Modbus on TCP/IP¶

For the standardized (Open)Modbus protocol two operating modes are distinguished. Controllers with Ethernet Communication Module can be operated as Modbus on TCP/IP client (master) as well as as server (slave). Simultaneous operation as client and server is also possible. In all operating modes, several Modbus on TCP/IP connections can be provided simultaneously. The maximum possible number of simultaneous connections is only limited by the number of available sockets. Here it has to be observed that each additional communication connection aside from Modbus on TCP/IP also requires one or more sockets.

Operation of the controller as Modbus server only requires a corresponding configuration for the Ethernet Communication Module to be set up. Operation as Modbus client furthermore requires the implementation of blocks in the user program.

Caution

The user program should not be implemented as a cyclic task (PLC_PRG) if high communication traffic is expected due to the operation as Modbus on TCP/IP client and/or server. A task configuration has to be implemented instead with the cycle time to be adjusted in a way that sufficient communication resources are available in addition to the actual processing time for the program.