Hi John,
What you're wanting to do depends entirely on the OPC Server, RSLInx in this case. You will have to check if RSLinx allows you to define a single Item that in reality is looking at two consecutive registers on the PLC.
If such items can be configured, the OPC Client will just read the data as a single Tag. I am guessing you're using DSC. You browse to this Item in RSLinx from the TCE and create a Tag for it.
If RSLinx doesn't support this, then one crude way would be to read the two items individually into two tags and then build a single value in your diagram and write it back to a Memory Tag to get a single Tag.
Hope this helps,
Khalid
