| Pin | Symbol | Description |
|---|
| 1 | (RESET) PC6 | reset (active low); port C |
| 2 | (RXD) PD0 | UART receive; port D |
| 3 | (TXD) PD1 | UART transmit; port D |
| 4 | (INT0) PD2 | external interrupt 0; port D |
| 5 | (INT1) PD3 | external interrupt 1; port D |
| 6 | (XCK/T0) PD4 | port D |
| 7 | Vcc | supply voltage |
| 8 | GND | ground |
| 9 | (XTAL1/TOSC1) PB6 | clock oscillator pin 1; port B |
| 10 | (XTAL2/TOSC2) PB7 | clock oscillator pin 2; port B |
| 11 | (T1) PD5 | port D |
| 12 | (AIN0) PD6 | port D |
| 13 | (AIN1) PD7 | port D |
| 14 | (ICP1) PB0 | port B |
| 15 | PB1 (OC1A) | port B |
| 16 | PB2 (SS/OC1B) | SPI slave select; port B |
| 17 | PB3 (MOSI/OC2) | SPI master output/slave input; port B |
| 18 | PB4 (MISO) | SPI master input/slave output; port B |
| 19 | PB5 (SCK) | SPI master clock; port B |
| 20 | AVcc | A/D converter supply voltage |
| 21 | AREF | analog reference for A/D converter |
| 22 | GND | ground |
| 23 | PC0 (ADC0) | port C |
| 24 | PC1 (ADC1) | port C |
| 25 | PC2 (ADC2) | port C |
| 26 | PC3 (ADC3) | port C |
| 27 | PC4 (ADC4/SCL) | 2-wire clock; port C |
| 28 | PC5 (ADC5/SDA) | 2-wire data; port C |