I moved the RC80B over to com1 so I could set the port speed and now have communication with the Thermostat. However the temp in the plugin stays at -48, the temp on the RC80 is correct. I get a lot of Timeout messages to / from the thermostat. I see a few posts with the same symptoms but all of those appear resolved. Odd enough disabling the backlight did appear to decrease the number of timeout messages. Any idea's?

As always it turns out to be my stupid mistake - I'm surprised it worked at all - I was looking at the pin out wrong on the DB9