Bingo!!

I've now fixed the tracing system so I can trace without a problem. I managed to single step through quite a bit of XeO3 which is a good sign. It appears to be pretty solid, I can stop/start and trace without any issue now - which is great. That means I have the core functionality now needed to progress. The current CPU and COMMS interface does have an issue however.... Single stepping on the spectrum (a 48k one at anyrate) isn't easy, and in order to make it better you really need to get the target to execute the single step so it can do it best for itself. However, getting the stub to do that takes quite a bit of memory and I dont want that, so I need to think about it a little longer....