Documentation

Comprehensive guide to Modbus protocols and how to use our tools

What is Modbus?

Understanding the Modbus protocol

Modbus is a serial communication protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). It has become a de facto standard communication protocol in industrial manufacturing environments.

Modbus is widely used to connect industrial electronic devices across various industries, including manufacturing, energy, building automation, and more. The protocol is simple, robust, and openly published, making it one of the most popular industrial protocols in use today.

Key Features

Open protocol with no licensing fees
Simple implementation and easy to maintain
Supports multiple physical layers (RS-232, RS-485, Ethernet)
Master-slave or client-server architecture
Wide industry adoption and support

Modbus Variants

Three main implementations of Modbus

Modbus RTU

Remote Terminal Unit variant uses binary encoding and CRC error checking. Typically transmitted over RS-232 or RS-485 serial connections. Most compact and efficient for bandwidth-limited applications.

Modbus TCP

Modbus encapsulated in TCP/IP packets for transmission over Ethernet networks. Uses MBAP (Modbus Application Protocol) header. Standard port is 502. Most common in modern industrial applications.

Modbus ASCII

Uses ASCII characters for message encoding with LRC (Longitudinal Redundancy Check) for error detection. Less efficient than RTU but easier to debug and troubleshoot visually.