I don't think there's any problem getting this sorted.. The non-sat-nav unit has a spare serial port available.. It's the sat-nav unit (which I'm keeping in my car, if the new maps work - and they have now landed!) that I'm going to have to pull the proverbial rabbit out of my dark hole which is the problem.
I've refined things a little - 8 lines each side. Double buffered surfaces, so there is absolutely no flicker at all now.
I also have a plan to multiplex the sat-nav serial port into two with special packet identifiers (that there's no way the sat-nav would ever send over serial). Well, it's a plan
