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Modbus is a communication protocol that connects industrial equipment to control systems and data platforms. A factory’s energy meter speaks Modbus. The IoT gateway reads the meter’s registers over an RS485 cable every minute and sends the data to a cloud dashboard. That is a typical Modbus deployment.
Modbus was published in 1979 and remains the most deployed industrial protocol globally because it is simple, open, and supported by almost every piece of industrial hardware ever made.
- Modbus RTU – binary encoding over RS485 wiring, the standard field implementation
- Modbus TCP – the same protocol framed over Ethernet and TCP/IP
- Master-slave – one master device polls multiple slave devices on the same bus
- Register types – coils (digital output), discrete inputs (digital input), holding registers (16-bit read/write), input registers (16-bit read)
- RS485 bus – supports 32 devices on a single two-wire cable up to 1,200 metres