Provides comprehensive pinout reference, board specifications, and Arduino C++ development guide for the Arduino Uno R3 (ATmega328P) microcontroller. Use when writing Arduino firmware for the Arduino Uno R3, wiring peripherals, or configuring pins. Keywords: Arduino, Uno, R3, ATmega328P, AVR, C++, pinout, GPIO, I2C, SPI, UART, analog, digital, PWM, 5V, 8-bit, arduino-cli.
Provides comprehensive reference for developing Arduino C++ firmware for the Arduino Uno R3 (ATmega328P).
Arduino-UnoR3-TinyGo skillArduino-UnoR4Minima-Arduino or Arduino-UnoR4WiFi-Arduino skillArduino-Nano-Arduino skillArduino-Mega2560-Arduino skill| Parameter | Value |
|---|---|
| MCU | ATmega328P |
| Architecture | 8-bit AVR |
| Clock Speed | 16 MHz |
| Flash | 32 KB (0.5 KB used by bootloader) |
| SRAM | 2 KB |
| EEPROM | 1 KB |
| USB | USB-B (via ATmega16U2 USB-serial) |
| Operating Voltage | 5V |
| Input Voltage (VIN) | 7–12V recommended (6–20V limit) |
| DC Current per I/O Pin | 20 mA |
| DC Current for 3.3V Pin | 50 mA |
| Dimensions | 68.6 × 53.4 mm |
| Weight | 25 g |
| Digital I/O | 14 (D0–D13) |
| PWM Outputs | 6 (D3, D5, D6, D9, D10, D11) |
| Analog Inputs | 6 (A0–A5, 10-bit ADC) |
| Built-in LED | D13 |
[USB-B] [Barrel Jack]
┌──────────────────────────────┐
│ RESET IOREF 5V GND VIN │ ← Power Header
│ 3.3V AREF GND │
├──────────────────────────────┤
SCL/A5 ──┤ A5 D13 ├── SCK / Built-in LED
SDA/A4 ──┤ A4 D12 ├── MISO
A3 ──┤ A3 ~D11 ├── MOSI / PWM
A2 ──┤ A2 ~D10 ├── SS / PWM
A1 ──┤ A1 ~D9 ├── PWM
A0 ──┤ A0 D8 ├──
│ │
│ [ATmega328P] │
│ │
│ D7 ├──
│ ~D6 ├── PWM
│ ~D5 ├── PWM
│ D4 ├──
│ ~D3 ├── PWM / INT1
│ D2 ├── INT0
TX ─────┤ D1 D1 ├── TX
RX ─────┤ D0 D0 ├── RX
├──────────────────────────────┤
│ [ICSP] │
└──────────────────────────────┘
~ = PWM capable INT = External interrupt
| Pin | Digital | Analog | PWM | Interrupt | SPI | I2C | UART | Other |
|---|---|---|---|---|---|---|---|---|
| D0 | ✓ | — | — | — | — | — | RX | — |
| D1 | ✓ | — | — | — | — | — | TX | — |
| D2 | ✓ | — | — | INT0 | — | — | — | — |
| D3 | ✓ | — | ✓ | INT1 | — | — | — | — |
| D4 | ✓ | — | — | — | — | — | — | — |
| D5 | ✓ | — | ✓ | — | — | — | — | — |
| D6 | ✓ | — | ✓ | — | — | — | — | — |
| D7 | ✓ | — | — | — | — | — | — | — |
| D8 | ✓ | — | — | — | — | — | — | — |
| D9 | ✓ | — | ✓ | — | — | — | — | — |
| D10 | ✓ | — | ✓ | — | SS | — | — | — |
| D11 | ✓ | — | ✓ | — | MOSI | — | — | — |
| D12 | ✓ | — | — | — | MISO | — | — | — |
| D13 | ✓ | — | — | — | SCK | — | — | Built-in LED |
| A0 | ✓ | ADC0 | — | — | — | — | — | — |
| A1 | ✓ | ADC1 | — | — | — | — | — | — |
| A2 | ✓ | ADC2 | — | — | — | — | — | — |
| A3 | ✓ | ADC3 | — | — | — | — | — | — |
| A4 | ✓ | ADC4 | — | — | — | SDA | — | — |
| A5 | ✓ | ADC5 | — | — | — | SCL | — | — |
| Pin | Function |
|---|---|
| VIN | Input voltage (7–12V recommended) |
| 5V | Regulated 5V output |
| 3.3V | Regulated 3.3V output (50 mA max) |
| GND | Ground (3 pins) |
| AREF | Analog reference voltage |
| IOREF | I/O reference voltage |
| RESET | Reset (active LOW) |
The Arduino Uno R3 is included in the built-in Arduino AVR core. No additional board manager URL is needed.