The Modbus protocol is a communications protocol based on a master/slave or client/server architecture. It is an open protocol, which was developed by Gould-Modicon in 1979 for communication between programmable logic controllers.
The Modbus TCP version has been part of the standard IEC 61158 since 2007.
Structure of a Modbus network
The Modbus protocol was originally developed for serial communication between devices. One master and multiple slaves can be connected in a Modbus network.
A distinction is made between three operating modes:
- Modbus ASCII
- Modbus RTU
- Modbus TCP
Each subscriber has a unique address, whereby the address 0 is reserved for broadcast. The subscribers send their messages via the bus.
The following product groups have a Modbus interface:
Configurable safety system PNOZmulti - Communication modules
Configurable small control system PNOZmulti Mini - Communication modules
Configurable control system PNOZmulti 2 - Communication module
Control systems PSSuniversal PLC and PSSuniversal multi