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Modbus TCP communication between two S7-1200 CPUs is presented. The instructions “MB_CLIENT” and “MB_SERVER” are called and parameterized in the user program of the S7-1200 CPU.
The “MB_CLIENT” instruction communicates as Modbus TCP client over the PROFINET onnection of the S7-1200 You do not need any additional hardware to use the instruction. You use the “MB_CLIENT” instruction to establish a connection between the client and the server, send requests and receive responses, and control the connection disconnection of the Modbus TCP server.
The “MB_SERVER” instruction communicates as Modbus TCP server over the PROFINET connection of the S7-1200 You do not need any additional hardware to use the instruction. The “MB_SERVER” instruction processes connection requests of a Modbus TCP client, receives requests from Modbus functions and sends response messages.
In this example 2 Modbus functions are presented. For each Modbus function a Modbus TCP connection is established over a Modbus block pair (MB_CLIENT and MB_SERVER).
Figure 1-1 shows an overview of the Modbus functions presented in this example and the Modbus block pair assignment
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