The Arduino UNO R4 WiFi keeps the familiar UNO layout but replaces the 8-bit ATmega328P architecture with a 48 MHz Renesas RA4M1 and adds a separate ESP32-S3-MINI-1-N8 connectivity processor.
It also adds two features that make its pinout more interesting than a normal UNO: a built-in 12×8 LED matrix and a dedicated 3.3 V Qwiic connector.
The result is a dual-MCU board where the RA4M1 runs the normal Arduino sketch while the ESP32-S3 normally provides Wi-Fi, Bluetooth and USB/connectivity support.
UNO R4 WiFi Specifications
| Feature | UNO R4 WiFi |
|---|---|
| Main MCU | Renesas RA4M1, Arm Cortex-M4 |
| Clock | 48 MHz |
| Logic voltage | 5 V |
| Flash | 256 kB |
| SRAM | 32 kB |
| Data memory | 8 kB |
| Connectivity MCU | ESP32-S3-MINI-1-N8 |
| Wireless | 2.4 GHz Wi-Fi and Bluetooth via ESP32-S3 |
| ADC | Up to 14-bit |
| DAC | 12-bit on A0 |
| CAN | Classic CAN controller; external transceiver required |
| RTC | Built in |
| USB | USB-C |
| LED matrix | 12×8, 96 red LEDs |
| Qwiic | Dedicated 3.3 V I²C connector |
UNO R4 WiFi Digital Pinout
| Arduino pin | RA4M1 pin | Main functions |
|---|---|---|
| D0 / RX | P301 | UART RX, digital I/O |
| D1 / TX | P302 | UART TX, digital I/O |
| D2 | P104 | GPIO, interrupt-capable |
| D3 | P105 | GPIO, PWM, interrupt-capable |
| D4 | P106 | GPIO, CAN TX |
| D5 | P107 | GPIO, PWM, CAN RX |
| D6 | P111 | GPIO, PWM |
| D7 | P112 | GPIO |
| D8 | P304 | GPIO |
| D9 | P303 | GPIO, PWM |
| D10 | P103 | GPIO, PWM, SPI CS |
| D11 | P411 | GPIO, PWM, SPI COPI/MOSI |
| D12 | P410 | GPIO, SPI CIPO/MISO |
| D13 | P102 | GPIO, SPI SCK, LED_BUILTIN |
PWM Pins
The officially supported PWM pins are:
|
1 2 3 4 5 6 7 8 9 |
D3 D5 D6 D9 D10 D11 |
The RA4M1 timer hardware can route PWM to additional pins internally, but these six are the supported Arduino header positions for portable sketches.
Analog Pins
| Pin | Main functions |
|---|---|
| A0 | ADC, 12-bit DAC output |
| A1 | ADC, OPAMP positive input |
| A2 | ADC, OPAMP negative input |
| A3 | ADC, OPAMP output |
| A4 | ADC, SDA / main I²C |
| A5 | ADC, SCL / main I²C |
The ADC defaults to 10-bit for Arduino compatibility but can be configured for 12- or 14-bit reads:
|
1 2 3 4 5 |
analogReadResolution(14); int value = analogRead(A0); |
True DAC on A0
A0 can output a real analog voltage using the RA4M1 12-bit DAC. This is different from PWM.
|
1 2 3 4 5 |
analogWriteResolution(12); analogWrite(A0, 2048); |
Integrated Operational Amplifier
The RA4M1 operational amplifier is exposed as:
|
1 2 3 4 5 6 |
A1 = OPAMP + A2 = OPAMP - A3 = OPAMP OUT |
This can be used for buffering, amplification and analog signal conditioning without an external op-amp in some applications.
Main I²C Bus
The normal UNO I²C bus is:
|
1 2 3 4 5 |
A4 / D18 = SDA A5 / D19 = SCL |
Use the standard Wire object.
Qwiic Connector: Separate 3.3 V I²C Bus
The Qwiic connector is not just a duplicate of A4/A5. It is a separate I²C interface operating at 3.3 V.
|
1 2 3 4 5 6 |
Qwiic SCL = RA4M1 P400 Qwiic SDA = RA4M1 P401 Qwiic power = 3.3 V |
In the current Arduino core it is accessed through Wire1.
Do not connect a 5 V-only Qwiic device. Arduino explicitly labels the connector as 3.3 V only.
SPI
|
1 2 3 4 5 6 7 |
D10 = CS D11 = COPI / MOSI D12 = CIPO / MISO D13 = SCK |
The board also provides the traditional 6-pin SPI/ICSP-style header.
UART
|
1 2 3 4 5 |
D0 = RX D1 = TX |
Use Serial1 for the physical UART and Serial for the USB connection.
CAN Bus
The RA4M1 includes a classic CAN controller. The header pins are:
|
1 2 3 4 5 |
D4 = CAN TX D5 = CAN RX |
You still need an external CAN transceiver between those logic-level pins and CANH/CANL.
Real-Time Clock
The RA4M1 includes an RTC capable of calendar timekeeping and alarms. The R4 family also exposes the VBATT/backup-power concept through its board architecture so time can be preserved when main power is removed when the hardware is configured correctly.
12×8 LED Matrix
The UNO R4 WiFi includes 96 red LEDs arranged as 12 columns by 8 rows.
The matrix uses Charlieplexing and eleven RA4M1 pins:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 |
P003 P004 P011 P012 P013 P015 P204 P205 P206 P212 P213 |
These are internal board connections rather than ordinary UNO header GPIO. The matrix is normally controlled with Arduino_LED_Matrix.
ESP32-S3-MINI-1-N8
The onboard ESP32-S3 is a real programmable MCU, but it does not normally run your main Arduino sketch.
The normal architecture is:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
Arduino sketch ↓ RA4M1 ↓ connectivity protocol ↓ ESP32-S3 ├── Wi-Fi ├── Bluetooth └── USB/connectivity services |
The module can be programmed separately through the dedicated ESP header, but doing so replaces Arduino’s bridge/connectivity firmware.
5 V Main GPIO, 3.3 V ESP/Qwiic Domain
The standard UNO headers use a 5 V logic environment. The ESP32-S3 and Qwiic side are 3.3 V.
Arduino uses onboard level translation where the two processors need to communicate. Do not assume that a 3.3 V Qwiic connector can accept 5 V just because the main UNO pins can.
USB-C
The USB-C connector is used for power, programming and serial communication. Arduino specifies 5 V on the USB-C input.
The board contains USB switching between the RA4M1 and ESP32-S3 architecture, which is why changing ESP32 bridge firmware can affect normal board detection.
Power
UNO R4 WiFi can be powered through USB-C or VIN/barrel jack. Arduino documents approximately 6–24 V on VIN.
Do not power motors or large servos from the board’s 5 V pin simply because the regulator can supply useful current; transient loads can cause resets and noise.
Quick Reference
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 |
UART D0 RX D1 TX CAN D4 TX D5 RX PWM D3 D5 D6 D9 D10 D11 SPI D10 CS D11 COPI/MOSI D12 CIPO/MISO D13 SCK I2C / Wire A4 SDA A5 SCL Qwiic / Wire1 P401 SDA P400 SCL 3.3 V ADC A0-A5 up to 14 bit DAC A0 12 bit OPAMP A1 + A2 - A3 OUT LED matrix 12×8 96 LEDs Main logic 5 V |
Final Thoughts
The UNO R4 WiFi is best understood as a modern 5 V RA4M1 Arduino with an ESP32-S3 coprocessor and several integrated peripherals.
For ordinary sketches, think of the board as:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
RA4M1 = your application ESP32-S3 = Wi-Fi / Bluetooth / bridge A4/A5 = main 5 V I2C Qwiic = separate 3.3 V I2C A0 = ADC + true DAC D4/D5 = CAN controller signals |
That architecture gives the UNO R4 WiFi much more capability than the UNO R3 while retaining the familiar shield layout and 5 V digital environment.