Arduino Uno shield headers consist of four rows of 0.1-inch pitch connectors: Power (8-pin), Digital (10-pin), Analog (6-pin), and Digital (8-pin), providing all Arduino I/O signals for shield add-on boards.
| Pin | Name | Function | Type |
|---|---|---|---|
| 1 | NC | Not connected | I/O |
| 2 | IOREF | I/O voltage reference | I/O |
| 3 | RESET | Reset active low | I/O |
| 4 | 3V3 | 3.3V power | PWR |
| 5 | 5V | 5V power | PWR |
| 6 | GND | Ground | GND |
| 7 | GND | Ground | GND |
| 8 | VIN | Input voltage 7-12V | PWR |
| A0 | A0 | Analog input 0 | ADC |
| A1 | A1 | Analog input 1 | ADC |
| A2 | A2 | Analog input 2 | ADC |
| A3 | A3 | Analog input 3 | ADC |
| A4 | A4 | Analog / SDA | ADC |
| A5 | A5 | Analog / SCL | ADC |
| D0 | D0 | RX UART receive | BUS |
| D1 | D1 | TX UART transmit | BUS |
| D2 | D2 | Digital I/O INT0 | I/O |
| D3 | D3 | Digital PWM INT1 | I/O |
| D4 | D4 | Digital I/O | I/O |
| D5 | D5 | Digital PWM | I/O |
| D6 | D6 | Digital PWM | I/O |
| D7 | D7 | Digital I/O | I/O |
| D8 | D8 | Digital I/O | I/O |
| D9 | D9 | Digital PWM | I/O |
| D10 | D10 | Digital SS SPI | BUS |
| D11 | D11 | Digital MOSI SPI | BUS |
| D12 | D12 | Digital MISO SPI | BUS |
| D13 | D13 | Digital SCK SPI LED | BUS |