Arduino Uno R4 WiFi pinout: every pin, and how it differs from an R3

The Arduino Uno R4 WiFi keeps the Uno’s outline and headers, so an Uno shield fits, but the chip behind them is a Renesas RA4M1, an Arm Cortex-M4 at 48 MHz, with an ESP32-S3 beside it for WiFi and a 12 by 8 LED matrix on top. This page lists every header pin, what it can do, the power pins and the limits, and the places where an R4 behaves differently from an Uno R3 with the same wiring.

The circuit above is the board in Mokxi drawing a beating heart on its matrix, with the L LED on pin 13 flashing in time. The table is read from the same board model the simulator runs, and where the simulator does less than the board, the page says so.

VIN takes 6 to 24 V, a wider range than an Uno R3’s, and the board makes its own 5 V from it. 5V is the regulated rail, from USB or from VIN. 3V3 is a small output for a sensor. IOREF is 5 V and tells a shield which logic level the board uses. The three GND holes are one ground.

The pins are 5 V, like an R3’s, but Arduino rates each one for only 8 mA where an R3’s gives 20. An LED on a 1 k resistor is fine; an LED on 220 ohms, a relay coil or a buzzer hung straight off a pin is asking too much. Use a transistor or a driver module for anything that needs current. Mokxi does not model a pin’s current limit, so it will not stop you; the board will.

The converter is fourteen bits, but analogRead returns ten, 0 to 1023, so an Uno sketch’s thresholds still mean the same thing. analogReadResolution(14) gives all fourteen. Full scale is the 5 V rail. On a real board A0 is also a 12-bit DAC output; Mokxi does not model the DAC.

PWM is on the same six pins as an Uno, 3, 5, 6, 9, 10 and 11, at 490 Hz in Mokxi. I2C is A4 and A5, also reachable as SDA and SCL by AREF, and SPI is 10 to 13. In Mokxi both buses run in software on those pins, because the chip’s I2C and SPI blocks are not modeled. The Qwiic socket on a real board is a second I2C bus, which Mokxi draws and does not model.