Glossary · Modbus
What is Modbus protocol?
A simple, open industrial protocol dating from 1979: a client asks, servers answer from numbered registers. It runs over RS485 (RTU) or Ethernet (TCP).
Data comes in four types: coils and discrete inputs for bits, holding and input registers for 16-bit words. A Float32 value takes two registers.
The usual problems are a duplicate address, the wrong word order, or a CRC error. The workshop’s Modbus toolkit computes the CRC and decodes floats in every order.
Related terms
- MQTT protocol
- A lightweight publish/subscribe messaging protocol through a broker, ideal for carrying sensor data from remote sites to a server.
- SCADA
- Supervisory control and data acquisition: collects readings from distributed controllers and sensors, presents them to operators, and manages alarms, commands and history.
- HART protocol
- A digital protocol carried on top of the 4-20 mA signal itself, allowing transmitter configuration, reading and diagnostics without interrupting the analogue measurement.