXDL2
R
0
LTXDL1
R
0
LTXDL0
R/W
0
LRXDL3
R/W
0
LRXDL2
R/W
0
LRXDL1
R/W
LRXDL0
LINDLR
0
R/W
0
LP1
R/W
LP0
0
R/W
0
R/W
LID5/LDL1
LID4/LDL0
0
0
0
R/W
0
LID3
R/W
0
LID2
R/W
0
LID1
R/W
LID0
LINIDR
1
R
0
—
R
—
R/W
—
R/W
0
—
R/W
0
LAINC
R/W
0
LINDX2
R/W
0
LINDX1
R/W
LINDX0
LINSEL
0
R
0
LDATA7
R
0
LDATA6
R
0
LDATA5
R
0
LDATA4
R/W
0
LDATA3
R/W
0
LDATA2
R/W
0
LDATA1
R/W
LDATA0
LINDAT
0
180
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
15.6.1
LIN Control Register - LINCR
Bit
7
6
5
4
3
2
1
0
LSWRES
LIN13
LCONF1
LCONF0
LENA
LCMD2
LCMD1
LCMD0
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
LINCR
• Bit 7 - LSWRES: Software Reset
– 0 = No action,
– 1 = Software reset (this bit is self-reset at the end of the reset procedure).
• Bit 6 - LIN13: LIN 1.3 mode
– 0 = LIN 2.1 (default),
– 1 = LIN 1.3.
• Bit 5:4 - LCONF[1:0]: Configuration
a. LIN mode (default = 00):
– 00 = LIN Standard configuration (listen mode “off”, CRC “on” & Frame_Time_Out
“on”,
– 01 = No CRC, No Frame_Time_Out (listen mode “off”),
– 10 = No Frame_Time_Out (listen mode “off” & CRC “on”),
– 11 = Listening mode (CRC “on” & Frame_Time_Out “on”).
b.
UART mode (default = 00):
– 00 = 8-bit, no parity (listen mode “off”),
– 01 = 8-bit, even parity (listen mode “off”),
– 10 = 8-bit, odd parity (listen mode “off”),
– 11 = Listening mode, 8-bit, no parity.
• Bit 3 - LENA: Enable
– 0 = Disable (both LIN and UART modes),
– 1 = Enable (both LIN and UART modes).
• Bit 2:0 - LCMD[2..0]: Command and mode
The command is only available if LENA is set.
– 000 = LIN Rx Header - LIN abort,
– 001 = LIN Tx Header,
– 010 = LIN Rx Response,
– 011 = LIN Tx Response,
– 100 = UART Rx & Tx Byte disable,
– 11x = UART Rx Byte enable,
– 1x1 = UART Tx Byte enable.
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15.6.2
LIN Status and Interrupt Register - LINSIR
Bit
7
6
5
4
3
2
1
0
LIDST2
LIDST1
LIDST0
LBUSY
LERR
LIDOK
LTXOK
LRXOK
Read/Write
R
R
R
R
R/Wone
R/Wone
R/Wone
R/Wone
Initial Value
0
0
0
0
0
0
0
0
LINSIR
• Bits 7:5 - LIDST[2:0]: Identifier Status
– 0xx = no specific identifier,
– 100 = Identifier 60 (0x3C),
– 101 = Identifier 61 (0x3D),
– 110 = Identifier 62 (0x3E),
– 111 = Identifier 63 (0x3F).
• Bit 4 - LBUSY: Busy Signal
– 0 = Not busy,
– 1 = Busy (receiving or transmitting).
• Bit 3 - LERR: Error Interrupt
It is a logical OR of LINERR register bits. This bit generates an interrupt if its respective
enable bit - LENERR - is set in LINENIR.
– 0 = No error,
– 1 = An error has occurred.
The user clears this bit by writing 1 in order to reset this interrupt. Resetting LERR also
resets all LINERR bits.
In UART mode, this bit is also cleared by reading LINDAT.
• Bit 2 - LIDOK: Identifier Interrupt
This bit generates an interrupt if its respective enable bit - LENIDOK - is set in LINENIR.
– 0 = No identifier,
– 1 = Slave task: Identifier present, master task: Tx Header complete.
The user clears this bit by writing 1, in order to reset this interrupt.
• Bit 1 - LTXOK: Transmit Performed Interrupt
This bit generates an interrupt if its respective enable bit - LENTXOK - is set in
LINENIR.
– 0 = No Tx,
– 1 = Tx Response complete.
The user clears this bit by writing 1, in order to reset this interrupt.
In UART mode, this bit is also cleared by writing LINDAT.
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ATtiny87/ATtiny167
• Bit 0 - LRXOK: Receive Performed Interrupt
This bit generates an interrupt if its respective enable bit - LENRXOK - is set in
LINENIR.
– 0 = No Rx
– 1 = Rx Response complete.
The user clears this bit by writing 1, in order to reset this interrupt.
In UART mode, this bit is also cleared by reading LINDAT.
15.6.3
LIN Enable Interrupt Register - LINENIR
Bit
Read/Write
Initial Value
7
R
0
6
R
0
5
R
0
4
R
0
3
LENERR
R/W
0
2
LENIDOK
R/W
0
1
LENTXOK
R/W
0
0
LENRXOK
R/W
0
LINENIR
• Bits 7:4 - Reserved Bits
These bits are reserved for future use. For compatibility with future devices, they must be
written to zero when LINENIR is written.
• Bit 3 - LENERR: Enable Error Interrupt
– 0 = Error interrupt masked,
– 1 = Error interrupt enabled.
• Bit 2 - LENIDOK: Enable Identifier Interrupt
– 0 = Identifier interrupt masked,
– 1 = Identifier interrupt enabled.
• Bit 1 - LENTXOK: Enable Transmit Performed Interrupt
– 0 = Transmit performed interrupt masked,
– 1 = Transmit performed interrupt enabled.
• Bit 0 - LENRXOK: Enable Receive Performed Interrupt
– 0 = Receive performed interrupt masked,
– 1 = Receive performed interrupt enabled.
15.6.4
LIN Error Register - LINERR
Bit
Read/Write
Initial Value
7
LABORT
R
0
6
LTOERR
R
0
5
LOVERR
R
0
4
LFERR
R
0
3
LSERR
R
0
2
LPERR
R
0
1
LCERR
R
0
0
LBERR
R
0
LINERR
• Bit 7 - LABORT: Abort Flag
– 0 = No warning,
– 1 = LIN abort command occurred.
This bit is cleared when LERR bit in LINSIR is cleared.
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7728D–AVR–07/09
• Bit 6 - LTOERR: Frame_Time_Out Error Flag
– 0 = No error,
– 1 = Frame_Time_Out error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 5 - LOVERR: Overrun Error Flag
– 0 = No error,
– 1 = Overrun error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 4 - LFERR: Framing Error Flag
– 0 = No error,
– 1 = Framing error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 3 - LSERR: Synchronization Error Flag
– 0 = No error,
– 1 = Synchronization error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 2 - LPERR: Parity Error Flag
– 0 = No error,
– 1 = Parity error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 1 - LCERR: Checksum Error Flag
– 0 = No error,
– 1 = Checksum error.
This bit is cleared when LERR bit in LINSIR is cleared.
• Bit 0 - LBERR: Bit Error Flag
– 0 = no error,
– 1 = Bit error.
This bit is cleared when LERR bit in LINSIR is cleared.
15.6.5
LIN Bit Timing Register - LINBTR
Bit
7
6
5
4
3
2
1
0
LDISR
-
LBT5
LBT4
LBT3
LBT2
LBT1
LBT0
Read/Write
R/W
R
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
R/(W)
Initial Value
0
0
1
0
0
0
0
0
LINBTR
• Bit 7 - LDISR: Disable Bit Timing Re synchronization
– 0 = Bit timing re-synchronization enabled (default),
– 1 = Bit timing re-synchronization disabled.
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• Bits 5:0 - LBT[5:0]: LIN Bit Timing
Gives the number of samples of a bit.
sample-time = (1 / fclki/o ) x (LDIV[11..0] + 1)
Default value: LBT[6:0]=32 — Min. value: LBT[6:0]=8 — Max. value: LBT[6:0]=63
15.6.6
LIN Baud Rate Register - LINBRR
Bit
7
6
5
4
3
2
1
0
LDIV7
LDIV6
LDIV5
LDIV4
LDIV3
LDIV2
LDIV1
LDIV0
LINBRRL
-
-
-
-
LDIV11
LDIV10
LDIV9
LDIV8
LINBRRH
Bit
15
14
13
12
11
10
9
8
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
• Bits 15:12 - Reserved Bits
These bits are reserved for future use. For compatibility with future devices, they must be
written to zero when LINBRR is written.
• Bits 11:0 - LDIV[11:0]: Scaling of clki/o Frequency
The LDIV value is used to scale the entering clki/o frequency to achieve appropriate LIN or
UART baud rate.
15.6.7
LIN Data Length Register - LINDLR
Bit
7
6
5
4
3
2
1
0
LTXDL3
LTXDL2
LTXDL1
LTXDL0
LRXDL3
LRXDL2
LRXDL1
LRXDL0
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
LINDLR
• Bits 7:4 - LTXDL[3:0]: LIN Transmit Data Length
In LIN mode, this field gives the number of bytes to be transmitted (clamped to 8 Max).
In UART mode this field is unused.
• Bits 3:0 - LRXDL[3:0]: LIN Receive Data Length
In LIN mode, this field gives the number of bytes to be received (clamped to 8 Max).
In UART mode this field is unused.
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15.6.8
LIN Identifier Register - LINIDR
Bit
7
6
5
4
3
2
1
0
LP1
LP0
LID5 /
LDL1
LID4 /
LDL0
LID3
LID2
LID1
LID0
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
LINIDR
• Bits 7:6 - LP[1:0]: Parity
In LIN mode:
LP0 = LID4 ^ LID2 ^ LID1 ^ LID0
LP1 = ! ( LID1 ^ LID3 ^ LID4 ^ LID5 )
In UART mode this field is unused.
• Bits 5:4 - LDL[1:0]: LIN 1.3 Data Length
In LIN 1.3 mode:
– 00 = 2-byte response,
– 01 = 2-byte response,
– 10 = 4-byte response,
– 11 = 8-byte response.
In UART mode this field is unused.
• Bits 3:0 - LID[3:0]: LIN 1.3 Identifier
In LIN 1.3 mode: 4-bit identifier.
In UART mode this field is unused.
• Bits 5:0 - LID[5:0]: LIN 2.1 Identifier
In LIN 2.1 mode: 6-bit identifier (no length transported).
In UART mode this field is unused.
15.6.9
LIN Data Buffer Selection Register - LINSEL
Bit
7
6
5
4
3
2
1
0
-
-
-
-
LAINC
LINDX2
LINDX1
LINDX0
Read/Write
-
-
-
-
R/W
R/W
R/W
R/W
Initial Value
-
-
-
-
0
0
0
0
LINSEL
• Bits 7:4 - Reserved Bits
These bits are reserved for future use. For compatibility with future devices, they must be
written to zero when LINSEL is written.
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• Bit 3 - LAINC: Auto Increment of Data Buffer Index
In LIN mode:
– 0 = Auto incrementation of FIFO data buffer index (default),
– 1 = No auto incrementation.
In UART mode this field is unused.
• Bits 2:0 - LINDX 2:0: FIFO LIN Data Buffer Index
In LIN mode: location (index) of the LIN response data byte into the FIFO data buffer.
The FIFO data buffer is accessed through LINDAT.
In UART mode this field is unused.
15.6.10
LIN Data Register - LINDAT
Bit
7
6
5
4
3
2
1
0
LDATA7
LDATA6
LDATA5
LDATA4
LDATA3
LDATA2
LDATA1
LDATA0
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
LINDAT
• Bits 7:0 - LDATA[7:0]: LIN Data In / Data out
In LIN mode: FIFO data buffer port.
In UART mode: data register (no data buffer - no FIFO).
– In Write access, data out.
– In Read access, data in.
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16. ISRC - Current Source
16.1
Features
• 100µA Constant current source
• ±10% Absolute Accuracy
The ATtiny87/167 features a 100µA ±10% Current Source. Up on request, the current is flowing through an external resistor. The voltage can be measured on the dedicated pin shared
with the ADC. Using a resistor in serie with a ≤ 0.5% tolerance is recommended. To protect the
device against big values, the ADC must be configured with AVcc as internal reference to perform the first measurement. Afterwards, another internal reference can be chosen according
to the previous measured value to refine the result.
When ISRCEN bit is set, the ISRC pin sources 100µA. Otherwise this pin keeps its initial
function.
Figure 16-1. Current Source Block Diagram
AVCC
100 uA
ISRCEN
ADCn/ ISRC
ADC Input
External
Resistor
16.2
16.2.1
Typical applications
LIN Current Source
During the configuration of a LIN node in a cluster, it may be necessary to attribute dynamically an unique physical address to every cluster node. The way to do it is not described in the
LIN protocol.
The Current Source offers an excellent solution to associate a physical address to the application supported by the LIN node. A full dynamic node configuration can be used to set-up the
LIN nodes in a cluster.
ATtiny87/167 proposes to have an external resistor used in conjunction with the Current
Source. The device measures the voltage to the boundaries of the resistance via the Analog to
Digital converter. The resulting voltage defines the physical address that the communication
handler will use when the node will participate in LIN communication.
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In automotive applications, distributed voltages are very disturbed. The internal Current
Source solution of ATtiny87/167 immunizes the address detection the against any kind of voltage variations.
Table 16-1.
Example of Resistor Values(±5%) for a 8-address System (AVcc = 5V(1))
Minimum
Reading with
a 2.56V ref
Typical
Reading with
a 2.56V ref
Physical
Address
Resistor Value
Rload (Ohm)
Typical Measured
Voltage (V)
0
1 000
0.1
40
1
2 200
0.22
88
2
3 300
0.33
132
3
4 700
0.47
188
4
6 800
0.68
272
5
10 000
1
400
6
15 000
1.5
600
7
22 000
2.2
880
Table 16-2.
Maximum
Reading with
a 2.56V ref
Example of Resistor Values(±1%) for a 16-address System (AVcc = 5V(1))
Minimum
Typical Measured Reading with
Voltage (V)
a 2.56V ref
Typical
Reading with
a 2.56V ref
Miximum
Reading with
a 2.56V ref
40
45
Physical
Address
Resistor Value
Rload (Ohm)
0
1 000
1
1 200
0.12
46
48
54
2
1500
0.15
57
60
68
3
1800
0.18
69
72
81
4
2200
0.22
84
88
99
5
2700
0.27
104
108
122
6
3300
0.33
127
132
149
7
4700
0.47
181
188
212
8
6 800
0.68
262
272
306
Note:
0.1
38
9
8 200
0.82
316
328
369
10
10 000
1.0
386
400
450
11
12 000
1.2
463
480
540
12
15 000
1.5
579
600
675
13
18 000
1.8
694
720
810
14
22 000
2.2
849
880
989
15
27 000
2.7
1023
1023
1023
1. 5V range: Max Rload 30KΩ
3V range: Max Rload 15KΩ
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16.2.2
Current Source for Low Cost Transducer
An external transducer based on a variable resistor can be connected to the Current Source.
This can be, for instance:
• A thermistor, or temperature-sensitive resistor, used as a temperature sensor,
• A CdS photoconductive cell, or luminosity-sensitive resistor, used as a luminosity sensor,
• ...
Using the Current Source with this type of transducer eliminates the need for additional parts
otherwise required in resistor network or Wheatstone bridge.
16.2.3
Voltage Reference for External Devices
An external resistor used in conjunction with the Current Source can be used as voltage reference for external devices. Using a resistor in serie with a lower tolerance than the Current
Source accuracy (≤2%) is recommended. Table 16-2 gives an example of voltage references
using standard values of resistors.
16.2.4
Threshold Reference for Internal Analog Comparator
An external resistor used in conjunction with the Current Source can be used as threshold reference for internal Analog Comparator (See ”AnaComp - Analog Comparator” on page 211.).
This can be connected to AIN0 (negative Analog Compare input pin) as well as AIN1 (positive
Analog Compare input pin). Using a resistor in serie with a lower tolerance than the Current
Source accuracy (≤2%) is recommended. Table 16-2 gives an example of threshold references
using standard values of resistors.
16.3
16.3.1
Control Register
AMISCR – Analog Miscellaneous Control Register
Bit
7
6
5
4
3
2
1
0
-
-
-
-
-
AREFEN
XREFEN
ISRCEN
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
AMISCR
• Bit 0 – ISRCEN: Current Source Enable
Writing this bit to one enables the Current Source as shown in Figure 16-1. It is recommended
to use DIDR register bit function when ISRCEN is set. It also recommended to turn off the Current Source as soon as possible ( ex: once the ADC measurement is done).
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17. ADC – Analog to Digital Converter
17.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
17.2
10-bit Resolution
1.0 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
13 - 260 µs Conversion Time (Low - High Resolution)
Up to 15 kSPS at Maximum Resolution
11 Multiplexed Single Ended Input Channels
8 Differential input pairs with selectable gain
Temperature sensor input channel
Voltage from Internal Current Source Driving (ISRC)
Optional Left Adjustment for ADC Result Readout
0 - AVcc ADC Input Voltage Range
Selectable 1.1V / 2.56V ADC Voltage Reference
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
Unipolar / Bipolar Input Mode
Input Polarity Reversal Mode
Overview
The ATtiny87/167 features a 10-bit successive approximation ADC. The ADC is connected to
a 11-channel Analog Multiplexer which allows 16 differential voltage input combinations and
11 single-ended voltage inputs constructed from the pins PA7..PA0 or PB7..PB4. The differential input is equipped with a programmable gain stage, providing amplification steps of 8x or
20x on the differential input voltage before the A/D conversion. The single-ended voltage
inputs refer to 0V (AGND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC
is held at a constant level during conversion. A block diagram of the ADC is shown in Figure
17-1.
Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. Alternatively,
AVcc can be used as reference voltage for single ended channels. There are also options to
output the internal 1.1V or 2.56V reference voltages or to input an external voltage reference
and turn-off the internal voltage reference. These options are selected using the REFS[1:0]
bits of the ADMUX control register and using AREFEN and XREFEN bits of the AMISCR control register.
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Figure 17-1. Analog to Digital Converter Block Schematic
Internal
2.56 / 1.1V
Reference
ADC Data Register
(ADCH / ADCL)
Trigger
Select
Interrupt
Flags
ADC[9..0]
ADSC
ADATE
ADTS[2..0]
ADIF
ADEN
BIN
ADLAR
MUX[4..0]
REFS0
REFS1
ADPS[2..0]
ADC Control & Status
Register A & B (ADCSRA/ADCSRB)
ADC Multiplexer
Select (ADMUX)
AREFEN
XREFEN
Analog Misc.
(AMISCR)
ADC Conversion
Complete IRQ
ADIF
ADIE
8-Bit Data Bus
Prescaler
Start
Mux.
Decoder
Conversion Logic
Sample & Hold
Comparator
AVCC
10-bit DAC
AGND
AVCC/
4
Bandgap
Reference
Temperature
Sensor
ADC10
ADC9
ADC8
AREF
ADC7
XREF
Pos.
Input
Mux.
ADC Multiplexer
Output
ADC6
ADC5
ADC4
ISRC / ADC3
Mux.
ADC2
ADC1
x8 / x20 Gain
Amplifier
ADC0
Neg.
Input
Mux.
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17.3
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value represents AGND and the maximum value represents the voltage
on AVcc, the voltage refrence on AREF pin or an internal 1.1V / 2.56V voltage reference.
The voltage reference for the ADC may be selected by writing to the REFS[1..0] bits in
ADMUX and AREFEN bit in AMISCR. The AVcc supply, the AREF pin or an internal 1.1V /
2.56V voltage reference may be selected as the ADC voltage reference.
The analog input channel and differential gain are selected by writing to the MUX[4..0] bits in
ADMUX register. Any of the 11 ADC input pins ADC[10..0] can be selected as single ended
inputs to the ADC. The positive and negative inputs to the differential gain amplifier are
described in Table 17-5.
If differential channels are selected, the differential gain stage amplifies the voltage difference
between the selected input pair by the selected gain factor 8x or 20x, according to the setting
of the MUX[4..0] bits in ADMUX register. This amplified value then becomes the analog input
to the ADC. If single ended channels are used, the gain amplifier is bypassed altogether.
The on-chip temperature sensor is selected by writing the code defined in Table 17-5 to the
MUX[4..0] bits in ADMUX register when its dedicated ADC channel is used as an ADC input.
A specific ADC channel (defined in Table 17-5) is used to measure the voltage to the boundaries of an external resistance flowing by a current driving by the Internal Current Source
(ISRC).
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA register. Voltage reference and input channel selections will not go into effect until ADEN is set. The ADC does not
consume power when ADEN is cleared, so it is recommended to switch off the ADC before
entering power saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and
ADCL. By default, the result is presented right adjusted, but can optionally be presented left
adjusted by setting the ADLAR bit in ADMUX register.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the data
registers belongs to the same conversion. Once ADCL is read, ADC access to data registers
is blocked. This means that if ADCL has been read, and a conversion completes before ADCH
is read, neither register is updated and the result from the conversion is lost. When ADCH is
read, ADC access to the ADCH and ADCL Registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When
ADC access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.
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17.4
Starting a Conversion
A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC.
This bit stays high as long as the conversion is in progress and will be cleared by hardware
when the conversion is completed. If a different data channel is selected while a conversion is
in progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering
is enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA register. The trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB register (see
description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on
the selected trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions at fixed intervals. If the trigger signal still is set when
the conversion completes, a new conversion will not be started. If another positive edge
occurs on the trigger signal during conversion, the edge will be ignored. Note that an Interrupt
Flag will be set even if the specific interrupt is disabled or the Global Interrupt Enable bit in
SREG register is cleared. A conversion can thus be triggered without causing an interrupt.
However, the Interrupt Flag must be cleared in order to trigger a new conversion at the next
interrupt event.
Figure 17-2. ADC Auto Trigger Logic
CLK IO
ADTS[2:0]
Start
ADIF
ADATE
SOURCE 1
ADC Prescaler
CLKADC
...
Conversion
Logic
...
...
...
SOURCE n
Edge
Detector
ADSC
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as
soon as the ongoing conversion has finished. The ADC then operates in Free Running mode,
constantly sampling and updating the ADC Data Register. The first conversion must be started
by writing a logical one to the ADSC bit in ADCSRA register. In this mode the ADC will perform
successive conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or
not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA
register to one. ADSC can also be used to determine if a conversion is in progress. The ADSC
bit will be read as one during a conversion, independently of how the conversion was started.
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17.5
Prescaling and Conversion Timing
Figure 17-3. ADC Prescaler
ADEN
Reset
Start
7-bit ADC Prescaler
CK/128
CK/64
CK/32
CK/8
CK/16
CK/4
CK/2
CLK IO
ADPS0
ADPS1
ADPS2
By default, the successive approximation circuitry requires an input clock frequency between
50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed,
the input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA
register. The prescaler starts counting from the moment the ADC is switched on by setting the
ADEN bit in ADCSRA register. The prescaler keeps running for as long as the ADEN bit is set,
and is continuously reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA register, the
conversion starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is
switched on (ADEN in ADCSRA register is set) takes 25 ADC clock cycles in order to initialize
the analog circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 14.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a
new conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This
assures a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold takes place 2 ADC clock cycles after the rising edge on the trigger source signal.
Three additional CPU clock cycles are used for synchronization logic.
In Free Running mode, a new conversion will be started immediately after the conversion
completes, while ADSC remains high. For a summary of conversion times, see Table 17-1.
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Figure 17-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
ycle Number
1
2
13
12
14
15
16
17
18
19
20
21
22
24
23
25
1
2
3
DC Clock
DEN
DSC
DIF
Sign and MSB of Result
DCH
LSB of Result
DCL
MUX and REFS
Update
MUX
and REFS
Update
Conversion
Complete
Sample & Hold
Figure 17-5. ADC Timing Diagram, Single Conversion
One Conversion
1
ycle Number
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
3
DC Clock
DSC
DIF
DCH
Sign and MSB of Result
DCL
LSB of Result
Sample & Hold
Conversion
Complete
MUX and REFS
Update
MUX and REFS
Update
Figure 17-6. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
ycle Number
1
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
DC Clock
igger
ource
DATE
DIF
DCH
Sign and MSB of Result
DCL
LSB of Result
Prescaler
Reset
196
Sample &
Hold
Conversion
Complete
Prescaler
Reset
MUX and REFS
Update
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 17-7. ADC Timing Diagram, Free Running Conversion
One Conversion
ycle Number
11
12
Next Conversion
13
1
2
3
4
DC Clock
DSC
DIF
DCH
Sign and MSB of Result
DCL
LSB of Result
Sample & Hold
Conversion
Complete
Table 17-1.
MUX and REFS
Update
ADC Conversion Time
Sample & Hold
(Cycles from Start of Conversion)
Conversion Time (Cycles)
First conversion
13.5 cycles
25 cycles
Normal conversions
1.5 cycles
13 cycles
2 cycles
13.5 cycles
Condition
Auto Triggered conversions
17.6
Changing Channel or Reference Selection
The MUX[4:0] and REFS[1:0] bits in the ADMUX register are single buffered through a temporary register to which the CPU has random access. This ensures that the channels and
reference selection only takes place at a safe point during the conversion. The channel and
reference selection is continuously updated until a conversion is started. Once the conversion
starts, the channel and reference selection is locked to ensure a sufficient sampling time for
the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion
completes (ADIF in ADCSRA register is set). Note that the conversion starts on the following
rising ADC clock edge after ADSC is written. The user is thus advised not to write new channel
or reference selection values to ADMUX until one ADC clock cycle after ADSC is written.
If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
a. When ADATE or ADEN is cleared.
b.
During conversion, minimum one ADC clock cycle after the trigger event.
c.
After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
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17.6.1
ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion. The
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the conversion to complete before changing the channel
selection.
In Free Running mode, always select the channel before starting the first conversion. The
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the first conversion to complete, and then change the channel selection. Since the next conversion has already started automatically, the next result will
reflect the previous channel selection. Subsequent conversions will reflect the new channel
selection.
17.6.2
17.7
ADC Voltage Reference
The voltage reference for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either AVcc, internal 1.1V / 2.56V voltage reference or external AREF pin. The first ADC conversion result after switching voltage reference source may be inaccurate, and the user is
advised to discard this result.
ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce
noise induced from the CPU core and other I/O peripherals. The noise canceler can be used
with ADC Noise Reduction and Idle mode. To make use of this feature, the following procedure should be used:
a. Make sure that the ADC is enabled and is not busy converting. Single Conversion
mode must be selected and the ADC conversion complete interrupt must be
enabled.
b.
Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted.
c.
If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt
routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt
request will be generated when the ADC conversion completes. The CPU will
remain in active mode until a new sleep command is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than
Idle mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before
entering such sleep modes to avoid excessive power consumption.
17.7.1
198
Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 17-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin,
regardless of whether that channel is selected as input for the ADC. When the channel is
selected, the source must drive the S/H capacitor through the series resistance (combined
resistance in the input path).
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher
impedance is used, the sampling time will depend on how long time the source needs to
charge the S/H capacitor, with can vary widely. The user is recommended to only use low
impedant sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor.
Signal components higher than the Nyquist frequency (fADC/2) should not be present to avoid
distortion from unpredictable signal convolution. The user is advised to remove high frequency
components with a low-pass filter before applying the signals as inputs to the ADC.
Figure 17-8. Analog Input Circuitry
IIH
ADCn
1..100 kO
IIL
CS/H= 14 pF
VCC/2
17.7.2
Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. If conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over
the analog ground plane, and keep them well away from high-speed switching
digital tracks.
17.7.3
b.
Use the ADC noise canceler function to reduce induced noise from the CPU.
c.
If any port pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress.
ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Ideal value: 0 LSB.
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Figure 17-9. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
VREF Input Voltage
• Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last
transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum).
Ideal value: 0 LSB
Figure 17-10. Gain Error
Output Code
Gain
Error
Ideal ADC
Actual ADC
VREF Input Voltage
• Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0
LSB.
200
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Figure 17-11. Integral Non-linearity (INL)
Output Code
INL
Ideal ADC
Actual ADC
VREF
Input Voltage
• Differential Non-linearity (DNL): The maximum deviation of the actual code width (the
interval between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0
LSB.
Figure 17-12. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
VREF Input Voltage
• Quantization Error: Due to the quantization of the input voltage into a finite number of
codes, a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5
LSB.
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared
to an ideal transition for any code. This is the compound effect of offset, gain error,
differential error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
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17.8
ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversion as there are three types of conversions: single ended conversion, unipolar differential conversion and bipolar differential conversion.
17.8.1
Single Ended Conversion
For single ended conversion, the result is:
V IN ⋅ 1024
ADC = ---------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 17-4 on page 205 and Table 17-5 on page 206). 0x000 represents analog ground, and
0x3FF represents the selected voltage reference minus one LSB. The result is presented in
one-sided form, from 0x3FF to 0x000.
17.8.2
Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is:
( V POS – V NEG ) ⋅ 1024
ADC = ----------------------------------------------------------- ⋅ GAIN
V REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference (see Table 17-4 on page 205 and Table 17-5 on page
206). The voltage on the positive pin must always be larger than the voltage on the negative
pin or otherwise the voltage difference is saturated to zero. The result is presented in
one-sided form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 8x or 20x.
17.8.3
Bipolar Differential Conversion
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writing the BIN bit in the ADCSRB register to one. In the bipolar input mode
two-sided voltage differences are allowed and thus the voltage on the negative input pin can
also be larger than the voltage on the positive input pin. If differential channels and a bipolar
input mode are used, the result is:
( V POS – V NEG ) ⋅ 512
ADC = ------------------------------------------------------- ⋅ GAIN
V REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference. The result is presented in two’s complement form,
from 0x200 (-512d) through 0x000 (+0d) to 0x1FF (+511d). The GAIN is either 8x or 20x.
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However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses
one bit of the converter dynamic range. Then, if the user wants to perform the conversion with
the maximum dynamic range, the user can perform a quick polarity check of the result and use
the unipolar differential conversion with selectable differential input pair. When the polarity
check is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH register). If the
bit is one, the result is negative, and if this bit is zero, the result is positive.
17.9
Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC input. MUX[4..0] bits in ADMUX register enables the temperature sensor.
The internal 1.1V voltage reference must also be selected for the ADC voltage reference
source in the temperature sensor measurement. When the temperature sensor is enabled, the
ADC converter can be used in single conversion mode to measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in Table 17-2.
The voltage sensitivity is approximately 1 LSB/°C and the accuracy of the temperature measurement is ±10°C using manufacturing calibration values (TS_GAIN, TS_OFFSET). The
values described in Table 17-2 are typical values. However, due to the process variation the
temperature sensor output varies from one chip to another.
Table 17-2.
Temperature vs. Sensor Output Voltage (Typical Case): Example ADC Values
Temperature/°C
17.9.1
–40°C
+25°C
+85°C
0x00F6
0x0144
0c01B8
Manufacturing Calibration
Calibration values determined during test are available in the signature row.
The temperature in degrees Celsius can be calculated using the formula:
( [ ( ADCH « 8 ) ADCL ] – ( 273 + 25 – TS_OFFSET ) ) × 128
T = ------------------------------------------------------------------------------------------------------------------------------------------------------- + 25
TS_GAIN
Where:
a. ADCH & ADCL are the ADC data registers,
b.
is the temperature sensor gain
c.
TSOFFSET is the temperature sensor offset correction term
TS_GAIN is the unsigned fixed point 8-bit temperature sensor gain factor in
1/128th units stored in the signature row
TS_OFFSET is the signed twos complement temperature sensor offset reading
stored in the signature row. See Table 20-1 on page 221 for signature row
parameter address.
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The following code example allows to read Signature Row data:
.equ TS_GAIN = 0x0007
.equ TS_OFFSET = 0x0005
LDI R30,LOW(TS_GAIN)
LDI R31,HIGH (TS_GAIN)
RCALL Read_signature_row
MOV R17,R16 ; Save R16 result
LDI R30,LOW(TS_OFFSET)
LDI R31,HIGH (TS_OFFSET)
RCALL Read_signature_row
; R16 holds TS_OFFSET and R17 holds TS_GAIN
Read_signature_row:
IN R16,SPMCSR ; Wait for SPMEN ready
SBRC R16,SPMEN ; Exit loop here when SPMCSR is free
RJMP Read_signature_row
LDI R16,((1<<SIGRD)|(1<<SPMEN)) ; We need to set SIGRD and SPMEN
together
OUT SPMCSR,R16 ; and execute the LPM within 3 cycles
LPM R16,Z
RET
17.10 Internal Voltage Reference Output
The internal voltage reference is output on XREF pin as described in Table 17-3 if the ADC is
turned on (See “Voltage Reference Enable Signals and Start-up Time” on page 53.). Addition
of an external filter capacitor (5 - 10 nF) on XREF pin may be necessary. XREF current load
must be from 1 µA to 100 µA with VCC from 2.7V to 5.5V for XREF = 1.1V and with VCC from
4.5V to 5.5V for XREF = 2.56V.
XREF pin can be coupled to an analog input of the ADC (See ”Pin Configuration” on page 5.).
Table 17-3.
Internal Voltage Reference Output
Voltage Reference Output (Iload ≤ 100 µA)
REFS1 (2)
REFS0 (2)
0
x
x
Hi-Z, the pin can be used as AREF input or other alternate
functions.
1 (1)
0
1
XREF = 1.1V (3)
1 (1)
1
1
XREF = 2.56V (3)(4)
XREFEN
Notes:
(1)
1. See ”Bit 1 – XREFEN: Internal Voltage Reference Output Enable” on page 210.
2. See ”Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits” on page 205.
3. In these configurations, the pin pull-up must be turned off and the pin digital output must be
set in Hi-Z.
4. Vcc in range 4.5 - 5.5V.
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17.11 Register Description
17.11.1
ADMUX – ADC Multiplexer Selection Register
Bit
7
6
5
4
3
2
1
0
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADMUX
• Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits
These bits and AREFEN bit from the Analog Miscellaneous Control Register (AMISCR) select
the voltage reference for the ADC, as shown in Table 17-4. If these bits are changed during a
conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSRA
register is set). Whenever these bits are changed, the next conversion will take 25 ADC clock
cycles. If active channels are used, using AVCC or an external AREF higher than (AVcc - 1V)
is not recommended, as this will affect ADC accuracy. The internal voltage reference options
may not be used if an external voltage is being applied to the AREF pin.
Table 17-4.
Voltage Reference Selections for ADC
REFS1
REFS0
AREFEN Voltage Reference (VREF) Selection
X
0
0
AVcc used as Voltage Reference, diconnected from AREF pin.
X
0
1
External Voltage Reference at AREF pin (AREF ≥ 2.0V)
0
1
0
Internal 1.1V Voltage Reference .
1
1
0
Internal 2.56V Voltage Reference .
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register. Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted.
Changing the ADLAR bit will affect the ADC Data Register immediately, regardless of any
ongoing conversions. For a complete description of this bit, see “ADCL and ADCH – The ADC
Data Register” on page 208.
• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
These bits select which combination of analog inputs are connected to the ADC. In case of differential input, gain selection is also made with these bits. Refer to Table 17-5 for details. If
these bits are changed during a conversion, the change will not go into effect until this
conversion is complete (ADIF in ADCSRA register is set).
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Table 17-5.
Input Channel Selections
MUX[4..0]
Single Ended Input
0 0000
ADC0 (PA0)
0 0001
ADC1 (PA1)
0 0010
ADC2 (PA2)
0 0011
ADC3 / ISRC (PA3)
0 0100
ADC4 (PA4)
0 0101
ADC5 (PA5)
0 0110
ADC6 (PA6)
0 0111
ADC7 / AREF (PA7)
0 1000
ADC8 (PB5)
0 1001
ADC9 (PB6)
0 1010
ADC10 (PB7)
0 1011
Temperature Sensor
0 1100
Bandgap Reference (1.1
V)
0 1101
AVcc/4
0 1110
GND (0V)
0 1111
(reserved)
Positive
Differential Input
Negative
Differential Input
Gain
NA
NA
NA
ADC0 (PA0)
ADC1 (PA1)
1 0000
8x
1 0001
20x
1 0010
8x
ADC1 (PA1)
ADC2 (PA2)
1 0011
20x
1 0100
8x
ADC2 (PA2)
ADC3 (PA3)
1 0101
20x
1 0110
8x
ADC4 (PA4)
ADC5 (PA5)
1 0111
20x
N/A
1 1000
8x
ADC5 (PA5)
ADC6 (PA6)
1 1001
20x
1 1010
8x
ADC6 (PA6)
ADC7 (PA7)
1 1011
20x
1 1100
8x
ADC8 (PB5)
ADC9 (PB6)
1 1101
20x
1 1110
8x
ADC9 (PB6)
1 1111
206
ADC10 (PB7)
20x
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
17.11.2
ADCSRA – ADC Control and Status Register A
Bit
7
6
5
4
3
2
1
0
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRA
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the
ADC off while a conversion is in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, write this bit to one to start each conversion. In Free Running
mode, write this bit to one to start the first conversion. The first conversion after ADSC has
been written after the ADC has been enabled, or if ADSC is written at the same time as the
ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion
performs initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a
conversion on a positive edge of the selected trigger signal. The trigger source is selected by
setting the ADC Trigger Select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The
ADC Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set.
ADIF is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if doing a
Read-Modify-Write on ADCSRA, a pending interrupt can be disabled. This also applies if the
SBI and CBI instructions are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete
Interrupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the system clock frequency and the input
clock to the ADC.
Table 17-6.
ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
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Table 17-6.
17.11.3
17.11.3.1
ADPS2
ADPS1
ADPS0
Division Factor
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
ADCL and ADCH – The ADC Data Register
ADLAR = 0
Bit
Read/Write
Initial Value
17.11.3.2
ADC Prescaler Selections (Continued)
15
14
13
12
11
10
9
8
–
–
–
–
–
–
ADC9
ADC8
ADCH
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ADLAR = 1
Bit
Read/Write
Initial Value
15
14
13
12
11
10
9
8
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
ADC1
ADC0
–
–
–
–
–
–
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently,
if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the
result is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result”
on page 202.
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17.11.4
ADCSRB – ADC Control and Status Register B
Bit
7
6
5
4
3
2
1
0
BIN
ACME
ACIR1
ACIR0
–
ADTS2
ADTS1
ADTS0
Read/Write
R/W
R/W
R/W
R/W
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 7– BIN: Bipolar Input Mode
The gain stage is working in the unipolar mode as default, but the bipolar mode can be
selected by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided
conversions are supported and the voltage on the positive input must always be larger than
the voltage on the negative input. Otherwise the result is saturated to the voltage reference. In
the bipolar mode two-sided conversions are supported and the result is represented in the
two’s complement form. In the unipolar mode the resolution is 10 bits and the bipolar mode the
resolution is 9 bits + 1 sign bit.
• Bit 3 – Res: Reserved Bit
This bit is reserved for future use. For compatibility with future devices it must be written to
zero when ADCSRB register is written.
• Bits 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA register is written to one, the value of these bits selects which source
will trigger an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect.
A conversion will be triggered by the rising edge of the selected Interrupt Flag. Note that
switching from a trigger source that is cleared to a trigger source that is set, will generate a
positive edge on the trigger signal. If ADEN in ADCSRA register is set, this will start a conversion. Switching to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the
ADC Interrupt Flag is set.
Table 17-7.
17.11.5
ADC Auto Trigger Source Selections
ADTS2
ADTS1
ADTS0
Trigger Source
0
0
0
Free Running mode
0
0
1
Analog Comparator
0
1
0
External Interrupt Request 0
0
1
1
Timer/Counter1 Compare Match A
1
0
0
Timer/Counter1 Overflow
1
0
1
Timer/Counter1 Compare Match B
1
1
0
Timer/Counter1 Capture Event
1
1
1
Watchdog Interrupt Request
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
ADC7D /
AIN1D
ADC6D /
AIN0D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR0
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• Bits 7:0 – ADC7D:ADC0D: ADC7:0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When
an analog signal is applied to the ADC7:0 pin and the digital input from this pin is not needed,
this bit should be written logic one to reduce power consumption in the digital input buffer.
17.11.6
DIDR1 – Digital Input Disable Register 1
Bit
7
6
5
4
3
2
1
-
ADC10D
ADC9D
ADC8D
-
-
-
0
-
Read/Write
R
R/W
R/W
R/W
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
DIDR1
• Bit 7 – Res: Reserved Bit
This bit is reserved for future use. For compatibility with future devices it must be written to
zero when DIDR1 register is written.
• Bits 6..4 – ADC10D..ADC8D: ADC10..8 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When
an analog signal is applied to the ADC10:8 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.
• Bits 3:0 - Reserved Bits
These bits are reserved for future use. For compatibility with future devices, they must be written to zero when DIDR1 is written.
17.11.7
AMISCR – Analog Miscellaneous Control Register
Bit
7
6
5
4
3
2
1
0
-
-
-
-
-
AREFEN
XREFEN
ISRCEN
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
AMISCR
• Bits 7:3 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, they must be written to zero when AMISCR is written.
• Bit 2 – AREFEN: External Voltage Reference Input Enable
When this bit is written logic one, the voltage reference for the ADC is input from AREF pin as
described in Table 17.10 on page 204. If active channels are used, using AVcc or an external
AREF higher than (AVcc - 1V) is not recommended, as this will affect ADC accuracy. The
internal voltage reference options may not be used if an external voltage is being applied to
the AREF pin. It is recommended to use DIDR register bit function (digital input disable) when
AREFEN is set.
• Bit 1 – XREFEN: Internal Voltage Reference Output Enable
When this bit is written logic one, the internal voltage reference 1.1V or 2.56V is output on
XREF pin as described in Table 17.10 on page 204. It is recommended to use DIDR register
bit function (digital input disable) when XREFEN is set.
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18. AnaComp - Analog Comparator
The Analog Comparator compares the input values on the positive pin (AIN1) and negative pin
(AIN0). When the voltage on the positive pin is higher than the voltage on the negative pin, the
Analog Comparator output, ACO, is set. The comparator can trigger a separate interrupt,
exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator
output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown
in Figure 18-1.
Figure 18-1. Analog Comparator Block Diagram(1)(2)
ADC Multiplexer
Output (1)
AVcc
ACME
ACO
ADEN
ACD
ACI 16-bit Timer/Counter
Input Capture
AIN1
(PA7)
Interrupt
Sensivity
Control
Analog Comparator
Interrupt
AIN0
(PA6)
(from ADC)
ACIS1
ACIRS
Internal
2.56 V
Reference
ACIE
ACIS0
2.56 V
1.28 V
REFS0
0.64 V
REFS1
0.32 V
ACIR0
ACIR1
Notes:
1. See Table 18-2 on page 214 and Table 18-3 on page 214
2. Refer to Figure 1-2 on page 5 and Table 9-3 on page 76 for Analog Comparator pin
placement.
18.1
18.1.1
Register Description
ADC Control and Status Register B – ADCSRB
Bit
7
6
5
4
3
2
1
0
BIN
ACME
ACIR1
ACIR0
—
ADTS2
ADTS1
ADTS0
Read/Write
R
R/W
R/W
R/W
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the
ADC multiplexer selects the positive input to the Analog Comparator. When this bit is written
logic zero, AIN1 is applied to the positive input of the Analog Comparator.
When the Analog to Digital Converter (ADC) is configured as single ended input channel, it is
possible to select any of the ADC[10..0] pins to replace the positive input to the Analog Comparator. The ADC multiplexer (MUX[4..0]) is used to select this input, and consequently, the
ADC must be switched off to utilize this feature.
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• Bits 5, 4 – ACIR1, ACIR0: Analog Comparator Internal Voltage Reference Select
When ACIRS bit is set in ADCSRA register, these bits select a voltage reference for the negative input to the Analog Comparator, see Table 18-3 on page 214.
18.1.2
ACSR – Analog Comparator Control and Status Register
Bit
7
6
5
4
3
2
1
0
ACD
ACIRS
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 of ACSR register. Otherwise an interrupt can occur when
the bit is changed.
• Bit 6 – ACIRS: Analog Comparator Internal Reference Select
When this bit is set an Internal Reference Voltage replaces the negative input to the Analog
Comparator (c.f. Table 18-3 on page 214).
If ACIRS is cleared, AIN0 is applied to the negative input to the Analog Comparator.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO.
The synchronization introduces a delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is
set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding
interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog
Comparator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to
the input capture front-end logic, making the comparator utilize the noise canceler and edge
select features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection 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 (TIMSK1) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt.
The different settings are shown in Table 18-1.
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Table 18-1.
ACIS1
ACIS0
0
0
Comparator Interrupt on Output Toggle.
0
1
Reserved
1
0
Comparator Interrupt on Falling Output Edge.
1
1
Comparator Interrupt on Rising Output Edge.
Note:
18.1.3
ACIS1 / ACIS0 Settings
Interrupt Mode
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.
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
ADC7D /
AIN1D
ADC6D /
AIN0D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR0
• Bits 7,6 – AIN1D, AIN0D: AIN1D and AIN0D Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding Analog Compare 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 AIN0/1 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.
18.2
18.2.1
Analog Comparator Inputs
Analog Compare Positive Input
It is possible to select any of the inputs of the ADC Positive Input Multiplexer to replace the
positive input to the Analog Comparator. The ADC multiplexer is used to select this input, and
consequently, the ADC must be switched off to utilize this feature. If the Analog Comparator
Multiplexer Enable bit (ACME in ADCSRB register) is set and the ADC is switched off (ADEN
in ADCSRA register is zero), MUX[4..0] in ADMUX register select the input pin to replace the
positive input to the Analog Comparator, as shown in Table 18-2. If ACME is cleared or ADEN
is set, AIN1 pin is applied to the positive input to the Analog Comparator.
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Table 18-2.
18.2.2
ACME
ADEN
MUX[4..0]
0
x
x xxxx b
AIN1
x
1
x xxxx b
AIN1
1
0
0 0000 b
ADC0
1
0
0 0001 b
ADC1
1
0
0 0010 b
ADC2
1
0
0 0011 b
ADC3 / ISRC
1
0
0 0100 b
ADC4
1
0
0 0101 b
ADC5
1
0
0 0110 b
ADC6
1
0
0 0111 b
ADC7
1
0
0 1000 b
ADC8
1
0
0 1001 b
ADC9
1
0
0 1010 b
ADC10
1
0
Other
Analog Comparator Positive Input - Comment
ADC Switched On
ADC Switched Off.
This doesn’t make sense - Don’t use.
Analog Compare Negative Input
It is possible to select an internal voltage reference to replace the negative input to the Analog
Comparator. The output of a 2-bit DAC using the Internal Voltage Reference of the DAC is
available when ACIRS bit of ACSR register is set. The voltage reference division factor is
done by ACIR[1..0] of ADCSRB register.
If ACIRS is cleared, AIN0 pin is applied to the negative input to the Analog Comparator.
Table 18-3.
214
Analog Comparator Positive Input
Analog Comparator Negative Input
ACIRS
ACIR[1..0]
REFS[1..0] Analog Comparator Negative Input - Comment
0
x
x
1
x
0 0b
0 1b
1 0b
Reserved
1
0 0b
1 1b
2.56 V - using Internal 2.56V Voltage Reference
1
0 1b
1 1b
1.28 V (1/2 of 2.56 V) - using Internal 2.56V Voltage Reference
1
1 0b
1 1b
0.64 V (1/4 of 2.56 V - using Internal 2.56V Voltage Reference
1
1 1b
1 1b
0.32 V (1/8 of 2.56 V) - using Internal 2.56V Voltage Reference
AIN0
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
19. DebugWIRE On-chip Debug System
19.1
Features
•
•
•
•
•
•
•
•
•
•
19.2
Complete Program Flow Control
Emulates All On-chip Functions, Both Digital and Analog, except RESET Pin
Real-time Operation
Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)
Unlimited Number of Program Break Points (Using Software Break Points)
Non-intrusive Operation
Electrical Characteristics Identical to Real Device
Automatic Configuration System
High-Speed Operation
Programming of Non-volatile Memories
Overview
The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatile
memories.
19.3
Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed, the debugWIRE system within the target device is activated. The RESET port pin is
configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes
the communication gateway between target and emulator.
Figure 19-1. The debugWIRE Setup
+1.8 - +5.5V
Vcc
dW
dW (RESET)
GND
Figure 19-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system clock is not affected by debugWIRE and will always be the clock
source selected by the CKSEL Fuses.
When designing a system where debugWIRE will be used, the following observations must be
made for correct operation:
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7728D–AVR–07/09
• Pull-up resistors on the dW/(RESET) line must not be smaller than 10kΩ. The pull-up
resistor is not required for debugWIRE functionality.
• Connecting the RESET pin directly to Vcc will not work.
• Capacitors connected to the RESET pin must be disconnected when using debugWire.
• All external reset sources must be disconnected.
19.4
Software Break Points
DebugWIRE supports Program memory break points by the AVR BREAK instruction. Setting a
break point in AVR Studio® will insert a BREAK instruction in the Program memory. The
instruction replaced by the BREAK instruction will be stored. When program execution is continued, the stored instruction will be executed before continuing from the Program memory. A
break can be inserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a break point is changed. This is automatically
handled by AVR Studio through the debugWIRE interface. The use of break points will therefore reduce the Flash Data retention. Devices used for debugging purposes should not be
shipped to end customers.
19.5
Limitations of DebugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is
enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken while
accessing some of the I/O Registers via the debugger (AVR Studio).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse
should be disabled when debugWire is not used.
19.6
DebugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.
19.6.1
DebugWIRE Data Register – DWDR
Bit
7
6
5
4
Read/Write
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
3
2
1
0
R/W
R/W
R/W
R/W
0
0
0
0
DWDR[7:0]
DWDR
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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ATtiny87/ATtiny167
20. Flash Programming
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 (i.e. LIN,
USART, ...) 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.
20.1
20.1.1
Self-Programming the Flash
Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “00000011 b” to SPMCSR
and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is
ignored. The page address must be written to PCPAGE in the Z-register. Other bits in the
Z-pointer will be ignored during this operation.
• The CPU is halted during the Page Erase operation.
20.1.2
Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001 b” 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.
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20.1.3
Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “00000101 b” to SPMCSR
and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is
ignored. The page address must be written to PCPAGE. Other bits in the Z-pointer must be
written to zero during this operation.
• The CPU is halted during the Page Write operation.
20.2
Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers ZL and ZH in the register file. The number of bits actually used is implementation
dependent.
Bit
Bit
15
14
13
12
11
10
9
8
Z15
Z14
Z13
Z12
Z11
Z10
Z9
Z8
ZH (R31)
Z7
Z6
Z5
Z4
Z3
Z2
Z1
Z0
ZL (R30)
7
6
5
4
3
2
1
0
Since the Flash is organized in pages (see Table 21-7 on page 228), 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 20-1.
Note that the Page Erase and Page Write operations are addressed independently. Therefore
it is of major importance that the software addresses the same page in both the Page Erase
and Page Write operation.
The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses
the Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
Figure 20-1. Addressing the Flash During SPM (1)
BIT
15
ZPCMSB
ZPAGEMSB
1 0
0
PCMSB
PROGRAM COUNTER
Z - POINTER
PAGEMSB
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PCWORD
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
218
1. The different variables used in Table 20-2 are listed in Table 21-7 on page 228.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
20.2.1
Store Program Memory Control and Status Register – SPMCSR
The Store Program Memory Control and Status Register contains the control bits needed to
control the Boot Loader operations.
Bit
7
6
5
4
3
2
1
0
–
RWWSB
SIGRD
CTPB
RFLB
PGWRT
PGERS
SPMEN
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPMCSR
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATtiny87/167 and will always read as zero.
• Bit 6 – RWWSB: Read-While-Write Section Busy
This bit is for compatibility with devices supporting Read-While-Write. It will always read as
zero in ATtiny87/167.
• Bit 5 – SIGRD: Signature Row Read
If this bit is written to one at the same time as SPMEN, the next LPM instruction within three
clock cycles will read a byte from the signature row into the destination register. See ”Reading
the Signature Row from Software” on page 221. for details. An SPM instruction within four
cycles after SIGRD and SPMEN are set will have no effect.
• Bit 4 – CTPB: Clear Temporary Page Buffer
If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will
be cleared and the data will be lost.
• Bit 3 – RFLB: Read Fuse and Lock Bits
An LPM instruction within three cycles after RFLB and SPMEN are set in the SPMCSR Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the
destination register. See ”Reading the Fuse and Lock Bits from Software” on page 220. for
details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four
clock cycles executes Page Write, with the data stored in the temporary buffer. The page
address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The
PGWRT bit will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire Page Write operation.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four
clock cycles executes Page Erase. The page address is taken from the high part of the
Zpointer. 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.
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• Bit 0 – SPMEN: Self Programming Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together
with either SIGRD, CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction will have
a special meaning, see description above. If only SPMEN is written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The
LSB of the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM
instruction, or if no SPM instruction is executed within four clock cycles. During Page Erase
and Page Write, the SPMEN bit remains high until the operation is completed.
Writing any other combination than “10 0001 b”, “01 0001 b”, “00 1001 b”, “00 0101 b”, “00 0011
b” or “00 0001 b” in the lower six bits will have no effect.
Note:
Only one SPM instruction should be active at any time.
20.2.2
EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading
the Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit (EEPE) in the EECR Register and
verifies that the bit is cleared before writing to the SPMCSR Register.
20.2.3
Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the RFLB and SPMEN bits are set in SPMCSR,
the value of the Lock bits will be loaded in the destination register. The RFLB and SPMEN bits
will auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When
RFLB and SPMEN are cleared, LPM will work as described in the Instruction set Manual.
Bit
7
6
5
4
3
2
1
0
Rd (Z=0x0001)
–
–
–
–
–
–
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the RFLB
and SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after
the RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will
be loaded in the destination register as shown below. See Table 21-5 on page 227 for a
detailed description and mapping of the Fuse Low byte.
Bit
Rd (Z=0x0000)
7
6
5
4
3
2
1
0
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the Fuse High byte (FHB), load 0x0003 in the Z-pointer. When an
LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the
SPMCSR, the value of the Fuse High byte will be loaded in the destination register as shown
below. See Table 21-4 on page 226 for detailed description and mapping of the Fuse High
byte.
Bit
Rd (Z=0x0003)
220
7
6
5
4
3
2
1
0
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Similarly, when reading the Extended Fuse byte (EFB), load 0x0002 in the Z-pointer. When an
LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the
SPMCSR, the value of the Extended Fuse byte will be loaded in the destination register as
shown below. See Table 21-3 on page 226 for detailed description and mapping of the
Extended Fuse byte.
Bit
7
6
5
4
3
2
1
0
Rd (Z=0x0002)
–
–
–
–
–
–
–
EFB0
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
20.2.4
Reading the Signature Row from Software
To read the Signature Row from software, load the Z-pointer with the signature byte address
given in Table 20-1 on page 221 and set the SIGRD and SPMEN bits in SPMCSR. When an
LPM instruction is executed within three CPU cycles after the SIGRD and SPMEN bits are set
in SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD
and SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if
no LPM instruction is executed within three CPU cycles. When SIGRD and SPMEN are
cleared, LPM will work as described in the Instruction set Manual.
Table 20-1.
Note:
Signature Row Addressing
Signature Byte
Z-Pointer Address
Device Signature Byte 0
0x0000
Device Signature Byte 1
0x0002
Device Signature Byte 2
0x0004
8MHz RC Oscillator Calibration Byte
0x0001
TSOFFSET - Temp Sensor Offset
0x0005
TSGAIN - Temp Sensor Gain
0x0007
All other addresses are reserved for future use.
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7728D–AVR–07/09
20.2.5
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.
20.2.6
Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 20-2 shows the typical programming time for Flash accesses from the CPU.
Table 20-2.
222
SPM Programming Time
Symbol
Min Programming Time
Max Programming Time
Flash write (Page Erase, Page Write,
and write Lock bits by SPM)
3.7 ms
4.5 ms
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
20.2.7
Simple Assembly Code Example for a Boot Loader
Note that the RWWSB bit will always be read as zero in ATtiny87/167. Nevertheless, it is
recommended to check this bit as shown in the code example, to ensure compatibility with
devices supporting Read-While-Write.
;- The routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y-pointer
; the first data location in Flash is pointed to by the Z-pointer
;- Error handling is not included
;- Registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
;
loophi (r25), spmcsrval (r20)
; - Storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
.equ PAGESIZEB = PAGESIZE*2
.org SMALLBOOTSTART
; AGESIZEB is page size in BYTES, not words
Write_page:
; Page Erase
ldi
spmcsrval, (1<<PGERS) | (1<<SELFPGEN)
rcall Do_spm
; Clear temporary page buffer
ldi
spmcsrval, (1<<CPTB) | (1<<SELFPGEN)
rcall Do_spm
; Transfer data from RAM to Flash temporary page buffer
ldi
looplo, low(PAGESIZEB)
; init loop variable
ldi
loophi, high(PAGESIZEB)
; not required for PAGESIZEB<=256
Wrloop:
ld
ld
ldi
rcall
adiw
sbiw
brne
r0, Y+
r1, Y+
spmcsrval, (1<<SELFPGEN)
Do_spm
ZH:ZL, 2
loophi:looplo, 2
; use subi for PAGESIZEB<=256
Wrloop
; Execute Page Write
subi
ZL, low(PAGESIZEB)
; restore pointer
sbci
ZH, high(PAGESIZEB)
; not required for PAGESIZEB<=256
ldi
spmcsrval, (1<<PGWRT) | (1<<SELFPGEN)
rcall Do_spm
; Clear temporary page buffer
ldi
spmcsrval, (1<<CPTB) | (1<<SELFPGEN)
rcall Do_spm
; Read
ldi
ldi
subi
sbci
back and check, optional
looplo, low(PAGESIZEB)
; init loop variable
loophi, high(PAGESIZEB) ; not required for PAGESIZEB<=256
YL, low(PAGESIZEB)
; restore pointer
YH, high(PAGESIZEB)
Rdloop:
lpm
r0, Z+
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ld
cpse
rjmp
sbiw
brne
r1, Y+
r0, r1
Error
loophi:looplo, 1
Rdloop
; use subi for PAGESIZEB<=256
; To ensure compatibility with devices supporting Read-While-Write
; Return to RWW section
; Verify that RWW section is safe to read
Return:
in
temp1, SPMCSR
sbrs
temp1, RWWSB
; If RWWSB is set, the RWW section is not ready
yet
ret
; Clear temporary page buffer
ldi
spmcsrval, (1<<CPTB) | (1<<SELFPGEN)
call
Do_spm
rjmp
Return
Do_spm:
; Check for previous SPM complete
Wait_spm:
in
temp1, SPMCSR
sbrc
temp1, SELFPGEN
rjmp
Wait_spm
; Input: spmcsrval determines SPM action
; Disable interrupts if enabled, store status
in
temp2, SREG
cli
; Check that no EEPROM write access is present
Wait_ee:
sbic
EECR, EEPE
rjmp
Wait_ee
; SPM timed sequence
out
SPMCSR, spmcsrval
spm
; Restore SREG (to enable interrupts if originally enabled)
out
SREG, temp2
ret
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ATtiny87/ATtiny167
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ATtiny87/ATtiny167
21. Memory Programming
21.1
Program and Data Memory Lock Bits
The ATtiny87/167 provides two Lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 21-2. The Lock bits can only be
erased to “1” with the Chip Erase command. The ATtiny87/167 has no separate Boot Loader
section.
Table 21-1.
Lock Bit Byte(Note:)
Lock Bit Byte
Note:
Bit No
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
5
–
1 (unprogrammed)
4
–
1 (unprogrammed)
3
–
1 (unprogrammed)
2
–
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
“1” means unprogrammed, “0” means programmed.
Table 21-2.
Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
LB2
LB1
1
1
1
No memory lock features enabled.
2
1
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)
3
0
0
Further programming and verification of the Flash and EEPROM
is disabled in Parallel and Serial Programming mode. The Fuse
bits are locked in both Serial and Parallel Programming mode.(1)
Notes:
1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
21.2
Fuse Bits
The ATtiny87/167 has three Fuse bytes. Table 21-3, Table 21-4 & Table 21-5 describe briefly
the functionality of all the fuses and how they are mapped into the Fuse bytes.
The SPM instruction is enabled for the whole Flash if the SELFPRGEN fuse is programmed
(“0”), otherwise it is disabled.
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Note that the fuses are read as logical zero, “0”, if they are programmed.
Table 21-3.
Extended Fuse Byte
Fuse Extended Byte
Bit No
Description
Default Value
–
7
–
1 (unprogrammed)
–
6
–
1 (unprogrammed)
–
5
–
1 (unprogrammed)
–
4
–
1 (unprogrammed)
–
3
–
1 (unprogrammed)
–
2
–
1 (unprogrammed)
–
1
–
1 (unprogrammed)
SELFPRGEN
0
Self Programming Enable
1 (unprogrammed)
Table 21-4.
Fuse High Byte
Fuse High Byte
Bit No Description
(1)
Default Value
RSTDISBL
7
External Reset Disable
1 (unprogrammed)
DWEN
6
DebugWIRE Enable
1 (unprogrammed)
SPIEN(2)
5
Enable Serial Program
and Data Downloading
0 (programmed,
SPI programming enabled)
WDTON(3)
4
Watchdog Timer always on
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
BODLEVEL2(4)
2
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL1
(4)
1
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL0
(4)
0
Brown-out Detector trigger level
1 (unprogrammed)
Notes:
1. See ”Alternate Functions of Port B” on page 81. for description of RSTDISBL Fuse.
2. The SPIEN Fuse is not accessible in serial programming mode.
3. See ”Watchdog Timer Control Register - WDTCR” on page 57. for details.
4. See Table 22-5 on page 247 for BODLEVEL Fuse coding.
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Table 21-5.
Fuse Low Byte
Fuse Low Byte
Bit No
Description
Default Value
CKDIV8(4)
7
Divide clock by 8
0 (programmed)
CKOUT(3)
6
Clock output
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)
Notes:
1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 4-4 on page 27 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See Table 4-3
on page 27 for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB5. See ”Clock Output Buffer” on page 31. for details.
4. See ”System Clock Prescaler” on page 37.for details.
21.2.1
21.3
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the
fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and parallel mode, also when the device is locked. The three
bytes reside in a separate address space.
Table 21-6.
Device
ATtiny87
ATtiny167
Signature Bytes
Address
Value
Signature Byte Description
0
0x1E
Indicates manufactured by Atmel
1
0x93
Indicates 8 KB Flash memory
2
0x87
Indicates ATtiny87 device when address 1 contains
0x93
0
0x1E
Indicates manufactured by Atmel
1
0x94
Indicates 16 KB Flash memory
2
0x87
Indicates ATtiny167 device when address 1 contains
0x94
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21.4
Calibration Byte
The ATtiny87/167 has a byte calibration value for the internal RC Oscillator. This byte resides
in the high byte of address 0x000 in the signature address space. During reset, this byte is
automatically written into the OSCCAL Register to ensure correct frequency of the calibrated
RC Oscillator.
21.5
Page Size
Table 21-7.
Device
Flash Size
Page Size
PCWORD
No. of Pages
PCPAGE
PCMSB
ATtiny87
4K words
64 words
PC[5:0]
64
PC[11:6]
11
ATtiny167
8K words
64 words
PC[5:0]
128
PC[12:6]
12
Table 21-8.
21.6
Number of Words in a Page and No. of Pages in the Flash
Number of Words in a Page and No. of Pages in the EEPROM
Device
EEPROM Size
ATtiny87
ATtiny167
512 bytes
Page Size PCWORD
4 bytes
No. of Pages
PCPAGE
EEAMSB
128
EEA[8:2]
8
EEA[1:0]
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 ATtiny87/167. Pulses are assumed to
be at least 250 ns unless otherwise noted.
21.6.1
Signal Names
In this section, some pins of the ATtiny87/167 are referenced by signal names describing their
functionality during parallel programming, see Figure 21-1 and Figure 21-9. 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 Figure 21-11.
When pulsing WR or OE, the command loaded determines the action executed. The different
commands are shown in Figure 21-12.
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ATtiny87/ATtiny167
Figure 21-1. Parallel programming
WR
PB0
XA0
PB1
XA1 / BS2
PB2
PAGEL / BS1
PB3
+4.5 - +5.5V
Vcc
+4.5 - +5.5V
AVcc
XTAL1 / PB4
OE
PB5
RDY / BSY
PB6
+12 V
PA7 - PA0
DATA
RESET / PB7
GND
Note:
Vcc - 0.3V < AVcc < Vcc + 0.3V, however, AVcc should always be within 4.5 - 5.5V
Table 21-9.
Pin Name Mapping
Signal Name in
Programming Mode
Pin Name
I/O
WR
PB0
I
Write Pulse (Active low).
XA0
PB1
I
XTAL1 Action Bit 0
XA1 / BS2
PB2
I
- XTAL1 Action Bit 1
- Byte Select 2
(“0” selects low byte, “1” selects 2’nd high byte)
PAGEL / BS1
PB3
I
- Program Memory and EEPROM data Page Load
- Byte Select 1
(“0” selects low byte, “1” selects high byte)
PB4
I
XTAL1 (Clock input)
OE
PB5
I
Output Enable (Active low).
RDY / BSY
PB6
O
0: Device is busy programming,
1: Device is ready for new command.
+12V
PB7
I
- Reset (Active low)
- Parallel programming mode (+12V).
DATA
PA7-PA0
I/O
Function
Bi-directional Data bus (Output when OE is low).
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Table 21-10. Pin Values Used to Enter Programming Mode
Pin
Symbol
Value
PAGEL / BS1
Prog_enable[3]
0
XA1 / BS2
Prog_enable[2]
0
XA0
Prog_enable[1]
0
WR
Prog_enable[0]
0
Table 21-11. 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 21-12. Command Byte Bit Coding
Command Byte
230
Command Executed
1000 0000 b
Chip Erase
0100 0000 b
Write Fuse bits
0010 0000 b
Write Lock bits
0001 0000 b
Write Flash
0001 0001 b
Write EEPROM
0000 1000 b
Read Signature bytes and Calibration byte
0000 0100 b
Read Fuse and Lock bits
0000 0010 b
Read Flash
0000 0011 b
Read EEPROM
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
21.7
21.7.1
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 21-10 on page 230 to “0000 b” 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.
21.7.2
Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient programming, the following should be considered.
• The command needs only be loaded once when writing or reading multiple memory
locations.
• Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
• Address high byte needs only be loaded before programming or reading a new 256 word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.
21.7.3
Chip Erase
The Chip Erase will erase the Flash and EEPROM(Note:) memories plus Lock bits. The Lock
bits are not reset until the program memory has been completely erased. The Fuse bits are
not changed. A Chip Erase must be performed before the Flash and/or EEPROM are
reprogrammed.
Note:
The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “1,0 ”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000 b”. 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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7728D–AVR–07/09
21.7.4
Programming the Flash
The Flash is organized in pages, see Table 21-7 on page 228. 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 “1,0”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000 b”. 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 “0,1”. 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 “0,1”. 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 21-3 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 21-2 on page 233. 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.
232
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ATtiny87/ATtiny167
G. Load Address High byte
1. Set XA1, XA0 to “0,0”. 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 21-3 for signal waveforms).
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 “1,0”. This enables command loading.
2. Set DATA to “0000 0000 b”. 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 21-2. Addressing the Flash Which is Organized in Pages
PCMSB
PROGRAM COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
1. PCPAGE and PCWORD are listed in
233
7728D–AVR–07/09
Figure 21-3. Programming the Flash Waveforms (1)
F
DATA
A
B
0x10
ADDR. LOW
C
DATA LOW
D
DATA HIGH
E
XX
B
ADDR. LOW
C
DATA LOW
D
DATA HIGH
E
XX
G
ADDR. HIGH
H
XX
XA1 / BS2
XA0
PAGEL / BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
Note:
21.7.5
1. “XX” is don’t care. The letters refer to the programming description above.
Programming the EEPROM
The EEPROM is organized in pages, see Table 21-8 on page 228. 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 232 for details on Command, Address and
Data loading):
A: Load Command “0001 0001 b”.
G: Load Address High Byte (0x00 - 0xFF).
B: Load Address Low Byte (0x00 - 0xFF).
C: Load Data (0x00 - 0xFF).
E: Latch data (give PAGEL a positive pulse).
K: Repeat A through E until the entire buffer is filled.
L: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 21-4
for signal waveforms).
234
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ATtiny87/ATtiny167
Figure 21-4. Programming the EEPROM Waveforms
K
A
DATA
0x11
G
ADDR. HIGH
B
ADDR. LOW
C
E
B
DATA
XX
ADDR. LOW
C
DATA
E
L
XX
XA1 / BS2
XA0
PAGEL / BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
21.7.6
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” on
page 232 for details on Command and Address loading):
1. A: Load Command “0000 0010 b”.
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 BS1 to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
21.7.7
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the
Flash” on page 232 for details on Command and Address loading):
1. A: Load Command “0000 0011 b”.
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”.
21.7.8
Programming the Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the
Flash” on page 232 for details on Command and Data loading):
1. A: Load Command “0100 0000 b”.
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.
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7728D–AVR–07/09
21.7.9
Programming the Fuse High Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming the
Flash” on page 232 for details on Command and Data loading):
1. A: Load Command “0100 0000 b”.
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.
21.7.10
Programming the Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming
the Flash” on page 232 for details on Command and Data loading):
1. A: Load Command “0100 0000 b”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS2 to “0”. This selects low data byte.
Figure 21-5. 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 / BS2
XA0
PAGEL / BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
21.7.11
Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on
page 232 for details on Command and Data loading):
1. A: Load Command “0010 0000 b”.
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 re-program the Lock bits
by any External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
4. The Lock bits can only be cleared by executing Chip Erase.
236
ATtiny87/ATtiny167
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ATtiny87/ATtiny167
21.7.12
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 232 for details on Command loading):
1. A: Load Command “0000 0100 b”.
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 21-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
Fuse Low Byte
0
Extended Fuse Byte
1
0
DATA
BS2
Lock Bits
0
Fuse High Byte
1
1
BS1
BS2
21.7.13
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash”
on page 232 for details on Command and Address loading):
1. A: Load Command “0000 1000 b”.
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”.
21.7.14
Reading the 8 MHz RC Oscillator Calibration Byte
The algorithm for reading the 8 MHz RC Oscillator Calibration byte is as follows (refer to “Programming the Flash” on page 232 for details on Command and Address loading):
1. A: Load Command “0000 1000 b”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The 8 MHz RC Oscillator Calibration byte can now be
read at DATA.
4. Set OE to “1”.
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7728D–AVR–07/09
21.7.15
Reading the Temperature Sensor Parameter Bytes
The algorithm for reading the Temperature Sensor parameter bytes is as follows (refer to “Programming the Flash” on page 232 for details on Command and Address loading):
1. A: Load Command “0000 1000 b”.
2. B: Load Address Low Byte, 0x0003 or 0x0005.
3. Set OE to “0”, and BS1 to “1”. The Temperature Sensor parameter byte can now be
read at DATA.
4. Set OE to “1”.
21.8
Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus
while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and
MISO (output). After RESET is set low, the Programming Enable instruction needs to be executed first before program/erase operations can be executed.
Note:
In Table 21-13, the pin mapping for SPI programming is listed. Not all parts use the SPI pins
dedicated for the internal SPI interface.
Figure 21-7. Serial Programming and Verify (Note:)
+2.7 - +5.5V
Vcc
MOSI
PA4
MISO
PA2
SCK
PA5
RESET / PB7
GND
Note:
If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
XTAL1 pin
Table 21-13. Pin Mapping Serial Programming
Symbol
Pin Name
I/O
Function
MOSI
PA4
I
Serial Data In
MISO
PA2
O
Serial Data Out
SCK
PA5
I
Serial Clock
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
238
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ATtiny87/ATtiny167
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
21.8.1
Serial Programming Algorithm
When writing serial data to the ATtiny87/167, data is clocked on the rising edge of SCK.
When reading data from the ATtiny87/167, data is clocked on the falling edge of SCK. See
Figure 21-7 and Figure 21-8 for timing details.
To program and verify the ATtiny87/167 in the Serial Programming mode, the following
sequence is recommended (see four byte instruction formats in Table 21-15 on page 240):
1. Power-up sequence:
Apply power between Vcc and GND while RESET and SCK are set to “0”. In some
systems, the programmer can not guarantee that SCK is held low during power-up. In
this case, RESET must be given a positive pulse of at least two CPU clock cycles
duration after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization. When in sync. the second byte (0x53), will echo back when issuing the
third byte of the Programming Enable instruction. Whether the echo is correct or not,
all four bytes of the instruction must be transmitted. If the 0x53 did not echo back,
give RESET a positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte
at a time by supplying the 5 LSB of the address and data together with the Load Program memory Page instruction. To ensure correct loading of the page, the data low
byte must be loaded before data high byte is applied for a given address. The Program memory Page is stored by loading the Write Program memory Page instruction
with the 6 MSB of the address. If polling (RDY/BSY) is not used, the user must wait at
least t WD_FLASH before issuing the next page. (See Table 21-14) 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 t WD_EEPROM before issuing the next byte. (See Table
21-14) In a chip erased device, no 0xFFs in the data file(s) need to be programmed.
B: The EEPROM array is programmed one page at a time. The Memory page is
loaded one byte at a time by supplying the 2 LSB of the address and data together
with the Load EEPROM Memory Page instruction. The EEPROM Memory Page is
stored by loading the Write EEPROM Memory Page Instruction with the 6 MSB of the
address. When using EEPROM page access only byte locations loaded with the
Load EEPROM Memory Page instruction is altered. The remaining locations remain
unchanged. If polling (RDY/BSY) is not used, the used must wait at least t WD_EEPROM
before issuing the next page (See Table 21-8). 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.
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7728D–AVR–07/09
7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn Vcc power off.
Table 21-14. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol
21.8.2
Minimum Wait Delay
t WD_FLASH
4.5 ms
t WD_EEPROM
4.0 ms
t WD_ERASE
4.0 ms
t WD_FUSE
4.5 ms
Serial Programming Instruction set
Table 21-15 on page 240 and Figure 21-8 on page 242 describes the Instruction set
Table 21-15. Serial Programming Instruction Set
Instruction Format
Instruction/Operation
Byte 1
Byte 2
Byte 3
Byte4
Programming Enable
0xAC
0x53
0x00
0x00
Chip Erase (Program Memory/EEPROM)
0xAC
0x80
0x00
0x00
Poll RDY/BSY
0xF0
0x00
0x00
data byte out
Load Extended Address byte(1)
0x4D
0x00
Extended add.
0x00
Load Program Memory Page, High byte
0x48
add. MSB
add. LSB
high data byte in
Load Program Memory Page, Low byte
0x40
add. MSB
add. LSB
low data byte in
Load EEPROM Memory Page (page access)
0xC1
0x00
0000 000aa b
data byte in
Read Program Memory, High byte
0x28
add. MSB
add. LSB
high data byte out
Read Program Memory, Low byte
0x20
add. MSB
add. LSB
low data byte out
Read EEPROM Memory
0xA0
0x00
00aa aaaa
data byte out
Read Lock bits
0x58
0x00
0x00
data byte out
Read Signature Byte
0x30
0x00
0000 000aa
data byte out
Read Fuse bits
0x50
0x00
0x00
data byte out
Read Fuse High bits
0x58
0x08
0x00
data byte out
Read Extended Fuse Bits
0x50
0x08
0x00
data byte out
Read Calibration Byte
0x38
0x00
0x00
data byte out
0x4C
add. MSB
add. LSB
0x00
Load Instructions
Read Instructions
Write Instructions
(6)
Write Program Memory Page
240
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Table 21-15. Serial Programming Instruction Set (Continued)
Instruction Format
Instruction/Operation
Byte 1
Byte 2
Byte 3
Byte4
Write EEPROM Memory
0xC0
0x00
00aa aaaa b
data byte in
Write EEPROM Memory Page (page access)
0xC2
0x00
00aa aa00 b
0x00
Write Lock bits
0xAC
0xE0
0x00
data byte in
Write Fuse bits
0xAC
0xA0
0x00
data byte in
Write Fuse High bits
0xAC
0xA8
0x00
data byte in
Write Extended Fuse Bits
0xAC
0xA4
0x00
data byte in
Notes:
1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (‘1’).
5. Refer to the corresponding section for Fuse and Lock bits, Calibration and Signature bytes
and Page size.
6. Instructions accessing program memory use a word address. This address may be random
within the page range.
7. See http://www.atmel.com/avr for Application Notes regarding programming and
programmers.
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until
this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 21-8 on page
242.
241
7728D–AVR–07/09
Figure 21-8. Serial programming Instruction Example
Serial Programming Instruction
Load Program Memory Page (High/Low Byte) /
Load EEPROM Memory Page (Page Access)
Byte 1
Byte 2
Addr. MSB
Bit 15
B
Byte 3
Write Program Memory Page /
Write EEPROM Memory Page
Byte 4
Byte 1
Byte 2
Addr. LSB
Addr. MSB
0
Bit 15
B
Byte 3
Byte 4
Addr. MSB
0
Page Buffer
Page Offset
Page 0
Page 1
Page 2
Page Number
Page N-1
Program Memory /
EEPROM Memory
21.9
Serial Programming Characteristics
Figure 21-9. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
For characteristics of the SPI module, See ”SPI Timing Characteristics” on page 253.
242
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ATtiny87/ATtiny167
22. Electrical Characteristics
Note:
All Characteristics contained in this data sheet are based on simulation and characterization of ATtiny87/167 AVR microcontrollers manufactured in a typical process technology. These values are preliminary values representing design targets, and will
be updated after characterization of actual Automotive silicon.
22.1
Absolute Maximum Ratings*
Operating Temperature.................................– 40°C to +125°C
*NOTICE:
Storage Temperature ....................................– 65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground .............................. – 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.
Voltage on Vcc with respect to Ground.............. – 0.5V to 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current Vcc and GND Pins................................. 200.0 mA
Injection Current at VCC = 0V to 5V(2) ...................... ±5.0mA(1)
Notes:
1. Maximum current per port = ±30mA
2. Functional corruption may occur .
22.2
DC Characteristics
TA = -40°C to +125°C, Vcc = 2.7V to 5.5V (unless otherwise noted)
Typ.(1)
Max.
Units
- 0.5
0.2 Vcc (2)
V
XTAL1 pin - External
Clock Selected
- 0.5
0.1 Vcc (2)
V
VIL2
RESET pin
0.2 Vcc (2)
V
VIL3
RESET pin as I/O
- 0.5
- 0.5
0.2 Vcc (2)
V
VIH
Except XTAL1 and
RESET pins
0.7 Vcc (3)
Vcc + 0.5
V
XTAL1 pin - External
Clock Selected
0.8 Vcc (3)
Vcc + 0.5
V
RESET pin
0.9 Vcc (3)
Vcc + 0.5
V
(3)
Vcc + 0.5
V
0.6
0.5
V
Symbol
Parameter
VIL
VIL1
VIH1
Input Low Voltage
Input High Voltage
VIH2
Condition
Min.
Except XTAL1 and
RESET pins
RESET pin as I/O
VIH3
VOL
Output Low Voltage (4)
(Ports A, B,)
IOL = 10 mA, Vcc = 5V
IOL = 5 mA, Vcc = 3V
VOH
Output High Voltage (5)
(Ports A, B)
IOH = – 10 mA, Vcc = 5V
IOH = – 5 mA, Vcc = 3V
0.7 Vcc
4.3
2.5
V
243
7728D–AVR–07/09
TA = -40°C to +125°C, Vcc = 2.7V to 5.5V (unless otherwise noted) (Continued)
Typ.(1)
Max.
Units
Vcc = 5.5V, pin low
(absolute value)
< 0.05
1
µA
Vcc = 5.5V, pin high
(absolute value)
< 0.05
1
µA
30
60
kΩ
20
50
kΩ
Symbol
Parameter
Condition
IIL
Input Leakage
Current I/O Pin
IIH
Input Leakage
Current I/O Pin
RRST
Reset Pull-up Resistor
Rpu
I/O Pin Pull-up Resistor
Power Supply Current
Active Mode
(external clock)
ICC
Power Supply Current
Idle Mode
(external clock)
(6)
(6)
Power Supply Current (7)
Power-down Mode
Min.
16 MHz, Vcc = 5V
10
13
mA
8 MHz, Vcc = 5V
5.5
7.0
mA
8 MHz, Vcc = 3V
2.8
3.5
mA
4 MHz, Vcc = 3V
1.8
2.5
mA
16 MHz, Vcc = 5V
3.5
5.0
mA
8 MHz, Vcc = 5V
1.8
2.5
mA
8 MHz, Vcc = 3V
1
1.5
mA
4 MHz, Vcc = 3V
0.5
0.8
mA
WDT enabled, Vcc = 5V
7
100
µA
WDT disabled, Vcc = 5V
0.18
70
µA
WDT enabled, Vcc = 3V
5
70
µA
WDT disabled, Vcc = 3V
0.15
45
µA
10
40
mV
50
nA
VACIO
Analog Comparator
Input Offset Voltage
Vcc = 5V
Vin = Vcc/2
-10
IACLK
Analog Comparator
Input Leakage Current
Vcc = 5V
Vin = Vcc/2
-50
Analog Comparator
Propagation Delay
Common Mode Vcc/2
Vcc = 2.7V
170
ns
tACID
Vcc = 5.0V
180
ns
Notes:
1. “Typ.", typical values at 25°C. Maximum values are characterized values and not test limits in production.
2. "Max.” means the highest value where the pin is guaranteed to be read as low.
3. “Min.” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10 mA at Vcc= 5V, 5 mA at Vcc = 3V) under steady state conditions (non-transient), the following must be observed:
- The sum of all IOL, for all ports, should not exceed 120 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:
- The sum of all IOH, for all ports, should not exceed 120 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
6. Values using methods described in “Minimizing Power Consumption” on page 45. Power Reduction is enabled
(PRR = 0xFF) and there is no I/O drive.
7. BOD Disabled.
244
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ATtiny87/ATtiny167
22.3
Speed Grades
Figure 22-1. Maximum Frequency vs. Vcc, ATtiny87/167
Frequency
16 MHz
8 MHz
Safe Operating Area
Voltage
2.7V
22.4
22.4.1
5.5V
Clock Characteristics
Calibrated Internal RC Oscillator Accuracy
Table 22-1.
Calibration and Accuracy of Internal RC Oscillator
Frequency
Vcc
Temperature
Accuracy
8.0 MHz
3V
25°C
±2%
Factory
Calibration
22.4.2
4.5V
External Clock Drive Waveforms
Figure 22-2. External Clock Drive Waveforms
V IH1
V IL1
245
7728D–AVR–07/09
22.4.3
External Clock Drive
Table 22-2.
Symbol
1/tCLCL
Vcc = 4.5 - 5.5V
Min.
Max.
Min.
Max.
Units
0
8
0
16
MHz
Oscillator Frequency
Clock Period
125
62.5
ns
tCHCX
High Time
50
25
ns
tCLCX
Low Time
50
25
ns
tCLCH
Rise Time
1.6
0.5
ms
tCHCL
Fall Time
1.6
0.5
ms
2
2
%
Change in period from one clock
cycle to the next
RESET Characteristics
Table 22-3.
Symbol
External Reset Characteristics
Parameter
Condition
Min
0.1 Vcc
Typ
Max
Units
0.9 Vcc
V
2.5
µs
1.1
1.2
V
70
µs
VRST
RESET Pin Threshold
Voltage
VCC = 5V
tRST
Minimum pulse width on
RESET Pin
VCC = 5V
VBG
Bandgap reference voltage
VCC = 2.7V,
TA = 25°C
tBG
Bandgap reference start-up
time
VCC = 2.7V,
TA = 25°C
40
IBG
Bandgap reference current
consumption
VCC = 2.7V,
TA = 25°C
15
Table 22-4.
Symbol
VPOT
1.0
µA
Power On Reset Characteristics
Parameter
Min
Power-on Reset Threshold Voltage (rising)
(1)
Power-on Reset Threshold Voltage (falling)
Typ
Max
Units
1.0
1.4
V
0.9
1.3
V
0.4
V
VPORMAX
VCC Max. start voltage to ensure internal
Power-on Reset signal
VPORMIN
VCC Min. start voltage to ensure internal
Power-on Reset signal
- 0.1
V
VCCRR
VCC Rise Rate to ensure Power-on Reset
0.01
V/ms
VRST
Note:
246
Parameter
Vcc = 2.7 - 5.5V
tCLCL
ΔtCLCL
22.5
External Clock Drive
RESET Pin Threshold Voltage
0.1 Vcc
0.9
Vcc
V
1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a Reset.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Table 22-5.
BODLEVEL Fuse Coding
BODLEVEL 2:0 Fuses
Min. VBOT(1)
Typ. VBOT
Max. VBOT
Units
BOD Disabled
1 1 1b
1 1 0b
1.7
1.8
2.0
1 0 1b
2.5
2.7
2.9
1 0 0b
4.1
4.3
4.5
0 1 1b
0 1 0b
V
Reserved
0 0 1b
0 0 0b
Notes:
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 = 101 for Low Operating Voltage and BODLEVEL = 100 for High operating
Voltage.
Table 22-6.
Symbol
VHYST
tBOD
22.6
Brown-out Characteristics
Parameter
Min.
Typ.
Max.
Units
Brown-out Detector Hysteresis
80
mV
Min Pulse Width on Brown-out Reset
2
µs
Internal Voltage Characteristics
Table 22-7.
Symbol
Internal Voltage Reference Characteristics
Parameter
Condition
Min.
Typ.
Max.
Units
VBG
Bandgap reference voltage
Vcc = 4.5
TA = 25°C
1.0
1.1
1.2
V
tBG
Bandgap reference start-up time
Vcc = 4.5
TA = 25°C
40
70
µs
IBG
Bandgap reference current consumption
Vcc = 4.5
TA = 25°C
10
µA
247
7728D–AVR–07/09
22.7
Current Source Characteristics
Table 22-8.
Symbol
22.8
Current Source Characteristics
Parameter
Condition
Min.
IISRC
Current
Vcc = 2.7 V / 5.5 V
T = -40°C / +125°C
tISRC
Current Source start-up time
Vcc = 4.5
TA = 25°C
Typ.
94
60
Max.
Units
106
µA
µs
ADC Characteristics
Table 22-9.
Symbol
ADC Characteristics, Single Ended Channels (-40°C/+125°C)
Parameter
Condition
Resolution
Single Ended Conversion
10
TUE
Absolute accuracy
Vcc = 4V, VRef = 4V,
ADC clock = 200 kHz
2.0
3.5
LSB
INL
Integral Non Linearity
Vcc = 4V, VRef = 4V,
ADC clock = 200 kHz
0.6
2.0
LSB
DNL
Differential Non Linearity
Vcc = 4V, VRef = 4V,
ADC clock = 200 kHz
0.3
0.8
LSB
Gain error
Vcc = 4V, VRef = 4V,
ADC clock = 200 kHz
-6.0
-2.5
2.0
LSB
Offset error
Vcc = 4V, VRef = 4V,
ADC clock = 200 kHz
-3.5
1.5
3.5
LSB
AVcc
V
VREF
Ref voltage
Min
Typ
2.56
Input bandwidth
Max
Bits
38.5
2.56
kHz
VINT
Internal voltage
RREF
Reference input resistance
32
kΩ
RAIN
Analog input resistance
100
MΩ
248
2.4
Units
2.7
V
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Table 22-10. ADC Characteristics, Differential Channels (-40°C/+125°C)
Symbol
TUE
INL
DNL
Parameter
Condition
Resolution
Differential conversion
8
Gain = 8x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
1.0
3.0
Gain = 20x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
1.5
3.5
Gain = 8x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
2.0
4.5
Gain = 20x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
2.0
6.0
Gain = 8x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.2
1.0
Gain = 20x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.4
1.5
Gain = 8x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.5
2.0
Gain = 20x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
1.6
5.0
Gain = 8x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.3
0.8
Gain = 20x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.3
0.8
Gain = 8x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.4
0.8
Gain = 20x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
0.6
1.6
Absolute accuracy
Integral Non Linearity
Differential Non Linearity
Gain error
Min
Typ
Max
Units
LSB
LSB
LSB
Gain = 8x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-3.0
1.0
3.0
Gain = 20x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-4.0
1.5
4.0
Gain = 8x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-5.0
-2.5
0.0
Gain = 20x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-4.0
-0.5
4.0
LSB
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7728D–AVR–07/09
Table 22-10. ADC Characteristics, Differential Channels (-40°C/+125°C) (Continued)
Symbol
Parameter
Offset error
Condition
Min
Typ
Max
Gain = 8x or 20x, BIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-2.0
0.5
2.0
Gain = 8x or 20x, UNIPOLAR
VREF = 4V, Vcc = 5V
ADC clock = 200 kHz
-2.0
LSB
Reference voltage
VREF
VDIFF
AVcc
Input differential voltage
Analog supply voltage
VIN
Input voltage
0.5
2.0
2.56
AVCC - 0.5
V
-VREF/Gain
+VREF/Gain
V
Vcc - 0.3
Vcc + 0.3
V
Differential conversion
ADC conversion output
Input bandwidth
Units
0
AVcc
V
-511
+511
LSB
Differential conversion
4
VINT
Internal voltage reference
RREF
Reference input resistance
32
kΩ
RAIN
Analog input resistance
100
MΩ
22.9
2.4
2.56
kHz
2.7
V
Parallel Programming Characteristics
Figure 22-3. Parallel Programming Timing, Including some General Timing Requirements
t XLWL
XTAL1
Data & Contol
(DATA, XA0,
XA1/BS2,
PAGEL/BS1)
t DVXH
t BVPH
t XHXL
t XLDX
t PLBX
t BVWL
t WLBX
t WLWH
WR
t PLWL
t RLRH
RDY/BSY
t WLRH
250
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 22-4. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA
(LOW BYTE)
LOAD DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
t XLXH
XTAL1
AGEL/BS1
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1/BS2
Note:
1. The timing requirements shown in Figure 22-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to
loading operation.
Figure 22-5. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(Note:)
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
t XLOL
XTAL1
t BVDV
AGEL/BS1
t OLDV
OE
DATA
t OHDZ
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1/BS2
Note:
The timing requirements shown in Figure 22-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading operation.
251
7728D–AVR–07/09
Table 22-11. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol
Parameter
Min
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
Max
Units
12.5
V
250
µA
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
tBVPH
BS1 Valid before PAGEL High
67
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
tWLRH_CE
(1)
WR Low to RDY/BSY High
(2)
WR Low to RDY/BSY High for Chip Erase
0
1
µs
3.7
4.5
ms
7.5
9
ms
tXLOL
XTAL1 Low to OE Low
0
tBVDV
BS1 Valid to DATA valid
0
tOLDV
tOHDZ
Notes:
252
Typ
ns
250
ns
OE Low to DATA Valid
250
ns
OE High to DATA Tri-stated
250
ns
1.
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.
2.
tWLRH_CE is valid for the Chip Erase command.
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
22.10 SPI Timing Characteristics
See Figure 22-6 and Figure 22-7 for details.
Table 22-12. SPI Timing Parameters
1
Description
Mode
Min.
Typ.
Max.
SCK period
Master
See Table 13-4
2
SCK high/low
Master
50% duty cycle
3
Rise/Fall time
Master
3.6
4
Setup
Master
10
5
Hold
Master
10
6
Out to SCK
Master
0.5 • tsck
7
SCK to out
Master
10
8
SCK to out high
Master
10
9
SS low to out
Slave
15
10
SCK period
Slave
4 • tck
11
SCK high/low (1)
Slave
2 • tck
12
Rise/Fall time
Slave
13
Setup
Slave
10
14
Hold
Slave
tck
15
SCK to out
Slave
16
SCK to SS high
Slave
17
SS high to tri-state
Slave
18
SS low to SCK
Slave
Note:
ns
1.6
15
µs
ns
20
10
2 • tck
In SPI Programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12 MHz
- 3 tCLCL for fCK >12 MHz
Figure 22-6. SPI Interface Timing Requirements (Master Mode)
SS
6
1
SCK
(CPOL = 0)
2
2
SCK
(CPOL = 1)
4
MISO
(Data Input)
5
3
MSB
...
LSB
8
7
MOSI
(Data Output)
MSB
...
LSB
253
7728D–AVR–07/09
Figure 22-7. SPI Interface Timing Requirements (Slave Mode)
18
SS
10
9
16
SCK
(CPOL = 0)
11
11
SCK
(CPOL = 1)
13
MOSI
(Data Input)
14
12
MSB
...
LSB
15
MISO
(Data Output)
254
MSB
17
...
LSB
X
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
23. Decoupling Capacitors
The operating frequency (i.e. system clock) of the processor determines in 95% of cases the
value needed for microcontroller decoupling capacitors.
The hypotheses used as first evaluation for decoupling capacitors are:
• The operating frequency (fop) supplies itself the maximum peak levels of noise. The main
peaks are located at fop and 2 • fop.
• An SMC capacitor connected to 2 micro-vias on a PCB has the following characteristics:
– 1.5 nH from the connection of the capacitor to the PCB,
– 1.5 nH from the capacitor intrinsic inductance.
Figure 23-1. Capacitor description
1.5 nH
0.75 nH
0.75 nH
Capacitor
PCB
According to the operating frequency of the product, the decoupling capacitances are chosen
considering the frequencies to filter, fop and 2 • fop.
The relation between frequencies to cut and decoupling characteristics are defined by:
f op
where:
1 = ---------------------2Π LC 1
and
1 2 • f op = ---------------------2Π LC 2
– L: the inductance equivalent to the global inductance on the Vcc/Gnd lines.
– C1 & C2: decoupling capacitors (C1 = 4 • C2).
Then, in normalized value range, the decoupling capacitors become:
Table 23-1.
Decoupling Capacitors vs. Frequency
fop , operating frequency
C1
C2
16 MHz
33 nF
10 nF
12 MHz
56 nF
15 nF
10 MHz
82 nF
22 nF
8 MHz
120 nF
33 nF
6 MHz
220 nF
56 nF
4 MHz
560 nF
120 nF
These decoupling capacitors must to be implemented as close as possible to each pair of
power supply pins:
– 16-17 for logic sub-system,
– 5-6 for analogical sub-system.
Nevertheless, a bulk capacitor of 10-47 µF is also needed on the power distribution network of
the PCB, near the power source.
For further information, please refer to Application Notes AVR040 “EMC Design Considerations“ and AVR042 “Hardware Design Considerations“ on the Atmel web site.
255
7728D–AVR–07/09
24. Typical Characteristics
The data contained in this section is largely based on simulations and characterization of similar devices in the same process and design methods. Thus, the data should be treated as
indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs
and with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as
clock source.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient 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.
24.1
Active Supply Current
Figure 24-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY
PRR=0xFF / ATD ON
1.4
6
1.2
5.5
5
ICC (mA)
1
4.5
0.8
4
3.6
0.6
3.3
0.4
3
2.7
0.2
2.4
2.1
0
0
0.1
0.2
0.3
0.4
0.5
Frequency (MHz)
0.6
0.7
0.8
0.9
1
2
1.8
1.6
256
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-2. Active Supply Current vs. Frequency (≥ 1 MHz)
Figure 24-3. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR 8MHz (No ATD influence)
9
8
ICC (mA)
7
6
150
5
125
85
4
25
3
-40
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
257
7728D–AVR–07/09
Figure 24-4. Active Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR 128 KHz / ATD ON
0.2
0.18
0.16
ICC (mA)
0.14
150
0.12
125
0.1
85
0.08
25
0.06
-40
0.04
0.02
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
24.2
Idle Supply Current
Figure 24-5. Idle Supply Current vs. Frequency (≥ 1 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
NO POWER REDUCTION ENABLED
10
9
8
6
ICC (mA)
7
5.5
6
5
5
4.5
4
4
3
3.6
2
3.3
1
3
2.7
0
0
2
4
6
8
10
12
14
16
18
20
2.4
Frequency (MHz)
258
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-6. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. V CC
INTERNAL RC OSCILLATOR 8MHz
3
2.5
150
ICC (mA)
2
125
1.5
85
25
1
-40
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
Figure 24-7. Idle Supply Current vs. VCC (Internal RC Oscillator, 128 kHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR 125 KHz
0.08
0.07
0.06
150
ICC (mA)
0.05
125
0.04
85
0.03
25
-40
0.02
0.01
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
259
7728D–AVR–07/09
24.3
Supply Current of I/O modules
The table below can be used to calculate the additional current consumption for the different
I/O modules Idle mode. The enabling or disabling of the I/O modules are controlled by the
Power Reduction Register. See Section 5.9.3 “PRR – Power Reduction Register” on page 47
for details.
Table 24-1.
24.4
Additional Current Consumption for the different I/O modules (absolute values)
Module
Vcc = 5.0 V
Freq. = 16 MHz
Vcc = 5.0 V
Freq. = 8 MHz
Vcc = 3.0 V
Freq. = 8 MHz
Vcc = 3.0 V
Freq. = 4 MHz
Units
LIN/UART
0.77
0.37
0.20
0.10
mA
SPI
0.31
0.14
0.08
0.04
mA
TIMER-1
0.28
0.13
0.08
0.04
mA
TIMER-0
0.41
0.20
0.10
0.05
mA
USI
0.14
0.05
0.04
0.02
mA
ADC
0.48
0.22
0.10
0.05
mA
Power-down Supply Current
Figure 24-8. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. V CC
WATCHDOG TIMER DISABLED
30
25
150
ICC (uA)
20
125
15
85
25
10
-40
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
260
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-9. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER ENABLED
40
35
30
150
ICC (uA)
25
125
20
85
15
25
-40
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
24.5
Pin Pull-up
Figure 24-10. I/O Pin pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7 V
90
80
IOP (uA)
70
60
150
50
125
40
85
30
25
20
-40
10
0
-10
0
0.5
1
1.5
2
2.5
3
V OP (V)
261
7728D–AVR–07/09
Figure 24-11. I/O Pin pull-up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5.0 V
160
140
120
150
IOP (uA)
100
125
80
85
60
25
40
-40
20
0
0
1
2
3
4
5
6
-20
V OP (V)
Figure 24-12. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 2.7 V
70
60
50
IRESET (uA)
150
40
125
30
85
25
20
-40
10
0
0
0.5
1
1.5
2
2.5
3
-10
V RESET (V)
262
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-13. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 5.0 V
120
100
IRESET (uA)
80
150
125
60
85
25
40
-40
20
0
0
1
2
3
4
5
6
-20
V RESET (V)
24.6
Pin Driver Strength
Figure 24-14. I/O Pin Output Voltage vs. Sink Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
Vcc = 3.0 V
2
1.8
1.6
150
1.4
125
V OL (V)
1.2
85
1
25
0.8
-40
0.6
0.4
0.2
0
0
2
4
6
8
10
12
14
16
18
IOL (mA)
263
7728D–AVR–07/09
Figure 24-15. I/O Pin Output Voltage vs. Sink Current (VCC = 5V)
I/O PIN OUTPUT VOLTAGE vs. SINK CURRENT
Vcc = 5.0V
1.2
1
150
V OL (V)
0.8
125
85
0.6
25
-40
0.4
0.2
0
0
5
10
15
20
25
IOL (mA)
Figure 24-16. I/O Pin Output Voltage vs. Source Current (VCC = 3V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
Vcc = 3.0 V
3
2.5
150
125
V OH (V)
2
85
1.5
25
-40
1
0.5
0
0
2
4
6
8
10
12
14
16
18
20
IOH (mA)
264
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-17. I/O Pin Output Voltage vs. Source Current (VCC = 5V)
I/O PIN OUTPUT VOLTAGE vs. SOURCE CURRENT
V cc = 5.0 V
5.1
4.9
150
4.7
V OH (V)
125
4.5
85
25
4.3
-40
4.1
3.9
3.7
0
2
4
6
8
10
12
14
16
18
20
IOH (mA )
24.7
Internal Oscillator Speed
Figure 24-18. Calibrated 8.0 MHz RC Oscillator Frequency vs. Vcc
265
7728D–AVR–07/09
Figure 24-19. Calibrated 8.0 MHz RC Oscillator Frequency vs. OSCCAL Value
24.8
Current Consumption in Reset
Figure 24-20. Reset Supply Current vs. Vcc, Frequencies 0.1 - 1.0 MHz
(Excluding CurrentThrough the Reset Pull-up)
RESET SUPPLY CURRENT vs. V CC
EXCLUDING CURRENT THROUGH THE RESET PULLUP
0.3
6
0.25
5.5
5
ICC (mA)
0.2
4.5
4
0.15
3.6
3.3
0.1
3
0.05
2.7
2.4
0
0
0.1
0.2
0.3
0.4
0.5
Frequency (MHz)
0.6
0.7
0.8
0.9
1
2.1
2
1.8
1.6
266
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Figure 24-21. Reset Supply Current vs. Vcc, Frequencies ≥ 1 MHz
(Excluding Current Through the Reset Pull-up)
RESET SUPPLY CURRENT vs. V CC
EXCLUDING CURRENT THROUGH THE RESET PULLUP
4.5
4
6
5.5
3.5
5
ICC (mA)
3
4.5
2.5
4
2
3.6
1.5
3.3
3
1
2.7
0.5
2.4
0
2.1
0
2
4
6
8
10
Frequency (MHz)
12
14
16
18
20
2
1.8
1.6
267
7728D–AVR–07/09
25. Register Summary
Address
Name
(0xFF)
Reserved
268
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0xFE)
Reserved
(0xFD)
Reserved
(0xFC)
Reserved
(0xFB)
Reserved
(0xFA)
Reserved
(0xF9)
Reserved
(0xF8)
Reserved
(0xF7)
Reserved
(0xF6)
Reserved
(0xF5)
Reserved
(0xF4)
Reserved
(0xF3)
Reserved
(0xF2)
Reserved
(0xF1)
Reserved
(0xF0)
Reserved
(0xEF)
Reserved
(0xEE)
Reserved
(0xED)
Reserved
(0xEC)
Reserved
(0xEB)
Reserved
(0xEA)
Reserved
(0xE9)
Reserved
(0xE8)
Reserved
(0xE7)
Reserved
(0xE6)
Reserved
(0xE5)
Reserved
(0xE4)
Reserved
(0xE3)
Reserved
(0xE2)
Reserved
(0xE1)
Reserved
(0xE0)
Reserved
(0xDF)
Reserved
(0xDE)
Reserved
(0xDD)
Reserved
(0xDC)
Reserved
(0xDB)
Reserved
(0xDA)
Reserved
(0xD9)
Reserved
(0xD8)
Reserved
(0xD7)
Reserved
(0xD6)
Reserved
(0xD5)
Reserved
(0xD4)
Reserved
(0xD3)
Reserved
(0xD2)
LINDAT
LDATA7
LDATA6
LDATA5
LDATA4
LDATA3
LDATA2
LDATA1
LDATA0
page 186
(0xD1)
LINSEL
–
–
–
–
/LAINC
LINDX2
LINDX1
LINDX0
page 186
(0xD0)
LINIDR
LP1
LP0
LID5 / LDL1
LID4 / LDL0
LID3
LID2
LID1
LID0
page 186
(0xCF)
LINDLR
LTXDL3
LTXDL2
LTXDL1
LTXDL0
LRXDL3
LRXDL2
LRXDL1
LRXDL0
page 185
(0xCE)
LINBRRH
–
–
–
–
LDIV11
LDIV10
LDIV9
LDIV8
page 185
(0xCD)
LINBRRL
LDIV7
LDIV6
LDIV5
LDIV4
LDIV3
LDIV2
LDIV1
LDIV0
page 185
(0xCC)
LINBTR
LDISR
–
LBT5
LBT4
LBT3
LBT2
LBT1
LBT0
page 184
(0xCB)
LINERR
LABORT
LTOERR
LOVERR
LFERR
LSERR
LPERR
LCERR
LBERR
page 183
(0xCA)
LINENIR
–
–
–
–
LENERR
LENIDOK
LENTXOK
LENRXOK
page 183
(0xC9)
LINSIR
LIDST2
LIDST1
LIDST0
LBUSY
LERR
LIDOK
LTXOK
LRXOK
page 182
(0xC8)
LINCR
LSWRES
LIN13
LCONF1
LCONF0
LENA
LCMD2
LCMD1
LCMD0
page 181
(0xC7)
Reserved
(0xC6)
Reserved
(0xC5)
Reserved
(0xC4)
Reserved
(0xC3)
Reserved
(0xC2)
Reserved
(0xC1)
Reserved
(0xC0)
Reserved
(0xBF)
Reserved
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Address
Name
(0xBE)
Reserved
(0xBD)
Reserved
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0xBC)
USIPP
USIPOS
page 161
(0xBB)
USIBR
USIB7
USIB6
USIB5
USIB4
USIB3
USIB2
USIB1
USIB0
page 157
(0xBA)
USIDR
USID7
USID6
USID5
USID4
USID3
USID2
USID1
USID0
page 156
(0xB9)
USISR
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
page 157
(0xB8)
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
page 158
(0xB7)
Reserved
–
EXCLK
AS0
TCN0UB
OCR0AUB
–
TCR0AUB
TCR0BUB
page 103
(0xB6)
ASSR
(0xB5)
Reserved
(0xB4)
Reserved
(0xB3)
Reserved
(0xB2)
Reserved
(0xB1)
Reserved
(0xB0)
Reserved
(0xAF)
Reserved
(0xAE)
Reserved
(0xAD)
Reserved
(0xAC)
Reserved
(0xAB)
Reserved
(0xAA)
Reserved
(0xA9)
Reserved
(0xA8)
Reserved
(0xA7)
Reserved
(0xA6)
Reserved
(0xA5)
Reserved
(0xA4)
Reserved
(0xA3)
Reserved
(0xA2)
Reserved
(0xA1)
Reserved
(0xA0)
Reserved
(0x9F)
Reserved
(0x9E)
Reserved
(0x9D)
Reserved
(0x9C)
Reserved
(0x9B)
Reserved
(0x9A)
Reserved
(0x99)
Reserved
(0x98)
Reserved
(0x97)
Reserved
(0x96)
Reserved
(0x95)
Reserved
(0x94)
Reserved
(0x93)
Reserved
(0x92)
Reserved
(0x91)
Reserved
(0x90)
Reserved
(0x8F)
Reserved
(0x8E)
Reserved
(0x8D)
Reserved
(0x8C)
Reserved
(0x8B)
OCR1BH
OCR1B15
OCR1B14
OCR1B13
OCR1B12
OCR1B11
OCR1B10
OCR1B9
OCR1B8
page 137
(0x8A)
OCR1BL
OCR1B7
OCR1B6
OCR1B5
OCR1B4
OCR1B3
OCR1B2
OCR1B1
OCR1B0
page 137
(0x89)
OCR1AH
OCR1A15
OCR1A14
OCR1A13
OCR1A12
OCR1A11
OCR1A10
OCR1A9
OCR1A8
page 137
(0x88)
OCR1AL
OCR1A7
OCR1A6
OCR1A5
OCR1A4
OCR1A3
OCR1A2
OCR1A1
OCR1A0
page 137
page 138
(0x87)
ICR1H
ICR115
ICR114
ICR113
ICR112
ICR111
ICR110
ICR19
ICR18
(0x86)
ICR1L
ICR17
ICR16
ICR15
ICR14
ICR13
ICR12
ICR11
ICR10
page 138
(0x85)
TCNT1H
TCNT115
TCNT114
TCNT113
TCNT112
TCNT111
TCNT110
TCNT19
TCNT18
page 137
(0x84)
TCNT1L
TCNT17
TCNT16
TCNT15
TCNT14
TCNT13
TCNT12
TCNT11
TCNT10
page 137
(0x83)
TCCR1D
OC1BX
OC1BW
OC1BV
OC1BU
OC1AX
OC1AW
OC1AV
OC1AU
page 136
(0x82)
TCCR1C
FOC1A
FOC1B
–
–
–
–
–
–
page 136
(0x81)
TCCR1B
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
page 135
(0x80)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1B0
–
–
WGM11
WGM10
page 132
–
ADC10D
(0x7F)
DIDR1
(0x7E)
DIDR0
(0x7D)
Reserved
ADC7D/AIN1D ADC6D/AIN0D
ADC9D
ADC8D
–
–
–
–
page 210
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
page 209, page 213
269
7728D–AVR–07/09
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0x7C)
ADMUX
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
page 205
(0x7B)
ADCSRB
BIN
ACME
ACIR1
ACIR0
–
ADTS2
ADTS1
ADTS0
page 209, page 211
(0x7A)
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
page 207
(0x79)
ADCH
- / ADC9
- / ADC8
- / ADC7
- / ADC6
- / ADC5
- / ADC4
ADC9 / ADC3
ADC8 / ADC2
page 208
(0x78)
ADCL
ADC7 / ADC1
ADC6 / ADC0
ADC5 / -
ADC4 / -
ADC3 / -
ADC2 / -
ADC1 / -
ADC0 /
page 208
(0x77)
AMISCR
–
–
–
–
–
AREFEN
XREFEN
ISRCEN
page 190, page 190
(0x76)
Reserved
(0x75)
Reserved
(0x74)
Reserved
(0x73)
Reserved
(0x72)
Reserved
(0x71)
Reserved
(0x70)
Reserved
(0x6F)
TIMSK1
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
page 138
(0x6E)
TIMSK0
–
–
–
–
–
–
OCIE0A
TOIE0
page 105
(0x6D)
Reserved
(0x6C)
PCMSK1
PCINT15
PCINT14
PCINT13
PCINT12
PCINT11
PCINT10
PCINT9
PCINT8
page 65
(0x6B)
PCMSK0
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
page 66
(0x6A)
Reserved
(0x69)
EICRA
–
–
–
–
ISC11
ISC10
ISC01
ISC00
page 63
(0x68)
PCICR
–
–
–
–
–
–
PCIE1
PCIE0
page 64
(0x67)
Reserved
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
page 37
(0x66)
OSCCAL
(0x65)
Reserved
(0x64)
PRR
–
–
PRLIN
PRSPI
PRTIM1
PRTIM0
PRUSI
PRADC
page 47
(0x63)
CLKSELR
–
COUT
CSUT1
CSUT0
CSEL3
CSEL2
CSEL1
CSEL0
page 40
(0x62)
CLKCSR
CLKCCE
–
–
CLKRDY
CLKC3
CLKC2
CLKC1
CLKC0
page 38
(0x61)
CLKPR
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
page 38
(0x60)
WDTCR
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
page 57
0x3F (0x5F)
SREG
I
T
H
S
V
N
Z
C
page 9
0x3E (0x5E)
SPH
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
page 11
0x3D (0x5D)
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
page 11
0x3C (0x5C)
Reserved
0x3B (0x5B)
Reserved
0x3A (0x5A)
Reserved
0x39 (0x59)
Reserved
0x38 (0x58)
Reserved
page 219
0x37 (0x57)
SPMCSR
–
RWWSB
SIGRD
CTPB
RFLB
PGWRT
PGERS
SPMEN
0x36 (0x56)
Reserved
–
–
–
–
–
–
–
–
0x35 (0x55)
MCUCR
–
BODS
BODSE
PUD
–
–
–
–
page 46, page 75
0x34 (0x54)
MCUSR
–
–
–
–
WDRF
BORF
EXTRF
PORF
page 52
0x33 (0x53)
SMCR
–
–
–
–
–
SM1
SM0
SE
page 46
0x32 (0x52)
Reserved
0x31 (0x51)
DWDR
DWDR7
DWDR6
DWDR5
DWDR4
DWDR3
DWDR2
DWDR1
DWDR0
page 216
0x30 (0x50)
ACSR
ACD
ACIRS
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
page 212
0x2F (0x4F)
Reserved
page 147
0x2E (0x4E)
SPDR
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
0x2D (0x4D)
SPSR
SPIF
WCOL
–
–
–
–
–
SPI2X
page 147
0x2C (0x4C)
SPCR
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
page 145
0x2B (0x4B)
GPIOR2
GPIOR27
GPIOR26
GPIOR25
GPIOR24
GPIOR23
GPIOR22
GPIOR21
GPIOR20
page 23
0x2A (0x4A)
GPIOR1
GPIOR17
GPIOR16
GPIOR15
GPIOR14
GPIOR13
GPIOR12
GPIOR11
GPIOR10
page 23
0x29 (0x49)
Reserved
0x28 (0x48)
OCR0A
OCR0A7
OCR0A6
OCR0A5
OCR0A4
OCR0A3
OCR0A2
OCR0A1
OCR0A0
page 103
0x27 (0x47)
TCNT0
TCNT07
TCNT06
TCNT05
TCNT04
TCNT03
TCNT02
TCNT01
TCNT00
page 103
0x26 (0x46)
TCCR0B
FOC0A
–
–
–
–
CS02
CS01
CS00
page 102
0x25 (0x45)
TCCR0A
COM0A1
COM0A0
–
–
–
–
WGM01
WGM00
page 100
0x24 (0x44)
Reserved
0x23 (0x43)
GTCCR
TSM
–
–
–
–
–
PSR0
PSR1
page 106, page 109
0x22 (0x42)
EEARH(1)
–
–
–
–
–
–
–
EEAR8
page 21
0x21 (0x41)
EEARL
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
page 21
0x20 (0x40)
EEDR
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
page 22
0x1F (0x3F)
EECR
–
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
page 22
0x1E (0x3E)
GPIOR0
GPIOR07
GPIOR06
GPIOR05
GPIOR04
GPIOR03
GPIOR02
GPIOR01
GPIOR00
page 23
0x1D (0x3D)
EIMSK
–
–
–
–
–
–
INT1
INT0
page 63
0x1C (0x3C)
EIFR
–
–
–
–
–
–
INTF1
INTF0
page 64
0x1B (0x3B)
PCIFR
–
–
–
–
–
–
PCIF1
PCIF0
page 65
270
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Address
Name
0x1A (0x3A)
Reserved
0x19 (0x39)
Reserved
0x18 (0x38)
Reserved
0x17 (0x37)
Reserved
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x16 (0x36)
TIFR1
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
page 139
0x15 (0x35)
TIFR0
–
–
–
–
–
–
OCF0A
TOV0
page 105
0x14 (0x34)
Reserved
0x13 (0x33)
Reserved
–
–
BBMB
BBMA
–
–
PUDB
PUDA
page 75
0x12 (0x32)
PORTCR
0x11 (0x31)
Reserved
0x10 (0x30)
Reserved
0x0F (0x2F)
Reserved
0x0E (0x2E)
Reserved
0x0D (0x2D)
Reserved
0x0C (0x2C)
Reserved
0x0B (0x2B)
Reserved
0x0A (0x2A)
Reserved
0x09 (0x29)
Reserved
0x08 (0x28)
Reserved
0x07 (0x27)
Reserved
0x06 (0x26)
Reserved
0x05 (0x25)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
page 86
0x04 (0x24)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
page 86
0x03 (0x23)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
page 86
0x02 (0x22)
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
page 86
0x01 (0x21)
DDRA
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
page 86
0x00 (0x20)
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
page 86
Notes:
1. Address bits exceeding EEAMSB (Table 21-8 on page 228) are don’t care.
2. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
3. 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.
4. 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.
5. 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. The ATtiny87/167 is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for the IN
and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.
271
7728D–AVR–07/09
26. Instruction Set Summary
Mnemonics
Operands
Description
Operation
Flags
#Clock
1
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
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
1
INC
Rd
Increment
Rd ←Rd + 1
Z,N,V
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
RJMP
k
Relative Jump
PC ←PC + k + 1
None
2
Indirect Jump to (Z)
PC ←Z
None
2
BRANCH INSTRUCTIONS
IJMP
JMP
k
Direct Jump
PC ←k
None
3
RCALL
k
Relative Subroutine Call
PC ←PC + k + 1
None
3
Indirect Call to (Z)
PC ←Z
None
3
Direct Subroutine Call
PC ←k
None
4
RET
Subroutine Return
PC ←STACK
None
4
RETI
Interrupt Return
PC ←STACK
I
4
Compare, Skip if Equal
if (Rd = Rr) PC ←PC + 2 or 3
None
1/2/3
ICALL
CALL
CPSE
k
Rd,Rr
CP
Rd,Rr
Compare
Rd −Rr
Z, N,V,C,H
1
CPC
Rd,Rr
Compare with Carry
Rd −Rr −C
Z, N,V,C,H
1
CPI
Rd,K
Compare Register with Immediate
Rd −K
Z, N,V,C,H
1
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ←PC + 2 or 3
None
1/2/3
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC ←PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b)=0) PC ←PC + 2 or 3
None
1/2/3
SBIS
P, b
Skip if Bit in I/O Register is Set
if (P(b)=1) PC ←PC + 2 or 3
None
1/2/3
BRBS
s, k
Branch if Status Flag Set
if (SREG(s) = 1) then PC←PC+k + 1
None
1/2
BRBC
s, k
Branch if Status Flag Cleared
if (SREG(s) = 0) then PC←PC+k + 1
None
1/2
BREQ
k
Branch if Equal
if (Z = 1) then PC ←PC + k + 1
None
1/2
BRNE
k
Branch if Not Equal
if (Z = 0) then PC ←PC + k + 1
None
1/2
BRCS
k
Branch if Carry Set
if (C = 1) then PC ←PC + k + 1
None
1/2
BRCC
k
Branch if Carry Cleared
if (C = 0) then PC ←PC + k + 1
None
1/2
BRSH
k
Branch if Same or Higher
if (C = 0) then PC ←PC + k + 1
None
1/2
BRLO
k
Branch if Lower
if (C = 1) then PC ←PC + k + 1
None
1/2
BRMI
k
Branch if Minus
if (N = 1) then PC ←PC + k + 1
None
1/2
BRPL
k
Branch if Plus
if (N = 0) then PC ←PC + k + 1
None
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V= 0) then PC ←PC + k + 1
None
1/2
BRLT
k
Branch if Less Than Zero, Signed
if (N ⊕ V= 1) then PC ←PC + k + 1
None
1/2
BRHS
k
Branch if Half Carry Flag Set
if (H = 1) then PC ←PC + k + 1
None
1/2
BRHC
k
Branch if Half Carry Flag Cleared
if (H = 0) then PC ←PC + k + 1
None
1/2
BRTS
k
Branch if T Flag Set
if (T = 1) then PC ←PC + k + 1
None
1/2
BRTC
k
Branch if T Flag Cleared
if (T = 0) then PC ←PC + k + 1
None
1/2
BRVS
k
Branch if Overflow Flag is Set
if (V = 1) then PC ←PC + k + 1
None
1/2
BRVC
k
Branch if Overflow Flag is Cleared
if (V = 0) then PC ←PC + k + 1
None
1/2
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ←PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ←PC + k + 1
None
1/2
BIT AND BIT-TEST INSTRUCTIONS
272
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
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
Mnemonics
Operands
Description
Operation
Flags
LSR
Rd
Logical Shift Right
Rd(n) ←Rd(n+1), Rd(7) ←0
Z,C,N,V
#Clock
1
ROL
Rd
Rotate Left Through Carry
Rd(0)←C,Rd(n+1)←Rd(n),C←Rd(7)
Z,C,N,V
1
ROR
Rd
Rotate Right Through Carry
Rd(7)←C,Rd(n)←Rd(n+1),C←Rd(0)
Z,C,N,V
1
ASR
Rd
Arithmetic Shift Right
Rd(n) ←Rd(n+1), n=0..6
Z,C,N,V
1
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
Set Half Carry Flag in SREG
H ←1
H
1
CLH
Clear Half Carry Flag in SREG
H ←0
H
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
Rd ←Rr
None
1
MOVW
Rd, Rr
Copy Register Word
Rd+1:Rd ←Rr+1:Rr
None
1
LDI
Rd, K
Load Immediate
Rd ←K
None
1
LD
Rd, X
Load Indirect
Rd ←(X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ←(X), X ←X + 1
None
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ←X - 1, Rd ←(X)
None
2
LD
Rd, Y
Load Indirect
Rd ←(Y)
None
2
2
LD
Rd, Y+
Load Indirect and Post-Inc.
Rd ←(Y), Y ←Y + 1
None
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
2
LD
Rd, Z
Load Indirect
Rd ←(Z)
None
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
LPM
Store Direct to SRAM
(k) ←Rr
None
2
Load Program Memory
R0 ←(Z)
None
3
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 Port
Rd ←P
None
1
1
SPM
IN
Rd, P
OUT
P, Rr
Out Port
P ←Rr
None
PUSH
Rr
Push Register on Stack
STACK ←Rr
None
2
POP
Rd
Pop Register from Stack
Rd ←STACK
None
2
None
1
None
1
MCU CONTROL INSTRUCTIONS
NOP
No Operation
SLEEP
Sleep
(see specific descr. for Sleep function)
WDR
Watchdog Reset
(see specific descr. for WDR/timer)
None
1
BREAK
Break
For On-chip Debug Only
None
N/A
273
7728D–AVR–07/09
27. Ordering Information
Engineering
Sample
Ordering Code
Speed (MHz)
Power Supply (V)
ATtiny167-ESSZ (3)
ATtiny167-ESMZ (3)
16
2.7 - 5.5
-40° to +125°C
TG
16
2.7 - 5.5
PN
ATtiny87-15XZ
6G
ATtiny167-15SZ
TG
16
2.7 - 5.5
ATtiny167-15XZ
Notes:
PN
6G
ATtiny87-15SZ
ATtiny167-15MZ
Operation Range
TG
ATtiny167-ESXZ (3)
ATtiny87-15MZ
Package (1)(2)
PN
-40° to +125°C
-40° to +125°C
6G
1. Green and ROHS packaging.
2. Tape and Reel with Dry-pack delivery.
3. Revision A engineering samples P/N given for reference. For revision C samples order ATtiny167-15SZ, ATtiny-15MZ,
ATtiny-15XZ
28. Packaging Information
Package Type
TG
20-pin, 0.300” Wide, Platic Gull-Wing Small Outline (EIAJ SOIC)
PN
32-pad, Quad Flat No Lead (QFN)
6G
20-pin, 4.5 mm Wide, Thin Shrink Small Outline Package (TSSOP)
274
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
28.1
SOIC20
275
7728D–AVR–07/09
28.2
276
QFN32
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
28.3
TSSOP20
277
7728D–AVR–07/09
29. Errata
29.1
29.1.1
Errata Summary
ATtiny87/167 RevB (Date code >1208)
• Gain control of the crystal oscillator.
• ‘Disable Clock Source’ command remains enabled.
29.1.2
ATtiny167 RevA (Date code >1207)
• CRC calculation of diagnostic frames in LIN 2.x.
• Gain control of the crystal oscillator.
• ‘Disable Clock Source’ command remains enabled.
• Comparison between ADC inputs and voltage references.
• Register bits of DIDR1.
29.2
Errata Description
1. CRC calculation of diagnostic frames in LIN 2.x.
Diagnostic frames of LIN 2.x use “classic checksum” calculation. Unfortunately, the setting
of the checksum model is enabled when the HEADER is transmitted/received. Usually, in
LIN 2.x the LIN/UART controller is initialized to process “enhanced checksums” and a
slave task does not know what kind of frame it will work on before checking the ID.
Problem fix / workaround.
This workaround is to be implemented only in case of transmission/reception of diagnostic
frames.
a. Slave task of master node:
Before enabling the HEADER, the master must set the appropriate LIN13 bit value in
LINCR register.
b.
For slaves nodes, the workaround is in 2 parts:
– Before enabling the RESPONSE, use the following function:
void lin_wa_head(void) {
unsigned char temp;
temp = LINBTR;
LINCR = 0x00;
// It is not a RESET !
LINBTR = (1<<LDISR)|temp;
LINCR
= (1<<LIN13)|(1<<LENA)|(0<<LCMD2)|(0<<LCMD1)|(0<<LCMD0);
LINDLR = 0x88;
// If it isn't already done
}
– Once the RESPONSE is received or sent (having RxOK or TxOK as well as
LERR), use the following function:
void lin_wa_tail(void)
LINCR = 0x00;
{
// It is not a RESET !
LINBTR = 0x00;
LINCR
= (0<<LIN13)|(1<<LENA)|(0<<LCMD2)|(0<<LCMD1)|(0<<LCMD0);
}
278
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
The time-out counter is disabled during the RESPONSE when this workaround is set.
2. Gain control of the crystal oscillator.
The crystal oscillator (0.4 -> 16 MHz) doesn’t latch its gain control (CKSEL/CSEL[2..0]
bits):
a. The ‘Recover System Clock Source’ command doesn’t returns CSEL[2..0] bits.
b. The gain control can be modified on the fly if CLKSELR changes.
Problem fix / workaround .
a. No workaround.
b. As soon as possible, after any CLKSELR modification, re-write the appropriate crystal
oscillator setting (CSEL[3]=1 and CSEL[2..0] / CSUT[1..0] bits) in CLKSELR.
Code example:
; Select crystal oscillator ( 16MHz crystal, fast rising power)
ldi
temp1,((0x0F<<CSEL0)|(0x02<<CSUT0))
sts
CLKSELR, temp1
; Enable clock source (crystal oscillator)
ldi
temp2,(1<<CLKCCE)
ldi
temp3,(0x02<<CLKC0)
; CSEL = "0010"
sts
CLKCSR,temp2
; Enable CLKCSR register access
sts
CLKCSR,temp3
; Enable crystal oscillator clock
; Clock source switch
ldi
temp3,(0x04<<CLKC0)
; CSEL = "0100"
sts
CLKCSR,temp2
; Enable CLKCSR register access
sts
CLKCSR,temp3
; Clock source switch
; Select watchdog clock ( 128KHz, fast rising power)
ldi
temp3,((0x03<<CSEL0)|(0x02<<CSUT0))
sts
CLKSELR, temp3
; (*)
; (*) !!! Loose gain control of crystal oscillator !!!
; ==> WORKAROUND ...
sts
CLKSELR, temp1
; ...
3. ‘Disable Clock Source’ command remains enabled.
In the Dynamic Clock Switch module, the ‘Disable Clock Source’ command remains running after disabling the targeted clock source (the clock source is set in the CLKSELR
register).
Problem fix / workaround.
After a ‘Disable Clock Source’ command, reset the CLKCSR register writing 0x80.
Code example:
; Select crystal oscillator
ldi
temp1,(0x0F<<CSEL0)
sts
CLKSELR, temp1
; Disable clock source (crystal oscillator)
ldi
temp2,(1<<CLKCCE)
ldi
temp3,(0x01<<CLKC0)
; CSEL = "0001"
sts
CLKCSR,temp2
; Enable CLKCSR register access
279
7728D–AVR–07/09
sts
CLKCSR,temp3
; (*) Disable crystal oscillator clock
; (*) !!! At this moment, if any other clock source is selected by
CLKSELR,
;
this clock source will also stop !!!
; ==> WORKAROUND ...
sts
CLKCSR,temp2
4. Comparison between ADC inputs and voltage references.
In the Analog Comparator module, comparing any ADC input (ADC[10..0]) with voltage
references (2.56V, 1.28V, 1.10V, 0.64V or 0.32V) fails.
Regardless, AIN1 input can be compared with the voltage references and any ADC input
can be compared with AIN0 input.
Problem fix / workaround.
Do not use this configuration.
5. Register bits of DIDR1.
ADC8D, ADC9D and ADC10D (Digital Input Disable) initially located at bit 4 up to 6 are
instead located at bit 0 up to 2. These register bits are also in write only mode.
Problem fix / workaround.
Allow for the change in bit locations and the access mode restriction.
280
ATtiny87/ATtiny167
7728D–AVR–07/09
ATtiny87/ATtiny167
30. Datasheet Revision History for ATtiny87/167
Please note that the referring page numbers in this section are referring to this document.
The referring revision in this section are referring to the document revision.
30.1
Changes from 7728C - 05/09 to 7728D 07/09
1. ISRC updated
2. Brown-out updated
3. Analog comparator updated
4. Temperature sensor updated
30.2
Changes from 7728B - 04/09 to 7728C 05/09
1. ATtiny87 devices added.
2. Updated “ADC Characteristics” on page 248.
3. Updated ADC parameter.
30.3
Changes from 7728A - 07/08 to 7728B 04/09
1. Added ATtiny87 specification (Table 1-1 on page 2, Table 3-1 on page 15, Table 7-1
on page 59, Table 21-6 on page 227, Table 21-7 on page 228, Table 21-8 on page
228 and “Ordering Information” on page 274).
2. Updated Figure 18-1 on page 211 and Table 18-3 on page 214 in Analog Comparator
chapter.
3. Updated DIDR1 register on page 210 and in register summary paragraph.
4. Updated “Errata” on page 278.
30.4
Document Creation
Revision: 7728A - 07/08
281
7728D–AVR–07/09
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7728D–AVR–07/09