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 Current package

QFN-32 33 contacts

PDIP-28 28 contacts

Microchip Technology · 28 numbered contacts. The underside pad appears below the contact map. See the individual package drawings for footprint dimensions.

32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM. Choose the marked order code for voltage, clock, and temperature.

QFN-28 pinout

Top view · Pin 1 at the upper left · Schematic outline
EP is the exposed center pad on the underside.

Selected pin details

1 · PD3

Bidirectional · GPIO

General-purpose digital I/O. Alternate assignments: OCB (TC2), INT1 (EXINT), PCINT19 (EXINT).

After reset · GPIO driver is high impedance during reset. Clock, debug, and alternate-function use depend on fuse and peripheral configuration.

DS40002061B · Pinout and peripheral signal descriptions

Electrical limits · Link to this pin

All 29 pins

Pin	Signal	Direction	Function
1	PD3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCB (TC2), INT1 (EXINT), PCINT19 (EXINT).
2	PD4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: XCK (USART0), T (TC0), PCINT20 (EXINT).
3	VCC Supply	Supply	Digital supply. Connect every VCC pin and place a local 100 nF ceramic bypass close to each VCC-to-ground pair.
4	GND Return	Return	Supply return. Connect every ground pin.
5	PB6 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TOSC1 (TC2), PCINT6 (EXINT), XTAL1 (CPU).
6	PB7 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TOSC2 (TC2), PCINT7 (EXINT), XTAL2 (CPU).
7	PD5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: T (TC1), OCB (TC0), PCINT21 (EXINT).
8	PD6 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: AIN0 (AC), OCA (TC0), PCINT22 (EXINT).
9	PD7 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: AIN1 (AC), PCINT23 (EXINT).
10	PB0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ICP (TC1), PCINT0 (EXINT), CLK0 (CPU).
11	PB1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCA (TC1), PCINT1 (EXINT).
12	PB2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCB (TC1), PCINT2 (EXINT), SS (SPI).
13	PB3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: OCA (TC2), PCINT3 (EXINT), MOSI (SPI).
14	PB4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT4 (EXINT), MISO (SPI).
15	PB5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT5 (EXINT), SCK (SPI).
16	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.
17	AREF Analog reference	Analog reference	ADC voltage reference terminal. Check the reference selection before driving this pin from an external voltage.
18	GND Return	Return	Supply return. Connect every ground pin.
19	PC0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC0 (ADC), PCINT8 (EXINT).
20	PC1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC1 (ADC), PCINT9 (EXINT).
21	PC2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC2 (ADC), PCINT10 (EXINT).
22	PC3 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: ADC3 (ADC), PCINT11 (EXINT).
23	PC4 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: SDA (TWI), ADC4 (ADC), PCINT12 (EXINT).
24	PC5 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: SCL (TWI), ADC5 (ADC), PCINT13 (EXINT).
25	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).
26	PD0 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: RXD (USART0), PCINT16 (EXINT).
27	PD1 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: TXD (USART0), PCINT17 (EXINT).
28	PD2 Bidirectional	Bidirectional	General-purpose digital I/O. Alternate assignments: PCINT18 (EXINT), INT0 (EXINT).
EP	EP Ground pad	Ground pad	Solder the exposed center pad to ground as shown in the package pinout notes. Connect the numbered ground contacts too.

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
Program flash32 KiB	32 KiB	Nonvolatile program memory. DS40002061B · Memory
SRAM2 KiB	2 KiB	Volatile data and stack storage. DS40002061B · Memory
EEPROM1 KiB	1 KiB	Nonvolatile data storage. DS40002061B · Memory
Clock and supplyOrder-code dependent	Order-code dependent	Use the grade table and the device’s speed-versus-voltage curve. DS40002061B · 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-MMH: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +85 °C
ATmega328-MMHR: 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-MMH: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +85 °C
ATmega328P-MMHR: 32 KiB flash · 2 KiB SRAM · 1 KiB EEPROM · 1.8–5.5 V · 20 MHz maximum · -40 to +85 °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.