Arduino AVR
Arduino Uno R3 Pinout
The Arduino Uno R3 is the canonical Arduino board: an ATmega328P running at 16 MHz with 14 digital I/O, 6 analog inputs, and a fixed pin layout that defines the shield ecosystem. Below is every pin with its alternate functions.
Specifications
- MCU
- ATmega328P, 16 MHz
- Flash
- 32 KB (0.5 KB used by bootloader)
- SRAM
- 2 KB
- Digital I/O
- 14 (6 PWM-capable)
- Analog inputs
- 6 (10-bit ADC)
- Operating voltage
- 5V (7–12V on VIN)
Pin reference
| Pin | Name | Type / functions | Notes |
|---|---|---|---|
| D0 | RX | Digital I/O, UART RX | Used by USB serial — avoid for I/O. |
| D1 | TX | Digital I/O, UART TX | Used by USB serial. |
| D2 | INT0 | Digital I/O, external interrupt | — |
| D3 | INT1 / PWM | Digital I/O, PWM, external interrupt | — |
| D4 | D4 | Digital I/O | — |
| D5 | PWM | Digital I/O, PWM | — |
| D6 | PWM | Digital I/O, PWM | — |
| D7 | D7 | Digital I/O | — |
| D8 | D8 | Digital I/O | — |
| D9 | PWM | Digital I/O, PWM | — |
| D10 | SS / PWM | Digital I/O, SPI SS, PWM | — |
| D11 | MOSI / PWM | Digital I/O, SPI MOSI, PWM | — |
| D12 | MISO | Digital I/O, SPI MISO | — |
| D13 | SCK / LED | Digital I/O, SPI SCK, onboard LED | — |
| A0 | Analog 0 | Analog input / Digital I/O | — |
| A1 | Analog 1 | Analog input / Digital I/O | — |
| A2 | Analog 2 | Analog input / Digital I/O | — |
| A3 | Analog 3 | Analog input / Digital I/O | — |
| A4 | SDA | Analog input / I2C SDA | — |
| A5 | SCL | Analog input / I2C SCL | — |
| AREF | Analog reference | Reference voltage for ADC | — |
| VIN | VIN | Power input, 7–12V | — |
| 5V | 5V output | Regulated 5V, ~500 mA | — |
| 3V3 | 3.3V output | Regulated 3.3V, ~50 mA | — |
| GND | Ground | Power | — |
| RESET | Reset | Pull LOW to reset | — |
Gotchas
- 01Each I/O pin can sink/source 20 mA max. Total across all pins should stay under 200 mA.
- 02D0 (RX) and D1 (TX) are shared with the USB-serial chip — using them for I/O will interfere with Serial.print and uploads.
- 03The 3.3V rail can only supply ~50 mA. Power-hungry 3.3V modules need an external regulator.
- 04Only D2 and D3 support hardware interrupts (attachInterrupt).
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