Aaah - I think I'm getting it now. I have a reasonably working bit of code - though I still need to understand how the switches work. I will try and get a test rig up over the weekend.

Incidentally, the original design for this board had two PICs, driving the two motors which direct the two axes. This was easy, since they do not need to work together. I am now thinking about automatic box pattern searches, which will need two motors to work in tandem.

This will be quite easy if one PIC can signal the other PIC to make its motor take a step. Is there any electrical reason why this should not be arranged by connecting a one of the RB output pins on the first PIC to an RA input pin on the second PIC? Then holding this pin high would be the equivalent of pressing an input button on the second PIC. Or is this not the way to do it...?