5201-DFNT-DH485 & WinCC (Tia Portal) Communication

Hi, if someone can help I would be very thankful.

I'm having some trouble trying to connect a Siemens MP377 19" Touch with a Prosoft 5201-DFNT-DH485 module. This module connects to an AB SLC503. The goal is to see the module's variables (and manipulate them) within the MP377.
Right now we are making tests with the communication between just the MP377 and the DFNT module. We have tried via OPC, but through Tia Portal we can't 'see' in the net the RSLinx OPC server.
The module works, because we have successfully connected it through RSLinx OPC Server, and the MP377 works fine too. The problem is the communication between both of them.
I appreciate any help!
Thanks,

Freddy

I forgot to mention, the connection between the MP377 and the module is via Ethernet. The RSLinx OPC Server is in a remote PC (connected to the DFNT module via DH485). Everything is connected via Ethernet to a switch with good addressing (all in the same net).
Thanks.