Sam Laur wrote: > There are a few different possible scenarios. The worst is that > the whole chip gets fried either due to latch-up or if the static > charge is large enough to destroy other stuff besides the I/Os. The strangest failure mode I ever saw (two times!) is a leakage current on one or more of the CIA host interface pins. I had one CIA that somewhow pulled the reset line so much, that the C64 resettet from time to time. Also, it put a load onto the data lines in such a way that everything in the C64 still worked, except the color RAM couldn't be read by the CPU anymore. The explanation is that the color RAM data is routed through a 4066 analog switch to the CPU, and the signal becomes too weak to override the noise/load from the faulty CIA. You can imagine that I had some trouble to find the faulty chip in this C64! The other CIA behaved almost the same (color RAM failure), but it didn't have problems with the reset line. I found this fault rather quickly :-) It's interesting that I'm pretty sure both CIAs were rather old 6526R4 models from '83 or '84. Since then I'll try to stay away from using those as a spare part or even using a C64 with them installed for interfacing anything. Nicolas Message was sent through the cbm-hackers mailing list
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