Hi Vladimr, I was playing around a little more with your Serial Tap and note the following:
When I only connected the TX+ on your Tap the Modbus Analyzer recognizes both my Master request and my Slave's response. This is perfect and just what I wanted.

I am a little confused as to why the RX lines were not reading the data as I expected?

Thank you Vladimir, that has worked. I do have a question related to Modbus data transmitted and received:
When I attached both the RX+ and RX- between my Master and Slave devices I only receive my Slave's response and the Modbus analyzer recognizes this. When I only keep the RX+ line connected I receive both thee Masteer and Slave data strings but the Modbus Analyzer does not recognize this. Am I doing something wrong or would I need a second IONinja Serial Tap to read both Masteer and Slave strings?

I set up my serial Tap as you recommended in a previous post (RX+ and RX- on the TAP) and set up Buad rates etc to suit. Started the Snooping tool but got the Port messages above. What settings do I need to set to read both RX+ and RX- data?

I don't know where to look to set the respective ports. Port A and B?