Arduino UNO R4 WiFi — which MCU is it really, and what voltage do the pins run at?
The main microcontroller is the Renesas RA4M1 (Cortex-M4 48 MHz with FPU), not an ESP32: a soldered ESP32-S3-MINI-1-N8 only serves Wi-Fi/BLE at 3.3 V behind a level translator. Board logic is 5 V, VIN is 6-24 V, GPIOs handle 8 mA. Sources from the pinned Arduino datasheet.
Question this page answers: "Does the UNO R4 WiFi run on an ESP32? And are its pins 5 V or 3.3 V?"
The main MCU is a Renesas RA4M1
The UNO R4 WiFi is based on the 32-bit RA4M1 series microcontroller, R7FA4M1AB3CFM#AA0 from Renesas — a 48 MHz Arm Cortex-M4 with an FPU. Per the datasheet it features:
- 256 kB flash / 32 kB SRAM / 8 kB data flash (EEPROM)
- RTC, 4x DMA controllers, 14-bit ADC, up to 12-bit DAC, OPAMP, and a CAN bus (CAN RX on D13, CAN TX on D10)
A note on a circulating error: some listings and even early internal notes have called the UNO R4 WiFi's main MCU an RA6M5 — that is wrong. This site's own early admission record made that mistake and superseded it with the datasheet: the chip on the board is the RA4M1.
The ESP32-S3 on board is a co-processor, not the brain
A soldered ESP32-S3-MINI-1-N8 module (Xtensa dual-core LX7, built-in antenna) acts as a secondary MCU: it provides Wi-Fi 4 (2.4 GHz) and Bluetooth 5 LE, runs at 3.3 V, and talks to the RA4M1 through a logic-level translator. It is not user-replaceable.
Two service features expose it:
- a 6-pin ESP header near the RESET button (ESP_IO42/MTMS, ESP_IO41/MTDI, ESP_TXD0, ESP_DOWNLOAD, ESP_RXD0, GND) for direct access and module reflashing;
- the USB bridge: by default the RA4M1 is programmed through the ESP32-S3; driving P408 high switches USB communication directly to the RA4M1, and soldering SJ1 makes that permanent. Naming trap: datasheet §6.2 prints "D40", but the schematic (U2/U6/SJ1) and the official variant (internal pin 21) are the primary evidence — this site records "D40" as a naming conflict.
Voltage: one board, two domains
| Domain | Voltage | Notes |
|---|---|---|
| Board logic / RA4M1 | 5 V | "The operating voltage for the RA4M1 is fixed at 5 V" for compatibility with UNO shields, accessories and circuits |
| ESP32-S3-MINI-1-N8 | 3.3 V | behind the logic-level translator |
| VIN input | 6-24 V | tech specs "Input voltage (VIN): 6-24 V" |
| GPIO current | 8 mA | "GPIOs... safely handle up to 8 mA"; more than that needs an external supply |
The datasheet's Pin Voltage note is explicit: it is very important that the ESP32-S3's pins (3.3 V) do not come into contact with any of the RA4M1's pins (5 V), as this may damage the circuits. The mixed 5 V/3.3 V domains are a property of this specific board design.
Also on board: a Qwiic connector on the secondary I2C0 bus (3.3 V, following the Qwiic standard) and a 12x8 charlieplexed LED matrix driven by RA4M1 pins.
What this page cannot tell you
- Per-pin voltage limits beyond the two domains above (for example a per-pin "5 V tolerant" rating or a maximum analog input figure): the pinned datasheet and tech specs do not state one, so this page does not either.
- Radio performance or antenna details — module datasheet territory.
Board
- Arduino UNO R4 WiFi — full header maps (analog, digital, ESP header, Qwiic), the LED matrix pin list and the bootloader entry method.
Sources
- Arduino UNO R4 WiFi datasheet — Microcontroller (RA4M1) (arduino/docs-content commit
cb938e9) — R7FA4M1AB3CFM#AA0, 48 MHz Cortex-M4 FPU, memory and peripheral list, 5 V operating voltage. - Datasheet — Wi-Fi/Bluetooth Module (ESP32-S3-MINI-1-N8), ESP header, USB bridge — secondary-MCU role, 3.3 V, level translator, 6-pin ESP header, P408/SJ1 switch.
- Datasheet — Pin Voltage / Pin Current — 5 V vs 3.3 V warning, 8 mA per GPIO.
- UNO R4 WiFi tech specs — "Input voltage (VIN): 6-24 V"; rendered page: docs.arduino.cc/hardware/uno-r4-wifi.