ATmega328 / ATmega328P / ATmega168 / ATmega8 connection guide

ATmega328 / ATmega328P / ATmega168 / ATmega8 PDIP-28 wiring guide with power, signal assignments, and bench checks.

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. Choose the marked order code for voltage, clock, and temperature.

Power and reset

Required

Use a current-limited supply at a voltage permitted by the order code and system clock. Tie the listed supply pins to that rail. Fit one 100 nF ceramic capacitor close to each supply-and-ground pair. Use a 10 kΩ reset pull-up for this bench circuit.

Target rail
- Bench supply positive
- VCC (7)
- AVCC (20)
Ground
- Bench supply return
- GND (8)
- GND (22)
Reset
- PC6 (1)

Bench checks

With power off, check for a short across the supply. Power on and measure voltage at every supply pin and at reset.
Check the clock source configured by CKSEL. If a used part expects an external clock, provide it before attempting serial programming.

AN2519 §§2–3 and 2545W · Pin descriptions and clock source

Connection scenarios

Connect USART0 to a logic-level serial adapter

Use a UART adapter that supports the target’s I/O voltage. Cross the transmit and receive lines. Leave adapter power disconnected when using the bench supply.

Transmit from MCU
- PD1 (3)
- Adapter RX
Receive into MCU
- PD0 (2)
- Adapter TX
Signal return
- GND (8)
- GND (22)
- Adapter GND

Bench checks

Configure both sides for the same baud rate, frame length, parity and stop bits. Base the MCU baud divider on the actual clock after prescaling.
Send a known byte such as 0x55 from the MCU and check that it arrives unchanged. If it fails, inspect TX idle voltage and bit period before attaching the adapter TX line.

2545W · USART0 asynchronous operation and pin assignments

PDIP-28 wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

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

Selected pin details

2 · PD0

Bidirectional · GPIO

General-purpose digital I/O. Alternate assignments: RXD (USART0), PCINT16 (EXINT).

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

2545W · Pinout and peripheral signal descriptions

Electrical limits · Pin in the reference

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.