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Modbus

A serial communication protocol standard for industrial automation.

Definition

Modbus is a serial communication protocol originally published by Modicon in 1979 for use with its programmable logic controllers (PLCs). It has become the de-facto standard data bus in industrial automation, connecting sensors, meters, drives, and SCADA systems. Modbus is simple, openly published, and requires no licensing fee, which explains its enduring popularity more than 40 years after introduction.

Quick Facts

Published1979 by Modicon
VariantsRTU, ASCII, TCP
Default port (TCP)502
Max devices (RTU)247 slaves

Related Terms

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ModPackQT Modbus Glossary · Updated 2026