MCU Quickstart

Audience: users who want to move from the host-side examples to actual MCU firmware.

This page points to the real-UART read-only samples for RP2040, ESP32-C3, and Arduino Mega 2560.

What The Sample Does

The sample:

• configures MelsecSerialClient with the sample's own default UART / protocol settings
• opens the board-specific UART entry used by the sample
• sends the client's pending_tx_frame()
• calls notify_tx_complete() after flush()
• feeds incoming UART bytes into on_rx_bytes()
• performs a read-only batch read of D100-D103

Those settings are intentionally simple sample defaults. They are not the authority for the current validated settings of every target. Before wiring real hardware, check HARDWARE_VALIDATION.md.

Sample source:

• ../../examples/platformio_rpipico_arduino_uart/platformio_rpipico_arduino_uart.cpp
• ../../examples/platformio_esp32c3_arduino_uart/platformio_esp32c3_arduino_uart.cpp
• ../../examples/platformio_arduino_mega2560_uart/platformio_arduino_mega2560_uart.cpp

Build

pio run -e rpipico-arduino-uart-example
pio run -e esp32-c3-devkitm-1-uart-example
pio run -e mega2560-arduino-uart-example

Default Sample Settings

• Serial: 19200 / 8E1
• Protocol: 4C ASCII Format4
• Terminator: CR/LF
• Sum check: off
• Station: 0
• Read-only device range: D100-D103

Use this section only to understand what the sample code does by default.

For exact validated target settings, use ../validation/reports/HARDWARE_VALIDATION.md.

The board environments also define default UART pins:

• rpipico-arduino-uart-example
  • TX=0
  • RX=1
• esp32-c3-devkitm-1-uart-example
  • TX=7
  • RX=6
• mega2560-arduino-uart-example
  • TX1=18
  • RX1=19

Treat these as starting values. Change them to match your actual board wiring.

Integration Notes

The sample is intentionally simple.

• Pico and ESP32-C3 samples use Serial for debug output and Serial1 for the PLC line.
• Mega 2560 uses Serial for debug output and Serial1 for the PLC line.
• It treats flush() as the TX completion point.
• It reads only, so it is safe to use during initial wiring bring-up.

In a production firmware port you may replace flush() with:

• TX complete interrupt
• DMA completion callback
• scheduler event when the UART peripheral finishes transmission

Recommended Sequence

1. Confirm the target settings in HARDWARE_VALIDATION.md.
2. Wire the MCU through a TTL <-> RS-232C level shifter.
3. Build the matching PlatformIO UART example.
4. Confirm a read-only D range works from the MCU.
5. Only then add write operations.