Thursday, 30 July 2009

IM2 interrupts not working!

I tried getting vectored interrupts working last night but after several bleary eyed hours in the early morning realised it was not my dodgy software but my even dodgier hardware!

I'd not realised that the Z80 doesn't assert /RD during an interrupt acknowledge cycle, meaning that the buffers are not allowing through D[0..7] to the processor. This was confirmed by rewriting the software to work from one vector at I*256+0HFF which worked (all lines are pulled high when /RD and /WR are not asserted)

Tonight I'll try changing the buffering arrangement to work solely on /WR....

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