The Modbus protocol is originally used in the industrial automation sector. It is based on a client/server architecture. It was developed by Gould-Modicon in 1979 for communication between its programmable logic controllers.
Using Modbus, a client ( previously known as a master) and several servers (e.g. measurement and control systems; previously known as slaves) can be connected. With Modbus, data is addressed via so-called registers, which represent a bit or a word (16 bits). There are two types of Modbus: A serial interface and one for Ethernet/IP.
Modbus RTU (RTU: Remote Terminal Unit) transfers the data in a binary form via twisted pair to the RS-485 specification. Modbus TCP is very similar to the Modbus RTU protocol. Essentially, the services and data that are familiar with RTU are transmitted almost unchanged via a TCP/IP connection. Port 502 is used for Modbus TCP.
Modbus has become a de facto standard in the industrial sector. In building technology, Modbus is also used in numerous building services. While Modbus RTU was initially used primarily in the fields of heating, air conditioning and ventilation, Modbus TCP has established itself as the standard for the control of PV inverters or vehicle charging stations.
In order to be able to connect these devices to KNX, Weinzierl offers gateways with high integration for both Modbus types, which allow Modbus data to be transformed into KNX-compatible data point types: