Siemens SIMATIC S7-1200 Manual page 161

A Modbus TCP client (master) must control the client-server connection with the
DISCONNECT parameter. The basic Modbus client actions are shown below.
1. Initiate a connection to a particular server (slave) IP address and IP port number
2. Initiate client transmission of a Modbus messages and receive the server responses
3. When required, initiate the disconnection of client and server to enable connection with a
Easy Book
Manual, 11/2011, A5E02486774-04
different server.
Easy to communicate between devices
7.10 PtP, USS, and Modbus communication protocols
161