enso wrote:
More likely a power distribution problem, possibly decoupling... Can you scope a few places, preferrably recording a lot of samples?
A noisy circuit that just barely works at 5.1V can stop working at 5.0V if the noise pokes through the floor... I think there is a bad spike when compact flash turns on (I seem to remember having to decouple a lot; one of my CF interfaces just never worked)...
I recently designed an adapter for my C02 Pocket SBC, which provides 16-bit access for Compact Flash and a DS1511Y RTC. Certain CF cards were (and still are) problematic... so I finally limited my interface for using authentic SanDisk cards (Note: there are a lot of remarked CF Cards which aren't true SanDisk). I also redesigned the PCB and added additional decoupling and filtering for the CF Card. Since then, it's been flawless (have 3 systems operating now) running my own test programs and using the newer ROM version of DOS/65 (supports CP/M disk formats). I still need to clean up some test code for the CF Card interface, but the last BIOS update appears to be very solid. I would also note that Bill (Plasmo here) found similar problems much earlier than I did and also came up with some clever ideas to help resolve the problems.
Back to regular programming now....