Arduino UNO R4 WiFi (ABX00087): the main microcontroller is a Renesas RA4M1 (Arm Cortex-M4, 5 V); a soldered ESP32-S3-MINI-1-N8 handles Wi-Fi 4 / BLE 5 as a 3.3 V secondary MCU. USB-C, 12x8 LED matrix, 12-bit DAC on A0, CAN on D13/D10.
The Arduino UNO R4 WiFi keeps the classic UNO footprint (68.85 x 53.34 mm, shield-compatible headers) but the part doing the work is not an ESP32 and not an ATmega: the main microcontroller is the Renesas RA4M1 (R7FA4M1AB3CFM#AA0), an Arm Cortex-M4 at 48 MHz that runs its I/O at 5 V for shield compatibility. A soldered ESP32-S3-MINI-1-N8 module sits beside it as the Wi-Fi 4 / Bluetooth 5 LE radio — a secondary MCU at 3.3 V behind a logic-level translator, not the processor you program by default. This page renders the MCUID data record: full header pinouts, the mixed-voltage boundary, and every published field tied to a fixed official source.
Two facts set this board apart on this site:
Main MCU and radio are different chips at different voltages. The RA4M1 runs at 5 V; the ESP32-S3 side runs at 3.3 V. The datasheet is explicit that their pins must never come into direct contact. (An earlier MCUID admission note listed the main MCU as RA6M5 — that was wrong; this record supersedes it.)
Programming paths can switch. By default the USB-C port programs the RA4M1 through the ESP32-S3; driving P408 high switches the USB link straight to the RA4M1, and soldering jumper SJ1 makes that permanent. (Datasheet §6.2 calls this pin "D40"; the schematic and the official ArduinoCore-renesas variant map it to internal pin 21 — recorded on this site as a naming conflict, not a header pin.)
Wiring safety — 5 V and 3.3 V domains: check the claims table below before connecting anything to the ESP header.
CAN and DAC — D13/D10 carry CAN RX/TX and A0 doubles as a 12-bit DAC; both are facts of the board, not shields.
Headers worth knowing
Analog side (1x14) — BOOT, IOREF, Reset, +3V3, +5V, GND x2, VIN (6-24 V), A0-A5; A0 is the DAC, A1-A3 expose the RA4M1 OPAMP, A4/A5 are the I2C bus.
Digital side (1x18) — SCL/SDA, AREF, GND, then D13…D0; D13/D10 add CANRX0/CANTX0, D11/D10/D9/D6/D5/D3 are PWM, D2/D3 the interrupt pins.
OFF header — power-supply control plus a VRTC pad for an RTC backup battery.
ICSP (2x3) and the Qwiic connector — the Qwiic port hangs on the secondary I2C0 bus at 3.3 V.
The ESP header is for the radio, not for you (usually)
The 6-pin header near the RESET button (ESP_IO42/IO41/TXD0/DOWNLOAD/RXD0/GND) reaches the ESP32-S3 module directly — Arduino's own tutorials use it to reflash the radio firmware. Day-to-day sketches talk to the RA4M1; Wi-Fi goes through the Arduino libraries over the internal link.
Recovery without external hardware
If a sketch locks the board, double-tapping the reset button right after power-up enters the bootloader and the board accepts a flash over USB again — documented behavior for all current Arduino boards.
Same name, different family
Looking for an ESP32 board to program directly? That is not this board: here the ESP32-S3 is Arduino's radio co-processor. The ESP32-C3-DevKitM-1 or Nano ESP32 put an ESP32 in the driver's seat. The UNO R4 Minima is this same RA4M1 board without the radio and LED matrix.