https://docs.arduino.cc/hardware/uno-rev3
pin definitions
pin table
Below is a comprehensive reference table for the Arduino Uno (Uno R3 / ATmega328P-based) pins and common functions.
| Pin Number | Pin Label | Type | Functions / Notes |
|---|---|---|---|
| 0 | RX | Digital | UART RX (Serial) |
| 1 | TX | Digital | UART TX (Serial) |
| 2 | D2 | Digital | External Interrupt 0 (INT0) |
| 3 | ~D3 | Digital (PWM) | PWM (OC2B), External Interrupt 1 (INT1) |
| 4 | D4 | Digital | General purpose |
| 5 | ~D5 | Digital (PWM) | PWM (OC0B) |
| 6 | ~D6 | Digital (PWM) | PWM (OC0A) |
| 7 | D7 | Digital | General purpose |
| 8 | D8 | Digital | General purpose |
| 9 | ~D9 | Digital (PWM) | PWM (OC1A) |
| 10 | ~D10 | Digital (PWM, SPI SS) | PWM (OC1B); SPI SS (hardware) |
| 11 | ~D11 | Digital (PWM, SPI MOSI) | PWM (OC2A); SPI MOSI |
| 12 | D12 | Digital (SPI MISO) | SPI MISO |
| 13 | D13 | Digital (LED, SPI SCK) | Built-in LED; SPI SCK |
| A0 (14) | A0 | Analog / Digital | ADC0; can be used as digital (D14) |
| A1 (15) | A1 | Analog / Digital | ADC1; digital (D15) |
| A2 (16) | A2 | Analog / Digital | ADC2; digital (D16) |
| A3 (17) | A3 | Analog / Digital | ADC3; digital (D17) |
| A4 (18) | A4 | Analog / I2C (SDA) | ADC4; I2C SDA (also digital D18 on some mappings) |
| A5 (19) | A5 | Analog / I2C (SCL) | ADC5; I2C SCL (also digital D19 on some mappings) |
| - | VIN | Power | Input to onboard regulator (7-12V recommended) |
| - | 5V | Power | Regulated 5V output (or USB input) |
| - | 3.3V | Power | 3.3V regulator output on some boards |
| - | GND | Power | Ground pins (multiple) |
| - | IOREF | Power / Reference | Provides reference voltage for shields (5V on Uno) |
| - | RESET | Control | Active-low reset input |
| - | AREF | Reference | External analog reference for ADC |
| - | ICSP | SPI header | MOSI, MISO, SCK for programming / SPI (6-pin header) |
Notes:
- PWM pins: ~3, ~5, ~6, ~9, ~10, ~11 (marked with ~ on board silkscreen).
- SPI pins: D11 = MOSI, D12 = MISO, D13 = SCK; D10 typically used as SS for SPI slave select.
- I2C: SDA = A4, SCL = A5. Uno R3 also exposes dedicated SDA / SCL pins near AREF.
- Digital pins can be used as inputs or outputs; analog pins can also be used as digital pins when referenced by number (A0 = 14, ... A5 = 19).
SCH
