Board
Arduino Uno R4 Minima simulator, the RA4M1 running
The Uno R4 Minima is the Uno everyone buys now: the same board, the same 5 V pins, an Arm Cortex-M4 underneath. Mokxi models the Renesas RA4M1 at 48 MHz on our own core (the port block with its per-pin PFS registers, GPT PWM, SCI2 as Serial1, a fourteen-bit ADC) and says plainly where the model stops.
- 8peripheral areas modeled
- 3projects ready to run
- Real timeon your own machine
Click to open it in the editor
The board is running real firmware right now. Click it to open the circuit in the editor.
The model
What is modeled
Taken from the board's own contract document and put in plain words, with what is missing listed underneath.
Core
Arm Cortex-M4 (ARMv7E-M) at 48 MHz, with the datasheet cycle count of every instruction. Soft float: the RA4M1 has an FPU and this core does not, so the runtime is built -mfloat-abi=soft and a VFP instruction faults rather than returning a wrong number.
Pins
One PmnPFS word per pin (direction, output latch, pull-up, open drain, analog switch), behind the PWPR write protection the real part has, plus PORTn’s PDR, PODR, PIDR and set/reset pair.
Time
SysTick at 1 kHz off the 48 MHz clock: reload 47,999, a whole number of cycles, so millis does not drift. micros comes from the same counter.
PWM
GPT channels on the six tilde pins (3, 5, 6, 9, 10 and 11) at 490.0 Hz, the rate an Uno’s phase-correct pins run at.
ADC14
A fourteen-bit conversion on A0 to A5 against the 5 V rail, timed at the converter’s own rate. analogRead returns ten bits by default, as the Arduino core does; analogReadResolution asks for the rest.
SCI2
Serial1 on D0 and D1, 8N1, paced at the configured baud rate, and the pin really idles high between frames.
USB
Serial, as a byte pipe with the register names on it: the socket goes straight to the chip, as on the real board.
Memory map
The real RA4M1 addresses: 256 KB of flash at zero with the option-setting word at 0x400, and 32 KB of SRAM. The link fails if you overrun either.
Not in the model
- A USB stack. Serial is a byte pipe: no enumeration, no descriptors, no SETUP. `while (!Serial)` returns at once here and pauses for a moment on a desk.
- The ICU’s event links, and so every peripheral interrupt: there is no attachInterrupt on this board, and a sketch polls. An ICU with invented event numbers would be worse than none.
- The AGT, the clock generation circuit, the watchdogs, I2C, SPI, CAN, the DTC, the RTC, the DAC and the touch unit.
- Vendor binaries: the Renesas FSP and the Arduino R4 core. The firmware runtime here is ours.
- Some addresses are this model’s belief rather than a page of the user’s manual: the GPT and ADC14 blocks, the USB registers, and which GPT channel each PWM pin is. docs/uno-r4.md section 7 lists every one of them.
Start here
Open one and press Run
Each of these opens in the editor exactly as it is drawn here.
Projects
Every built-in project on the Uno R4
Each has its own page with the circuit running, the code and a parts list.
Libraries
Arduino libraries that compile as they are
Paste a tutorial that includes one of these and it builds: each is written for Mokxi, on its own drivers, under the name the tutorials use. For any other library the build names the Mokxi header that does the same job.
Servo.h
attach, write, writeMicroseconds, read, detach, on any pin
Wire.h
I2C as a master; Wire.begin() puts it on A4 (SDA) and A5 (SCL)
SPI.h
transfer and transactions, on the board’s usual SPI pins
EEPROM.h
read, write, update, get, put and EEPROM[i], kept in 4 KB of RAM, which a reset clears: this board has no EEPROM to write
LiquidCrystal_I2C.h
the 16x2 LCD behind its I2C backpack
Adafruit_GFX.h and Adafruit_SSD1306.h
the 128x64 I2C OLED: text, pixels, lines, rectangles, circles, triangles and bitmaps
DHT.h
the DHT11 and DHT22: temperature, humidity and the heat index, as floats you can print
OneWire.h and DallasTemperature.h
DS18B20 thermometers, any number on one pin, found by the 1-Wire search
Adafruit_BME280.h, Adafruit_BMP280.h and SparkFunBME280.h
the Bosch pressure sensors: temperature, pressure, humidity and altitude
RTClib.h
the DS3231 and DS1307 clocks, with DateTime and TimeSpan
Adafruit_SHT31.h
the SHT31’s temperature and humidity, CRC checked
LedControl.h
MAX7219 eight-digit displays and 8x8 matrices: digits, characters, rows and single LEDs
Adafruit_LEDBackpack.h
the HT16K33 four-digit backpack: numbers, raw segments, the colon, brightness and blink
Adafruit_TCS34725.h
the TCS34725’s red, green, blue and clear counts, lux and color temperature
Adafruit_SGP30.h
the SGP30’s CO2eq and TVOC, its baseline and humidity compensation
Adafruit_INA219.h
current, bus voltage and power through the INA219’s shunt
Adafruit_ADS1X15.h
the ADS1115’s four sixteen-bit inputs, single or differential
Adafruit_MCP23X17.h
the MCP23017’s sixteen pins, one at a time or a port at once
HX711.h
the HX711 load cell amplifier: tare, set_scale and get_units, the units as floats you can print
Questions
Is it free?
Yes. Every board and every part is on the free plan, with no account needed.
Which Uno R4 is this?
The Minima, the one with the USB-C socket and no WiFi. The Uno R4 WiFi has a page of its own: the same chip with an LED matrix and a simulated network.
How is it different from an Uno R3?
Same shape, same 5 V pins, same shield header. Underneath it is an Arm Cortex-M4 at 48 MHz rather than an 8-bit AVR at 16: more flash, more RAM, a fourteen-bit ADC, and Serial on the USB rather than on pins 0 and 1.
Why does analogRead give me 0 to 1023 when the ADC is fourteen bits?
Because that is what the Arduino core does, so a sketch written for an Uno reads the same numbers. Call analogReadResolution(14) and you get 0 to 16383; the register always held all fourteen.
Is Serial the same as Serial1?
No, and that is the R4. Serial is the USB socket and reaches no header pin. Serial1 is SCI2, a real UART on D0 and D1. Both show up in the monitor here; only Serial1 moves a pin.
Can I use attachInterrupt?
Not on this board. The RA4M1 routes a peripheral event to an interrupt through the ICU, and this model does not implement the ICU rather than guess at its event numbers. Poll the pin instead.
Will my firmware run on a real Uno R4?
The core, the pins, the port registers and SCI are the real ones. The GPT and ADC addresses, the USB registers and the PWM pin-to-channel map are marked unverified in docs/uno-r4.md section 7. Check that list first, and it is a short one.
Also here
The other boards
Every one of these runs today, and every one is free.
Looking for the shorter introduction? See the Arduino Uno R4 simulator page.
ESP32-C3-DevKitM-1
runs nowA RISC-V core at 160 MHz with GPIO, UART, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 4 and LEDC PWM on any pin, on the real memory map.
Firmware for the modeled peripherals uses the board’s memory map. The contract also marks register addresses inside the SAR ADC and LEDC that are still unverified.
Open the board page
Arduino Uno R3
runs nowA complete ATmega328P, with three timers in every mode, USART0, the ADC, interrupts and sleep.
Blink, serial, a held button and a hardware PWM fade, at 16 MHz and real time.
Open the board page
Arduino Nano
runs nowThe Uno's ATmega328P on a board 45 by 18 mm, so it pushes into the breadboard instead of standing beside it.
Two more analog inputs than an Uno, and the same firmware runs on both.
Open the board page
Arduino Mega 2560
runs nowThe big Arduino: fifty-four digital pins, sixteen analog inputs and four serial ports, on the ATmega2560.
Everything an Uno sketch knows how to do, with enough pins left over to do it to twelve things at once.
Open the board page
Arduino Leonardo
runs nowAn Uno-shaped board whose USB goes to the chip itself: Serial is a USB CDC endpoint and Serial1 is pins 0 and 1.
The ATmega32U4 with its ten-bit timer, fourteen ADC channels and five external interrupts, at 16 MHz.
Open the board page
ESP32-C6-DevKitC-1
runs nowA second RISC-V board: thirty-one GPIOs, 512 KB of SRAM in one window, UART0, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 6 and LEDC PWM on any pin.
The contract says plainly which addresses come from the manual, which are believed rather than verified, and what is not modeled at all.
Open the board page
ESP32 DevKit V1
runs nowThe classic ESP32 on an Xtensa LX6 at 240 MHz: the GPIO matrix, UART0, timer group 0, a twelve-bit ADC1 and the eight LEDC PWM channels, on the real memory map.
One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab.
Open the board page
ESP32-S3-DevKitC-1
runs nowThe ESP32-S3 on an Xtensa LX7 at 240 MHz: GPIO matrix, UART0, USB serial, ADC1, LEDC PWM and the RMT driving the RGB LED, on the real memory map.
One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab.
Open the board page
ESP8266 NodeMCU V1.0
runs nowThe Xtensa LX106 at 80 MHz in the call0 ABI, with D0 to D8 that are not GPIO numbers, two active-low LEDs, and PWM done in software because the chip has none.
WiFi uses a simulated network, with no radio or real internet. The ADC is the one block whose registers are this model’s own, because Espressif never published the chip’s.
Open the board page
Raspberry Pi Pico
runs nowRP2040 on our own ARMv6-M core, with SIO GPIO, the 1 MHz timer and alarms, UART0 and eight PWM slices.
Blink, a button, serial and a fade at real time, with sleep parked on WFI.
Open the board page
Raspberry Pi Pico W
runs nowThe same RP2040 and the same forty pins as the Pico, so the same ELF runs on it.
The CYW43439 is not modeled. WiFi uses a simulated network, and the on-board LED is driven through the board runtime rather than GP25.
Open the board page
Seeed XIAO SAMD21
runs nowA thumbnail-sized Cortex-M0+ at 48 MHz: eleven pads, every one of them an analog input, with PWM on ten of them.
Serial is the chip’s own USB, modeled as a byte pipe with no stack above it, and Serial1 is a real USART on D6 and D7.
Open the board page
BBC micro:bit V2
runs nowThe nRF52833 on our own Cortex-M4 core at 64 MHz, with GPIO, GPIOTE, three TIMERs, RTC0 and UARTE0 on the real register map.
The 5x5 LED matrix scanned as the hardware scans it, buttons A and B, the speaker and three rings on the edge connector.
Open the board page
ATtiny85
runs nowA whole microcontroller in an 8-pin DIP, straight into the breadboard: six I/O, two timers, an ADC and a USI.
Blink, a button on INT0, a knob on the ADC and a serial port it bit-bangs for itself.
Open the board page
STM32F411 Black Pill
runs nowCortex-M4 with Thumb-2, NVIC and SysTick at 84 MHz, with GPIO, TIM2 to TIM5 and USART1 on the real register map.
Blink on PC13, a button, serial and a PWM fade, all at real time.
Open the board page
STM32 Blue Pill (F103)
runs nowCortex-M3 at 72 MHz, with GPIO on the F1’s CRL and CRH, TIM1 to TIM4, USART1 and a twelve-bit ADC.
Blink on PC13, a button, serial with a live reading, and a PWM fade, all at real time.
Open the board page
Arduino Pro Mini
runs nowThe Uno’s ATmega328P on the smallest Arduino there is, with no USB on it, in both builds: 5 V at 16 MHz and 3.3 V at 8 MHz.
The 3.3 V board really runs at 8 MHz, so a sketch built for 16 MHz keeps half time on it, as it does on the bench.
Open the board page
Arduino Micro
runs nowThe Leonardo’s ATmega32U4 on a board that pushes into a breadboard, with the L LED on pin 13 and the SPI pins on holes of their own.
Serial is the chip’s own USB and Serial1 is pins 0 and 1, and the Leonardo’s programs run on it unchanged.
Open the board page
SparkFun Pro Micro
runs nowThe ATmega32U4 in a Pro Mini’s footprint with a USB socket on the end, running the Leonardo’s programs.
No LED on pin 13: its lamps are RX and TX, lit by pulling their pins low.
Open the board page
Wemos D1 mini
runs nowThe NodeMCU’s ESP8266 on a board a third the size, with the same D0 to D8 names and only the holes that do something.
WiFi on a simulated network, and your own sketch compiles in the tab.
Open the board page
ESP-01S
runs nowAn ESP8266 with eight pins, four of them GPIO, and a blue LED that lights when its pin is low.
Wired with jumpers, because its two rows will not sit in a breadboard. WiFi is simulated.
Open the board page
Seeed XIAO ESP32-C3
runs nowThe ESP32-C3 at 160 MHz on the XIAO’s thumbnail outline: fourteen pads, and D0 to D10 that are the XIAO’s numbers, not GPIOs.
No user LED to blink, WiFi on a simulated network, and sketches that compile in the tab.
Open the board page
ESP32-C3 SuperMini
runs nowThe smallest ESP32-C3 board in common use, sixteen pins named by GPIO, at 160 MHz.
Its blue LED on GPIO 8 lights when the pin is LOW, the other way around from the DevKit’s.
Open the board page
Arduino Uno R4 WiFi
runs nowThe Uno R4’s RA4M1 with a 12 x 8 LED matrix to draw on through Arduino_LED_Matrix.h.
WiFi through WiFiS3.h on a simulated network: no radio, no ESP32-S3 in the model, no real internet.
Open the board page
Try it on your own firmware
What you build here runs on the board on your desk, unchanged. Nothing to install and no account needed.