Hi Robin,
The UNO is connected to the PI via I/O pins which are marked for TX/RX so they are (should be) hardware UARTS. Currently getting the serial port (of any type) on the PI to work is a bit of a mystery and requires changing a number of config files etc. I know I got through that part because it does communicate (most of the time).
I will dig around and find something to use with a PC and do some further experimenting. I have another UNO on order as a back-up so I could use that too. I also have a logic analyzer around here somewhere. Have not used it in years but that should allow me to see what the signals are actually sending.
I suspect this could be hardware related as well. Once I get the new UNO and PI back-ups, I am going to run the same tests and trials on them to see if they behave differently.
Thank you very much for all your help and assistance on this crazy problem. Thanks also for your patience!
It will probably be a couple of weeks before I can try all these other things. If I find anything that is conclusive I will report back here with the details.
Thanks again!
Chris D