I am working on a Large Machine with alot of TCP/Modbus I/O. I had to track alot of info on what was what, and where it went and what it did.
So, I made a MS Word TCP Output Mapping document and a TCP Input Mapping document. Both are set up as tables and are editable for your use. Just Change the information at the Top to reflect your situation. The one I put up is for using 2 PLC's one for input and one for output.
The system shows the flow of data going in to mach and out from mach, as it travels to and from: The PLC, Mod Bus, Brains, Macropump (if applicable), Functional discription, and Data/Target Page.
It could easily be adapted for Serial Modbus, or just "Record keeping" on your systems I/O.
they are attached as a Zip called: TCP_IO.zip
Scott