Arduino Uno R4 WiFi — TinyGo Development Guide

Pinout Diagram

                              [USB-C]         [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 ├── CIPO (MISO)
              A3 ──┤ A3                       ~D11 ├── COPI (MOSI) / PWM
              A2 ──┤ A2                       ~D10 ├── CS (SS) / PWM
              A1 ──┤ A1                        ~D9 ├── PWM
          DAC/A0 ──┤ A0                         D8 ├──
                    │                               │
                    │  [RA4M1]    [12×8 LED Matrix] │
                    │  [ESP32-S3]   [Qwiic I2C]    │
                    │                               │
                    │                          D7 ├──
                    │                         ~D6 ├── PWM
                    │                         ~D5 ├── PWM
                    │                          D4 ├──
                    │                         ~D3 ├── PWM / INT1
                    │                          D2 ├── INT0
           TX ─────┤ D1                        D1 ├── TX
           RX ─────┤ D0                        D0 ├── RX
                    ├──────────────────────────────┤
                    │    [ICSP]    [ESP32 Header]   │
                    └──────────────────────────────┘

  ~ = PWM capable    INT = External interrupt
  CAN TX/RX on dedicated header    Qwiic = secondary I2C (3.3V)
  ⚠ ESP32 header near USB-C is 3.3V only

Pin Reference Table

Additional Interfaces

Power Pins

TinyGo Setup

Target Name

⚠ TinyGo support for the Arduino Uno R4 WiFi may not be available yet. The RA4M1 MCU target exists (arduino-uno-r4-minima), but the WiFi variant with ESP32-S3 co-processor may not have a dedicated TinyGo target. Check the latest TinyGo release notes.

arduino-uno-r4-minima

Note: You may be able to use the arduino-uno-r4-minima target for basic GPIO/I2C/SPI/UART on the RA4M1, but WiFi, BLE, and LED matrix features (which require the ESP32-S3) will NOT be available through TinyGo.

Installation

1. Install TinyGo: https://tinygo.org/getting-started/install/
2. Check if the target is available:

   tinygo info -target=arduino-uno-r4-minima
   

Build and Flash

# Build only (using the R4 Minima target)
tinygo build -target=arduino-uno-r4-minima -o firmware.bin ./main.go

# Build and flash
tinygo flash -target=arduino-uno-r4-minima ./main.go

# Monitor serial output
tinygo monitor -target=arduino-uno-r4-minima

Note: If the board is not detected, double-tap the reset button to enter bootloader mode.

TinyGo Support Status

• Status: Partial — RA4M1 GPIO/peripherals may work; ESP32-S3 features unavailable
• GPIO: Supported (RA4M1 pins)
• ADC: Supported (14-bit configurable)
• DAC: Check TinyGo release notes
• PWM: Supported on D3, D5, D6, D9, D10, D11
• I2C: Supported (machine.I2C0) — main bus on A4/A5
• SPI: Supported (machine.SPI0)
• UART: Supported (machine.UART0)
• USB CDC: Supported (native USB)
• WiFi: ❌ Not available in TinyGo (requires ESP32-S3)
• BLE: ❌ Not available in TinyGo (requires ESP32-S3)
• LED Matrix: ❌ Not available in TinyGo (requires ESP32-S3 communication)
• CAN Bus: Not yet supported in TinyGo
• Qwiic I2C: May work as machine.I2C1 — check TinyGo support

Known Limitations (TinyGo on R4 WiFi)

• No WiFi/BLE — The ESP32-S3 handles wireless; TinyGo targets the RA4M1 only
• No LED Matrix — The 12×8 LED matrix is controlled via the ESP32-S3
• No Qwiic guarantee — The secondary I2C bus (Wire1/Qwiic) may not be mapped in TinyGo
• CAN Bus — Not supported in TinyGo
• For WiFi/BLE/LED matrix — Use the Arduino/C++ framework instead (Arduino-UnoR4WiFi-Arduino skill)

Example: Blink (TinyGo)

package main

import (
    "machine"
    "time"
)

func main() {
    led := machine.D13 // Built-in LED
    led.Configure(machine.PinConfig{Mode: machine.PinOutput})

    for {
        led.High()
        time.Sleep(500 * time.Millisecond)
        led.Low()
        time.Sleep(500 * time.Millisecond)
    }
}

Communication Protocols

I2C (Main Bus)

• SDA: A4
• SCL: A5
• TinyGo bus: machine.I2C0

i2c := machine.I2C0
err := i2c.Configure(machine.I2CConfig{
    SDA:       machine.SDA_PIN, // A4
    SCL:       machine.SCL_PIN, // A5
    Frequency: 400000,          // 400 kHz fast mode
})
if err != nil {
    println("I2C init failed:", err)
}

// Write to device
data := []byte{0x00, 0x01}
i2c.Tx(0x3C, data, nil)

// Read from device
buf := make([]byte, 2)
i2c.Tx(0x3C, []byte{0x00}, buf)

I2C (Qwiic — Secondary Bus)

• Qwiic connector: Secondary I2C bus at 3.3V only
• TinyGo bus: machine.I2C1 (if supported)

⚠ Warning: The Qwiic connector operates at 3.3V. Do NOT connect 5V I2C devices to the Qwiic port. TinyGo support for the secondary I2C bus may be limited.

SPI

• SCK: D13
• CIPO (MISO): D12
• COPI (MOSI): D11
• CS: D10 (or any GPIO)
• TinyGo bus: machine.SPI0

spi := machine.SPI0
err := spi.Configure(machine.SPIConfig{
    SCK:       machine.D13,
    SDO:       machine.D11, // COPI (MOSI)
    SDI:       machine.D12, // CIPO (MISO)
    Frequency: 4000000,     // 4 MHz
})
if err != nil {
    println("SPI init failed:", err)
}

cs := machine.D10
cs.Configure(machine.PinConfig{Mode: machine.PinOutput})
cs.High()

cs.Low()
result := make([]byte, 1)
spi.Tx([]byte{0x00}, result)
cs.High()

UART

• TX: D1
• RX: D0
• TinyGo bus: machine.UART0

uart := machine.UART0
uart.Configure(machine.UARTConfig{
    TX:       machine.UART_TX_PIN, // D1
    RX:       machine.UART_RX_PIN, // D0
    BaudRate: 9600,
})
uart.Write([]byte("Hello from Uno R4 WiFi\r\n"))

Analog Read (ADC)

adc := machine.ADC{Pin: machine.ADC0} // A0
adc.Configure(machine.ADCConfig{
    Resolution: 14, // Up to 14-bit on RA4M1
})
value := adc.Get() // Returns 16-bit scaled value
println("ADC:", value)

Power Management

Voltage and Current

• Logic level: 5V on RA4M1 GPIO pins; 3.3V on ESP32-S3 and Qwiic
• Max current per pin: 8 mA
• 5V output: From USB-C or regulated from VIN
• 3.3V output: From onboard regulator
• VIN range: 6–24V

⚠ Mixed Voltage Warning

The Uno R4 WiFi has two voltage domains:

• 5V: All standard Arduino header pins (D0–D13, A0–A5)
• 3.3V: ESP32-S3 header near USB-C and Qwiic connector

Do NOT connect 5V signals to the ESP32-S3 header or Qwiic connector — this will damage the ESP32-S3.

⚠ Lower Current per Pin

The Uno R4 WiFi has a maximum of 8 mA per GPIO pin:

• Use current-limiting resistors for LEDs (470Ω–1kΩ)
• Use transistor/MOSFET drivers for motors and relays

Special Features

• WiFi 802.11 b/g/n — Via ESP32-S3 (not accessible from TinyGo)
• BLE 5.0 — Via ESP32-S3 (not accessible from TinyGo)
• 12×8 LED Matrix — 96 programmable LEDs (not accessible from TinyGo)
• Qwiic/STEMMA QT connector — Secondary I2C at 3.3V for easy sensor connection
• 14-bit ADC — Configurable resolution
• 12-bit DAC on A0 — True analog output
• CAN Bus — Hardware CAN (requires external transceiver)
• RTC — Built-in real-time clock
• HID support — Native USB keyboard/mouse emulation
• USB-C — Modern connector with native USB
• Uno R3 shield compatible — Same header layout

For WiFi, BLE, and LED matrix features, use the Arduino/C++ framework — these require the ESP32-S3 co-processor which TinyGo cannot access.

Common Gotchas / Notes

1. No WiFi/BLE in TinyGo — These features require the ESP32-S3; use Arduino/C++ instead
2. No LED matrix in TinyGo — The 12×8 matrix is controlled via ESP32-S3
3. 5V logic on headers — Standard pins are 5V; use level shifters for 3.3V devices
4. 3.3V on Qwiic/ESP32 header — Do NOT connect 5V to these interfaces
5. 8 mA per pin — Lower than Uno R3; use drivers for loads
6. D0/D1 shared with UART — External devices conflict with serial
7. D13 LED flickers during SPI — Built-in LED shares SPI SCK
8. Double-tap reset for bootloader — If upload fails, double-tap reset
9. USB-C cable matters — Use a data-capable cable
10. TinyGo target — Use arduino-uno-r4-minima target; WiFi-specific target may not exist

Reference Links

• Arduino Uno R4 WiFi docs: https://docs.arduino.cc/hardware/uno-r4-wifi/
• TinyGo RA4M1 target: https://tinygo.org/docs/reference/microcontrollers/arduino-uno-r4-minima/
• Renesas RA4M1 datasheet: https://www.renesas.com/us/en/document/dst/ra4m1-group-datasheet
• ESP32-S3 datasheet: https://www.espressif.com/sites/default/files/documentation/esp32-s3_datasheet_en.pdf
• Pinout PDF: https://docs.arduino.cc/resources/pinouts/ABX00087-full-pinout.pdf
• Datasheet: https://docs.arduino.cc/resources/datasheets/ABX00087-datasheet.pdf