How to Set Up Modbus RTU Communication on an ESP32 with RS-485

A new tutorial published on DEV Community guides developers through implementing Modbus RTU master communication on an ESP32 microcontroller using an RS-485 bus. Modbus RTU is a widely used industrial protocol dating back to 1979, enabling one master device to poll up to 247 slave devices such as energy meters, PLCs, and temperature transmitters. The guide covers hardware wiring, including the need for a TTL-to-RS-485 transceiver like the MAX485 to bridge the ESP32's 3.3V logic to the differential RS-485 signal, or alternatively using an industrial ESP32 board with a built-in transceiver. It also explains the four Modbus register types — coils, discrete inputs, input registers, and holding registers — and their respective uses. The tutorial concludes with library installation steps and sample Arduino code that polls holding registers from a slave device every half-second and prints results to the serial monitor.