What is Modbus?

Understand what Modbus is and why every industrial engineer needs to know it.

Modbus is a serial communication protocol invented in 1979 by Modicon. Today it is the most widely deployed protocol in industrial automation — you'll find it in PLCs, energy meters, temperature controllers, VFDs, and thousands of other devices.

The protocol is simple by design: one device asks a question (a request), and one device answers (a response). There are no subscriptions, no handshakes, and no background traffic — just request and response.

Modbus comes in two physical flavors: • Modbus RTU — runs over RS-485 or RS-232 serial cable. Bytes are binary. Fast and compact. • Modbus TCP/IP — runs over Ethernet. The same PDU (protocol data unit) is wrapped in a TCP packet. No CRC needed — TCP handles that.

This tutorial uses a simulated Modbus bus in your browser. Every request and response is real Modbus — just without a cable. The hex bytes you see are exactly what a real device would send.