# Uno R3 (ATmega328P): specs and pinout

> Arduino-compatible board built around the ATmega328P, with a CH340G USB-to-serial chip and 14 digital I/O pins.

[HTML version](https://soldr.ai/docs/boards/uno-r3)

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Arduino-compatible board built around the ATmega328P, with a CH340G USB-to-serial chip and 14 digital I/O pins.

Every value cites its sourceOfficial pinout

[Buy on Compoden](https://compoden.com/products/uno-r3-ch340g-atmega328p-board-arduino-compatible)

## Specs

| Spec | Value | Source |
|---|---|---|
| Microcontroller | ATmega328P | Arduino datasheet A000066 |
| Operating voltage | 5 V | Compoden listing |
| VIN input voltage | 6-20 V | Arduino official pinout diagram |
| USB input voltage (max) | 5.5 V | Arduino datasheet A000066 |
| Flash | 32 kB | Arduino datasheet A000066 |
| SRAM | 2 kB | Arduino datasheet A000066 |
| EEPROM | 1 kB | Arduino datasheet A000066 |
| Clock speed | up to 16 MHz | Arduino datasheet A000066 |
| Digital I/O pins | 14 | Arduino datasheet A000066 |
| PWM channels | Six PWM channels | Arduino datasheet A000066 |
| Analog inputs | 6 | Arduino datasheet A000066 |
| Max current per I/O pin | 20 mA | Arduino official pinout diagram |
| Max current per +3.3V pin | 50 mA | Arduino official pinout diagram |
| I2C | A4/SDA, A5/SCL (also D18/SDA, D19/SCL) | Arduino official pinout diagram |
| SPI | D13 SCK, D12 CIPO, D11 COPI, D10 SS | Arduino official pinout diagram |
| UART | D0/RX, D1/TX | Arduino official pinout diagram |

## Power

| | Value | Source |
|---|---|---|
| Supply | VIN 6-20 V via barrel jack or VIN pin; USB 5.5 V max | Arduino official pinout diagram |

## Pinout

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| NC | NC | | Not connected | Arduino official pinout diagram |
| IOREF | IOREF | 5 V | Reference for digital logic V - connected to 5V | Arduino datasheet A000066 |
| RESET | Reset | | | Arduino datasheet A000066 |
| 3V3 | +3V3 Power Rail | 3.3 V | Diagram prints +3V3; max current per +3.3V pin 50 mA | Arduino official pinout diagram |
| 5V | +5V Power Rail | 5 V | | Arduino datasheet A000066 |
| GND | Ground | | | Arduino datasheet A000066 |
| GND (2) | Ground | | | Arduino datasheet A000066 |
| VIN | Voltage Input | 6-20 V | VIN 6-20 V input to the board | Arduino official pinout diagram |
| A0 | Analog input 0 /GPIO (ADC[0], PC0) | | | Arduino official pinout diagram |
| A1 | Analog input 1 /GPIO (ADC[1], PC1) | | | Arduino official pinout diagram |
| A2 | Analog input 2 /GPIO (ADC[2], PC2) | | | Arduino official pinout diagram |
| A3 | Analog input 3 /GPIO (ADC[3], PC3) | | | Arduino official pinout diagram |
| A4/SDA | Analog input 4 /I2C Data line (PC4) | | Also D18/SDA | Arduino official pinout diagram |
| A5/SCL | Analog input 5 /I2C Clock line (PC5) | | Also D19/SCL | Arduino official pinout diagram |
| D0/RX | Digital input 0 /GPIO (PD0) | | UART RXD | Arduino official pinout diagram |
| D1/TX | Digital input 1 /GPIO (PD1) | | UART TXD | Arduino official pinout diagram |
| D2 | Digital input 2 /GPIO (PD2) | | | Arduino official pinout diagram |
| D3 | Digital input 3 /GPIO (PD3), PWM | | ~D3 on the board | Arduino official pinout diagram |
| D4 | Digital input 4 /GPIO (PD4) | | | Arduino official pinout diagram |
| D5 | Digital input 5 /GPIO (PD5), PWM | | ~D5 on the board | Arduino official pinout diagram |
| D6 | Digital input 6 /GPIO (PD6), PWM | | ~D6 on the board | Arduino official pinout diagram |
| D7 | Digital input 7 /GPIO (PD7) | | | Arduino official pinout diagram |
| D8 | Digital input 8 /GPIO (PB0) | | | Arduino official pinout diagram |
| D9 | Digital input 9 /GPIO (PB1), PWM | | ~D9 on the board | Arduino official pinout diagram |
| D10 | Digital input 10 /GPIO (PB2), SS, PWM | | ~D10; SPI SS | Arduino official pinout diagram |
| D11 | COPI (MOSI), PWM (PB3) | | ~D11; CIPO/COPI were previously called MISO/MOSI | Arduino official pinout diagram |
| D12 | CIPO (MISO) (PB4) | | | Arduino official pinout diagram |
| D13 | SCK (PB5), LED_BUILTIN | | | Arduino official pinout diagram |
| AREF | Analog Reference Voltage | | | Arduino datasheet A000066 |
| D18/SDA | Digital input 18 /I2C Dataline (PC4) | | | Arduino official pinout diagram |
| D19/SCL | Digital input 19 /I2C Dataline (PC5) | | | Arduino official pinout diagram |

## Common mistakes

- Driving more than 20 mA from one I/O pin; the maximum is 20 mA per I/O pin [Arduino official pinout diagram]
- Feeding VIN outside 6-20 V [Arduino official pinout diagram]
- Reading CIPO/COPI as MISO/MOSI: the official pinout says CIPO/COPI were previously called MISO/MOSI [Arduino official pinout diagram]

## What we could not confirm

- Compatible board: the listing names a CH340G USB chip; the official datasheet describes the Arduino UNO R3 (ATmega16U2 USB). Pinout taken from the official UNO R3; this clone's layout is not confirmed.
- Conflict: listing says VIN accepts 7-12V; official pinout says VIN 6-20 V. The official value is used.
- Conflict: datasheet features say up to 16 MHz, section 3.2 says up to 20 MHz. 16 MHz used.
- Per-pin current: official 20 mA max per I/O pin is from the pinout diagram; the datasheet ratings table prints 'xx mA' for power consumption (not used).
- Typical current draw not stated in an official source.

## Sources

- Arduino datasheet A000066
- Arduino official pinout diagram
- Arduino official documentation
- [link](https://compoden.com/products/uno-r3-ch340g-atmega328p-board-arduino-compatible)

Building with the Uno R3 (ATmega328P)? [Describe your project on Soldr](https://app.soldr.ai): it assigns pins from the board's published pinout, checks power and logic levels, and shows how to wire every part.