Modbus

Modbus is a simple, open industrial communication protocol that lets controllers and field devices exchange data using a request-response model. Originally serial (Modbus RTU and ASCII) and later extended to TCP/IP, it remains one of the most widely supported protocols in automation.

Modbus organises device data into registers and coils that a master polls from one or more slaves. Its simplicity, openness, and minimal overhead made it a de facto standard for connecting PLCs, drives, meters, and sensors. Modbus matters because nearly every industrial device supports it, making it a reliable lingua franca for integration, though it lacks built-in security and deterministic timing, so it is often used alongside more capable industrial Ethernet protocols.