Siemens SIMATIC S7 Manual page 17

Unspecified
Connection with
"CP is server"
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
If you have got a communication with CP as MODBUS server, the
communication is set up as "unspecified connection". The client must carry
out active connection establishment.
After selecting Insert
connection" will come up.
Select here "unspecified" instead of the communication partner and use
"TCP Connection" for the connection. Put a check mark on "Show properties
dialog"
New Connection... the dialog box "Insert new
Commissioning
3-7