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PROTOCOLS · BASICS

What Is Modbus?

Modbus is an open communication protocol that lets industrial devices such as PLCs, sensors, meters, drives and HMIs exchange data. First published by Modicon in 1979, it uses a simple request and response model: one device asks for or writes values, and another replies. It runs over serial lines as Modbus RTU and over Ethernet as Modbus TCP.

01

The Short Answer

Modbus organises data into four simple tables: coils and discrete inputs for on/off values, and input and holding registers for numbers such as temperatures, speeds and setpoints. A client sends a function code, such as read holding registers, with an address, and the server replies with the values. That simplicity is why almost every industrial device supports it.

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    Open and free No license fees, so it is built into equipment from many manufacturers.
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    Simple to implement A small set of function codes covers most reading and writing.
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    Runs on serial and Ethernet RS-485 for field devices, TCP/IP for networks and SCADA.
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    Easy to bridge Gateways and edge computers translate Modbus to cloud and IT protocols.
02

Why It Matters

Our Modbus RTU vs Modbus TCP FAQ compares the two main variants, and our RS-485 FAQ explains the serial link. Edge AI systems often read Modbus data through an IIoT gateway; see our industrial IoT gateways and the supermarket HMI case study.