Non-interrupt use of uPD765/8272

That would make a lot of sense. IIRC the Z80-PIO can produce a Z80-style vectored interrupt on change of state of some of the inputs. Another favourite trick was to use a spare channel on a Z80-CTC, pre-loaded with 1, so that on the first clock pulse (i.e. the IRQ singnal from some other IC) it decrements ot 0 and genereates a Z80 interrupt. How hard would it be to trace out the scheamtic sof this board? My experience is that it is often quicker and less frustrating to do the lot than to attempt to see what happens to one signal. When tracign the complete scheamtic, you can often 'eliminate' large numbers of ICs -- teven TTL gages, etc, to things like the adress decoder, laving only a few parts that are invovled with mystey signals. [...] Some years ago I wrote a program in Turbo Pascal that directly drove the PC flopppy controller. I found it much easier to use a trivial interrupt handler (I think it just set a boolean variable) than to figure out if there was a way round it. -tony