Hi Darrel
I changed the bit of maths and hey presto the programme instantly came good. It is cycle accurate all the way up. I'm really pleased...so many thanks. Now I'll get back to studying your programme to see how it works. The bit that is confusing is adding the reload value to the timer value - I didn't realise it then subtracted the timer value to the point of reset. You did this using ASM. Presumably this could also be done in PBP?
Regards Adrian