ATtiny40 datasheet - Atmel Corporation

8-bit Atmel tinyAVR Microcontroller with
4K Bytes In-System Programmable Flash
ATtiny40
Features
• High Performance, Low Power AVR® 8-Bit Microcontroller
• Advanced RISC Architecture
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– 54 Powerful Instructions – Most Single Clock Cycle Execution
– 16 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 12 MIPS Throughput at 12 MHz
Non-volatile Program and Data Memories
– 4K Bytes of In-System Programmable Flash Program Memory
– 256 Bytes Internal SRAM
– Flash Write/Erase Cycles: 10,000
– Data Retention: 20 Years at 85oC / 100 Years at 25oC
Peripheral Features
– One 8-bit Timer/Counter with Two PWM Channels
– One 8/16-bit Timer/Counter
– 10-bit Analog to Digital Converter
• 12 Single-Ended Channels
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
– Master/Slave SPI Serial Interface
– Slave TWI Serial Interface
Special Microcontroller Features
– In-System Programmable
– External and Internal Interrupt Sources
– Low Power Idle, ADC Noise Reduction, Stand-by and Power-down Modes
– Enhanced Power-on Reset Circuit
– Internal Calibrated Oscillator
I/O and Packages
– 20-pin SOIC: 18 Programmable I/O Lines
– 20-pin TSSOP: 18 Programmable I/O Lines
– 20-pad VQFN: 18 Programmable I/O Lines
Operating Voltage:
– 1.8 – 5.5V
Programming Voltage:
– 5V
Speed Grade
– 0 – 4 MHz @ 1.8 – 5.5V
– 0 – 8 MHz @ 2.7 – 5.5V
– 0 – 12 MHz @ 4.5 – 5.5V
Industrial Temperature Range
Low Power Consumption
– Active Mode:
• 200 µA at 1 MHz and 1.8V
– Idle Mode:
• 25 µA at 1 MHz and 1.8V
– Power-down Mode:
• < 0.1 µA at 1.8V
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1. Pin Configurations
Pinout of ATtiny40
SOIC/TSSOP
(PCINT8/ADC8) PB0
(PCINT7/ADC7) PA7
(PCINT6/ADC6) PA6
(PCINT5/ADC5/OC0B) PA5
(PCINT4/ADC4/T0) PA4
(PCINT3/ADC3) PA3
(PCINT2/ADC2/AIN1) PA2
(PCINT1/ADC1/AIN0) PA1
(PCINT0/ADC0) PA0
GND
1
2
3
4
5
6
7
8
9
10
PB1 (ADC9/PCINT9)
PB2 (ADC10/PCINT10)
PB3 (ADC11/PCINT11)
PC0 (OC0A/SS/PCINT12)
PC1 (SCK/SCL/ICP1/T1/PCINT13)
PC2 (INT0/CLKO/MISO/PCINT14)
PC3 (RESET/PCINT15)
PC4 (MOSI/SDA/TPIDATA/PCINT16)
PC5 (CLKI/TPICLK/PCINT17)
VCC
20
19
18
17
16
15
14
13
12
11
PA7 (ADC7/PCINT7)
PB0 (ADC8/PCINT8)
PB1 (ADC9/PCINT9)
PB2 (ADC10/PCINT10)
PB3 (ADC11/PCINT11)
20
19
18
17
16
VQFN
3
13
PC2 (INT0/CLKO/MISO/PCINT14)
(PCINT3/ADC3) PA3
4
12
PC3 (RESET/PCINT15)
(PCINT2/ADC2/AIN1) PA2
5
11
PC4 (MOSI/SDA/TPIDATA/PCINT16)
(PCINT17/CLKI/TPICLK) PC5
10
PC1 (SCK/SCL/ICP1/T1/PCINT13)
9
14
VCC
2
(PCINT4/ADC4/T0) PA4
8
(PCINT5/ADC5/OC0B) PA5
7
PC0 (OC0A/SS/PCINT12)
GND
15
(PCINT0/ADC0) PA0
1
6
(PCINT6/ADC6) PA6
(PCINT1/ADC1/AIN0) PA1
Figure 1-1.
NOTE: Bottom pad should be soldered to ground.
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1.1
Pin Description
1.1.1
VCC
Supply voltage.
1.1.2
GND
Ground.
1.1.3
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock
is not running and provided the reset pin has not been disabled. The minimum pulse length is given in Table 20-4
on page 155. Shorter pulses are not guaranteed to generate a reset.
The reset pin can also be used as a (weak) I/O pin.
1.1.4
Port A (PA7:PA0)
Port A is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port A output buffers
have symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are
externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a
reset condition becomes active, even if the clock is not running.
Port A has alternate functions as analog inputs for the ADC, analog comparator and pin change interrupt as
described in “Alternate Port Functions” on page 47.
1.1.5
Port B (PB3:PB0)
Port B is a 4-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers
have symmetrical drive characteristics with both high sink and source capability. 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.
The port also serves the functions of various special features of the ATtiny40, as listed on page 37.
1.1.6
Port C (PC5:PC0)
Port C is a 6-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port C output buffers have symmetrical drive characteristics with both high sink and source capability except PC3 which has the
RESET capability. To use pin PC3 as an I/O pin, instead of RESET pin, program (‘0’) RSTDISBL fuse. As inputs,
Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins
are tri-stated when a reset condition becomes active, even if the clock is not running.
Port C has alternate functions as analog inputs for the ADC, analog comparator and pin change interrupt as
described in “Alternate Port Functions” on page 47.
The port also serves the functions of various special features of the ATtiny40, as listed on page 37.
2. Overview
ATtiny40 is a low-power CMOS 8-bit microcontroller based on the compact AVR enhanced RISC architecture. By
executing powerful instructions in a single clock cycle, the ATtiny40 achieves throughputs approaching 1 MIPS per
MHz allowing the system designer to optimize power consumption versus processing speed.
Figure 2-1.
Block Diagram
The AVR core combines a rich instruction set with 16 general purpose working registers and system registers. All
registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be
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VCC
RESET
PROGRAMMING
LOGIC
PROGRAM
COUNTER
INTERNAL
OSCILLATOR
CALIBRATED
OSCILLATOR
PROGRAM
FLASH
STACK
POINTER
WATCHDOG
TIMER
TIMING AND
CONTROL
INSTRUCTION
REGISTER
SRAM
RESET FLAG
REGISTER
INSTRUCTION
DECODER
INTERRUPT
UNIT
MCU STATUS
REGISTER
CONTROL
LINES
GENERAL
PURPOSE
REGISTERS
TIMER/
COUNTER0
X
Y
Z
ISP
INTERFACE
TIMER/
COUNTER1
ALU
SPI
ANALOG
COMPARATOR
STATUS
REGISTER
TWI
ADC
8-BIT DATA BUS
DIRECTION
REG. PORT A
DATA REGISTER
PORT A
DRIVERS
PORT A
PA[7:0]
DATA REGISTER
PORT B
DIRECTION
REG. PORT B
DIRECTION
REG. PORT C
DATA REGISTER
PORT C
DRIVERS
PORT B
DRIVERS
PORT C
PB[3:0]
PC[5:0]
GND
accessed in one single instruction executed in one clock cycle. The resulting architecture is compact and code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
The ATtiny40 provides the following features: 4K bytes of In-System Programmable Flash, 256 bytes of SRAM,
twelve general purpose I/O lines, 16 general purpose working registers, an 8-bit Timer/Counter with two PWM
channels, a 8/16-bit Timer/Counter, Internal and External Interrupts, an eight-channel, 10-bit ADC, a programmable Watchdog Timer with internal oscillator, a slave two-wire interface, a master/slave serial peripheral interface,
an internal calibrated oscillator, and four software selectable power saving modes.
Idle mode stops the CPU while allowing the Timer/Counter, ADC, Analog Comparator, SPI, TWI, and interrupt system to continue functioning. ADC Noise Reduction mode minimizes switching noise during ADC conversions by
stopping the CPU and all I/O modules except the ADC. In Power-down mode registers keep their contents and all
chip functions are disabled until the next interrupt or hardware reset. In Standby mode, the oscillator is running
while the rest of the device is sleeping, allowing very fast start-up combined with low power consumption.
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The device is manufactured using Atmel’s high density non-volatile memory technology. The on-chip, in-system
programmable Flash allows program memory to be re-programmed in-system by a conventional, non-volatile
memory programmer.
The ATtiny40 AVR is supported by a suite of program and system development tools, including macro assemblers
and evaluation kits.
3. General Information
3.1
Resources
A comprehensive set of drivers, application notes, data sheets and descriptions on development tools are available
for download at http://www.atmel.com/avr.
3.2
Code Examples
This documentation contains simple code examples that briefly show how to use various parts of the device. These
code examples assume that the part specific header file is included before compilation. Be aware that not all C
compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent.
Please confirm with the C compiler documentation for more details.
3.3
Capacitive Touch Sensing
Atmel QTouch Library provides a simple to use solution for touch sensitive interfaces on Atmel AVR microcontrollers. The QTouch Library includes support for QTouch® and QMatrix® acquisition methods.
Touch sensing is easily added to any application by linking the QTouch Library and using the Application Programming Interface (API) of the library to define the touch channels and sensors. The application then calls the API to
retrieve channel information and determine the state of the touch sensor.
The QTouch Library is free and can be downloaded from the Atmel website. For more information and details of
implementation, refer to the QTouch Library User Guide – also available from the Atmel website.
3.4
Data Retention
Reliability Qualification results show that the projected data retention failure rate is much less than 1 PPM over 20
years at 85°C or 100 years at 25°C.
3.5
Disclaimer
Typical values contained in this datasheet are based on simulations and characterization of other AVR microcontrollers manufactured on the same process technology.
4. CPU Core
This section discusses the AVR core architecture in general. The main function of the CPU core is to ensure correct program execution. The CPU must therefore be able to access memories, perform calculations, control
peripherals, and handle interrupts.
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Architectural Overview
Figure 4-1.
Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Program
Counter
Status
and Control
16 x 8
General
Purpose
Registrers
Instruction
Decoder
Control Lines
Indirect Addressing
Instruction
Register
Direct Addressing
4.1
Interrupt
Unit
Watchdog
Timer
Analog
Comparator
ADC
ALU
Timer/Counter 0
Timer/Counter 1
Data
SRAM
SPI
TWI Slave
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 16 x 8-bit general purpose working registers with a single clock cycle
access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed, and the result is stored back in the Register File
– in one clock cycle.
Six of the 16 registers can be used as three 16-bit indirect address register pointers for data space addressing –
enabling efficient address calculations. These added function registers are the 16-bit X-, Y-, and Z-register,
described later in this section.
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The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single
register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated
to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, capable of directly addressing
the whole address space. Most AVR instructions have a single 16-bit word format but 32-bit wide instructions also
exist. The actual instruction set varies, as some devices only implement a part of the instruction set.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the Stack. The Stack
is effectively allocated in the general data SRAM, and consequently the Stack size is only limited by the 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 four 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 as the data space locations, 0x0000 - 0x003F.
4.2
ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 16 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 bitfunctions. Some implementations of the architecture also provide a powerful multiplier supporting both
signed/unsigned multiplication and fractional format. See document “AVR Instruction Set” and section “Instruction
Set Summary” on page 191 for a detailed description.
4.3
Status Register
The Status Register contains information about the result of the most recently executed arithmetic instruction. This
information can be used for altering program flow in order to perform conditional operations. Note that the Status
Register is updated after all ALU operations, as specified in document “AVR Instruction Set” and section “Instruction Set Summary” on page 191. 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.
4.4
General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve the required performance and flexibility, the following input/output schemes are supported by the Register File:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 4-2 below shows the structure of the 16 general purpose working registers in the CPU.
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Figure 4-2.
AVR CPU General Purpose Working Registers
7
0
R16
R17
Note:
General
R18
Purpose
…
Working
R26
X-register Low Byte
Registers
R27
X-register High Byte
R28
Y-register Low Byte
R29
Y-register High Byte
R30
Z-register Low Byte
R31
Z-register High Byte
A typical implementation of the AVR register file includes 32 general prupose registers but ATtiny40 implements only
16 registers. For reasons of compatibility the registers are numbered R16...R31 and not R0...R15.
Most of the instructions operating on the Register File have direct access to all registers, and most of them are single cycle instructions.
4.4.1
The X-register, Y-register, and Z-register
Registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit
address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are
defined as described in Figure 4-3.
Figure 4-3.
The X-, Y-, and Z-registers
15
X-register
XH
7
XL
0
7
R27
15
Y-register
YL
0
7
R29
15
Z-register
0
ZL
0
R31
0
R28
ZH
7
0
R26
YH
7
0
7
0
0
R30
In different addressing modes these address registers function as automatic increment and automatic decrement
(see document “AVR Instruction Set” and section “Instruction Set Summary” on page 191 for details).
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4.5
Stack Pointer
The stack is mainly used for storing temporary data, local variables and return addresses after interrupts and subroutine calls. The Stack Pointer Registers(SPH and SPL) always point to the top of the stack. Note that the stack
grows from higher memory locations to lower memory locations. This means that the PUSH instruction decreases
and the POP instruction increases the stack pointer value.
The stack pointer points to the area of data memory where subroutine and interrupt stacks are located. This stack
space must be defined by the program before any subroutine calls are executed or interrupts are enabled.
The pointer is decremented by one when data is put on the stack with the PUSH instruction, and incremented by
one when data is fetched with the POP instruction. It is decremented by two when the return address is put on the
stack by a subroutine call or a jump to an interrupt service routine, and incremented by two when data is fetched by
a return from subroutine (the RET instruction) or a return from interrupt service routine (the RETI instruction).
The AVR stack pointer is typically implemented as two 8-bit registers in the I/O register file. The width of the stack
pointer and the number of bits implemented is device dependent. In some AVR devices all data memory can be
addressed using SPL, only. In this case, the SPH register is not implemented.
The stack pointer must be set to point above the I/O register areas, the minimum value being the lowest address of
SRAM. See Figure 5-1 on page 14.
4.6
Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the
CPU clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used.
Figure 4-4.
The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 4-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture
and the fast access Register File concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with
the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit.
Figure 4-5 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.
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Figure 4-5.
Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
4.7
Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset Vector each have a
separate Program Vector in the program memory space. All interrupts are assigned individual enable bits which
must be written logic one together with the Global Interrupt Enable bit in the Status Register in order to enable the
interrupt.
The lowest addresses in the program memory space are by default defined as the Reset and Interrupt Vectors.
The complete list of vectors is shown in “Interrupts” on page 35. The list also determines the priority levels of the
different interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next
is INT0 – the External Interrupt Request 0.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current
interrupt routine. The I-bit is automatically set when a Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the Interrupt Flag. For
these interrupts, the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt
handling routine, and hardware clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s) to be cleared. If an interrupt condition occurs while the corresponding
interrupt enable bit is 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.
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When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in the following example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep
; enter sleep, waiting for interrupt
; note: will enter sleep before any pending interrupt(s)
Note:
4.7.1
See “Code Examples” on page 5.
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.
4.8
4.8.1
Register Description
CCP – Configuration Change Protection Register
Bit
7
6
5
4
0x3C
3
2
1
0
CCP[7:0]
CCP
Read/Write
W
W
W
W
W
W
W
W
Initial Value
0
0
0
0
0
0
0
0
• Bits 7:0 – CCP[7:0]: Configuration Change Protection
In order to change the contents of a protected I/O register the CCP register must first be written with the correct
signature. After CCP is written the protected I/O registers may be written to during the next four CPU instruction
cycles. All interrupts are ignored during these cycles. After these cycles interrupts are automatically handled again
by the CPU, and any pending interrupts will be executed according to their priority.
When the protected I/O register signature is written, CCP0 will read as one as long as the protected feature is
enabled, while CCP[7:1] will always read as zero.
Table 4-1 shows the signatures that are in recognised.
Table 4-1.
Signature
Signatures Recognised by the Configuration Change Protection Register
Group
Description
(1)
(2)
0xD8
IOREG: CLKMSR, CLKPSR, WDTCSR , MCUCR
Notes:
1. Only WDE and WDP[3:0] bits are protected in WDTCSR.
Protected I/O register
2. Only BODS bit is protected in MCUCR.
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4.8.2
SPH and SPL – Stack Pointer Register
Bit
15
14
13
12
11
10
9
8
0x3E
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
0x3D
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
Read/Write
R
R
R
R
R
R
R
R
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
Initial Value
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
RAMEND
• Bits 15:0 – SP[15:0]: Stack Pointer
The Stack Pointer register points to the top of the stack, which is implemented as growing from higher memory
locations to lower memory locations. Hence, a stack PUSH command decreases the Stack Pointer. The 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 in ATtiny40 is implemented as two 8-bit registers in the I/O space.
4.8.3
SREG – Status Register
Bit
7
6
5
4
3
2
1
0
0x3F
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 document “AVR Instruction
Set” and “Instruction Set Summary” on page 191.
• 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 document “AVR Instruction Set” and section “Instruction Set Summary” on page 191 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
document “AVR Instruction Set” and section “Instruction Set Summary” on page 191 for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See document “AVR Instruction
Set” and section “Instruction Set Summary” on page 191 for detailed information.
• Bit 2 – N: Negative Flag
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The Negative Flag N indicates a negative result in an arithmetic or logic operation. See document “AVR Instruction
Set” and section “Instruction Set Summary” on page 191 for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See document “AVR Instruction Set” and
section “Instruction Set Summary” on page 191 for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See document “AVR Instruction Set” and
section “Instruction Set Summary” on page 191 for detailed information.
5. Memories
This section describes the different memories in the ATtiny40. The device has two main memory areas, the program memory space and the data memory space.
5.1
In-System Re-programmable Flash Program Memory
The ATtiny40 contains 4K byte on-chip, in-system reprogrammable Flash memory for program storage. Since all
AVR instructions are 16 or 32 bits wide, the Flash is organized as 2048 x 16.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny40 Program Counter (PC) is
11 bits wide, thus capable of addressing the 2048 program memory locations, starting at 0x000. “Memory Programming” on page 143 contains a detailed description on Flash data serial downloading.
Constant tables can be allocated within the entire address space of program memory. Since program memory can
not be accessed directly, it has been mapped to the data memory. The mapped program memory begins at byte
address 0x4000 in data memory (see Figure 5-1 on page 14). Although programs are executed starting from
address 0x000 in program memory it must be addressed starting from 0x4000 when accessed via the data
memory.
Internal write operations to Flash program memory have been disabled and program memory therefore appears to
firmware as read-only. Flash memory can still be written to externally but internal write operations to the program
memory area will not be succesful.
Timing diagrams of instruction fetch and execution are presented in “Instruction Execution Timing” on page 9.
5.2
Data Memory
Data memory locations include the I/O memory, the internal SRAM memory, the non-volatile memory lock bits, and
the Flash memory. See Figure 5-1 on page 14 for an illustration on how the ATtiny40 memory space is organized.
The first 64 locations are reserved for I/O memory, while the following 256 data memory locations (from 0x0040 to
0x013F) address the internal data SRAM.
The non-volatile memory lock bits and all the Flash memory sections are mapped to the data memory space.
These locations appear as read-only for device firmware.
The four different addressing modes for data memory are direct, indirect, indirect with pre-decrement, and indirect
with post-increment. In the register file, registers R26 to R31 function as pointer registers for indirect addressing.
The IN and OUT instructions can access all 64 locations of I/O memory. Direct addressing using the LDS and STS
instructions reaches the lowest 128 locations between 0x0040 and 0x00BF.
The indirect addressing reaches the entire data memory space. When using indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented.
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Figure 5-1.
I/O SPACE
0x0000 ... 0x003F
SRAM DATA MEMORY
0x0040 ... 0x013F
(reserved)
0x0140 ... 0x3EFF
NVM LOCK BITS
0x3F00 ... 0x3F01
(reserved)
0x3F02 ... 0x3F3F
CONFIGURATION BITS
0x3F40 ... 0x3F41
(reserved)
0x3F42 ... 0x3F7F
CALIBRATION BITS
0x3F80 ... 0x3F81
(reserved)
0x3F82 ... 0x3FBF
DEVICE ID BITS
0x3FC0 ... 0x3FC3
(reserved)
0x3FC4 ... 0x3FFF
FLASH PROGRAM MEMORY
0x4000 ... 0x47FF
(reserved)
0x4800 ... 0xFFFF
Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The internal data SRAM
access is performed in two clkCPU cycles as described in Figure 5-2.
On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Compute Address
Address valid
Data
Write
Figure 5-2.
WR
Data
Read
5.2.1
Data Memory Map (Byte Addressing)
RD
Memory Access Instruction
Next Instruction
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5.2.2
Internal SRAM
The internal SRAM is mapped in the Data Memory space starting at address 0x0040. SRAM is accessed from the
CPU by using direct addressing, indirect addressing or via the RAM interface. The registers R26 to R31 function
as pointer register for indirect addressing. The pointer pre-decrement and post-increment functions are also supported in connection with the indirect addressing. Direct addressing using the LDS and STS instructions reaches
only the lowest 128 locations between 0x0040 and 0x00BF. The locations beyond the first 128 bytes between
0x00C0 and 0x013F must be accessed using either indirect addressing mode (LD and ST instructions) or via the
RAM interface.
The user must pay particular attention to the RAM addressing when using the RAM interface. The direct and indirect addressing modes use virtual RAM address, but the RAM interface uses physical RAM address. The virtual
RAM address space mapping to physical addresses is described in Table 5-1.
For example, if the data is written to RAM using the virtual RAM address 0x0100 (instruction STS or ST), it is
mapped to physical RAM address 0x0000. Thus the physical RAM address 0x0000 must be written to the RAMAR
register when the same data location is read back via the RAM interface. On the other hand, if the same data location is read back using direct or indirect addressing mode (instruction LDS or LD), the same virtual RAM address
0x0100 is used.
Table 5-1.
5.2.3
SRAM Address Space
Virtual RAM
Address
Physical RAM
Address
0x0040
0x0040
–
–
–
–
–
–
0x00FF
0x00FF
0x0100
0x0000
–
–
–
–
–
–
0x013F
0x003F
RAM Interface
The RAM Interface consists of two registers, RAM Address Register (RAMAR) and RAM Data Register (RAMDR).
The registers are accessible in I/O space.
To write a location the user must first write the RAM address into RAMAR and then the data into RAMDR. Writing
the data into RAMDR triggers the write operation and the data from the source register is written to RAM in address
given by RAMAR within the same instruction cycle.
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To read a location the user must first write the RAM address into RAMAR and then read the data from RAMDR.
Reading the data from RAMDR triggers the read operation and the data from RAM address given by RAMAR is
fetched and written to the destination register within the same instruction cycle.
Assembly Code Example
RAM_write:
; Set up address (r17) in address register
out RAMAR, r17
; Write data (r16) to data register
out RAMDR, r16
ret
RAM_read:
; Set up address (r17) in address register
out RAMAR, r17
; Read data (r16) from data register
in
r16, RAMDR
ret
C Code Example
void RAM_write(unsigned char ucAddress, unsigned char ucData)
{
/* Set up address register */
RAMAR = ucAddress;
/* Write data into RAMDR */
RAMDR = ucData;
}
void RAM_read(unsigned char ucAddress, unsigned char ucData)
{
/* Set up address register */
RAMAR = ucAddress;
/* Read data from RAMDR */
ucData = RAMDR;
}
5.3
I/O Memory
The I/O space definition of the ATtiny40 is shown in “Register Summary” on page 189.
All ATtiny40 I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed using the LD and
ST instructions, enabling data transfer between the 16 general purpose working registers and the I/O space. I/O
Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. See document
“AVR Instruction Set” and section “Instruction Set Summary” on page 191 for more details. When using the I/O
specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must 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.
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Some of the status flags are cleared by writing a logical one to them. Note that CBI and SBI instructions will only
operate on the specified bit, and can therefore be used on registers containing such status flags. The CBI and SBI
instructions work on registers in the address range 0x00 to 0x1F, only.
The I/O and Peripherals Control Registers are explained in later sections.
5.4
5.4.1
Register Description
RAMAR – RAM Address Register
Bit
7
6
5
4
3
2
1
0
RAMAR7
RAMAR6
RAMAR5
RAMAR4
RAMAR3
RAMAR2
RAMAR1
RAMAR0
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
0x20
RAMAR
• Bits 7:0 – RAMAR[7:0]: RAM Address
The RAMAR register contains the RAM address bits. The RAM data bytes are addressed linearly in the range
0..255. The initial value of RAMAR is undefined and a proper value must be therefore written before the RAM may
be accessed.
5.4.2
RAMDR – RAM Data Register
Bit
7
6
5
4
3
2
1
0
RAMDR7
RAMDR6
RAMDR5
RAMDR4
RAMDR3
RAMDR2
RAMDR1
RAMDR0
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
0x1F
RAMDR
• Bits 7:0 – RAMDR[7:0]: RAM Data
For the RAM write operation, the RAMDR register contains the RAM data to be written to the RAM in address given
by the RAMAR register. For the RAM read operation, the RAMDR contains the data read out from the RAM at the
address given by RAMAR.
6. Clock System
Figure 6-1 presents the principal clock systems and their distribution in ATtiny40. All of the clocks need not be
active at a given time. In order to reduce power consumption, the clocks to modules not being used can be halted
by using different sleep modes and power reduction register bits, as described in “Power Management and Sleep
Modes” on page 23. The clock systems is detailed below.
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Figure 6-1.
Clock Distribution
ANALOG-TO-DIGITAL
CONVERTER
clk ADC
GENERAL
I/O MODULES
CPU
CORE
clk I/O
NVM
RAM
clk NVM
clk CPU
CLOCK CONTROL UNIT
SOURCE CLOCK
RESET
LOGIC
WATCHDOG
CLOCK
CLOCK
PRESCALER
WATCHDOG
TIMER
CLOCK
SWITCH
EXTERNAL
CLOCK
6.1
WATCHDOG
OSCILLATOR
CALIBRATED
OSCILLATOR
Clock Subsystems
The clock subsystems are detailed in the sections below.
6.1.1
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR Core. Examples of such modules are the General Purpose Register File, the System Registers and the SRAM data memory. Halting the CPU
clock inhibits the core from performing general operations and calculations.
6.1.2
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counter. The I/O clock is also used by the
External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing
such interrupts to be detected even if the I/O clock is halted.
6.1.3
NVM clock - clkNVM
The NVM clock controls operation of the Non-Volatile Memory Controller. The NVM clock is usually active simultaneously with the CPU clock.
6.1.4
ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce
noise generated by digital circuitry. This gives more accurate ADC conversion results.
6.2
Clock Sources
All synchronous clock signals are derived from the main clock. The device has three alternative sources for the
main clock, as follows:
• Calibrated Internal 8 MHz Oscillator (see page 19)
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• External Clock (see page 19)
• Internal 128 kHz Oscillator (see page 19)
See Table 6-3 on page 21 on how to select and change the active clock source.
6.2.1
Calibrated Internal 8 MHz Oscillator
The calibrated internal oscillator provides an approximately 8 MHz clock signal. Though voltage and temperature
dependent, this clock can be very accurately calibrated by the user. See Table 20-2 on page 154, and “Internal
Oscillator Speed” on page 186 for more details.
This clock may be selected as the main clock by setting the Clock Main Select bits CLKMS[1:0] in CLKMSR to
0b00. Once enabled, the oscillator will operate with no external components. During reset, hardware loads the calibration byte into the OSCCAL register and thereby automatically calibrates the oscillator. The accuracy of this
calibration is shown as Factory calibration in Table 20-2 on page 154.
When this oscillator is used as the main clock, the watchdog oscillator will still be used for the watchdog timer and
reset time-out. For more information on the pre-programmed calibration value, see section “Calibration Section” on
page 147.
6.2.2
External Clock
To use the device with an external clock source, CLKI should be driven as shown in Figure 6-2. The external clock
is selected as the main clock by setting CLKMS[1:0] bits in CLKMSR to 0b10.
Figure 6-2.
External Clock Drive Configuration
EXTERNAL
CLOCK
SIGNAL
CLKI
GND
When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure
stable operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to
unpredictable behavior. It is required to ensure that the MCU is kept in reset during such changes in the clock
frequency.
6.2.3
Internal 128 kHz Oscillator
The internal 128 kHz oscillator is a low power oscillator providing a clock of 128 kHz. The frequency depends on
supply voltage, temperature and batch variations. This clock may be select as the main clock by setting the
CLKMS[1:0] bits in CLKMSR to 0b01.
6.2.4
Switching Clock Source
The main clock source can be switched at run-time using the “CLKMSR – Clock Main Settings Register” on page
21. When switching between any clock sources, the clock system ensures that no glitch occurs in the main clock.
6.2.5
Default Clock Source
The calibrated internal 8 MHz oscillator is always selected as main clock when the device is powered up or has
been reset. The synchronous system clock is the main clock divided by 8, controlled by the System Clock Prescaler. The Clock Prescaler Select Bits can be written later to change the system clock frequency. See “System
Clock Prescaler”.
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6.3
System Clock Prescaler
The system clock is derived from the main clock via the System Clock Prescaler. The system clock can be divided
by setting the “CLKPSR – Clock Prescale Register” on page 22. The system clock prescaler can be used to
decrease power consumption at times when requirements for processing power is low or to bring the system clock
within limits of maximum frequency. The prescaler can be used with all main clock source options, and it will affect
the clock frequency of the CPU and all synchronous peripherals.
The System Clock Prescaler can be used to implement run-time changes of the internal clock frequency while still
ensuring stable operation.
6.3.1
Switching Prescaler Setting
When switching between prescaler settings, the system clock prescaler ensures that no glitch occurs in the system
clock and that no intermediate frequency is higher than neither the clock frequency corresponding 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 main 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, two active clock edges are produced. Here, T1 is the previous clock period, and
T2 is the period corresponding to the new prescaler setting.
6.4
Starting
6.4.1
Starting from Reset
The internal reset is immediately asserted when a reset source goes active. The internal reset is kept asserted until
the reset source is released and the start-up sequence is completed. The start-up sequence includes three steps,
as follows.
1. The first step after the reset source has been released consists of the device counting the reset start-up
time. The purpose of this reset start-up time is to ensure that supply voltage has reached sufficient levels.
The reset start-up time is counted using the internal 128 kHz oscillator. See Table 6-1 for details of reset
start-up time.
Note that the actual supply voltage is not monitored by the start-up logic. The device will count until the
reset start-up time has elapsed even if the device has reached sufficient supply voltage levels earlier.
2. The second step is to count the oscillator start-up time, which ensures that the calibrated internal oscillator has reached a stable state before it is used by the other parts of the system. The calibrated internal
oscillator needs to oscillate for a minimum number of cycles before it can be considered stable. See Table
6-1 for details of the oscillator start-up time.
3. The last step before releasing the internal reset is to load the calibration and the configuration values from
the Non-Volatile Memory to configure the device properly. The configuration time is listed in Table 6-1.
Table 6-1.
Start-up Times when Using the Internal Calibrated Oscillator
Reset
Oscillator
Configuration
64 ms
6 cycles
21 cycles
Notes:
Total start-up time
64 ms + 6 oscillator cycles + 21 system clock cycles (1)(2)
1. After powering up the device or after a reset the system clock is automatically set to calibrated internal 8 MHz oscillator, divided by 8
2. When the Brown-out Detection is enabled, the reset start-up time is 128 ms after powering up the device.
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6.4.2
Starting from Power-Down Mode
When waking up from Power-down sleep mode, the supply voltage is assumed to be at a sufficient level and only
the oscillator start-up time is counted to ensure the stable operation of the oscillator. The oscillator start-up time is
counted on the selected main clock, and the start-up time depends on the clock selected. See Table 6-2 for details.
Table 6-2.
Notes:
Start-up Time from Power-Down Sleep Mode.
Oscillator start-up time
Total start-up time
6 cycles
6 oscillator cycles (1)(2)
1. The start-up time is measured in main clock oscillator cycles.
2. When using software BOD disable, the wake-up time from sleep mode will be approximately 60µs.
6.4.3
Starting from Idle / ADC Noise Reduction / Standby Mode
When waking up from Idle, ADC Noise Reduction or Standby Mode, the oscillator is already running and no oscillator start-up time is introduced.
6.5
Register Description
6.5.1
CLKMSR – Clock Main Settings Register
Bit
7
6
5
4
3
2
1
0
0x37
–
–
–
–
–
–
CLKMS1
CLKMS0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
CLKMSR
• Bits 7:2 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 1:0 – CLKMS[1:0]: Clock Main Select Bits
These bits select the main clock source of the system. The bits can be written at run-time to switch the source of
the main clock. The clock system ensures glitch free switching of the main clock source.
The main clock alternatives are shown in Table 6-3.
Table 6-3.
Selection of Main Clock
CLKM1
CLKM0
Main Clock Source
0
0
Calibrated Internal 8 MHzOscillator
0
1
Internal 128 kHz Oscillator (WDT Oscillator)
1
0
External clock
1
1
Reserved
To avoid unintentional switching of main clock source, a protected change sequence must be followed to change
the CLKMS bits, as follows:
1. Write the signature for change enable of protected I/O register to register CCP
2. Within four instruction cycles, write the CLKMS bits with the desired value
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6.5.2
CLKPSR – Clock Prescale Register
Bit
7
6
5
4
3
2
1
0
0x36
–
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
1
1
CLKPSR
• Bits 7:4 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 3:0 – CLKPS[3:0]: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system clock. These bits
can be written at run-time to vary the clock frequency and suit the application requirements. As the prescaler
divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced accordingly. The
division factors are given in Table 6-4.
Table 6-4.
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 (default)
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
To avoid unintentional changes of clock frequency, a protected change sequence must be followed to change the
CLKPS bits:
1. Write the signature for change enable of protected I/O register to register CCP
2. Within four instruction cycles, write the desired value to CLKPS bits
At start-up, the CLKPS bits will be reset to 0b0011 to select the clock division factor of 8. 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.
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6.5.3
OSCCAL – Oscillator Calibration Register
.
Bit
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x39
OSCCAL
• Bits 7:0 – CAL[7:0]: Oscillator Calibration Value
The oscillator calibration register is used to trim the calibrated internal oscillator and remove process variations
from the oscillator frequency. A pre-programmed calibration value is automatically written to this register during
chip reset, giving the factory calibrated frequency as specified in Table 20-2, “Calibration Accuracy of Internal RC
Oscillator,” on page 154.
The application software can write this register to change the oscillator frequency. The oscillator can be calibrated
to frequencies as specified in Table 20-2, “Calibration Accuracy of Internal RC Oscillator,” on page 154. Calibration
outside the range given is not guaranteed.
The CAL[7:0] bits are used to tune the frequency of the oscillator. A setting of 0x00 gives the lowest frequency, and
a setting of 0xFF gives the highest frequency.
7. Power Management and Sleep Modes
The high performance and industry leading code efficiency makes the AVR microcontrollers an ideal choise for low
power applications. In addition, sleep modes enable the application to shut down unused modules in the MCU,
thereby saving power. The AVR provides various sleep modes allowing the user to tailor the power consumption to
the application’s requirements.
Sleep Modes
Figure 6-1 on page 18 presents the different clock systems and their distribution in ATtiny40. The figure is helpful in
selecting an appropriate sleep mode. Table 7-1 shows the different sleep modes and their wake up sources.
Table 7-1.
Active Clock Domains and Wake-up Sources in Different Sleep Modes.
Main Clock
Source Enabled
INT0 and
Pin Change
Watchdog
Interrupt
TWI Slave
ADC
Other I/O
X
X
X
X
X
X
X
X
ADC Noise Reduction
Standby
Power-down
Notes:
Wake-up Sources
clkADC
Idle
Oscillators
clkIO
Sleep Mode
clkNVM
Active Clock Domains
clkCPU
7.1
X
X
X
X
(1)
X
(2)
X
(1)
X
X
X
X(1)
X
X(2)
X
(2)
1. For INT0, only level interrupt.
2. Only TWI address match interrupt.
To enter any of the four sleep modes, the SE bits in MCUCR must be written to logic one and a SLEEP instruction
must be executed. The SM[2:0] bits in the MCUCR register select which sleep mode (Idle, ADC Noise Reduction,
Standby or Power-down) will be activated by the SLEEP instruction. See Table 7-2 for a summary.
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If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for
four cycles in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP. The contents of the Register File and SRAM are unaltered when the device wakes up from
sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the Reset Vector.
Note that if a level triggered interrupt is used for wake-up the changed level must be held for some time to wake up
the MCU (and for the MCU to enter the interrupt service routine). See “External Interrupts” on page 37 for details.
7.1.1
Idle Mode
When bits SM[2:0] are written to 000, the SLEEP instruction makes the MCU enter Idle mode, stopping the CPU
but allowing the analog comparator, ADC, timer/counters, watchdog, TWI, SPI and the interrupt system to continue
operating. This sleep mode basically halts clkCPU and clkNVM, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the timer
overflow. If wake-up from the analog comparator interrupt is not required, the analog comparator can be powered
down by setting the ACD bit in “ACSRA – Analog Comparator Control and Status Register” on page 95. This will
reduce power consumption in idle mode. If the ADC is enabled, a conversion starts automatically when this mode
is entered.
7.1.2
ADC Noise Reduction Mode
When bits SM[2:0] are written to 001, the SLEEP instruction makes the MCU enter ADC Noise Reduction mode,
stopping the CPU but allowing the ADC, the external interrupts, TWI and the watchdog to continue operating (if
enabled). This sleep mode halts clkI/O, clkCPU, and clkNVM, while allowing the other clocks to run.
This mode 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.
7.1.3
Power-down Mode
When bits SM[2:0] are written to 010, the SLEEP instruction makes the MCU enter Power-down mode. In this
mode, the oscillator is stopped, while the external interrupts, TWI and the watchdog continue operating (if
enabled). Only a watchdog reset, an external level interrupt on INT0, a pin change interrupt, or a TWI slave interrupt can wake up the MCU. This sleep mode halts all generated clocks, allowing operation of asynchronous
modules only.
7.1.4
Standby Mode
When bits SM[2:0] are written to 100, the SLEEP instruction makes the MCU enter Standby mode. This mode is
identical to Power-down with the exception that the oscillator is kept running. This reduces wake-up time, because
the oscillator is already running and doesn't need to be started up.
7.2
Software BOD Disable
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses (see Table 19-5 on page 146), the BOD is
actively monitoring the supply voltage during a sleep period. In some devices it is possible to save power by disabling the BOD by software in Power-down and Stand-by sleep modes. The sleep mode power consumption will
then be at the same level as when BOD is globally disabled by fuses.
If BOD is disabled by software, the BOD function is turned off immediately after entering the sleep mode. Upon
wake-up from sleep, BOD is automatically enabled again. This ensures safe operation in case the VCC level has
dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately 60 µs to ensure that
the BOD is working correctly before the MCU continues executing code.
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BOD disable is controlled by the BODS (BOD Sleep) bit of MCU Control Register, see “MCUCR – MCU Control
Register” on page 26. Writing this bit to one turns off BOD in Power-down and Stand-by, while writing a zero keeps
the BOD active. The default setting is zero, i.e. BOD active.
Writing to the BODS bit is controlled by a timed sequence, see “MCUCR – MCU Control Register” on page 26.
7.3
Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 27, provides a method to
reduce power consumption by stopping the clock to individual peripherals. When the clock for a peripheral is
stopped then:
• The current state of the peripheral is frozen.
• The associated registers can not be read or written.
• Resources used by the peripheral will remain occupied.
The peripheral should in most cases be disabled before stopping the clock. Clearing the PRR bit wakes up the
peripheral and puts it in the same state as before shutdown.
Peripheral shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. See “Supply Current of I/O Modules” on page 159 for examples. In all other sleep modes, the clock is already
stopped.
7.4
Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR Core controlled
system. In general, sleep modes should be used as much as possible, and the sleep mode should be selected so
that as few as possible of the device’s functions are operating. All functions not needed should be disabled. In particular, the following modules may need special consideration when trying to achieve the lowest possible power
consumption.
7.4.1
Analog Comparator
When entering Idle mode, the analog comparator should be disabled if not used. In the power-down mode, the
analog comparator is automatically disabled. See “Analog Comparator” on page 94 for further details.
7.4.2
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering
any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion.
See “Analog to Digital Converter” on page 98 for details on ADC operation.
7.4.3
Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be turned off. If the Watchdog Timer is
enabled, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this
will contribute significantly to the total current consumption. Refer to “Watchdog Timer” on page 31 for details on
how to configure the Watchdog Timer.
7.4.4
Brown-out Detector
If the Brown-out Detector is not needed in the application, this module should be turned off. If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes, and hence, always consume power.
In the deeper sleep modes, this will contribute significantly to the total current consumption. See “Brown-out Detection” on page 30 and “Software BOD Disable” on page 24 for details on how to configure the Brown-out Detector.
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7.4.5
Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The most important thing
is then to ensure that no pins drive resistive loads. In sleep modes where the I/O clock (clkI/O) is stopped, the input
buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed.
In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the
section “Digital Input Enable and Sleep Modes” on page 46 for details on which pins are enabled. If the input buffer
is enabled and the input signal is left floating or has an analog signal level close to VCC/2, the input buffer will use
excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to VCC/2
on an input pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to
the Digital Input Disable Register (DIDR0). Refer to “DIDR0 – Digital Input Disable Register 0” on page 97 for
details.
7.5
Register Description
7.5.1
MCUCR – MCU Control Register
The MCU Control Register contains bits for controlling external interrupt sensing and power management.
Bit
7
6
5
4
3
2
1
0
ISC01
ISC00
–
BODS
SM2
SM1
SM0
SE
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
0x3A
MCUCR
• Bit 5 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 4 – BODS: BOD Sleep
In order to disable BOD during sleep (see Table 7-1 on page 23) the BODS bit must be written to logic one. This is
controlled by a protected change sequence, as follows:
1. Write the signature for change enable of protected I/O registers to register CCP.
2. Within four instruction cycles write the BODS bit.
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 when the device wakes up. Alternatively the BODS bit can be cleared by
writing logic zero to it. This does not require protected sequence.
• Bits 3:1 – SM[2:0]: Sleep Mode Select Bits 2, 1 and 0
These bits select between available sleep modes, as shown in Table 7-2.
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Table 7-2.
Sleep Mode Select
SM2
SM1
SM0
Sleep Mode
0
0
0
Idle
0
0
1
ADC noise reduction
0
1
0
Power-down
0
1
1
Reserved
1
0
0
Standby
1
0
1
Reserved
1
1
0
Reserved
1
1
1
Reserved
• 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.
7.5.2
PRR – Power Reduction Register
Bit
7
6
5
4
3
2
1
0
0x35
–
–
–
PRTWI
PRSPI
PRTIM1
PRTIM0
PRADC
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
PRR
• Bits 7:5 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bit 4 – PRTWI: Power Reduction Two-Wire Interface
Writing a logic one to this bit shuts down the Two-Wire Interface module.
• Bit 3 – PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit shuts down the Serial Peripheral Interface module.
• Bit 2 – 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 1 – PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will continue like before the shutdown.
• Bit 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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8. System Control and Reset
8.1
Resetting the AVR
During reset, all I/O registers are set to their initial values, and the program starts execution from the Reset Vector.
The instruction placed at the Reset Vector must be a RJMP – Relative Jump – instruction to the reset handling routine. If the program never enables an interrupt source, the interrupt vectors are not used, and regular program code
can be placed at these locations. The circuit diagram in Figure 8-1 shows the reset logic. Electrical parameters of
the reset circuitry are defined in section “System and Reset Characteristics” on page 155.
Figure 8-1.
Reset Logic
DATA BUS
WDRF
EXTRF
BORF
BROWN OUT
RESET CIRCUIT
VCC
PULL-UP
RESISTOR
RESET
PORF
RESET FLAG REGISTER
(RSTFLR)
BODLEVEL[2:0]
S
POWER-ON
RESET CIRCUIT
COUNTER RESET
TIMEOUT
SPIKE
FILTER
EXTERNAL
RESET CIRCUIT
Q
INTERNAL
RESET
R
DELAY
COUNTERS
CK
WATCHDOG
TIMER
RSTDISBL
WATCHDOG
OSCILLATOR
CLOCK
GENERATOR
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 start up sequence is described in “Starting from
Reset” on page 20.
8.2
Reset Sources
The ATtiny40 has four sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset threshold (VPOT)
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer than the minimum
pulse length
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the Watchdog is enabled
• Brown Out Reset. The MCU is reset when the Brown-Out Detector is enabled and supply voltage is below the
brown-out threshold (VBOT)
8.2.1
Power-on Reset
A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The detection level is defined in section “System and Reset Characteristics” on page 155. 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.
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Figure 8-2.
MCU Start-up, RESET High before Initial Time-out
V CC
V POT
RESET
V RST
TIME-OUT
t TOUT
INTERNAL
RESET
Figure 8-3.
MCU Start-up, RESET Extended Externally
V CC
V POT
> t TOUT
RESET
TIME-OUT
V RST
t TOUT
INTERNAL
RESET
8.2.2
External Reset
An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer than the minimum
pulse width (see section “System and Reset Characteristics” on page 155) will generate a reset, even if the clock is
not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the Reset
Threshold Voltage – VRST – on its positive edge, the delay counter starts the MCU after the time-out period – tTOUT
– has expired. External reset is ignored during Power-on start-up count. After Power-on reset the internal reset is
extended only if RESET pin is low when the initial Power-on delay count is complete. See Figure 8-2 and Figure 83.
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Figure 8-4.
External Reset During Operation
CC
8.2.3
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse. On the falling edge of this pulse, the delay timer
starts counting the time-out period tTOUT. See page 30 for details on operation of the Watchdog Timer and Table
20-4 on page 155 for details on reset time-out.
Figure 8-5.
Watchdog Reset During Operation
CC
CK
8.2.4
Brown-out Detection
ATtiny40 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL Fuses. The trigger
level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the detection level should be
interpreted as VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure 8-6 on page 31),
the Brown-out Reset is immediately activated. When VCC increases above the trigger level (VBOT+ in Figure 8-6),
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 “System and Reset Characteristics” on page 155.
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Figure 8-6.
Brown-out Reset During Operation
VCC
VBOT-
VBOT+
RESET
TIME-OUT
tTOUT
INTERNAL
RESET
8.3
Internal Voltage Reference
ATtiny40 features an internal bandgap reference. This reference is used for Brown-out Detection, and it can be
used as an input to the Analog Comparator or the ADC. The bandgap voltage varies with supply voltage and
temperature.
8.3.1
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given
in “System and Reset Characteristics” on page 155. To save power, the reference is not always turned on. The reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL[2:0] Fuse).
2. When the internal reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow
the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is
turned off before entering Power-down mode.
8.4
Watchdog Timer
The Watchdog Timer is clocked from an on-chip oscillator, which runs at 128 kHz. See Figure 8-7. By controlling
the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table 8-2 on page 34.
The WDR – Watchdog Reset – instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is
disabled and when a device reset occurs. Ten different clock cycle periods can be selected to determine the reset
period. If the reset period expires without another Watchdog Reset, the ATtiny40 resets and executes from the
Reset Vector. For timing details on the Watchdog Reset, refer to Table 8-3 on page 34.
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Watchdog Timer
WDP0
WDP1
WDP2
WDP3
OSC/512K
OSC/1024K
OSC/256K
OSC/64K
OSC/128K
OSC/8K
OSC/4K
OSC/2K
WATCHDOG
RESET
OSC/32K
WATCHDOG
PRESCALER
128 kHz
OSCILLATOR
OSC/16K
Figure 8-7.
MUX
WDE
MCU RESET
The Wathdog Timer can also be configured to generate an interrupt instead of a reset. This can be very helpful
when using the Watchdog to wake-up from Power-down.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period, two different safety
levels are selected by the fuse WDTON as shown in Table 8-1 on page 32. See “Procedure for Changing the
Watchdog Timer Configuration” on page 32 for details.
Table 8-1.
WDT Configuration as a Function of the Fuse Settings of WDTON
WDTON
Safety
Level
WDT
Initial State
How to
Disable the WDT
How to
Change Time-out
Unprogrammed
1
Disabled
Protected change
sequence
No limitations
Programmed
2
Enabled
Always enabled
Protected change
sequence
8.4.1
Procedure for Changing the Watchdog Timer Configuration
The sequence for changing configuration differs between the two safety levels, as follows:
8.4.1.1
Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit to one without any
restriction. A special sequence is needed when disabling an enabled Watchdog Timer. To disable an enabled
Watchdog Timer, the following procedure must be followed:
1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, in the same operation, write WDE and WDP bits
8.4.1.2
Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A protected change
is needed when changing the Watchdog Time-out period. To change the Watchdog Time-out, the following procedure must be followed:
1. Write the signature for change enable of protected I/O registers to register CCP
2. Within four instruction cycles, write the WDP bit. The value written to WDE is irrelevant
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8.4.2
Code Examples
The following code example shows how to turn off the WDT. The example assumes that interrupts are controlled
(e.g., by disabling interrupts globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example
WDT_off:
wdr
; Clear WDRF in RSTFLR
in
andi
out
r16, RSTFLR
r16, ~(1<<WDRF)
RSTFLR, r16
; Write signature for change enable of protected I/O register
ldi r16, 0xD8
out CCP, r16
; Within four instruction cycles, turn off WDT
ldi r16, (0<<WDE)
out WDTCSR, r16
ret
Note:
8.5
8.5.1
See “Code Examples” on page 5.
Register Description
WDTCSR – Watchdog Timer Control and Status Register
Bit
7
6
5
4
3
2
1
0
WDIF
WDIE
WDP3
–
WDE
WDP2
WDP1
WDP0
Read/Write
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
0
0
0
0x31
WDTCSR
• Bit 7 – WDIF: Watchdog Timer 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 WDIE is set, the Watchdog Time-out Interrupt is requested.
• Bit 6 – WDIE: Watchdog Timer Interrupt Enable
When this bit is written to one, the Watchdog interrupt request is enabled. If WDE is cleared in combination with
this setting, the Watchdog Timer is in Interrupt Mode, and the corresponding interrupt is requested 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
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of the Watchdog System Reset mode. If the interrupt is not executed before the next time-out, a System Reset will
be applied.
Table 8-2.
(1)
WDTON
Watchdog Timer Configuration
WDE
WDIE
Mode
Action on Time-out
1
0
0
Stopped
None
1
0
1
Interrupt
Interrupt
1
1
0
System Reset
Reset
1
1
1
Interrupt and System Reset
Interrupt, then go to System Reset Mode
0
x
x
System Reset
Reset
Note:
1. WDTON configuration bit set to “0“ means programmed and “1“ means unprogrammed.
• Bit 4 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 3 – WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in RSTFLR. 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.
• Bits 5, 2:0 – WDP[3:0]: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP[3:0] 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 8-3 on page 34.
Table 8-3.
Watchdog Timer Prescale Select
WDP3
WDP2
WDP1
WDP0
Number of
WDT Oscillator Cycles
Typical Time-out
at VCC = 5.0V
0
0
0
0
2K (2048) cycles
16 ms
0
0
0
1
4K (4096) cycles
32 ms
0
0
1
0
8K (8192) cycles
64 ms
0
0
1
1
16K (16384) cycles
0.125 s
0
1
0
0
32K (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
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Table 8-3.
Watchdog Timer Prescale Select (Continued)
WDP3
WDP2
WDP1
WDP0
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
Number of
WDT Oscillator Cycles
Typical Time-out
at VCC = 5.0V
Reserved
8.5.2
RSTFLR – Reset Flag Register
The Reset Flag Register provides information on which reset source caused an MCU Reset.
Bit
7
6
5
4
3
2
1
0
0x3B
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
X
X
X
RSTFLR
• Bits 7:4 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the
flag.
• Bit 2 – BORF: Brown-Out Reset Flag
This bit is set if a Brown-Out Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the
flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag.
• Bit 0 – PORF: Power-On Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and then reset the RSTFLR 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.
9. Interrupts
This section describes the specifics of the interrupt handling as performed in ATtiny40. For a general explanation
of the AVR interrupt handling, see “Reset and Interrupt Handling” on page 10.
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9.1
Interrupt Vectors
The interrupt vectors of ATtiny40 are described in Table 9-1 below.
Table 9-1.
Vector No.
Program Address
Label
Interrupt Source
1
0x0000
RESET
External Pin, Power-on Reset,
Brown-Out Reset, Watchdog Reset
2
0x0001
INT0
External Interrupt Request 0
3
0x0002
PCINT0
Pin Change Interrupt Request 0
4
0x0003
PCINT1
Pin Change Interrupt Request 1
5
0x0004
PCINT2
Pin Change Interrupt Request 2
6
0x0005
WDT
Watchdog Time-out
7
0x0006
TIM1_CAPT
Timer/Counter1 Input Capture
8
0x0007
TIM1_COMPA
Timer/Counter1 Compare Match A
9
0x0008
TIM1_COMPB
Timer/Counter1 Compare Match B
10
0x0009
TIM1_OVF
Timer/Counter1 Overflow
11
0x000A
TIM0_COMPA
Timer/Counter0 Compare Match A
12
0x000B
TIM0_COMPB
Timer/Counter0 Compare Match B
13
0x000C
TIM0_OVF
Timer/Counter0 Overflow
14
0x000D
ANA_COMP
Analog Comparator
15
0x000E
ADC
ADC Conversion Complete
16
0x000F
TWI_SLAVE
Two-Wire Interface
17
0x0010
SPI
Serial Peripheral Interface
18
1.
Reset and Interrupt Vectors
0x0011
QTRIP
(1)
Touch Sensing
The touch sensing interrupt source is related to the QTouch library support.
In case the program never enables an interrupt source, the Interrupt Vectors will not be used and, consequently,
regular program code can be placed at these locations.
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The most typical and general setup for interrupt vector addresses in ATtiny40 is shown in the program example
below.
Assembly Code Example
.org 0x0000
;Set address of next statement
rjmp RESET
; Address 0x0000
rjmp INT0_ISR
; Address 0x0001
rjmp PCINT0_ISR
; Address 0x0002
rjmp PCINT1_ISR
; Address 0x0003
rjmp PCINT2_ISR
; Address 0x0004
rjmp WDT_ISR
; Address 0x0005
rjmp TIM1_CAPT_ISR
; Address 0x0006
rjmp TIM1_COMPA_ISR
; Address 0x0007
rjmp TIM1_COMPB_ISR
; Address 0x0008
rjmp TIM1_OVF_ISR
; Address 0x0009
rjmp TIM0_COMPA_ISR
; Address 0x000A
rjmp TIM0_COMPB_ISR
; Address 0x000B
rjmp TIM0_OVF_ISR
; Address 0x000C
rjmp ANA_COMP_ISR
; Address 0x000D
rjmp ADC_ISR
; Address 0x000E
rjmp TWI_SLAVE_ISR
; Address 0x000F
rjmp SPI_ISR
; Address 0x0010
rjmp QTRIP_ISR
; Address 0x0011
RESET:
<instr>
; Main program start
; Address 0x0012
...
Note:
9.2
See “Code Examples” on page 5.
External Interrupts
External Interrupts are triggered by the INT0 pin or any of the PCINT[17:0] pins. Observe that, if enabled, the interrupts will trigger even if the INT0 or PCINT[17:0] pins are configured as outputs. This feature provides a way of
generating a software interrupt.
Pin change 0 interrupts PCI0 will trigger if any enabled PCINT[7:0] pin toggles. Pin change 1 interrupts PCI1 will
trigger if any enabled PCINT[11:8] pin toggles. Pin change 2 interrupts PCI1 will trigger if any enabled
PCINT[17:12] pin toggles. The PCMSK0, PCMSK1 and PCMSK2 Registers control which pins contribute to the pin
change interrupts. Pin change interrupts on PCINT[17:0] are detected asynchronously, which means that these
interrupts can be used for waking the part also from sleep modes other than Idle mode.
The INT0 interrupt can be triggered by a falling or rising edge or a low level. This is set up as shown in “MCUCR –
MCU Control Register” on page 38. When the INT0 interrupt is enabled and configured as level triggered, the interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising edge interrupts on INT0
requires the presence of an I/O clock, as described in “Clock System” on page 17.
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9.2.1
Low Level Interrupt
A low level interrupt on INT0 is detected asynchronously. This means that the interrupt source can be used for
waking the part also from sleep modes other than Idle (the I/O clock is halted in all sleep modes except Idle).
Note that if a level triggered interrupt is used for wake-up from Power-down, the required level must be held long
enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of
the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined as
described in “Clock System” on page 17.
If the low level on the interrupt pin is removed before the device has woken up then program execution will not be
diverted to the interrupt service routine but continue from the instruction following the SLEEP command.
9.2.2
Pin Change Interrupt Timing
A timing example of a pin change interrupt is shown in Figure 9-1.
Figure 9-1.
Timing of pin change interrupts
pin_lat
PCINT(0)
D
pcint_in_(0)
Q
clk
0
pcint_syn
pcint_setflag
PCIF
pin_sync
LE
x
PCINT(0) in PCMSK(x)
clk
clk
PCINT(0)
pin_lat
pin_sync
pcint_in_(0)
pcint_syn
pcint_setflag
PCIF
9.3
Register Description
9.3.1
MCUCR – MCU Control Register
The MCU Control Register contains bits for controlling external interrupt sensing and power management.
Bit
0x3A
Read/Write
7
6
5
4
3
2
1
0
ISC01
ISC00
–
BODS
SM2
SM1
SM0
SE
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
MCUCR
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Initial Value
0
0
0
0
0
0
0
0
• Bits 7:6 – ISC0[1:0]: Interrupt Sense Control
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt
mask are set. The level and edges on the external INT0 pin that activate the interrupt are defined in Table 9-2. The
value on the INT0 pin is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If
low level interrupt is selected, the low level must be held until the completion of the currently executing instruction
to generate an interrupt.
Table 9-2.
9.3.2
Interrupt 0 Sense Control
ISC01
ISC00
Description
0
0
The low level of INT0 generates an interrupt request.
0
1
Any logical change on INT0 generates an interrupt request.
1
0
The falling edge of INT0 generates an interrupt request.
1
1
The rising edge of INT0 generates an interrupt request.
GIMSK – General Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0
0x0C
–
PCIE2
PCIE1
PCIE0
–
–
–
INT0
Read/Write
R
R/W
R/W
R/W
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
GIMSK
• Bit 7 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 6 – PCIE2: Pin Change Interrupt Enable 2
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 2 is
enabled. Any change on any enabled PCINT[17:12] pin will cause an interrupt. The corresponding interrupt of Pin
Change Interrupt Request is executed from the PCI0 Interrupt Vector. PCINT[17:12] pins are enabled individually
by the PCMSK2 Register.
• Bit 5 – PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 1 is
enabled. Any change on any enabled PCINT[11:8] pin will cause an interrupt. The corresponding interrupt of Pin
Change Interrupt Request is executed from the PCI1 Interrupt Vector. PCINT[11:8] pins are enabled individually by
the PCMSK1 Register.
• Bit 4 – PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 0 is
enabled. Any change on any enabled PCINT[7:0] pin will cause an interrupt. The corresponding interrupt of Pin
Change Interrupt Request is executed from the PCI0 Interrupt Vector. PCINT[7:0] pins are enabled individually by
the PCMSK0 Register.
• Bits 3:1 – Res: Reserved Bits
These bits are reserved and will always read as zero.
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• 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 Control bits (ISC01 and ISC00) in the MCU Control Register (MCUCR) define
whether the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on
the pin will cause an interrupt request even if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt Vector.
9.3.3
GIFR – General Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x0B
–
PCIF2
PCIF1
PCIF0
–
–
–
INTF0
Read/Write
R
R/W
R/W
R/W
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
GIFR
• Bit 7 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 6 – PCIF2: Pin Change Interrupt Flag 2
When a logic change on any PCINT[17:12] pin triggers an interrupt request, PCIF2 becomes set (one). If the I-bit in
SREG and the PCIE2 bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag
is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 5 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT[11:8] pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in
SREG and the PCIE1 bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag
is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 4 – PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT[7:0] pin triggers an interrupt request, PCIF becomes set (one). If the I-bit in
SREG and the PCIE0 bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag
is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bits 3:1 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• 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 GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag
is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
This flag is always cleared when INT0 is configured as a level interrupt.
9.3.4
PCMSK2 – Pin Change Mask Register 2
Bit
7
6
5
4
3
2
1
0
0x1A
–
–
PCINT17
PCINT16
PCINT15
PCINT14
PCINT13
PCINT12
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
PCMSK2
• Bits 7:6 – Res: Reserved Bits
These bits are reserved and will always read as zero.
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• Bits 5:0 – PCINT[17:12]: Pin Change Enable Mask 17:12
Each PCINT[17:12] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If
PCINT[17:12] is set and the PCIE2 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O
pin. If PCINT[17:12] is cleared, pin change interrupt on the corresponding I/O pin is disabled.
9.3.5
PCMSK1 – Pin Change Mask Register 1
Bit
7
6
5
4
3
2
1
0
0x0A
–
–
–
–
PCINT11
PCINT10
PCINT9
PCINT8
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCMSK1
• Bits 7:4 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 3:0 – PCINT[11:8]: Pin Change Enable Mask 11:8
Each PCINT[11:8] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[11:8]
is set and the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If
PCINT[11:8] is cleared, pin change interrupt on the corresponding I/O pin is disabled.
9.3.6
PCMSK0 – Pin Change Mask Register 0
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
0x09
PCMSK0
• Bits 7:0 – PCINT[7:0]: Pin Change Enable Mask 7:0
Each PCINT[7:0] bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT[7:0] is
set and the PCIE0 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT[7:0]
is cleared, pin change interrupt on the corresponding I/O pin is disabled.
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10. I/O Ports
10.1
Overview
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. Each output buffer has symmetrical drive characteristics with both high sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable
pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both VCC and
Ground as indicated in Figure 10-1 on page 42. See “Electrical Characteristics” on page 152 for a complete list of
parameters.
Figure 10-1. I/O Pin Equivalent Schematic
Rpu
Logic
Pxn
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for the port, and a lower case “n” represents the bit number. However, when using the register or bit
defines in a program, the precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description” on
page 58.
Four I/O memory address locations are allocated for each port, one each for the Data Register – PORTx, Data
Direction Register – DDRx, Pull-up Enable Register – PUEx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register, the Data Direction Register, and the Pull-up Enable 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.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page 43. 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 47. Refer to the individual module sections
for a full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port
as general digital I/O.
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10.2
Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 10-2 shows a functional description of
one I/O-port pin, here generically called Pxn.
Figure 10-2. General Digital I/O(1)
REx
Q
D
PUExn
Q CLR
RESET
Q
WEx
D
DDxn
Q CLR
WDx
RESET
DATA BUS
RDx
1
Q
Pxn
D
0
PORTxn
Q CLR
RESET
WRx
SLEEP
WPx
RRx
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
SLEEP:
clk I/O :
Note:
10.2.1
SLEEP CONTROL
I/O CLOCK
WEx:
REx:
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE PUEx
READ PUEx
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
1. WEx, WRx, WPx, WDx, REx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, and SLEEP
are common to all ports.
Configuring the Pin
Each port pin consists of four register bits: DDxn, PORTxn, PUExn, and PINxn. As shown in “Register Description”
on page 58, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address, the
PUExn bits at the PUEx 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.
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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).
The pull-up resistor is activated, if the PUExn is written logic one. To switch the pull-up resistor off, PUExn has to
be written logic zero.
Table 10-1 summarizes the control signals for the pin value.
Table 10-1.
Port Pin Configurations
DDxn
PORTxn
PUExn
I/O
Pull-up
Comment
0
X
0
Input
No
Tri-state (hi-Z)
0
X
1
Input
Yes
Sources current if pulled low externally
1
0
0
Output
No
Output low (sink)
1
0
1
Output
Yes
NOT RECOMMENDED.
Output low (sink) and internal pull-up active.
Sources current through the internal pull-up
resistor and consumes power constantly
1
1
0
Output
No
Output high (source)
1
1
1
Output
Yes
Output high (source) and internal pull-up active
Port pins are tri-stated when a reset condition becomes active, even when no clocks are running.
10.2.2
Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI
instruction can be used to toggle one single bit in a port.
10.2.3
Break-Before-Make Switching
In Break-Before-Make mode, switching the DDRxn bit from input to output introduces an immediate tri-state period
lasting one system clock cycle, as indicated in Figure 10-3. For example, if the system clock is 4 MHz and the
DDRxn is written to make an output, an 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 mode applies to the entire port and it is activated by the BBMx bit. For more details, see
“PORTCR – Port Control Register” on page 58.
When switching the DDRxn bit from output to input no immediate tri-state period is introduced.
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Figure 10-3. Switching Between Input and Output in Break-Before-Make-Mode
SYSTEM CLK
r16
0x02
r17
0x01
INSTRUCTIONS
out DDRx, r16
nop
PORTx
DDRx
0x55
0x02
0x01
Px0
Px1
out DDRx, r17
0x01
tri-state
tri-state
tri-state
intermediate tri-state cycle
10.2.4
intermediate tri-state cycle
Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the PINxn Register bit. As
shown in Figure 10-2 on page 43, the PINxn Register bit and the preceding latch constitute a synchronizer. This is
needed to avoid metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. Figure 10-4 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 10-4. 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 10-5
on page 46. The out instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the
delay tpd through the synchronizer is one system clock period.
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Figure 10-5. 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
10.2.5
Digital Input Enable and Sleep Modes
As shown in Figure 10-2 on page 43, the digital input signal can be clamped to ground at the input of the schmitttrigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down and Standby
modes to avoid high power consumption if some input signals are left floating, or have an analog signal level close
to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled,
SLEEP is active also for these pins. SLEEP is also overridden by various other alternate functions as described in
“Alternate Port Functions” on page 47.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “Interrupt on Rising
Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt is not enabled, the corresponding
External Interrupt Flag will be set when resuming from the above mentioned Sleep mode, as the clamping in these
sleep mode produces the requested logic change.
10.2.6
Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of
the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to
reduce current consumption in all other modes where the digital inputs are enabled (Reset, Active mode and Idle
mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the
pull-up will be disabled during reset. If low power consumption during reset is important, it is recommended to use
an external pull-up or pulldown. Connecting unused pins directly to VCC or GND is not recommended, since this
may cause excessive currents if the pin is accidentally configured as an output.
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10.2.7
Program Example
The following code example shows how to set port B pin 0 high, pin 1 low, and define the port pins from 2 to 3 as
input with a pull-up assigned to port pin 2. The resulting pin values are read back again, but as previously discussed, a nop instruction is included to be able to read back the value recently assigned to some of the pins.
Assembly Code Example
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16,(1<<PUEB2)
ldi
r17,(1<<PB0)
ldi
r18,(1<<DDB1)|(1<<DDB0)
out
PUEB,r16
out
PORTB,r17
out
DDRB,r18
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINB
...
Note:
10.3
See “Code Examples” on page 5.
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. In Figure 10-6 below is shown how
the port pin control signals from the simplified Figure 10-2 on page 43 can be overridden by alternate functions.
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Figure 10-6. Alternate Port Functions(1)
PUOExn
REx
PUOVxn
1
Q
0
D
PUExn
Q CLR
DDOExn
RESET
WEx
DDOVxn
1
Q
D
DDxn
0
Q CLR
WDx
PVOExn
RESET
RDx
1
DATA BUS
PVOVxn
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
WPx
DIEOVxn
RESET
WRx
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
D
Q
PINxn
L
CLR
Q
CLR
Q
clk
I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
Note:
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP CONTROL
Pxn, PORT TOGGLE OVERRIDE ENABLE
WEx:
REx:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clk I/O :
DIxn:
AIOxn:
WRITE PUEx
READ PUEx
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. WEx, WRx, WPx, WDx, REx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, and SLEEP
are common to all ports. All other signals are unique for each pin.
The illustration in the figure above serves as a generic description applicable to all port pins in the AVR microcontroller family. Some overriding signals may not be present in all port pins.
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Table 10-2 on page 49 summarizes the function of the overriding signals. The pin and port indexes from Figure 106 on page 48 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
Table 10-2.
Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
PUOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
PUExn = 0b1.
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 PUExn Register bit.
DDOE
Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled by the
DDOV signal. If this signal is cleared, the Output driver is
enabled by the DDxn Register bit.
DDOV
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled when
DDOV is set/cleared, regardless of the setting of the DDxn
Register bit.
PVOE
Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the port
value is controlled by the PVOV signal. If PVOE is cleared, and
the Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.
PVOV
Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless of the
setting of the PORTxn Register bit.
PTOE
Port Toggle
Override Enable
If PTOE is set, the PORTxn Register bit is inverted.
DIEOE
Digital Input
Enable Override
Enable
If this bit is set, the Digital Input Enable is controlled by the
DIEOV signal. If this signal is cleared, the Digital Input Enable
is determined by MCU state (Normal mode, sleep mode).
DIEOV
Digital Input
Enable Override
Value
If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state (Normal
mode, sleep mode).
DI
Digital Input
This is the Digital Input to alternate functions. In the figure, the
signal is connected to the output of the schmitt-trigger but
before the synchronizer. Unless the Digital Input is used as a
clock source, the module with the alternate function will use its
own synchronizer.
AIO
Analog
Input/Output
This is the Analog Input/Output to/from alternate functions. The
signal is connected directly to the pad, and can be used bidirectionally.
The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to
the alternate function. Refer to the alternate function description for further details.
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10.3.1
Alternate Functions of Port A
The Port A pins with alternate function are shown in Table 10-3.
Table 10-3.
Port A Pins Alternate Functions
Port Pin
Alternate Function
PA0
ADC0: ADC Input Channel 0
PCINT0: Pin Change Interrupt 0, Source 0
PA1
ADC1: ADC Input Channel 1
AIN0:
Analog Comparator, Positive Input
PCINT1:Pin Change Interrupt 0, Source 1
PA2
ADC2: ADC Input Channel 2
AIN1:
Analog Comparator, Negative Input
PCINT2: Pin Change Interrupt 0, Source 2
PA3
ADC3: ADC Input Channel 3
PCINT3: Pin Change Interrupt 0, Source 3
PA4
ADC4: ADC Input Channel 4
T0:
Timer/Counter0 Clock Source
PCINT4: Pin Change Interrupt 0, Source 4
PA5
ADC5: ADC Input Channel 5
OC0B: Timer/Counter0 Compare Match B Output
PCINT5: Pin Change Interrupt 0, Source 5
PA6
ADC6: ADC Input Channel 6
PCINT6: Pin Change Interrupt 0, Source 6
PA7
ADC7: ADC Input Channel 7
PCINT7: Pin Change Interrupt 0, Source 7
• Port A, Bit 0 – ADC0/PCINT0
• ADC0: Analog to Digital Converter, Channel 0.
• PCINT0: Pin Change Interrupt source 0. The PA0 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 1 – ADC1/AIN0/PCINT1
• ADC1: Analog to Digital Converter, Channel 1.
• AIN0: Analog Comparator Positive Input. Configure the port pin as input with the internal pull-up switched off to
avoid the digital port function from interfering with the function of the Analog Comparator.
• PCINT1: Pin Change Interrupt source 1. The PA1 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 2 – ADC2/AIN1/PCINT2
• ADC2: Analog to Digital Converter, Channel 2.
• AIN1: Analog Comparator Negative Input. Configure the port pin as input with the internal pull-up switched off to
avoid the digital port function from interfering with the function of the Analog Comparator.
• PCINT2: Pin Change Interrupt source 2. The PA2 pin can serve as an external interrupt source for pin change
interrupt 0.
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• Port A, Bit 3 – ADC3/PCINT3
• ADC3: Analog to Digital Converter, Channel 3.
• PCINT3: Pin Change Interrupt source 3. The PA3 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 4 – ADC4/T0/PCINT4
• ADC4: Analog to Digital Converter, Channel 4.
• T0: Timer/Counter0 counter source.
• PCINT4: Pin Change Interrupt source 4. The PA4 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 5 – ADC5/OC0B/PCINT5
• ADC5: Analog to Digital Converter, Channel 5.
• OC0B: Output Compare Match output. The PA5 pin can serve as an external output for the Timer/Counter0
Compare Match B. The pin has to be configured as an output (DDA5 set (one)) to serve this function. This is
also the output pin for the PWM mode timer function.
• PCINT5: Pin Change Interrupt source 5. The PA5 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 6 – ADC6/PCINT6
• ADC6: Analog to Digital Converter, Channel 6.
• PCINT6: Pin Change Interrupt source 6. The PA6 pin can serve as an external interrupt source for pin change
interrupt 0.
• Port A, Bit 7 – ADC7/PCINT7
• ADC7: Analog to Digital Converter, Channel 7.
• PCINT7: Pin Change Interrupt source 7. The PA7 pin can serve as an external interrupt source for pin change
interrupt 0.
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Table 10-4 and Table 10-5 relate the alternate functions of Port A to the overriding signals shown in Figure 10-6 on
page 48.
Table 10-4.
Overriding Signals for Alternate Functions in PA[7:5]
Signal
Name
PA7/ADC7/PCINT7
PA6/ADC6/PCINT6
PA5/ADC5/PCINT5
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
0
0
DDOV
0
0
0
PVOE
0
0
OC0B_ENABLE
PVOV
0
0
OC0B
PTOE
0
0
0
DIEOE
PCINT7 • PCIE0 + ADC7D
PCINT6 • PCIE0 + ADC6D
PCINT5 • PCIE0 + ADC5D
DIEOV
PCINT7 • PCIE0
PCINT6 • PCIE0
PCINT5 • PCIE0
PCINT7 Input
PCINT6 Input
PCINT5 Input
ADC7 Input
ADC6 Input
ADC5 Input
DI
AIO
Note:
When TWI is enabled the slew rate control and spike filter are activated on PA7. This is not illustrated in Figure 10-6 on
page 48. The spike filter is connected between AIOxn and the TWI module.
Table 10-5.
Overriding Signals for Alternate Functions in PA[4:2]
Signal
Name
PA4/ADC4/PCINT4
PA3/ADC3/PCINT3
PA2/ADC2/AIN1/PCINT2
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
0
0
DDOV
0
0
0
PVOE
0
0
0
PVOV
0
0
0
PTOE
0
0
0
DIEOE
(PCINT4 • PCIE0) + ADC4D
(PCINT3 • PCIE0) + ADC3D
(PCINT2 • PCIE0) + ADC2D
DIEOV
PCINT4 • PCIE0
PCINT3 • PCIE0
PCINT3 • PCIE0
T0 / PCINT4 input
PCINT1 Input
PCINT0 Input
ADC4 Input
ADC3 Input
ADC2 / Analog Comparator
Negative Input
DI
AIO
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Table 10-6.
Overriding Signals for Alternate Functions in PA[1:0]
Signal
Name
PA1/ADC1/AIN0/PCINT1
PA0/ADC0/PCINT0
PUOE
0
0
PUOV
0
0
DDOE
0
0
DDOV
0
0
PVOE
0
0
PVOV
0
0
PTOE
0
0
DIEOE
PCINT1 • PCIE0 + ADC1D
PCINT0 • PCIE0 + ADC0D
DIEOV
PCINT1 • PCIE0
PCINT0 • PCIE0
PCINT1 Input
PCINT0 Input
ADC1 / Analog Comparator Positive Input
ADC1 Input
DI
AIO
10.3.2
Alternate Functions of Port B
The Port B pins with alternate function are shown in Table 10-7.
Table 10-7.
Port B Pins Alternate Functions
Port Pin
Alternate Function
PB0
ADC8: ADC Input Channel 8
PCINT8: Pin Change Interrupt 1, Source 8
PB1
ADC9: ADC Input Channel 9
PCINT9: Pin Change Interrupt 1, Source 9
PB2
ADC10: ADC Input Channel 10
PCINT10:Pin Change Interrupt 1, Source 10
PB3
ADC11: ADC Input Channel 11
PCINT11:Pin Change Interrupt 1, Source 11.
• Port B, Bit 0 – ADC8/PCINT8
• ADC8: Analog to Digital Converter, Channel 8.
• PCINT8: Pin Change Interrupt source 8. The PB0 pin can serve as an external interrupt source for pin change
interrupt 1.
• Port B, Bit 1 – ADC9/PCINT9
• ADC9: Analog to Digital Converter, Channel 9.
• PCINT9: Pin Change Interrupt source 9. The PB1 pin can serve as an external interrupt source for pin change
interrupt 1.
• Port B, Bit 2 – ADC10/PCINT10
• ADC10: Analog to Digital Converter, Channel 10.
• PCINT10: Pin Change Interrupt source 10. The PB2 pin can serve as an external interrupt source for pin
change interrupt 1.
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• Port B, Bit 3 – ADC11/PCINT11
• ADC11: Analog to Digital Converter, Channel 11.
• PCINT11: Pin Change Interrupt source 11. The PB3 pin can serve as an external interrupt source for pin
change interrupt 1.
Table 10-8 on page 54 and Table 10-9 on page 54 relate the alternate functions of Port B to the overriding signals
shown in Figure 10-6 on page 48.
Table 10-8.
Overriding Signals for Alternate Functions in PB[3:2]
Signal
Name
PB3/ADC11/PCINT11
PB2/ADC10/PCINT10
PUOE
0
0
PUOV
0
0
DDOE
0
0
DDOV
0
0
PVOE
0
0
PVOV
0
0
PTOE
0
0
DIEOE
PCINT11 • PCIE1 • ADC11D
PCINT10 • PCIE1 • ADC10D
DIEOV
PCINT11 • PCIE1
PCINT10 • PCIE1
DI
PCINT11 Input
INT0 / PCINT10 / SPI Master Input
AIO
ASDC11 Input
ADC10 Input
Table 10-9.
Overriding Signals for Alternate Functions in PB[1:0]
Signal
Name
PB1/ADC9/PCINT9
PB0/ADC8/PCINT8
PUOE
0
0
PUOV
0
0
DDOE
0
0
DDOV
0
0
PVOE
0
0
PVOV
0
0
PTOE
0
0
DIEOE
PCINT9 • PCIE1 • ADC9D
PCINT8 • PCIE1 • ADC8D
DIEOV
PCINT9 • PCIE1
PCINT8 • PCIE1
PCINT9
PCINT8
ADC9 Input
ADC8 Input
DI
AIO
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10.3.3
Alternate Functions of Port C
The Port C pins with alternate function are shown in Table 10-10.
Table 10-10. Port A Pins Alternate Functions
Port Pin
Alternate Function
PC0
OC0A: Timer/Counter0 Compare Match A output
SS :
SPI Slave Select
PCINT12:Pin Change Interrupt 0, Source 12
PC1
SCK:
SPI Clock
SCL : TWI Clock
ICP1:
Timer/Counter1 Input Capture Pin
T1:
Timer/Counter1 Clock Source
PCINT13:Pin Change Interrupt 0, Source 13
PC2
INT0:
External Interrupt 0 Input
CLKO: System Clock Output
MISO: SPI Master Input / Slave Output
PCINT14:Pin Change Interrupt 0, Source 14
PC3
RESET: Reset pin
PCINT15:Pin Change Interrupt 0, Source 15
PC4
MOSI: SPI Master Output / Slave Input
SDA:
TWI Data Input /Output
TPIDATA:Serial Programming Data
PCINT16:Pin Change Interrupt 0, Source 16
PC5
CLKI:
External Clock Input
TPICLK: Serial Programming Clock
PCINT17:Pin Change Interrupt 0, Source 17
• Port C, Bit 0 – OC0A/PCINT12
• OC0A: Output Compare Match output. Provided that the pin has been configured as an output it serves as an
external output for Timer/Counter0 Compare Match A. This pin is also the output for the timer/counter PWM
mode function.
• SS: Slave Select Input. Regardless of DDC0, this pin is automatically configured as an input when SPI is
enabled as a slave. The data direction of this pin is controlled by DDC0 when SPI is enabled as a master.
• PCINT12: Pin Change Interrupt source 12. The PC0 pin can serve as an external interrupt source for pin
change interrupt 2.
• Port C, Bit 1 – SCK/SCL/ICP1/T1/PCINT13
• SCK: SPI Clock.
• SCL: TWI Clock. The pin is disconnected from the part and becomes the serial clock for the TWI when TWEN in
TWSCRA is set. In this mode of operation, the pin is driven by an open drain driver with slew rate limitation and
a spike filter.
• ICP1: Timer/Counter1 Input Capture Pin.
• T1: Timer/Counter1 counter source.
• PCINT13: Pin Change Interrupt source 13. The PC1 pin can serve as an external interrupt source for pin
change interrupt 2.
• Port C, Bit 2 – INT0/CLKO/MISO/PCINT14
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• INT0: The PC2 pin can serve as an External Interrupt source 0.
• CLKO: The divided system clock can be output on the PB5 pin, if the CKOUT Fuse is programmed, regardless
of the PORTB5 and DDB5 settings. It will also be output during reset.
• MISO: SPI Master Input / Slave Output. Regardless of DDC2, this pin is automatically configured as an input
when SPI is enabled as a master. The data direction of this pin is controlled by DDC2 when SPI is enabled as a
slave.
• PCINT14: Pin Change Interrupt source 14. The PC2 pin can serve as an external interrupt source for pin
change interrupt 2.
• Port C, Bit 3 – RESET/PCINT15
• RESET: External Reset input is active low and enabled by unprogramming (“1”) the RSTDISBL Fuse. Pullup is
activated and output driver and digital input are deactivated when the pin is used as the RESET pin.
• PCINT15: Pin Change Interrupt source 15. The PC3 pin can serve as an external interrupt source for pin
change interrupt 2.
• Port C, Bit 4 – MOSI/SDA/TPIDATA/PCINT16
• MOSI: SPI Master Output / Slave Input. Regardless of DDC4, this pin is automatically configured as an input
when SPI is enabled as a slave. The data direction of this pin is controlled by DDC4 when SPI is enabled as a
master.
• SDA: TWI Data. The pin is disconnected from the port and becomes the serial data for the TWI when TWEN in
TWSCRA is set. In this mode of operation, the pin is driven by an open drain driver with slew rate limitation and
a spike filter.
• TPIDATA: Serial Programming Data.
• PCINT16: Pin Change Interrupt source 16. The PC4 pin can serve as an external interrupt source for pin
change interrupt 2.
• Port C, Bit 5 – CLKI/PCINT17
• CLKI: Clock Input from an external clock source, see “External Clock” on page 19.
• TPICLK: Serial Programming Clock.
• PCINT17: Pin Change Interrupt source 17. The PC5 pin can serve as an external interrupt source for pin
change interrupt 2.
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Table 10-11 and Table 10-12 relate the alternate functions of Port C to the overriding signals shown in Figure 10-6
on page 48.
Table 10-11. Overriding Signals for Alternate Functions in PC[5:3]
Signal
Name
PUOE
PC5/CLKI/PCINT17
(1)
EXT_CLOCK
PUOV
DDOE
0
(1)
EXT_CLOCK
DDOV
PVOE
0
(1)
EXT_CLOCK
PC4/MOSI/SDA/PCINT16
PC3/RESET/PCINT15
0
RSTDISBL(2)
0
1
(SPE • MSTR) + TWEN
RSTDISBL(2)
TWEN • SDA_OUT
0
TWEN + (SPE • MSTR)
RSTDISBL(2)
PVOV
0
TWEN • SPE • MSTR •
SPI_MASTER_OUT +
TWEN • (SPE + MSTR)
0
PTOE
0
0
0
DIEOE
EXT_CLOCK + (PCINT17 •
PCIE2)
PCINT16 • PCIE2
RSTDISBL(2) + (PCINT15 •
PCIE2)
DIEOV
(EXT_CLOCK • PWR_DOWN )
+ (EXT_CLOCK(1) • PCINT17 •
PCIE2)
PCINT16 • PCIE2
RSTDISBL(2) • PCINT15 •
PCIE2
CLOCK / PCINT17 Input
PCINT16 / SPI Slave Input
PCINT15 Input
DI
AIO
Notes:
SDA Input
1. EXT_CLOCK = external clock is selected as system clock.
2. x RSTDISBL is 1 when the configuration bit is “0” (programmed).
3. When TWI is enabled the slew rate control and spike filter are activated on PC4. This is not illustrated in Figure 106 on page 48. The spike filter is connected between AIOxn and the TWI.
Table 10-12. Overriding Signals for Alternate Functions in PC[2:0]
Signal
Name
PC2/INT0/CLKO/MISO/
PCINT14
PC1/SCK/SCL/ICP1/T1/
PCINT13
PC0/OC0A/SS/PCINT12
0
0
0
0
TWEN + (SPE • MSTR)
SPE • MSTR
TWEN + SCL_OUT
0
+ (SPE • MSTR)
TWEN + (SPE • MSTR)
OC0A_ENABLE
PVOV
CKOUT • System Clock +
CKOUT • SPE • MSTR •
SPI_SLAVE_OUT
TWEN • (SPE • MSTR •
SCK_OUT • (SPE +
MSTR))
OC0A
PTOE
0
0
0
DIEOE
(PCINT14 • PCIE2) + INT0
PCINT13 • PCIE2
PCINT12 • PCIE2
DIEOV
(PCINT14 • PCIE2) + INT0
PCINT13 • PCIE2
PCINT12 • PCIE2
INT0 / PCINT14 / SPI Master
Input
ICP1 / SCK / T1 / SCL /
PCINT13 Input
SPI SS / PCINT12 Input
PUOE
CKOUT
PUOV
DDOE
0
(1)
CKOUT
DDOV
PVOE
(1)
+ (SPE • MSTR)
CKOUT
(1)
CKOUT
(1)
DI
AIO
SCL Input
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Notes:
1. CKOUT is 1 when the configuration bit is “0” (programmed).
2. When TWI is enabled the slew rate control and spike filter are activated on PC1. This is not illustrated in Figure 106 on page 48. The spike filter is connected between AIOxn and the TWI.
10.4
10.4.1
Register Description
PORTCR – Port Control Register
Bit
7
6
5
4
3
2
1
0
ADC11D
ADC10D
ADC9D
ADC8D
–
BBMC
BBMB
BBMA
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
0x08
PORTCR
• Bit 3 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 2 – BBMC: Break-Before-Make Mode Enable
When this bit is set the Break-Before-Make mode is activated for the entire Port C. The intermediate tri-state cycle
is then inserted when writing DDRCn to make an output. For further information, see “Break-Before-Make Switching” on page 44
• Bit 1 – BBMB: Break-Before-Make Mode Enable
When this bit is set the Break-Before-Make mode is activated for the entire Port B. The intermediate tri-state cycle
is then inserted when writing DDRBn to make an output. For further information, see “Break-Before-Make Switching” on page 44.
• Bit 0 – BBMA: Break-Before-Make Mode Enable
When this bit is set the Break-Before-Make mode is activated for the entire Port A. The intermediate tri-state cycle
is then inserted when writing DDRAn to make an output. For further information, see “Break-Before-Make Switching” on page 44.
10.4.2
PUEA – Port A Pull-up Enable Control Register
Bit
7
6
5
4
3
2
1
0
PUEA7
PUEA6
PUEA5
PUEA4
PUEA3
PUEA2
PUEA1
PUEA0
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
0x03
10.4.3
PORTA – Port A Data Register
Bit
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
0x02
10.4.4
PUEA
PORTA
DDRA – Port A Data Direction Register
Bit
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
0x01
DDRA
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10.4.5
PINA – Port A Input Pins
Bit
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
0x00
10.4.6
10.4.7
10.4.8
10.4.9
10.4.10
10.4.11
10.4.12
PINA
PUEB – Port B Pull-up Enable Control Register
Bit
7
6
5
4
3
2
1
0
0x07
–
–
–
–
PUEB3
PUEB2
PUEB1
PUEB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PUEB
PORTB – Port B Data Register
Bit
7
6
5
4
3
2
1
0
0x06
–
–
–
–
PORTB3
PORTB2
PORTB1
PORTB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PORTB
DDRB – Port B Data Direction Register
Bit
7
6
5
4
3
2
1
0
0x05
–
–
–
–
DDB3
DDB2
DDB1
DDB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DDRB
PINB – Port B Input Pins
Bit
7
6
5
4
3
2
1
0
0x04
–
–
–
–
PINB3
PINB2
PINB1
PINB0
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
N/A
N/A
N/A
N/A
PINB
PUEC – Port C Pull-up Enable Control Register
Bit
7
6
5
4
3
2
1
0
0x1E
–
–
PUEC5
PUEC4
PUEC3
PUEC2
PUEC1
PUEC0
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
PUEC
PORTC – Port C Data Register
Bit
7
6
5
4
3
2
1
0
0x1D
–
–
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
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
PORTC
DDRC – Port C Data Direction Register
Bit
7
6
5
4
3
2
1
0
0x1C
–
–
PINC5
PINC4
DDC3
DDC2
DDC1
DDC0
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
DDRC
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10.4.13
PINC – Port C Input Pins
Bit
7
6
5
4
3
2
1
0
0x1B
–
–
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
N/A
N/A
N/A
N/A
PINC
11. Timer/Counter0
11.1
Features
•
•
•
•
•
•
•
11.2
Two Independent Output Compare Units
Double Buffered Output Compare Registers
Clear Timer on Compare Match (Auto Reload)
Glitch Free, Phase Correct Pulse Width Modulator (PWM)
Variable PWM Period
Frequency Generator
Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
Overview
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output Compare Units,
and with PWM support. It allows accurate program execution timing (event management) and wave generation.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 11-1 on page 61. For the actual placement
of I/O pins, refer to Figure 1-1 on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown
in bold. The device-specific I/O Register and bit locations are listed in the “Register Description” on page 71.
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Figure 11-1. 8-bit Timer/Counter Block Diagram
Count
Clear
Direction
TOVn
(Int.Req.)
Control Logic
clkTn
Clock Select
Edge
Detector
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCnA
DATA BUS
OCRnA
Fixed
TOP
Value
Waveform
Generation
=
OCnB
OCRnB
TCCRnA
11.2.1
OCnB
(Int.Req.)
TCCRnB
Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit registers. Interrupt
request (abbreviated to Int.Req. in Figure 11-1) signals are all visible in the Timer Interrupt Flag Register (TIFR). All
interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and TIMSK are not shown
in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T0 pin. The
Clock Select logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement)
its value. The Timer/Counter is inactive when no clock source is selected. The output from the Clock Select logic is
referred to as the timer clock (clkT0).
The double buffered Output Compare Registers (OCR0A and OCR0B) is compared with the Timer/Counter value
at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and OC0B). See “Output Compare Unit” on page 63 for details.
The Compare Match event will also set the Compare Flag (OCF0A or OCF0B) which can be used to generate an
Output Compare interrupt request.
11.2.2
Definitions
Many register and bit references in this section are written in general form. A lower case “n” replaces the
Timer/Counter number, in this case 0. A lower case “x” replaces the Output Compare Unit, in this case Compare
Unit A or Compare Unit B. However, when using the register or bit defines in a program, the precise form must be
used, i.e., TCNT0 for accessing Timer/Counter0 counter value and so on.
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The definitions in Table 11-1 are also used extensively throughout the document.
Table 11-1.
11.3
Definitions
Constant
Description
BOTTOM
The counter reaches BOTTOM when it becomes 0x00
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the
value stored in the OCR0A Register. The assignment depends on the mode of operation
Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the
Clock Select logic which is controlled by the Clock Select (CS0[2:0]) bits located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and prescaler, see “Timer/Counter Prescaler” on page 92.
11.4
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 11-2 on page 62
shows a block diagram of the counter and its surroundings.
Figure 11-2. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
count
clear
TCNTn
Control Logic
clkTn
Edge
Detector
Tn
direction
( From Prescaler )
bottom
top
Signal description (internal signals):
count
direction
clear
clkTn
top
bottom
Increment or decrement TCNT0 by 1.
Select between increment and decrement.
Clear TCNT0 (set all bits to zero).
Timer/Counter clock, referred to as clkT0 in the following.
Signalize that TCNT0 has reached maximum value.
Signalize that TCNT0 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock
(clk T0 ). clk T0 can be generated from an external or internal clock source, selected by the Clock Select bits
(CS0[2:0]). When no clock source is selected (CS0[2:0] = 0) the timer is stopped. However, the TCNT0 value can
be accessed by the CPU, regardless of whether clkT0 is present or not. A CPU write overrides (has priority over) all
counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter
Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter Control Register B (TCCR0B). There
are close connections between how the counter behaves (counts) and how waveforms are generated on the Out-
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put Compare output OC0A. For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page 65.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by the WGM0[1:0]
bits. TOV0 can be used for generating a CPU interrupt.
11.5
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers (OCR0A and OCR0B).
Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock cycle. If the corresponding interrupt is enabled, the Output
Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when
the interrupt is executed. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location. The Waveform Generator uses the match signal to generate an output according to operating mode set by the
WGM0[2:0] bits and Compare Output mode (COM0x[1:0]) bits. The max and bottom signals are used by the Waveform Generator for handling the special cases of the extreme values in some modes of operation. See “Modes of
Operation” on page 65.
Figure 11-3 on page 63 shows a block diagram of the Output Compare unit.
Figure 11-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
8-BIT COMPARATOR
OCFnx (Int.Req.)
top
bottom
WAVEFORM GENERATOR
OCnx
FOCn
WGMn[2:0]
COMnX[1:0]
The OCR0x Registers are double buffered when using any of the Pulse Width Modulation (PWM) modes. For the
normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR0x Compare Registers to either top or bottom of the counting sequence.
The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the
output glitch-free.
The OCR0x Register access may seem complex, but this is not case. When the double buffering is enabled, the
CPU has access to the OCR0x Buffer Register, and if double buffering is disabled the CPU will access the OCR0x
directly.
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11.5.1
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to
the Force Output Compare (0x) bit. Forcing Compare Match will not set the OCF0x Flag or reload/clear the timer,
but the OC0x pin will be updated as if a real Compare Match had occurred (the COM0x[1:0] bits settings define
whether the OC0x pin is set, cleared or toggled).
11.5.2
Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any Compare Match that occur in the next timer clock
cycle, even when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0
without triggering an interrupt when the Timer/Counter clock is enabled.
11.5.3
Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all Compare Matches for one timer clock cycle, there are
risks involved when changing TCNT0 when using the Output Compare Unit, independently of whether the
Timer/Counter is running or not. If the value written to TCNT0 equals the OCR0x value, the Compare Match will be
missed, resulting in incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM
when the counter is down-counting.
The setup of the OC0x should be performed before setting the Data Direction Register for the port pin to output.
The easiest way of setting the OC0x value is to use the Force Output Compare (0x) strobe bits in Normal mode.
The OC0x Registers keep their values even when changing between Waveform Generation modes.
Be aware that the COM0x[1:0] bits are not double buffered together with the compare value. Changing the
COM0x[1:0] bits will take effect immediately.
11.6
Compare Match Output Unit
The Compare Output mode (COM0x[1:0]) bits have two functions. The Waveform Generator uses the COM0x[1:0]
bits for defining the Output Compare (OC0x) state at the next Compare Match. Also, the COM0x[1:0] bits control
the OC0x pin output source. Figure 11-4 on page 65 shows a simplified schematic of the logic affected by the
COM0x[1:0] bit setting. The I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of
the general I/O Port Control Registers (DDR and PORT) that are affected by the COM0x[1:0] bits are shown. When
referring to the OC0x state, the reference is for the internal OC0x Register, not the OC0x pin. If a system reset
occur, the OC0x Register is reset to “0”.
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Figure 11-4. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCn
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform Generator if either
of the COM0x[1:0] bits are set. However, the OC0x pin direction (input or output) is still controlled by the Data
Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC0x pin (DDR_OC0x) must be
set as output before the OC0x value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0x state before the output is enabled.
Note that some COM0x[1:0] bit settings are reserved for certain modes of operation, see “Register Description” on
page 71
11.6.1
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0x[1:0] bits differently in Normal, CTC, and PWM modes. For all modes,
setting the COM0x[1:0] = 0 tells the Waveform Generator that no action on the OC0x Register is to be performed
on the next Compare Match. For compare output actions in the non-PWM modes refer to Table 11-2 on page 71.
For fast PWM mode, refer to Table 11-3 on page 72, and for phase correct PWM refer to Table 11-4 on page 72.
A change of the COM0x[1:0] bits state will have effect at the first Compare Match after the bits are written. For nonPWM modes, the action can be forced to have immediate effect by using the Force Output Compare bits. See
“TCCR0B – Timer/Counter Control Register B” on page 74.
11.7
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the
combination of the Waveform Generation mode (WGM0[2:0]) and Compare Output mode (COM0x[1:0]) bits. The
Compare Output mode bits do not affect the counting sequence, while the Waveform Generation mode bits do.
The COM0x[1:0] bits control whether the PWM output generated should be inverted or not (inverted or noninverted PWM). For non-PWM modes the COM0x[1:0] bits control whether the output should be set, cleared, or
toggled at a Compare Match (See “Modes of Operation” on page 65).
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For detailed timing information refer to Figure 11-8 on page 70, Figure 11-9 on page 70, Figure 11-10 on page 70
and Figure 11-11 on page 71 in “Timer/Counter Timing Diagrams” on page 69.
11.7.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM0[2:0] = 0). In this mode the counting direction is always
up (incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8bit value (TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow
Flag (TOV0) will be set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case
behaves like a ninth bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV0 Flag, the timer resolution can be increased by software. There are no special
cases to consider in the Normal mode, a new counter value can be written anytime.
The Output Compare Unit can be used to generate interrupts at some given time. Using the Output Compare to
generate waveforms in Normal mode is not recommended, since this will occupy too much of the CPU time.
11.7.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM0[2:0] = 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 11-5 on page 66. The counter value (TCNT0) increases
until a Compare Match occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.
Figure 11-5. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCnA
(Toggle)
Period
(COMnA[1:0] = 1)
1
2
3
4
An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A Flag. If the
interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP
to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with
care since the CTC mode does not have the double buffering feature. If the new value written to OCR0A is lower
than the current value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical level on each
Compare Match by setting the Compare Output mode bits to toggle mode (COM0A[1:0] = 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 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 + OCRnA 
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The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the counter counts
from MAX to 0x00.
11.7.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM0[2:0] = 3 or 7) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter
counts from BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM0[2:0] = 3, and
OCR0A when WGM0[2:0] = 7. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared on
the Compare Match between TCNT0 and OCR0x, and set at BOTTOM. In inverting Compare Output mode, the
output is set on Compare Match and cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the phase correct PWM mode that use dual-slope
operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors), and therefore
reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then
cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 11-6 on
page 67. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the single-slope operation.
The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0
slopes represent Compare Matches between OCR0x and TCNT0.
Figure 11-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx[1:0] = 2)
OCnx
(COMnx[1:0] = 3)
Period
1
2
3
4
5
6
7
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the
interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the
COM0x[1:0] bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting
the COM0x[1:0] to three: Setting the COM0A[1:0] bits to one allowes the OC0A pin to toggle on Compare Matches
if the WGM02 bit is set. This option is not available for the OC0B pin (See Table 11-3 on page 72). The actual
OC0x value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the OC0x Register at the Compare Match between OCR0x and TCNT0,
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and clearing (or setting) the OC0x Register at the timer clock cycle the counter is cleared (changes from TOP to
BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ---------------------------------N   TOP + 1 
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0x Register represents special cases when generating a PWM waveform output in
the fast PWM mode. If OCR0x is set equal to BOTTOM, the output will be a narrow spike for each TOP+1 timer
clock cycle. Setting the OCR0x equal to TOP will result in a constantly high or low output (depending on the polarity
of the output set by the COM0x[1:0] 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 (COM0A[1:0] = 1). The waveform generated will have a maximum frequency of fclk_I/O/2 when OCR0A is set to zero. This feature is similar to the OC0A toggle in CTC mode, except the
double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
11.7.4
Phase Correct PWM Mode
The phase correct PWM mode (WGM0[2:0] = 1 or 5) provides a high resolution phase correct PWM waveform generation option. The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly
from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM0[2:0] = 1, and
OCR0A when WGM0[2:0] = 5. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared on
the Compare Match between TCNT0 and OCR0x while upcounting, and set on the Compare Match while 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.
Figure 11-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx[1:0] = 2)
OCxn
(COMnx[1:0] = 3)
Period
1
2
3
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In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter
reaches TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock cycle. The
timing diagram for the phase correct PWM mode is shown on Figure 11-7. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches
between OCR0x and TCNT0.
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The Interrupt Flag can
be used to generate an interrupt each time the counter reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting
the COM0x[1:0] bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting
the COM0x[1:0] to three: Setting the COM0A0 bits to one allows the OC0A pin to toggle on Compare Matches if
the WGM02 bit is set. This option is not available for the OC0B pin (See Table 11-4 on page 72). The actual OC0x
value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is
generated by clearing (or setting) the OC0x Register at the Compare Match between OCR0x and TCNT0 when the
counter increments, and setting (or clearing) the OC0x Register at Compare Match between OCR0x and TCNT0
when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = ------------------------------2  N  TOP
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0x Register represent special cases when generating a PWM waveform output in
the phase correct PWM mode. If the OCR0x 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.
At the very start of period 2 in Figure 11-7 on page 68 OCnx has a transition from high to low even though there is
no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases
that give a transition without Compare Match.
• OCR0x changes its value from TOP, like in Figure 11-7 on page 68. When the OCR0x value is TOPthe OCnx
pin value is the same as the result of a down-counting Compare Match. To ensure symmetry around BOTTOM
the OCnx value at TOP must correspond to the result of an up-counting Compare Match.
• The timer starts counting from a value higher than the one in OCR0x, and for that reason misses the Compare
Match and hence the OCnx change that would have happened on the way up.
11.8
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a clock enable signal
in the following figures. The figures include information on when Interrupt Flags are set. Figure 11-8 on page 70
contains timing data for basic Timer/Counter operation. The figure shows the count sequence close to the MAX
value in all modes other than phase correct PWM mode.
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Figure 11-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 11-9 on page 70 shows the same timing data, but with the prescaler enabled.
Figure 11-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 11-10 on page 70 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC mode and
PWM mode, where OCR0A is TOP.
Figure 11-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 11-11 on page 71 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast PWM
mode where OCR0A is TOP.
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Figure 11-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP
OCRnx
OCFnx
11.9
11.9.1
Register Description
TCCR0A – Timer/Counter Control Register A
Bit
7
6
5
4
3
2
1
0
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x19
TCCR0A
• Bits 7:6 – COM0A[1:0]: Compare Match Output A Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A[1:0] bits are set, the
OC0A output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data
Direction Register (DDR) bit corresponding to the OC0A pin must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A[1:0] bits depends on the WGM0[2:0] bit setting.
Table 11-2 shows the COM0A[1:0] bit functionality when the WGM0[2:0] bits are set to a normal or CTC mode
(non-PWM).
Table 11-2.
Compare Output Mode, non-PWM Mode
COM0A1
COM0A0
Description
0
0
Normal port operation, OC0A disconnected.
0
1
Toggle OC0A on Compare Match
1
0
Clear OC0A on Compare Match
1
1
Set OC0A on Compare Match
Table 11-3 shows COM0A[1:0] bit functionality when WGM0[1:0] bits are set to fast PWM mode.
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Table 11-3.
Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected
WGM02 = 1: Toggle OC0A on Compare Match
1
0
Clear OC0A on Compare Match
Set OC0A at BOTTOM (non-inverting mode)
1
1
Set OC0A on Compare Match
Clear OC0A at BOTTOM (inverting mode)
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored,
but the set or clear is done at BOTTOM. See “Fast PWM Mode” on page 67 for more details.
Table 11-4 shows COM0A[1:0] bit functionality when WGM0[2:0] bits are set to phase correct PWM mode.
Table 11-4.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.
1
1
Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.
Note:
Description
1. When OCR0A equals TOP and COM0A1 is set, the Compare Match is ignored, but the set or clear is done at TOP.
See “Phase Correct PWM Mode” on page 68 for more details.
• Bits 5:4 – COM0B[1:0]: Compare Match Output B Mode
These bits control the Output Compare pin (OC0B) behavior. If one or both of COM0B[1:0] bits are set, the OC0B
output overrides the normal port functionality of the I/O pin it is connected to. The Data Direction Register (DDR) bit
corresponding to the OC0B pin must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of COM0B[1:0] bits depend on WGM0[2:0] bit setting. Table 11-5
shows COM0B[1:0] bit functionality when WGM0[2:0] bits are set to normal or CTC mode (non-PWM).
Table 11-5.
Compare Output Mode, non-PWM Mode
COM0B1
COM0B0
Description
0
0
Normal port operation, OC0B disconnected.
0
1
Toggle OC0B on Compare Match
1
0
Clear OC0B on Compare Match
1
1
Set OC0B on Compare Match
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Table 11-6 shows COM0B[1:0] bit functionality when WGM0[2:0] bits are set to fast PWM mode.
Table 11-6.
Compare Output Mode, Fast PWM Mode(1)
COM0B1
COM0B0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match, set OC0B at BOTTOM
(non-inverting mode)
1
1
Set OC0B on Compare Match, clear OC0B at BOTTOM
(inverting mode)
Note:
Description
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored,
but the set or clear is done at BOTTOM. See “Fast PWM Mode” on page 67 for more details.
Table 11-7 shows the COM0B[1:0] bit functionality when the WGM0[2:0] bits are set to phase correct PWM mode.
Table 11-7.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1
COM0B0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.
1
1
Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.
Note:
Description
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored,
but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page 68 for more details.
• Bits 3:2 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 1:0 – WGM0[1:0]: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B Register, these bits control the counting sequence of the
counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see
Table 11-8. Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), Clear Timer on
Compare Match (CTC) mode, and two types of Pulse Width Modulation (PWM) modes (see “Modes of Operation”
on page 65).
Table 11-8.
Waveform Generation Mode Bit Description
Timer/Counter
Mode of Operation
TOP
Update of
OCRx at
TOV Flag
Set on(1)
0
Normal
0xFF
Immediate
MAX
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
BOTTOM
MAX
4
1
0
0
Reserved
–
–
–
Mode
WGM02
WGM01
WGM00
0
0
0
1
0
2
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Table 11-8.
Timer/Counter
Mode of Operation
TOP
Update of
OCRx at
TOV Flag
Set on(1)
OCRA
TOP
BOTTOM
Reserved
–
–
–
Fast PWM
OCRA
BOTTOM
TOP
Mode
WGM02
WGM01
WGM00
5
1
0
1
PWM, Phase
Correct
6
1
1
0
7
1
1
1
Note:
11.9.2
Waveform Generation Mode Bit Description (Continued)
1. MAX
= 0xFF
BOTTOM = 0x00
TCCR0B – Timer/Counter Control Register B
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
TSM
PSR
WGM02
CS02
CS01
CS00
Read/Write
W
W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x18
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 COM0A[1:0] bits setting. Note that
the FOC0A bit is implemented as a strobe. Therefore it is the value present in the COM0A[1:0] 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 always reads as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when
operating in PWM mode. When writing a logical one to the FOC0B bit, an immediate Compare Match is forced on
the Waveform Generation unit. The OC0B output is changed according to its COM0B[1:0] bits setting. Note that
the FOC0B bit is implemented as a strobe. Therefore it is the value present in the COM0B[1:0] bits that determines
the effect of the forced compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0B as TOP.
The FOC0B bit always reads as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “TCCR0A – Timer/Counter Control Register A” on page 71.
• Bits 2:0 – CS0[2:0]: Clock Select
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The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 11-9.
Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
No clock source (Timer/Counter stopped)
0
0
1
clkI/O/(No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on T0 pin. Clock on falling edge.
1
1
1
External clock source on T0 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the
pin is configured as an output. This feature allows software control of the counting.
11.9.3
TCNT0 – Timer/Counter Register
Bit
7
6
5
4
0x17
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit
counter. Writing to the TCNT0 Register blocks (removes) the Compare Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running, introduces a risk of missing a Compare Match between
TCNT0 and the OCR0x Registers.
11.9.4
OCR0A – Output Compare Register A
Bit
7
6
5
4
0x16
3
2
1
0
OCR0A[7:0]
OCR0A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared with the counter value
(TCNT0). A match can be used to generate an Output Compare interrupt, or to generate a waveform output on the
OC0A pin.
11.9.5
OCR0B – Output Compare Register B
Bit
7
6
5
0x15
4
3
2
1
0
OCR0B[7:0]
OCR0B
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register B contains an 8-bit value that is continuously compared with the counter value
(TCNT0). A match can be used to generate an Output Compare interrupt, or to generate a waveform output on the
OC0B pin.
11.9.6
TIMSK – Timer/Counter Interrupt Mask Register
Bit
0x26
7
6
5
4
3
2
1
0
ICIE1
–
OCIE1B
OCIE1A
TOIE1
OCIE0B
OCIE0A
TOIE0
TIMSK
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Read/Write
R/W
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter Compare
Match B interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter occurs,
i.e., when the OCF0B bit is set in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Compare
Match A interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter0
occurs, i.e., when the OCF0A bit is set in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an overflow in Timer/Counter0 occurs, i.e., when the
TOV0 bit is set in the Timer/Counter Interrupt Flag Register – TIFR.
11.9.7
TIFR – Timer/Counter Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x25
ICF1
–
OCF1B
OCF1A
TOV1
OCF0B
OCF0A
TOV0
Read/Write
R/W
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR
• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 2 – OCF0B: Output Compare Flag 0 B
The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in OCR0B – Output
Compare Register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF0B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0B (Timer/Counter
Compare B Match Interrupt Enable), and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed.
• Bit 1 – OCF0A: Output Compare Flag 0 A
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling
vector. Alternatively, OCF0A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0A
(Timer/Counter0 Compare Match Interrupt Enable), and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set, the Timer/Counter0 Overflow
interrupt is executed.
The setting of this flag is dependent of the WGM0[2:0] bit setting. See Table 11-8 on page 73 and “Waveform Generation Mode Bit Description” on page 73.
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12. Timer/Counter1
12.1
Features
•
•
•
•
•
12.2
Clear Timer on Compare Match (Auto Reload)
One Input Capture unit
Four Independent Interrupt Sources (TOV1, OCF1A, OCF1B, ICF1)
8-bit Mode with Two Independent Output Compare Units
16-bit Mode with One Independent Output Compare Unit
Overview
Timer/Counter1 is a general purpose 8/16-bit Timer/Counter module, with two/one Output Compare units and Input
Capture feature.
The general operation of Timer/Counter1 is described in 8/16-bit mode. A simplified block diagram of the 8/16-bit
Timer/Counter is shown in Figure 12-1. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in
bold. For actual placement of I/O pins, refer to “Pin Description” on page 3. Device-specific I/O Register and bit
locations are listed in the “Register Description” on page 88.
Figure 12-1. 8/16-bit Timer/Counter Block Diagram
TOVn (Int. Req.)
Count
Clear
Clock Select
Control Logic
Direction
clk Tn
Edge
Detector
Tn
( From Prescaler )
TOP
Timer/Counter
TCNTnH
=
TCNTnL
Fixed TOP value
=
OCnA (Int. Req.)
=
DATA BUS
OCnB (Int. Req.)
ICFn (Int. Req.)
OCRnB
TCCRnA
12.2.1
OCRnA
Edge
Detector
Noise
Canceler
ICPn
Registers
The Timer/Counter1 Low Byte Register (TCNT1L) and Output Compare Registers (OCR1A and OCR1B) are 8-bit
registers. Interrupt request (abbreviated Int.Req. in Figure 12-1) signals are all visible in the Timer Interrupt Flag
Register (TIFR). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and
TIMSK are not shown in the figure.
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In 16-bit mode one more 8-bit register is available, the Timer/Counter1 High Byte Register (TCNT1H). Also, in 16bit mode, there is only one output compare unit as the two Output Compare Registers, OCR1A and OCR1B, are
combined to one, 16-bit Output Compare Register, where OCR1A contains the low byte and OCR1B contains the
high byte of the word. When accessing 16-bit registers, special procedures described in section “Accessing Registers in 16-bit Mode” on page 84 must be followed.
12.2.2
Definitions
Many register and bit references in this section are written in general form. A lower case “n” replaces the
Timer/Counter number, in this case 1. A lower case “x” replaces the Output Compare Unit, in this case Compare
Unit A or Compare Unit B. However, when using the register or bit defines in a program, the precise form must be
used, i.e. TCNT1L for accessing Timer/Counter1 counter value, and so on.
The definitions in Table 11-1 are also used extensively throughout the document.
Table 12-1.
12.3
Definitions
Constant
Description
BOTTOM
The counter reaches BOTTOM when it becomes 0x00
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255)
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the
value stored in the OCR1A Register. The assignment depends on the mode of operation
Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the
Clock Select logic which is controlled by the Clock Select (CS1[2:0]) bits located in the Timer/Counter Control Register (TCCR1A). For details on clock sources and prescaler, see “Timer/Counter Prescaler” on page 92.
12.4
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 12-2 shows a
block diagram of the counter and its surroundings.
Table 12-2.
Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
TCNTn
count
Control Logic
Edge
Detector
clkTn
Tn
( From Prescaler )
top
Signal description (internal signals):
count
clkTn
top
Increment or decrement TCNT1 by 1.
Timer/Counter clock, referred to as clkT1 in the following.
Signalize that TCNT1 has reached maximum value.
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The counter is incremented at each timer clock (clkT1) until it passes its TOP value and then restarts from BOTTOM. The counting sequence is determined by the setting of the CTC1 bit located in the Timer/Counter Control
Register (TCCR1A). For more details about counting sequences, see “Modes of Operation” on page 81. clkT1 can
be generated from an external or internal clock source, selected by the Clock Select bits (CS1[2:0]). When no clock
source is selected (CS1[2:0] = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU,
regardless of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count
operations. The Timer/Counter Overflow Flag (TOV1) is set when the counter reaches the maximum value and it
can be used for generating a CPU interrupt.
12.5
Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events and give them a timestamp 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 12-2. The elements of the block diagram
that are not directly a part of the Input Capture unit are gray shaded.
Figure 12-2. Input Capture Unit Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
OCR0B (8-bit)
WRITE
ICP0
OCR0A (8-bit)
TCNT0H (8-bit)
ICR0 (16-bit Register)
TCNT0L (8-bit)
TCNT0 (16-bit Counter)
ICNC0
ICES0
Noise
Canceler
Edge
Detector
ICF0 (Int.Req.)
The Output Compare Register OCR1A is a dual-purpose register that is also used as an 8-bit Input Capture Register ICR1. In 16-bit Input Capture mode the Output Compare Register OCR1B serves as the high byte of the Input
Capture Register ICR1. In 8-bit Input Capture mode the Output Compare Register OCR1B is free to be used as a
normal Output Compare Register, but in 16-bit Input Capture mode the Output Compare Unit cannot be used as
there are no free Output Compare Register(s). Even though the Input Capture register is called ICR1 in this section, it is refering to the Output Compare Register(s).
When a change of the logic level (an event) occurs on the Input Capture pin (ICP1), and this change confirms to
the setting of the edge detector, a capture will be triggered. When a capture is triggered, the value of the counter
(TCNT1) is written to the Input Capture Register (ICR1). The Input Capture Flag (ICF1) is set at the same system
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clock as the TCNT1 value is copied into Input Capture 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.
12.5.1
Input Capture Trigger Source
The trigger source for the Input Capture unit is the Input Capture pin (ICP1).
The Input Capture pin (ICP1) input is sampled using the same technique as for the T1 pin (Figure 12-4 on page
88). 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. An Input Capture can also be triggered by software by controlling the port of the ICP1 pin.
12.5.2
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 A (TCCR1A). 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.
12.5.3
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity for handling the
incoming events. The time between two events is critical. If the processor has not read the captured value in the
ICR1 Register before the next event occurs, the ICR1 will be overwritten with a new value. In this case the result of
the capture will be incorrect.
When using the Input Capture interrupt, the ICR1 Register should be read as early in the interrupt handler routine
as possible. The maximum interrupt response time is dependent on the maximum number of clock cycles it takes
to handle any of the other interrupt requests.
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 trigger edge change is not required (if an interrupt handler is used).
12.6
Output Compare Unit
The comparator continuously compares Timer/Counter (TCNT1) with the Output Compare Registers (OCR1A and
OCR1B), and whenever the Timer/Counter equals to the Output Compare Regisers, the comparator signals a
match. A match will set the Output Compare Flag at the next timer clock cycle. In 8-bit mode the match can set
either the Output Compare Flag OCF1A or OCF1B, but in 16-bit mode the match can set only the Output Compare
Flag OCF1A as there is only one Output Compare Unit. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when the
interrupt is executed. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location.
Figure 12-3 shows a block diagram of the Output Compare unit.
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Figure 12-3. Output Compare Unit, Block Diagram
DATA BUS
TCNTn
OCRnx
= (8/16-bit Comparator )
OCFnx (Int.Req.)
12.6.1
Compare Match Blocking by TCNT1 Write
All CPU write operations to the TCNT1H/L Register will block any Compare Match that occur 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.
12.6.2
Using the Output Compare Unit
Since writing TCNT1H/L will block all Compare Matches for one timer clock cycle, there are risks involved when
changing TCNT1H/L when using the Output Compare Unit, independently of whether the Timer/Counter is running
or not. If the value written to TCNT1H/L equals the OCR1A/B value, the Compare Match will be missed.
12.7
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the
Timer/Counter Width (TCW1), Input Capture Enable (ICEN1) and CTC Mode (CTC1) bits. See “TCCR1A –
Timer/Counter1 Control Register A” on page 88.
Table 12-3 summarises the different modes of operation.
Table 12-3.
Modes of operation
Mode
ICEN1
TCW1
CTC1
Mode of Operation
TOP
Update of OCRx at
TOV Flag Set on
0
0
0
0
Normal, 8-bit Mode
0xFF
Immediate
MAX (0xFF)
1
0
0
1
CTC Mode, 8-bit
OCR0A
Immediate
MAX (0xFF)
2
0
1
X
Normal, 16-bit Mode
0xFFFF
Immediate
MAX (0xFFFF)
3
1
0
X
Input Capture Mode, 8-bit
0xFF
Immediate
MAX (0xFF)
4
1
1
X
Input Capture Mode, 16-bit
0xFFFF
Immediate
MAX (0xFFFF)
12.7.1
Normal, 8-bit Mode
In Normal 8-bit mode (see Table 12-3), the counter (TCNT1L) is incrementing until it overruns when it passes its
maximum 8-bit value (MAX = 0xFF) and then restarts from the bottom (0x00). The Overflow Flag (TOV1) is set in
the same timer clock cycle as when TCNT1L becomes zero. The TOV1 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 TOV1 Flag, the timer resolution can be increased by software. There are no special cases to consider in the
Normal 8-bit mode, a new counter value can be written anytime. The Output Compare Unit can be used to generate interrupts at some given time.
12.7.2
Clear Timer on Compare Match (CTC) 8-bit Mode
In Clear Timer on Compare or CTC mode, see Table 12-3 on page 81, the OCR1A Register is used to manipulate
the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT1) matches the
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OCR1A. The OCR1A defines the top value for the counter, hence also its resolution. This mode allows greater control of the Compare Match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 12-4. The counter value (TCNT1) increases until a Compare Match occurs between TCNT1 and OCR1A, and then counter (TCNT1) is cleared.
Figure 12-4. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCnA
(Toggle)
Period
(COMnA[1:0] = 1)
1
2
3
4
An interrupt can be generated each time the counter value reaches the TOP value by using the OCF1A Flag. If the
interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP
to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with
care since the CTC mode does not have the double buffering feature. If the new value written to OCR1A 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 (0xFF) and wrap around starting at 0x00 before the Compare Match can occur. 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
0x00.
12.7.3
Normal, 16-bit Mode
In 16-bit mode, see Table 12-3 on page 81, the counter (TCNT1H/L) is a incrementing until it overruns when it
passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the bottom (0x0000). The Overflow Flag
(TOV1) will be set in the same timer clock cycle as the TCNT1H/L 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 Output Compare Unit can
be used to generate interrupts at some given time.
12.7.4
8-bit Input Capture Mode
The Timer/Counter1 can also be used in an 8-bit Input Capture mode, see Table 12-3 on page 81 for bit settings.
For full description, see the section “Input Capture Unit” on page 79.
12.7.5
16-bit Input Capture Mode
The Timer/Counter1 can also be used in a 16-bit Input Capture mode, see Table 12-3 on page 81 for bit settings.
For full description, see the section “Input Capture Unit” on page 79.
12.8
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. Figure 12-5 contains timing
data for basic Timer/Counter operation. The figure shows the count sequence close to the MAX value.
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Figure 12-5. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
BOTTOM
BOTTOM + 1
TOVn
Figure 12-6 shows the same timing data, but with the prescaler enabled.
Figure 12-6. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
TOVn
Figure 12-7 on page 83 shows the setting of OCF1A and OCF1B in Normal mode.
Figure 12-7. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 12-8 shows the setting of OCF1A and the clearing of TCNT1 in CTC mode.
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Figure 12-8. Timer/Counter Timing Diagram, CTC mode, with Prescaler (fclk_I/O/8)
clkPCK
clkTn
(clkPCK /8)
TCNTn
(CTC)
TOP - 1
OCRnx
TOP
BOTTOM
BOTTOM + 1
TOP
OCFnx
12.9
Accessing Registers in 16-bit Mode
In 16-bit mode (the TCW1 bit is set to one) the TCNT1H/L and OCR1A/B or TCNT1L/H and OCR1B/A 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. The 16-bit Timer/Counter 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. 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.
There is one exception in the temporary register usage. In the Output Compare mode the 16-bit Output Compare
Register OCR1A/B is read without the temporary register, because the Output Compare Register contains a fixed
value that is only changed by CPU access. However, in 16-bit Input Capture mode the ICR1 register formed by the
OCR1A and OCR1B registers must be accessed with 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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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 registers.
Assembly Code Example
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
C Code Example
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1H = 0x01;
TCNT1L = 0xff;
/* Read TCNT1 into i */
i = TCNT1L;
i |= ((unsigned int)TCNT1H << 8);
...
Note:
See “Code Examples” on page 5.
The assembly code example returns the TCNT1H/L 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
OCR1 register can be done by using the same principle.
Assembly Code Example
TIM1_ReadTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
unsigned int TIM1_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT1 into i */
i = TCNT1L;
i |= ((unsigned int)TCNT1H << 8);
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
See “Code Examples” on page 5.
The assembly code example returns the TCNT1H/L value in the r17:r16 register pair.
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The following code examples show how to do an atomic write of the TCNT1H/L register contents. Writing any of
the OCR1A/B registers can be done by using the same principle.
Assembly Code Example
TIM1_WriteTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TCNT1H,r17
out TCNT1L,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
void TIM1_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TCNT1H = (i >> 8);
TCNT1L = (unsigned char)i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
See “Code Examples” on page 5.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1H/L.
12.9.1
Reusing the temporary high byte register
If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte
only needs to be written once. However, note that the same rule of atomic operation described previously also
applies in this case.
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12.10 Register Description
12.10.1
TCCR1A – Timer/Counter1 Control Register A
Bit
7
6
5
4
3
2
1
0
TCW1
ICEN1
ICNC1
ICES1
CTC1
CS12
CS11
CS10
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x24
TCCR1A
• Bit 7 – TCW1: Timer/Counter1 Width
When this bit is written to one, 16-bit mode is selected as described Figure 12-5 on page 83. Timer/Counter1 width
is set to 16-bits and the Output Compare Registers OCR1A and OCR1B are combined to form one 16-bit Output
Compare Register. Because the 16-bit registers TCNT1H/L and OCR1B/A are accessed by the AVR CPU via the
8-bit data bus, special procedures must be followed. These procedures are described in section “Accessing Registers in 16-bit Mode” on page 84.
• Bit 6 – ICEN1: Input Capture Mode Enable
When this bit is written to one, the Input Capture Mode is enabled.
• Bit 5 – ICNC1: Input Capture Noise Canceler
Setting this bit 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 System Clock cycles when the noise
canceler is enabled.
• Bit 4 – 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. 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.
• Bit 3 – CTC1: Waveform Generation Mode
This bit controls the counting sequence of the counter, the source for maximum (TOP) counter value, see Figure
12-5 on page 83. Modes of operation supported by the Timer/Counter unit are: Normal mode (counter) and Clear
Timer on Compare Match (CTC) mode (see “Modes of Operation” on page 81).
• Bits 2:0 – CS1[2:0]: Clock Select1, Bits 2, 1, and 0
The Clock Select1 bits 2, 1, and 0 define the prescaling source of Timer1.
Table 12-4.
Clock Select Bit Description
CS12
CS11
CS10
Description
0
0
0
No clock source (Timer/Counter stopped)
0
0
1
clkI/O/(No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
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Table 12-4.
Clock Select Bit Description (Continued)
CS12
CS11
CS10
Description
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on T1 pin. Clock on falling edge.
1
1
1
External clock source on T1 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the counter even if the
pin is configured as an output. This feature allows software control of the counting.
12.10.2
TCNT1L – Timer/Counter1 Register Low Byte
Bit
7
6
5
0x23
4
3
2
1
0
TCNT1L[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 Timer/Counter1 Register Low Byte, TCNT1L, gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT1L Register blocks (disables) the Compare Match on the following timer clock. Modifying the counter (TCNT1L) while the counter is running, introduces a risk of missing a
Compare Match between TCNT1L and the OCR1x Registers. In 16-bit mode the TCNT1L register contains the
lower part of the 16-bit Timer/Counter1 Register.
12.10.3
TCNT1H – Timer/Counter1 Register High Byte
Bit
7
6
5
0x27
4
3
2
1
0
TCNT1H[7:0]
TCNT1H
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
When 16-bit mode is selected (the TCW1 bit is set to one) the Timer/Counter Register TCNT1H combined to the
Timer/Counter Register TCNT1L gives direct access, both for read and 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 Registers in 16-bit Mode” on page 84
12.10.4
OCR1A – Timer/Counter1 Output Compare Register A
Bit
7
6
5
0x22
4
3
2
1
0
OCR1A[7:0]
OCR1A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared with the counter value
(TCNT1L). A match can be used to generate an Output Compare interrupt.
In 16-bit mode the OCR1A register contains the low byte of the 16-bit Output Compare Register. To ensure that
both the high and the 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 Registers in 16-bit Mode” on page 84.
12.10.5
OCR1B – Timer/Counter1 Output Compare Register B
Bit
7
6
5
0x21
4
3
2
1
0
OCR1B[7:0]
OCR1B
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
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The Output Compare Register B contains an 8-bit value that is continuously compared with the counter value
(TCNT1L in 8-bit mode and TCNTH in 16-bit mode). A match can be used to generate an Output Compare
interrupt.
In 16-bit mode the OCR1B register contains the high byte of the 16-bit Output Compare Register. To ensure that
both the high and the 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 Registers in 16-bit Mode” on page 84.
12.10.6
TIMSK – Timer/Counter1 Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0
0x26
ICIE1
–
OCIE1B
OCIE1A
TOIE1
OCIE0B
OCIE0A
TOIE0
Read/Write
R/W
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK
• Bit 7 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the
Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt Vector (See “Interrupts” on page
35.) is executed when the ICF1 flag, located in TIFR, is set.
• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 5 – OCIE1B: Timer/Counter1 Output Compare Match B Interrupt Enable
When the OCIE1B bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter Compare
Match B interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter occurs,
i.e., when the OCF1B bit is set in the Timer/Counter Interrupt Flag Register – TIFR1.
• Bit 4 – OCIE1A: Timer/Counter1 Output Compare Match A Interrupt Enable
When the OCIE1A bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter1 Compare
Match A interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter1
occurs, i.e., when the OCF1A bit is set in the Timer/Counter 1 Interrupt Flag Register – TIFR1.
• Bit 3 – TOIE1: Timer/Counter1 Overflow Interrupt Enable
When the TOIE1 bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter1 Overflow interrupt is enabled. The corresponding interrupt is executed if an overflow in Timer/Counter1 occurs, i.e., when the
TOV1 bit is set in the Timer/Counter 1 Interrupt Flag Register – TIFR1.
12.10.7
TIFR – Timer/Counter1 Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x25
ICF1
–
OCF1B
OCF1A
TOV1
OCF0B
OCF0A
TOV0
Read/Write
R/W
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR
• Bit 7 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register (ICR1) is set 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.
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• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 5 – OCF1B: Output Compare Flag 1 B
The OCF1B bit is set when a Compare Match occurs between the Timer/Counter and the data in OCR1B – Output
Compare Register1 B. OCF1B is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF1B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE1B (Timer/Counter
Compare B Match Interrupt Enable), and OCF1B are set, the Timer/Counter Compare Match Interrupt is executed.
The OCF1B is not set in 16-bit Output Compare mode when the Output Compare Register OCR1B is used as the
high byte of the 16-bit Output Compare Register or in 16-bit Input Capture mode when the Output Compare Register OCR1B is used as the high byte of the Input Capture Register.
• Bit 4 – OCF1A: Output Compare Flag 1 A
The OCF1A bit is set when a Compare Match occurs between the Timer/Counter1 and the data in OCR1A – Output Compare Register1. OCF1A is cleared by hardware when executing the corresponding interrupt handling
vector. Alternatively, OCF1A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE1A
(Timer/Counter1 Compare Match Interrupt Enable), and OCF1A are set, the Timer/Counter1 Compare Match Interrupt is executed.
The OCF1A is also set in 16-bit mode when a Compare Match occurs between the Timer/Counter and 16-bit data
in OCR1B/A. The OCF1A is not set in Input Capture mode when the Output Compare Register OCR1A is used as
an Input Capture Register.
• Bit 3 – TOV1: Timer/Counter1 Overflow Flag
The bit TOV1 is set when an overflow occurs in Timer/Counter1. TOV1 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV1 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE1 (Timer/Counter1 Overflow Interrupt Enable), and TOV1 are set, the Timer/Counter1 Overflow
interrupt is executed.
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13. Timer/Counter Prescaler
Timer/Counter0 and Timer/Counter1 share the same prescaler module, but the Timer/Counters can have different
prescaler settings. The description below applies to both Timer/Counters. Tn is used as a general name, n = 0, 1.
The Timer/Counter can be clocked directly by the system clock (by setting the CSn[2:0] = 1). This provides the
fastest operation, with a maximum Timer/Counter clock frequency equal to system clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a clock source. The prescaled clock has a frequency of
either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024.
13.1
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the Timer/CounterCounter,
and it is shared by the Timer/Counter Tn. Since the prescaler is not affected by the Timer/Counter’s clock select,
the state of the prescaler will have implications for situations where a prescaled clock is used. One example of
prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (CSn[2:0] = 2, 3, 4, or 5). The
number of system clock cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program execution.
13.2
External Clock Source
An external clock source applied to the Tn pin can be used as Timer/Counter clock (clkTn). The Tn pin is sampled
once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed
through the edge detector. Figure 13-1 shows a functional equivalent block diagram of the Tn synchronization and
edge detector logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch is
transparent in the high period of the internal system clock.
The edge detector generates one clkT0 pulse for each positive (CSn[2:0] = 7) or negative (CSn[2:0] = 6) edge it
detects.
Figure 13-1. T0 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an edge has
been applied to the Tn pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn has been stable for at least one system clock
cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sampling. The external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2)
given a 50/50% duty cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it
can detect is half the sampling 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.
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Figure 13-2. Prescaler for Timer/Counter0
clk I/O
Clear
PSR
T0
Synchronization
clkT0
Note:
13.3
13.3.1
1. The synchronization logic on the input pins (T0) is shown in Figure 13-1 on page 92.
Register Description
TCCR0B – Timer/Counter Control Register B
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
TSM
PSR
WGM02
CS02
CS01
CS00
Read/Write
W
W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x18
TCCR0B
• Bit 5 – 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 PSR bit is kept, hence keeping the Prescaler Reset signal asserted. This ensures that the Timer/Counter
is halted and can be configured without the risk of advancing during configuration. When the TSM bit is written to
zero, the PSR bit is cleared by hardware, and the Timer/Counter start counting.
• Bit 4 – PSR: Prescaler Reset Timer/Counter
When this bit is one, the Timer/Counter prescaler will be Reset. This bit is normally cleared immediately by hardware, except if the TSM bit is set.
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14. Analog Comparator
The analog comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin AIN1, the Analog Comparator Output,
ACO, is set. The comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can
select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 14-1.
Figure 14-1. Analog Comparator Block Diagram
BANDGAP
REFERENCE
VCC
ACBG
ACD
ACIE
AIN0
+
_
INTERRUPT
SELECT
ACI
AIN1
ACIS1
ACME
ANALOG
COMPARATOR
IRQ
ACIS0
ACIC
HSEL
To T/C1 Capture
Trigger MUX
HLEV
ADC MULTIPLEXER
OUTPUT (1)
Notes:
ACO
1. See Table 14-1 on page 95.
See Figure 1-1 on page 2 and Table 10-9 on page 54 for Analog Comparator pin placement.
The ADC Power Reduction bit, PRADC, must be disabled in order to use the ADC input multiplexer. This is done
by clearing the PRADC bit in the Power Reduction Register, PRR. See “PRR – Power Reduction Register” on page
27 for more details.
When the supply voltage is below 2.7V, it is recommended to disable the ADC Power Reduction bit, PRADC, in
order to use AIN0, AIN1, or a bandgap reference as an analog comparator input.
14.1
Analog Comparator Multiplexed Input
When the Analog to Digital Converter (ADC) is configurated as single ended input channel, it is possible to select
any of the ADC[7:0] pins to replace the negative input to the Analog Comparator. The ADC multiplexer is used to
select this input. If the Analog Comparator Multiplexer Enable bit (ACME in ADCSRB) is set, MUX bits in ADMUX
select the input pin to replace the negative input to the analog comparator.
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Table 14-1.
14.2
14.2.1
Analog Comparator Multiplexed Input
ACME
MUX[3:0]
Analog Comparator Negative Input
0
XXXX
AIN1
1
0000
ADC0
1
0001
ADC1
1
0010
ADC2
1
0011
ADC3
1
0100
ADC4
1
0101
ADC5
1
0110
ADC6
1
0111
ADC7
1
1000
ADC8
1
1001
ADC9
1
1010
ADC10
1
1011
ADC11
Register Description
ACSRA – Analog Comparator Control and Status Register
Bit
7
6
5
4
3
2
1
0
0x14
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
N/A
0
0
0
0
0
ACSRA
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit can be set at any
time to turn off the Analog Comparator. This will reduce power consumption in Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an
interrupt can occur when the bit is changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed, internal bandgap reference voltage replaces the positive input to the Analog Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog Comparator.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The synchronization
introduces a delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and
ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI
is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by
writing a logic one to the flag.
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• 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 then 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 inter-rupt, the ICIE1 bit in the Timer Interrupt Mask
Register (TIMSK) must be set.
• Bits 1:0 – ACIS[1:0]: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings
are shown in Table 14-2.
Table 14-2.
ACIS1/ACIS0 Settings
ACIS1
ACIS0
Interrupt Mode
0
0
Comparator Interrupt on Output Toggle.
0
1
Reserved
1
0
Comparator Interrupt on Falling Output Edge.
1
1
Comparator Interrupt on Rising Output Edge.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt
Enable bit in the ACSR Register. Otherwise an interrupt can occur when the bits are changed.
14.2.2
ACSRB – Analog Comparator Control and Status Register B
Bit
7
6
5
4
3
2
1
0
HSEL
HLEV
ACLP
–
ACCE
ACME
ACIRS1
ACIRS0
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
0x13
ACSRB
• Bit 7 – HSEL: Hysteresis Select
When this bit is written logic one, the hysteresis of the analog comparator is enabled. The level of hysteresis is
selected by the HLEV bit.
• Bit 6 – HLEV: Hysteresis Level
When enabled via the HSEL bit, the level of hysteresis can be set using the HLEV bit, as shown in Table 14-3.
Table 14-3.
Selecting Level of Analog Comparator Hysteresis
HSEL
HLEV
Hysteresis of Analog Comparator
0
X
Not enabled
0
20 mV
1
50 mV
1
• Bit 5 – ACLP
This bit is reserved for QTouch, always write as zero.
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• Bit 4 – Reserved
This bit is reserved and will always read as zero.
• Bit 3 – ACCE
This bit is reserved for QTouch, always write as zero.
• Bit 2 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer
selects the negative input to the Analog Comparator. When this bit is written logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed description of this bit, see “Analog Comparator Multiplexed
Input” on page 94.
• Bit 1 – ACIRS1
This bit is reserved for QTouch, always write as zero.
• Bit 0 – ACIRS0
This bit is reserved for QTouch, always write as zero.
14.2.3
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x0D
DIDR0
• Bits 2:1 – ADC2D, ADC1D: ADC[2:1] Digital Input Buffer Disable
When this bit is written logic one, the digital input buffer on the AIN[1:0] pin is disabled. The corresponding PIN
Register bit will always read as zero when this bit is set. When used as an analog input but not required as a digital
input the power consumption in the digital input buffer can be reduced by writing this bit to logic one.
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15. Analog to Digital Converter
15.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
15.2
10-bit Resolution
1 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
13 µs Conversion Time
15 kSPS at Maximum Resolution
12 Multiplexed Single Ended Input Channels
Temperature Sensor Input Channel
Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
1.1V ADC Reference Voltage
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
Overview
ATtiny40 features a 10-bit, successive approximation Analog-to-Digital Converter (ADC). The ADC is wired to a
13-channel analog multiplexer, which allows the ADC to measure the voltage at 12 single-ended input pins, or from
one internal, single-ended voltage channel coming from the internal temperature sensor. Voltage inputs are
referred to 0V (GND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a constant
level during conversion. A block diagram of the ADC is shown in Figure 15-1 on page 99.
Internal reference voltage of nominally 1.1V is provided on-chip. Alternatively, VCC can be used as reference voltage for single ended channels.
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Figure 15-1. Analog to Digital Converter Block Schematic
ADCH+ADCL
ADIE
ADEN
ADPS0
ADPS1
ADPS2
ADSC
ADCSRA
ADATE
ADTS[2:0]
ADCSRB
ADLAR
MUX[3:0]
REFS
ADMUX
INTERRUPT FLAGS
8-BIT DATA BUS
ADC IRQ
TRIGGER
SELECT
PRESCALER
ADIF
START
CHANNEL
DECODER
CONVERSION LOGIC
VCC
10-BIT DAC
INTERNAL
REFERENCE
+
SAMPLE & HOLD
COMPARATOR
TEMPERATURE
SENSOR
ADC11
ADC10
ADC9
ADC MUX OUTPUT
ADC8
ADC7
INPUT
MUX
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
AGND
15.3
Operation
In order to be able to use the ADC the Power Reduction bit, PRADC, in the Power Reduction Register must be disabled. This is done by clearing the PRADC bit. See “PRR – Power Reduction Register” on page 27 for more
details.
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage reference and input channel selections will not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is
recommended to switch off the ADC before entering power saving sleep modes.
The ADC converts an analog input voltage to a 10-bit digital value using successive approximation. The minimum
value represents GND and the maximum value represents the reference voltage. The ADC voltage reference is
selected by writing the REFS bit in the ADMUX register. Alternatives are the VCC supply pin and the internal 1.1V
voltage reference.
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The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the ADC input pins can be
selected as single ended inputs to the ADC.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and ADCL. By default,
the result is presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in
ADCSRB.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH, only. 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.
15.4
Starting a Conversion
Make sure the ADC is powered by clearing the ADC Power Reduction bit, PRADC, in the Power Reduction Register, PRR (see “PRR – Power Reduction Register” on page 27).
A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC. This bit stays high as
long as the conversion is in progress and will be cleared by hardware when the conversion is completed. If a different data channel is selected while a conversion is in progress, the ADC will finish the current conversion before
performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is enabled by setting
the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is selected by setting the ADC Trigger
Select bits, ADTS in ADCSRB (see description of the ADTS bits for a list of the trigger sources). When a positive
edge occurs on the selected trigger signal, the ADC prescaler is reset and a conversion is started. This provides a
method of starting conversions at fixed intervals. If the trigger signal still is set when the conversion completes, a
new conversion will not be started. If another positive edge occurs on the trigger signal during conversion, the edge
will be ignored. Note that an Interrupt Flag will be set even if the specific interrupt is disabled or the Global Interrupt
Enable bit in SREG is cleared. A conversion can thus be triggered without causing an interrupt. However, the Interrupt Flag must be cleared in order to trigger a new conversion at the next interrupt event.
Figure 15-2. ADC Auto Trigger Logic
ADTS[2:0]
PRESCALER
START
ADIF
CLKADC
ADATE
SOURCE 1
.
.
.
.
SOURCE n
CONVERSION
LOGIC
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. In
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this mode the ADC will perform successive conversions independently of whether the ADC Interrupt Flag, ADIF is
cleared or not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to one. ADSC can
also be used to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion,
independently of how the conversion was started.
Prescaling and Conversion Timing
By default, the successive approximation circuitry requires an input clock frequency between 50 kHz and 200 kHz
to get maximum resolution. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can
be higher than 200 kHz to get a higher sample rate. It is not recommended to use a higher input clock frequency
than 1 MHz.
Figure 15-3. ADC Prescaler
ADEN
START
Reset
7-BIT ADC PRESCALER
CK/64
CK/128
CK/32
CK/8
CK/16
CK/4
CK
CK/2
15.5
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
The ADC module contains a prescaler, as illustrated in Figure 15-3 on page 101, which generates an acceptable
ADC clock frequency from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit in ADCSRA. The
prescaler keeps running for as long as the ADEN bit is set, and is continuously reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles, as summarised in Table 15-1 on page 104. The first conversion
after the ADC is switched on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog
circuitry, as shown in Figure 15-4 below.
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Figure 15-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
Cycle Number
1
2
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
2
3
ADC Clock
ADEN
ADSC
ADIF
Sign and MSB of Result
ADCH
LSB of Result
ADCL
MUX and REFS
Update
Conversion
Complete
Sample & Hold
MUX and REFS
Update
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC
clock cycles after the start of a first conversion. See Figure 15-5. When a conversion is complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion mode, ADSC is cleared simultaneously. The
software may then set ADSC again, and a new conversion will be initiated on the first rising ADC clock edge.
Figure 15-5. ADC Timing Diagram, Single Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
3
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
MUX and REFS
Update
Conversion
Complete
MUX and REFS
Update
When Auto Triggering is used, the prescaler is reset when the trigger event occurs, as shown in Figure 15-6 below.
This assures a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold takes
place two ADC clock cycles after the rising edge on the trigger source signal. Three additional CPU clock cycles
are used for synchronization logic.
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Figure 15-6. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
1
Cycle Number
2
3
4
5
6
7
8
Next Conversion
10
9
11
12
13
1
2
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Prescaler
Reset
Sample &
Hold
Prescaler
Reset
Conversion
Complete
MUX and REFS
Update
In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC
remains high. See Figure 15-7.
Figure 15-7. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
12
13
Next Conversion
14
1
2
3
4
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Conversion
Complete
Sample & Hold
MUX and REFS
Update
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For a summary of conversion times, see Table 15-1.
Table 15-1.
ADC Conversion Time
Condition
Sample & Hold (Cycles from
Start of Conversion)
First conversion
13.5
25
Normal conversions
1.5
13
2
13.5
2.5
14
Auto Triggered conversions
Free Running conversion
15.6
Conversion Time (Cycles)
Changing Channel or Reference Selection
The MUX and REFS bits in the ADMUX Register are single buffered through a temporary register to which the
CPU has random access. This ensures that the channels and reference selection only takes place at a safe point
during the conversion. The channel and reference selection is continuously updated until a conversion is started.
Once the conversion starts, the channel and reference selection is locked to ensure a sufficient sampling time for
the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in
ADCSRA is set). Note that the conversion starts on the following rising ADC clock edge after ADSC is written. The
user is thus advised not to write new channel or reference selection values to ADMUX until one ADC clock cycle
after ADSC is written.
If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken
when updating the ADMUX Register, in order to control which conversion will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX Register is
changed in this period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX
can be safely updated in the following ways:
• When ADATE or ADEN is cleared.
• During conversion, minimum one ADC clock cycle after the trigger event.
• After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion.
15.6.1
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.
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15.6.2
ADC Voltage Reference
The ADC reference voltage (VREF) indicates the conversion range for the ADC. Single ended channels that exceed
VREF will result in codes close to 0x3FF. VREF can be selected as either VCC, or internal 1.1V reference. The internal
1.1V reference is generated from the internal bandgap reference (VBG) through an internal amplifier.
The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is
advised to discard this result.
15.7
ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode. This reduces noise induced from
the CPU core and other I/O peripherals. The noise canceler can be used with ADC Noise Reduction and Idle
mode. To make use of this feature, the following procedure should be used:
• Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be selected and
the ADC conversion complete interrupt must be enabled.
• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been
halted.
• If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and
execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up the CPU before the ADC
conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt request will
be generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep
command is executed.
Note that the ADC will not automatically be turned off when entering other sleep modes than Idle mode and ADC
Noise Reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid
excessive power consumption.
15.8
Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 15-8. An analog source applied to ADCn
is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as
input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 k or less. If such a source
is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling time will
depend on how long time the source needs to charge the S/H capacitor, which can vary widely. The user is recommended to only use low impedance sources with slowly varying signals, since this minimizes the required charge
transfer to the S/H capacitor.
In order to avoid distortion from unpredictable signal convolution, signal components higher than the Nyquist frequency (fADC/2) should not be present. The user is advised to remove high frequency components with a low-pass
filter before applying the signals as inputs to the ADC.
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Figure 15-8. Analog Input Circuitry
IIH
ADCn
1..100 kohm
CS/H= 14 pF
IIL
VCC/2
Note:
15.9
The capacitor in the figure depicts the total capacitance, including the sample/hold capacitor and any stray or parasitic
capacitance inside the device. The value given is worst case.
Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. When conversion accuracy is critical, the noise level can be reduced by applying the following techniques:
• Keep analog signal paths as short as possible.
• Make sure analog tracks run over the analog ground plane.
• Keep analog tracks well away from high-speed switching digital tracks.
• If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.
• Place bypass capacitors as close to VCC and GND pins as possible.
Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as described in Section 15.7 on page 105. This is especially the case when system clock frequency is above 1 MHz, or when the ADC
is used for reading the internal temperature sensor, as described in Section 15.12 on page 109. A good system
design with properly placed, external bypass capacitors does reduce the need for using ADC Noise Reduction
Mode
15.10 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps (LSBs). The lowest code
is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior, as follows:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 LSB). Ideal
value: 0 LSB.
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Figure 15-9. 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 15-10. 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.
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Figure 15-11. 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 15-12. Differential Non-linearity (DNL)
Output Code
0xFF
1 LSB
DNL
0x00
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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15.11 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC Data Registers
(ADCL, ADCH). The result is, as follows:
V IN  1024
ADC = -------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 15-3 on page
110 and Table 15-4 on page 110). 0x000 represents analog ground, and 0x3FF represents the selected reference
voltage minus one LSB. The result is presented in one-sided form, from 0x3FF to 0x000.
15.12 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a single ended ADC
channel. The temperature sensor is measured via channel ADC12 and is enabled by writing MUX bits in ADMUX
register to “1110”. The internal 1.1V reference must also be selected for the ADC reference source in the temperature sensor measurement. When the temperature sensor is enabled, the ADC converter can be used in single
conversion mode to measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in Table 15-2 The sensitivity is
approximately 1 LSB / C and the accuracy depends on the method of user calibration. Typically, the measurement
accuracy after a single temperature calibration is ±10C, assuming calibration at room temperature. Better
accuracies are achieved by using two temperature points for calibration.
Table 15-2.
Temperature vs. Sensor Output Voltage (Typical Case)
Temperature
ADC
-40C
+25C
+85C
230 LSB
300 LSB
370 LSB
The values described in Table 15-2 are typical values. However, due to process variation the temperature sensor
output voltage varies from one chip to another. To be capable of achieving more accurate results the temperature
measurement can be calibrated in the application software. The sofware calibration can be done using the formula:
T = k * [(ADCH << 8) | ADCL] + TOS
where ADCH and ADCL are the ADC data registers, k is the fixed slope coefficient and TOS is the temperature sensor offset. Typically, k is very close to 1.0 and in single-point calibration the coefficient may be omitted. Where
higher accuracy is required the slope coefficient should be evaluated based on measurements at two
temperatures.
15.13 Register Description
15.13.1
ADMUX – ADC Multiplexer Selection Register
Bit
7
6
5
4
3
2
1
0
0x10
–
REFS
REFEN
ADC0EN
MUX3
MUX2
MUX1
MUX0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADMUX
• Bit 7 – Res: Reserved Bit
This bit is reserved and will always read as zero.
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• Bit 6 – REFS: Reference Selection Bit
This bit selects the voltage reference for the ADC, as shown in Table 15-3.
Table 15-3.
Voltage Reference Selections for ADC
REFS
Voltage Reference Selection
0
VCC used as analog reference
1
Internal 1.1V voltage reference
If this bit is changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in
ADCSR is set). Also note, that when these bits are changed, the next conversion will take 25 ADC clock cycles.
• Bit 5 – REFEN
This bit is reserved for QTouch, always write as zero.
• Bit 4 – ADC0EN
This bit is reserved for QTouch, always write as zero.
• Bits 3:0 – MUX[3:0]: Analog Channel and Gain Selection Bits
The value of these bits selects which analog input is connected to the ADC, as shown in Table 15-4. Selecting
channel ADC12 enables temperature measurement.
Table 15-4.
Single-Ended Input channel Selections
Single Ended Input
MUX[3:0]
ADC0 (PA0)
0000
ADC1 (PA1)
0001
ADC2 (PA2)
0010
ADC3 (PA3)
0011
ADC4 (PA4)
0100
ADC5 (PA5)
0101
ADC6 (PA6)
0110
ADC7 (PA7)
0111
ADC8 (PB0)
1000
ADC9 (PB1)
1001
ADC10 (PB2)
1010
ADC11 (PB3)
1011
0V (AGND)
1100
(1)
1101
1.1V (I Ref)
ADC12 (Temperature Sensor)
(2)
Reserved
Notes:
1110
1111
1. After switching to internal voltage reference the ADC requires a settling time of 1ms before measurements are stable. Conversions starting before this may not be reliable. The ADC must be enabled during the settling time.
2. See “Temperature Measurement” on page 109.
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If these bits are changed during a conversion, the change will not go into effect until this conversion is complete
(ADIF in ADCSRA is set).
15.13.2
ADCL and ADCH – ADC Data Register
15.13.2.1
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
0x0F
–
–
–
–
–
–
ADC9
ADC8
ADCH
0x0E
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
Read/Write
Initial Value
15.13.2.2
ADLAR = 1
Bit
15
14
13
12
11
10
9
8
0x0F
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
0x0E
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
Read/Write
Initial Value
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if the result is left
adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read
first, then ADCH.
The ADLAR bit in ADCSRB, and the MUX 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.
• ADC[9:0]: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on page 109.
15.13.3
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
0x12
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.
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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.
• 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 – ADPS[2:0]: ADC Prescaler Select Bits
These bits determine the division factor between the system clock frequency and the input clock to the ADC.
Table 15-5.
15.13.4
ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
ADCSRB – ADC Control and Status Register B
Bit
7
6
5
4
3
2
1
0
VDEN
VDPD
–
–
ADLAR
ADTS2
ADTS1
ADTS0
Read/Write
R/W
R/W
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x11
ADCSRB
• Bit 7 – VDEN
This bit is reserved for QTouch, always write as zero.
• Bit 6 – VDPD
This bit is reserved for QTouch, always write as zero.
• Bits 5:4 – Res: Reserved Bits
These are reserved bits. For compatibility with future devices always write these bits to zero.
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• Bit 3 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register. Write one to
ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC
Data Register immediately, regardless of any ongoing conversions. For a comple the description of this bit, see
“ADCL and ADCH – ADC Data Register” on page 111.
• Bits 2:0 – ADTS[2:0]: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion.
If ADATE is cleared, the ADTS[2:0] settings will have no effect. A conversion will be triggered by the rising edge of
the selected Interrupt Flag. Note that switching from a trigger source that is cleared to a trigger source that is set,
will generate a positive edge on the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching
to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
Table 15-6.
15.13.5
ADC Auto Trigger Source Selections
ADTS2
ADTS1
ADTS0
Trigger Source
0
0
0
Free Running mode
0
0
1
Analog Comparator
0
1
0
External Interrupt Request 0
0
1
1
Timer/Counter0 Compare Match A
1
0
0
Timer/Counter0 Overflow
1
0
1
Timer/Counter1 Compare Match B
1
1
0
Timer/Counter1 Overflow
1
1
1
Timer/Counter1 Capture Event
DIDR0 – Digital Input Disable Register 0
Bit
7
6
5
4
3
2
1
0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x0D
DIDR0
• Bits 7:0 – ADC7D:ADC0D: ADC[7:0] Digital Input Disable
When a bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC[7:0]
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.
15.13.6
PORTCR – Port Control Register
Bit
7
6
5
4
3
2
1
0
ADC11D
ADC10D
ADC9D
ADC8D
–
BBMC
BBMB
BBMA
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
0x08
PORTCR
• Bits 7:4 – ADC11D:ADC8D: ADC[11:8] Digital Input Disable
When a bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC[11:8]
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.
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16. SPI – Serial Peripheral Interface
16.1
Features
•
•
•
•
•
•
•
•
Overview
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the ATtiny40 and
peripheral devices or between several AVR devices. The SPI module is illustrated in Figure 16-1.
Figure 16-1. SPI Block Diagram
CLKIO
DIVIDER
/2/4/8/16/32/64/128
SS
SPI2X
SPI2X
16.2
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
Note:
Refer to Figure 1-1 on page 2, and Table 16-1 on page 116 for SPI pin placement.
To enable the SPI module, the PRSPI bit in the Power Reduction Register must be written to zero. See “PRR –
Power Reduction Register” on page 27.
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The interconnection between Master and Slave CPUs with SPI is shown in Figure 16-2 on page 115. 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 16-2. 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 minimum low and high periods should be:
Low periods: Longer than 2 CPU clock cycles.
High periods: Longer than 2 CPU clock cycles.
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When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to
Table 16-1 on page 116. For more details on automatic port overrides, refer to “Alternate Port Functions” on page
47.
Table 16-1.
Pin
SPI Pin Overrides
Direction, Master SPI
Direction, Slave SPI
MOSI
User Defined
Input
MISO
Input
User Defined
SCK
User Defined
Input
SS
User Defined
Input
Note:
See “Alternate Functions of Port B” on page 53 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 PB5, replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Assembly Code Example(1)
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
r16, SPSR
sbrsr16, SPIF
rjmp Wait_Transmit
ret
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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. See ”Code Examples” on page 5.
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
in
r16, SPSR
sbrs r16, SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in
r16,SPDR
ret
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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:
1. See ”Code Examples” on page 5.
16.3
SS Pin Functionality
16.3.1
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.
16.3.2
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.
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16.4
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 16-3 on page 119 and Figure 16-4 on
page 119.
Figure 16-3. 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 16-4. 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)
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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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 shown in Table 16-2, which is a summary of Table 16-3 on page 120 and Table 16-4 on
page 121.
Table 16-2.
SPI Modes
SPI Mode
16.5
16.5.1
Conditions
Leading Edge
Trailing eDge
0
CPOL=0, CPHA=0
Sample (Rising)
Setup (Falling)
1
CPOL=0, CPHA=1
Setup (Rising)
Sample (Falling)
2
CPOL=1, CPHA=0
Sample (Falling)
Setup (Rising)
3
CPOL=1, CPHA=1
Setup (Falling)
Sample (Rising)
Register Description
SPCR – SPI Control Register
Bit
7
6
5
4
3
2
1
0
0x30
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 the 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.
• 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 16-3 and Figure 16-4 for an example. The CPOL functionality is summarized below:
Table 16-3.
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 16-3 and Figure 16-4 for an example. The CPOL functionality is summarized below:
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Table 16-4.
CPHA Functionality
CPHA
Leading Edge
Trailing Edge
0
Sample
Setup
1
Setup
Sample
• Bits 1:0 – SPR[1:0]: 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 I/O Clock frequency fclk_I/O is shown in the following table:
Table 16-5.
16.5.2
Relationship Between SCK and the I/O Clock Frequency
SPI2X
SPR1
SPR0
SCK Frequency
0
0
0
fclk_I/O/4
0
0
1
fclk_I/O/16
0
1
0
fclk_I/O/64
0
1
1
fclk_I/O/128
1
0
0
fclk_I/O/2
1
0
1
fclk_I/O/8
1
1
0
fclk_I/O/32
1
1
1
fclk_I/O/64
SPSR – SPI Status Register
Bit
7
6
5
4
3
2
1
0
0x2F
SPIF
WCOL
–
–
–
–
–
SPI2X
Read/Write
R/W
R/W
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.
• Bits 5:1 – Res: Reserved Bits
These bits are reserved 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 16-5). 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 fclk_I/O/4 or lower.
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16.5.3
SPDR – SPI Data Register
Bit
7
6
5
4
3
2
1
0
0x2E
MSB
LSB
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
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.
17. TWI – Two Wire Interface (Slave)
17.1
Features
•
•
•
•
•
•
•
•
•
•
•
17.2
Phillips I2C compatible
SMBus compatible (with reservations)
100 kHz and 400 kHz support at low system clock frequencies
Slew-Rate Limited Output Drivers
Input Filter provides noise suppression
7-bit, and General Call Address Recognition in Hardware
Address mask register for address masking or dual address match
10-bit addressing supported
Optional Software Address Recognition Provides Unlimited Number of Slave Addresses
Operates in all sleep modes, including Power Down
Slave Arbitration allows support for SMBus Address Resolve Protocol (ARP)
Overview
The Two Wire Interface (TWI) is a bi-directional, bus communication interface, which uses only two wires. The TWI
is I2C compatible and, with reservations, SMBus compatible (see “Compatibility with SMBus” on page 128).
A device connected to the bus must act as a master or slave.The master initiates a data transaction by addressing
a slave on the bus, and telling whether it wants to transmit or receive data. One bus can have several masters, and
an arbitration process handles priority if two or more masters try to transmit at the same time.
The TWI module in ATtiny40 implements slave functionality, only. Lost arbitration, errors, collisions and clock holds
on the bus are detected in hardware and indicated in separate status flags.
Both 7-bit and general address call recognition is implemented in hardware. 10-bit addressing is also supported. A
dedicated address mask register can act as a second address match register or as a mask register for the slave
address to match on a range of addresses. The slave logic continues to operate in all sleep modes, including
Power down. This enables the slave to wake up from sleep on TWI address match. It is possible to disable the
address matching and let this be handled in software instead. This allows the slave to detect and respond to several addresses. Smart Mode can be enabled to auto trigger operations and reduce software complexity.
The TWI module includes bus state logic that collects information to detect START and STOP conditions, bus collision and bus errors. The bus state logic continues to operate in all sleep modes including Power down.
17.3
General TWI Bus Concepts
The Two-Wire Interface (TWI) provides a simple two-wire bi-directional bus consisting of a serial clock line (SCL)
and a serial data line (SDA). The two lines are open collector lines (wired-AND), and pull-up resistors (Rp) are the
only external components needed to drive the bus. The pull-up resistors will provide a high level on the lines when
none of the connected devices are driving the bus. A constant current source can be used as an alternative to the
pull-up resistors.
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The TWI bus is a simple and efficient method of interconnecting multiple devices on a serial bus. A device connected to the bus can be a master or slave, where the master controls the bus and all communication.
Figure 17-1 illustrates the TWI bus topology.
Figure 17-1. TWI Bus Topology
A unique address is assigned to all slave devices connected to the bus, and the master will use this to address a
slave and initiate a data transaction. 7-bit or 10-bit addressing can be used.
Several masters can be connected to the same bus, and this is called a multi-master environment. An arbitration
mechanism is provided for resolving bus ownership between masters since only one master device may own the
bus at any given time.
A device can contain both master and slave logic, and can emulate multiple slave devices by responding to more
than one address.
A master indicates the start of transaction by issuing a START condition (S) on the bus. An address packet with a
slave address (ADDRESS) and an indication whether the master wishes to read or write data (R/W), is then sent.
After all data packets (DATA) are transferred, the master issues a STOP condition (P) on the bus to end the transaction. The receiver must acknowledge (A) or not-acknowledge (A) each byte received.
Figure 17-2 shows a TWI transaction.
Figure 17-2. Basic TWI Transaction Diagram Topology
The master provides the clock signal for the transaction, but a device connected to the bus is allowed to stretch the
low level period of the clock to decrease the clock speed.
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17.3.1
Electrical Characteristics
The TWI follows the electrical specifications and timing of I2C and SMBus. See“Two-Wire Serial Interface Characteristics” on page 156 and “Compatibility with SMBus” on page 128.
17.3.2
START and STOP Conditions
Two unique bus conditions are used for marking the beginning (START) and end (STOP) of a transaction. The
master issues a START condition(S) by indicating a high to low transition on the SDA line while the SCL line is kept
high. The master completes the transaction by issuing a STOP condition (P), indicated by a low to high transition
on the SDA line while SCL line is kept high.
Figure 17-3. START and STOP Conditions
Multiple START conditions can be issued during a single transaction. A START condition not directly following a
STOP condition, are named a Repeated START condition (Sr).
17.3.3
Bit Transfer
As illustrated by Figure 17-4 a bit transferred on the SDA line must be stable for the entire high period of the SCL
line. Consequently the SDA value can only be changed during the low period of the clock. This is ensured in hardware by the TWI module.
Figure 17-4. Data Validity
Combining bit transfers results in the formation of address and data packets. These packets consist of 8 data bits
(one byte) with the most significant bit transferred first, plus a single bit not-acknowledge (NACK) or acknowledge
(ACK) response. The addressed device signals ACK by pulling the SCL line low, and NACK by leaving the line
SCL high during the ninth clock cycle.
17.3.4
Address Packet
After the START condition, a 7-bit address followed by a read/write (R/W) bit is sent. This is always transmitted by
the Master. A slave recognizing its address will ACK the address by pulling the data line low the next SCL cycle,
while all other slaves should keep the TWI lines released, and wait for the next START and address. The 7-bit
address, the R/W bit and the acknowledge bit combined is the address packet. Only one address packet for each
START condition is given, also when 10-bit addressing is used.
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The R/W specifies the direction of the transaction. If the R/W bit is low, it indicates a Master Write transaction, and
the master will transmit its data after the slave has acknowledged its address. Opposite, for a Master Read operation the slave will start to transmit data after acknowledging its address.
17.3.5
Data Packet
Data packets succeed an address packet or another data packet. All data packets are nine bits long, consisting of
one data byte and an acknowledge bit. The direction bit in the previous address packet determines the direction in
which the data is transferred.
17.3.6
Transaction
A transaction is the complete transfer from a START to a STOP condition, including any Repeated START conditions in between. The TWI standard defines three fundamental transaction modes: Master Write, Master Read, and
combined transaction.
Figure 17-5 illustrates the Master Write transaction. The master initiates the transaction by issuing a START condition (S) followed by an address packet with direction bit set to zero (ADDRESS+W).
Figure 17-5. Master Write Transaction
Given that the slave acknowledges the address, the master can start transmitting data (DATA) and the slave will
ACK or NACK (A/A) each byte. If no data packets are to be transmitted, the master terminates the transaction by
issuing a STOP condition (P) directly after the address packet. There are no limitations to the number of data packets that can be transferred. If the slave signal a NACK to the data, the master must assume that the slave cannot
receive any more data and terminate the transaction.
Figure 17-6 illustrates the Master Read transaction. The master initiates the transaction by issuing a START condition followed by an address packet with direction bit set to one (ADRESS+R). The addressed slave must
acknowledge the address for the master to be allowed to continue the transaction.
Figure 17-6. Master Read Transaction
Given that the slave acknowledges the address, the master can start receiving data from the slave. There are no
limitations to the number of data packets that can be transferred. The slave transmits the data while the master signals ACK or NACK after each data byte. The master terminates the transfer with a NACK before issuing a STOP
condition.
Figure 17-7 illustrates a combined transaction. A combined transaction consists of several read and write transactions separated by a Repeated START conditions (Sr).
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Figure 17-7. Combined Transaction
17.3.7
Clock and Clock Stretching
All devices connected to the bus are allowed to stretch the low period of the clock to slow down the overall clock
frequency or to insert wait states while processing data. A device that needs to stretch the clock can do this by
holding/forcing the SCL line low after it detects a low level on the line.
Three types of clock stretching can be defined as shown in Figure 17-8.
Figure 17-8. Clock Stretching
If the device is in a sleep mode and a START condition is detected the clock is stretched during the wake-up period
for the device.
A slave device can slow down the bus frequency by stretching the clock periodically on a bit level. This allows the
slave to run at a lower system clock frequency. However, the overall performance of the bus will be reduced
accordingly. Both the master and slave device can randomly stretch the clock on a byte level basis before and after
the ACK/NACK bit. This provides time to process incoming or prepare outgoing data, or performing other time critical tasks.
In the case where the slave is stretching the clock the master will be forced into a wait-state until the slave is ready
and vice versa.
17.3.8
Arbitration
A master can only start a bus transaction if it has detected that the bus is idle. As the TWI bus is a multi master
bus, it is possible that two devices initiate a transaction at the same time. This results in multiple masters owning
the bus simultaneously. This is solved using an arbitration scheme where the master loses control of the bus if it is
not able to transmit a high level on the SDA line. The masters who lose arbitration must then wait until the bus
becomes idle (i.e. wait for a STOP condition) before attempting to reacquire bus ownership. Slave devices are not
involved in the arbitration procedure.
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Figure 17-9. TWI Arbitration
Figure 17-9 shows an example where two TWI masters are contending for bus ownership. Both devices are able to
issue a START condition, but DEVICE1 loses arbitration when attempting to transmit a high level (bit 5) while
DEVICE2 is transmitting a low level.
Arbitration between a repeated START condition and a data bit, a STOP condition and a data bit, or a repeated
START condition and STOP condition are not allowed and will require special handling by software.
17.3.9
Synchronization
A clock synchronization algorithm is necessary for solving situations where more than one master is trying to control the SCL line at the same time. The algorithm is based on the same principles used for clock stretching
previously described. Figure 17-10 shows an example where two masters are competing for the control over the
bus clock. The SCL line is the wired-AND result of the two masters clock outputs.
Figure 17-10. Clock Synchronization
A high to low transition on the SCL line will force the line low for all masters on the bus and they start timing their
low clock period. The timing length of the low clock period can vary between the masters. When a master
(DEVICE1 in this case) has completed its low period it releases the SCL line. However, the SCL line will not go
high before all masters have released it. Consequently the SCL line will be held low by the device with the longest
low period (DEVICE2). Devices with shorter low periods must insert a wait-state until the clock is released. All masters start their high period when the SCL line is released by all devices and has become high. The device which
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first completes its high period (DEVICE1) forces the clock line low and the procedure are then repeated. The result
of this is that the device with the shortest clock period determines the high period while the low period of the clock
is determined by the longest clock period.
17.3.10
Compatibility with SMBus
As with any other I2C-compliant interface there are known compatibility issues the designer should be aware of
before connecting a TWI device to SMBus devices. For use in SMBus environments, the following should be
noted:
• All I/O pins of an AVR, including those of the two-wire interface, have protection diodes to both supply voltage
and ground. See Figure 10-1 on page 42. This is in contradiction to the requirements of the SMBus
specifications. As a result, supply voltage mustn’t be removed from the AVR or the protection diodes will pull the
bus lines down. Power down and sleep modes is not a problem, provided supply voltages remain.
• The data hold time of the TWI is lower than specified for SMBus. The TWSHE bit of TWSCRA can be used to
increase the hold time. See “TWSCRA – TWI Slave Control Register A” on page 130.
• SMBus has a low speed limit, while I2C hasn’t. As a master in an SMBus environment, the AVR must make sure
bus speed does not drop below specifications, since lower bus speeds trigger timeouts in SMBus slaves. If the
AVR is configured a slave there is a possibility of a bus lockup, since the TWI module doesn't identify timeouts.
17.4
TWI Slave Operation
The TWI slave is byte-oriented with optional interrupts after each byte. There are separate interrupt flags for Data
Interrupt and Address/Stop Interrupt. Interrupt flags can be set to trigger the TWI interrupt, or be used for polled
operation. There are dedicated status flags for indicating ACK/NACK received, clock hold, collision, bus error and
read/write direction.
When an interrupt flag is set, the SCL line is forced low. This will give the slave time to respond or handle any data,
and will in most cases require software interaction. Figure 17-11. shows the TWI slave operation. The diamond
shapes symbols (SW) indicate where software interaction is required.
Figure 17-11. TWI Slave Operation
The number of interrupts generated is kept at a minimum by automatic handling of most conditions. Quick Command can be enabled to auto trigger operations and reduce software complexity.
Promiscuous Mode can be enabled to allow the slave to respond to all received addresses.
17.4.1
Receiving Address Packets
When the TWI slave is properly configured, it will wait for a START condition to be detected. When this happens,
the successive address byte will be received and checked by the address match logic, and the slave will ACK the
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correct address. If the received address is not a match, the slave will not acknowledge the address and wait for a
new START condition.
The slave Address/Stop Interrupt Flag is set when a START condition succeeded by a valid address packet is
detected. A general call address will also set the interrupt flag.
A START condition immediately followed by a STOP condition, is an illegal operation and the Bus Error flag is set.
The R/W Direction flag reflects the direction bit received with the address. This can be read by software to determine the type of operation currently in progress.
Depending on the R/W direction bit and bus condition one of four distinct cases (1 to 4) arises following the
address packet. The different cases must be handled in software.
17.4.1.1
Case 1: Address packet accepted - Direction bit set
If the R/W Direction flag is set, this indicates a master read operation. The SCL line is forced low, stretching the
bus clock. If ACK is sent by the slave, the slave hardware will set the Data Interrupt Flag indicating data is needed
for transmit. If NACK is sent by the slave, the slave will wait for a new START condition and address match.
17.4.1.2
Case 2: Address packet accepted - Direction bit cleared
If the R/W Direction flag is cleared this indicates a master write operation. The SCL line is forced low, stretching the
bus clock. If ACK is sent by the slave, the slave will wait for data to be received. Data, Repeated START or STOP
can be received after this. If NACK is indicated the slave will wait for a new START condition and address match.
17.4.1.3
Case 3: Collision
If the slave is not able to send a high level or NACK, the Collision flag is set and it will disable the data and
acknowledge output from the slave logic. The clock hold is released. A START or repeated START condition will
be accepted.
17.4.1.4
Case 4: STOP condition received.
Operation is the same as case 1 or 2 above with one exception. When the STOP condition is received, the Slave
Address/Stop flag will be set indicating that a STOP condition and not an address match occurred.
17.4.2
Receiving Data Packets
The slave will know when an address packet with R/W direction bit cleared has been successfully received. After
acknowledging this, the slave must be ready to receive data. When a data packet is received the Data Interrupt
Flag is set, and the slave must indicate ACK or NACK. After indicating a NACK, the slave must expect a STOP or
Repeated START condition.
17.4.3
Transmitting Data Packets
The slave will know when an address packet, with R/W direction bit set, has been successfully received. It can then
start sending data by writing to the Slave Data register. When a data packet transmission is completed, the Data
Interrupt Flag is set. If the master indicates NACK, the slave must stop transmitting data, and expect a STOP or
Repeated START condition.
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17.5
17.5.1
Register Description
TWSCRA – TWI Slave Control Register A
Bit
7
6
5
4
3
2
1
0
TWSHE
–
TWDIE
TWASIE
TWEN
TWSIE
TWPME
TWSME
Read/Write
R/W
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x2D
TWSCRA
• Bit 7 – TWSHE: TWI SDA Hold Time Enable
When this bit is set each negative transition of SCL triggers an additional internal delay, before the device is
allowed to change the SDA line. The added delay is approximately 50ns in length.
This may be useful in SMBus systems.
• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 5 – TWDIE: TWI Data Interrupt Enable
When this bit is set and interrupts are enabled, a TWI interrupt will be generated when the data interrupt flag
(TWDIF) in TWSSRA is set.
• Bit 4 – TWASIE: TWI Address/Stop Interrupt Enable
When this bit is set and interrupts are enabled, a TWI interrupt will be generated when the address/stop interrupt
flag (TWASIF) in TWSSRA is set.
• Bit 3 – TWEN: Two-Wire Interface Enable
When this bit is set the slave Two-Wire Interface is enabled.
• Bit 2 – TWSIE: TWI Stop Interrupt Enable
Setting the Stop Interrupt Enable (TWSIE) bit will set the TWASIF in the TWSSRA register when a STOP condition
is detected.
• Bit 1 – TWPME: TWI Promiscuous Mode Enable
When this bit is set the address match logic of the slave TWI responds to all received addresses. When this bit is
cleared the address match logic uses the TWSA register to determine which address to recognize as its own.
• Bit 0 – TWSME: TWI Smart Mode Enable
When this bit is set the TWI slave enters Smart Mode, where the Acknowledge Action is sent immediately after the
TWI data register (TWSD) has been read. Acknowledge Action is defined by the TWAA bit in TWSCRB.
When this bit is cleared the Acknowledge Action is sent after TWCMDn bits in TWSCRB are written to 1X.
17.5.2
TWSCRB – TWI Slave Control Register B
Bit
7
6
5
4
3
2
1
0
0x2C
–
–
–
–
–
TWAA
TWCMD1
TWCMD0
Read/Write
R
R
R
R
R
R/W
W
W
Initial Value
0
0
0
0
0
0
0
0
TWSCRB
• Bits 7:3 – Res: Reserved Bits
These bits are reserved and will always read as zero.
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• Bit 2 – TWAA: TWI Acknowledge Action
This bit defines the slave's acknowledge behavior after an address or data byte has been received from the master. Depending on the TWSME bit in TWSCRA the Acknowledge Action is executed either when a valid command
has been written to TWCMDn bits, or when the data register has been read. Acknowledge action is also executed
if clearing TWAIF flag after address match or TWDIF flag during master transmit. See Table 17-1 for details.
Table 17-1.
TWAA
0
1
Acknowledge Action of TWI Slave
Action
TWSME
When
0
When TWCMDn bits are written to 10 or 11
1
When TWSD is read
0
When TWCMDn bits are written to 10 or 11
1
When TWSD is read
Send ACK
Send NACK
• Bits 1:0 – TWCMD[1:0]: TWI Command
Writing these bits triggers the slave operation as defined by Table 17-2. The type of operation depends on the TWI
slave interrupt flags, TWDIF and TWASIF. The Acknowledge Action is only executed when the slave receives data
bytes or address byte from the master.
Table 17-2.
TWI Slave Command
TWCMD[1:0]
TWDIR
Operation
00
X
No action
01
X
Reserved
Used to complete transaction
10
0
Execute Acknowledge Action, then wait for any START (S/Sr) condition
1
Wait for any START (S/Sr) condition
Used in response to an Address Byte (TWASIF is set)
0
Execute Acknowledge Action, then receive next byte
1
Execute Acknowledge Action, then set TWDIF
11
Used in response to a Data Byte (TWDIF is set)
0
Execute Acknowledge Action, then wait for next byte
1
No action
Writing the TWCMD bits will automatically release the SCL line and clear the TWCH and slave interrupt flags.
TWAA and TWCMDn bits can be written at the same time. Acknowledge Action will then be executed before the
command is triggered.
The TWCMDn bits are strobed and always read zero.
17.5.3
TWSSRA – TWI Slave Status Register A
Bit
7
6
5
4
3
2
1
0
TWDIF
TWASIF
TWCH
TWRA
TWC
TWBE
TWDIR
TWAS
Read/Write
R/W
R/W
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x2B
TWSCRA
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• Bit 7 – TWDIF: TWI Data Interrupt Flag
This flag is set when a data byte has been successfully received, i.e. no bus errors or collisions have occurred during the operation. When this flag is set the slave forces the SCL line low, stretching the TWI clock period. The SCL
line is released by clearing the interrupt flags.
Writing a one to this bit will clear the flag. This flag is also automatically cleared when writing a valid command to
the TWCMDn bits in TWSCRB.
• Bit 6 – TWASIF: TWI Address/Stop Interrupt Flag
This flag is set when the slave detects that a valid address has been received, or when a transmit collision has
been detected. When this flag is set the slave forces the SCL line low, stretching the TWI clock period. The SCL
line is released by clearing the interrupt flags.
If TWASIE in TWSCRA is set, a STOP condition on the bus will also set TWASIF. STOP condition will set the flag
only if system clock is faster than the minimum bus free time between STOP and START.
Writing a one to this bit will clear the flag. This flag is also automatically cleared when writing a valid command to
the TWCMDn bits in TWSCRB.
• Bit 5 – TWCH: TWI Clock Hold
This bit is set when the slave is holding the SCL line low.
This bit is read-only, and set when TWDIF or TWASIF is set. The bit can be cleared indirectly by clearing the interrupt flags and releasing the SCL line.
• Bit 4 – TWRA: TWI Receive Acknowledge
This bit contains the most recently received acknowledge bit from the master.
This bit is read-only. When zero, the most recent acknowledge bit from the maser was ACK and, when one, the
most recent acknowledge bit was NACK.
• Bit 3 – TWC: TWI Collision
This bit is set when the slave was not able to transfer a high data bit or a NACK bit. When a collision is detected,
the slave will commence its normal operation, and disable data and acknowledge output. No low values are shifted
out onto the SDA line.
This bit is cleared by writing a one to it. The bit is also cleared automatically when a START or Repeated START
condition is detected.
• Bit 2 – TWBE: TWI Bus Error
This bit is set when an illegal bus condition has occured during a transfer. An illegal bus condition occurs if a
Repeated START or STOP condition is detected, and the number of bits from the previous START condition is not
a multiple of nine.
This bit is cleared by writing a one to it.
• Bit 1 – TWDIR: TWI Read/Write Direction
This bit indicates the direction bit from the last address packet received from a master. When this bit is one, a master read operation is in progress. When the bit is zero a master write operation is in progress.
• Bit 0 – TWAS: TWI Address or Stop
This bit indicates why the TWASIF bit was last set. If zero, a stop condition caused TWASIF to be set. If one,
address detection caused TWASIF to be set.
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17.5.4
TWSA – TWI Slave Address Register
Bit
7
6
5
4
0x2A
3
2
1
0
TWSA[7:0]
TWSA
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 slave address register contains the TWI slave address used by the slave address match logic to determine if a
master has addressed the slave. When using 7-bit or 10-bit address recognition mode, the high seven bits of the
address register (TWSA[7:1]) represent the slave address. The least significant bit (TWSA0) is used for general
call address recognition. Setting TWSA0 enables general call address recognition logic.
When using 10-bit addressing the address match logic only support hardware address recognition of the first byte
of a 10-bit address. If TWSA[7:1] is set to "0b11110nn", 'nn' will represent bits 9 and 8 of the slave address. The
next byte received is then bits 7 to 0 in the 10-bit address, but this must be handled by software.
When the address match logic detects that a valid address byte has been received, the TWASIF is set and the
TWDIR flag is updated.
If TWPME in TWSCRA is set, the address match logic responds to all addresses transmitted on the TWI bus.
TWSA is not used in this mode.
17.5.5
TWSD – TWI Slave Data Register
Bit
7
6
5
4
0x28
3
2
1
0
TWSD[7:0]
TWSD
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 data register is used when transmitting and received data. During transfer, data is shifted from/to the TWSD
register and to/from the bus. Therefore, the data register cannot be accessed during byte transfers. This is protected in hardware. The data register can only be accessed when the SCL line is held low by the slave, i.e. when
TWCH is set.
When a master reads data from a slave, the data to be sent must be written to the TWSD register. The byte transfer is started when the master starts to clock the data byte from the slave. It is followed by the slave receiving the
acknowledge bit from the master. The TWDIF and the TWCH bits are then set.
When a master writes data to a slave, the TWDIF and the TWCH flags are set when one byte has been received in
the data register. If Smart Mode is enabled, reading the data register will trigger the bus operation, as set by the
TWAA bit in TWSCRB.
Accessing TWSD will clear the slave interrupt flags and the TWCH bit.
17.5.6
TWSAM – TWI Slave Address Mask Register
Bit
7
6
5
0x29
4
3
2
1
TWSAM[7:0]
0
TWAE
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
TWSAM
• Bits 7:1 – TWSAM[7:1]: TWI Address Mask
These bits can act as a second address match register, or an address mask register, depending on the TWAE
setting.
If TWAE is set to zero, TWSAM can be loaded with a 7-bit slave address mask. Each bit in TWSAM can mask (disable) the corresponding address bit in the TWSA register. If the mask bit is one the address match between the
incoming address bit and the corresponding bit in TWSA is ignored. In other words, masked bits will always match.
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If TWAE is set to one, TWSAM can be loaded with a second slave address in addition to the TWSA register. In this
mode, the slave will match on 2 unique addresses, one in TWSA and the other in TWSAM.
• Bit 0 – TWAE: TWI Address Enable
By default, this bit is zero and the TWSAM bits acts as an address mask to the TWSA register. If this bit is set to
one, the slave address match logic responds to the two unique addresses in TWSA and TWSAM.
18. Programming Interface
18.1
Features
• Physical Layer:
– Synchronous Data Transfer
– Bi-directional, Half-duplex Receiver And Transmitter
– Fixed Frame Format With One Start Bit, 8 Data Bits, One Parity Bit And 2 Stop Bits
– Parity Error Detection, Frame Error Detection And Break Character Detection
– Parity Generation And Collision Detection
– Automatic Guard Time Insertion Between Data Reception And Transmission
• Access Layer:
– Communication Based On Messages
– Automatic Exception Handling Mechanism
– Compact Instruction Set
– NVM Programming Access Control
– Tiny Programming Interface Control And Status Space Access Control
– Data Space Access Control
18.2
Overview
The Tiny Programming Interface (TPI) supports external programming of all Non-Volatile Memories (NVM). Memory programming is done via the NVM Controller, by executing NVM controller commands as described in “Memory
Programming” on page 143.
The Tiny Programming Interface (TPI) provides access to the programming facilities. The interface consists of two
layers: the access layer and the physical layer. The layers are illustrated in Figure 18-1.
Figure 18-1. The Tiny Programming Interface and Related Internal Interfaces
TINY PROGRAMMING INTERFACE (TPI)
RESET
TPICLK
TPIDATA
PHYSICAL
LAYER
ACCESS
LAYER
NVM
CONTROLLER
NON-VOLATILE
MEMORIES
DATA BUS
Programming is done via the physical interface. This is a 3-pin interface, which uses the RESET pin as enable, the
TPICLK pin as the clock input, and the TPIDATA pin as data input and output.
NVM can be programmed at 5V, only.
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18.3
Physical Layer of Tiny Programming Interface
The TPI physical layer handles the basic low-level serial communication. The TPI physical layer uses a bi-directional, half-duplex serial receiver and transmitter. The physical layer includes serial-to-parallel and parallel-to-serial
data conversion, start-of-frame detection, frame error detection, parity error detection, parity generation and collision detection.
The TPI is accessed via three pins, as follows:
RESET:
TPICLK:
TPIDATA:
Tiny Programming Interface enable input
Tiny Programming Interface clock input
Tiny Programming Interface data input/output
In addition, the VCC and GND pins must be connected between the external programmer and the device.
18.3.1
Enabling
The following sequence enables the Tiny Programming Interface:
• Apply 5V between VCC and GND
• Depending on the method of reset to be used:
– Either: wait tTOUT (see Table 20-4 on page 155) and then set the RESET pin low. This will reset the
device and enable the TPI physical layer. The RESET pin must then be kept low for the entire
programming session
– Or: if the RSTDISBL configuration bit has been programmed, apply 12V to the RESET pin. The RESET
pin must be kept at 12V for the entire programming session
• Wait tRST (see Table 20-4 on page 155)
• Keep the TPIDATA pin high for 16 TPICLK cycles
See Figure 18-2 for guidance.
Figure 18-2. Sequence for enabling the Tiny Programming Interface
t
RST
16 x TPICLK CYCLES
RESET
TPICLK
TPIDATA
18.3.2
Disabling
Provided that the NVM enable bit has been cleared, the TPI is automatically disabled if the RESET pin is released
to inactive high state or, alternatively, if VHV is no longer applied to the RESET pin.
If the NVM enable bit is not cleared a power down is required to exit TPI programming mode.
See NVMEN bit in “TPISR – Tiny Programming Interface Status Register” on page 143.
18.3.3
Frame Format
The TPI physical layer supports a fixed frame format. A frame consists of one character, eight bits in length, and
one start bit, a parity bit and two stop bits. Data is transferred with the least significant bit first.
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Figure 18-3. Serial frame format.
TPICLK
TPIDATA
IDLE
ST
D0
D1
D7
P
SP1
SP2
IDLE/ST
Symbols used in Figure 18-3:
ST:
D0-D7:
P:
SP1:
SP2:
18.3.4
Start bit (always low)
Data bits (least significant bit sent first)
Parity bit (using even parity)
Stop bit 1 (always high)
Stop bit 2 (always high)
Parity Bit Calculation
The parity bit is always calculated using even parity. The value of the bit is calculated by doing an exclusive-or of
all the data bits, as follows:
P = D0  D1  D2  D3  D4  D5  D6  D7  0
where:
P:
D0-D7:
18.3.5
Parity bit using even parity
Data bits of the character
Supported Characters
The BREAK character is equal to a 12 bit long low level. It can be extended beyond a bit-length of 12.
The IDLE character is equal to a 12 bit long high level. It can be extended beyond a bit-length of 12.
Figure 18-4. Supported characters.
DATA CHARACTER
TPIDATA
IDLE
ST
D0
D1
D7
P
SP1
SP2
IDLE/ST
BREAK CHARACTER
TPIDATA
IDLE
IDLE/ST
IDLE CHARACTER
TPIDATA
18.3.6
IDLE
IDLE/ST
Operation
The TPI physical layer operates synchronously on the TPICLK provided by the external programmer. The dependency between the clock edges and data sampling or data change is shown in Figure 18-5. Data is changed at
falling edges and sampled at rising edges.
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Figure 18-5. Data changing and Data sampling.
TPICLK
TPIDATA
SAMPLE
SETUP
The TPI physical layer supports two modes of operation: Transmit and Receive. By default, the layer is in Receive
mode, waiting for a start bit. The mode of operation is controlled by the access layer.
18.3.7
Serial Data Reception
When the TPI physical layer is in receive mode, data reception is started as soon as a start bit has been detected.
Each bit that follows the start bit will be sampled at the rising edge of the TPICLK and shifted into the shift register
until the second stop bit has been received. When the complete frame is present in the shift register the received
data will be available for the TPI access layer.
There are three possible exceptions in the receive mode: frame error, parity error and break detection. All these
exceptions are signalized to the TPI access layer, which then enters the error state and puts the TPI physical layer
into receive mode, waiting for a BREAK character.
• Frame Error Exception. The frame error exception indicates the state of the stop bit. The frame error exception
is set if the stop bit was read as zero.
• Parity Error Exception. The parity of the data bits is calculated during the frame reception. After the frame is
received completely, the result is compared with the parity bit of the frame. If the comparison fails the parity
error exception is signalized.
• Break Detection Exception. The Break detection exception is given when a complete frame of all zeros has
been received.
18.3.8
Serial Data Transmission
When the TPI physical layer is ready to send a new frame it initiates data transmission by loading the shift register
with the data to be transmitted. When the shift register has been loaded with new data, the transmitter shifts one
complete frame out on the TPIDATA line at the transfer rate given by TPICLK.
If a collision is detected during transmission, the output driver is disabled. The TPI access layer enters the error
state and the TPI physical layer is put into receive mode, waiting for a BREAK character.
18.3.9
Collision Detection Exception
The TPI physical layer uses one bi-directional data line for both data reception and transmission. A possible drive
contention may occur, if the external programmer and the TPI physical layer drive the TPIDATA line simultaneously. In order to reduce the effect of the drive contention, a collision detection mechanism is supported. The
collision detection is based on the way the TPI physical layer drives the TPIDATA line.
The TPIDATA line is driven by a tri-state, push-pull driver with internal pull-up. The output driver is always enabled
when a logical zero is sent. When sending successive logical ones, the output is only driven actively during the first
clock cycle. After this, the output driver is automatically tri-stated and the TPIDATA line is kept high by the internal
pull-up. The output is re-enabled, when the next logical zero is sent.
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The collision detection is enabled in transmit mode, when the output driver has been disabled. The data line should
now be kept high by the internal pull-up and it is monitored to see, if it is driven low by the external programmer. If
the output is read low, a collision has been detected.
There are some potential pit-falls related to the way collision detection is performed. For example, collisions cannot
be detected when the TPI physical layer transmits a bit-stream of successive logical zeros, or bit-stream of alternating logical ones and zeros. This is because the output driver is active all the time, preventing polling of the
TPIDATA line. However, within a single frame the two stop bits should always be transmitted as logical ones,
enabling collision detection at least once per frame (as long as the frame format is not violated regarding the stop
bits).
The TPI physical layer will cease transmission when it detects a collision on the TPIDATA line. The collision is signalized to the TPI access layer, which immediately changes the physical layer to receive mode and goes to the
error state. The TPI access layer can be recovered from the error state only by sending a BREAK character.
18.3.10
Direction Change
In order to ensure correct timing of the half-duplex operation, a simple guard time mechanism has been added to
the physical layer. When the TPI physical layer changes from receive to transmit mode, a configurable number of
additional IDLE bits are inserted before the start bit is transmitted. The minimum transition time between receive
and transmit mode is two IDLE bits. The total IDLE time is the specified guard time plus two IDLE bits.
The guard time is configured by dedicated bits in the TPIPCR register. The default guard time value after the physical layer is initialized is 128 bits.
The external programmer looses control of the TPIDATA line when the TPI target changes from receive mode to
transmit. The guard time feature relaxes this critical phase of the communication. When the external programmer
changes from receive mode to transmit, a minimum of one IDLE bit should be inserted before the start bit is
transmitted.
18.4
Access Layer of Tiny Programming Interface
The TPI access layer is responsible for handling the communication with the external programmer. The communication is based on a message format, where each message comprises an instruction followed by one or more bytesized operands. The instruction is always sent by the external programmer but operands are sent either by the
external programmer or by the TPI access layer, depending on the type of instruction issued.
The TPI access layer controls the character transfer direction on the TPI physical layer. It also handles the recovery from the error state after exception.
The Control and Status Space (CSS) of the Tiny Programming Interface is allocated for control and status registers
in the TPI access Layer. The CSS consist of registers directly involved in the operation of the TPI itself. These register are accessible using the SLDCS and SSTCS instructions.
The access layer can also access the data space, either directly or indirectly using the Pointer Register (PR) as the
address pointer. The data space is accessible using the SLD, SST, SIN and SOUT instructions. The address
pointer can be stored in the Pointer Register using the SLDPR instruction.
18.4.1
Message format
Each message comprises an instruction followed by one or more byte operands. The instruction is always sent by
the external programmer. Depending on the instruction all the following operands are sent either by the external
programmer or by the TPI.
The messages can be categorized in two types based on the instruction, as follows:
• Write messages. A write message is a request to write data. The write message is sent entirely by the external
programmer. This message type is used with the SSTCS, SST, STPR, SOUT and SKEY instructions.
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• Read messages. A read message is a request to read data. The TPI reacts to the request by sending the byte
operands. This message type is used with the SLDCS, SLD and SIN instructions.
All the instructions except the SKEY instruction require the instruction to be followed by one byte operand. The
SKEY instruction requires 8 byte operands. For more information, see the TPI instruction set on page 139.
18.4.2
Exception Handling and Synchronisation
Several situations are considered exceptions from normal operation of the TPI. When the TPI physical layer is in
receive mode, these exceptions are:
• The TPI physical layer detects a parity error.
• The TPI physical layer detects a frame error.
• The TPI physical layer recognizes a BREAK character.
When the TPI physical layer is in transmit mode, the possible exceptions are:
• The TPI physical layer detects a data collision.
All these exceptions are signalized to the TPI access layer. The access layer responds to an exception by aborting
any on-going operation and enters the error state. The access layer will stay in the error state until a BREAK character has been received, after which it is taken back to its default state. As a consequence, the external
programmer can always synchronize the protocol by simply transmitting two successive BREAK characters.
18.5
Instruction Set
The TPI has a compact instruction set that is used to access the TPI Control and Status Space (CSS) and the data
space. The instructions allow the external programmer to access the TPI, the NVM Controller and the NVM memories. All instructions except SKEY require one byte operand following the instruction. The SKEY instruction is
followed by 8 data bytes. All instructions are byte-sized.
The TPI instruction set is summarised in Table 18-1.
Table 18-1.
Instruction Set Summary
Mnemonic
Operand
Description
Operation
SLD
data, PR
Serial LoaD from data space using indirect
addressing
data  DS[PR]
SLD
data, PR+
Serial LoaD from data space using indirect
addressing and post-increment
data  DS[PR]
PR  PR+1
SST
PR, data
Serial STore to data space using indirect
addressing
DS[PR]  data
SST
PR+, data
Serial STore to data space using indirect
addressing and post-increment
DS[PR]  data
PR  PR+1
SSTPR
PR, a
Serial STore to Pointer Register using direct
addressing
PR[a]  data
SIN
data, a
Serial IN from data space
data  I/O[a]
SOUT
a, data
Serial OUT to data space
I/O[a]  data
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Table 18-1.
18.5.1
Mnemonic
Operand
Description
Operation
SLDCS
data, a
Serial LoaD from Control and Status space
using direct addressing
data  CSS[a]
SSTCS
a, data
Serial STore to Control and Status space
using direct addressing
CSS[a]  data
SKEY
Key, {8{data}}
Serial KEY
Key  {8{data}}
SLD - Serial LoaD from data space using indirect addressing
The SLD instruction uses indirect addressing to load data from the data space to the TPI physical layer shift-register for serial read-out. The data space location is pointed by the Pointer Register (PR), where the address must
have been stored before data is accessed. The Pointer Register can either be left unchanged by the operation, or
it can be post-incremented, as shown in Table 18-2.
Table 18-2.
18.5.2
Opcode
Remarks
Register
data  DS[PR]
0010 0000
PR  PR
Unchanged
data  DS[PR]
0010 0100
PR  PR + 1
Post increment
SST - Serial STore to data space using indirect addressing
The SST instruction uses indirect addressing to store into data space the byte that is shifted into the physical layer
shift register. The data space location is pointed by the Pointer Register (PR), where the address must have been
stored before the operation. The Pointer Register can be either left unchanged by the operation, or it can be postincremented, as shown in Table 18-3.
The Serial Store to Data Space (SLD) Instruction
Operation
Opcode
Remarks
Register
DS[PR] data
0110 0000
PR  PR
Unchanged
DS[PR] data
0110 0100
PR  PR + 1
Post increment
SSTPR - Serial STore to Pointer Register
The SSTPR instruction stores the data byte that is shifted into the physical layer shift register to the Pointer Register (PR). The address bit of the instruction specifies which byte of the Pointer Register is accessed, as shown in
Table 18-4.
Table 18-4.
18.5.4
The Serial Load from Data Space (SLD) Instruction
Operation
Table 18-3.
18.5.3
Instruction Set Summary (Continued)
The Serial Store to Pointer Register (SSTPR) Instruction
Operation
Opcode
Remarks
PR[a] data
0110 100a
Bit ‘a’ addresses Pointer Register byte
SIN - Serial IN from i/o space using direct addressing
The SIN instruction loads data byte from the I/O space to the shift register of the physical layer for serial read-out.
The instuction uses direct addressing, the address consisting of the 6 address bits of the instruction, as shown in
Table 18-5.
Table 18-5.
The Serial IN from i/o space (SIN) Instruction
Operation
Opcode
Remarks
data I/O[a]
0aa1 aaaa
Bits marked ‘a’ form the direct, 6-bit addres
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18.5.5
SOUT - Serial OUT to i/o space using direct addressing
The SOUT instruction stores the data byte that is shifted into the physical layer shift register to the I/O space. The
instruction uses direct addressing, the address consisting of the 6 address bits of the instruction, as shown in Table
18-6.
Table 18-6.
18.5.6
Operation
Opcode
Remarks
I/O[a] data
1aa1 aaaa
Bits marked ‘a’ form the direct, 6-bit addres
SLDCS - Serial LoaD data from Control and Status space using direct addressing
The SLDCS instruction loads data byte from the TPI Control and Status Space to the TPI physical layer shift register for serial read-out. The SLDCS instruction uses direct addressing, the direct address consisting of the 4
address bits of the instruction, as shown in Table 18-7.
Table 18-7.
18.5.7
Opcode
Remarks
data CSS[a]
1000 aaaa
Bits marked ‘a’ form the direct, 4-bit addres
SSTCS - Serial STore data to Control and Status space using direct addressing
The SSTCS instruction stores the data byte that is shifted into the TPI physical layer shift register to the TPI Control
and Status Space. The SSTCS instruction uses direct addressing, the direct address consisting of the 4 address
bits of the instruction, as shown in Table 18-8.
The Serial STore data to Control and Status space (SSTCS) Instruction
Operation
Opcode
Remarks
CSS[a] data
1100 aaaa
Bits marked ‘a’ form the direct, 4-bit addres
SKEY - Serial KEY signaling
The SKEY instruction is used to signal the activation key that enables NVM programming. The SKEY instruction is
followed by the 8 data bytes that includes the activation key, as shown in Table 18-9.
Table 18-9.
18.6
The Serial Load Data from Control and Status space (SLDCS) Instruction
Operation
Table 18-8.
18.5.8
The Serial OUT to i/o space (SOUT) Instruction
The Serial KEY signaling (SKEY) Instruction
Operation
Opcode
Remarks
Key {8[data}}
1110 0000
Data bytes follow after instruction
Accessing the Non-Volatile Memory Controller
By default, NVM programming is not enabled. In order to access the NVM Controller and be able to program the
non-volatile memories, a unique key must be sent using the SKEY instruction. The 64-bit key that will enable NVM
programming is given in Table 18-10.
Table 18-10. Enable Key for Non-Volatile Memory Programming
Key
Value
NVM Program Enable
0x1289AB45CDD888FF
After the key has been given, the Non-Volatile Memory Enable (NVMEN) bit in the TPI Status Register (TPISR)
must be polled until the Non-Volatile memory has been enabled.
NVM programming is disabled by writing a logical zero to the NVMEN bit in TPISR.
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18.7
Control and Status Space Register Descriptions
The control and status registers of the Tiny Programming Interface are mapped in the Control and Status Space
(CSS) of the interface. These registers are not part of the I/O register map and are accessible via SLDCS and
SSTCS instructions, only. The control and status registers are directly involved in configuration and status monitoring of the TPI.
A summary of CSS registers is shown in Table 18-11.
Table 18-11. Summary of Control and Status Registers
18.7.1
Addr.
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
0x0F
TPIIR
0x0E
Reserved
–
–
–
–
–
0x0D
Reserved
–
–
–
–
0x0C
Reserved
–
–
–
0x0B
Reserved
–
–
0x0A
Reserved
–
0x09
Reserved
0x08
Bit 2
Bit 1
Bit 0
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Reserved
–
–
–
–
–
–
–
–
0x07
Reserved
–
–
–
–
–
–
–
–
0x06
Reserved
–
–
–
–
–
–
–
–
0x05
Reserved
–
–
–
–
–
–
–
–
0x04
Reserved
–
–
–
–
–
–
–
–
0x03
Reserved
–
–
–
–
–
–
–
–
0x02
TPIPCR
–
–
–
–
–
GT2
GT1
GT0
0x01
Reserved
–
–
–
–
–
–
–
–
0x00
TPISR
–
–
–
–
–
–
NVMEN
–
Tiny Programming Interface Identification Code
TPIIR – Tiny Programming Interface Identification Register
Bit
7
6
CSS: 0x0F
5
4
3
2
1
0
Programming Interface Identification Code
TPIIR
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
• Bits 7:0 – TPIIC: Tiny Programming Interface Identification Code
These bits give the identification code for the Tiny Programming Interface. The code can be used be the external
programmer to identify the TPI. The identification code of the Tiny Programming Interface is shown in Table 18-12.
Table 18-12. Identification Code for Tiny Programming Interface
18.7.2
Code
Value
Interface Identification
0x80
TPIPCR – Tiny Programming Interface Physical Layer Control Register
Bit
7
6
5
4
3
2
1
0
CSS: 0x02
–
–
–
–
–
GT2
GT1
GT0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TPIPCR
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• Bits 7:3 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 2:0 – GT[2:0]: Guard Time
These bits specify the number of additional IDLE bits that are inserted to the idle time when changing from reception mode to transmission mode. Additional delays are not inserted when changing from transmission mode to
reception.
The total idle time when changing from reception to transmission mode is Guard Time plus two IDLE bits. Table
18-13 shows the available Guard Time settings.
Table 18-13. Guard Time Settings
GT2
GT1
GT0
Guard Time (Number of IDLE bits)
0
0
0
+128 (default value)
0
0
1
+64
0
1
0
+32
0
1
1
+16
1
0
0
+8
1
0
1
+4
1
1
0
+2
1
1
1
+0
The default Guard Time is 128 IDLE bits. To speed up the communication, the Guard Time should be set to the
shortest safe value.
18.7.3
TPISR – Tiny Programming Interface Status Register
Bit
7
6
5
4
3
2
1
CSS: 0x00
–
–
–
–
–
–
NVMEN
0
–
Read/Write
R
R
R
R
R
R
R/W
R
Initial Value
0
0
0
0
0
0
0
0
TPISR
• Bits 7:2, 0 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bit 1 – NVMEN: Non-Volatile Memory Programming Enabled
NVM programming is enabled when this bit is set. The external programmer can poll this bit to verify the interface
has been successfully enabled.
NVM programming is disabled by writing this bit to zero.
19. Memory Programming
19.1
Features
• Two Embedded Non-Volatile Memories:
– Non-Volatile Memory Lock bits (NVM Lock bits)
– Flash Memory
• Four Separate Sections Inside Flash Memory:
– Code Section (Program Memory)
– Signature Section
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•
•
•
•
19.2
– Configuration Section
– Calibration Section
Read Access to All Non-Volatile Memories from Application Software
Read and Write Access to Non-Volatile Memories from External programmer:
– Read Access to All Non-Volatile Memories
– Write Access to NVM Lock Bits, Flash Code Section and Flash Configuration Section
External Programming:
– Support for In-System and Mass Production Programming
– Programming Through the Tiny Programming Interface (TPI)
High Security with NVM Lock Bits
Overview
The Non-Volatile Memory (NVM) Controller manages all access to the Non-Volatile Memories. The NVM Controller
controls all NVM timing and access privileges, and holds the status of the NVM.
During normal execution the CPU will execute code from the code section of the Flash memory (program memory).
When entering sleep and no programming operations are active, the Flash memory is disabled to minimize power
consumption.
All NVM are mapped to the data memory. Application software can read the NVM from the mapped locations of
data memory using load instruction with indirect addressing.
The NVM has only one read port and, therefore, the next instruction and the data can not be read simultaneously.
When the application reads data from NVM locations mapped to the data space, the data is read first before the
next instruction is fetched. The CPU execution is here delayed by one system clock cycle.
Internal programming operations to NVM have been disabled and the NVM therefore appears to the application
software as read-only. Internal write or erase operations of the NVM will not be successful.
The method used by the external programmer for writing the Non-Volatile Memories is referred to as external programming. External programming can be done both in-system or in mass production. The external programmer
can read and program the NVM via the Tiny Programming Interface (TPI).
In the external programming mode all NVM can be read and programmed, except the signature and the calibration
sections which are read-only.
NVM can be programmed at 5V, only.
19.3
Non-Volatile Memories
The ATtiny40 has the following, embedded NVM:
• Non-Volatile Memory Lock Bits
• Flash memory with four separate sections
19.3.1
Non-Volatile Memory Lock Bits
The ATtiny40 provides two Lock Bits, as shown in Table 19-1.
Table 19-1.
Lock Bit
Lock Bit Byte
Bit No
Description
Default Value
7
1 (unprogrammed)
6
1 (unprogrammed)
5
1 (unprogrammed)
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Table 19-1.
Lock Bit
Lock Bit Byte
Bit No
Description
Default Value
4
1 (unprogrammed)
3
1 (unprogrammed)
2
1 (unprogrammed)
NVLB2
1
Non-Volatile Lock Bit
1 (unprogrammed)
NVLB1
0
Non-Volatile Lock Bit
1 (unprogrammed)
The Lock Bits can be left unprogrammed ("1") or can be programmed ("0") to obtain the additional security shown
in Table 19-2. Lock Bits can be erased to "1" with the Chip Erase command, only.
Table 19-2.
Lock Bit Protection Modes
Memory Lock Bits (1)
Lock Mode
NVLB2 (2)
NVLB1 (2)
1
1
1
No Memory Lock feature Enabled
0
Further Programming of the Flash memory is disabled in
the external programming mode. The configuration
section bits are locked in the external programming
mode
0
Further programming and verification of the flash is
disabled in the external programming mode. The
configuration section bits are locked in the external
programming mode
2
1
3
Notes:
0
Protection Type
1. Program the configuration section bits before programming NVLB1 and NVLB2.
2. "1" means unprogrammed, "0" means programmed
19.3.2
Flash Memory
The embedded Flash memory of ATtiny40 has four separate sections, as shown in Table 19-3.
Table 19-3.
Number of Words and Pages in the Flash
Section
Code (program memory)
Configuration
Signature
(1)
Calibration (1)
Notes:
Size (Bytes)
Page Size (Words)
Pages
WADDR
PADDR
4096
32
64
[5:1]
[11:6]
32
32
1
[5:1]
–
32
16
2
[4:1]
[5:5]
32
32
1
[5:1]
–
1. This section is read-only.
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19.3.3
Configuration Section
ATtiny40 has one configuration byte, which resides in the configuration section. See Table 19-4.
Table 19-4.
Configuration bytes
Configuration word data
Configuration word address
High byte
Low byte
0x00
Reserved
Configuration Byte 0
0x01 ... 0x1F
Reserved
Reserved
Table 19-5 briefly describes the functionality of all configuration bits and how they are mapped into the configuration byte.
Table 19-5.
Configuration Byte 0
Bit
Bit Name
Description
Default Value
7
–
Reserved
1 (unprogrammed)
6
BODLEVEL2(1)
Brown-out Detector trigger level
1 (unprogrammed)
5
(1)
Brown-out Detector trigger level
1 (unprogrammed)
(1)
BODLEVEL1
4
BODLEVEL0
Brown-out Detector trigger level
1 (unprogrammed)
3
–
Reserved
1 (unprogrammed)
2
CKOUT
System Clock Output
1 (unprogrammed)
1
WDTON
Watchdog Timer always on
1 (unprogrammed)
0
RSTDISBL
External Reset disable
1 (unprogrammed)
Notes:
1. See Table 20-6 on page 155 for BODLEVEL Fuse decoding.
Configuration bits are not affected by a chip erase but they can be cleared using the configuration section erase
command (see “Erasing the Configuration Section” on page 150). Note that configuration bits are locked if NonVolatile Lock Bit 1 (NVLB1) is programmed.
19.3.3.1
Latching of Configuration Bits
All configuration bits are latched either when the device is reset or when the device exits the external programming
mode. Changes to configuration bit values have no effect until the device leaves the external programming mode.
19.3.4
Signature Section
The signature section is a dedicated memory area used for storing miscellaneous device information, such as the
device signature. Most of this memory section is reserved for internal use, as shown in Table 19-6.
Table 19-6.
Signature bytes
Signature word data
Signature word address
High byte
Low byte
0x00
Device ID 1
Manufacturer ID
0x01
Reserved for internal use
Device ID 2
0x02 ... 0x3F
Reserved for internal use
Reserved for internal use
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ATtiny40 has a three-byte signature code, which can be used to identify the device. The three bytes reside in the
signature section, as shown in Table 19-6. The signature data for ATtiny40 is given in Table 19-7.
Table 19-7.
Signature codes
Signature Bytes
Part
Manufacturer ID
Device ID 1
Device ID 2
0x1E
0x92
0x0E
ATtiny40
19.3.5
Calibration Section
ATtiny40 has one calibration byte. The calibration byte contains the calibration data for the internal oscillator and
resides in the calibration section, as shown in Table 19-8. During reset, the calibration byte is automatically written
into the OSCCAL register to ensure correct frequency of the calibrated internal oscillator.
Table 19-8.
Calibration byte
Calibration word data
Calibration word address
High byte
Low byte
0x00
Reserved
Internal oscillator calibration value
0x01 ... 0x1F
Reserved
Reserved
19.3.5.1
Latching of Calibration Value
To ensure correct frequency of the calibrated internal oscillator the calibration value is automatically written into the
OSCCAL register during reset.
19.4
Accessing the NVM
NVM lock bits, and all Flash memory sections are mapped to the data space as shown in Figure 5-1 on page 14.
The NVM can be accessed for read and programming via the locations mapped in the data space.
The NVM Controller recognises a set of commands that can be used to instruct the controller what type of programming task to perform on the NVM. Commands to the NVM Controller are issued via the NVM Command
Register. See “NVMCMD – Non-Volatile Memory Command Register” on page 151. After the selected command
has been loaded, the operation is started by writing data to the NVM locations mapped to the data space.
When the NVM Controller is busy performing an operation it will signal this via the NVM Busy Flag in the NVM Control and Status Register. See “NVMCSR – Non-Volatile Memory Control and Status Register” on page 151. The
NVM Command Register is blocked for write access as long as the busy flag is active. This is to ensure that the
current command is fully executed before a new command can start.
Programming any part of the NVM will automatically inhibit the following operations:
• All programming to any other part of the NVM
• All reading from any NVM location
The ATtiny40 supports only external programming. Internal programming operations to the NVM have been disabled, which means any internal attempt to write or erase NVM locations will fail.
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19.4.1
Addressing the Flash
The data space uses byte accessing but since the Flash sections are accessed as words and organized in pages,
the byte-address of the data space must be converted to the word-address of the Flash section. This is illustrated
in Figure 19-1. Also, see Table 19-3 on page 145.
Figure 19-1. Addressing the Flash Memory
16
PADDRMSB
WADDRMSB+1 WADDRMSB
PADDR
WADDR
1
0/1
ADDRESS POINTER
LOW/HIGH
BYTE SELECT
FLASH
SECTION
FLASH
PAGE
00
00
01
01
02
...
...
...
PAGE
PAGE ADDRESS
WITHIN A FLASH
SECTION
WORD
WORD ADDRESS
WITHIN A FLASH
PAGE
...
...
...
PAGEEND
SECTIONEND
The most significant bits of the data space address select the NVM Lock bits or the Flash section mapped to the
data memory. The word address within a page (WADDR) is held by the bits [WADDRMSB:1], and the page
address (PADDR) is held by the bits [PADDRMSB:WADDRMSB+1]. Together, PADDR and WADDR form the
absolute address of a word in the Flash section.
The least significant bit of the Flash section address is used to select the low or high byte of the word.
19.4.2
Reading the Flash
The Flash can be read from the data memory mapped locations one byte at a time. For read operations, the least
significant bit (bit 0) is used to select the low or high byte in the word address. If this bit is zero, the low byte is read,
and if it is one, the high byte is read.
19.4.3
Programming the Flash
The Flash can be written four words at a time. Before writing a Flash words, the Flash target location must be
erased. Writing to an un-erased Flash word will corrupt its content.
The Flash is written four words at a time but the data space uses byte-addressing to access Flash that has been
mapped to data memory. It is therefore important to write the four words in the correct order to the Flash, namely
low bytes before high bytes. The low byte of the first word is first written to the temporary buffer, then the high byte.
Writing the low byte and then the high byte to the buffer latches the four words into the Flash write buffer, starting
the actual Flash write operation.
The Flash erase operations can only performed for the entire Flash sections.
The Flash programming sequence is as follows:
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1. Perform a Flash section erase or perform a Chip erase
2. Write the Flash section four words at a time
19.4.3.1
Chip Erase
The Chip Erase command will erase the entire code section of the Flash memory and the NVM Lock Bits. For
security reasons, however, the NVM Lock Bits are not reset before the code section has been completely erased.
The Configuration, Signature and Calibration sections are not changed.
Before starting the Chip erase, the NVMCMD register must be loaded with the CHIP_ERASE command. To start
the erase operation a dummy byte must be written into the high byte of a word location that resides inside the Flash
code section. The NVMBSY bit remains set until erasing has been completed. While the Flash is being erased neither Flash buffer loading nor Flash reading can be performed.
The Chip Erase can be carried out as follows:
1. Write the CHIP_ERASE command to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the code
section
3. Wait until the NVMBSY bit has been cleared
19.4.3.2
Erasing the Code Section
The algorithm for erasing all pages of the Flash code section is as follows:
1. Write the SECTION_ERASE command to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the code
section
3. Wait until the NVMBSY bit has been cleared
19.4.3.3
Writing Flash Code Words
The algorithm for writing four words to the code section is as follows:
1. Write the CODE_WRITE command to the NVMCMD register
2. Write the low byte of the 1st word to the low byte of a target word location
3. Write the high byte of the 1st word to the high byte of the same target word location
4. Send IDLE character as described in section “Supported Characters” on page 136
5. Write the low byte of the 2nd word to the low byte of the next target word location
6. Write the high byte of the 2nd word to the high byte of the same target word location.
7. Send IDLE character as described in section “Supported Characters” on page 136
8. Write the low byte of the 3rd word to the low byte of a target word location
9. Write the high byte of the 3rd word to the high byte of the same target word location
10. Send IDLE character as described in section “Supported Characters” on page 136
11. Write the low byte of the 4th word to the low byte of the next target word location
12. Write the high byte of the 4th word to the high byte of the same target word location. This will start the
Flash write operation
13. Wait until the NVMBSY bit has been cleared
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19.4.3.4
Erasing the Configuration Section
The algorithm for erasing the Configuration section is as follows:
1. Write the SECTION_ERASE command to the NVMCMD register
2. Start the erase operation by writing a dummy byte to the high byte of any word location inside the configuration section
3. Wait until the NVMBSY bit has been cleared
19.4.3.5
Writing a Configuration Word
The algorithm for writing a Configuration word is as follows.
1. Write the CODE_WRITE command to the NVMCMD register
2. Write the low byte of the data word to the low byte of the configuration word location
3. Write the high byte of the data word to the high byte of the same configuration word location
4. Send IDLE character as described in section “Supported Characters” on page 136
5. Write a dummy byte to the low byte of the next configuration word location
6. Write a dummy byte to the high byte of the same configuration word location.
7. Send IDLE character as described in section “Supported Characters” on page 136
8. Write a dummy byte to the low byte of the next configuration word location
9. Write a dummy byte to the high byte of the same configuration word location.
10. Send IDLE character as described in section “Supported Characters” on page 136
11. Write a dummy byte to the low byte of the next configuration word location
12. Write a dummy byte to the high byte of the same configuration word location. This will start the Flash write
operation
13. Wait until the NVMBSY bit has been cleared
19.4.4
Reading NVM Lock Bits
The Non-Volatile Memory Lock Byte can be read from the mapped location in data memory.
19.4.5
Writing NVM Lock Bits
The algorithm for writing the Lock bits is as follows.
1. Write the CODE_WRITE command to the NVMCMD register.
2. Write the lock bits value to the Non-Volatile Memory Lock Byte location. This is the low byte of the NonVolatile Memory Lock Word.
3. Start the NVM Lock Bit write operation by writing a dummy byte to the high byte of the NVM Lock Word
location.
4. Wait until the NVMBSY bit has been cleared.
19.5
Self programming
The ATtiny40 doesn't support internal programming.
19.6
External Programming
The method for programming the Non-Volatile Memories by means of an external programmer is referred to as
external programming. External programming can be done both in-system or in mass production.
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The Non-Volatile Memories can be externally programmed via the Tiny Programming Interface (TPI). For details
on the TPI, see “Programming Interface” on page 134. Using the TPI, the external programmer can access the
NVM control and status registers mapped to I/O space and the NVM memory mapped to data memory space.
19.6.1
Entering External Programming Mode
The TPI must be enabled before external programming mode can be entered. The following procedure describes,
how to enter the external programming mode after the TPI has been enabled:
1. Make a request for enabling NVM programming by sending the NVM memory access key with the SKEY
instruction.
2. Poll the status of the NVMEN bit in TPISR until it has been set.
Refer to the Tiny Programming Interface description on page 134 for more detailed information of enabling the TPI
and programming the NVM.
19.6.2
Exiting External Programming Mode
Clear the NVM enable bit to disable NVM programming, then release the RESET pin.
See NVMEN bit in “TPISR – Tiny Programming Interface Status Register” on page 143.
19.7
19.7.1
Register Description
NVMCMD – Non-Volatile Memory Command Register
• Bits 7:6 – Res: Reserved Bits
These bits are reserved and will always read as zero.
• Bits 5:0 – NVMCMD[5:0]: Non-Volatile Memory Command
These bits define the programming commands for the flash, as shown in Table 19-9.
Table 19-9.
NVM Programming commands
NVMCMD
Operation Type
Binary
Hex
Mnemonic
Description
0b000000
0x00
NO_OPERATION
No operation
0b010000
0x10
CHIP_ERASE
Chip erase
Section
0b010100
0x14
SECTION_ERASE
Section erase
Flash Words
0b011101
0x1D
CODE_WRITE
Write Flash words
General
19.7.2
NVMCSR – Non-Volatile Memory Control and Status Register
• Bit 7 – NVMBSY: Non-Volatile Memory Busy
This bit indicates the NVM memory (Flash memory and Lock Bits) is busy, being programmed. This bit is set when
a program operation is started, and it remains set until the operation has been completed.
• Bits 6:0 – Res: Reserved Bits
These bits are reserved and will always read as zero.
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20. Electrical Characteristics
20.1
Absolute Maximum Ratings*
Operating Temperature.................................. -55C to +125C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins ................................ 200.0 mA
20.2
DC Characteristics
Table 20-1.
Symbol
DC Characteristics. TA = -40C to +85C
Parameter
Condition
Min
Typ(1)
Max
Units
(3)
Input Low Voltage
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
0.2VCC
0.3VCC(3)
V
Input High-voltage
Except RESET pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC +0.5
V
Input High-voltage
RESET pin
VCC = 1.8V - 5.5V
0.9VCC(2)
VCC +0.5
V
VOL
Output Low Voltage(4)
Except RESET pin(6)
IOL = 10 mA, VCC = 5V
IOL = 5 mA, VCC = 3V
0.6
0.5
V
VOH
Output High-voltage(5)
Except RESET pin(6)
IOH = -10 mA, VCC = 5V
IOH = -5 mA, VCC = 3V
ILIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value)
<0.05
1
µA
ILIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value)
<0.05
1
µA
RRST
Reset Pull-up Resistor
VCC = 5.5V, input low
30
60
k
RPU
I/O Pin Pull-up Resistor
VCC = 5.5V, input low
20
50
k
IACLK
Analog Comparator
Input Leakage Current
VCC = 5V
Vin = VCC/2
-50
50
nA
VIL
VIH
4.3
2.5
V
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Table 20-1.
Symbol
DC Characteristics. TA = -40C to +85C (Continued)
Parameter
Power Supply Current(7)
ICC
Power-down mode(8)
Notes:
Typ(1)
Max
Units
Active 1MHz, VCC = 2V
0.2
0.6
mA
Active 4MHz, VCC = 3V
1.1
2
mA
Active 8MHz, VCC = 5V
3.2
5
mA
Idle 1MHz, VCC = 2V
0.03
0.2
mA
Idle 4MHz, VCC = 3V
0.2
0.5
mA
Idle 8MHz, VCC = 5V
0.8
1.5
mA
WDT enabled, VCC = 3V
4.5
10
µA
WDT disabled, VCC = 3V
0.15
2
µA
Condition
Min
1. Typical values at 25C.
2. “Min” means the lowest value where the pin is guaranteed to be read as high.
3. “Max” means the highest value where the pin is guaranteed to be read as low.
4. Although each I/O port can sink more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the sum of all IOL (for all ports) should not exceed 60 mA. If IOL exceeds the test conditions, VOL
may exceed the related specification. Pins are not guaranteed to sink current greater than the listed test condition.
5. Although each I/O port can source more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state
conditions (non-transient), the sum of all IOH (for all ports) should not exceed 60 mA. If IOH exceeds the test condition, VOH
may exceed the related specification. Pins are not guaranteed to source current greater than the listed test condition.
6. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence,
has a weak drive strength as compared to regular I/O pins. See Figure 21-32 to Figure 21-37, starting from page 175.
7. Values are with external clock using methods described in “Minimizing Power Consumption” on page 25. Power Reduction is
enabled (PRR = 0xFF) and there is no I/O drive.
8. BOD Disabled.
20.3
Speed
The maximum operating frequency of the device depends on VCC . As shown in Figure 20-1, the relationship
between maximum frequency vs. VCC is linear between 1.8V < VCC < 2.7V, and 2.7V < VCC < 4.5V.
Figure 20-1. Maximum Frequency vs. VCC
12 MHz
8 MHz
4 MHz
1.8V
2.7V
4.5V
5.5V
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20.4
Clock Characteristics
20.4.1
Accuracy of Calibrated Internal Oscillator
It is possible to manually calibrate the internal oscillator to be more accurate than default factory calibration. Note
that the oscillator frequency depends on temperature and voltage. Voltage and temperature characteristics can be
found in Figure 21-55 on page 187 and Figure 21-56 on page 187.
Table 20-2.
Calibration Accuracy of Internal RC Oscillator
Calibration
Method
Target Frequency
VCC
Temperature
Accuracy at given Voltage
& Temperature(1)
Factory
Calibration
8.0 MHz
3V
25C
±10%
User
Calibration
Fixed frequency within:
7.3 – 8.1 MHz
Fixed voltage within:
1.8V – 5.5V
Fixed temp. within:
-40C to +85C
±1%
Notes:
1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
20.4.2
External Clock Drive
Figure 20-2. External Clock Drive Waveform
V IH1
V IL1
Table 20-3.
External Clock Drive Characteristics
VCC = 1.8 - 5.5V
VCC = 2.7 - 5.5V
VCC = 4.5 - 5.5V
Min.
Max.
Min.
Max.
Min.
Max.
Units
0
4
0
8
0
12
MHz
Symbol
Parameter
1/tCLCL
Clock Frequency
tCLCL
Clock Period
250
125
83
ns
tCHCX
High Time
100
40
20
ns
tCLCX
Low Time
100
40
20
ns
tCLCH
Rise Time
2.0
1.6
0.5
µs
tCHCL
Fall Time
2.0
1.6
0.5
µs
tCLCL
Change in period from one clock cycle to the next
2
2
2
%
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20.5
System and Reset Characteristics
Table 20-4.
Symbol
20.5.1
Reset and Internal Voltage Characteristics
Parameter
Condition
VRST
RESET Pin Threshold
Voltage
VBG
Internal bandgap voltage
VCC = 2.7V
TA = 25°C
tRST
Minimum pulse width on
RESET Pin
VCC = 1.8V
VCC = 3V
VCC = 5V
tTOUT
Time-out after reset
Min
Typ
0.2 VCC
1.0
Max
Units
0.9VCC
V
1.2
V
1.1
2000
700
400
64
ns
128
ms
Power-On Reset
Table 20-5.
Symbol
VPOR
Characteristics of Enhanced Power-On Reset. TA = -40 to +85C
Parameter
Release threshold of power-on reset
Typ(1)
Max(1)
Units
1.1
1.4
1.6
V
0.6
1.3
1.6
V
(2)
VPOA
Activation threshold of power-on reset
SRON
Power-on Slope Rate
Note:
Min(1)
(3)
0.01
V/ms
1. Values are guidelines, only
2. Threshold where device is released from reset when voltage is rising
3. The Power-on Reset will not work unless the supply voltage has been below VPOT (falling)
20.5.2
Brown-Out Detection
Table 20-6.
VBOT vs. BODLEVEL Fuse Coding
BODLEVEL[2:0] Fuses
Min(1)
111
Max(1)
Units
BOD Disabled
110
1.7
1.8
2.0
101
2.5
2.7
2.9
100
4.1
4.3
4.5
0XX
Note:
Typ(1)
V
Reserved
1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case, the
device is tested down to VCC = VBOT during the production test. This guarantees that a Brown-out Reset will occur
before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed.
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20.6
Two-Wire Serial Interface Characteristics
The following data is based on simulations and characterisations. Parameters listed in Table 20-7 are not tested in production. Symbols refer to Figure 20-3.
Table 20-7.
Two-Wire Serial Interface Characteristics
Symbol
Parameter
VIL
Condition
Min
Max
Unit
Input Low voltage
-0.5
0.3 VCC
V
VIH
Input High voltage
0.7 VCC
VCC + 0.5
V
VHYS
Hysteresis of Schmitt-trigger inputs
VOL
Output Low voltage
tSP
Spikes suppressed by input filter
VCC  2.7V
0.05 VCC
VCC < 2.7V
0
IOL = 3mA, VCC > 2.7V
V
–
0
0.4
V
0
50
ns
0
400
kHz
IOL = 2mA, VCC < 2.7V
(1)
fSCL
SCL clock frequency
tHD:STA
Hold time (repeated) START Condition
0.6
–
µs
tLOW
Low period of SCL clock
1.3
–
µs
tHIGH
High period of SCL clock
0.6
–
µs
tSU:STA
Set-up time for repeated START condition
0.6
–
µs
tHD:DAT
Data hold time
0
0.9
µs
tSU:DAT
Data setup time
100
–
ns
tSU:STO
Setup time for STOP condition
0.6
–
µs
tBUF
Bus free time between STOP and START condition
1.3
–
µs
Notes:
fCK > max(16fSCL, 250kHz)
1. fCK = CPU clock frequency.
Figure 20-3. Two-Wire Serial Bus Timing
tOF
tHIGH
tLOW
SCL
tSU:STA
tHD:STA
tR
tLOW
tHD:DAT
tSU:DAT
tSU:STO
SDA
tBUF
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20.7
Analog Comparator Characteristics
Table 20-8.
Analog Comparator Characteristics, TA = -40C to +85C
Symbol
Parameter
Condition
VAIO
Input Offset Voltage
VCC = 5V, VIN = VCC / 2
ILAC
Input Leakage Current
VCC = 5V, VIN = VCC / 2
Analog Propagation Delay
(from saturation to slight overdrive)
VCC = 2.7V
750
VCC = 4.0V
500
Analog Propagation Delay
(large step change)
VCC = 2.7V
100
VCC = 4.0V
75
tDPD
Digital Propagation Delay
VCC = 1.8V - 5.5
1
20.8
ADC Characteristics
tAPD
Table 20-9.
Symbol
Min
Units
< 10
40
mV
50
nA
ns
2
CLK
ADC Characteristics. T = -40C to +85C. VCC = 2.5V – 5.5V
Parameter
Absolute accuracy
(Including INL, DNL, and
Quantization, Gain and Offset
Errors)
Condition
Min
Typ
Max
Units
10
Bits
VREF = VCC = 4V,
ADC clock = 200 kHz
2
LSB
VREF = VCC = 4V,
ADC clock = 1 MHz
3
LSB
VREF = VCC = 4V,
ADC clock = 200 kHz
Noise Reduction Mode
1.5
LSB
VREF = VCC = 4V,
ADC clock = 1 MHz
Noise Reduction Mode
2.5
LSB
Integral Non-Linearity (INL)
(Accuracy after Offset and
Gain Calibration)
VREF = VCC = 4V,
ADC clock = 200 kHz
1
LSB
Differential Non-linearity
(DNL)
VREF = VCC = 4V,
ADC clock = 200 kHz
0.5
LSB
Gain Error
VREF = VCC = 4V,
ADC clock = 200 kHz
2.5
LSB
Offset Error
VREF = VCC = 4V,
ADC clock = 200 kHz
1.5
LSB
Conversion Time
Free Running Conversion
Clock Frequency
RAIN
Max
-50
Resolution
VIN
Typ
Input Voltage
13
260
µs
50
1000
kHz
GND
VREF
V
Input Bandwidth
38.5
kHz
Analog Input Resistance
100
M
ADC Conversion Output
0
1023
LSB
ATtiny40 [DATASHEET]
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20.9
Serial Programming Characteristics
Figure 20-4. Serial Programming Timing
Receive Mode
Transmit Mode
TPIDATA
t IVCH
t CLOV
t CHIX
TPICLK
t CLCH
t CHCL
t CLCL
Table 20-10. Serial Programming Characteristics, TA = -40C to +85C, VCC = 5V ±5%
Symbol
1/tCLCL
Parameter
Min
Clock Frequency
Typ
Max
Units
2
MHz
tCLCL
Clock Period
500
ns
tCLCH
Clock Low Pulse Width
200
ns
tCHCH
Clock High Pulse Width
200
ns
tIVCH
Data Input to Clock High Setup Time
50
ns
tCHIX
Data Input Hold Time After Clock High
100
ns
tCLOV
Data Output Valid After Clock Low Time
200
ns
ATtiny40 [DATASHEET]
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21. Typical Characteristics
The data contained in this section is largely based on simulations and characterization of similar devices in the
same process and design methods. Thus, the data should be treated as indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing. During characterisation devices are operated at frequencies higher than test limits but they are not guaranteed to function properly
at frequencies higher than the ordering code indicates.
All current consumption measurements are performed with all I/O pins configured as inputs and with internal pullups enabled. Current consumption is a function of several factors such as operating voltage, operating frequency,
loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are
operating voltage and frequency.
A sine wave generator with rail-to-rail output is used as clock source but current consumption in Power-down mode
is independent of clock selection. The difference between current consumption in Power-down mode with Watchdog Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn
by the Watchdog Timer.
The current drawn from pins with a capacitive load may be estimated (for one pin) as follows:
I CP  V CC  C L  f SW
where VCC = operating voltage, CL = load capacitance and fSW = average switching frequency of pin.
21.1
Supply Current of I/O Modules
The tables and formulas below can be used to calculate the additional current consumption for the different I/O
modules in Active and Idle mode. The enabling or disabling of the I/O modules is controlled by the Power Reduction Register. See “Power Reduction Register” on page 25 for details.
Table 21-1.
Additional Current Consumption for different I/O modules (absolute values)
PRR bit
Typical numbers
VCC = 2V, f = 1MHz
VCC = 3V, f = 4MHz
VCC = 5V, f = 8MHz
PRTIM0
4 µA
25 µA
110 µA
PRTIM1
5 µA
35 µA
150 µA
PRADC
190 µA
260 µA
470 µA
PRSPI
3 µA
15 µA
75 µA
PRTWI
5 µA
35 µA
160 µA
Table 21-2 below can be used for calculating typical current consumption for other supply voltages and frequencies
than those mentioned in the Table 21-1 above.
Table 21-2.
Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Current consumption additional to
active mode with external clock
(see Table 21-1 and Table 21-2)
Current consumption additional to
idle mode with external clock
(see Table 21-7 and Table 21-8)
PRTIM0
2%
15 %
PRTIM1
3%
20 %
PRADC
See Figure 21-16 on page 167
See Figure 21-16 on page 167
PRSPI
2%
10 %
PRTWI
4%
20 %
ATtiny40 [DATASHEET]
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Current Consumption in Active Mode
Figure 21-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
0,9
0,8
5.5 V
0,7
5.0 V
0,6
ICC [mA]
4.5 V
0,5
4.0 V
0,4
3.3 V
0,3
2.7 V
0,2
1.8 V
0,1
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Frequency [MHz]
Figure 21-2. Active Supply Current vs. Frequency (1 - 12 MHz)
6
5.5 V
5
5.0 V
4.5 V
4
ICC [mA]
21.2
4.0 V
3
3.3 V
2
2.7 V
1
1.8 V
0
0
2
4
6
8
10
12
Frequency [MHz]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
160
Figure 21-3. Active Supply Current vs. VCC (Internal Oscillator, 8 MHz)
4,5
85 °C
25 °C
-40 °C
4
3,5
ICC [mA]
3
2,5
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-4. Active Supply Current vs. VCC (Internal Oscillator, 1 MHz)
1
85 °C
25 °C
-40 °C
0,9
0,8
0,7
ICC [mA]
0,6
0,5
0,4
0,3
0,2
0,1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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Figure 21-5. Active Supply Current vs. VCC (Internal Oscillator, 128 kHz)
0,12
-40 °C
25 °C
85 °C
0,1
ICC [mA]
0,08
0,06
0,04
0,02
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-6. Active Supply Current vs. VCC (Internal Oscillator, 32kHz)
0,045
0,04
-40 °C
25 °C
85 °C
0,035
ICC [mA]
0,03
0,025
0,02
0,015
0,01
0,005
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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Current Consumption in Idle Mode
Figure 21-7. Idle Supply Current vs. Low Frequency (0.1 - 1.0 MHz)
0,12
5.5 V
0,1
5.0 V
4.5 V
ICC [mA]
0,08
4.0 V
0,06
3.3 V
0,04
2.7 V
1.8 V
0,02
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Frequency [MHz]
Figure 21-8. Idle Supply Current vs. Frequency (1 - 12 MHz)
1,4
5.5 V
1,2
5.0 V
1
4.5 V
0,8
ICC [mA]
21.3
4.0 V
0,6
3.3 V
0,4
2.7 V
0,2
1.8 V
0
0
2
4
6
8
10
12
Frequency [MHz]
ATtiny40 [DATASHEET]
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163
Figure 21-9. Idle Supply Current vs. VCC (Internal Oscillator, 8 MHz)
1
85 °C
25 °C
-40 °C
0,9
0,8
0,7
ICC [mA]
0,6
0,5
0,4
0,3
0,2
0,1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-10. Idle Supply Current vs. VCC (Internal Oscillator, 1 MHz)
0,3
-40 °C
25 °C
85 °C
0,25
ICC [mA]
0,2
0,15
0,1
0,05
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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Figure 21-11. Idle Supply Current vs. VCC (Internal Oscillator, 128 kHz)
0,03
-40 °C
25 °C
85 °C
0,025
ICC [mA]
0,02
0,015
0,01
0,005
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-12. Idle Supply Current vs. VCC (Internal Oscillator, 32kHz)
0,025
-40 °C
25 °C
85 °C
0,02
ICC [mA]
0,015
0,01
0,005
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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165
Current Consumption in Power-down Mode
Figure 21-13. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
0,8
85 °C
0,7
0,6
ICC [uA]
0,5
0,4
0,3
0,2
25 °C
-40 °C
0,1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-14. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
12
-40 °C
10
25 °C
85 °C
8
ICC [uA]
21.4
6
4
2
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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21.5
Current Consumption in Reset
Figure 21-15. Reset Supply Current vs. VCC (excluding Current Through the Reset Pull-up and No Clock
4,5
4
3,5
ICC [mA]
3
2,5
2
1,5
85 °C
1
-40 °C
25 °C
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
4
4,5
5
5,5
VCC [V]
Current Consumption of Peripheral Units
Figure 21-16. ADC Current vs. VCC
400
350
300
250
ICC [uA]
21.6
200
150
100
50
0
1,5
2
2,5
3
3,5
VCC [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
167
Figure 21-17. Analog Comparator Current vs. VCC (Frequency 1 MHz)
140
120
100
ICC [uA]
80
60
40
20
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-18. Watchdog Timer Current vs. VCC
12
-40 °C
10
25 °C
85 °C
ICC [uA]
8
6
4
2
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
168
Figure 21-19. Brownout Detector Current vs. VCC
30
25
85 °C
25 °C
-40 °C
ICC [uA]
20
15
10
5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Pull-up Resistors
Figure 21-20. I/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
50
45
40
35
30
IOP [uA]
21.7
25
20
15
10
5
25 °C
85 °C
-40 °C
0
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
VOP [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
169
Figure 21-21. I/O Pin Pull-up Resistor Current vs. input Voltage (VCC = 2.7V)
80
70
60
IOP [uA]
50
40
30
20
10
25 °C
85 °C
-40 °C
0
0
0,5
1
1,5
2
2,5
3
VOP [V]
Figure 21-22. I/O pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
160
140
120
IOP [uA]
100
80
60
40
20
25 °C
85 °C
-40 °C
0
0
1
2
3
4
5
6
VOP [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
170
Figure 21-23. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
40
35
30
IRESET [uA]
25
20
15
10
5
25 °C
-40 °C
85 °C
0
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
VRESET [V]
Figure 21-24. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
60
50
IRESET [uA]
40
30
20
10
25 °C
-40 °C
85 °C
0
0
0,5
1
1,5
2
2,5
3
VRESET [V]
ATtiny40 [DATASHEET]
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Figure 21-25. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
120
100
IRESET [uA]
80
60
40
20
25 °C
-40 °C
85 °C
0
0
1
2
3
5
4
6
VRESET [V]
Output Driver Strength
Figure 21-26. VOL: Output Voltage vs. Sink Current (I/O Pin, VCC = 1.8V)
0,8
0,7
85 °C
0,6
0,5
VOL [V]
21.8
25 °C
0,4
-40 °C
0,3
0,2
0,1
0
0
1
2
3
4
5
IOL [mA]
ATtiny40 [DATASHEET]
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172
Figure 21-27. VOL: Output Voltage vs. Sink Current (I/O Pin, VCC = 3V)
0,8
0,7
85 °C
0,6
VOL [V]
0,5
25 °C
0,4
-40 °C
0,3
0,2
0,1
0
0
1
2
3
4
5
6
7
8
9
10
IOL [mA]
Figure 21-28. VOL: Output Voltage vs. Sink Current (I/O Pin, VCC = 5V)
1
85 °C
0,8
25 °C
0,6
VOL [V]
-40 °C
0,4
0,2
0
0
2
4
6
8
10
12
14
16
18
20
IOL [mA]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
173
Figure 21-29. VOH: Output Voltage vs. Source Current (I/O Pin, VCC = 1.8V)
2
1,8
1,6
1,4
-40 °C
VOH [V]
1,2
25 °C
1
85 °C
0,8
0,6
0,4
0,2
0
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
IOH [mA]
Figure 21-30. VOH: Output Voltage vs. Source Current (I/O Pin, VCC = 3V)
3,5
3
-40 °C
25 °C
85 °C
2,5
VOH [V]
2
1,5
1
0,5
0
0
1
2
3
4
5
6
7
8
9
10
IOH [mA]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
174
Figure 21-31. VOH: Output Voltage vs. Source Current (I/O Pin, VCC = 5V)
5,1
5
4,9
4,8
VOH [V]
4,7
4,6
4,5
-40 °C
4,4
4,3
25 °C
4,2
85 °C
4,1
0
2
4
6
8
10
12
14
16
18
20
IOH [mA]
Figure 21-32. VOL: Output Voltage vs. Sink Current (Reset Pin as I/O, VCC = 1.8V)
1
0,8
VOL [V]
0,6
0,4
85 °C
25 °C
-40 °C
0,2
0
0
0,1
0,2
0,3
0,4
0,5
0,6
IOL [mA]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
175
Figure 21-33. VOL: Output Voltage vs. Sink Current (Reset Pin as I/O, VCC = 3V)
2
1,8
1,6
1,4
VOL [V]
1,2
85 °C
1
0,8
25 °C
0,6
-40 °C
0,4
0,2
0
0
0,5
1
1,5
2,5
2
3
IOL [mA]
Figure 21-34. VOL: Output Voltage vs. Sink Current (Reset Pin as I/O, VCC = 5V)
2
1,8
1,6
1,4
VOL [V]
1,2
1
85 °C
0,8
25 °C
0,6
-40 °C
0,4
0,2
0
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
IOL [mA]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
176
Figure 21-35. VOH: Output Voltage vs. Source Current (Reset Pin as I/O, VCC = 1.8V
1,6
1,4
1,2
VOH [V]
1
0,8
0,6
85 °C
0,4
25 °C
-40 °C
0,2
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
IOH [mA]
Figure 21-36. VOH: Output Voltage vs. Source Current (Reset Pin as I/O, VCC = 3V
3
2,5
VOH [V]
2
1,5
85 °C
25 °C
-40 °C
1
0,5
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
IOH [mA]
ATtiny40 [DATASHEET]
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177
Figure 21-37. VOH: Output Voltage vs. Source Current (Reset Pin as I/O, VCC = 5V
4,5
4
3,5
85 °C
25 °C
-40 °C
VOH [V]
3
2,5
2
1,5
1
0,5
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
IOH [mA]
Input Thresholds and Hysteresis
Figure 21-38. VIH: Input Threshold Voltage vs. VCC (I/O Pin, Read as ‘1’)
3
85 °C
25 °C
-40 °C
2,5
2
Threshold [V]
21.9
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
178
Figure 21-39. VIL: Input Threshold Voltage vs. VCC (I/O Pin, Read as ‘0’)
2,5
85 °C
25 °C
-40 °C
Threshold [V]
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
4
4,5
5
5,5
VCC [V]
Figure 21-40. VIH-VIL: Input Hysteresis vs. VCC (I/O Pin)
0,6
-40 °C
0,5
25 °C
Hysteresis [V]
0,4
85 °C
0,3
0,2
0,1
0
1,5
2
2,5
3
3,5
VCC [V]
ATtiny40 [DATASHEET]
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179
Figure 21-41. VIH: Input Threshold Voltage vs. VCC (Reset Pin as I/O, Read as ‘1’)
3,5
3
-40 °C
25 °C
85 °C
Threshold [V]
2,5
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-42. VIL: Input Threshold Voltage vs. VCC (Reset Pin as I/O, Read as ‘0’)
2,5
85 °C
25 °C
-40 °C
Threshold [V]
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
180
Figure 21-43. VIH-VIL: Input Hysteresis vs. VCC (Reset Pin as I/O)
0,8
-40 °C
0,7
0,6
25 °C
Hysteresis [V]
0,5
85 °C
0,4
0,3
0,2
0,1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
21.10 BOD, Bandgap and Reset
Figure 21-44. BOD Threshold vs Temperature (BODLEVEL is 4.3V)
4,34
VCC RISING
4,32
4,3
Threshold [V]
4,28
4,26
VCC FALLING
4,24
4,22
4,2
4,18
4,16
-40
-20
0
20
40
60
80
100
Temperature [°C]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
181
Figure 21-45. BOD Threshold vs Temperature (BODLEVEL is 2.7V)
2,76
VCC RISING
2,74
Threshold [V]
2,72
2,7
VCC FALLING
2,68
2,66
2,64
2,62
-40
-20
0
20
40
60
80
100
Temperature [°C]
Figure 21-46. BOD Threshold vs Temperature (BODLEVEL is 1.8V)
1,83
1,82
VCC RISING
1,81
Threshold [V]
1,8
VCC FALLING
1,79
1,78
1,77
1,76
1,75
-40
-20
0
20
40
60
80
100
Temperature [°C]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
182
Figure 21-47. Bandgap Voltage vs. Supply Voltage
1,09
1,085
1,08
Bandgap [V]
1,075
85 °C
1,07
1,065
25 °C
1,06
1,055
-40 °C
1,05
1,045
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-48. VIH: Input Threshold Voltage vs. VCC (Reset Pin, Read as ‘1’)
2,5
-40 °C
25 °C
85 °C
Threshold [V]
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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Figure 21-49. VIL: Input Threshold Voltage vs. VCC (Reset Pin, Read as ‘0’)
2,5
-40 °C
25 °C
85 °C
Threshold [V]
2
1,5
1
0,5
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-50. VIH-VIL: Input Hysteresis vs. VCC (Reset Pin )
0,6
-40 °C
0,5
Hysteresis [V]
0,4
25 °C
0,3
85 °C
0,2
0,1
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
ATtiny40 [DATASHEET]
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Figure 21-51. Minimum Reset Pulse Width vs. VCC
2500
Pulsewidth [ns]
2000
1500
1000
500
85 °C
25 °C
-40 °C
0
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
21.11 Analog Comparator Offset
Figure 21-52. Analog Comparator Offset vs. Vin (VCC = 5V)
0
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
-0,002
Offset [V]
-0,004
-0,006
85 °C
-0,008
25 °C
-0,01
-0,012
-40 °C
-0,014
Vin [V]
ATtiny40 [DATASHEET]
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21.12 Internal Oscillator Speed
Figure 21-53. Watchdog Oscillator Frequency vs. VCC
0,109
0,108
0,107
-40 °C
0,106
FRC [MHz]
0,105
25 °C
0,104
0,103
0,102
0,101
85 °C
0,1
0,099
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-54. Watchdog Oscillator Frequency vs. Temperature
0,109
0,108
0,107
0,106
FRC [MHz]
0,105
0,104
1.8 V
0,103
0,102
2.8 V
0,101
3.5 V
4.0 V
0,1
5.5 V
0,099
-40
-20
0
20
40
60
80
100
Temperature [°C ]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
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Figure 21-55. Calibrated Oscillator Frequency vs. VCC
8,5
8,4
-40 °C
8,3
25 °C
FRC [MHz]
8,2
8,1
85 °C
8
7,9
7,8
7,7
1,5
2
2,5
3
3,5
4
4,5
5
5,5
VCC [V]
Figure 21-56. Calibrated Oscillator Frequency vs. Temperature
8,3
8,2
FRC [MHz]
8,1
8
5.0 V
7,9
3.0 V
7,8
1.8 V
7,7
-40
-20
0
20
40
60
80
100
Temperature [°C ]
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
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Figure 21-57. Calibrated Oscillator Frequency vs, OSCCAL Value
16
-40 °C
25 °C
85 °C
14
12
FRC [MHz]
10
8
6
4
2
0
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL [X1]
ATtiny40 [DATASHEET]
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22. Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x3F
SREG
I
T
H
S
V
N
Z
C
Page 12
0x3E
SPH
Stack Pointer High Byte
Page 12
0x3D
SPL
Stack Pointer Low Byte
Page 12
Note:
0x3C
CCP
0x3B
RSTFLR
–
–
–
0x3A
MCUCR
ISC01
ISC00
–
0x39
OSCCAL
Oscillator Calibration Register
0x38
Reserved
–
0x37
CLKMSR
–
–
–
–
–
–
CLKMS1
CLKMS0
0x36
CLKPSR
–
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Page 22
0x35
–
–
–
PRTWI
PRSPI
PRTIM1
QTouch Control and Status Register
PRTIM0
PRADC
Page 27
0x34
PRR
QTCSR
0x33
NVMCMD
–
–
0x32
NVMCSR
NVMBSY
–
–
–
–
–
–
–
0x31
WDTCSR
WDIF
WDIE
WDP3
–
WDE
WDP2
WDP1
WDP0
Page 33
0x30
SPCR
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
Page 120
SPIF
WCOL
–
–
–
–
–
SPI2X
0x2F
SPSR
0x2E
SPDR
CPU Change Protection Register
Page 11
–
WDRF
BORF
EXTRF
PORF
Page 35
BODS
SM2
SM1
SM0
SE
Pages 26, 38
Page 23
Page 21
Page 5
NVM Command Register
Page 151
Page 151
Page 121
SPI Data Register
Page 122
0x2D
TWSCRA
TWSHE
–
TWDIE
TWASIE
TWEN
TWSIE
0x2C
TWSCRB
–
–
–
–
–
TWAA
0x2B
TWSSRA
TWDIF
TWASIF
TWCH
TWRA
TWC
TWBE
0x2A
TWSA
TWI Slave Address Register
0x29
TWSAM
TWI Slave Address Mask Register
Page 133
0x28
TWSD
TWI Slave Data Register
Page 133
0x27
TCNT1H
0x26
TIMSK
TWPME
TWSME
TWCMD[1.0]
TWDIR
TWAS
–
OCIE1B
OCIE1A
Page 131
Page 133
Timer/Counter1 – Counter Register High Byte
ICIE1
Page 130
Page 130
Page 89
TOIE1
OCIE0B
OCIE0A
TOIE0
Pages 75, 90
0x25
TIFR
ICF1
–
OCF1B
OCF1A
TOV1
OCF0B
OCF0A
TOV0
Pages 76, 90
0x24
TCCR1A
TCW1
ICEN1
ICNC1
ICES1
CTC1
CS12
CS11
CS10
Page 88
0x23
TCNT1L
Timer/Counter1 – Counter Register Low Byte
Page 89
0x22
OCR1A
Timer/Counter1 – Compare Register A
Page 89
0x21
OCR1B
Timer/Counter1 – Compare Register B
Page 89
0x20
RAMAR
RAM Address Register
Page 17
0x1F
RAMDR
0x1E
PUEC
–
–
PUEC5
PUEC4
RAM Data Register
PUEC3
PUEC2
PUEC1
PUEC0
Page 17
0x1D
PORTC
–
–
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
Page 59
0x1C
DDRC
–
–
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
Page 59
0x1B
PINC
–
–
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
Page 59
0x1A
PCMSK2
–
–
PCINT17
PCINT16
PCINT15
PCINT14
PCINT13
PCINT12
Page 40
0x19
TCCR0A
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
Page 71
0x18
TCCR0B
FOC0A
FOC0B
TSM
PSR
WGM02
CS02
CS01
CS00
Pages 74, 93
Page 59
0x17
TCNT0
Timer/Counter0 – Counter Register
Page 75
0x16
OCR0A
Timer/Counter0 – Compare Register A
Page 75
0x15
OCR0B
0x14
ACSRA
ACD
ACBG/ACIRE
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
0x13
ACSRB
HSEL
HLEV
ACLP
–
ACCE
ACME
ACIRS1
ACIRS0
Page 96
0x12
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
Page 111
0x11
ADCSRB
VDEN
VDPD
–
–
ADLAR
ADTS2
ADTS1
ADTS0
Page 112
0x10
ADMUX
–
REFS
REFEN
ADC0EN
MUX3
MUX2
MUX1
MUX0
0x0F
ADCH
Timer/Counter0 – Compare Register B
Page 75
Page 95
Page 109
ADC Conversion Result – High Byte
Page 111
0x0E
ADCL
0x0D
DIDR0
ADC7D
ADC6D
ADC5D
ADC Conversion Result – Low Byte
ADC4D
ADC3D
ADC2D
ADC1D
Page 111
0x0C
GIMSK
–
PCIE2
PCIE1
PCIE0
–
–
0x0B
GIFR
–
PCIF2
PCIF1
PCIF0
–
–
0x0A
PCMSK1
–
–
–
–
PCINT11
ADC0D
Pages 97, 113
–
INT0
Page 39
–
INTF0
Page 40
PCINT10
PCINT9
PCINT8
Page 41
0x09
PCMSK0
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
Page 41
0x08
PORTCR
ADC11D
ADC10D
ADC9D
ADC8D
–
BBMC
BBMB
BBMA
Pages 58, 113
0x07
PUEB
–
–
–
–
PUEB3
PUEB2
PUEB1
PUEB0
Page 59
0x06
PORTB
–
–
–
–
PORTB3
PORTB2
PORTB1
PORTB0
Page 59
0x05
DDRB
–
–
–
–
DDRB3
DDRB2
DDRB1
DDRB0
Page 59
0x04
PINB
–
–
–
–
PINB3
PINB2
PINB1
PINB0
Page 59
0x03
PUEA
PUEA7
PUEA6
PUEA5
PUEA4
PUEA3
PUEA2
PUEA1
PUEA0
Page 58
0x02
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
Page 58
0x01
DDRA
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
Page 58
0x00
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Page 59
1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
189
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
ATtiny40 [DATASHEET]
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23. Instruction Set Summary
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD
Rd, Rr
Add without Carry
Rd  Rd + Rr
Z,C,N,V,S,H
ADC
Rd, Rr
Add with Carry
Rd  Rd + Rr + C
Z,C,N,V,S,H
1
SUB
Rd, Rr
Subtract without Carry
Rd  Rd - Rr
Z,C,N,V,S,H
1
SUBI
Rd, K
Subtract Immediate
Rd  Rd - K
Z,C,N,V,S,H
1
SBC
Rd, Rr
Subtract with Carry
Rd  Rd - Rr - C
Z,C,N,V,S,H
1
SBCI
Rd, K
Subtract Immediate with Carry
Rd  Rd - K - C
Z,C,N,V,S,H
1
1
1
AND
Rd, Rr
Logical AND
Rd Rd  Rr
Z,N,V,S
ANDI
Rd, K
Logical AND with Immediate
Rd  Rd K
Z,N,V,S
1
OR
Rd, Rr
Logical OR
Rd  Rd v Rr
Z,N,V,S
1
ORI
Rd, K
Logical OR with Immediate
Rd Rd v K
Z,N,V,S
1
EOR
Rd, Rr
Exclusive OR
Rd  Rd  Rr
Z,N,V,S
1
COM
Rd
One’s Complement
Rd  $FF  Rd
Z,C,N,V,S
1
NEG
Rd
Two’s Complement
Rd  $00  Rd
Z,C,N,V,S,H
1
SBR
Rd,K
Set Bit(s) in Register
Rd  Rd v K
Z,N,V,S
1
CBR
Rd,K
Clear Bit(s) in Register
Rd  Rd  ($FFh - K)
Z,N,V,S
1
INC
Rd
Increment
Rd  Rd + 1
Z,N,V,S
1
DEC
Rd
Decrement
Rd  Rd  1
Z,N,V,S
1
TST
Rd
Test for Zero or Minus
Rd  Rd  Rd
Z,N,V,S
1
CLR
Rd
Clear Register
Rd  Rd  Rd
Z,N,V,S
1
SER
Rd
Set Register
Rd  $FF
None
1
2
BRANCH INSTRUCTIONS
RJMP
k
IJMP
RCALL
k
Relative Jump
PC PC + k + 1
None
Indirect Jump to (Z)
PC(15:0)  Z, PC(21:16)  0
None
2
Relative Subroutine Call
PC  PC + k + 1
None
3/4
ICALL
Indirect Call to (Z)
PC(15:0)  Z, PC(21:16)  0
None
3/4
RET
Subroutine Return
PC  STACK
None
4/5
RETI
Interrupt Return
PC  STACK
I
Compare, Skip if Equal
if (Rd = Rr) PC PC + 2 or 3
None
CPSE
Rd,Rr
4/5
1/2/3
CP
Rd,Rr
Compare
Rd  Rr
Z, C,N,V,S,H
1
CPC
Rd,Rr
Compare with Carry
Rd  Rr  C
Z, C,N,V,S,H
1
CPI
Rd,K
Compare with Immediate
Rd  K
Z, C,N,V,S,H
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC  PC + 2 or 3
None
1/2/3
1
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC  PC + 2 or 3
None
1/2/3
SBIC
A, b
Skip if Bit in I/O Register Cleared
if (I/O(A,b)=0) PC  PC + 2 or 3
None
1/2/3
SBIS
A, b
Skip if Bit in I/O Register is Set
if (I/O(A,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
LSL
Rd
Logical Shift Left
Rd(n+1)  Rd(n), Rd(0)  0
Z,C,N,V,H
LSR
Rd
Logical Shift Right
Rd(n)  Rd(n+1), Rd(7)  0
Z,C,N,V
1
ROL
Rd
Rotate Left Through Carry
Rd(0)C,Rd(n+1) Rd(n),CRd(7)
Z,C,N,V,H
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
SBI
A, b
Set Bit in I/O Register
I/O(A, b)  1
None
1
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
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191
Mnemonics
Operands
Description
Operation
Flags
#Clocks
CBI
A, b
Clear Bit in I/O Register
I/O(A, b)  0
None
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
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 Two’s Complement Overflow.
V1
V
1
CLV
Clear Two’s Complement Overflow
V0
V
1
SET
Set T in SREG
T1
T
1
CLT
Clear T in SREG
T0
T
1
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
H1
H0
H
H
1
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Copy Register
Rd  Rr
None
1
LDI
Rd, K
Load Immediate
Rd  K
None
1
LD
Rd, X
Load Indirect
Rd  (X)
None
1/2
LD
Rd, X+
Load Indirect and Post-Increment
Rd  (X), X  X + 1
None
2
LD
Rd, - X
Load Indirect and Pre-Decrement
X  X - 1, Rd  (X)
None
2/3
LD
Rd, Y
Load Indirect
Rd  (Y)
None
1/2
LD
Rd, Y+
Load Indirect and Post-Increment
Rd  (Y), Y  Y + 1
None
2
LD
Rd, - Y
Load Indirect and Pre-Decrement
Y  Y - 1, Rd  (Y)
None
2/3
LD
Rd, Z
Load Indirect
Rd  (Z)
None
1/2
LD
Rd, Z+
Load Indirect and Post-Increment
Rd  (Z), Z  Z+1
None
2
LD
Rd, -Z
Load Indirect and Pre-Decrement
Z  Z - 1, Rd  (Z)
None
2/3
LDS
Rd, k
Store Direct from SRAM
Rd k)
None
1
ST
X, Rr
Store Indirect
(X) Rr
None
1
ST
X+, Rr
Store Indirect and Post-Increment
(X) Rr, X  X + 1
None
1
ST
- X, Rr
Store Indirect and Pre-Decrement
X  X - 1, (X)  Rr
None
2
ST
Y, Rr
Store Indirect
(Y)  Rr
None
1
ST
Y+, Rr
Store Indirect and Post-Increment
(Y)  Rr, Y  Y + 1
None
1
ST
- Y, Rr
Store Indirect and Pre-Decrement
Y  Y - 1, (Y)  Rr
None
2
ST
Z, Rr
Store Indirect
(Z)  Rr
None
1
ST
Z+, Rr
Store Indirect and Post-Increment.
(Z)  Rr, Z  Z + 1
None
1
ST
-Z, Rr
Store Indirect and Pre-Decrement
Z  Z - 1, (Z)  Rr
None
2
1
STS
k, Rr
Store Direct to SRAM
(k)  Rr
None
IN
Rd, A
In from I/O Location
Rd  I/O (A)
None
1
OUT
A, Rr
Out to I/O Location
I/O (A)  Rr
None
1
PUSH
Rr
Push Register on Stack
STACK  Rr
None
2
POP
Rd
Pop Register from Stack
Rd  STACK
None
2
MCU CONTROL INSTRUCTIONS
BREAK
Break
(see specific descr. for Break)
NOP
No Operation
SLEEP
WDR
Sleep
Watchdog Reset
(see specific descr. for Sleep)
(see specific descr. for WDR)
None
1
None
1
None
None
1
ATtiny40 [DATASHEET]
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1
192
24. Ordering Information
Speed (MHz)
12
Notes:
Power Supply
Ordering Code(1)
Package(2)
1.8 - 5.5V
ATtiny40-SU
ATtiny40-SUR
ATtiny40-XU
ATtiny40-XUR
ATtiny40-MMH(3)
ATtiny40-MMHR(3)
20S2
20S2
20X
20X
20M2(3)
20M2(3)
Operational Range
Industrial
(-40C to +85C)(4)
1. Code indicators:
– H: NiPdAu lead finish
– U: matte tin
– R: tape & reel
2. All packages are Pb-free, halide-free and fully green and they comply with the European directive for Restriction of Hazardous Substances (RoHS).
3. Topside marking for ATtiny40:
– 1st Line: T40
– 2nd & 3rd Line: manufacturing data
4. These devices can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information and minimum quantities.
Package Type
20S2
20-lead, 0.300" Wide Body, Plastic Gull Wing Small Outline Package (SOIC)
20X
20-lead, 4.4 mm Body, Plastic Thin Shrink Small Outline Package (TSSOP)
20M2
20-pad, 3 x 3 x 0.85 mm Body, Very Thin Quad Flat No Lead Package (VQFN)
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25. Packaging Information
25.1
20S2
ATtiny40 [DATASHEET]
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25.2
20X
Dimensions in Millimeters and (Inches).
Controlling dimension: Millimeters.
JEDEC Standard MO-153 AC
INDEX MARK
PIN
1
4.50 (0.177) 6.50 (0.256)
4.30 (0.169) 6.25 (0.246)
6.60 (.260)
6.40 (.252)
0.65 (.0256) BSC
0.30 (0.012)
0.19 (0.007)
1.20 (0.047) MAX
0.15 (0.006)
0.05 (0.002)
SEATING
PLANE
0.20 (0.008)
0.09 (0.004)
0º ~ 8º
0.75 (0.030)
0.45 (0.018)
10/23/03
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
20X, (Formerly 20T), 20-lead, 4.4 mm Body Width,
Plastic Thin Shrink Small Outline Package (TSSOP)
DRAWING NO.
REV.
20X
C
ATtiny40 [DATASHEET]
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25.3
20M2
D
C
y
Pin 1 ID
E
SIDE VIEW
TOP VIEW
A1
A
D2
16
17
18
19
20
COMMON DIMENSIONS
(Unit of Measure = mm)
C0.18 (8X)
15
SYMBOL
1
Pin #1 Chamfer
(C 0.3)
14
2
e
E2 13
3
12
4
11
5
MIN
NOM
MAX
A
0.75
0.80
0.85
A1
0.00
0.02
0.05
b
0.17
0.22
0.27
C
D
b
10
9
8
7
6
K
L
BOTTOM VIEW
0.3 Ref (4x)
NOTE
0.152
2.90
3.00
3.10
D2
1.40
1.55
1.70
E
2.90
3.00
3.10
E2
1.40
1.55
1.70
e
–
0.45
–
L
0.35
0.40
0.45
K
0.20
–
–
y
0.00
–
0.08
10/24/08
Package Drawing Contact:
packagedrawings@atmel.com
GPC
TITLE
20M2, 20-pad, 3 x 3 x 0.85 mm Body, Lead Pitch 0.45 mm,
ZFC
1.55 x 1.55 mm Exposed Pad, Thermally Enhanced
Plastic Very Thin Quad Flat No Lead Package (VQFN)
DRAWING NO.
REV.
20M2
B
26. Errata
The revision letters in this section refer to the revision of the corresponding ATtiny40 device.
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26.1
Rev. B
• MISO output driver is not disabled by Slave Select (SS) signal.
• Current consumption in sleep modes may exceed specifications.
1. MISO output driver is not disabled by Slave Select (SS) signal.
When SPI is configured as a slave and the MISO pin is configured as an output the pin output driver is constantly enabled, even when the SS pin is high. If other slave devices are connected to the same MISO line this
behaviour may cause drive contention.
Problem Fix / Workaround
Monitor SS pin by software and use the DDRC2 bit of DDRC to control the MISO pin driver.
2. Current consumption in sleep mode may exceed specifications.
Some settings of register R27 may increase current consumption in sleep mode.
Problem Fix / Workaround
Before entering sleep mode, make sure register R27 is not loaded with 0x00 or 0x01.
26.2
Rev. A
Not sampled.
27. Datasheet Revision History
27.1
Rev. 8263B – 01/2013
1. Removed Preliminary status
2. Updated
– Idle Mode description on page 4
– “Capacitive Touch Sensing” on page 5 (section updated and moved)
– “Disclaimer” on page 5
– Description on 16-bit registers on page 6
– Description on Stack Pointer on page 9
– List of active modules in “Idle Mode” on page 24
– Description on reset pulse width in “Watchdog Reset” on page 30
– Bit description in Figure 11-3 on page 63
– “Modes of Operation” on page 65, simplified 0 = fclk_I/O/2 to fclk_I/O/2 (on two locations)
– Section “Compare Output Mode and Waveform Generation” on page 65
– Figure 11-5 on page 66, Figure 11-6 on page 67, and Figure 11-7 on page 68
– Equations on page 66, page 68, and page 69
– Terminology in sections describing extreme values on page 68, and page 69
– Description on creating frequency waveforms on page 69
– Description on signal source impedance on page 105
– SPI slave assembly code example on page 117
– “Speed” on page 153
– Characteristics in Figure 21-3 on page 161, and Figure 21-9 on page 164
– Last page
3. Added:
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– Note on internal voltage reference in Table 15-4 on page 110
– “Compatibility with SMBus” on page 128
– “Two-Wire Serial Interface Characteristics” on page 156
– “Errata” on page 196
27.2
Rev. 8263A – 08/10
1. Initial revision
ATtiny40 [DATASHEET]
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Table of Contents
Features ..................................................................................................... 1
1
Pin Configurations ................................................................................... 2
1.1
Pin Description ..................................................................................................3
2
Overview ................................................................................................... 3
3
General Information ................................................................................. 5
4
5
6
7
3.1
Resources .........................................................................................................5
3.2
Code Examples .................................................................................................5
3.3
Capacitive Touch Sensing .................................................................................5
3.4
Data Retention ...................................................................................................5
3.5
Disclaimer ..........................................................................................................5
CPU Core ................................................................................................... 5
4.1
Architectural Overview .......................................................................................6
4.2
ALU – Arithmetic Logic Unit ...............................................................................7
4.3
Status Register ..................................................................................................7
4.4
General Purpose Register File ..........................................................................7
4.5
Stack Pointer .....................................................................................................9
4.6
Instruction Execution Timing .............................................................................9
4.7
Reset and Interrupt Handling ...........................................................................10
4.8
Register Description ........................................................................................11
Memories ................................................................................................. 13
5.1
In-System Re-programmable Flash Program Memory ....................................13
5.2
Data Memory ...................................................................................................13
5.3
I/O Memory ......................................................................................................16
5.4
Register Description ........................................................................................17
Clock System .......................................................................................... 17
6.1
Clock Subsystems ...........................................................................................18
6.2
Clock Sources .................................................................................................18
6.3
System Clock Prescaler ..................................................................................20
6.4
Starting ............................................................................................................20
6.5
Register Description ........................................................................................21
Power Management and Sleep Modes ................................................. 23
7.1
Sleep Modes ....................................................................................................23
7.2
Software BOD Disable .....................................................................................24
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8
9
7.3
Power Reduction Register ...............................................................................25
7.4
Minimizing Power Consumption ......................................................................25
7.5
Register Description ........................................................................................26
System Control and Reset ..................................................................... 28
8.1
Resetting the AVR ...........................................................................................28
8.2
Reset Sources .................................................................................................28
8.3
Internal Voltage Reference ..............................................................................31
8.4
Watchdog Timer ..............................................................................................31
8.5
Register Description ........................................................................................33
Interrupts ................................................................................................. 35
9.1
Interrupt Vectors ..............................................................................................36
9.2
External Interrupts ...........................................................................................37
9.3
Register Description ........................................................................................38
10 I/O Ports .................................................................................................. 42
10.1
Overview ..........................................................................................................42
10.2
Ports as General Digital I/O .............................................................................43
10.3
Alternate Port Functions ..................................................................................47
10.4
Register Description ........................................................................................58
11 Timer/Counter0 ....................................................................................... 60
11.1
Features ..........................................................................................................60
11.2
Overview ..........................................................................................................60
11.3
Clock Sources .................................................................................................62
11.4
Counter Unit ....................................................................................................62
11.5
Output Compare Unit .......................................................................................63
11.6
Compare Match Output Unit ............................................................................64
11.7
Modes of Operation .........................................................................................65
11.8
Timer/Counter Timing Diagrams ......................................................................69
11.9
Register Description ........................................................................................71
12 Timer/Counter1 ....................................................................................... 77
12.1
Features ..........................................................................................................77
12.2
Overview ..........................................................................................................77
12.3
Clock Sources .................................................................................................78
12.4
Counter Unit ....................................................................................................78
12.5
Input Capture Unit ...........................................................................................79
12.6
Output Compare Unit .......................................................................................80
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12.7
Modes of Operation .........................................................................................81
12.8
Timer/Counter Timing Diagrams ......................................................................82
12.9
Accessing Registers in 16-bit Mode ................................................................84
12.10
Register Description ........................................................................................88
13 Timer/Counter Prescaler ........................................................................ 92
13.1
Prescaler Reset ...............................................................................................92
13.2
External Clock Source .....................................................................................92
13.3
Register Description ........................................................................................93
14 Analog Comparator ................................................................................ 94
14.1
Analog Comparator Multiplexed Input .............................................................94
14.2
Register Description ........................................................................................95
15 Analog to Digital Converter ................................................................... 98
15.1
Features ..........................................................................................................98
15.2
Overview ..........................................................................................................98
15.3
Operation .........................................................................................................99
15.4
Starting a Conversion ....................................................................................100
15.5
Prescaling and Conversion Timing ................................................................101
15.6
Changing Channel or Reference Selection ...................................................104
15.7
ADC Noise Canceler .....................................................................................105
15.8
Analog Input Circuitry ....................................................................................105
15.9
Noise Canceling Techniques .........................................................................106
15.10
ADC Accuracy Definitions .............................................................................106
15.11
ADC Conversion Result .................................................................................109
15.12
Temperature Measurement ...........................................................................109
15.13
Register Description ......................................................................................109
16 SPI – Serial Peripheral Interface ......................................................... 114
16.1
Features ........................................................................................................114
16.2
Overview ........................................................................................................114
16.3
SS Pin Functionality ......................................................................................118
16.4
Data Modes ...................................................................................................119
16.5
Register Description ......................................................................................120
17 TWI – Two Wire Interface (Slave) ........................................................ 122
17.1
Features ........................................................................................................122
17.2
Overview ........................................................................................................122
17.3
General TWI Bus Concepts ...........................................................................122
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17.4
TWI Slave Operation .....................................................................................128
17.5
Register Description ......................................................................................130
18 Programming Interface ........................................................................ 134
18.1
Features ........................................................................................................134
18.2
Overview ........................................................................................................134
18.3
Physical Layer of Tiny Programming Interface ..............................................135
18.4
Access Layer of Tiny Programming Interface ................................................138
18.5
Instruction Set ................................................................................................139
18.6
Accessing the Non-Volatile Memory Controller .............................................141
18.7
Control and Status Space Register Descriptions ...........................................142
19 Memory Programming ......................................................................... 143
19.1
Features ........................................................................................................143
19.2
Overview ........................................................................................................144
19.3
Non-Volatile Memories ..................................................................................144
19.4
Accessing the NVM .......................................................................................147
19.5
Self programming ..........................................................................................150
19.6
External Programming ...................................................................................150
19.7
Register Description ......................................................................................151
20 Electrical Characteristics .................................................................... 152
20.1
Absolute Maximum Ratings* .........................................................................152
20.2
DC Characteristics .........................................................................................152
20.3
Speed ............................................................................................................153
20.4
Clock Characteristics .....................................................................................154
20.5
System and Reset Characteristics ................................................................155
20.6
Two-Wire Serial Interface Characteristics .....................................................156
20.7
Analog Comparator Characteristics ...............................................................157
20.8
ADC Characteristics ......................................................................................157
20.9
Serial Programming Characteristics ..............................................................158
21 Typical Characteristics ........................................................................ 159
21.1
Supply Current of I/O Modules ......................................................................159
21.2
Current Consumption in Active Mode ............................................................160
21.3
Current Consumption in Idle Mode ................................................................163
21.4
Current Consumption in Power-down Mode ..................................................166
21.5
Current Consumption in Reset ......................................................................167
21.6
Current Consumption of Peripheral Units ......................................................167
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21.7
Pull-up Resistors ...........................................................................................169
21.8
Output Driver Strength ...................................................................................172
21.9
Input Thresholds and Hysteresis ...................................................................178
21.10
BOD, Bandgap and Reset .............................................................................181
21.11
Analog Comparator Offset .............................................................................185
21.12
Internal Oscillator Speed ...............................................................................186
22 Register Summary ................................................................................ 189
23 Instruction Set Summary ..................................................................... 191
24 Ordering Information ........................................................................... 193
25 Packaging Information ......................................................................... 194
25.1
20S2 ..............................................................................................................194
25.2
20X ................................................................................................................195
25.3
20M2 ..............................................................................................................196
26 Errata ..................................................................................................... 196
26.1
Rev. B ............................................................................................................197
26.2
Rev. A ............................................................................................................197
27 Datasheet Revision History ................................................................. 197
27.1
Rev. 8263B – 01/2013 ...................................................................................197
27.2
Rev. 8263A – 08/10 .......................................................................................198
Table of Contents ....................................................................................... i
Features1 i
Table of Contents1 v
ATtiny40 [DATASHEET]
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v
Atmel Corporation
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Atmel Asia Limited
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© 2013 Atmel Corporation. All rights reserved. / Rev.: 8263B–AVR–01/2013
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