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Arduino Uno R3

The classic 5 V board (A000066): ATmega328P at 16 MHz, 32 KB flash, 2 KB SRAM, an ATmega16U2 USB-serial bridge on the USB-B port, and the shield headers every other board copies. On LabWired the Uno runs real Arduino-core firmware on the AVR8 interpreter, with all three I/O ports, USART0, SPI, I2C and the ADC reaching the canvas.

Live status

The tables below are a maintained snapshot. Authoritative automation:

Uno R3 top view: USB-B and DC jack on the left, digital header along the top, power and analog headers along the bottom, ATmega328P DIP-28 lower right

Status at a glance

Aspect Status
Chip descriptor configs/chips/atmega328p.yaml
System YAML configs/systems/arduino-uno.yaml
Examples examples/arduino-uno-blinky/ (smoke) · examples/arduino-uno-io/ (every port)
Playground board id arduino-uno
Hosted compile Arduino (PlatformIO uno) and Rust (avr-none, atmega328p)
Tier (snapshot) L1 smoke. Datasheet-derived. No silicon capture yet.

The Nano (configs/systems/arduino-nano.yaml) is the same chip in the TQFP package, which adds ADC6/ADC7. Everything on this page applies to it except the header layout.

Flash / firmware artifact

Use Artifact Notes
Twin / CLI ELF from avr-gcc Loaded at flash address 0. No bootloader runs.
Bench HEX through the Optiboot bootloader avrdude -c arduino -p m328p -b 115200 -P <port> -U flash:w:firmware.hex
Playground Hosted compile, board arduino-uno Browser flashing to a physical Uno is not wired.

Twin vs USB cable

On the Uno the USB-B cable is not native USB. The 16U2 bridges it to USART0 on D0/D1, so the serial pane and the Serial Monitor carry the same bytes.

Twin USB-B cable
Console USART0 TX, captured as the serial pane 16U2 USB CDC, same USART0 bytes
LED L board_io LED on PB5 (D13) Yellow LED on D13
Load ELF at address 0 HEX over Optiboot at 115200 baud

Pins

Uno R3 pinout: Arduino pin numbers, AVR port bits and alternate functions for every header pin

Open the pinout full size to read the tags.

Header silk and functions from ArduinoCore-avr variants/standard/pins_arduino.h and the ATmega328P datasheet.

Digital header (top, left to right)

Silk Arduino AVR Functions
(none) SCL PC5 I2C SCL. Same copper as A5.
(none) SDA PC4 I2C SDA. Same copper as A4.
AREF AREF — ADC external reference
GND GND —
13 D13 PB5 SPI SCK, LED L
12 D12 PB4 SPI MISO
~11 D11 PB3 PWM (OC2A), SPI MOSI
~10 D10 PB2 PWM (OC1B), SPI SS
~9 D9 PB1 PWM (OC1A)
8 D8 PB0
7 D7 PD7
~6 D6 PD6 PWM (OC0A)
~5 D5 PD5 PWM (OC0B)
4 D4 PD4
~3 D3 PD3 PWM (OC2B), INT1
2 D2 PD2 INT0
TX→1 D1 PD1 USART0 TX
RX←0 D0 PD0 USART0 RX

Power and analog headers (bottom, left to right)

Silk Arduino AVR Functions
(none) NC — Not connected
IOREF IOREF — 5 V I/O reference for shields
RESET RESET PC6 Active-low reset
3.3V 3V3 — 3.3 V output
5V 5V —
GND GND — Two pins
Vin VIN — 7-12 V input, shared with the DC jack
A0 A0 PC0 ADC0
A1 A1 PC1 ADC1
A2 A2 PC2 ADC2
A3 A3 PC3 ADC3
A4 A4 PC4 ADC4, I2C SDA
A5 A5 PC5 ADC5, I2C SCL

In the Playground, every pin in the atmega328p pin bank is a wire target: D0-D13, A0-A5, AREF, 5V, 3V3, VIN and GND. SCL, SDA, IOREF, RESET, NC and the second GND are drawn as sockets but carry no wire of their own.

Support matrix

Mark Meaning
✅ Modeled well enough for the demos we ship
⚠️ Present but partial, or easy to misuse
❌ Not simulated. Use the bench.
Block Twin Notes
AVR8 instruction set ✅ Arduino-core sketches run. An unknown opcode faults instead of being skipped.
Flash 32 KB / SRAM 2 KB ✅
GPIO ports B, C, D (D0-D13, A0-A5) ✅ Outputs reach canvas LEDs; buttons reach digitalRead.
INPUT_PULLUP with nothing wired ⚠️ Reads LOW. A canvas button supplies the released HIGH level.
Timer0 overflow (millis, delay, micros) ✅
Timer0 compare outputs, Timer1 ❌ analogWrite PWM and the Servo library do not drive their pins.
Timer2 normal and CTC (tone, noTone) ✅ Compare-match A/B and overflow interrupts, with Timer2's prescalers. OC2A/OC2B PWM outputs are not driven, so analogWrite on D3 and D11 still does not.
USART0 TX (Serial.print) ✅ Transmit completes immediately.
USART0 RX (Serial.read) ✅ UDR0 returns what a peer on usart0 sends or the host injects; RXC0 and the RX-complete interrupt work. A peer is an RS-485 transceiver with its slaves, or a UART device. No framing, parity or overrun errors.
SPI master ✅ With devices attached from the parts catalog.
I2C (TWI) master ✅ With devices attached from the parts catalog. ACK/NACK status codes follow the datasheet.
SPI / I2C slave mode ❌
ADC, channels A0-A5 ✅ Converts the millivolts a canvas analog part drives. Unconnected channels read 512.
ADC bandgap (1.1 V) and REFS ✅ AREF is taken as 5 V; the internal 1.1 V reference is modeled.
ADC conversion time ⚠️ A conversion completes as soon as ADSC is set.
ADC temperature sensor ❌ Reads 0.
External interrupts INT0/INT1, pin change ❌ attachInterrupt never fires.
EEPROM ❌ No EECR/EEDR model and no persistence.
Watchdog ❌
SLEEP ⚠️ Treated as a no-op. The CPU does not stop.
ATmega16U2 USB bridge ⚠️ Not modeled as a chip. Its effect, USART0 on the cable, is what the serial pane shows.
Potentiometer part on a 5 V board ⚠️ The part model runs from a 3.3 V rail, so full travel reads about 675. Wire its top leg to 3.3V on the bench to match.

What it catches vs bench

Sim is strong for: sketch logic and state machines; digital I/O on every header pin; millis-based timing; Serial output; SPI and I2C driver bring-up against catalog parts; analogRead against a knob or sensor; deterministic CI runs.

Still use the bench for: PWM (analogWrite) and the Servo library; interrupts on pins; serial input; EEPROM; power, brown-out and analog accuracy; the bootloader and USB enumeration.

How to run

CLI (oracle / CI)

cargo run -q -p labwired-cli -- test \
  --script examples/arduino-uno-blinky/io-smoke.yaml \
  --no-uart-stdout

cargo run -q -p labwired-cli -- test \
  --script examples/arduino-uno-io/io-smoke.yaml \
  --no-uart-stdout

AVR firmware runs through its system manifest, which is what test --script does.

Playground

  1. Open app.labwired.com.
  2. Board: Arduino Uno R3 (ATmega328P).
  3. Write or paste a sketch, then Run.
  4. Assert on GPIO, Serial and analog inputs, not on ❌ rows.

Agent (MCP)

  1. Connect MCP.
  2. labwired_describe → arduino-uno or atmega328p.
  3. labwired_compile → labwired_run → labwired_verify.
Path What
configs/systems/arduino-uno.yaml Board manifest
examples/arduino-uno-blinky Blink and Serial smoke, board docs pack, images
examples/arduino-uno-io Button on D2, LED on D7, potentiometer on A0
crates/core/tests/avr_uno_io.rs Drives each port from outside and checks what the sketch prints
Arduino Nano Same chip, TQFP package