Hi JoakimGoin,

For understanding of the OPC communication you could take a look at the sample program for SET30

https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&objId=39863979&nodeid4=20229805&load=content&lang=en&siteid=cseus&aktprim=4&objaction=csview&extranet=standard&viewreg=WW

This example is with the use of wincc runtime advanced but the send and receive from PLC to the TCSB is the same. (if you have the “simatic net tools” than you can use OPC scout to see if the data is coming in to the OPC server )

The demo also includes a manual where you can see how the communication is working.

Before you can use TC_send and recv you need to use TC_CON to set up a connection to the server. IP address of the server need to be set in the HW config of the CP-1242-7 (Telecontrol interface -> Operating mode -> Telecontrol server (Name of IP address))

TC_send and recv are to me not really sending and receiving the data but they are more like putting and getting the data from the CP1242-7 Process image.