ATmega328 / ATmega328P / ATmega168 / ATmega8 pinout

Package pin assignments for ATmega328, ATmega328P, ATmega168, ATmega8, with peripheral signals, clock grades and a serial programming guide.

TQFP-32 32 contacts

QFN-28 29 contacts

QFN-32 33 contacts

PDIP-28

28 contacts Current package

Microchip Technology · 28 numbered contacts. See the individual package drawings for footprint dimensions.

16 KiB flash · 1 KiB SRAM · 512 B EEPROM · 2.7–5.5 V · 20 MHz maximum · -40 to +85 °C

PDIP-28 pinout

Top view · Pin 1 at the upper left · Schematic outline

Selected pin details

22 · GND

Return · Ground

Supply return. Connect every ground pin.

2545W · Pinout and peripheral signal descriptions

Electrical limits · Link to this pin

All 28 pins

Pin	Signal	Direction	Function
1	PC6 Input / I/O	Input / I/O	Active-low reset input by default. Use as GPIO only where the reset-disable fuse is supported and configured. Alternate assignments: PCINT14 (EXINT).
2	PD0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: RXD (USART0), PCINT16 (EXINT).
3	PD1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TXD (USART0), PCINT17 (EXINT).
4	PD2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT18 (EXINT), INT0 (EXINT).
5	PD3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCB (TC2), INT1 (EXINT), PCINT19 (EXINT).
6	PD4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: XCK (USART0), T (TC0), PCINT20 (EXINT).
7	VCC Supply	Supply	Digital supply. Connect every VCC pin and place a local 100 nF ceramic bypass close to each VCC-to-ground pair.
8	GND Return	Return	Supply return. Connect every ground pin.
9	PB6 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TOSC1 (TC2), PCINT6 (EXINT), XTAL1 (CPU).
10	PB7 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TOSC2 (TC2), PCINT7 (EXINT), XTAL2 (CPU).
11	PD5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: T (TC1), OCB (TC0), PCINT21 (EXINT).
12	PD6 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: AIN0 (AC), OCA (TC0), PCINT22 (EXINT).
13	PD7 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: AIN1 (AC), PCINT23 (EXINT).
14	PB0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ICP (TC1), PCINT0 (EXINT), CLK0 (CPU).
15	PB1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCA (TC1), PCINT1 (EXINT).
16	PB2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCB (TC1), PCINT2 (EXINT), SS (SPI).
17	PB3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCA (TC2), PCINT3 (EXINT), MOSI (SPI).
18	PB4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT4 (EXINT), MISO (SPI).
19	PB5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT5 (EXINT), SCK (SPI).
20	AVCC Supply	Supply	Analog supply. Connect it to the supply even if analog conversion is unused. Follow the data sheet’s filtering guidance for precision conversion.
21	AREF Analog reference	Analog reference	ADC voltage reference terminal. Check the reference selection before driving this pin from an external voltage.
22	GND Return	Return	Supply return. Connect every ground pin.
23	PC0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC0 (ADC), PCINT8 (EXINT).
24	PC1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC1 (ADC), PCINT9 (EXINT).
25	PC2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC2 (ADC), PCINT10 (EXINT).
26	PC3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC3 (ADC), PCINT11 (EXINT).
27	PC4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: SDA (TWI), ADC4 (ADC), PCINT12 (EXINT).
28	PC5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: SCL (TWI), ADC5 (ADC), PCINT13 (EXINT).

Signal assignments

USART0 · Serial

Use TXD and RXD for asynchronous serial. XCK is for synchronous mode. The signal levels follow the microcontroller supply domain. TXD → PD1 · RXD → PD0 · XCK → PD4

TWI / I²C

Connect SDA and SCL to the bus with pull-ups to a voltage supported by all devices. Verify the pull-up value for the bus capacitance and rate. SDA → PC4 · SCL → PC5

Timer/Counter 1

Review each signal assignment and the peripheral enable conditions in the data sheet. T → PD5 · ICP → PB0 · OCA → PB1 · OCB → PB2

Timer/Counter 2

Review each signal assignment and the peripheral enable conditions in the data sheet. OCA → PB3 · OCB → PD3 · TOSC1 → PB6 · TOSC2 → PB7

Analog-to-digital converter

Select the analog channel and reference in firmware. The reference choice and supply constrain the input range. ADC0 → PC0 · ADC1 → PC1 · ADC2 → PC2 · ADC3 → PC3 · ADC4 → PC4 · ADC5 → PC5

Analog comparator

Review each signal assignment and the peripheral enable conditions in the data sheet. AIN0 → PD6 · AIN1 → PD7

Timer/Counter 0

Review each signal assignment and the peripheral enable conditions in the data sheet. T → PD4 · OCB → PD5 · OCA → PD6

External interrupts

Review each signal assignment and the peripheral enable conditions in the data sheet. INT1 → PD3 · PCINT19 → PD3 · PCINT20 → PD4 · PCINT6 → PB6 · PCINT7 → PB7 · PCINT21 → PD5 · PCINT22 → PD6 · PCINT23 → PD7 · PCINT0 → PB0 · PCINT1 → PB1 · PCINT2 → PB2 · PCINT3 → PB3 · PCINT4 → PB4 · PCINT5 → PB5 · PCINT8 → PC0 · PCINT9 → PC1 · PCINT10 → PC2 · PCINT11 → PC3 · PCINT12 → PC4 · PCINT13 → PC5 · PCINT14 → PC6 · PCINT16 → PD0 · PCINT17 → PD1 · PCINT18 → PD2 · INT0 → PD2

SPI peripheral

Use SCK, MOSI, MISO and a chip-select line. Firmware selects direction and clock phase. Check the separate ISP mapping when programming. SS → PB2 · MOSI → PB3 · MISO → PB4 · SCK → PB5

System clock

Review each signal assignment and the peripheral enable conditions in the data sheet. CLK0 → PB0 · XTAL1 → PB6 · XTAL2 → PB7

Electrical limits

Parameter	Limit	Conditions and source
Supply and clock grade2.7–5.5 V · 20 MHz maximum	2.7–5.5 V · 20 MHz maximum	Follow the speed-grade curve for the selected voltage. The headline clock figure is the maximum at its specified supply and temperature. 2545W · Speed grades and ordering information
Ambient temperature grade-40 to +85 °C	-40 to +85 °C	For this order code. Verify silicon revision and errata in the current manufacturer documentation. 2545W · Ordering information
Program flash16 KiB	16 KiB	Nonvolatile program memory. 2545W · Memory
SRAM1 KiB	1 KiB	Volatile data and stack storage. 2545W · Memory
EEPROM512 B	512 B	Nonvolatile data storage. 2545W · Memory
Clock and supplyOrder-code dependent	Order-code dependent	Use the grade table and the device’s speed-versus-voltage curve. 2545W · Electrical Characteristics

Models and documents

Each package lists the documented order codes and variants covered by this map. Select the marked model to see its peripheral assignments and memory. Check the exact order code and datasheet revision before laying out a PCB.

ATmega328: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM. Choose the marked order code for voltage, clock, and temperature.
ATmega328-PU: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +85 °C
ATmega328P: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM. Choose the marked order code for voltage, clock, and temperature.
ATmega328P-PU: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +85 °C
ATmega328P-PN: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +105 °C
ATmega168: 16 KiB flash · 1 KiB SRAM · 512 B EEPROM. Choose the marked order code for voltage, clock, and temperature.
ATmega168V-10PU: 16 KiB flash · 1 KiB SRAM · 512 B EEPROM · 1.8–5.5 V · 10 MHz maximum · -40 to +85 °C
ATmega168-20PU: 16 KiB flash · 1 KiB SRAM · 512 B EEPROM · 2.7–5.5 V · 20 MHz maximum · -40 to +85 °C
ATmega8: 8 KiB flash · 1 KiB SRAM · 512 B EEPROM. Choose the marked order code for voltage, clock, and temperature.
ATmega8L-8PU: 8 KiB flash · 1 KiB SRAM · 512 B EEPROM · 2.7–5.5 V · 8 MHz maximum · -40 to +85 °C
ATmega8-16PU: 8 KiB flash · 1 KiB SRAM · 512 B EEPROM · 4.5–5.5 V · 16 MHz maximum · -40 to +85 °C
ATmega8L-8PN: 8 KiB flash · 1 KiB SRAM · 512 B EEPROM · 2.7–5.5 V · 8 MHz maximum · -40 to +105 °C
ATmega8-16PN: 8 KiB flash · 1 KiB SRAM · 512 B EEPROM · 4.5–5.5 V · 16 MHz maximum · -40 to +105 °C

ATmega328/ATmega328P data sheet· DS40002061B · Pin configuration, electrical characteristics, ordering table and serial programming.
ATmega168 data sheet· 2545W · Pin configuration, electrical characteristics, ordering table and serial programming.
ATmega8 data sheet· 2486AA · Pin configuration, electrical characteristics, ordering table and serial programming.
ATmega_DFP Device Family Pack· Machine-readable device definition: package contacts, peripheral routes, and memory sizes.
AVR Microcontroller Hardware Design Considerations· Power supply, reset network, and programmer connection guidance.
ATmega328 documentation and errata· Check current manufacturer documentation, ordering status and silicon revision applicability.
ATmega328P documentation and errata· Check current manufacturer documentation, ordering status and silicon revision applicability.
ATmega168 documentation and errata· Check current manufacturer documentation, ordering status and silicon revision applicability.
ATmega8 documentation and errata· Check current manufacturer documentation, ordering status and silicon revision applicability.
AVR source register· Source identifiers, applicability, retrieval dates, and SHA-256 digests.