Siemens SIMATIC S7-1200 - Page 1190

Communication processor and Modbus TCP
13.5 Modbus communication
S7-1200 Programmable controller
1190 System Manual, V4.2, 09/2016, A5E02486680-AK
Example: MB_CLIENT 4: Coordinating multiple requests
You must ensure that each individual Modbus TCP request finishes execution. The
execution sequence must be controlled by your program logic. The example below shows
how the outputs of the first and second client requests can control the execution sequence.
The example shows both clients using the same CONNECT connection data (used at
different times). The clients transfer holding register data from the same remote Modbus
TCP server to the same local CPU memory M address. Also, a returned error is captured
which is optional.
Network 1:
Modbus function 3 - Read Modbus TCP server holding register words
Network 2:
Modbus function 3 - Read Modbus TCP server holding register words