What is Modbus RTU? A Beginner's Guide

Modbus RTU (Remote Terminal Unit) is one of the most widely used industrial communication protocols. It was developed by Modicon (now Schneider Electric) in 1979 and has since become an industry standard.

How Modbus RTU Works

Modbus RTU operates over serial communication, typically RS485. It uses a master-slave architecture where one master device communicates with up to 247 slave devices on the same network.

Each message contains:

Slave Address: Identifies the target device

Function Code: Specifies the operation (read, write, etc.)

Data: The actual data payload

CRC: Error checking

Common Function Codes

01: Read Coils

02: Read Discrete Inputs

03: Read Holding Registers

04: Read Input Registers

05: Write Single Coil

06: Write Single Register

Why Modbus RTU is Still Relevant

Despite being decades old, Modbus RTU remains popular because:

It's simple and easy to implement

Works reliably over long distances (up to 1200m)

Supported by virtually all industrial equipment

Royalty-free and open standard

Getting Started with PAOLU DADA

The M1 Modbus Explorer makes it easy to work with Modbus RTU. It's a portable Modbus master tool with an intuitive display and MQTT connectivity.