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Farnell PDF
ATmega48/88/168 - Atmel - Farnell Element 14
ATmega48/88/168 - Atmel - Farnell Element 14
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Farnell Element 14 :
See the trailer for the next exciting episode of The Ben Heck show. Check back on Friday to be among the first to see the exclusive full show on element…
Connect your Raspberry Pi to a breadboard, download some code and create a push-button audio play project.
Puce électronique / Microchip :
Sans fil - Wireless :
Texas instrument :
Ordinateurs :
Logiciels :
Tutoriels :
Autres documentations :
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Features
• High performance, low power Atmel® AVR® 8-bit microcontroller
• Advanced RISC architecture
– 131 powerful instructions – most single clock cycle execution
– 32 × 8 general purpose working registers
– Fully static operation
– Up to 20 MIPS throughput at 20MHz
– On-chip 2-cycle multiplier
• High endurance non-volatile memory segments
– 4/8/16 Kbytes of in-system self-programmable flash program memory
– 256/512/512 bytes EEPROM
– 512/1K/1Kbytes internal SRAM
– Write/erase cyles: 10,000 flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C()
– Optional boot code section with independent lock bits
In-system programming by on-chip boot program
True read-while-write operation
– Programming lock for software security
• QTouch® library support
– Capacitive touch buttons, sliders and wheels
– QTouch and QMatrix acquisition
– Up to 64 sense channels
• Peripheral features
– Two 8-bit timer/counters with separate prescaler and compare mode
– One 16-bit timer/counter with separate prescaler, compare mode, and capture mode
– Real time counter with separate oscillator
– Six PWM channels
– 8-channel 10-bit ADC in TQFP and QFN/MLF package
– 6-channel 10-bit ADC in PDIP Package
– Programmable serial USART
– Master/slave SPI serial interface
– Byte-oriented 2-wire serial interface (Philips I2
C compatible)
– Programmable watchdog timer with separate on-chip oscillator
– On-chip analog comparator
– Interrupt and wake-up on pin change
• Special microcontroller features
– DebugWIRE on-chip debug system
– Power-on reset and programmable brown-out detection
– Internal calibrated oscillator
– External and internal interrupt sources
– Five sleep modes: Idle, ADC noise reduction, power-save, power-down, and standby
• I/O and packages
– 23 programmable I/O lines
– 28-pin PDIP, 32-lead TQFP, 28-pad QFN/MLF and 32-pad QFN/MLF
• Operating voltage:
– 1.8V - 5.5V for Atmel ATmega48V/88V/168V
– 2.7V - 5.5V for Atmel ATmega48/88/168
• Temperature range:
– -40°C to 85°C
• Speed grade:
– ATmega48V/88V/168V: 0 - 4MHz @ 1.8V - 5.5V, 0 - 10MHz @ 2.7V - 5.5V
– ATmega48/88/168: 0 - 10MHz @ 2.7V - 5.5V, 0 - 20MHz @ 4.5V - 5.5V
• Low power consumption
– Active mode:
250µA at 1MHz, 1.8V
15µA at 32kHz, 1.8V (including oscillator)
– Power-down mode:
0.1µA at 1.8V
Note: 1. See “Data retention” on page 8 for details.
8-bit Atmel
Microcontroller
with 4/8/16K
Bytes In-System
Programmable
Flash
ATmega48/V
ATmega88/V
ATmega168/V
Rev. 2545T–AVR–05/112
2545T–AVR–05/11
ATmega48/88/168
1. Pin configurations
Figure 1-1. Pinout Atmel ATmega48/88/168.
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
(PCINT19/OC2B/INT1) PD3
(PCINT20/XCK/T0) PD4
GND
VCC
GND
VCC
(PCINT6/XTAL1/TOSC1) PB6
(PCINT7/XTAL2/TOSC2) PB7
PC1 (ADC1/PCINT9)
PC0 (ADC0/PCINT8)
ADC7
GND
AREF
ADC6
AVCC
PB5 (SCK/PCINT5)
32
31
30
29
28
27
26
25
9
10
11
12
13
14
15
16
(PCINT21/OC0B/T1) PD5
(PCINT22/OC0A/AIN0) PD6
(PCINT23/AIN1) PD7
(PCINT0/CLKO/ICP1) PB0
(PCINT1/OC1A) PB1
(PCINT2/SS/OC1B) PB2
(PCINT3/OC2A/MOSI) PB3
(PCINT4/MISO) PB4
PD2 (INT0/PCINT18)
PD1 (TXD/PCINT17)
PD0 (RXD/PCINT16)
PC6 (RESET/PCINT14)
PC5 (ADC5/SCL/PCINT13)
PC4 (ADC4/SDA/PCINT12)
PC3 (ADC3/PCINT11)
PC2 (ADC2/PCINT10)
TQFP Top View
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
(PCINT14/RESET) PC6
(PCINT16/RXD) PD0
(PCINT17/TXD) PD1
(PCINT18/INT0) PD2
(PCINT19/OC2B/INT1) PD3
(PCINT20/XCK/T0) PD4
VCC
GND
(PCINT6/XTAL1/TOSC1) PB6
(PCINT7/XTAL2/TOSC2) PB7
(PCINT21/OC0B/T1) PD5
(PCINT22/OC0A/AIN0) PD6
(PCINT23/AIN1) PD7
(PCINT0/CLKO/ICP1) PB0
PC5 (ADC5/SCL/PCINT13)
PC4 (ADC4/SDA/PCINT12)
PC3 (ADC3/PCINT11)
PC2 (ADC2/PCINT10)
PC1 (ADC1/PCINT9)
PC0 (ADC0/PCINT8)
GND
AREF
AVCC
PB5 (SCK/PCINT5)
PB4 (MISO/PCINT4)
PB3 (MOSI/OC2A/PCINT3)
PB2 (SS/OC1B/PCINT2)
PB1 (OC1A/PCINT1)
PDIP
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
32
31
30
29
28
27
26
25
9
10
11
12
13
14
15
16
32 MLF Top View
(PCINT19/OC2B/INT1) PD3
(PCINT20/XCK/T0) PD4
GND
VCC
GND
VCC
(PCINT6/XTAL1/TOSC1) PB6
(PCINT7/XTAL2/TOSC2) PB7
PC1 (ADC1/PCINT9)
PC0 (ADC0/PCINT8)
ADC7
GND
AREF
ADC6
AVCC
PB5 (SCK/PCINT5)
(PCINT21/OC0B/T1) PD5
(PCINT22/OC0A/AIN0) PD6
(PCINT23/AIN1) PD7
(PCINT0/CLKO/ICP1) PB0
(PCINT1/OC1A) PB1
(PCINT2/SS/OC1B) PB2
(PCINT3/OC2A/MOSI) PB3
(PCINT4/MISO) PB4
PD2 (INT0/PCINT18)
PD1 (TXD/PCINT17)
PD0 (RXD/PCINT16)
PC6 (RESET/PCINT14)
PC5 (ADC5/SCL/PCINT13)
PC4 (ADC4/SDA/PCINT12)
PC3 (ADC3/PCINT11)
PC2 (ADC2/PCINT10)
NOTE: Bottom pad should be soldered to ground.
1
2
3
4
5
6
7
21
20
19
18
17
16
15
28
27
26
25
24
23
22
8
9
10
11
12
13
14
28 MLF Top View
(PCINT19/OC2B/INT1) PD3
(PCINT20/XCK/T0) PD4
VCC
GND
(PCINT6/XTAL1/TOSC1) PB6
(PCINT7/XTAL2/TOSC2) PB7
(PCINT21/OC0B/T1) PD5
(PCINT22/OC0A/AIN0) PD6
(PCINT23/AIN1) PD7
(PCINT0/CLKO/ICP1) PB0
(PCINT1/OC1A) PB1
(PCINT2/SS/OC1B) PB2
(PCINT3/OC2A/MOSI) PB3
(PCINT4/MISO) PB4
PD2 (INT0/PCINT18)
PD1 (TXD/PCINT17)
PD0 (RXD/PCINT16)
PC6 (RESET/PCINT14)
PC5 (ADC5/SCL/PCINT13)
PC4 (ADC4/SDA/PCINT12)
PC3 (ADC3/PCINT11)
PC2 (ADC2/PCINT10)
PC1 (ADC1/PCINT9)
PC0 (ADC0/PCINT8)
GND
AREF
AVCC
PB5 (SCK/PCINT5)
NOTE: Bottom pad should be soldered to ground.3
2545T–AVR–05/11
ATmega48/88/168
1.1 Pin descriptions
1.1.1 VCC
Digital supply voltage.
1.1.2 GND
Ground.
1.1.3 Port B (PB7:0) XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Depending on the clock selection fuse settings, PB6 can be used as input to the inverting Oscillator
amplifier and input to the internal clock operating circuit.
Depending on the clock selection fuse settings, PB7 can be used as output from the inverting
Oscillator amplifier.
If the Internal Calibrated RC Oscillator is used as chip clock source, PB7..6 is used as TOSC2..1
input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.
The various special features of Port B are elaborated in “Alternate functions of port B” on page
78 and “System clock and clock options” on page 27.
1.1.4 Port C (PC5:0)
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
PC5..0 output buffers have symmetrical drive characteristics with both high sink and source
capability. 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.
1.1.5 PC6/RESET
If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical characteristics
of PC6 differ from those of the other pins of Port C.
If the RSTDISBL Fuse is unprogrammed, PC6 is used as a Reset input. A low level on this pin
for longer than the minimum pulse length will generate a Reset, even if the clock is not running.
The minimum pulse length is given in Table 29-3 on page 307. Shorter pulses are not guaranteed
to generate a Reset.
The various special features of Port C are elaborated in “Alternate functions of port C” on page
81.
1.1.6 Port D (PD7:0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up4
2545T–AVR–05/11
ATmega48/88/168
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
The various special features of Port D are elaborated in “Alternate functions of port D” on page
84.
1.1.7 AVCC
AVCC is the supply voltage pin for the A/D Converter, PC3:0, and ADC7:6. It should be externally
connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC
through a low-pass filter. Note that PC6..4 use digital supply voltage, VCC.
1.1.8 AREF
AREF is the analog reference pin for the A/D Converter.
1.1.9 ADC7:6 (TQFP and QFN/MLF package only)
In the TQFP and QFN/MLF package, ADC7:6 serve as analog inputs to the A/D converter.
These pins are powered from the analog supply and serve as 10-bit ADC channels.5
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2. Overview
The Atmel ATmega48/88/168 is a low-power CMOS 8-bit microcontroller based on the AVR
enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the
ATmega48/88/168 achieves throughputs approaching 1 MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
2.1 Block diagram
Figure 2-1. Block diagram.
The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting
PORT D (8) PORT B (8) PORT C (7)
USART 0
8bit T/C 2
8bit T/C 0 16bit T/C 1 A/D conv.
Internal
bandgap
Analog
comp.
SPI TWI
Flash SRAM
EEPROM
Watchdog
oscillator
Watchdog
timer
Oscillator
circuits /
clock
generation
Power
supervision
POR / BOD &
RESET
GND
VCC
PROGRAM
LOGIC
debugWIRE
2
GND
AREF
AVCC
DATABUS
PD[0..7] PB[0..7] PC[0..6] ADC[6..7]
6
RESET
XTAL[1..2]
CPU6
2545T–AVR–05/11
ATmega48/88/168
architecture is more code efficient while achieving throughputs up to ten times faster than conventional
CISC microcontrollers.
The Atmel ATmega48/88/168 provides the following features: 4K/8K/16K bytes of In-System
Programmable Flash with Read-While-Write capabilities, 256/512/512 bytes EEPROM,
512/1K/1K bytes SRAM, 23 general purpose I/O lines, 32 general purpose working registers,
three flexible Timer/Counters with compare modes, internal and external interrupts, a serial programmable
USART, a byte-oriented 2-wire Serial Interface, an SPI serial port, a 6-channel 10-bit
ADC (8 channels in TQFP and QFN/MLF packages), a programmable Watchdog Timer with
internal Oscillator, and five software selectable power saving modes. The Idle mode stops the
CPU while allowing the SRAM, Timer/Counters, USART, 2-wire Serial Interface, SPI port, and
interrupt system to continue functioning. The Power-down mode saves the register contents but
freezes the Oscillator, disabling all other chip functions until the next interrupt or hardware reset.
In Power-save mode, the asynchronous timer continues to run, allowing the user to maintain a
timer base while the rest of the device is sleeping. The ADC Noise Reduction mode stops the
CPU and all I/O modules except asynchronous timer and ADC, to minimize switching noise during
ADC conversions. In Standby mode, the crystal/resonator Oscillator is running while the rest
of the device is sleeping. This allows very fast start-up combined with low power consumption.
Atmel offers the QTouch Library for embedding capacitive touch buttons, sliders and wheels
functionality into AVR microcontrollers. The patented charge-transfer signal acquisition offers
robust sensing and includes fully debounced reporting of touch keys and includes Adjacent Key
Suppression® (AKS®) technology for unambigiuous detection of key events. The easy-to-use
QTouch Suite toolchain allows you to explore, develop and debug your own touch applications.
The device is manufactured using the Atmel high density non-volatile memory technology. The
On-chip ISP Flash allows the program memory to be reprogrammed In-System through an SPI
serial interface, by a conventional non-volatile memory programmer, or by an On-chip Boot program
running on the AVR core. The Boot program can use any interface to download the
application program in the Application Flash memory. Software in the Boot Flash section will
continue to run while the Application Flash section is updated, providing true Read-While-Write
operation. By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a
monolithic chip, the Atmel ATmega48/88/168 is a powerful microcontroller that provides a highly
flexible and cost effective solution to many embedded control applications.
The ATmega48/88/168 AVR is supported with a full suite of program and system development
tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators,
and Evaluation kits.
2.2 Comparison between Atmel ATmega48, Atmel ATmega88, and Atmel ATmega168
The ATmega48, ATmega88 and ATmega168 differ only in memory sizes, boot loader support,
and interrupt vector sizes. Table 2-1 summarizes the different memory and interrupt vector sizes
for the three devices.
Table 2-1. Memory size summary.
Device Flash EEPROM RAM Interrupt vector size
ATmega48 4Kbytes 256Bytes 512Bytes 1 instruction word/vector
ATmega88 8Kbytes 512Bytes 1Kbytes 1 instruction word/vector
ATmega168 16Kbytes 512Bytes 1Kbytes 2 instruction words/vector7
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ATmega48/88/168
ATmega88 and ATmega168 support a real Read-While-Write Self-Programming mechanism.
There is a separate Boot Loader Section, and the SPM instruction can only execute from there.
In ATmega48, there is no Read-While-Write support and no separate Boot Loader Section. The
SPM instruction can execute from the entire Flash.8
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ATmega48/88/168
3. Resources
A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
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.
5. About code examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation
for more details.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
6. Capacitive touch sensing
The Atmel QTouch Library provides a simple to use solution to realize touch sensitive interfaces
on most Atmel AVR microcontrollers. The QTouch Library includes support for the QTouch and
QMatrix acquisition methods.
Touch sensing can be added to any application by linking the appropriate Atmel QTouch Library
for the AVR Microcontroller. This is done by using a simple set of APIs to define the touch channels
and sensors, and then calling the touch sensing API’s to retrieve the channel information
and determine the touch sensor states.
The QTouch Library is FREE and downloadable from the Atmel website at the following location:
www.atmel.com/qtouchlibrary. For implementation details and other information, refer to the
Atmel QTouch Library User Guide - also available for download from the Atmel website.9
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7. AVR CPU core
7.1 Overview
This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
7.2 Architectural overview
Figure 7-1. Block diagram of the AVR architecture.
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.
Flash
program
memory
Instruction
register
Instruction
decoder
Program
counter
Control lines
32 x 8
general
purpose
registrers
ALU
Status
and control
I/O lines
EEPROM
Data bus 8-bit
Data
SRAM
Direct addressing
Indirect addressing
Interrupt
unit
SPI
unit
Watchdog
timer
Analog
comparator
I/O module 2
I/O module 1
I/O module n10
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ATmega48/88/168
The fast-access Register File contains 32 × 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical
ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash program memory. These
added function registers are the 16-bit X-register, Y-register, and Z-register, described later in
this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic operation,
the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word format.
Every program memory address contains a 16-bit or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position.
The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers,
SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F. In addition, the
ATmega48/88/168 has Extended I/O space from 0x60 - 0xFF in SRAM where only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
7.3 ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See “Instruction set summary” on page 347 for a detailed description.11
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7.4 Status register
The Status Register contains information about the result of the most recently executed arithmetic
instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
7.4.1 SREG – AVR Status Register
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Global interrupt enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt
enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit copy storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination
for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half carry flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s complement overflow flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
Bit 7 6 5 4 3 2 1 0
0x3F (0x5F) I T H S V N Z C SREG
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 0 012
2545T–AVR–05/11
ATmega48/88/168
• Bit 0 – C: Carry flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
7.5 General purpose register file
The register file is optimized for the AVR enhanced RISC instruction set. In order to achieve the
required performance and flexibility, the following input/output schemes are supported by the
register file:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 7-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 7-2. AVR CPU general purpose working registers.
Most of the instructions operating on the register file have direct access to all registers, and most
of them are single cycle instructions.
As shown in Figure 7-2, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically implemented
as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
purpose R15 0x0F
working R16 0x10
registers R17 0x11
…
R26 0x1A X-register low byte
R27 0x1B X-register high byte
R28 0x1C Y-register low byte
R29 0x1D Y-register high byte
R30 0x1E Z-register low byte
R31 0x1F Z-register high byte13
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ATmega48/88/168
7.5.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers
are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 7-3.
Figure 7-3. The X-, Y-, and Z-registers.
In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
7.6 Stack pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations
to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x0100, preferably RAMEND. The Stack Pointer is decremented by one when data
is pushed onto the Stack with the PUSH instruction, and it is decremented by two when the
return address is pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is
incremented by one when data is popped from the Stack with the POP instruction, and it is incremented
by two when data is popped from the Stack with return from subroutine RET or return
from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementations
of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
15 XH XL 0
X-register 7 07 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 7 07 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 70 7 0
R31 (0x1F) R30 (0x1E)14
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ATmega48/88/168
7.6.1 SPH and SPL – Stack pointer high and stack pointer low register
7.7 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 7-4 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 7-4. The parallel instruction fetches and instruction executions.
Figure 7-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destination
register.
Figure 7-5. Single cycle ALU operation.
Bit 15 14 13 12 11 10 9 8
0x3E (0x5E) SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
0x3D (0x5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
clk
1st instruction fetch
1st instruction execute
2nd instruction fetch
2nd instruction execute
3rd instruction fetch
3rd instruction execute
4th instruction fetch
T1 T2 T3 T4
CPU
Total execution time
Register operands fetch
ALU operation execute
Result write back
T1 T2 T3 T4
clkCPU15
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ATmega48/88/168
7.8 Reset and interrupt handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory programming”
on page 285 for details.
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 56. 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. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL
bit in the MCU Control Register (MCUCR). Refer to “Interrupts” on page 56 for more information.
The Reset Vector can also be moved to the start of the Boot Flash section by programming the
BOOTRST Fuse, see “Boot loader support – Read-while-write self-programming, Atmel
ATmega88 and Atmel ATmega168” on page 269.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled.
The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector
in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence.16
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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 this example.
7.8.1 Interrupt response time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum.
After four clock cycles the program vector address for the actual interrupt handling routine
is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is increased by four clock cycles. This increase comes in addition to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and the I-bit in SREG is set.
Assembly code example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMPE ; start EEPROM write
sbi EECR, EEPE
out SREG, r16 ; restore SREG value (I-bit)
C code example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1< xxx
... ... ... ...
22 0x015 ADC ADC conversion complete
23 0x016 EE READY EEPROM ready
24 0x017 ANALOG COMP Analog comparator
25 0x018 TWI 2-wire serial interface
26 0x019 SPM READY Store program memory ready
Table 12-1. Reset and interrupt vectors in ATmega48. (Continued)
Vector no. Program address Source Interrupt definition58
2545T–AVR–05/11
ATmega48/88/168
12.3 Interrupt vectors in Atmel ATmega88
Notes: 1. When the BOOTRST fuse is programmed, the device will jump to the boot loader address at
reset, see “Boot loader support – Read-while-write self-programming, Atmel ATmega88 and
Atmel ATmega168” on page 269.
2. When the IVSEL bit in MCUCR is set, interrupt vectors will be moved to the start of the boot
flash section. The address of each Interrupt Vector will then be the address in this table added
to the start address of the boot flash section.
Table 12-3 on page 59 shows reset and interrupt vectors placement for the various combinations
of BOOTRST and IVSEL settings. If the program never enables an interrupt source, the
Interrupt Vectors are not used, and regular program code can be placed at these locations. This
is also the case if the reset vector is in the application section while the interrupt vectors are in
the boot section or vice versa.
Table 12-2. Reset and interrupt vectors in ATmega88.
Vector no.
Program
address(2) Source Interrupt definition
1 0x000(1) RESET External pin, power-on reset, brown-out reset and watchdog system reset
2 0x001 INT0 External interrupt request 0
3 0x002 INT1 External interrupt request 1
4 0x003 PCINT0 Pin change interrupt request 0
5 0x004 PCINT1 Pin change interrupt request 1
6 0x005 PCINT2 Pin change interrupt request 2
7 0x006 WDT Watchdog time-out interrupt
8 0x007 TIMER2 COMPA Timer/Counter2 compare match A
9 0x008 TIMER2 COMPB Timer/Counter2 compare match B
10 0x009 TIMER2 OVF Timer/Counter2 overflow
11 0x00A TIMER1 CAPT Timer/Counter1 capture event
12 0x00B TIMER1 COMPA Timer/Counter1 compare match A
13 0x00C TIMER1 COMPB Timer/Coutner1 compare match B
14 0x00D TIMER1 OVF Timer/Counter1 overflow
15 0x00E TIMER0 COMPA Timer/Counter0 compare match A
16 0x00F TIMER0 COMPB Timer/Counter0 compare match B
17 0x010 TIMER0 OVF Timer/Counter0 overflow
18 0x011 SPI, STC SPI serial transfer complete
19 0x012 USART, RX USART Rx complete
20 0x013 USART, UDRE USART, data register empty
21 0x014 USART, TX USART, Tx complete
22 0x015 ADC ADC conversion complete
23 0x016 EE READY EEPROM ready
24 0x017 ANALOG COMP Analog comparator
25 0x018 TWI 2-wire serial interface
26 0x019 SPM READY Store program memory ready59
2545T–AVR–05/11
ATmega48/88/168
Note: 1. The boot reset address is shown in Table 27-6 on page 281. For the BOOTRST Fuse “1”
means unprogrammed while “0” means programmed.
The most typical and general program setup for the reset and interrupt vector addresses in
ATmega88 is:
Address Labels Code Comments
0x000 rjmp RESET ; Reset Handler
0x001 rjmp EXT_INT0 ; IRQ0 Handler
0x002 rjmp EXT_INT1 ; IRQ1 Handler
0x003 rjmp PCINT0 ; PCINT0 Handler
0x004 rjmp PCINT1 ; PCINT1 Handler
0x005 rjmp PCINT2 ; PCINT2 Handler
0x006 rjmp WDT ; Watchdog Timer Handler
0x007 rjmp TIM2_COMPA ; Timer2 Compare A Handler
0X008 rjmp TIM2_COMPB ; Timer2 Compare B Handler
0x009 rjmp TIM2_OVF ; Timer2 Overflow Handler
0x00A rjmp TIM1_CAPT ; Timer1 Capture Handler
0x00B rjmp TIM1_COMPA ; Timer1 Compare A Handler
0x00C rjmp TIM1_COMPB ; Timer1 Compare B Handler
0x00D rjmp TIM1_OVF ; Timer1 Overflow Handler
0x00E rjmp TIM0_COMPA ; Timer0 Compare A Handler
0x00F rjmp TIM0_COMPB ; Timer0 Compare B Handler
0x010 rjmp TIM0_OVF ; Timer0 Overflow Handler
0x011 rjmp SPI_STC ; SPI Transfer Complete Handler
0x012 rjmp USART_RXC ; USART, RX Complete Handler
0x013 rjmp USART_UDRE ; USART, UDR Empty Handler
0x014 rjmp USART_TXC ; USART, TX Complete Handler
0x015 rjmp ADC ; ADC Conversion Complete Handler
0x016 rjmp EE_RDY ; EEPROM Ready Handler
0x017 rjmp ANA_COMP ; Analog Comparator Handler
0x018 rjmp TWI ; 2-wire Serial Interface Handler
0x019 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
0x01ARESET: ldi r16, high(RAMEND); Main program start
0x01B out SPH,r16 ; Set Stack Pointer to top of RAM
0x01C ldi r16, low(RAMEND)
0x01D out SPL,r16
0x01E sei ; Enable interrupts
0x01F xxx
Table 12-3. Reset and interrupt vectors placement in Atmel ATmega88(1).
BOOTRST IVSEL Reset address Interrupt vectors start address
1 0 0x000 0x001
1 1 0x000 Boot reset address + 0x001
0 0 Boot reset address 0x001
0 1 Boot reset address Boot reset address + 0x00160
2545T–AVR–05/11
ATmega48/88/168
When the BOOTRST fuse is unprogrammed, the boot section size set to 2Kbytes and the IVSEL
bit in the MCUCR register is set before any interrupts are enabled, the most typical and general
program setup for the reset and interrupt vector addresses in Atmel ATmega88 is:
Address Labels Code Comments
0x000 RESET: ldi r16,high(RAMEND); Main program start
0x001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x002 ldi r16,low(RAMEND)
0x003 out SPL,r16
0x004 sei ; Enable interrupts
0x005 xxx
;
.org 0xC01
0xC01 rjmp EXT_INT0 ; IRQ0 Handler
0xC02 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0xC19 rjmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST fuse is programmed and the boot section size set to 2Kbytes, the most
typical and general program setup for the reset and interrupt vector addresses in ATmega88 is:
Address Labels Code Comments
.org 0x001
0x001 rjmp EXT_INT0 ; IRQ0 Handler
0x002 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x019 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0xC00
0xC00 RESET: ldi r16,high(RAMEND); Main program start
0xC01 out SPH,r16 ; Set Stack Pointer to top of RAM
0xC02 ldi r16,low(RAMEND)
0xC03 out SPL,r16
0xC04 sei ; Enable interrupts
0xC05 xxx
When the BOOTRST fuse is programmed, the boot section size set to 2Kbytes and the IVSEL
bit in the MCUCR register is set before any interrupts are enabled, the most typical and general
program setup for the reset and interrupt vector addresses in ATmega88 is:
Address Labels Code Comments
;
.org 0xC00
0xC00 rjmp RESET ; Reset handler
0xC01 rjmp EXT_INT0 ; IRQ0 Handler
0xC02 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0xC19 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
0xC1A RESET: ldi r16,high(RAMEND); Main program start
0xC1B out SPH,r16 ; Set Stack Pointer to top of RAM61
2545T–AVR–05/11
ATmega48/88/168
0xC1C ldi r16,low(RAMEND)
0xC1D out SPL,r16
0xC1E sei ; Enable interrupts
0xC1F xxx
12.4 Interrupt vectors in Atmel ATmega168
Notes: 1. When the BOOTRST fuse is programmed, the device will jump to the boot loader address at
reset, see “Boot loader support – Read-while-write self-programming, Atmel ATmega88 and
Atmel ATmega168” on page 269.
2. When the IVSEL bit in MCUCR is set, interrupt vectors will be moved to the start of the boot
flash section. The address of each Interrupt Vector will then be the address in this table added
to the start address of the boot flash section.
Table 12-4. Reset and interrupt vectors in ATmega168.
Vector no.
Program
address(2) Source Interrupt definition
1 0x0000(1) RESET External pin, power-on reset, brown-out reset and watchdog system reset
2 0x0002 INT0 External interrupt request 0
3 0x0004 INT1 External interrupt request 1
4 0x0006 PCINT0 Pin change interrupt request 0
5 0x0008 PCINT1 Pin change interrupt request 1
6 0x000A PCINT2 Pin change interrupt request 2
7 0x000C WDT Watchdog time-out interrupt
8 0x000E TIMER2 COMPA Timer/Counter2 compare match A
9 0x0010 TIMER2 COMPB Timer/Counter2 compare match B
10 0x0012 TIMER2 OVF Timer/Counter2 overflow
11 0x0014 TIMER1 CAPT Timer/Counter1 capture event
12 0x0016 TIMER1 COMPA Timer/Counter1 compare match A
13 0x0018 TIMER1 COMPB Timer/Coutner1 compare match B
14 0x001A TIMER1 OVF Timer/Counter1 overflow
15 0x001C TIMER0 COMPA Timer/Counter0 compare match A
16 0x001E TIMER0 COMPB Timer/Counter0 compare match B
17 0x0020 TIMER0 OVF Timer/Counter0 overflow
18 0x0022 SPI, STC SPI serial transfer complete
19 0x0024 USART, RX USART Rx complete
20 0x0026 USART, UDRE USART, data register empty
21 0x0028 USART, TX USART, Tx complete
22 0x002A ADC ADC conversion complete
23 0x002C EE READY EEPROM ready
24 0x002E ANALOG COMP Analog comparator
25 0x0030 TWI 2-wire serial interface
26 0x0032 SPM READY Store program memory ready62
2545T–AVR–05/11
ATmega48/88/168
Table 12-5 shows reset and interrupt vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the interrupt
vectors are not used, and regular program code can be placed at these locations. This is also
the case if the reset vector is in the application section while the interrupt vectors are in the boot
section or vice versa.
Note: 1. The boot reset address is shown in Table 27-6 on page 281. For the BOOTRST fuse “1”
means unprogrammed while “0” means programmed.
The most typical and general program setup for the reset and interrupt vector addresses in
ATmega168 is:
Address Labels Code Comments
0x0000 jmp RESET ; Reset Handler
0x0002 jmp EXT_INT0 ; IRQ0 Handler
0x0004 jmp EXT_INT1 ; IRQ1 Handler
0x0006 jmp PCINT0 ; PCINT0 Handler
0x0008 jmp PCINT1 ; PCINT1 Handler
0x000A jmp PCINT2 ; PCINT2 Handler
0x000C jmp WDT ; Watchdog Timer Handler
0x000E jmp TIM2_COMPA ; Timer2 Compare A Handler
0x0010 jmp TIM2_COMPB ; Timer2 Compare B Handler
0x0012 jmp TIM2_OVF ; Timer2 Overflow Handler
0x0014 jmp TIM1_CAPT ; Timer1 Capture Handler
0x0016 jmp TIM1_COMPA ; Timer1 Compare A Handler
0x0018 jmp TIM1_COMPB ; Timer1 Compare B Handler
0x001A jmp TIM1_OVF ; Timer1 Overflow Handler
0x001C jmp TIM0_COMPA ; Timer0 Compare A Handler
0x001E jmp TIM0_COMPB ; Timer0 Compare B Handler
0x0020 jmp TIM0_OVF ; Timer0 Overflow Handler
0x0022 jmp SPI_STC ; SPI Transfer Complete Handler
0x0024 jmp USART_RXC ; USART, RX Complete Handler
0x0026 jmp USART_UDRE ; USART, UDR Empty Handler
0x0028 jmp USART_TXC ; USART, TX Complete Handler
0x002A jmp ADC ; ADC Conversion Complete Handler
0x002C jmp EE_RDY ; EEPROM Ready Handler
0x002E jmp ANA_COMP ; Analog Comparator Handler
0x0030 jmp TWI ; 2-wire Serial Interface Handler
0x0032 jmp SPM_RDY ; Store Program Memory Ready Handler
;
0x0033RESET: ldi r16, high(RAMEND); Main program start
Table 12-5. Reset and interrupt vectors placement in Atmel ATmega168(1).
BOOTRST IVSEL Reset address Interrupt vectors start address
1 0 0x000 0x001
1 1 0x000 Boot reset address + 0x0002
0 0 Boot reset address 0x001
0 1 Boot reset address Boot reset address + 0x000263
2545T–AVR–05/11
ATmega48/88/168
0x0034 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0035 ldi r16, low(RAMEND)
0x0036 out SPL,r16
0x0037 sei ; Enable interrupts
0x0038 xxx
... ... ... ...
When the BOOTRST fuse is unprogrammed, the boot section size set to 2Kbytes and the IVSEL
bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general
program setup for the reset and interrupt vector addresses in Atmel ATmega168 is:
Address Labels Code Comments
0x0000 RESET: ldi r16,high(RAMEND); Main program start
0x0001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0002 ldi r16,low(RAMEND)
0x0003 out SPL,r16
0x0004 sei ; Enable interrupts
0x0005 xxx
;
.org 0xC02
0x1C02 jmp EXT_INT0 ; IRQ0 Handler
0x1C04 jmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x1C32 jmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST fuse is programmed and the boot section size set to 2Kbytes, the most
typical and general program setup for the reset and interrupt vector addresses in ATmega168 is:
Address Labels Code Comments
.org 0x0002
0x0002 jmp EXT_INT0 ; IRQ0 Handler
0x0004 jmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x0032 jmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0x1C00
0x1C00 RESET: ldi r16,high(RAMEND); Main program start
0x1C01 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C02 ldi r16,low(RAMEND)
0x1C03 out SPL,r16
0x1C04 sei ; Enable interrupts
0x1C05 xxx
When the BOOTRST fuse is programmed, the boot section size set to 2Kbytes and the IVSEL
bit in the MCUCR register is set before any interrupts are enabled, the most typical and general
program setup for the reset and interrupt vector addresses in ATmega168 is:64
2545T–AVR–05/11
ATmega48/88/168
Address Labels Code Comments
;
.org 0x1C00
0x1C00 jmp RESET ; Reset handler
0x1C02 jmp EXT_INT0 ; IRQ0 Handler
0x1C04 jmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x1C32 jmp SPM_RDY ; Store Program Memory Ready Handler
;
0x1C33 RESET: ldi r16,high(RAMEND); Main program start
0x1C34 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C35 ldi r16,low(RAMEND)
0x1C36 out SPL,r16
0x1C37 sei ; Enable interrupts
0x1C38 xxx
12.4.1 Moving interrupts between application and boot space, Atmel ATmega88 and Atmel ATmega168
The MCU control register controls the placement of the interrupt vector table.
12.5 Register description
12.5.1 MCUCR – MCU control register
• Bit 1 – IVSEL: Interrupt vector select
When the IVSEL bit is cleared (zero), the interrupt vectors are placed at the start of the flash
memory. When this bit is set (one), the interrupt vectors are moved to the beginning of the boot
loader section of the flash. The actual address of the start of the boot flash section is determined
by the BOOTSZ fuses. Refer to the section “Boot loader support – Read-while-write self-programming,
Atmel ATmega88 and Atmel ATmega168” on page 269 for details. To avoid
unintentional changes of interrupt vector tables, a special write procedure must be followed to
change the IVSEL bit:
a. Write the interrupt vector change enable (IVCE) bit to one.
b. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled
in the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the status
register is unaffected by the automatic disabling.
Note: If interrupt vectors are placed in the boot loader section and boot lock bit BLB02 is programmed,
interrupts are disabled while executing from the Application section. If interrupt vectors are placed
in the Application section and boot lock bit BLB12 is programmed, interrupts are disabled while
executing from the Boot Loader section. Refer to the section “Boot loader support – Read-whilewrite
self-programming, Atmel ATmega88 and Atmel ATmega168” on page 269 for details on
Boot Lock bits.
This bit is not available in Atmel ATmega48.
Bit 7 6 5 4 3 2 1 0
0x35 (0x55) – – – PUD – – IVSEL IVCE MCUCR
Read/write R R R R/W R R R/W R/W
Initial value 0 0 0 0 0 0 0 065
2545T–AVR–05/11
ATmega48/88/168
• Bit 0 – IVCE: Interrupt vector change enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by
hardware four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disable
interrupts, as explained in the IVSEL description above. See code example below.
This bit is not available in Atmel ATmega48.
Assembly code example
Move_interrupts:
; Get MCUCR
in r16, MCUCR
mov r17, r16
; Enable change of Interrupt Vectors
ori r16, (1< CSn2:0 > 1). The number of system clock
cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system
clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution.
However, care must be taken if the other Timer/Counter that shares the same prescaler
also uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is
connected to.
17.0.3 External clock source
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization
logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 17-1
shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector
logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch
is transparent in the high period of the internal system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative
(CSn2:0 = 6) edge it detects.
Figure 17-1. T1/T0 pin sampling.
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the T1/T0 pin to the counter is updated.
Tn_sync
(to clock
select logic)
Synchronization Edge detector
D Q D Q
LE
Tn D Q
clkI/O138
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ATmega48/88/168
Enabling and disabling of the clock input must be done when T1/T0 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the system
clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling frequency
(Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is
recommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 17-2. Prescaler for timer/counter0 and timer/counter1(1).
Note: 1. The synchronization logic on the input pins (T1/T0) is shown in Figure 17-1 on page 137.
PSRSYNC
Clear
clkT1 clkT0
T1
T0
clkI/O
Synchronization
Synchronization139
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ATmega48/88/168
17.1 Register description
17.1.1 GTCCR – General timer/counter control register
• Bit 7 – TSM: Timer/counter synchronization mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the
value that is written to the PSRASY and PSRSYNC bits is kept, hence keeping the corresponding
prescaler reset signals asserted. This ensures that the corresponding Timer/Counters are
halted and can be configured to the same value without the risk of one of them advancing during
configuration. When the TSM bit is written to zero, the PSRASY and PSRSYNC bits are cleared
by hardware, and the Timer/Counters start counting simultaneously.
• Bit 0 – PSRSYNC: Prescaler reset
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This bit is normally
cleared immediately by hardware, except if the TSM bit is set. Note that Timer/Counter1
and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both
timers.
Bit 7 6 5 4 3 2 1 0
0x23 (0x43) TSM – – – – – PSRASY PSRSYNC GTCCR
Read/write R/W R R R R R R/W R/W
Initial value 0 0 0 0 0 0 0 0140
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ATmega48/88/168
18. 8-bit Timer/Counter2 with PWM and asynchronous operation
18.1 Features • Single channel counter
• Clear timer on compare match (auto reload)
• Glitch-free, phase correct pulse width modulator (PWM)
• Frequency generator
• 10-bit clock prescaler
• Overflow and compare match interrupt sources (TOV2, OCF2A and OCF2B)
• Allows clocking from external 32kHz watch crystal independent of the I/O clock
18.2 Overview
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. A simplified
block diagram of the 8-bit Timer/Counter is shown in Figure 18-1. For the actual placement of
I/O pins, refer to “Pinout Atmel ATmega48/88/168.” 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 153.
The PRTIM2 bit in “Minimizing power consumption” on page 41 must be written to zero to enable
Timer/Counter2 module.
Figure 18-1. 8-bit timer/counter block diagram.
Clock select
Timer/counter
DATA BUS
OCRnA
OCRnB
=
=
TCNTn
Waveform
generation
Waveform
generation
OCnA
OCnB
=
Fixed
TOP
value
Control logic
= 0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.req.)
OCnA
(Int.req.)
OCnB
(Int.req.)
TCCRnA TCCRnB
Tn Edge
detector
(From prescaler)
clkTn141
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ATmega48/88/168
18.2.1 Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A and OCR2B) are 8-bit registers.
Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag
Register (TIFR2). All interrupts are individually masked with the Timer Interrupt Mask Register
(TIMSK2). TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from
the TOSC1/2 pins, as detailed later in this section. The asynchronous operation is controlled by
the Asynchronous Status Register (ASSR). The Clock Select logic block controls which clock
source he 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 (clkT2).
The double buffered Output Compare Register (OCR2A and OCR2B) are 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 (OC2A and
OC2B). See “Output compare unit” on page 142. for details. The compare match event will also
set the Compare Flag (OCF2A or OCF2B) which can be used to generate an Output Compare
interrupt request.
18.2.2 Definitions
Many register and bit references in this document are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 2. However, when using the register or bit
defines in a program, the precise form must be used, that is, TCNT2 for accessing
Timer/Counter2 counter value and so on.
The definitions in Table 18-1 are also used extensively throughout the section.
18.3 Timer/counter clock sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source clkT2 is by default equal to the MCU clock, clkI/O. When the AS2
bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter
Oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation, see “ASSR
– Asynchronous status register” on page 159. For details on clock sources and prescaler, see
“Timer/counter prescaler” on page 152.
18.4 Counter unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
18-2 on page 142 shows a block diagram of the counter and its surrounding environment.
Table 18-1. Definitions.
BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00).
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be the fixed value 0xFF
(MAX) or the value stored in the OCR2A Register. The assignment is dependent
on the mode of operation.142
2545T–AVR–05/11
ATmega48/88/168
Figure 18-2. Counter unit block diagram.
Signal description (internal signals):
count Increment or decrement TCNT2 by 1.
direction Selects between increment and decrement.
clear Clear TCNT2 (set all bits to zero).
clkTn Timer/Counter clock, referred to as clkT2 in the following.
top Signalizes that TCNT2 has reached maximum value.
bottom Signalizes that TCNT2 has reached minimum value (zero).
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT2). clkT2 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS22:0). When no clock source is selected (CS22:0 = 0) the
timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clkT2 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 WGM21 and WGM20 bits located in
the Timer/Counter Control Register (TCCR2A) and the WGM22 located in the Timer/Counter
Control Register B (TCCR2B). There are close connections between how the counter behaves
(counts) and how waveforms are generated on the Output Compare outputs OC2A and OC2B.
For more details about advanced counting sequences and waveform generation, see “Modes of
operation” on page 145.
The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation selected by
the WGM22:0 bits. TOV2 can be used for generating a CPU interrupt.
18.5 Output compare unit
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register
(OCR2A and OCR2B). Whenever TCNT2 equals OCR2A or OCR2B, the comparator signals a
match. A match will set the Output Compare Flag (OCF2A or OCF2B) 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 Output Compare 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 WGM22:0 bits and Compare Output mode (COM2x1:0)
bits. The max and bottom signals are used by the Waveform Generator for handling the special
cases of the extreme values in some modes of operation (“Modes of operation” on page 145).
Figure 18-3 on page 143 shows a block diagram of the Output Compare unit.
DATA BUS
TCNTn Control logic
count
TOVn
(Int.req.)
bottom top
direction
clear
TOSC1
T/C
oscillator
TOSC2
Prescaler
clkI/O
clk Tn143
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ATmega48/88/168
Figure 18-3. Output compare unit, block diagram.
The OCR2x Register is double buffered when using any of the Pulse Width Modulation (PWM)
modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, the double
buffering is disabled. The double buffering synchronizes the update of the OCR2x Compare
Register to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR2x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR2x Buffer Register, and if double buffering is disabled
the CPU will access the OCR2x directly.
18.5.1 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 (FOC2x) bit. Forcing compare match will not set the
OCF2x Flag or reload/clear the timer, but the OC2x pin will be updated as if a real compare
match had occurred (the COM2x1:0 bits settings define whether the OC2x pin is set, cleared or
toggled).
18.5.2 Compare match blocking by TCNT2 write
All CPU write operations to the TCNT2 Register will block any compare match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR2x to be initialized
to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is
enabled.
18.5.3 Using the output compare unit
Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT2 when using the Output Compare channel,
independently of whether the Timer/Counter is running or not. If the value written to TCNT2
equals the OCR2x value, the compare match will be missed, resulting in incorrect waveform
generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
downcounting.
OCFnx (int.req.)
= (8-bit comparator)
OCRnx
OCnx
DATA BUS
TCNTn
WGMn1:0
Waveform generator
top
FOCn
COMnX1:0
bottom144
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The setup of the OC2x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC2x value is to use the Force Output Compare
(FOC2x) strobe bit in Normal mode. The OC2x Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM2x1:0 bits are not double buffered together with the compare value.
Changing the COM2x1:0 bits will take effect immediately.
18.6 Compare match output unit
The Compare Output mode (COM2x1:0) bits have two functions. The Waveform Generator uses
the COM2x1:0 bits for defining the Output Compare (OC2x) state at the next compare match.
Also, the COM2x1:0 bits control the OC2x pin output source. Figure 18-4 shows a simplified
schematic of the logic affected by the COM2x1:0 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 COM2x1:0 bits are shown. When referring to the
OC2x state, the reference is for the internal OC2x Register, not the OC2x pin.
Figure 18-4. Compare match output unit, schematic.
The general I/O port function is overridden by the Output Compare (OC2x) from the Waveform
Generator if either of the COM2x1:0 bits are set. However, the OC2x 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 OC2x pin (DDR_OC2x) must be set as output before the OC2x 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 OC2x state before the output
is enabled. Note that some COM2x1:0 bit settings are reserved for certain modes of
operation. See “Register description” on page 153.
PORT
DDR
D Q
D Q
OCnx
OCnx pin
D Q Waveform
generator
COMnx1
COMnx0
0
1
DATA BUS
FOCnx
clkI/O145
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18.6.1 Compare output mode and waveform generation
The Waveform Generator uses the COM2x1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COM2x1:0 = 0 tells the Waveform Generator that no action on the
OC2x Register is to be performed on the next compare match. For compare output actions in the
non-PWM modes refer to Table 18-5 on page 154. For fast PWM mode, refer to Table 18-6 on
page 155, and for phase correct PWM refer to Table 18-7 on page 155.
A change of the COM2x1:0 bits state will have effect at the first compare match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC2x strobe bits.
18.7 Modes of operation
The mode of operation, that is, the behavior of the Timer/Counter and the Output Compare pins,
is defined by the combination of the Waveform Generation mode (WGM22:0) and Compare Output
mode (COM2x1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM2x1:0 bits control whether the PWM output
generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM2x1:0 bits control whether the output should be set, cleared, or toggled at a compare
match (See “Compare match output unit” on page 144.).
For detailed timing information refer to “Timer/counter timing diagrams” on page 149.
18.7.1 Normal mode
The simplest mode of operation is the Normal mode (WGM22:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bottom
(0x00). In normal operation the Timer/Counter Overflow Flag (TOV2) will be set in the same
timer clock cycle as the TCNT2 becomes zero. The TOV2 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 TOV2 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.
18.7.2 Clear timer on compare match (CTC) mode
In Clear Timer on Compare or CTC mode (WGM22:0 = 2), the OCR2A Register is used to
manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter
value (TCNT2) matches the OCR2A. The OCR2A 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 18-5 on page 146. The counter value
(TCNT2) increases until a compare match occurs between TCNT2 and OCR2A, and then counter
(TCNT2) is cleared.146
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Figure 18-5. CTC mode, timing diagram.
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF2A 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 OCR2A is lower than the current
value of TCNT2, 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 OC2A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM2A1:0 = 1). The OC2A 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 fOC2A =
fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following
equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the normal mode of operation, the TOV2 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
18.7.3 Fast PWM mode
The fast Pulse Width Modulation or fast PWM mode (WGM22:0 = 3 or 7) provides a high frequency
PWM waveform generation option. The fast PWM differs from the other PWM option by
its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOTTOM.
TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7. In noninverting
Compare Output mode, the Output Compare (OC2x) is cleared on the compare match
between TCNT2 and OCR2x, and set at BOTTOM. In inverting Compare Output mode, the output
is set on compare match and cleared at BOTTOM. Due to the single-slope operation, the
operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that uses dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
TCNTn
OCnx
(toggle)
OCnx interrupt flag set
Period 1 2 3 4
(COMnx1:0 = 1)
f
OCnx
f
clk_I/O
2 ⋅ ⋅ N ( ) 1 + OCRnx = -------------------------------------------------147
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ATmega48/88/168
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 18-6. The TCNT2 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 TCNT2 slopes represent compare
matches between OCR2x and TCNT2.
Figure 18-6. Fast PWM mode, timing diagram.
The Timer/Counter Overflow Flag (TOV2) 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 OC2x pin.
Setting the COM2x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM2x1:0 to three. TOP is defined as 0xFF when WGM2:0 = 3,
and OCR2A when MGM2:0 = 7. (See Table 18-3 on page 154). The actual OC2x 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 OC2x Register at the compare match between
OCR2x and TCNT2, and clearing (or setting) the OC2x 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:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR2A is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR2A equal to MAX will result
in a constantly high or low output (depending on the polarity of the output set by the COM2A1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting
OC2x to toggle its logical level on each compare match (COM2x1:0 = 1). The waveform
TCNTn
OCRnx update and
TOVn interrupt flag set
Period 1 2 3
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx interrupt flag set
4 5 6 7
f
OCnxPWM
f
clk_I/O
N ⋅ 256 = ------------------148
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ATmega48/88/168
generated will have a maximum frequency of foc2 = fclk_I/O/2 when OCR2A is set to zero. This feature
is similar to the OC2A toggle in CTC mode, except the double buffer feature of the Output
Compare unit is enabled in the fast PWM mode.
18.7.4 Phase correct PWM mode
The phase correct PWM mode (WGM22:0 = 1 or 5) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dual-slope
operation. The counter counts repeatedly from BOTTOM to TOP and then from TOP to BOTTOM.
TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7. In noninverting
Compare Output mode, the Output Compare (OC2x) is cleared on the compare match
between TCNT2 and OCR2x while upcounting, and set on the compare match while downcounting.
In inverting Output Compare mode, the operation is inverted. The dual-slope operation has
lower maximum operation frequency than single slope operation. However, due to the symmetric
feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP.
When the counter reaches TOP, it changes the count direction. The TCNT2 value will be equal
to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown
on Figure 18-7. The TCNT2 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 TCNT2 slopes represent compare matches between OCR2x
and TCNT2.
Figure 18-7. Phase correct PWM mode, timing diagram.
The Timer/Counter Overflow Flag (TOV2) 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
OC2x pin. Setting the COM2x1:0 bits to two will produce a non-inverted PWM. An inverted PWM
TOVn interrupt flag set
OCnx interrupt flag set
1 2 3
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx update149
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ATmega48/88/168
output can be generated by setting the COM2x1:0 to three. TOP is defined as 0xFF when
WGM2:0 = 3, and OCR2A when MGM2:0 = 7 (See Table 18-4 on page 154). The actual OC2x
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 OC2x Register at the compare match
between OCR2x and TCNT2 when the counter increments, and setting (or clearing) the OC2x
Register at compare match between OCR2x and TCNT2 when the counter decrements. The
PWM frequency for the output when using phase correct PWM can be calculated by the following
equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR2A is set equal to BOTTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 18-7 on page 148 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.
• OCR2A changes its value from MAX, like in Figure 18-7 on page 148. When the OCR2A value
is MAX the OCn pin value is the same as the result of a down-counting compare match. To
ensure symmetry around BOTTOM the OCn value at MAX must correspond to the result of an
up-counting Compare Match
• The timer starts counting from a value higher than the one in OCR2A, and for that reason
misses the Compare Match and hence the OCn change that would have happened on the way
up
18.8 Timer/counter timing diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock (clkT2)
is therefore shown as a clock enable signal. In asynchronous mode, clkI/O should be replaced by
the Timer/Counter Oscillator clock. The figures include information on when Interrupt Flags are
set. Figure 18-8 contains timing data for basic Timer/Counter operation. The figure shows the
count sequence close to the MAX value in all modes other than phase correct PWM mode.
Figure 18-8. Timer/counter timing diagram, no prescaling.
Figure 18-9 on page 150 shows the same timing data, but with the prescaler enabled.
f
OCnxPCPWM
f
clk_I/O
N ⋅ 510 = ------------------
clkTn
(clkI/O/1)
TOVn
clkI/O
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1150
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ATmega48/88/168
Figure 18-9. Timer/counter timing diagram, with prescaler (fclk_I/O/8).
Figure 18-10 shows the setting of OCF2A in all modes except CTC mode.
Figure 18-10. Timer/counter timing diagram, setting of OCF2A, with prescaler (fclk_I/O/8).
Figure 18-11 shows the setting of OCF2A and the clearing of TCNT2 in CTC mode.
Figure 18-11. Timer/counter timing diagram, clear timer on compare match mode, with prescaler
(fclk_I/O/8).
TOVn
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
clkI/O
clkTn
(clkI/O/8)
OCFnx
OCRnx
TCNTn
OCRnx value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clkI/O
clkTn
(clkI/O/8)
OCFnx
OCRnx
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clkI/O/8)151
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18.9 Asynchronous operation of Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2x, and TCCR2x might be corrupted. A safe
procedure for switching clock source is:
a. Disable the Timer/Counter2 interrupts by clearing OCIE2x and TOIE2.
b. Select clock source by setting AS2 as appropriate.
c. Write new values to TCNT2, OCR2x, and TCCR2x.
d. To switch to asynchronous operation: Wait for TCN2xUB, OCR2xUB, and TCR2xUB.
e. Clear the Timer/Counter2 Interrupt Flags.
f. Enable interrupts, if needed.
• The CPU main clock frequency must be more than four times the Oscillator frequency
• When writing to one of the registers TCNT2, OCR2x, or TCCR2x, the value is transferred to a
temporary register, and latched after two positive edges on TOSC1. The user should not write
a new value before the contents of the temporary register have been transferred to its
destination. Each of the five mentioned registers have their individual temporary register, which
means that, for example, writing to TCNT2 does not disturb an OCR2x write in progress. To
detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented
• When entering Power-save or ADC Noise Reduction mode after having written to TCNT2,
OCR2x, or TCCR2x, the user must wait until the written register has been updated if
Timer/Counter2 is used to wake up the device. Otherwise, the MCU will enter sleep mode
before the changes are effective. This is particularly important if any of the Output Compare2
interrupt is used to wake up the device, since the Output Compare function is disabled during
writing to OCR2x or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode
before the corresponding OCR2xUB bit returns to zero, the device will never receive a
compare match interrupt, and the MCU will not wake up
• If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise Reduction
mode, precautions must be taken if the user wants to re-enter one of these modes: If reentering
sleep mode within the TOSC1 cycle, the interrupt will immidiately occur and the
device wake up again. The result is multiple interrupts and wake-ups within one TOSC1 cycle
from the first interrupt. If the user is in doubt whether the time before re-entering Power-save or
ADC Noise Reduction mode is sufficient, the following algorithm can be used to ensure that
one TOSC1 cycle has elapsed:
a. Write a value to TCCR2x, TCNT2, or OCR2x.
b. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
c. Enter Power-save or ADC Noise Reduction mode.
• When the asynchronous operation is selected, the 32.768kHz Oscillator for Timer/Counter2 is
always running, except in Power-down and Standby modes. After a Power-up Reset or wakeup
from Power-down or Standby mode, the user should be aware of the fact that this Oscillator
might take as long as one second to stabilize. The user is advised to wait for at least one
second before using Timer/Counter2 after power-up or wake-up from Power-down or Standby
mode. The contents of all Timer/Counter2 Registers must be considered lost after a wake-up
from Power-down or Standby mode due to unstable clock signal upon start-up, no matter
whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin152
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• Description of wake up from Power-save or ADC Noise Reduction mode when the timer is
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
cycles, it executes the interrupt routine, and resumes execution from the instruction following
SLEEP
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an incorrect
result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2 must be
done through a register synchronized to the internal I/O clock domain. Synchronization takes
place for every rising TOSC1 edge. When waking up from Power-save mode, and the I/O clock
(clkI/O) again becomes active, TCNT2 will read as the previous value (before entering sleep)
until the next rising TOSC1 edge. The phase of the TOSC clock after waking up from Powersave
mode is essentially unpredictable, as it depends on the wake-up time. The recommended
procedure for reading TCNT2 is thus as follows:
a. Write any value to either of the registers OCR2x or TCCR2x.
b. Wait for the corresponding Update Busy Flag to be cleared.
c. Read TCNT2.
During asynchronous operation, the synchronization of the Interrupt Flags for the asynchronous
timer takes 3 processor cycles plus one timer cycle. The timer is therefore advanced by at least
one before the processor can read the timer value causing the setting of the Interrupt Flag. The
Output Compare pin is changed on the timer clock and is not synchronized to the processor
clock.
18.10 Timer/counter prescaler
Figure 18-12. Prescaler for Timer/Counter2.
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
clkI/O clkT2S
TOSC1
AS2
CS20
CS21
CS22
clkT2S/8
clkT2S/64
clkT2S/128
clkT2S/1024
clkT2S/256
clkT2S/32
PSRASY 0
Clear
clkT2153
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ATmega48/88/168
The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main
system I/O clock clkIO. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously
clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real Time Counter
(RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from Port C. A crystal can
then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock
source for Timer/Counter2. The Oscillator is optimized for use with a 32.768kHz crystal.
For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64,
clkT2S/128, clkT2S/256, and clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected.
Setting the PSRASY bit in GTCCR resets the prescaler. This allows the user to operate with a
predictable prescaler.
18.11 Register description
18.11.1 TCCR2A – Timer/counter control register A
• Bits 7:6 – COM2A1:0: Compare match output A mode
These bits control the Output Compare pin (OC2A) behavior. If one or both of the COM2A1:0
bits are set, the OC2A 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 OC2A pin
must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the
WGM22:0 bit setting. Table 18-2 shows the COM2A1:0 bit functionality when the WGM22:0 bits
are set to a normal or CTC mode (non-PWM).
Table 18-3 on page 154 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set
to fast PWM mode.
Bit 7 6 5 4 3 2 1 0
(0xB0) COM2A1 COM2A0 COM2B1 COM2B0 – – WGM21 WGM20 TCCR2A
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
Table 18-2. Compare output mode, non-PWM mode.
COM2A1 COM2A0 Description
0 0 Normal port operation, OC2A disconnected
0 1 Toggle OC2A on compare match
1 0 Clear OC2A on compare match
1 1 Set OC2A on compare match154
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Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the Compare
Match is ignored, but the set or clear is done at TOP. See “Fast PWM mode” on page 146
for more details.
Table 18-4 shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to phase correct
PWM mode.
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 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 148 for more details.
• Bits 5:4 – COM2B1:0: Compare match output B mode
These bits control the Output Compare pin (OC2B) behavior. If one or both of the COM2B1:0
bits are set, the OC2B 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 OC2B pin
must be set in order to enable the output driver.
When OC2B is connected to the pin, the function of the COM2B1:0 bits depends on the
WGM22:0 bit setting. Table 18-5 shows the COM2B1:0 bit functionality when the WGM22:0 bits
are set to a normal or CTC mode (non-PWM).
Table 18-3. Compare output mode, fast PWM mode(1).
COM2A1 COM2A0 Description
0 0 Normal port operation, OC2A disconnected
0 1 WGM22 = 0: Normal port operation, OC0A disconnected
WGM22 = 1: Toggle OC2A on compare match
1 0 Clear OC2A on compare match, set OC2A at BOTTOM,
(non-inverting mode)
1 1 Set OC2A on compare match, clear OC2A at BOTTOM,
(inverting mode)
Table 18-4. Compare output mode, phase correct PWM Mode(1).
COM2A1 COM2A0 Description
0 0 Normal port operation, OC2A disconnected
0 1 WGM22 = 0: Normal port operation, OC2A disconnected
WGM22 = 1: Toggle OC2A on compare match
1 0 Clear OC2A on compare match when up-counting
Set OC2A on compare match when down-counting
1 1 Set OC2A on compare match when up-counting
Clear OC2A on compare match when down-counting
Table 18-5. Compare output mode, non-PWM mode.
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected
0 1 Toggle OC2B on compare match
1 0 Clear OC2B on compare match
1 1 Set OC2B on compare match155
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Table 18-6 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 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 148 for more details.
Table 18-7 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to phase correct
PWM mode.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 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 148 for more details.
• Bits 3, 2 – Res: Reserved bits
These bits are reserved bits in the Atmel ATmega48/88/168 and will always read as zero.
• Bits 1:0 – WGM21:0: Waveform generation mode
Combined with the WGM22 bit found in the TCCR2B 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 18-8 on page 156. 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
145).
Table 18-6. Compare output mode, fast PWM mode(1).
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected
0 1 Reserved
1 0 Clear OC2B on compare match, set OC2B at BOTTOM,
(non-inverting mode)
1 1 Set OC2B on compare match, clear OC2B at BOTTOM,
(invertiing mode)
Table 18-7. Compare output mode, phase correct PWM mode(1).
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected
0 1 Reserved
1 0 Clear OC2B on compare match when up-counting
Set OC2B on compare match when down-counting
1 1 Set OC2B on compare match when up-counting
Clear OC2B on compare match when down-counting156
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Notes: 1. MAX= 0xFF
2. BOTTOM= 0x00
18.11.2 TCCR2B – Timer/counter control register B
• Bit 7 – FOC2A: Force output compare A
The FOC2A 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
TCCR2B is written when operating in PWM mode. When writing a logical one to the FOC2A bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC2A output is
changed according to its COM2A1:0 bits setting. Note that the FOC2A bit is implemented as a
strobe. Therefore it is the value present in the COM2A1:0 bits that determines the effect of the
forced compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6 – FOC2B: Force output compare B
The FOC2B 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
TCCR2B is written when operating in PWM mode. When writing a logical one to the FOC2B bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC2B output is
changed according to its COM2B1:0 bits setting. Note that the FOC2B bit is implemented as a
strobe. Therefore it is the value present in the COM2B1:0 bits that determines the effect of the
forced compare.
Table 18-8. Waveform generation mode bit description.
Mode WGM2 WGM1 WGM0
Timer/counter
mode of
operation TOP
Update of
OCRx at
TOV flag
set on(1)(2)
0 0 0 0 Normal 0xFF Immediate MAX
10 0 1 PWM,
phase correct 0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF BOTTOM MAX
4 1 0 0 Reserved – – –
51 0 1 PWM,
phase correct OCRA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA BOTTOM TOP
Bit 7 6 5 4 3 2 1 0
(0xB1) FOC2A FOC2B – – WGM22 CS22 CS21 CS20 TCCR2B
Read/write W W R R R R R/W R/W
Initial value 0 0 0 0 0 0 0 0157
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A FOC2B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR2B as TOP.
The FOC2B bit is always read as zero.
• Bits 5:4 – Res: Reserved bits
These bits are reserved bits in the Atmel ATmega48/88/168 and will always read as zero.
• Bit 3 – WGM22: Waveform generation mode
See the description in the “TCCR2A – Timer/counter control register A” on page 153.
• Bit 2:0 – CS22:0: Clock select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table
18-9.
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.
18.11.3 TCNT2 – Timer/counter register
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT2) while the counter is running,
introduces a risk of missing a Compare Match between TCNT2 and the OCR2x Registers.
18.11.4 OCR2A – Output compare register A
Table 18-9. Clock select bit description.
CS22 CS21 CS20 Description
0 0 0 No clock source (timer/counter stopped)
0 0 1 clkT2S/(no prescaling)
0 1 0 clkT2S/8 (from prescaler)
0 1 1 clkT2S/32 (from prescaler)
1 0 0 clkT2S/64 (from prescaler)
1 0 1 clkT2S/128 (from prescaler)
1 1 0 clkT2S/256 (from prescaler)
1 1 1 clkT2S/1024 (from prescaler)
Bit 7 6 5 4 3 2 1 0
(0xB2) TCNT2[7:0] TCNT2
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
(0xB3) OCR2A[7:0] OCR2A
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 0158
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The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT2). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC2A pin.
18.11.5 OCR2B – Output compare register B
The Output Compare Register B contains an 8-bit value that is continuously compared with the
counter value (TCNT2). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC2B pin.
18.11.6 TIMSK2 – Timer/Counter2 interrupt mask register
• Bit 2 – OCIE2B: Timer/Counter2 output compare match B interrupt enable
When the OCIE2B bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match B interrupt is enabled. The corresponding interrupt is executed
if a compare match in Timer/Counter2 occurs, that is, when the OCF2B bit is set in the
Timer/Counter 2 Interrupt Flag Register – TIFR2.
• Bit 1 – OCIE2A: Timer/Counter2 output compare match A interrupt enable
When the OCIE2A bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a compare match in Timer/Counter2 occurs, that is, when the OCF2A bit is set in the
Timer/Counter 2 Interrupt Flag Register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 overflow interrupt enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter2 occurs, that is, when the TOV2 bit is set in the Timer/Counter2 Interrupt
Flag Register – TIFR2.
18.11.7 TIFR2 – Timer/Counter2 interrupt flag register
• Bit 2 – OCF2B: Output compare flag 2 B
The OCF2B bit is set (one) when a compare match occurs between the Timer/Counter2 and the
data in OCR2B – Output Compare Register2. OCF2B is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF2B is cleared by writing a logic
one to the flag. When the I-bit in SREG, OCIE2B (Timer/Counter2 Compare match Interrupt
Enable), and OCF2B are set (one), the Timer/Counter2 Compare match Interrupt is executed.
Bit 7 6 5 4 3 2 1 0
(0xB4) OCR2B[7:0] OCR2B
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
(0x70) – – – – – OCIE2B OCIE2A TOIE2 TIMSK2
Read/write R R R R R R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
0x17 (0x37) – – – – – OCF2B OCF2A TOV2 TIFR2
Read/write R R R R R R/W R/W R/W
Initial value 0 0 0 0 0 0 0 0159
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• Bit 1 – OCF2A: Output compare flag 2 A
The OCF2A bit is set (one) when a compare match occurs between the Timer/Counter2 and the
data in OCR2A – Output Compare Register2. OCF2A is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF2A is cleared by writing a logic
one to the flag. When the I-bit in SREG, OCIE2A (Timer/Counter2 Compare match Interrupt
Enable), and OCF2A are set (one), the Timer/Counter2 Compare match Interrupt is executed.
• Bit 0 – TOV2: Timer/Counter2 overflow flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared
by writing a logic one to the flag. When the SREG I-bit, TOIE2A (Timer/Counter2 Overflow Interrupt
Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In
PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
18.11.8 ASSR – Asynchronous status register
• Bit 7 – RES: Reserved bit
This bit is reserved and will always read as zero.
• Bit 6 – EXCLK: Enable external clock input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input buffer
is enabled and an external clock can be input on Timer Oscillator 1 (TOSC1) pin instead of a
32kHz crystal. Writing to EXCLK should be done before asynchronous operation is selected.
Note that the crystal Oscillator will only run when this bit is zero.
• Bit 5 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When AS2 is
written to one, Timer/Counter2 is clocked from a crystal Oscillator connected to the Timer Oscillator
1 (TOSC1) pin. When the value of AS2 is changed, the contents of TCNT2, OCR2A,
OCR2B, TCCR2A and TCCR2B might be corrupted.
• Bit 4 – TCN2UB: Timer/Counter2 update busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set.
When TCNT2 has been updated from the temporary storage register, this bit is cleared by hardware.
A logical zero in this bit indicates that TCNT2 is ready to be updated with a new value.
• Bit 3 – OCR2AUB: Output compare Register2 update busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes set.
When OCR2A has been updated from the temporary storage register, this bit is cleared by hardware.
A logical zero in this bit indicates that OCR2A is ready to be updated with a new value.
• Bit 2 – OCR2BUB: Output compare Register2 update busy
When Timer/Counter2 operates asynchronously and OCR2B is written, this bit becomes set.
When OCR2B has been updated from the temporary storage register, this bit is cleared by hardware.
A logical zero in this bit indicates that OCR2B is ready to be updated with a new value.
Bit 7 6 5 4 3 2 1 0
(0xB6) – EXCLK AS2 TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB ASSR
Read/write R R/W R/W R R R R R
Initial value 0 0 0 0 0 0 0 0160
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• Bit 1 – TCR2AUB: Timer/counter control Register2 update busy
When Timer/Counter2 operates asynchronously and TCCR2A is written, this bit becomes set.
When TCCR2A has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCCR2A is ready to be updated with a new
value.
• Bit 0 – TCR2BUB: Timer/counter control Register2 update busy
When Timer/Counter2 operates asynchronously and TCCR2B is written, this bit becomes set.
When TCCR2B has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCCR2B is ready to be updated with a new
value.
If a write is performed to any of the five Timer/Counter2 Registers while its update busy flag is
set, the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B are different.
When reading TCNT2, the actual timer value is read. When reading OCR2A, OCR2B, TCCR2A
and TCCR2B the value in the temporary storage register is read.
18.11.9 GTCCR – General timer/counter control register
• Bit 1 – PSRASY: Prescaler reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared
immediately by hardware. If the bit is written when Timer/Counter2 is operating in asynchronous
mode, the bit will remain one until the prescaler has been reset. The bit will not be cleared by
hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/counter synchronization
mode” on page 139 for a description of the Timer/Counter Synchronization mode.
Bit 7 6 5 4 3 2 1 0
0x23 (0x43) TSM – – – – – PSRASY PSRSYNC GTCCR
Read/write R/W R R R R R R/W R/W
Initial value 0 0 0 0 0 0 0 0161
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19. SPI – Serial peripheral interface
19.1 Features • Full-duplex, three-wire synchronous data transfer
• Master or slave operation
• LSB first or MSB first data transfer
• Seven programmable bit rates
• End of transmission interrupt flag
• Write collision flag protection
• Wake-up from idle mode
• Double speed (CK/2) master SPI mode
19.2 Overview
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the
Atmel ATmega48/88/168 and peripheral devices or between several AVR devices.
The USART can also be used in Master SPI mode, see “USART in SPI mode” on page 199. The
PRSPI bit in “Minimizing power consumption” on page 41 must be written to zero to enable SPI
module.162
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Figure 19-1. SPI block diagram(1).
Note: 1. Refer to Figure 1-1 on page 2, and Table 14-3 on page 78 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 19-2 on page
163. 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 SPI2X SPI2X
DIVIDER
/2/4/8/16/32/64/128163
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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 19-2. SPI master-slave interconnection.
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.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 19-1. For more details on automatic port overrides, refer to “Alternate port
functions” on page 76.
Note: See “Alternate functions of port B” on page 78 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. For example if MOSI is placed on pin PB3, replace
DD_MOSI with DDB3 and DDR_SPI with DDRB.
Table 19-1. SPI pin overrides(Note:).
Pin Direction, master SPI Direction, slave SPI
MOSI User defined Input
MISO Input User defined
SCK User defined Input
SS User defined Input
SHIFT
ENABLE164
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Note: 1. See ”About code examples” on page 8.
Assembly code example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi r17,(1<>8);
UBRR0L = (unsigned char)ubrr;
Enable receiver and transmitter */
UCSR0B = (1<> 1) & 0x01;
return ((resh << 8) | resl);
}184
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20.7.3 Receive complete flag and interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXCn) Flag indicates if there are unread data present in the receive buffer.
This flag is one when unread data exist in the receive buffer, and zero when the receive
buffer is empty (that is, does not contain any unread data). If the Receiver is disabled (RXENn =
0), the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the Receive Complete Interrupt Enable (RXCIEn) in UCSRnB is set, the USART Receive
Complete interrupt will be executed as long as the RXCn Flag is set (provided that global interrupts
are enabled). When interrupt-driven data reception is used, the receive complete routine
must read the received data from UDRn in order to clear the RXCn Flag, otherwise a new interrupt
will occur once the interrupt routine terminates.
20.7.4 Receiver error flags
The USART Receiver has three Error Flags: Frame Error (FEn), Data OverRun (DORn) and
Parity Error (UPEn). All can be accessed by reading UCSRnA. Common for the Error Flags is
that they are located in the receive buffer together with the frame for which they indicate the
error status. Due to the buffering of the Error Flags, the UCSRnA must be read before the
receive buffer (UDRn), since reading the UDRn I/O location changes the buffer read location.
Another equality for the Error Flags is that they can not be altered by software doing a write to
the flag location. However, all flags must be set to zero when the UCSRnA is written for upward
compatibility of future USART implementations. None of the Error Flags can generate interrupts.
The Frame Error (FEn) Flag indicates the state of the first stop bit of the next readable frame
stored in the receive buffer. The FEn Flag is zero when the stop bit was correctly read (as one),
and the FEn Flag will be one when the stop bit was incorrect (zero). This flag can be used for
detecting out-of-sync conditions, detecting break conditions and protocol handling. The FEn
Flag is not affected by the setting of the USBSn bit in UCSRnC since the Receiver ignores all,
except for the first, stop bits. For compatibility with future devices, always set this bit to zero
when writing to UCSRnA.
The Data OverRun (DORn) Flag indicates data loss due to a receiver buffer full condition. A
Data OverRun occurs when the receive buffer is full (two characters), it is a new character waiting
in the Receive Shift Register, and a new start bit is detected. If the DORn Flag is set there
was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing
to UCSRnA. The DORn Flag is cleared when the frame received was successfully moved from
the Shift Register to the receive buffer.
The Parity Error (UPEn) Flag indicates that the next frame in the receive buffer had a Parity
Error when received. If Parity Check is not enabled the UPEn bit will always be read zero. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA. For more
details see “Parity bit calculation” on page 176 and “Parity checker” on page 184.
20.7.5 Parity checker
The Parity Checker is active when the high USART Parity mode (UPMn1) bit is set. Type of Parity
Check to be performed (odd or even) is selected by the UPMn0 bit. When enabled, the Parity
Checker calculates the parity of the data bits in incoming frames and compares the result with
the parity bit from the serial frame. The result of the check is stored in the receive buffer together
with the received data and stop bits. The Parity Error (UPEn) Flag can then be read by software
to check if the frame had a Parity Error.185
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The UPEn bit is set if the next character that can be read from the receive buffer had a Parity
Error when received and the Parity Checking was enabled at that point (UPMn1 = 1). This bit is
valid until the receive buffer (UDRn) is read.
20.7.6 Disabling the receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing
receptions will therefore be lost. When disabled (that is, the RXENn is set to zero) the Receiver
will no longer override the normal function of the RxDn port pin. The Receiver buffer FIFO will be
flushed when the Receiver is disabled. Remaining data in the buffer will be lost
20.7.7 Flushing the receive buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, that is, the buffer will be
emptied of its contents. Unread data will be lost. If the buffer has to be flushed during normal
operation, due to for instance an error condition, read the UDRn I/O location until the RXCn Flag
is cleared. The following code example shows how to flush the receive buffer.
Note: 1. See ”About code examples” on page 8.
20.8 Asynchronous data reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data
reception. The clock recovery logic is used for synchronizing the internally generated baud rate
clock to the incoming asynchronous serial frames at the RxDn pin. The data recovery logic samples
and low pass filters each incoming bit, thereby improving the noise immunity of the
Receiver. The asynchronous reception operational range depends on the accuracy of the internal
baud rate clock, the rate of the incoming frames, and the frame size in number of bits.
20.8.1 Asynchronous clock recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 20-5
on page 186 illustrates the sampling process of the start bit of an incoming frame. The sample
rate is 16 times the baud rate for Normal mode, and eight times the baud rate for Double Speed
mode. The horizontal arrows illustrate the synchronization variation due to the sampling process.
Note the larger time variation when using the Double Speed mode (U2Xn = 1) of
operation. Samples denoted zero are samples done when the RxDn line is idle (that is, no communication
activity).
Assembly code example(1)
USART_Flush:
sbis UCSRnA, RXCn
ret
in r16, UDRn
rjmp USART_Flush
C code example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSRnA & (1< 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck >= 12MHz
High: > 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck >= 12MHz
VCC
GND
XTAL1
SCK
MISO
MOSI
RESET
+1.8V - 5.5V
AVCC
+1.8V - 5.5V(2)299
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28.8.1 Serial programming pin mapping
28.8.2 Serial programming algorithm
When writing serial data to the Atmel ATmega48/88/168, data is clocked on the rising edge of
SCK.
When reading data from the ATmega48/88/168, data is clocked on the falling edge of SCK. See
Figure 28-9 on page 302 for timing details.
To program and verify the ATmega48/88/168 in the serial programming mode, the following
sequence is recommended (See Serial Programming Instruction set in Table 28-17 on page
300):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems,
the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization.
When in sync. the second byte (0x53), will echo back when issuing the third
byte of the Programming Enable instruction. Whether the echo is correct or not, all four
bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at a
time by supplying the 6 LSB of the address and data together with the Load Program
Memory Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program Memory
Page is stored by loading the Write Program Memory Page instruction with the 7 MSB of
the address. If polling (RDY/BSY) is not used, the user must wait at least tWD_FLASH before
issuing the next page (see Table 28-16 on page 300). Accessing the serial programming
interface before the Flash write operation completes can result in incorrect programming.
5. A: The EEPROM array is programmed one byte at a time by supplying the address and
data together with the appropriate Write instruction. An EEPROM memory location is first
automatically erased before new data is written. If polling (RDY/BSY) is not used, the
user must wait at least tWD_EEPROM before issuing the next byte (see Table 28-16 on page
300). In a chip erased device, no 0xFFs in the data file(s) need to be programmed.
B: The EEPROM array is programmed one page at a time. The Memory page is loaded
one byte at a time by supplying the 6 LSB of the address and data together with the Load
EEPROM Memory Page instruction. The EEPROM Memory Page is stored by loading
the Write EEPROM Memory Page Instruction with the 7 MSB of the address. When using
EEPROM page access only byte locations loaded with the Load EEPROM Memory Page
instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is
not used, the used must wait at least tWD_EEPROM before issuing the next byte (See Table
Table 28-15. Pin mapping serial programming.
Symbol Pins I/O Description
MOSI PB3 I Serial Data in
MISO PB4 O Serial Data out
SCK PB5 I Serial Clock300
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ATmega48/88/168
28-16 on page 300). In a chip erased device, no 0xFF in the data file(s) need to be
programmed.
6. Any memory location can be verified by using the Read instruction which returns the content
at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
28.8.3 Serial programming instruction set
Table 28-17 and Figure 28-8 on page 302 describes the instruction set.
Table 28-16. Typical wait delay before writing the next flash or EEPROM location.
Symbol Minimum wait delay
tWD_FLASH 4.5ms
tWD_EEPROM 3.6ms
tWD_ERASE 9.0ms
Table 28-17. Serial programming instruction set (hexadecimal values).
Instruction/operation
Instruction format
Byte 1 Byte 2 Byte 3 Byte 4
Programming enable $AC $53 $00 $00
Chip erase (program memory/EEPROM) $AC $80 $00 $00
Poll RDY/BSY $F0 $00 $00 data byte out
Load instructions
Load extended address byte(1) $4D $00 Extended adr $00
Load program memory page, high byte $48 $00 adr LSB high data byte in
Load program memory page, low byte $40 $00 adr LSB low data byte in
Load EEPROM memory page (page access) $C1 $00 0000 000aa data byte in
Read instructions
Read program memory, high byte $28 adr MSB adr LSB high data byte out
Read program memory, low byte $20 adr MSB adr LSB low data byte out
Read EEPROM memory $A0 0000 00aa aaaa aaaa data byte out
Read lock bits $58 $00 $00 data byte out
Read signature byte $30 $00 0000 000aa data byte out
Read fuse bits $50 $00 $00 data byte out
Read fuse high bits $58 $08 $00 data byte out
Read extended fuse bits $50 $08 $00 data byte out
Read calibration byte $38 $00 $00 data byte out301
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ATmega48/88/168
Notes: 1. Not all instructions are applicable for all parts.
2. a = address.
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused fuses and lock bits should be unprogrammed (‘1’).
5. Refer to the correspondig section for fuse and lock bits, calibration and signature bytes and page size.
6. Instructions accessing program memory use a word address. This word may be random within the page range.
7. See htt://www.atmel.com/avr for application notes regarding programming and programmers.
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until
this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 28-8.
Write instructions(6)
Write program memory page $4C adr MSB adr LSB $00
Write EEPROM memory $C0 0000 00aa aaaa aaaa data byte in
Write EEPROM memory page (page access) $C2 0000 00aa aaaa aa00 $00
Write lock bits $AC $E0 $00 data byte in
Write fuse bits $AC $A0 $00 data byte in
Write fuse high bits $AC $A8 $00 data byte in
Write extended fuse bits $AC $A4 $00 data byte in
Table 28-17. Serial programming instruction set (hexadecimal values). (Continued)
Instruction/operation
Instruction format
Byte 1 Byte 2 Byte 3 Byte 4302
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ATmega48/88/168
Figure 28-8. Serial programming instruction example.
28.8.4 SPI serial programming characteristics
Figure 28-9. Serial programming waveforms.
For characteristics of the SPI module see “SPI timing characteristics” on page 309.
Byte 1 Byte 2 Byte 3 Byte 4
Adr MSB Adr LSB
Bit 15 B 0
Serial programming instruction
Program memory/
EEPROM memory
Page 0
Page 1
Page 2
Page N-1
Page buffer
Write program memory page/
Write EEPROM memory page
Load program memory page (high/low byte)/
Load EEPROM memory page (page access)
Byte 1 Byte 2 Byte 3 Byte 4
Bit 15 B 0
Adr MSB Adr LSB
Page offset
Page number
Adr MSB Adr LSB
MSB
MSB
LSB
LSB
SERIAL CLOCK INPUT
(SCK)
SERIAL DATA INPUT
(MOSI)
(MISO)
SAMPLE
SERIAL DATA OUTPUT303
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29. Electrical characteristics
29.1 Absolute maximum ratings*
29.2 DC characteristics
Operating temperature................................... -55°C to +125°C *NOTICE: 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.
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
Maximum operating voltage.............................................. 6.0V
DC current per I/O pin.................................................. 40.0mA
DC current VCC and GND pins .................................. 200.0mA
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted).
Symbol Parameter Condition Minimum Typical Maximum Units
VIL
Input low voltage, except
XTAL1 and RESET pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
-0.5
0.2VCC(1)
0.3VCC(1)
V
VIH
Input high voltage, except
XTAL1 and RESET pins
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC + 0.5
VCC + 0.5
VIL1
Input low voltage,
XTAL1 pin VCC = 1.8V - 5.5V -0.5 0.1VCC(1)
VIH1
Input high voltage,
XTAL1 pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.8VCC(2)
0.7VCC(2)
VCC + 0.5
VCC + 0.5
VIL2
Input low voltage,
RESET pin VCC = 1.8V - 5.5V -0.5 0.2VCC(1)
VIH2
Input high voltage,
RESET pin VCC = 1.8V - 5.5V 0.9VCC(2) VCC + 0.5
VIL3
Input low voltage,
RESET pin as I/O
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
-0.5
0.2VCC(1)
0.3VCC(1)
VIH3
Input high voltage,
RESET pin as I/O
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC + 0.5
VCC + 0.5
VOL
Output low voltage(3),
RESET pin as I/O
I
OL = 20mA, VCC = 5V
IOL = 6mA, VCC = 3V
0.7
0.5
VOH
Output high voltage(4),
RESET pin as I/O
I
OH = -20mA, VCC = 5V
I
OH = -10mA, VCC = 3V
4.2
2.3
IIL
Input leakage
current I/O pin
VCC = 5.5V, pin low
(absolute value) 1
µA
I
IH
Input leakage
current I/O pin
VCC = 5.5V, pin high
(absolute value) 1
RRST Reset pull-up resistor 30 60
kΩ
RPU I/O pin pull-up resistor 20 50304
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ATmega48/88/168
Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
ATmega48/88/168:
1] The sum of all IOL, for ports C0 - C5, ADC7, ADC6 should not exceed 100mA.
2] The sum of all IOL, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 100mA.
3] The sum of all IOL, for ports D0 - D4, RESET should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
ATmega48/88/168:
1] The sum of all IOH, for ports C0 - C5, D0- D4, ADC7, RESET should not exceed 150mA.
2] The sum of all IOH, for ports B0 - B5, D5 - D7, ADC6, XTAL1, XTAL2 should not exceed 150mA.
If IIOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
5. Values with “Minimizing power consumption” on page 41 enabled (0xFF).
ICC
Power supply current(5)
Active 1MHz, VCC = 2V
(Atmel ATmega48/88/168V) 0.55
mA
Active 4MHz, VCC = 3V
(Atmel ATmega48/88/168L) 3.5
Active 8MHz, VCC = 5V
(Atmel ATmega48/88/168) 12
Idle 1MHz, VCC = 2V
(ATmega48/88/168V) 0.25 0.5
Idle 4MHz, VCC = 3V
(ATmega48/88/168L) 1.5
Idle 8MHz, VCC = 5V
(ATmega48/88/168) 5.5
Power-down mode
WDT enabled, VCC = 3V 8 15
µA
WDT disabled, VCC = 3V 1 2
VACIO
Analog comparator
input offset voltage
VCC = 5V
Vin = VCC/2 10 40 mV
IACLK
Analog comparator
input leakage current
VCC = 5V
Vin = VCC/2 -50 50 nA
t
ACID
Analog comparator
propagation delay
VCC = 2.7V
VCC = 4.0V
750
500 ns
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted). (Continued)
Symbol Parameter Condition Minimum Typical Maximum Units305
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ATmega48/88/168
29.3 Speed grades
Maximum frequency is dependent on VCC. As shown in Figure 29-1 and Figure 29-2, the Maximum
Frequency vs. VCC curve is linear between 1.8V < VCC < 2.7V and between 2.7V < VCC <
4.5V.
Figure 29-1. Maximum frequency vs. VCC, Atmel ATmega48V/88V/168V.
Figure 29-2. Maximum frequency vs. VCC, ATmega48/88/168.
10MHz
4MHz
1.8V 2.7V 5.5V
Safe operating area
20MHz
10MHz
2.7V 4.5V 5.5V
Safe operating area306
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ATmega48/88/168
29.4 Clock characteristics
29.4.1 Calibrated internal RC oscillator accuracy
Notes: 1. Voltage range for Atmel ATmega48V/88V/168V.
2. Voltage range for Atmel ATmega48/88/168.
29.4.2 External clock drive waveforms
Figure 29-3. External clock drive waveforms.
29.4.3 External clock drive
Table 29-1. Calibration accuracy of internal RC oscillator.
Frequency VCC Temperature Calibration accuracy
Factory calibration 8.0MHz 3V 25°C ±10%
User calibration 7.3MHz - 8.1MHz 1.8V - 5.5V(1)
2.7V - 5.5V(2) -40°C - 85°C ±1%
VIL1
VIH1
Table 29-2. External clock drive.
Symbol Parameter
VCC = 1.8V - 5.5V VCC = 2.7V - 5.5V VCC = 4.5V - 5.5V
Min. Max. Min. Max. Min. Max. Units
1/tCLCL
Oscillator
frequency 0 4 0 10 0 20 MHz
tCLCL Clock period 250 100 50
tCHCX High time 100 40 20 ns
tCLCX Low time 100 40 20
tCLCH Rise time 2.0 1.6 0.5
μs
tCHCL Fall time 2.0 1.6 0.5
ΔtCLCL
Change in period
from one clock
cycle to the next
2 2 2%307
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ATmega48/88/168
29.5 System and reset characteristics
Note: 1. The power-on reset will not work unless the supply voltage has been below VPOT (falling).
Notes: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case, the device is
tested down to VCC = VBOT during the production test. This guarantees that a brown-out reset will occur before VCC drops to
a voltage where correct operation of the microcontroller is no longer guaranteed. The test is performed using
BODLEVEL = 110 and BODLEVEL = 101 for Atmel ATmega48V/88V/168V, and BODLEVEL = 101 and BODLEVEL = 100
for Atmel ATmega48/88/168.
Table 29-3. Reset, brown-out and internal voltage characteristics.
Symbol Parameter Condition Min. Typ. Max. Units
VPOT
Power-on reset threshold voltage (rising) 0.7 1.0 1.4
V
Power-on reset threshold voltage (falling)(1) 0.05 0.9 1.3
VPONSR Power-on slope rate 0.01 4.5 V/ms
VRST RESET pin threshold voltage 0.2VCC 0.9VCC V
tRST Minimum pulse width on RESET pin 2.5 µs
VHYST Brown-out detector hysteresis 50 mV
tBOD Min pulse width on brown-out reset 2 µs
VBG Bandgap reference voltage VCC = 2.7
TA = 25°C 1.0 1.1 1.2 V
t
BG Bandgap reference start-up time VCC = 2.7
TA = 25°C 40 70 µs
I
BG Bandgap reference current consumption VCC = 2.7
TA = 25°C 10 µA
Table 29-4. BODLEVEL fuse coding(1).
BODLEVEL 2:0 Fuses Min. VBOT Typ. VBOT Max. VBOT Units
111 BOD disabled
110 1.7 1.8 2.0
101 2.5 2.7 2.9 V
100 4.1 4.3 4.5
011
Reserved
010
001
000308
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ATmega48/88/168
29.6 2-wire serial interface characteristics
Table 29-5 describes the requirements for devices connected to the 2-wire Serial Bus. The Atmel ATmega48/88/168 2-wire
Serial Interface meets or exceeds these requirements under the noted conditions.
Timing symbols refer to Figure 29-4 on page 309.
Notes: 1. In ATmega48/88/168, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100kHz.
Table 29-5. 2-wire serial bus requirements.
Symbol Parameter Condition Min. Max. Units
VIL Input low-voltage -0.5 0.3VCC
V
VIH Input high-voltage 0.7VCC VCC + 0.5
Vhys(1) Hysteresis of schmitt trigger inputs 0.05VCC(2) –
VOL(1) Output low-voltage 3mA sink current 0 0.4
tr
(1) Rise time for both SDA and SCL 20 + 0.1Cb
(3)(2) 300
tof ns (1) Output fall time from VIHmin to VILmax 10pF < Cb < 400pF(3) 20 + 0.1Cb
(3)(2) 250
tSP(1) Spikes suppressed by input filter 0 50(2)
Ii Input current each I/O pin 0.1VCC < Vi
< 0.9VCC -10 10 µA
Ci
(1) Capacitance for each I/O pin – 10 pF
fSCL SCL clock frequency fCK(4) > max(16fSCL, 250kHz)(5) 0 400 kHz
Rp Value of pull-up resistor
fSCL ≤ 100kHz
fSCL > 100kHz
tHD;STA Hold time (repeated) START condition
fSCL ≤ 100kHz 4.0 –
µs
fSCL > 100kHz 0.6 –
tLOW Low period of the SCL clock
fSCL ≤ 100kHz 4.7 –
fSCL > 100kHz 1.3 –
tHIGH High period of the SCL clock
fSCL ≤ 100kHz 4.0 –
fSCL > 100kHz 0.6 –
tSU;STA Setup time for a repeated START condition
fSCL ≤ 100kHz 4.7 –
fSCL > 100kHz 0.6 –
tHD;DAT Data hold time
fSCL ≤ 100kHz 0 3.45
fSCL > 100kHz 0 0.9
tSU;DAT Data setup time
fSCL ≤ 100kHz 250 –
ns
fSCL > 100kHz 100 –
tSU;STO Setup time for STOP condition
fSCL ≤ 100kHz 4.0 –
µs
fSCL > 100kHz 0.6 –
tBUF
Bus free time between a STOP and START
condition
fSCL ≤ 100kHz 4.7 –
fSCL > 100kHz 1.3 –
VCC – 0.4V
3mA ---------------------------- 1000ns
Cb
-----------------
Ω
VCC – 0.4V
3mA ---------------------------- 300ns
Cb
--------------309
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ATmega48/88/168
3. Cb = capacitance of one bus line in pF.
4. fCK = CPU clock frequency.
5. This requirement applies to all Atmel ATmega48/88/168 2-wire Serial Interface operation. Other devices connected to the 2-
wire Serial Bus need only obey the general fSCL requirement.
Figure 29-4. 2-wire serial bus timing.
29.7 SPI timing characteristics
See Figure 29-5 on page 310 and Figure 29-6 on page 310 for details.
Note: 1. In SPI programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12MHz
- 3 tCLCL for fCK > 12MHz
t
SU;STA
t
LOW
t
HIGH
t
LOW
t
of
t
HD;STA t
HD;DAT t
SU;DAT t
SU;STO
t
BUF
SCL
SDA
t
r
Table 29-6. SPI timing parameters.
Description Mode Minimum Typical Maximum
1 SCK period Master See Table 19-5
on page 169
ns
2 SCK high/low Master 50% duty cycle
3 Rise/fall time Master 3.6
4 Setup Master 10
5 Hold Master 10
6 Out to SCK Master 0.5 • tsck
7 SCK to out Master 10
8 SCK to out high Master 10
9 SS low to out Slave 15
10 SCK period Slave 4 • tck
11 SCK high/low(1) Slave 2 • tck
12 Rise/fall time Slave 1600
13 Setup Slave 10
14 Hold Slave tck
15 SCK to out Slave 15
16 SCK to SS high Slave 20
17 SS high to tri-state Slave 10
18 SS low to SCK Slave 20310
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Figure 29-5. SPI interface timing requirements (master mode).
Figure 29-6. SPI interface timing requirements (slave mode).
MOSI
(Data output)
SCK
(CPOL = 1)
MISO
(Data input)
SCK
(CPOL = 0)
SS
MSB LSB
MSB LSB
...
...
6 1
2 2
4 5 3
7 8
MISO
(Data output)
SCK
(CPOL = 1)
MOSI
(Data input)
SCK
(CPOL = 0)
SS
MSB LSB
MSB LSB
...
...
10
11 11
13 14 12
15 17
9
X
16311
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29.8 ADC characteristics
Note: 1. AVCC absolute min./max.: 1.8V/5.5V
Table 29-7. ADC characteristics.
Symbol Parameter Condition Minimum Typical Maximum Units
Resolution 10 Bits
Absolute accuracy (Including
INL, DNL, quantization error,
gain and offset error)
VREF = 4V, VCC = 4V,
ADC clock = 200kHz 2
LSB
VREF = 4V, VCC = 4V,
ADC clock = 1MHz 4.5
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
Noise reduction mode
2
VREF = 4V, VCC = 4V,
ADC clock = 1MHz
Noise reduction mode
4.5
Integral non-linearity (INL) VREF = 4V, VCC = 4V,
ADC clock = 200kHz 0.5
Differential non-linearity (DNL) VREF = 4V, VCC = 4V,
ADC clock = 200kHz 0.25
Gain error VREF = 4V, VCC = 4V,
ADC clock = 200kHz 2
Offset error VREF = 4V, VCC = 4V,
ADC clock = 200kHz 2
Conversion time Free running conversion 13 260 µs
Clock frequency 50 1000 kHz
AVCC(1) Analog supply voltage VCC - 0.3 VCC + 0.3
VREF Reference voltage 1.0 AVCC V
VIN Input voltage GND VREF
Input bandwidth 38.5 kHz
VINT Internal voltage reference 1.0 1.1 1.2 V
RREF Reference input resistance 32 kΩ
RAIN Analog input resistance 100 MΩ312
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29.9 Parallel programming characteristics
Figure 29-7. Parallel programming timing, including some general timing requirements.
Figure 29-8. Parallel programming timing, loading sequence with timing requirements(1).
Note: 1. The timing requirements shown in Figure 29-7 (that is, tDVXH, tXHXL, and tXLDX) also apply to
loading operation.
Data & contol
(DATA, XA0/1, BS1, BS2)
XTAL1 t
XHXL
t
WLWH
t
DVXH t
XLDX
t
PLWL
t
WLRH
WR
RDY/BSY
PAGEL t
PHPL
t
PLBX t
BVPH
t
XLWL
t
WLBX
tBVWL
WLRL
XTAL1
PAGEL
t XLXH PLXH t t
XLPH
DATA ADDR0 (low byte) DATA (low byte) DATA (high byte) ADDR1 (low byte)
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
LOAD DATA
(LOW BYTE)
LOAD DATA
(HIGH BYTE)
LOAD DATA LOAD ADDRESS
(LOW BYTE)313
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Figure 29-9. Parallel programming timing, reading sequence (within the same page) with timing
requirements(1).
Note: 1. The timing requirements shown in Figure 29-7 on page 312 (that is, tDVXH, tXHXL, and tXLDX)
also apply to reading operation.
Table 29-8. Parallel programming characteristics, VCC = 5V ±10%.
Symbol Parameter Min. Typ. Max. Units
VPP Programming enable voltage 11.5 12.5 V
IPP Programming enable current 250 µA
tDVXH Data and control valid before XTAL1 high 67
ns
tXLXH XTAL1 low to XTAL1 high 200
tXHXL XTAL1 pulse width high 150
tXLDX Data and control hold after XTAL1 low 67
tXLWL XTAL1 low to WR low 0
tXLPH XTAL1 low to PAGEL high 0
tPLXH PAGEL low to XTAL1 high 150
tBVPH BS1 valid before PAGEL high 67
tPHPL PAGEL pulse width high 150
tPLBX BS1 hold after PAGEL low 67
tWLBX BS2/1 hold after WR low 67
tPLWL PAGEL low to WR low 67
tBVWL BS1 valid to WR low 67
tWLWH WR pulse width low 150
tWLRL WR low to RDY/BSY low 0 1 µs
tWLRH WR low to RDY/BSY high(1) 3.7 4.5
ms
tWLRH_CE WR low to RDY/BSY high for chip erase(2) 7.5 9
XTAL1
OE
DATA ADDR0 (low byte) DATA (low byte) DATA (high byte) ADDR1 (low byte)
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
t
BVDV
t
OLDV
t
XLOL
t
OHDZ314
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Notes: 1. tWLRH is valid for the write flash, write EEPROM, write fuse bits and write lock bits commands.
2. tWLRH_CE is valid for the chip erase command.
t
XLOL XTAL1 low to OE low 0
ns
t
BVDV BS1 valid to DATA valid 0 250
tOLDV OE low to DATA valid 250
t
OHDZ OE high to DATA tri-stated 250
Table 29-8. Parallel programming characteristics, VCC = 5V ±10%. (Continued)
Symbol Parameter Min. Typ. Max. Units315
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30. Typical characteristics
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. A square wave generator with rail-to-rail output is used as clock
source.
All Active- and Idle current consumption measurements are done with all bits in the PRR register
set and thus, the corresponding I/O modules are turned off. Also the Analog Comparator is disabled
during these measurements. Table 30-1 on page 321 and Table 30-2 on page 321 show
the additional current consumption compared to ICC Active and ICC Idle for every I/O module controlled
by the Power Reduction Register. See “Power reduction register” on page 41 for details.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature.
The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential current
drawn by the Watchdog Timer.
30.1 Active supply current
Figure 30-1. Active supply current vs. frequency (0.1MHz - 1.0MHz).
5.5V
5.0V
4.5V
4.0V
3.3V
2.7V
1.8V
0
0.2
0.4
0.6
0.8
1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
ICC (mA)316
2545T–AVR–05/11
ATmega48/88/168
Figure 30-2. Active supply current vs. frequency (1MHz - 24MHz).
Figure 30-3. Active supply current vs. VCC (internal RC oscillator, 128kHz).
0
2
4
6
8
10
12
14
16
18
0 4 8 12 16 20 24
Frequency (MHz)
ICC (mA)
2.7V
1.8V
3.3V
4.0V
4.5V
5.0V
5.5V
,
85°C
25°C
-40°C
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)317
2545T–AVR–05/11
ATmega48/88/168
Figure 30-4. Active supply current vs. VCC (internal RC oscillator, 1MHz).
Figure 30-5. Active supply current vs. VCC (internal RC oscillator, 8MHz).
,
85°C
25°C
-40°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)
,
85°C
25°C
-40°C
0
1
2
3
4
5
6
7
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)318
2545T–AVR–05/11
ATmega48/88/168
Figure 30-6. Active supply current vs. VCC (32kHz external oscillator).
30.2 Idle supply current
Figure 30-7. Idle supply current vs. frequency (0.1MHz - 1.0MHz).
25°C
0
10
20
30
40
50
60
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
5.5V
5.0V
4.5V
4.0V
3.3V
2.7V
1.8V
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
ICC (mA)319
2545T–AVR–05/11
ATmega48/88/168
Figure 30-8. Idle supply current vs. frequency (1MHz - 24MHz).
Figure 30-9. Idle supply current vs. VCC (internal RC oscillator, 128kHz).
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 4 8 12 16 20 24
Frequency (MHz)
ICC (mA)
2.7V
1.8V
3.3V
4.0V
4.5V
5.0V
5.5V
85°C
25°C
-40°C
0
0.005
0.01
0.015
0.02
0.025
0.03
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)320
2545T–AVR–05/11
ATmega48/88/168
Figure 30-10. Idle supply current vs. VCC (internal RC oscillator, 1MHz).
Figure 30-11. Idle supply current vs. VCC (internal RC oscillator, 8MHz).
,
85°C
25°C
-40°C
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)
,
85°C
25°C
-40°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)321
2545T–AVR–05/11
ATmega48/88/168
Figure 30-12. Idle supply current vs. VCC (32kHz external oscillator).
30.3 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
are controlled by the Power Reduction Register. See “Power reduction register” on page 41 for
details.
25°C
0
5
10
15
20
25
30
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
Table 30-1. Additional current consumption for the different I/O modules (absolute values).
PRR bit Typical numbers
VCC = 2V, F = 1MHz VCC = 3V, F = 4MHz VCC = 5V, F = 8MHz
PRUSART0 8.0µA 51µA 220µA
PRTWI 12µA 75µA 315µA
PRTIM2 11µA 72µA 300µA
PRTIM1 5.0µA 32µA 130µA
PRTIM0 4.0µA 24µA 100µA
PRSPI 15µA 95µA 400µA
PRADC 12µA 75µA 315µA
Table 30-2. Additional current consumption (percentage) in active and idle mode.
PRR bit
Additional current consumption
compared to active with external clock
(see Figure 30-1 on page 315 and
Figure 30-2 on page 316)
Additional current consumption
compared to Idle with external clock
(see Figure 30-7 on page 318 and
Figure 30-8 on page 319)
PRUSART0 3.3% 18%
PRTWI 4.8% 26%
PRTIM2 4.7% 25%322
2545T–AVR–05/11
ATmega48/88/168
It is possible to calculate the typical current consumption based on the numbers from Table 30-2
on page 321 for other VCC and frequency settings than listed in Table 30-1 on page 321.
30.3.0.1 Example 1
Calculate the expected current consumption in idle mode with USART0, TIMER1, and TWI
enabled at VCC = 3.0V and F = 1MHz. From Table 30-2 on page 321, third column, we see that
we need to add 18% for the USART0, 26% for the TWI, and 11% for the TIMER1 module. Reading
from Figure 30-7 on page 318, we find that the idle current consumption is ~0.075mA at VCC
= 3.0V and F = 1MHz. The total current consumption in idle mode with USART0, TIMER1, and
TWI enabled, gives:
30.3.0.2 Example 2
Same conditions as in example 1, but in active mode instead. From Table 30-2 on page 321,
second column we see that we need to add 3.3% for the USART0, 4.8% for the TWI, and 2.0%
for the TIMER1 module. Reading from Figure 30-1 on page 315, we find that the active current
consumption is ~0.42mA at VCC = 3.0V and F = 1MHz. The total current consumption in idle
mode with USART0, TIMER1, and TWI enabled, gives:
30.3.0.3 Example 3
All I/O modules should be enabled. Calculate the expected current consumption in active mode
at VCC = 3.6V and F = 10MHz. We find the active current consumption without the I/O modules
to be ~ 4.0mA (from Figure 30-2 on page 316). Then, by using the numbers from Table 30-2 on
page 321 - second column, we find the total current consumption:
PRTIM1 2.0% 11%
PRTIM0 1.6% 8.5%
PRSPI 6.1% 33%
PRADC 4.9% 26%
Table 30-2. Additional current consumption (percentage) in active and idle mode. (Continued)
PRR bit
Additional current consumption
compared to active with external clock
(see Figure 30-1 on page 315 and
Figure 30-2 on page 316)
Additional current consumption
compared to Idle with external clock
(see Figure 30-7 on page 318 and
Figure 30-8 on page 319)
ICCtotal ≈ ≈ 0.075mA • ( ) 1 0.18 0.26 0.11 +++ 0.116mA
ICCtotal ≈ ≈ 0.42mA • ( ) 1 0.033 0.048 0.02 +++ 0.46mA
ICCtotal ≈ ≈ 4.0mA • ( ) 1 0.033 0.048 0.047 0.02 0.016 0.061 0.049 + + + ++ + + 5.1mA323
2545T–AVR–05/11
ATmega48/88/168
30.4 Power-down supply current
Figure 30-13. Power-down supply current vs. VCC (watchdog timer disabled).
Figure 30-14. Power-down supply current vs. VCC (watchdog timer enabled).
85°C
25°C
-40°C
0
0.5
1
1.5
2
2.5
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
85°C
25°C
-40°C
0
2
4
6
8
10
12
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)324
2545T–AVR–05/11
ATmega48/88/168
30.5 Power-save supply current
Figure 30-15. Power-save supply current vs. VCC (watchdog timer disabled).
30.6 Standby supply current
Figure 30-16. Standby supply current vs. VCC (low power crystal oscillator).
25°C
0
2
4
6
8
10
12
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
6MHz Xtal
6MHz Res.
4MHz Xtal
4MHz Res.
455kHz Res.
32kHz Xtal
2MHz Xtal
2MHz Res.
1MHz Res.
0
20
40
60
80
100
120
140
160
180
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)325
2545T–AVR–05/11
ATmega48/88/168
Figure 30-17. Standby supply current vs. VCC (full swing crystal oscillator).
30.7 Pin pull-up
Figure 30-18. I/O pin pull-up resistor current vs. input voltage (VCC = 5V).
6MHz Xtal
(ckopt)
4MHz Xtal
(ckopt)
2MHz Xtal
(ckopt)
16MHz Xtal
12MHz Xtal
0
50
100
150
200
250
300
350
400
450
500
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
85°C 25°C
-40°C
0
20
40
60
80
100
120
140
160
0123456
VOP (V)
IOP (µA)326
2545T–AVR–05/11
ATmega48/88/168
Figure 30-19. I/O pin pull-up resistor current vs. input voltage (VCC = 2.7V).
Figure 30-20. Reset pull-up resistor current vs. reset pin voltage (VCC = 5V).
85°C 25°C
-40°C
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5 3
VOP (V)
IOP (µA)
0
20
40
60
80
100
120
0123456
VRESET (V)
IRESET (µA)
-40°C 25°C
85°C327
2545T–AVR–05/11
ATmega48/88/168
Figure 30-21. Reset pull-up resistor current vs. reset pin voltage (VCC = 2.7V).
30.8 Pin driver strength
Figure 30-22. I/O pin source current vs. output voltage (VCC = 5V).
-40°C
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3
VRESET (V)
IRESET (µA)
25°C
85°C
85°C
25°C
-40°C
0
10
20
30
40
50
60
70
80
90
0123456
VOH (V)
IOH (mA)328
2545T–AVR–05/11
ATmega48/88/168
Figure 30-23. I/O pin source current vs. output voltage (VCC = 2.7V).
Figure 30-24. I/O pin source current vs. output voltage (VCC = 1.8V).
85°C
25°C
-40°C
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2 2.5 3
VOH (V)
IOH (mA)
85°C
25°C -40°C
0
1
2
3
4
5
6
7
8
9
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOH (V)
IOH (mA)329
2545T–AVR–05/11
ATmega48/88/168
Figure 30-25. I/O pin sink current vs. output voltage (VCC = 5V).
Figure 30-26. I/O pin sink current vs. output voltage (VCC = 2.7V).
85°C
25°C
0
10
20
30
40
50
60
70
80
0 0.5 1 1.5 2 2.5
VOL (V)
IOL (mA)
85°C
25°C
-40°C
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5
VOL (V)
IOL (mA)330
2545T–AVR–05/11
ATmega48/88/168
Figure 30-27. I/O pin sink current vs. output voltage (VCC = 1.8V).
30.9 Pin thresholds and hysteresis
Figure 30-28. I/O pin input threshold voltage vs. VCC (VIH, I/O pin read as '1').
85°C
25°C
-40°C
0
2
4
6
8
10
12
14
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOL (V)
IOL (mA)
85°C
25°C
-40°C
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Threshold (V)331
2545T–AVR–05/11
ATmega48/88/168
Figure 30-29. I/O pin input threshold voltage vs. VCC (VIL, I/O pin read as '0').
Figure 30-30. I/O pin input hystreresis vs. Vcc.
85°C
25°C
-40°C
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Threshold (V)
85°C
25°C
-40°C
0
0.1
0.2
0.3
0.4
0.5
0.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Input hysteresis (V)332
2545T–AVR–05/11
ATmega48/88/168
Figure 30-31. Reset input threshold voltage vs. VCC (VIH, reset pin read as '1').
Figure 30-32. Reset input threshold voltage vs. VCC (VIL, reset pin read as '0').
85°C
25°C
-40°C
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Threshold (V)
85°C
25°C
-40°C
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Threshold (V)333
2545T–AVR–05/11
ATmega48/88/168
Figure 30-33. Reset input pin hysteresis vs. VCC.
30.10 BOD thresholds and analog comparator offset
Figure 30-34. BOD thresholds vs. temperature (BODLEVEL is 4.3V).
VIL
0
100
200
300
400
500
600
2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Input hysteresis (mV)
4.2
4.25
4.3
4.35
4.4
4.45
4.5
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
Threshold (V)
Rising Vcc
Falling Vcc334
2545T–AVR–05/11
ATmega48/88/168
Figure 30-35. BOD thresholds vs. temperature (BODLEVEL is 2.7V).
Figure 30-36. BOD thresholds vs. temperature (BODLEVEL is 1.8V).
2.6
2.65
2.7
2.75
2.8
2.85
2.9
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
Threshold (V)
Rising Vcc
Falling Vcc
1.76
1.78
1.8
1.82
1.84
1.86
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
Threshold (V)
Rising Vcc
Falling Vcc335
2545T–AVR–05/11
ATmega48/88/168
Figure 30-37. Bandgap voltage vs. VCC.
Figure 30-38. Analog comparator offset voltage vs. common mode voltage (VCC = 5V).
-40°C
85°C
1.08
1.085
1.09
1.095
1.1
1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
VCC (V)
Bandgap voltage (V)
-40°C
85°C
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Common Mode Voltage (V)
Analog comparator offset voltage (V)336
2545T–AVR–05/11
ATmega48/88/168
Figure 30-39. Analog comparator offset voltage vs. common mode voltage (VCC = 2.7V).
30.11 Internal oscillator speed
Figure 30-40. Watchdog oscillator frequency vs. VCC.
-40°C
85°C
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.5 1 1.5 2 2.5
Common Mode Voltage (V)
Analog comparator offset voltage
(mV)
85°C
25°C
-40°C
95
100
105
110
115
120
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
FRC (kHz)337
2545T–AVR–05/11
ATmega48/88/168
Figure 30-41. Calibrated 8MHz RC oscillator frequency vs. temperature.
Figure 30-42. Calibrated 8MHz RC oscillator frequency vs. VCC.
5.0V
2.7V
1.8V
7.4
7.5
7.6
7.7
7.8
7.9
8
8.1
8.2
8.3
8.4
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (°C)
FRC (MHz)
85°C
25°C
-40°C
7.4
7.6
7.8
8
8.2
8.4
8.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
FRC (MHz)338
2545T–AVR–05/11
ATmega48/88/168
Figure 30-43. Calibrated 8MHz RC oscillator frequency vs. osccal value.
30.12 Current consumption of peripheral units
Figure 30-44. Brownout detector current vs. VCC.
85°C
25°C
-40°C
3.5
5.5
7.5
9.5
11.5
13.5
0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
OSCCAL VALUE
FRC (MHz)
85°C
25°C
-40°C
18
20
22
24
26
28
30
32
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)339
2545T–AVR–05/11
ATmega48/88/168
Figure 30-45. ADC current vs. VCC (AREF = AVCC).
Figure 30-46. AREF external reference current vs. VCC.
85°C
25°C
-40°C
150
200
250
300
350
400
450
500
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
85°C
25°C
-40°C
0
20
40
60
80
100
120
140
160
180
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)340
2545T–AVR–05/11
ATmega48/88/168
Figure 30-47. Analog comparator current vs. VCC.
Figure 30-48. Programming current vs. VCC.
85°C
25°C
-40°C
0
20
40
60
80
100
120
140
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (µA)
85°C
25°C
-40°C
0
2
4
6
8
10
12
14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)
85°C
25°C
-40°C
0
2
4
6
8
10
12
14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)341
2545T–AVR–05/11
ATmega48/88/168
30.13 Current consumption in reset and reset pulse width
Figure 30-49. Reset supply current vs. VCC (0.1MHz - 1.0MHz, excluding current through the
reset pull-up).
Figure 30-50. Reset supply current vs. VCC (1MHz - 24MHz, excluding current through the reset
pull-up).
5.5V
5.0V
4.5V
4.0V
3.3V
2.7V
1.8V
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
ICC (mA)
,
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 4 8 12 16 20 24
Frequency (MHz)
ICC (mA)
2.7V
1.8V
3.3V
4.0V
4.5V
5.0V
5.5V342
2545T–AVR–05/11
ATmega48/88/168
Figure 30-51. Reset pulse width vs. VCC.
85°C
25°C
-40°C
0
500
1000
1500
2000
2500
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Pulsewidth (ns)343
2545T–AVR–05/11
ATmega48/88/168
31. Register summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
(0xFF) Reserved – – – – – – – –
(0xFE) Reserved – – – – – – – –
(0xFD) Reserved – – – – – – – –
(0xFC) Reserved – – – – – – – –
(0xFB) Reserved – – – – – – – –
(0xFA) Reserved – – – – – – – –
(0xF9) Reserved – – – – – – – –
(0xF8) Reserved – – – – – – – –
(0xF7) Reserved – – – – – – – –
(0xF6) Reserved – – – – – – – –
(0xF5) Reserved – – – – – – – –
(0xF4) Reserved – – – – – – – –
(0xF3) Reserved – – – – – – – –
(0xF2) Reserved – – – – – – – –
(0xF1) Reserved – – – – – – – –
(0xF0) Reserved – – – – – – – –
(0xEF) Reserved – – – – – – – –
(0xEE) Reserved – – – – – – – –
(0xED) Reserved – – – – – – – –
(0xEC) Reserved – – – – – – – –
(0xEB) Reserved – – – – – – – –
(0xEA) Reserved – – – – – – – –
(0xE9) Reserved – – – – – – – –
(0xE8) Reserved – – – – – – – –
(0xE7) Reserved – – – – – – – –
(0xE6) Reserved – – – – – – – –
(0xE5) Reserved – – – – – – – –
(0xE4) Reserved – – – – – – – –
(0xE3) Reserved – – – – – – – –
(0xE2) Reserved – – – – – – – –
(0xE1) Reserved – – – – – – – –
(0xE0) Reserved – – – – – – – –
(0xDF) Reserved – – – – – – – –
(0xDE) Reserved – – – – – – – –
(0xDD) Reserved – – – – – – – –
(0xDC) Reserved – – – – – – – –
(0xDB) Reserved – – – – – – – –
(0xDA) Reserved – – – – – – – –
(0xD9) Reserved – – – – – – – –
(0xD8) Reserved – – – – – – – –
(0xD7) Reserved – – – – – – – –
(0xD6) Reserved – – – – – – – –
(0xD5) Reserved – – – – – – – –
(0xD4) Reserved – – – – – – – –
(0xD3) Reserved – – – – – – – –
(0xD2) Reserved – – – – – – – –
(0xD1) Reserved – – – – – – – –
(0xD0) Reserved – – – – – – – –
(0xCF) Reserved – – – – – – – –
(0xCE) Reserved – – – – – – – –
(0xCD) Reserved – – – – – – – –
(0xCC) Reserved – – – – – – – –
(0xCB) Reserved – – – – – – – –
(0xCA) Reserved – – – – – – – –
(0xC9) Reserved – – – – – – – –
(0xC8) Reserved – – – – – – – –
(0xC7) Reserved – – – – – – – –
(0xC6) UDR0 USART I/O data register 190
(0xC5) UBRR0H USART baud rate register high 194
(0xC4) UBRR0L USART baud rate register low 194
(0xC3) Reserved – – – – – – – –
(0xC2) UCSR0C UMSEL01 UMSEL00 UPM01 UPM00 USBS0 UCSZ01 /UDORD0 UCSZ00 / UCPHA0 UCPOL0 192/207
(0xC1) UCSR0B RXCIE0 TXCIE0 UDRIE0 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 191
(0xC0) UCSR0A RXC0 TXC0 UDRE0 FE0 DOR0 UPE0 U2X0 MPCM0 190344
2545T–AVR–05/11
ATmega48/88/168
(0xBF) Reserved – – – – – – – –
(0xBE) Reserved – – – – – – – –
(0xBD) TWAMR TWAM6 TWAM5 TWAM4 TWAM3 TWAM2 TWAM1 TWAM0 – 239
(0xBC) TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE 236
(0xBB) TWDR 2-wire serial interface data register 238
(0xBA) TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE 239
(0xB9) TWSR TWS7 TWS6 TWS5 TWS4 TWS3 – TWPS1 TWPS0 238
(0xB8) TWBR 2-wire serial interface bit rate register 236
(0xB7) Reserved – – – – – – –
(0xB6) ASSR – EXCLK AS2 TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB 159
(0xB5) Reserved – – – – – – – –
(0xB4) OCR2B Timer/Counter2 output compare register B 158
(0xB3) OCR2A Timer/Counter2 output compare register A 157
(0xB2) TCNT2 Timer/Counter2 (8-bit) 157
(0xB1) TCCR2B FOC2A FOC2B – – WGM22 CS22 CS21 CS20 156
(0xB0) TCCR2A COM2A1 COM2A0 COM2B1 COM2B0 – – WGM21 WGM20 153
(0xAF) Reserved – – – – – – – –
(0xAE) Reserved – – – – – – – –
(0xAD) Reserved – – – – – – – –
(0xAC) Reserved – – – – – – – –
(0xAB) Reserved – – – – – – – –
(0xAA) Reserved – – – – – – – –
(0xA9) Reserved – – – – – – – –
(0xA8) Reserved – – – – – – – –
(0xA7) Reserved – – – – – – – –
(0xA6) Reserved – – – – – – – –
(0xA5) Reserved – – – – – – – –
(0xA4) Reserved – – – – – – – –
(0xA3) Reserved – – – – – – – –
(0xA2) Reserved – – – – – – – –
(0xA1) Reserved – – – – – – – –
(0xA0) Reserved – – – – – – – –
(0x9F) Reserved – – – – – – – –
(0x9E) Reserved – – – – – – – –
(0x9D) Reserved – – – – – – – –
(0x9C) Reserved – – – – – – – –
(0x9B) Reserved – – – – – – – –
(0x9A) Reserved – – – – – – – –
(0x99) Reserved – – – – – – – –
(0x98) Reserved – – – – – – – –
(0x97) Reserved – – – – – – – –
(0x96) Reserved – – – – – – – –
(0x95) Reserved – – – – – – – –
(0x94) Reserved – – – – – – – –
(0x93) Reserved – – – – – – – –
(0x92) Reserved – – – – – – – –
(0x91) Reserved – – – – – – – –
(0x90) Reserved – – – – – – – –
(0x8F) Reserved – – – – – – – –
(0x8E) Reserved – – – – – – – –
(0x8D) Reserved – – – – – – – –
(0x8C) Reserved – – – – – – – –
(0x8B) OCR1BH Timer/Counter1 - output compare register B high byte 134
(0x8A) OCR1BL Timer/Counter1 - output compare register B low byte 134
(0x89) OCR1AH Timer/Counter1 - output compare register A high byte 134
(0x88) OCR1AL Timer/Counter1 - output compare register A low byte 134
(0x87) ICR1H Timer/Counter1 - input capture register high byte 135
(0x86) ICR1L Timer/Counter1 - input capture register low byte 135
(0x85) TCNT1H Timer/Counter1 - counter register high byte 134
(0x84) TCNT1L Timer/Counter1 - counter register low byte 134
(0x83) Reserved – – – – – – – –
(0x82) TCCR1C FOC1A FOC1B – – – – – – 133
(0x81) TCCR1B ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 132
(0x80) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 130
(0x7F) DIDR1 – – – – – – AIN1D AIN0D 243
(0x7E) DIDR0 – – ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D 259
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page345
2545T–AVR–05/11
ATmega48/88/168
(0x7D) Reserved – – – – – – – –
(0x7C) ADMUX REFS1 REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 255
(0x7B) ADCSRB – ACME – – – ADTS2 ADTS1 ADTS0 258
(0x7A) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 256
(0x79) ADCH ADC data register high byte 258
(0x78) ADCL ADC data register low byte 258
(0x77) Reserved – – – – – – – –
(0x76) Reserved – – – – – – – –
(0x75) Reserved – – – – – – – –
(0x74) Reserved – – – – – – – –
(0x73) Reserved – – – – – – – –
(0x72) Reserved – – – – – – – –
(0x71) Reserved – – – – – – – –
(0x70) TIMSK2 – – – – – OCIE2B OCIE2A TOIE2 158
(0x6F) TIMSK1 – – ICIE1 – – OCIE1B OCIE1A TOIE1 135
(0x6E) TIMSK0 – – – – – OCIE0B OCIE0A TOIE0 106
(0x6D) PCMSK2 PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 70
(0x6C) PCMSK1 – PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 70
(0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 70
(0x6A) Reserved – – – – – – – –
(0x69) EICRA – – – – ISC11 ISC10 ISC01 ISC00 67
(0x68) PCICR – – – – – PCIE2 PCIE1 PCIE0
(0x67) Reserved – – – – – – – –
(0x66) OSCCAL Oscillator calibration register 37
(0x65) Reserved – – – – – – – –
(0x64) PRR PRTWI PRTIM2 PRTIM0 – PRTIM1 PRSPI PRUSART0 PRADC 41
(0x63) Reserved – – – – – – – –
(0x62) Reserved – – – – – – – –
(0x61) CLKPR CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 37
(0x60) WDTCSR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 53
0x3F (0x5F) SREG I T H S V N Z C 11
0x3E (0x5E) SPH – – – – – (SP10) 5. SP9 SP8 13
0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 13
0x3C (0x5C) Reserved – – – – – – – –
0x3B (0x5B) Reserved – – – – – – – –
0x3A (0x5A) Reserved – – – – – – – –
0x39 (0x59) Reserved – – – – – – – –
0x38 (0x58) Reserved – – – – – – – –
0x37 (0x57) SPMCSR SPMIE (RWWSB)5. – (RWWSRE)5. BLBSET PGWRT PGERS SELFPRGEN 283
0x36 (0x56) Reserved – – – – – – – –
0x35 (0x55) MCUCR – – – PUD – – IVSEL IVCE
0x34 (0x54) MCUSR – – – – WDRF BORF EXTRF PORF
0x33 (0x53) SMCR – – – – SM2 SM1 SM0 SE 39
0x32 (0x52) Reserved – – – – – – – –
0x31 (0x51) Reserved – – – – – – – –
0x30 (0x50) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 242
0x2F (0x4F) Reserved – – – – – – – –
0x2E (0x4E) SPDR SPI data register 170
0x2D (0x4D) SPSR SPIF WCOL – – – – – SPI2X 169
0x2C (0x4C) SPCR SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 168
0x2B (0x4B) GPIOR2 General purpose I/O register 2 26
0x2A (0x4A) GPIOR1 General purpose I/O register 1 26
0x29 (0x49) Reserved – – – – – – – –
0x28 (0x48) OCR0B Timer/Counter0 output compare register B
0x27 (0x47) OCR0A Timer/Counter0 output compare register A
0x26 (0x46) TCNT0 Timer/Counter0 (8-bit)
0x25 (0x45) TCCR0B FOC0A FOC0B – – WGM02 CS02 CS01 CS00
0x24 (0x44) TCCR0A COM0A1 COM0A0 COM0B1 COM0B0 – – WGM01 WGM00
0x23 (0x43) GTCCR TSM – – – – – PSRASY PSRSYNC 139/160
0x22 (0x42) EEARH (EEPROM address register high byte) 5. 22
0x21 (0x41) EEARL EEPROM address register low byte 22
0x20 (0x40) EEDR EEPROM data register 22
0x1F (0x3F) EECR – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE 22
0x1E (0x3E) GPIOR0 General purpose I/O register 0 26
0x1D (0x3D) EIMSK – – – – – – INT1 INT0 68
0x1C (0x3C) EIFR – – – – – – INTF1 INTF0 68
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page346
2545T–AVR–05/11
ATmega48/88/168
Note: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operate on the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O
Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATmega48/88/168 is a complex microcontroller with more peripheral units than can be supported within the 64 location
reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for ATmega88/168
0x1B (0x3B) PCIFR – – – – – PCIF2 PCIF1 PCIF0
0x1A (0x3A) Reserved – – – – – – – –
0x19 (0x39) Reserved – – – – – – – –
0x18 (0x38) Reserved – – – – – – – –
0x17 (0x37) TIFR2 – – – – – OCF2B OCF2A TOV2 158
0x16 (0x36) TIFR1 – – ICF1 – – OCF1B OCF1A TOV1 136
0x15 (0x35) TIFR0 – – – – – OCF0B OCF0A TOV0
0x14 (0x34) Reserved – – – – – – – –
0x13 (0x33) Reserved – – – – – – – –
0x12 (0x32) Reserved – – – – – – – –
0x11 (0x31) Reserved – – – – – – – –
0x10 (0x30) Reserved – – – – – – – –
0x0F (0x2F) Reserved – – – – – – – –
0x0E (0x2E) Reserved – – – – – – – –
0x0D (0x2D) Reserved – – – – – – – –
0x0C (0x2C) Reserved – – – – – – – –
0x0B (0x2B) PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 88
0x0A (0x2A) DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 88
0x09 (0x29) PIND PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 88
0x08 (0x28) PORTC – PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 87
0x07 (0x27) DDRC – DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 87
0x06 (0x26) PINC – PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 87
0x05 (0x25) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 87
0x04 (0x24) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 87
0x03 (0x23) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 87
0x02 (0x22) Reserved – – – – – – – –
0x01 (0x21) Reserved – – – – – – – –
0x0 (0x20) Reserved – – – – – – – –
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page347
2545T–AVR–05/11
ATmega48/88/168
32. Instruction set summary
Mnemonics Operands Description Operation Flags #Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD Rd, Rr Add two registers Rd ← Rd + Rr Z, C, N, V, H 1
ADC Rd, Rr Add with carry two registers Rd ← Rd + Rr + C Z, C, N, V, H 1
ADIW Rdl,K Add immediate to word Rdh:Rdl ← Rdh:Rdl + K Z, C, N, V, S 2
SUB Rd, Rr Subtract two registers Rd ← Rd - Rr Z, C, N, V, H 1
SUBI Rd, K Subtract constant from register Rd ← Rd - K Z, C, N, V, H 1
SBC Rd, Rr Subtract with carry two registers Rd ← Rd - Rr - C Z, C, N, V, H 1
SBCI Rd, K Subtract with carry constant from reg. Rd ← Rd - K - C Z, C, N, V, H 1
SBIW Rdl,K Subtract immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z, C, N, V, S 2
AND Rd, Rr Logical AND registers Rd ← Rd • Rr Z, N, V 1
ANDI Rd, K Logical AND register and constant Rd ← Rd • K Z, N, V 1
OR Rd, Rr Logical OR registers Rd ← Rd v Rr Z, N, V 1
ORI Rd, K Logical OR register and constant Rd ← Rd v K Z, N, V 1
EOR Rd, Rr Exclusive OR registers Rd ← Rd ⊕ Rr Z, N, V 1
COM Rd One’s complement Rd ← 0xFF − Rd Z, C, N, V 1
NEG Rd Two’s complement Rd ← 0x00 − Rd Z, C, N, V, H 1
SBR Rd,K Set bit(s) in register Rd ← Rd v K Z, N, V 1
CBR Rd,K Clear bit(s) in register Rd ← Rd • (0xFF - K) Z, N, V 1
INC Rd Increment Rd ← Rd + 1 Z, N, V 1
DEC Rd Decrement Rd ← Rd − 1 Z, N, V 1
TST Rd Test for zero or minus Rd ← Rd • Rd Z, N, V 1
CLR Rd Clear register Rd ← Rd ⊕ Rd Z, N, V 1
SER Rd Set register Rd ← 0xFF None 1
MUL Rd, Rr Multiply unsigned R1:R0 ← Rd x Rr Z, C 2
MULS Rd, Rr Multiply signed R1:R0 ← Rd x Rr Z, C 2
MULSU Rd, Rr Multiply signed with unsigned R1:R0 ← Rd x Rr Z, C 2
FMUL Rd, Rr Fractional multiply unsigned R1:R0 ← (Rd x Rr) << 1 Z, C 2
FMULS Rd, Rr Fractional multiply signed R1:R0 ← (Rd x Rr) << 1 Z, C 2
FMULSU Rd, Rr Fractional multiply signed with unsigned R1:R0 ← (Rd x Rr) << 1 Z, C 2
BRANCH INSTRUCTIONS
RJMP k Relative jump PC ← PC + k + 1 None 2
IJMP Indirect jump to (Z) PC ← Z None 2
JMP(1) k Direct jump PC ← k None 3
RCALL k Relative subroutine call PC ← PC + k + 1 None 3
ICALL Indirect call to (Z) PC ← Z None 3
CALL(1) k Direct subroutine call PC ← k None 4
RET Subroutine return PC ← STACK None 4
RETI Interrupt return PC ← STACK I 4
CPSE Rd,Rr Compare, skip if equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N, V, C, H 1
CPC Rd,Rr Compare with carry Rd − Rr − C Z, N, V, C, H 1
CPI Rd,K Compare register with immediate Rd − K Z, N, V, C, H 1
SBRC Rr, b Skip if bit in register cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if bit in register is set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if bit in I/O register cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if bit in I/O register is set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if status flag set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2
BRBC s, k Branch if status flag cleared if (SREG(s) = 0) then PC←PC+k + 1 None 1/2
BREQ k Branch if equal if (Z = 1) then PC ← PC + k + 1 None 1/2
BRNE k Branch if not equal if (Z = 0) then PC ← PC + k + 1 None 1/2
BRCS k Branch if carry set if (C = 1) then PC ← PC + k + 1 None 1/2
BRCC k Branch if carry cleared if (C = 0) then PC ← PC + k + 1 None 1/2
BRSH k Branch if same or higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if minus if (N = 1) then PC ← PC + k + 1 None 1/2
BRPL k Branch if plus if (N = 0) then PC ← PC + k + 1 None 1/2
BRGE k Branch if greater or equal, signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if less than zero, signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if half carry flag set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if half carry flag cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T flag set if (T = 1) then PC ← PC + k + 1 None 1/2
BRTC k Branch if T flag cleared if (T = 0) then PC ← PC + k + 1 None 1/2
BRVS k Branch if overflow flag is set if (V = 1) then PC ← PC + k + 1 None 1/2
BRVC k Branch if overflow flag is cleared if (V = 0) then PC ← PC + k + 1 None 1/2348
2545T–AVR–05/11
ATmega48/88/168
BRIE k Branch if interrupt enabled if ( I = 1) then PC ← PC + k + 1 None 1/2
BRID k Branch if interrupt disabled if ( I = 0) then PC ← PC + k + 1 None 1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI P,b Set bit in I/O register I/O(P,b) ← 1 None 2
CBI P,b Clear bit in I/O register I/O(P,b) ← 0 None 2
LSL Rd Logical shift left Rd(n+1) ← Rd(n), Rd(0) ← 0 Z, C, N, V 1
LSR Rd Logical shift right Rd(n) ← Rd(n+1), Rd(7) ← 0 Z, C, N, V 1
ROL Rd Rotate left through carry Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7) Z, C, N, V 1
ROR Rd Rotate right through carry Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0) Z, C, N, V 1
ASR Rd Arithmetic shift right Rd(n) ← Rd(n+1), n=0..6 Z, C, N, V 1
SWAP Rd Swap nibbles Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0) None 1
BSET s Flag set SREG(s) ← 1 SREG(s) 1
BCLR s Flag clear SREG(s) ← 0 SREG(s) 1
BST Rr, b Bit store from register to T T ← Rr(b) T 1
BLD Rd, b Bit load from T to register Rd(b) ← T None 1
SEC Set carry C ← 1 C1
CLC Clear carry C ← 0 C 1
SEN Set negative flag N ← 1 N1
CLN Clear negative flag N ← 0 N 1
SEZ Set zero flag Z ← 1 Z1
CLZ Clear zero flag Z ← 0 Z 1
SEI Global interrupt enable I ← 1 I1
CLI Global interrupt disable I ← 0 I 1
SES Set signed test flag S ← 1 S1
CLS Clear signed test flag S ← 0 S 1
SEV Set Twos complement overflow V ← 1 V1
CLV Clear Twos complement overflow V ← 0 V 1
SET Set T in SREG T ← 1 T1
CLT Clear T in SREG T ← 0 T 1
SEH Set half carry flag in SREG H ← 1 H1
CLH Clear half carry flag in SREG H ← 0 H 1
DATA TRANSFER INSTRUCTIONS
MOV Rd, Rr Move between registers Rd ← Rr None 1
MOVW Rd, Rr Copy register Word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load immediate Rd ← K None 1
LD Rd, X Load indirect Rd ← (X) None 2
LD Rd, X+ Load indirect and post-inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load indirect and pre-dec. X ← X - 1, Rd ← (X) None 2
LD Rd, Y Load indirect Rd ← (Y) None 2
LD Rd, Y+ Load indirect and post-inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load indirect and pre-dec. Y ← Y - 1, Rd ← (Y) None 2
LDD Rd,Y+q Load indirect with displacement Rd ← (Y + q) None 2
LD Rd, Z Load indirect Rd ← (Z) None 2
LD Rd, Z+ Load indirect and post-inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load indirect and pre-dec. Z ← Z - 1, Rd ← (Z) None 2
LDD Rd, Z+q Load indirect with displacement Rd ← (Z + q) None 2
LDS Rd, k Load direct from SRAM Rd ← (k) None 2
ST X, Rr Store indirect (X) ← Rr None 2
ST X+, Rr Store indirect and post-inc. (X) ← Rr, X ← X + 1 None 2
ST - X, Rr Store indirect and pre-dec. X ← X - 1, (X) ← Rr None 2
ST Y, Rr Store indirect (Y) ← Rr None 2
ST Y+, Rr Store indirect and post-inc. (Y) ← Rr, Y ← Y + 1 None 2
ST - Y, Rr Store indirect and pre-dec. Y ← Y - 1, (Y) ← Rr None 2
STD Y+q,Rr Store indirect with displacement (Y + q) ← Rr None 2
ST Z, Rr Store indirect (Z) ← Rr None 2
ST Z+, Rr Store indirect and post-inc. (Z) ← Rr, Z ← Z + 1 None 2
ST -Z, Rr Store indirect and pre-dec. Z ← Z - 1, (Z) ← Rr None 2
STD Z+q,Rr Store indirect with displacement (Z + q) ← Rr None 2
STS k, Rr Store direct to SRAM (k) ← Rr None 2
LPM Load program memory R0 ← (Z) None 3
LPM Rd, Z Load program memory Rd ← (Z) None 3
LPM Rd, Z+ Load program memory and post-inc Rd ← (Z), Z ← Z+1 None 3
SPM Store program memory (Z) ← R1:R0 None -
IN Rd, P In port Rd ← P None 1
OUT P, Rr Out port P ← Rr None 1
PUSH Rr Push register on stack STACK ← Rr None 2
Mnemonics Operands Description Operation Flags #Clocks349
2545T–AVR–05/11
ATmega48/88/168
Note: 1. These instructions are only available in Atmel ATmega168.
POP Rd Pop register from stack Rd ← STACK None 2
MCU CONTROL INSTRUCTIONS
NOP No operation None 1
SLEEP Sleep (See specific descr. for sleep function) None 1
WDR Watchdog reset (See specific descr. for WDR/timer) None 1
BREAK Break For on-chip debug only None N/A
Mnemonics Operands Description Operation Flags #Clocks350
2545T–AVR–05/11
ATmega48/88/168
33. Ordering information
33.1 Atmel ATmega48
Note: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive).
Also Halide free and fully Green.
3. See Figure 29-1 on page 305 and Figure 29-2 on page 305.
4. NiPdAu lead finish.
5. Tape & Reel.
Speed (MHz) Power supply Ordering code(2) Package(1) Operational range
10(3) 1.8V - 5.5V
ATmega48V-10AUR(5)
ATmega48V-10MUR(5)
ATmega48V-10AU
ATmega48V-10MMU
ATmega48V-10MMUR(5)
ATmega48V-10MMH(4)
ATmega48V-10MMHR(4)(5)
ATmega48V-10MU
ATmega48V-10PU
32A
32M1-A
32A
28M1
28M1
28M1
28M1
32M1-A
28P3
Industrial
(-40°C to 85°C)
20(3) 2.7V - 5.5V
ATmega48-20AUR(5)
ATmega48-20MUR(5)
ATmega48-20AU
ATmega48-20MMU
ATmega48-20MMUR(5)
ATmega48-20MMH(4)
ATmega48-20MMHR(4)(5)
ATmega48-20MU
ATmega48-20PU
32A
32M1-A
32A
28M1
28M1
28M1
28M1
32M1-A
28P3
Industrial
(-40°C to 85°C)
Package type
32A 32-lead, thin (1.0mm) plastic quad flat package (TQFP)
28M1 28-pad, 4 × 4 × 1.0 body, lead pitch 0.45mm quad flat no-lead/micro lead frame package (QFN/MLF)
32M1-A 32-pad, 5 × 5 × 1.0 body, lead pitch 0.50mm quad flat no-lead/micro lead frame package (QFN/MLF)
28P3 28-lead, 0.300” wide, plastic dual inline package (PDIP)351
2545T–AVR–05/11
ATmega48/88/168
33.2 Atmel ATmega88
Note: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive).
Also Halide free and fully Green.
3. See Figure 29-1 on page 305 and Figure 29-2 on page 305.
4. Tape & reel
Speed (MHz) Power supply Ordering code(2) Package(1) Operational range
10(3) 1.8V - 5.5V
ATmega88V-10AUR(4)
ATmega88V-10MUR(4)
ATmega88V-10AU
ATmega88V-10MU
ATmega88V-10PU
32A
32M1-A
32A
32M1-A
28P3
Industrial
(-40°C to 85°C)
20(3) 2.7V - 5.5V
ATmega88-20AUR(4)
ATmega88-20MUR(4)
ATmega88-20AU
ATmega88-20MU
ATmega88-20PU
32A
32M1-A
32A
32M1-A
28P3
Industrial
(-40°C to 85°C)
Package type
32A 32-lead, thin (1.0mm) plastic quad flat package (TQFP)
32M1-A 32-pad, 5 × 5 × 1.0 body, lead pitch 0.50mm quad flat no-lead/micro lead frame package (QFN/MLF)
28P3 28-lead, 0.300” wide, plastic dual inline package (PDIP)352
2545T–AVR–05/11
ATmega48/88/168
33.3 Atmel ATmega168
Note: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive).
Also Halide free and fully Green.
3. See Figure 29-1 on page 305 and Figure 29-2 on page 305.
4. Tape & reel
Speed (MHz)(3) Power supply Ordering code(2) Package(1) Operational range
10 1.8V - 5.5V
ATmega168V-10AUR(4)
ATmega168V-10MUR(4)
ATmega168V-10AU
ATmega168V-10MU
ATmega168V-10PU
32A
32M1-A
32A
32M1-A
28P3
Industrial
(-40°C to 85°C)
20 2.7V - 5.5V
ATmega168-20AUR(4)
ATmega168-20MUR(4)
ATmega168-20AU
ATmega168-20MU
ATmega168-20PU
32A
32M1-A
32A
32M1-A
28P3
Industrial
(-40°C to 85°C)
Package type
32A 32-lead, thin (1.0mm) plastic quad flat package (TQFP)
32M1-A 32-pad, 5 × 5 × 1.0 body, lead pitch 0.50mm quad flat no-lead/micro lead frame package (QFN/MLF)
28P3 28-lead, 0.300” wide, plastic dual inline package (PDIP)353
2545T–AVR–05/11
ATmega48/88/168
34. Packaging information
34.1 32A
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
32A, 32-lead, 7 x 7mm Body Size, 1.0mm Body Thickness,
0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP) 32A C
2010-10-20
PIN 1 IDENTIFIER
0°~7°
PIN 1
L
C
A1 A2 A
D1
D
e E1 E
B
Notes:
1. This package conforms to JEDEC reference MS-026, Variation ABA.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10mm maximum.
A – – 1.20
A1 0.05 – 0.15
A2 0.95 1.00 1.05
D 8.75 9.00 9.25
D1 6.90 7.00 7.10 Note 2
E 8.75 9.00 9.25
E1 6.90 7.00 7.10 Note 2
B 0.30 – 0.45
C 0.09 – 0.20
L 0.45 – 0.75
e 0.80 TYP
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE354
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ATmega48/88/168
34.2 28M1
TITLE GPC DRAWING NO. REV.
Package Drawing Contact:
packagedrawings@atmel.com ZBV B 28M1
28M1, 28-pad, 4 x 4 x 1.0mm Body, Lead Pitch 0.45mm,
2.4 x 2.4mm Exposed Pad, Thermally Enhanced
Plastic Very Thin Quad Flat No Lead Package (VQFN)
10/24/08
SIDE VIEW
Pin 1 ID
BOTTOM VIEW
TOP VIEW
Note: The terminal #1 ID is a Laser-marked Feature.
D
E
e
K
A1
C
A
D2
E2
y
L
1
2
3
b
1
2
3
0.45 COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A 0.80 0.90 1.00
A1 0.00 0.02 0.05
b 0.17 0.22 0.27
C 0.20 REF
D 3.95 4.00 4.05
D2 2.35 2.40 2.45
E 3.95 4.00 4.05
E2 2.35 2.40 2.45
e 0.45
L 0.35 0.40 0.45
y 0.00 – 0.08
K 0.20 – –
R 0.20
0.4 Ref
(4x)355
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ATmega48/88/168
34.3 32M1-A
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
32M1-A, 32-pad, 5 x 5 x 1.0mm Body, Lead Pitch 0.50mm, 32M1-A E
5/25/06
3.10mm Exposed Pad, Micro Lead Frame Package (MLF)
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
D1
D
E1 E
b e
A3
A2
A1
A
D2
E2
0.08 C
L
1
2
3
P
P
0
1
2
3
A 0.80 0.90 1.00
A1 – 0.02 0.05
A2 – 0.65 1.00
A3 0.20 REF
b 0.18 0.23 0.30
D
D1
D2 2.95 3.10 3.25
4.90 5.00 5.10
4.70 4.75 4.80
4.70 4.75 4.80
4.90 5.00 5.10
E
E1
E2 2.95 3.10 3.25
e 0.50 BSC
L 0.30 0.40 0.50
P – – 0.60
– – 12o
Note: JEDEC Standard MO-220, Fig. 2 (Anvil Singulation), VHHD-2.
TOP VIEW
SIDE VIEW
BOTTOM VIEW
0
Pin 1 ID
Pin #1 Notch
(0.20 R)
K 0.20 – –
K
K356
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ATmega48/88/168
34.4 28P3
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
28P3, 28-lead (0.300"/7.62mm Wide) Plastic Dual
Inline Package (PDIP) 28P3 B
09/28/01
PIN
1
E1
A1
B
REF
E
B1
C
L
SEATING PLANE
A
0º ~ 15º
D
e
eB
B2
(4 PLACES)
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A – – 4.5724
A1 0.508 – –
D 34.544 – 34.798 Note 1
E 7.620 – 8.255
E1 7.112 – 7.493 Note 1
B 0.381 – 0.533
B1 1.143 – 1.397
B2 0.762 – 1.143
L 3.175 – 3.429
C 0.203 – 0.356
eB – – 10.160
e 2.540 TYP
Note: 1. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25mm (0.010"). 357
2545T–AVR–05/11
ATmega48/88/168
35. Errata
35.1 Errata Atmel ATmega48
The revision letter in this section refers to the revision of the ATmega48 device.
35.1.1 Rev. D
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.1.2 Rev. C
• Reading EEPROM when system clock frequency is below 900kHz may not work
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Reading EEPROM when system clock frequency is below 900kHz may not work
Reading Data from the EEPROM at system clock frequency below 900kHz may result in
wrong data read.
Problem fix/workaround
Avoid using the EEPROM at clock frequency below 900kHz.
2. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.1.3 Rev. B
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).358
2545T–AVR–05/11
ATmega48/88/168
35.1.4 Rev A
• Part may hang in reset
• Wrong values read after erase only operation
• Watchdog timer interrupt disabled
• Start-up time with crystal oscillator is higher than expected
• High power consumption in power-down with external clock
• Asynchronous oscillator does not stop in power-down
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Part may hang in reset
Some parts may get stuck in a reset state when a reset signal is applied when the internal
reset state-machine is in a specific state. The internal reset state-machine is in this state for
approximately 10ns immediately before the part wakes up after a reset, and in a 10ns window
when altering the system clock prescaler. The problem is most often seen during InSystem
Programming of the device. There are theoretical possibilities of this happening also
in run-mode. The following three cases can trigger the device to get stuck in a reset-state:
- Two succeeding resets are applied where the second reset occurs in the 10ns window
before the device is out of the reset-state caused by the first reset.
- A reset is applied in a 10ns window while the system clock prescaler value is updated by
software.
- Leaving SPI-programming mode generates an internal reset signal that can trigger this
case.
The two first cases can occur during normal operating mode, while the last case occurs only
during programming of the device.
Problem fix/workaround
The first case can be avoided during run-mode by ensuring that only one reset source is
active. If an external reset push button is used, the reset start-up time should be selected
such that the reset line is fully debounced during the start-up time.
The second case can be avoided by not using the system clock prescaler.
The third case occurs during In-System programming only. It is most frequently seen when
using the internal RC at maximum frequency.
If the device gets stuck in the reset-state, turn power off, then on again to get the device out
of this state.
2. Wrong values read after erase only operation
At supply voltages below 2.7V, an EEPROM location that is erased by the Erase Only operation
may read as programmed (0x00).
Problem fix/workaround
If it is necessary to read an EEPROM location after Erase Only, use an Atomic Write operation
with 0xFF as data in order to erase a location. In any case, the Write Only operation can
be used as intended. Thus no special considerations are needed as long as the erased location
is not read before it is programmed.359
2545T–AVR–05/11
ATmega48/88/168
3. Watchdog timer interrupt disabled
If the watchdog timer interrupt flag is not cleared before a new timeout occurs, the watchdog
will be disabled, and the interrupt flag will automatically be cleared. This is only applicable in
interrupt only mode. If the Watchdog is configured to reset the device in the watchdog timeout
following an interrupt, the device works correctly.
Problem fix/workaround
Make sure there is enough time to always service the first timeout event before a new
watchdog timeout occurs. This is done by selecting a long enough time-out period.
4. Start-up time with crystal oscillator is higher than expected
The clock counting part of the start-up time is about two times higher than expected for all
start-up periods when running on an external Crystal. This applies only when waking up by
reset. Wake-up from power down is not affected. For most settings, the clock counting parts
is a small fraction of the overall start-up time, and thus, the problem can be ignored. The
exception is when using a very low frequency crystal like for instance a 32kHz clock crystal.
Problem fix/workaround
No known workaround.
5. High power consumption in power-down with external clock
The power consumption in power down with an active external clock is about 10 times
higher than when using internal RC or external oscillators.
Problem fix/workaround
Stop the external clock when the device is in power down.
6. Asynchronous oscillator does not stop in power-down
The Asynchronous oscillator does not stop when entering power down mode. This leads to
higher power consumption than expected.
Problem fix/workaround
Manually disable the asynchronous timer before entering power down.
7. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).360
2545T–AVR–05/11
ATmega48/88/168
35.2 Errata Atmel ATmega88
The revision letter in this section refers to the revision of the ATmega88 device.
35.2.1 Rev. D
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.2.2 Rev. B/C
Not sampled.
35.2.3 Rev. A
• Writing to EEPROM does not work at low operating voltages
• Part may hang in reset
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Writing to EEPROM does not work at low operating voltages
Writing to the EEPROM does not work at low voltages.
Problem fix/workaround
Do not write the EEPROM at voltages below 4.5 Volts.
This will be corrected in rev. B.
2. Part may hang in reset
Some parts may get stuck in a reset state when a reset signal is applied when the internal
reset state-machine is in a specific state. The internal reset state-machine is in this state for
approximately 10ns immediately before the part wakes up after a reset, and in a 10ns window
when altering the system clock prescaler. The problem is most often seen during InSystem
Programming of the device. There are theoretical possibilities of this happening also
in run-mode. The following three cases can trigger the device to get stuck in a reset-state:
- Two succeeding resets are applied where the second reset occurs in the 10ns window
before the device is out of the reset-state caused by the first reset.
- A reset is applied in a 10ns window while the system clock prescaler value is updated by
software.
- Leaving SPI-programming mode generates an internal reset signal that can trigger this
case.
The two first cases can occur during normal operating mode, while the last case occurs only
during programming of the device.361
2545T–AVR–05/11
ATmega48/88/168
Problem fix/workaround
The first case can be avoided during run-mode by ensuring that only one reset source is
active. If an external reset push button is used, the reset start-up time should be selected
such that the reset line is fully debounced during the start-up time.
The second case can be avoided by not using the system clock prescaler.
The third case occurs during In-System programming only. It is most frequently seen when
using the internal RC at maximum frequency.
If the device gets stuck in the reset-state, turn power off, then on again to get the device out
of this state.
3. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.3 Errata Atmel ATmega168
The revision letter in this section refers to the revision of the ATmega168 device.
35.3.1 Rev C
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.3.2 Rev B
• Part may hang in reset
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Part may hang in reset
Some parts may get stuck in a reset state when a reset signal is applied when the internal
reset state-machine is in a specific state. The internal reset state-machine is in this state for
approximately 10ns immediately before the part wakes up after a reset, and in a 10ns window
when altering the system clock prescaler. The problem is most often seen during InSystem
Programming of the device. There are theoretical possibilities of this happening also
in run-mode. The following three cases can trigger the device to get stuck in a reset-state:
- Two succeeding resets are applied where the second reset occurs in the 10ns window
before the device is out of the reset-state caused by the first reset.362
2545T–AVR–05/11
ATmega48/88/168
- A reset is applied in a 10ns window while the system clock prescaler value is updated by
software.
- Leaving SPI-programming mode generates an internal reset signal that can trigger this
case.
The two first cases can occur during normal operating mode, while the last case occurs only
during programming of the device.
Problem fix/workaround
The first case can be avoided during run-mode by ensuring that only one reset source is
active. If an external reset push button is used, the reset start-up time should be selected
such that the reset line is fully debounced during the start-up time.
The second case can be avoided by not using the system clock prescaler.
The third case occurs during In-System programming only. It is most frequently seen when
using the internal RC at maximum frequency.
If the device gets stuck in the reset-state, turn power off, then on again to get the device out
of this state.
2. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
35.3.3 Rev A
• Wrong values read after erase only operation
• Part may hang in reset
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Wrong values read after erase only operation
At supply voltages below 2.7V, an EEPROM location that is erased by the Erase Only operation
may read as programmed (0x00).
Problem fix/workaround
If it is necessary to read an EEPROM location after Erase Only, use an Atomic Write operation
with 0xFF as data in order to erase a location. In any case, the Write Only operation can
be used as intended. Thus no special considerations are needed as long as the erased location
is not read before it is programmed.
2. Part may hang in reset
Some parts may get stuck in a reset state when a reset signal is applied when the internal
reset state-machine is in a specific state. The internal reset state-machine is in this state for
approximately 10ns immediately before the part wakes up after a reset, and in a 10ns window
when altering the system clock prescaler. The problem is most often seen during InSystem
Programming of the device. There are theoretical possibilities of this happening also
in run-mode. The following three cases can trigger the device to get stuck in a reset-state:363
2545T–AVR–05/11
ATmega48/88/168
- Two succeeding resets are applied where the second reset occurs in the 10ns window
before the device is out of the reset-state caused by the first reset.
- A reset is applied in a 10ns window while the system clock prescaler value is updated by
software.
- Leaving SPI-programming mode generates an internal reset signal that can trigger this
case.
The two first cases can occur during normal operating mode, while the last case occurs only
during programming of the device.
Problem fix/workaround
The first case can be avoided during run-mode by ensuring that only one reset source is
active. If an external reset push button is used, the reset start-up time should be selected
such that the reset line is fully debounced during the start-up time.
The second case can be avoided by not using the system clock prescaler.
The third case occurs during In-System programming only. It is most frequently seen when
using the internal RC at maximum frequency.
If the device gets stuck in the reset-state, turn power off, then on again to get the device out
of this state.
2. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).364
2545T–AVR–05/11
ATmega48/88/168
36. Datasheet revision history
Please note that the referring page numbers in this section are referred to this document. The
referring revision in this section are referring to the document revision.
36.1 Rev. 2545T-04/11
36.2 Rev. 2545S-07/10
36.3 Rev. 2545R-07/09
36.4 Rev. 2545Q-06/09
36.5 Rev. 2545P-02/09
1. Ordering information has been updated by removing AI and MI and added AUR and
MUR (tape & reel).
2. Added and corrected cross references and short-cuts.
3. Document updated according to new Atmel standard.
4. QTouch Library Support Features
1. Note 6 and Note 7 in Table 29-5, “2-wire serial bus requirements.,” on page 308 have
been removed.
2. Document updated according to Atmel standard.
1. Updated “Errata” on page 357.
2. Updated the last page with the Atmel new addresses.
1. Removed the heading “About”. The subsections of this sectionis now separate sections,
“Resources”, “Data Retention” and “About Code Examples”
2. Updated “Ordering information” on page 350.
1. Removed Power-off slope rate from Table 29-3 on page 307. 365
2545T–AVR–05/11
ATmega48/88/168
36.6 Rev. 2545O-02/09
36.7 Rev. 2545N-01/09
36.8 Rev. 2545M-09/07
36.9 Rev. 2545L-08/07
36.10 Rev. 2545K-04/07
36.11 Rev. 2545J-12/06
1. Changed minimum Power-on Reset Threshold Voltage (falling) to 0.05V in Table 29-
3 on page 307.
2. Removed section “Power-on slope rate” from “System and reset characteristics” on
page 307.
1. Updated “Features” on page 1 and added the note “Not recommended for new
designs”.
2. Merged the sections Resources, Data Retention and About Code Examples under
one common section, “Resources” on page 8.
3. Updated Figure 9-4 on page 35.
4. Updated “System clock prescaler” on page 36.
5. Updated “Alternate functions of port B” on page 78.
6. Added section “” on page 307.
7. Updated “Pin thresholds and hysteresis” on page 330.
1. Added “Data retention” on page 8.
2. Updated “ADC characteristics” on page 311.
3. “Preliminary“ removed through the datasheet.
1. Updated “Features” on page 1.
2. Updated code example in “MCUCR – MCU control register” on page 64.
3. Updated “System and reset characteristics” on page 307.
4. Updated Note in Table 9-3 on page 30, Table 9-5 on page 31, Table 9-8 on page 34,
Table 9-10 on page 34.
1. Updated “Interrupts” on page 56.
2. Updated“Errata Atmel ATmega48” on page 357 .
3. Changed description in “Analog-to-digital converter” on page 244.
1. Updated “Features” on page 1.366
2545T–AVR–05/11
ATmega48/88/168
36.12 Rev. 2545I-11/06
36.13 Rev. 2545H-10/06
36.14 Rev. 2545G-06/06
2. Updated Table 1-1 on page 2.
3. Updated “Ordering information” on page 350.
4. Updated “Packaging information” on page 353.
1. Updated “Features” on page 1.
2. Updated Features in “2-wire serial interface” on page 209.
3. Fixed typos in Table 29-3 on page 307.
1. Updated typos.
2. Updated “Features” on page 1.
3. Updated “Calibrated internal RC oscillator” on page 33.
4. Updated “System control and reset” on page 45.
5. Updated “Brown-out detection” on page 47.
6. Updated “Fast PWM mode” on page 121.
7. Updated bit description in “TCCR1C – Timer/Counter1 control register C” on page
133.
8. Updated code example in “SPI – Serial peripheral interface” on page 161.
9. Updated Table 15-3 on page 101, Table 15-6 on page 102, Table 15-8 on page 103,
Table 16-2 on page 130, Table 16-3 on page 131, Table 16-4 on page 132, Table 18-
3 on page 154, Table 18-6 on page 155, Table 18-8 on page 156, and Table 28-5 on
page 287.
10. Added Note to Table 26-1 on page 265, Table 27-5 on page 279, and Table 28-17 on
page 300.
11. Updated “Setting the boot loader lock bits by SPM” on page 277.
12. Updated “Signature bytes” on page 288
13. Updated “Electrical characteristics” on page 303.
14. Updated “Errata” on page 357.
1. Added Addresses in Registers.
2. Updated “Calibrated internal RC oscillator” on page 33.
3. Updated Table 9-12 on page 35, Table 10-1 on page 39, Table 11-1 on page 54,
Table 14-3 on page 78.
4. Updated “ADC noise reduction mode” on page 40.
5. Updated note for Table 10-2 on page 43.
6. Updatad “Bit 2 - PRSPI: Power reduction serial peripheral interface” on page 44.
7. Updated “TCCR0B – Timer/counter control register B” on page 104.
8. Updated “Fast PWM mode” on page 121.
9. Updated “Asynchronous operation of Timer/Counter2” on page 151.
10. Updated “SPI – Serial peripheral interface” on page 161.367
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36.15 Rev. 2545F-05/05
36.16 Rev. 2545E-02/05
36.17 Rev. 2545D-07/04
11. Updated “UCSRnA – USART MSPIM control and status register n A” on page 206.
12. Updated note in “Bit rate generator unit” on page 216.
13. Updated “Bit 6 – ACBG: Analog comparator bandgap select” on page 242.
14. Updated Features in “Analog-to-digital converter” on page 244.
15. Updated “Prescaling and conversion timing” on page 247.
16. Updated “Limitations of debugWIRE” on page 261.
17 Added Table 29-1 on page 306.
18. Updated Figure 16-7 on page 122, Figure 30-45 on page 339.
19. Updated rev. A in “Errata Atmel ATmega48” on page 357.
20. Added rev. C and D in “Errata Atmel ATmega48” on page 357.
1. Added Section 3. “Resources” on page 8
2. Update Section 9.6 “Calibrated internal RC oscillator” on page 33.
3. Updated Section 28.8.3 “Serial programming instruction set” on page 300.
4. Table notes in Section 29.2 “DC characteristics” on page 303 updated.
5. Updated Section 35. “Errata” on page 357.
1. MLF-package alternative changed to “Quad Flat No-Lead/Micro Lead Frame Package
QFN/MLF”.
2. Updated “EECR – The EEPROM control register” on page 22.
3. Updated “Calibrated internal RC oscillator” on page 33.
4. Updated “External clock” on page 35.
5. Updated Table 29-3 on page 307, Table 29-6 on page 309, Table 29-2 on page 306
and Table 28-16 on page 300
6. Added “Pin change interrupt timing” on page 66
7. Updated “8-bit timer/counter block diagram.” on page 90.
8. Updated “SPMCSR – Store program memory control and status register” on page
267.
9. Updated “Enter programming mode” on page 291.
10. Updated “DC characteristics” on page 303.
11. Updated “Ordering information” on page 350.
12. Updated “Errata Atmel ATmega88” on page 360 and “Errata Atmel ATmega168” on
page 361.
1. Updated instructions used with WDTCSR in relevant code examples.
2. Updated Table 9-5 on page 31, Table 29-4 on page 307, Table 27-9 on page 282,
and Table 27-11 on page 283.
3. Updated “System clock prescaler” on page 36.368
2545T–AVR–05/11
ATmega48/88/168
36.18 Rev. 2545C-04/04
36.19 Rev. 2545B-01/04
4. Moved “TIMSK2 – Timer/Counter2 interrupt mask register” on page 158 and
“TIFR2 – Timer/Counter2 interrupt flag register” on page 158 to
“Register description” on page 153.
5. Updated cross-reference in “Electrical interconnection” on page 210.
6. Updated equation in “Bit rate generator unit” on page 216.
7. Added “Page size” on page 289.
8. Updated “Serial programming algorithm” on page 299.
9. Updated Ordering Information for “Atmel ATmega168” on page 352.
10. Updated “Errata Atmel ATmega88” on page 360 and “Errata Atmel ATmega168” on
page 361.
11. Updated equation in “Bit rate generator unit” on page 216.
1. Speed Grades changed: 12MHz to 10MHz and 24MHz to 20MHz
2. Updated “Speed grades” on page 305.
3. Updated “Ordering information” on page 350.
4. Updated “Errata Atmel ATmega88” on page 360.
1. Added PDIP to “I/O and Packages”, updated “Speed Grade” and Power Consumption
Estimates in 36.“Features” on page 1.
2. Updated “Stack pointer” on page 13 with RAMEND as recommended Stack Pointer
value.
3. Added section “Power reduction register” on page 41 and a note regarding the use of
the PRR bits to 2-wire, Timer/Counters, USART, Analog Comparator and ADC
sections.
4. Updated “Watchdog timer” on page 49.
5. Updated Figure 16-2 on page 130 and Table 16-3 on page 131.
6. Extra Compare Match Interrupt OCF2B added to features in section “8-bit
Timer/Counter2 with PWM and asynchronous operation” on page 140
7. Updated Table 10-1 on page 39, Table 24-5 on page 259, Table 28-4 to Table 28-7
on page 286 to 288 and Table 24-1 on page 249. Added note 2 to Table 28-1 on page
285. Fixed typo in Table 13-1 on page 67.
8. Updated whole “Typical characteristics” on page 315.
9. Added item 2 to 5 in “Errata Atmel ATmega48” on page 357.
10. Renamed the following bits:
- SPMEN to SELFPRGEN
- PSR2 to PSRASY
- PSR10 to PSRSYNC
- Watchdog Reset to Watchdog System Reset
11. Updated C code examples containing old IAR syntax.
12. Updated BLBSET description in “SPMCSR – Store program memory control and status
register” on page 283.i
2545T–AVR–05/11
ATmega48/88/168
Table of contents
Features ..................................................................................................... 1
1 Pin configurations ................................................................................... 2
1.1Pin descriptions .........................................................................................................3
2 Overview ................................................................................................... 5
2.1Block diagram ............................................................................................................5
2.2Comparison between Atmel ATmega48, Atmel ATmega88, and Atmel ATmega168 .
6
3 Resources ................................................................................................. 8
4 Data retention ........................................................................................... 8
5 About code examples .............................................................................. 8
6 Capacitive touch sensing ........................................................................ 8
7 AVR CPU core .......................................................................................... 9
7.1Overview ...................................................................................................................9
7.2Architectural overview ...............................................................................................9
7.3ALU – Arithmetic Logic Unit ....................................................................................10
7.4Status register .........................................................................................................11
7.5General purpose register file ...................................................................................12
7.6Stack pointer ...........................................................................................................13
7.7Instruction execution timing .....................................................................................14
7.8Reset and interrupt handling ...................................................................................15
8 AVR memories ....................................................................................... 17
8.1Overview .................................................................................................................17
8.2In-system reprogrammable flash program memory .................................................17
8.3SRAM data memory ................................................................................................19
8.4EEPROM data memory ...........................................................................................20
8.5I/O memory ..............................................................................................................21
8.6Register description .................................................................................................22
9 System clock and clock options .......................................................... 27
9.1Clock systems and their distribution ........................................................................27
9.2Clock sources ..........................................................................................................28
9.3Low power crystal oscillator ....................................................................................29
9.4Full swing crystal oscillator ......................................................................................31ii
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9.5Low frequency crystal oscillator ..............................................................................33
9.6Calibrated internal RC oscillator ..............................................................................33
9.7128kHz internal oscillator ........................................................................................34
9.8External clock ..........................................................................................................35
9.9Clock output buffer ..................................................................................................35
9.10Timer/counter oscillator .........................................................................................36
9.11System clock prescaler .........................................................................................36
9.12Register description ...............................................................................................37
10 Power management and sleep modes ................................................. 39
10.1Sleep modes .........................................................................................................39
10.2Idle mode ...............................................................................................................39
10.3ADC noise reduction mode ...................................................................................40
10.4Power-down mode ................................................................................................40
10.5Power-save mode .................................................................................................40
10.6Standby mode .......................................................................................................41
10.7Power reduction register .......................................................................................41
10.8Minimizing power consumption .............................................................................41
10.9Register description ...............................................................................................43
11 System control and reset ...................................................................... 45
11.1Resetting the AVR .................................................................................................45
11.2Reset sources .......................................................................................................45
11.3Power-on reset ......................................................................................................46
11.4External reset ........................................................................................................47
11.5Brown-out detection ..............................................................................................47
11.6Watchdog system reset .........................................................................................48
11.7Internal voltage reference ......................................................................................48
11.8Watchdog timer .....................................................................................................49
11.9Register description ...............................................................................................53
12 Interrupts ................................................................................................ 56
12.1Overview ...............................................................................................................56
12.2Interrupt vectors in ATmega48 ..............................................................................56
12.3Interrupt vectors in Atmel ATmega88 ....................................................................58
12.4Interrupt vectors in Atmel ATmega168 ..................................................................61
12.5Register description ...............................................................................................64
13 External interrupts ................................................................................. 66iii
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13.1Pin change interrupt timing ....................................................................................66
13.2Register description ...............................................................................................67
14 I/O-ports .................................................................................................. 71
14.1Overview ...............................................................................................................71
14.2Ports as general digital I/O ....................................................................................72
14.3Alternate port functions .........................................................................................76
14.4Register description ...............................................................................................87
15 8-bit Timer/Counter0 with PWM ............................................................ 89
15.1Features ................................................................................................................89
15.2Overview ...............................................................................................................89
15.3Timer/counter clock sources .................................................................................91
15.4Counter unit ...........................................................................................................91
15.5Output compare unit ..............................................................................................92
15.6Compare match output unit ...................................................................................93
15.7Modes of operation ................................................................................................94
15.8Timer/counter timing diagrams ..............................................................................99
15.9Register description .............................................................................................101
16 16-bit Timer/Counter1 with PWM ........................................................ 108
16.1Features ..............................................................................................................108
16.2Overview .............................................................................................................108
16.3Accessing 16-bit registers ...................................................................................110
16.4Timer/counter clock sources ...............................................................................113
16.5Counter unit .........................................................................................................114
16.6Input capture unit .................................................................................................115
16.7Output compare units ..........................................................................................116
16.8Compare match output unit .................................................................................118
16.9Modes of operation ..............................................................................................119
16.10Timer/counter timing diagrams ..........................................................................127
16.11Register description ...........................................................................................130
17 Timer/Counter0 and Timer/Counter1 prescalers .............................. 137
17.1Register description .............................................................................................139
18 8-bit Timer/Counter2 with PWM and asynchronous operation ........ 140
18.1Features ..............................................................................................................140
18.2Overview .............................................................................................................140iv
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18.3Timer/counter clock sources ...............................................................................141
18.4Counter unit .........................................................................................................141
18.5Output compare unit ............................................................................................142
18.6Compare match output unit .................................................................................144
18.7Modes of operation ..............................................................................................145
18.8Timer/counter timing diagrams ............................................................................149
18.9Asynchronous operation of Timer/Counter2 ........................................................151
18.10Timer/counter prescaler ....................................................................................152
18.11Register description ...........................................................................................153
19 SPI – Serial peripheral interface ......................................................... 161
19.1Features ..............................................................................................................161
19.2Overview .............................................................................................................161
19.3SS pin functionality ..............................................................................................166
19.4Data modes .........................................................................................................166
19.5Register description .............................................................................................168
20 USART0 ................................................................................................. 171
20.1Features ..............................................................................................................171
20.2Overview .............................................................................................................171
20.3Clock generation .................................................................................................172
20.4Frame formats .....................................................................................................175
20.5USART initialization .............................................................................................176
20.6Data transmission – The USART transmitter ......................................................179
20.7Data reception – The USART receiver ................................................................181
20.8Asynchronous data reception ..............................................................................185
20.9Multi-processor communication mode .................................................................188
20.10Register description ...........................................................................................190
20.11Examples of baud rate setting ...........................................................................194
21 USART in SPI mode ............................................................................. 199
21.1Features ..............................................................................................................199
21.2Overview .............................................................................................................199
21.3Clock generation .................................................................................................199
21.4SPI data modes and timing .................................................................................200
21.5Frame formats .....................................................................................................201
21.6Data transfer ........................................................................................................203
21.7AVR USART MSPIM vs. AVR SPI ......................................................................205v
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21.8Register description .............................................................................................206
22 2-wire serial interface .......................................................................... 209
22.1Features ..............................................................................................................209
22.22-wire serial interface bus definition ....................................................................209
22.3Data transfer and frame format ...........................................................................210
22.4Multi-master bus systems, arbitration and synchronization .................................213
22.5Overview of the TWI module ...............................................................................216
22.6Using the TWI ......................................................................................................218
22.7Transmission modes ...........................................................................................222
22.8Multi-master systems and arbitration ...................................................................235
22.9Register description .............................................................................................236
23 Analog comparator .............................................................................. 241
23.1Overview .............................................................................................................241
23.2Analog comparator multiplexed input ..................................................................241
23.3Register description .............................................................................................242
24 Analog-to-digital converter ................................................................. 244
24.1Features ..............................................................................................................244
24.2Overview .............................................................................................................244
24.3Starting a conversion ...........................................................................................246
24.4Prescaling and conversion timing ........................................................................247
24.5Changing channel or reference selection ............................................................249
24.6ADC noise canceler .............................................................................................250
24.7ADC conversion result .........................................................................................255
24.8Register description .............................................................................................255
25 debugWIRE on-chip debug system .................................................... 260
25.1Features ..............................................................................................................260
25.2Overview .............................................................................................................260
25.3Physical interface ................................................................................................260
25.4Software break points ..........................................................................................261
25.5Limitations of debugWIRE ...................................................................................261
25.6Register description .............................................................................................261
26 Self-programming the flash, Atmel ATmega48 ................................. 262
26.1Overview .............................................................................................................262
26.2Addressing the flash during self-programming ....................................................263vi
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26.3Register description .............................................................................................267
27 Boot loader support – Read-while-write self-programming, Atmel
ATmega88 and Atmel ATmega168 269
27.1Features ..............................................................................................................269
27.2Overview .............................................................................................................269
27.3Application and boot loader flash sections ..........................................................269
27.4Read-while-write and no read-while-write flash sections .....................................270
27.5Boot loader lock bits ............................................................................................272
27.6Entering the boot loader program ........................................................................273
27.7Addressing the flash during self-programming ....................................................274
27.8Self-programming the flash .................................................................................275
27.9Register description .............................................................................................283
28 Memory programming ......................................................................... 285
28.1Program and data memory lock bits ....................................................................285
28.2Fuse bits ..............................................................................................................286
28.3Signature bytes ...................................................................................................288
28.4Calibration byte ...................................................................................................288
28.5Page size .............................................................................................................289
28.6Parallel programming parameters, pin mapping, and commands .......................289
28.7Parallel programming ..........................................................................................291
28.8Serial downloading ..............................................................................................298
29 Electrical characteristics ..................................................................... 303
29.1Absolute maximum ratings* .................................................................................303
29.2DC characteristics ...............................................................................................303
29.3Speed grades ......................................................................................................305
29.4Clock characteristics ...........................................................................................306
29.5System and reset characteristics ........................................................................307
29.62-wire serial interface characteristics ..................................................................308
29.7SPI timing characteristics ....................................................................................309
29.8ADC characteristics .............................................................................................311
29.9Parallel programming characteristics ..................................................................312
30 Typical characteristics ........................................................................ 315
30.1Active supply current ...........................................................................................315
30.2Idle supply current ...............................................................................................318
30.3Supply current of I/O modules .............................................................................321vii
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30.4Power-down supply current .................................................................................323
30.5Power-save supply current ..................................................................................324
30.6Standby supply current ........................................................................................324
30.7Pin pull-up ...........................................................................................................325
30.8Pin driver strength ...............................................................................................327
30.9Pin thresholds and hysteresis .............................................................................330
30.10BOD thresholds and analog comparator offset .................................................333
30.11Internal oscillator speed ....................................................................................336
30.12Current consumption of peripheral units ...........................................................338
30.13Current consumption in reset and reset pulse width .........................................341
31 Register summary ................................................................................ 343
32 Instruction set summary ..................................................................... 347
33 Ordering information ........................................................................... 350
33.1Atmel ATmega48 .................................................................................................350
33.2Atmel ATmega88 .................................................................................................351
33.3Atmel ATmega168 ...............................................................................................352
34 Packaging information ........................................................................ 353
34.132A ......................................................................................................................353
34.228M1 ...................................................................................................................354
34.332M1-A ................................................................................................................355
34.428P3 ....................................................................................................................356
35 Errata ..................................................................................................... 357
35.1Errata Atmel ATmega48 ......................................................................................357
35.2Errata Atmel ATmega88 ......................................................................................360
35.3Errata Atmel ATmega168 ....................................................................................361
36 Datasheet revision history .................................................................. 364
36.1Rev. 2545T-04/11 ................................................................................................364
36.2Rev. 2545S-07/10 ...............................................................................................364
36.3Rev. 2545R-07/09 ...............................................................................................364
36.4Rev. 2545Q-06/09 ...............................................................................................364
36.5Rev. 2545P-02/09 ...............................................................................................364
36.6Rev. 2545O-02/09 ...............................................................................................365
36.7Rev. 2545N-01/09 ...............................................................................................365
36.8Rev. 2545M-09/07 ...............................................................................................365viii
2545T–AVR–05/11
ATmega48/88/168
36.9Rev. 2545L-08/07 ................................................................................................365
36.10Rev. 2545K-04/07 .............................................................................................365
36.11Rev. 2545J-12/06 ..............................................................................................365
36.12Rev. 2545I-11/06 ...............................................................................................366
36.13Rev. 2545H-10/06 .............................................................................................366
36.14Rev. 2545G-06/06 .............................................................................................366
36.15Rev. 2545F-05/05 ..............................................................................................367
36.16Rev. 2545E-02/05 .............................................................................................367
36.17Rev. 2545D-07/04 .............................................................................................367
36.18Rev. 2545C-04/04 .............................................................................................368
36.19Rev. 2545B-01/04 .............................................................................................368
Table of contents ....................................................................................... i2545T–AVR–05/11
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Rev. 8207L-AT42-05/12
Atmel QTouch Library
User Guide
Supports QTouch® and QMatrix® acquisition for Keys, Sliders
and Rotors 2 8207L-AT42-05/12
Rev. 8207L-AT42-05/12
Table of Contents
TABLE OF CONTENTS ..............................................................................................................................2
1 PREFACE..............................................................................................................................................8
2 INTRODUCTION .................................................................................................................................9
3 OVERVIEW ........................................................................................................................................10
4 ABBREVIATIONS AND DEFINITIONS.........................................................................................11
4.1 DEFINITIONS...................................................................................................................................11
5 GENERIC QTOUCH LIBRARIES...................................................................................................12
5.1 INTRODUCTION...............................................................................................................................12
5.2 ACQUISITION METHODS .................................................................................................................13
5.2.1 QTouch acquisition method...................................................................................................13
5.2.1.1 Sensor schematics for a QTouch acquisition method design............................................................ 14
5.2.2 QMatrix acquisition method ..................................................................................................14
5.2.3 Sensor schematics for a QMatrix acquisition method design................................................15
5.3 GLOBAL SETTINGS COMMON TO ALL SENSORS OF A SPECIFIC ACQUISITION METHOD......................15
5.3.1 Recalibration Threshold ........................................................................................................16
5.3.2 Detect Integration..................................................................................................................16
5.3.3 Drift Hold Time .....................................................................................................................16
5.3.4 Maximum ON Duration .........................................................................................................17
5.3.5 Positive / Negative Drift ........................................................................................................17
5.3.6 Positive Recalibration Delay .................................................................................................18
5.4 SENSOR SPECIFIC SETTINGS ............................................................................................................18
5.4.1 Detect threshold.....................................................................................................................18
5.4.2 Hysteresis...............................................................................................................................18
5.4.3 Position Resolution................................................................................................................19
5.4.4 Position Hysteresis ................................................................................................................19
5.4.5 Adjacent Key Suppression (AKS)...........................................................................................20
5.5 USING THE SENSORS.......................................................................................................................20
5.5.1 Avoiding Cross-talk ...............................................................................................................20
5.5.2 Multiple measurements..........................................................................................................20
5.5.3 Guard Channel ......................................................................................................................21
5.6 QTOUCH API AND USAGE..............................................................................................................22
5.6.1 QTouch Library API..............................................................................................................22
5.6.2 touch_api.h - public header file.............................................................................................22
5.6.3 Type Definitions and enumerations used in the library.........................................................22
5.6.3.1 Typedefs........................................................................................................................................... 22
5.6.3.2 Enumerations ................................................................................................................................... 22
5.6.3.2.1 sensor_type_t.............................................................................................................................. 22
5.6.3.2.2 aks_group_t................................................................................................................................ 23
5.6.3.2.3 channel_t.................................................................................................................................... 23
5.6.3.2.4 hysteresis_t................................................................................................................................. 23
5.6.3.2.5 resolution_t................................................................................................................................. 24
5.6.3.2.6 recal_threshold_t........................................................................................................................ 24
5.6.4 Data structures......................................................................................................................25
5.6.4.1 qt_touch_status_t.............................................................................................................................. 25
5.6.4.2 qt_touch_lib_config_data_t.............................................................................................................. 25
5.6.4.3 qt_touch_lib_measure_data_t........................................................................................................... 26
5.6.4.4 qt_burst_lengths............................................................................................................................... 26
5.6.4.5 tag_sensor_t ..................................................................................................................................... 27
5.6.4.6 qt_lib_siginfo_t ................................................................................................................................ 27
5.6.5 Public Functions....................................................................................................................283
5.6.5.1 qt_set_parameters............................................................................................................................. 28
5.6.5.2 qt_enable_key .................................................................................................................................. 29
5.6.5.3 qt_enable_rotor ................................................................................................................................ 29
5.6.5.4 qt_enable_slider ............................................................................................................................... 30
5.6.5.5 qt_init_sensing ................................................................................................................................. 30
5.6.5.6 qt_measure_sensors.......................................................................................................................... 31
5.6.5.7 qt_calibrate_sensing......................................................................................................................... 31
5.6.5.8 qt_reset_sensing ............................................................................................................................... 32
5.6.5.9 qt_get_sensor_delta.......................................................................................................................... 32
5.6.5.10 qt_get_library_sig ........................................................................................................................ 32
5.6.6 Sequence of Operations and Using the API...........................................................................33
5.6.6.1 Channel Numbering ......................................................................................................................... 33
5.6.6.1.1 Channel numbering when using QTouch acquisition method .................................................... 33
5.6.6.1.2 Channel numbering when using QMatrix acquisition method ................................................... 39
5.6.6.2 Sensor Numbering............................................................................................................................ 41
5.6.6.3 Filtering Signal Measurements......................................................................................................... 42
5.6.6.4 Allocating unused Port Pins for User Application............................................................................ 43
5.6.6.5 Disabling and Enabling of Pull-up for AVR devices........................................................................ 44
5.6.7 Constraints.............................................................................................................................44
5.6.7.1 QTouch acquisition method constraints........................................................................................... 44
5.6.7.2 QMatrix acquisition method constraints........................................................................................... 45
5.6.7.3 Design Guidelines for QMatrix acquisition method systems ........................................................... 46
5.6.8 Frequency of operation (Vs) Charge cycle/dwell cycle times: ..............................................46
5.6.9 Interrupts...............................................................................................................................47
5.6.10 Integrating QTouch libraries in your application .................................................................48
5.6.10.1 Directory structure of the library files.......................................................................................... 48
5.6.10.2 Integrating QTouch acquisition method libraries in your application.......................................... 50
5.6.10.2.1 Example for 8bit AVR ............................................................................................................. 52
5.6.10.2.2 Example for ATSAM ............................................................................................................... 54
5.6.10.2.3 Checklist of items for integrating QTouch acquisition method libraries.................................. 55
5.6.10.3 Integrating QMatrix acquisition method libraries in your application ......................................... 55
5.6.10.3.1 Example for 8bit AVR ............................................................................................................. 55
5.6.10.3.2 Example for 32bit AVR ........................................................................................................... 62
5.6.10.3.3 Checklist of items for integrating QMatrix Capacitive sensing libraries.................................. 66
5.6.10.4 Common checklist items.............................................................................................................. 66
5.6.10.4.1 Configuring the stack size for the application .......................................................................... 66
5.6.11 Example project files .............................................................................................................67
5.6.11.1 Using the Sample projects ........................................................................................................... 68
5.6.11.2 Example applications for QTouch acquisition method libraries.................................................. 68
5.6.11.2.1 Selecting the right configuration .............................................................................................. 68
5.6.11.2.2 Changing the settings to match your device ............................................................................. 69
5.6.11.2.3 Changing the library configuration parameters ........................................................................ 70
5.6.11.2.4 Using the example projects ...................................................................................................... 72
5.6.11.3 Example applications for QMatrix acquisition method libraries.................................................. 73
5.6.11.3.1 Selecting the right configuration .............................................................................................. 73
5.6.11.3.2 Changing the library configuration parameters ........................................................................ 74
5.6.11.3.3 Using the example projects ...................................................................................................... 75
5.6.11.4 Adjusting the Stack size when using IAR IDE ............................................................................ 76
5.6.11.5 Optimization levels...................................................................................................................... 76
5.6.11.6 Debug Support in Example applications...................................................................................... 77
5.6.11.6.1 Debug Support in the sample applications for EVK2080 and QT600 boards .......................... 77
5.6.11.6.2 How to turn on the debug option.............................................................................................. 77
5.6.11.6.3 Debug Interface if USB Bridge board is not available ............................................................. 78
5.7 LIBRARY VARIANTS .......................................................................................................................79
5.7.1 QTouch Acquisition method library variants.........................................................................79
5.7.1.1 Introduction...................................................................................................................................... 79
5.7.1.2 Support for different compiler tool chains........................................................................................ 79
5.7.1.3 QTouch Acquisition method library naming conventions................................................................ 79
5.7.1.3.1 Naming convention for libraries to be used with GCC tool chain.............................................. 79
5.7.1.3.2 Naming convention for libraries to be used with IAR Embedded Workbench........................... 80
5.7.1.4 QTouch acquisition method library variants .................................................................................... 804 8207L-AT42-05/12
5.7.1.5 Port combinations supported for SNS and SNSK pin configurations............................................... 81
5.7.1.5.1 Tips on pin assignments for the sensor design using one pair of SNS/SNSK ports ................... 81
5.7.1.5.2 Port combinations supported for two port pair SNS and SNSK pin configurations................... 83
5.7.1.6 Sample applications and Memory requirements for QTouch acquisition method libraries.............. 84
5.7.2 QMatrix acquisition method library variants........................................................................84
5.7.2.1 Introduction...................................................................................................................................... 84
5.7.2.2 Support for different compiler tool chains........................................................................................ 84
5.7.2.3 QMatrix Acquisition method library naming conventions............................................................... 84
5.7.2.4 QMatrix acquisition method library variants.................................................................................... 87
5.7.2.4.1 Devices supported for QMatrix Acquisition............................................................................... 87
5.8 PIN CONFIGURATION FOR QTOUCH LIBRARIES .............................................................................87
5.8.1 Pin Configuration for QTouch Acquisition Method ..............................................................87
5.8.1.1 Rules for configurable SNS-SNSK Mask Generation...................................................................... 88
5.8.1.1.1 Example for 8 channel interport mask Calculation with one port pair ....................................... 89
5.8.1.1.2 Example for 8 channel intraport mask Calculation with two port pairs...................................... 90
5.8.1.1.3 Example for 12 channel intraport-interport mask Calculation with two port pairs.................... 91
5.8.1.1.4 Example for 16 channel intreport-interport mask Calculation with two port pairs.................... 92
5.8.1.2 How to Use QTouch Studio For Pin Configurability ....................................................................... 93
5.8.2 Pin Configuration for QMatrix Acquisition Method............................................................101
5.8.2.1 Configuration Rules: ...................................................................................................................... 101
5.8.2.2 How to use QTouch Studio for Pin Configurability:...................................................................... 102
5.9 MISRA COMPLIANCE REPORT.....................................................................................................109
5.9.1 What is covered ...................................................................................................................110
5.9.2 Target Environment.............................................................................................................110
5.9.3 Deviations from MISRA C Standards..................................................................................110
5.9.3.1 QTouch acquisition method libraries ............................................................................................. 110
5.9.3.2 QMatrix acquisition method libraries............................................................................................. 111
5.10 KNOWN ISSUES.............................................................................................................................111
5.11 CHECKLIST...................................................................................................................................112
6 DEVICE SPECIFIC LIBRARIES ...................................................................................................113
6.1 INTRODUCTION.............................................................................................................................113
6.2 DEVICES SUPPORTED ....................................................................................................................113
6.3 QTOUCH LIBRARY FOR AT32UC3L DEVICES ..............................................................................113
6.3.1 Salient Features of QTouch Library for UC3L....................................................................113
6.3.1.1 QMatrix method sensor.................................................................................................................. 113
6.3.1.2 QTouch method sensor................................................................................................................... 113
6.3.1.3 Autonomous QTouch sensor.......................................................................................................... 114
6.3.1.4 Additional Features........................................................................................................................ 114
6.3.2 Device variants supported for UC3L...................................................................................114
6.3.3 Development tool support for UC3L ...................................................................................114
Table 8 Development tool support for UC3L QTouch Library ................................................................... 114
6.3.4 Overview of QTouch Library API for UC3L .......................................................................115
Figure 35 Overview diagram of QTouch Library for UC3L ....................................................................... 115
6.3.5 Acquisition method support for UC3L.................................................................................116
Table 9 Acquisition method specific API.................................................................................................... 116
6.3.6 API State machine for UC3L ...............................................................................................116
Figure 36 State Diagram of QTouch Library for UC3L .............................................................................. 117
6.3.7 QMatrix method sensor operation for UC3L.......................................................................117
6.3.7.1 QMatrix method pin selection for UC3L........................................................................................ 117
Table 10 QMatrix Resistive drive pin option .............................................................................................. 118
6.3.7.2 QMatrix method Schematic for UC3L........................................................................................... 118
6.3.7.2.1 Internal Discharge mode .......................................................................................................... 118
6.3.7.2.2 External Discharge mode ......................................................................................................... 119
6.3.7.2.3 SMP Discharge Mode .............................................................................................................. 119
6.3.7.2.4 VDIVEN Voltage Divider Enable option................................................................................. 119
6.3.7.2.5 SYNC pin option...................................................................................................................... 119
Figure 37 QMatrix method schematic ......................................................................................................... 120
6.3.7.3 QMatrix method hardware resource requirement for UC3L .......................................................... 121
6.3.7.4 QMatrix method Channel and Sensor numbering for UC3L.......................................................... 1215
Figure 38 QMatrix channel numbering for UC3L....................................................................................... 121
6.3.7.5 QMatrix method API Flow for UC3L............................................................................................ 121
Figure 39 QMatrix API Flow diagram for UC3L........................................................................................ 122
6.3.7.6 QMatrix method Disable and Re-enable Sensor for UC3L............................................................ 124
6.3.8 QTouch Group A/B method sensor operation for UC3L .....................................................124
6.3.8.1 QTouch Group A/B method pin selection for UC3L...................................................................... 124
Table 11 QTouch Resistive drive pin option ............................................................................................... 125
6.3.8.2 QTouch Group A/B method Schematic for UC3L ......................................................................... 125
6.3.8.2.1 Resistive Drive option.............................................................................................................. 125
6.3.8.2.2 SYNC pin option...................................................................................................................... 125
Figure 40 QTouch Group A/B and Autonomous QTouch schematic arrangement ..................................... 126
6.3.8.3 QTouch Group A/B method hardware resource requirement for UC3L ........................................ 126
6.3.8.4 QTouch Group A/B method Channel and Sensor numbering for UC3L........................................ 127
Figure 41 QTouch method Channel/Sensor numbering............................................................................... 127
Figure 42 QTouch method Channel/Sensor numbering when Group A and B are used together................ 127
6.3.8.5 QTouch Group A/B method API Flow for UC3L.......................................................................... 128
Figure 43 QTouch method API Flow diagram ............................................................................................ 129
6.3.8.6 QTouch Group A/B method Disable and Re-enable Sensor for UC3L.......................................... 130
6.3.9 Autonomous QTouch sensor operation for UC3L ...............................................................130
6.3.9.1 Autonomous QTouch Sensor pin selection for UC3L.................................................................... 130
6.3.9.2 Autonomous QTouch sensor Schematic for UC3L........................................................................ 130
6.3.9.3 Autonomous QTouch method hardware resource requirement for UC3L...................................... 130
Table 12 Sleep mode support for Autonomous QTouch ............................................................................. 130
6.3.9.4 Autonomous QTouch Sensor API Flow for UC3L ........................................................................ 131
Figure 44 Autonomous QTouch API Flow diagram.................................................................................... 131
6.3.9.5 Autonomous QTouch method Enable and Disable Sensor for UC3L ............................................ 131
6.3.10 Raw acquisition mode support for UC3L ............................................................................132
Figure 45 Raw acquisition mode API Flow diagram................................................................................... 132
6.3.11 Library Configuration parameters for UC3L ......................................................................133
Table 13 QTouch Library for UC3L Configuration parameters.................................................................. 133
6.3.12 Example projects for QTouch Library for UC3L.................................................................134
6.3.12.1 Example Project usage............................................................................................................... 134
Figure 46 GNU Example project usage with AVR32 Studio ...................................................................... 134
Figure 47 IAR Example project usage with IAR Embedded Workbench for AVR32................................. 134
6.3.12.2 QMatrix Example Project .......................................................................................................... 135
6.3.12.3 QTouch Group A Example Project............................................................................................ 135
6.3.12.4 Autonomous QTouch Example Project ..................................................................................... 135
6.3.13 Code and Data Memory requirements for UC3L ................................................................136
6.3.13.1 QMatrix method memory requirement ...................................................................................... 136
Table 14 Typical Code and Data memory for Standalone QMatrix operation ........................................... 136
6.3.13.2 QTouch Group A/B method memory requirement .................................................................... 136
Table 15 Typical Code and Data memory for Standalone QTouch Group A/B operation .......................... 137
6.3.13.3 Autonomous QTouch memory requirement .............................................................................. 137
Table 16 Minimum Code and Data for Standalone Autonomous QTouch sensor....................................... 137
6.3.14 Public header files of QTouch Library for UC3L................................................................137
6.3.15 Type Definitions and enumerations used in the library.......................................................137
6.3.15.1 Typedefs .................................................................................................................................... 137
6.3.15.1.1 touch_acq_status_t ................................................................................................................. 138
6.3.15.1.2 touch_qt_grp_t ....................................................................................................................... 138
6.3.15.2 Enumerations............................................................................................................................. 138
6.3.15.2.1 touch_ret_t.............................................................................................................................. 139
6.3.15.2.2 touch_lib_state_t .................................................................................................................... 139
6.3.15.2.3 touch_acq_mode_t ................................................................................................................. 140
6.3.15.2.4 sensor_type_t.......................................................................................................................... 140
6.3.15.2.5 aks_group_t............................................................................................................................ 140
6.3.15.2.6 hysteresis_t............................................................................................................................. 140
6.3.15.2.7 recal_threshold_t.................................................................................................................... 141
6.3.15.2.8 resolution_t............................................................................................................................. 141
6.3.15.2.9 at_status_change_t ................................................................................................................. 142
6.3.15.2.10 x_pin_options_t.................................................................................................................... 142
6.3.15.2.11 y_pin_options_t.................................................................................................................... 1426 8207L-AT42-05/12
6.3.15.2.12 qt_pin_options_t................................................................................................................... 142
6.3.15.2.13 general_pin_options_t .......................................................................................................... 142
6.3.16 Data structures....................................................................................................................143
6.3.16.1 sensor_t...................................................................................................................................... 143
6.3.16.2 touch_global_param_t ............................................................................................................... 143
6.3.16.3 touch_filter_data_t..................................................................................................................... 144
6.3.16.4 touch_measure_data_t ............................................................................................................... 144
6.3.16.5 touch_qm_param_t .................................................................................................................... 144
6.3.16.6 touch_at_param_t ...................................................................................................................... 145
6.3.16.7 touch_qt_param_t ...................................................................................................................... 146
6.3.16.8 touch_at_status .......................................................................................................................... 146
6.3.16.9 touch_qm_dma_t ....................................................................................................................... 146
6.3.16.10 touch_qm_pin_t......................................................................................................................... 146
6.3.16.11 touch_at_pin_t ........................................................................................................................... 147
6.3.16.12 touch_qt_pin_t........................................................................................................................... 147
6.3.16.13 touch_qm_reg_t ......................................................................................................................... 148
6.3.16.14 touch_at_reg_t ........................................................................................................................... 149
6.3.16.15 touch_qt_reg_t........................................................................................................................... 149
6.3.16.16 touch_qm_config_t.................................................................................................................... 149
6.3.16.17 touch_at_config_t ...................................................................................................................... 150
6.3.16.18 touch_qt_config_t...................................................................................................................... 151
6.3.16.19 touch_general_config_t.............................................................................................................. 151
6.3.16.20 touch_config_t ........................................................................................................................... 152
6.3.16.21 touch_info_t............................................................................................................................... 152
6.3.17 Public Functions of QTouch Library for UC3L...................................................................152
6.3.17.1 QMatrix API.............................................................................................................................. 152
6.3.17.1.1 touch_qm_sensors_init........................................................................................................... 152
6.3.17.1.2 touch_qm_sensor_config........................................................................................................ 153
6.3.17.1.3 touch_qm_sensor_update_config ........................................................................................... 154
6.3.17.1.4 touch_qm_sensor_get_config................................................................................................. 154
6.3.17.1.5 touch_qm_channel_udpate_burstlen ...................................................................................... 154
6.3.17.1.6 touch_qm_update_global_param............................................................................................ 155
6.3.17.1.7 touch_qm_get_global_param ................................................................................................. 155
6.3.17.1.8 touch_qm_sensors_calibrate................................................................................................... 155
6.3.17.1.9 touch_qm_sensors_start_acquisition...................................................................................... 156
6.3.17.1.10 touch_qm_get_libinfo .......................................................................................................... 156
6.3.17.1.11 touch_qm_sensor_get_delta ................................................................................................. 157
6.3.17.2 QTouch Group A and QTouch Group B API ............................................................................ 157
6.3.17.2.1 touch_qt_sensors_init............................................................................................................. 157
6.3.17.2.2 touch_qt_sensor_config.......................................................................................................... 158
6.3.17.2.3 touch_qt_sensor_update_config ............................................................................................. 158
6.3.17.2.4 touch_qt_sensor_get_config................................................................................................... 159
6.3.17.2.5 touch_qt_update_global_param.............................................................................................. 159
6.3.17.2.6 touch_qt_get_global_param ................................................................................................... 159
6.3.17.2.7 touch_qt_sensors_calibrate..................................................................................................... 160
6.3.17.2.8 touch_qt_sensors_start_acquisition ........................................................................................ 160
6.3.17.2.9 touch_qt _sensor_ disable....................................................................................................... 161
6.3.17.2.10 touch_qt _sensor_ reenable .................................................................................................. 161
6.3.17.2.11 touch_qt_get_libinfo ............................................................................................................ 162
6.3.17.2.12 touch_qt_sensor_get_delta ................................................................................................... 162
6.3.18 Autonomous touch API ........................................................................................................162
6.3.18.1.1 touch_at_sensor_init............................................................................................................... 162
6.3.18.1.2 touch_at_sensor_enable.......................................................................................................... 163
6.3.18.1.3 touch_at_sensor_disable......................................................................................................... 163
6.3.18.1.4 touch_at_sensor_update_config ............................................................................................. 163
6.3.18.1.5 touch_at_sensor_get_config ................................................................................................... 164
6.3.18.1.6 touch_at_get_libinfo............................................................................................................... 164
6.3.18.2 Common API............................................................................................................................. 164
6.3.18.2.1 touch_event_dispatcher.......................................................................................................... 164
6.3.18.2.2 touch_deinit............................................................................................................................ 164
6.3.19 Integrating QTouch libraries for AT32UC3L in your application ......................................165
6.3.20 MISRA Compliance Report of QTouch Library for UC3L ..................................................1657
6.3.21 What is covered ...................................................................................................................165
6.3.22 Target Environment.............................................................................................................165
6.3.23 Deviations from MISRA C Standards..................................................................................165
6.3.24 Known Issues with QTouch Library for UC3L ....................................................................166
6.4 QTOUCH LIBRARY FOR ATTINY20 DEVICE ..................................................................................167
6.4.1 Salient Features of QTouch Library for ATtiny20...............................................................167
6.4.1.1 QTouch method sensor................................................................................................................... 167
6.4.2 Compiler tool chain support for ATtiny20...........................................................................167
Table 17 Compiler tool chains support for ATtiny20 QTouch Library....................................................... 167
6.4.3 Overview of QTouch Library for ATtiny20..........................................................................167
Figure 48 Schematic overview of QTouch on Tiny20................................................................................. 168
6.4.4 API Flow diagram for ATtiny20 ..........................................................................................168
Figure 49 Linker configuration options for Tiny20 ..................................................................................... 168
Figure 50 QTouch method for Tiny20 API Flow diagram .......................................................................... 169
6.4.5 QTouch Library configuration parameters for ATtiny20 ....................................................169
Table 18 QTouch Library for ATtiny20 Configuration parameters............................................................. 170
6.4.6 QTouch Library ATtiny20 Example projects.......................................................................171
6.4.7 QTouch Library ATtiny20 code and data memory requirements ........................................171
Table 19 QTouch Library for ATtiny20 Memory requirements.................................................................. 171
6.5 QTOUCH LIBRARY FOR ATTINY40 DEVICE ..................................................................................172
6.5.1 Salient Features of QTouch Library for ATtiny40...............................................................172
6.5.1.1 QTouch method sensor................................................................................................................... 172
6.5.2 Compiler tool chain support for ATtiny40...........................................................................173
Table 20 Compiler tool chains support for ATtiny40 QTouch Library....................................................... 173
6.5.3 Overview of QTouch Library for ATtiny40..........................................................................173
Figure 51 Schematic overview of QTouch on Tiny40................................................................................. 173
6.5.4 API Flow diagram for ATtiny40 ..........................................................................................174
Figure 52 QTouch method for Tiny40 API Flow diagram .......................................................................... 175
6.5.5 QTouch Library configuration parameters for ATtiny40 ....................................................175
Table 21 QTouch Library for ATtiny40 Configuration parameters............................................................. 176
6.5.6 QTouch Library ATtiny40 Example projects.......................................................................177
6.5.7 QTouch Library ATtiny40 code and data memory requirements ........................................177
Table 22 QTouch Library for ATtiny40 Memory requirements.................................................................. 177
6.5.8 Interrupt Handling in QTouch ADC....................................................................................177
7 GENERIC QTOUCH LIBRARIES FOR 2K DEVICES...............................................................178
7.1 INTRODUCTION.............................................................................................................................178
7.2 DEVICES SUPPORTED ....................................................................................................................178
7.3 SALIENT FEATURES OF QTOUCH LIBRARY FOR 2K DEVICES........................................................178
7.4 LIBRARY VARIANTS .....................................................................................................................178
7.5 QTOUCH API FOR 2K DEVICES AND USAGE.................................................................................178
7.5.1 touch_api_2kdevice.h - public header file ...........................................................................178
7.5.2 Sequence of Operations and Using the API.........................................................................179
7.5.2.1 Channel Numbering ....................................................................................................................... 179
7.5.2.1.1 Channel numbering when routing SNS and SNSK pins to different ports............................... 179
7.5.2.1.2 Channel numbering when routing SNS and SNSK pins to the same port ................................ 180
7.5.2.2 Rules For Configuring SNS and SNSK masks for 2K Devices...................................................... 180
7.5.2.2.1 Configuring SNS and SNSK masks in case of Interport: ......................................................... 180
7.5.2.2.2 Configuring SNS and SNSK masks in case of Intraport: ......................................................... 181
7.5.3 Integrating QTouch libraries for 2K Devices in your application.......................................181
7.6 MISRA COMPLIANCE REPORT.....................................................................................................182
7.6.1 What is covered ...................................................................................................................182
7.6.2 Target Environment.............................................................................................................182
7.6.3 Deviations from MISRA C Standards..................................................................................182
7.6.3.1 QTouch acquisition method libraries for 2K devices..................................................................... 182
8 REVISION HISTORY......................................................................................................................183
DISCLAIMER ...........................................................................................................................................1858 8207L-AT42-05/12
1 Preface
This manual contains information that enables customers to implement capacitive touch solutions
on ATMEL AVR® microcontrollers and ARM®
-based AT91SAM microcontrollers using ATMEL
QTouch libraries. This guide is a functional description of the library software, its programming
interface and it also describes its use on the supported reference systems.
Use of this software is bound by the Software License Agreement included with the Library. This
user guide is applicable for Atmel QTouch® Library 5.0 .
Related documents from ATMEL
Documents related to QTouch capacitive sensing solutions from ATMEL are
• TS2080A/B data sheet.
• QT600 users guide
• Release Notes for ATMEL QTouch libraries.
• A library selection excel workbook that is used for the selection of the appropriate library
variant from the package available under in the install directory. The default location is
C:\Program Files\Atmel\Atmel_QTouch_Libraries_5.x\
• Capacitive touch sensor design guide
http://www.atmel.com/dyn/resources/prod_documents/doc10620.pdf .
If you need Assistance
For assistance with QTouch capacitive sensing software libraries and related issues, contact your
local ATMEL sales representative or send an email to touch@atmel.com for AVR libraries and
at91support@atmel.com for SAM libraries.9
2 Introduction
ATMEL QTouch Library is a royalty free software library (available for GCC and IAR compiler tool
chains) for developing touch applications on standard AVR and SAM microcontrollers. Customers
can link the library into their applications in order to provide touch sensing capability in their
projects. The Library can be used to develop single chip solutions for control applications which
have touch sensing capabilities, or to develop standalone touch sensing solutions which interface
with other host or control devices.
Features of ATMEL QTouch Library include
• Capacitive touch sensing using patented charge-transfer signal acquisition for robust
sensing.
• Support for a wide range of 8- and 32-bit AVRs.
• Support for 32-bit ARM microcontrollers.
• Support for 8-bit tiny AVRs having flash of 2K bytes.
• Support both QTouch and QMatrix acquisition methods and autonomous touch for UC3L.
• Support up to 64 touch sense channels for generic libraries and up to 136 channels for
UC3L libraries.
• Flexible choice of touch sensing functionality (keys, sliders, wheels) in a variety of
combinations.
• Includes Adjacent Key Suppression® (AKS®
) technology for the unambiguous detection of
key events.
• Support for both IAR and GCC compiler tool chains.
• A comparison of various features and parameters between QTouch Libraries for Generic
8-bit and 32-bit AVRs as well as Device Specific Libraries is provided in the table below.
Feature Comparison between Generic QTouch Libraries and Device Specific Libraries
Parameter/Func
tionality
Generic
Libraries,
Tiny_Meg
a_Xmega
Tiny 2K
Libraries
Tiny20
Libraries
Tiny40
Libraries
Generic
Libraries,
32 Bit
AVR
UC3L
Libraries
ATSAM
Libraries
Technology QTouch,
QMatrix
QTouch QTouchADC
QTouchADC
QTouch,
QMatrix
QTouch,
QMatrix
QTouch
Rotors/Sliders
Support
Yes No No No Yes Yes Yes
Filter Callback Yes Yes No Yes Yes Yes Yes
Library Status
Flags
Yes Yes No Yes(Only
Burst Again
Flag)
Yes Yes Yes
Library
Signature
Yes No No No Yes Yes Yes
Calibrate
Sensing
Yes Yes (Only
burst_again
flag)
No Yes Yes Yes Yes
Reset Sensing Yes Yes No Yes Yes Yes Yes
Sensor Deltas Yes Yes No Yes Yes Yes Yes
Maximum AKS
Groups
7 7 1 7 7 7 710 8207L-AT42-05/12
Maximum
Channels, QT
16 4 5 12 32 17 32
Maximum
Rotors/Sliders,
QT
4 0 0 0 8 8
Maximum
Channels, QM
64 0 0 0 64 64 0
Maximum
Rotors/Sliders,
QM
8 0 0 0 8 0
Autonomous
Touch
No No No No No Yes No
Sensor
Reconfiguratio
n
Yes Yes No No Yes Yes Yes
Frequency
Hopping SS
Enabled
Always If
_POWER_
OPTIMIZA
TION = 0
Never Never Always Programma
ble
Always
Delay Cycles
Parameter
QT_DELAY
_CLCYES
(QT
Values: 1 to
255
QM Values:
1,2,3,4,5,10
,25,50)
QT_DELAY
_CLCYES
(Value: 1 to
255)
DEF_CHA
RGE_SHA
RE_DELAY
(Value: 1 to
255)
DEF_QT_C
HARGE_S
HARE_DEL
AY
(Value: 1 to
255)
QT_DELAY
_CYCLES
(QT Values
: 1 to 255
QM Values:
1,2,3,4,5,10
,25,50)
xx_CHLEN,
xx_SELEN
(QT/QM
Value: 3 to
255)
QT_DELAY
_CLCYES
(Value: 3 to
255)
Debug Interface
Enable Macro
_DEBUG_I
NTERFAC
E_
None NDEBUG _DEBUG_
QTOUCH_
STUDIO_
_DEBUG_I
NTERFAC
E_
DEF_TOU
CH_QDEB
UG_ENAB
LE
_DEBUG_I
NTERFAC
E_
This user guide describes the content, design and use of the QTouch Libraries. This should be
read in conjunction with all of the applicable documents listed below
• Device datasheet for the selected ATMEL device used for touch sensing.
• Data sheet for the selected evaluation board.
• A library selection guide that is used for the selection of the appropriate library from the
released package. Default path:
C:\ Program Files\Atmel\Atmel_QTouch_Libaries_5.x\Library_Selection_Guide.xls
The intended readers of this document are engineers, who use the QTouch Library on ATMEL
microcontrollers to realize capacitive touch sensing solutions.
3 Overview
This chapter gives a brief introduction to each of the chapters that make up this document
1. Preface
2. Introduction: Provides an introduction to the scope and use of the QTouch Library.
3. Overview: This chapter
4. Abbreviations and Definitions: Provides a description of the abbreviations and
definitions used in this document
5. Generic QTouch Libraries: Provides an overview of the QTouch libraries and the
different acquisition methods for generic ATMEL devices.
6. Device Specific Libraries: Provides an overview of the QTouch libraries and the
different acquisition methods for ATMEL devices specific for touch sensing.
7. Revision History: Provides a revision history of this document11
4 Abbreviations and Definitions
4.1 Definitions
• AVR: refers to a device(s) in the tinyAVR®, megaAVR®, XMEGA™ and UC3
microcontroller family.
• ARM: refers to a device in the ATSAM ARM® basedmicrocontroller family.
• ATMEL QTouch Library: The combination of libraries for both touch sensing acquisition
methods (QTouch and QMatrix).
• QTouch Technology: A type of capacitive touch sensing technology using self
capacitance - each channel has only one electrode.
• QMatrix Technology: A type of capacitive touch sensing technology using mutual
capacitance – each channel has an drive electrode (X) and an receive electrode (Y).
• Sensor: A channel or group of channels used to form a touch sensor. Sensors are of 3
types (keys, rotors or sliders).
• KEY: a single channel forms a single KEY type sensor, also known as a BUTTON
• ROTOR, also known as a WHEEL, a group of channels forms a ROTOR sensor to detect
angular position of touch.
o A Rotor is composed of 3 channels for a QTouch acquisition method.
o A Rotor can be composed of 3 to 8 channels for QMatrix acquisition method.
• SLIDER, a group of channels forms a SLIDER sensor to detect the linear position of
touch.
o A Slider is composed of 3 channels for a QTouch acquisition method.
o A Slider can be composed of 3 to 8 channels for QMatrix acquisition method.
• AKS: Adjacent Key Suppression. See Section 5.4.5
• SNS PIN: Sense line for capacitive measurement using the QTouch Technology -
connected to Cs.
• SNSK PIN: Sense Key line for capacitive measurement using the QTouch Technology -
connected to channel electrode through Rs.
• X Line: The drive electrode (or drive line) used for QMatrix Technology.
• Y Line: The receive electrode (or receive line) used for QMatrix Technology.
• Port Pair: A combination of SNS port and SNSK port to which sensors are connected for
QTouch technology. The SNS and SNSK ports used in a port pair can be located in the
same AVR Port (8 pins for 4 sensors), or they may be in different 2 different AVR Ports
(8+8 pins for 8 sensors).
• Charge Cycle Period: It is the width of the charging pulse applied to the channel
capacitor.
• Dwell Cycle: In a QMatrix acquisition method, the duration in which charge coupled from
X to Y is captured.
• Acquisition: A single capacitive measurement process.
• Electrode: Electrodes are typically areas of copper on a printed circuit board but can also
be areas of clear conductive indium tin oxide (ITO) on a glass or plastic touch screen.12 8207L-AT42-05/12
• Intra-port: A configuration for QTouch acquisition method libraries, when the sensor SNS
and SNSK pins are available on the same port.
• Inter-port: A configuration for QTouch acquisition method libraries, when the sensor SNS
and SNSK pins are available on distinct ports.
5 Generic QTouch Libraries
5.1 Introduction
ATMEL QTouch provides a simple to use solution to realize touch sensing solutions on a range of
supported ATMEL AVR Microcontrollers. The QTouch libraries provide support for both QTouch
and QMatrix acquisition methods.
Touch sensing using QMatrix or QTouch acquisition methods can be added to an application by
linking the appropriate ATMEL QTouch Library for the AVR Microcontroller and using a simple set
of API to define the touch channels and sensors and then calling the touch sensing API’s
periodically (or based on application needs) to retrieve the channel information and determine
touch sensor states.
Figure 5-1 shows a typical configuration of channels when using an AVR and using the ATMEL
QTouch Library. The ATMEL QTouch Library has been added to a host application running on an
AVR microcontroller. The sample configuration illustrates using the library that supports eight
touch channels numbered 0 to 7. The sensors are configured in the following order,
• Sensor 0 on channels 0 to 2 have been configured as a rotor sensor.
• Sensor 1 on channels 3 to 5 have been configured as a slider sensor.
• Sensor 2 on channel 6 is configured as key sensor.
• Sensor 3 on channel 7 is configured as key sensor.
The host application uses the QTouch Library API’s to configure these channels and sensors,
and to initiate detection of a touch using capacitive measurements.
channel 0
channel 1
channel 2
channel 3
channel 4
channel 5
channel 6
channel 7
Atmel QTouch
Library
Host
Application
sensor0
sensor1
sensor2
sensor3
Figure 5-1 : Typical interface of the ATMEL QTouch library with the host application.
The QTouch libraries use minimal resources of the microcontroller. The sampling of the sensors
is controlled by the QTouch library, while the sampling period is controlled by the application
(possibly using timers, sleep periods, varying the CPU clock, external events like interrupts or
communications, etc).13
5.2 Acquisition Methods
There are two methods available for touch acquisition namely
1. QTouch acquisition method.
2. QMatrix acquisition method.
Libraries for AVR microcontrollers include both acquisition methods. Libraries for ATSAM
microcontrollers include only QTouch acquisition method.
5.2.1 QTouch acquisition method
The QTouch acquisition method charges an electrode of unknown capacitance to a known
potential. The resulting charge is transferred into a measurement capacitor (Cs). The cycle is
repeated until the voltage across Cs reaches a voltage Vih. The signal level is the number of
charge transfer cycles it took to reach that voltage. Placing a finger on the touch surface
introduces external capacitance that increases the amount of charge transferred each cycle,
reducing the total number of cycles required for Cs to reach the voltage. When the signal level
(number of cycles) goes below the present threshold, then the sensor is reported to be in
detected.
QTouch acquisition method sensors can drive single or multiple keys. Where multiple keys are
used, each key can be set for an individual sensitivity level. Keys of different sizes and shapes
can be used to meet both functional and aesthetic requirements.
NOTE: It is recommended to keep the size of the keys larger than 6mmx6mm to ensure reliable
and robust measurements, although actual key design requirements also depend on panel
thickness and material. Refer to the ATMEL Capacitive touch sensor design guide for details.
QTouch acquisition method can be used in two ways
• normal touch contact (i.e. when pressing buttons on a panel), and
• high sensitivity proximity mode (i.e. when a panel lights up before you actually contact it).
Figure 5-2 : QTouch Acquisition
QTouch circuits offers high signal-to-noise ratio, very good low power performance, and the
easiest sensor layout.14 8207L-AT42-05/12
5.2.1.1 Sensor schematics for a QTouch acquisition method design
Electrode
Microcontroller
Used for touch
application
PB1
PC1
SNSK
SNS
Sampling
capacitor
Rs
Cs
Rs- 1k
Cs- 22nF
----------------
Port requirements:
SNS: generic I/O pin
SNSK: generic I/O pin
Rs- Series resistor, Cs – Sample capacitor, PB1- PortB bit1, and PC1- PortC bit1
Typical
values:
Figure 5-3 : Schematics for a QTouch acquisition method design
5.2.2 QMatrix acquisition method
QMatrix devices detect touch using a scanned passive matrix of electrode sets. A single QMatrix
device can drive a large number of keys, enabling a very low cost-per-key to be achieved.
Figure 5-4 : QMatrix Acquisition method15
QMatrix uses a pair of sensing electrodes for each channel. One is an emitting electrode into
which a charge consisting of logic pulses is driven in burst mode. The other is a receive electrode
that couples to the emitter via the overlying panel dielectric. When a finger touches the panel the
field coupling is changed, and touch is detected. The drive electrode (or drive line) used for
QMatrix charge transfer is labeled as the X line. The receiver electrode (or receive line) used for
QMatrix charge transfer is labeled as the Y line.
QMatrix circuits offer good immunity to moisture films, extreme levels of temperature stability,
superb low power characteristics, and small IC package sizes for a given key count.
5.2.3 Sensor schematics for a QMatrix acquisition method design
Atmel MCU
X0
...
Xn
Y0A
...
YmA
...
Y0B
YmB
SMP
Vref
RX0
RXn
RY0
RYm
CS0 CSm
RYB0 RYBm
Sensor
0,0
Sensor
n,0
Sensor
n,m
Sensor
0,m
Sensors,
X,Y
Typical values:
RX: 1k
RY: 1k
CS: 4.7nF
RYB: 470k
----------------------------------
Port-pin count =
n + (2 * m) + 2
n – number of X lines
m – number of Y lines
----------------------------------
Port requirements:
X: Configurable I/O pin
YA:Configurable I/O pin (*)
YB: ADC port (*)
SMP: Configurable I/O pin
Vref: AIN0 (Comparator)
(*): The port I/O pin should
be in consecutive order
Figure 5-5 : Schematics for a QMatrix acquisition method design
5.3 Global settings common to all sensors of a specific
acquisition method
The touch sensing using QTouch library could be fine tuned by using a number of configurable
settings. This section explains the settings that are common to all sensors of a specific acquisition
method like QMatrix or QTouch.16 8207L-AT42-05/12
For example, if recalibration threshold (one of the global settings) of QMatrix acquisition method
is set as 1, all QMatrix sensors will have recalibration threshold of 1.
5.3.1 Recalibration Threshold
Recalibration threshold is the level above which automatic recalibration occurs. Recalibration
threshold is expressed as a percentage of the detection threshold setting. This setting is an
enumerated value and its settings are as follows:
• Setting of 0 = 100% of detect threshold (RECAL_100)
• Setting of 1 = 50% of detect threshold (RECAL_50)
• Setting of 2 = 25% of detect threshold (RECAL_25)
• Setting of 3 = 12.5% of detect threshold