I've checked combinations of pin 20 UD6/7/8/9 and see that the waves are the same, and are smack next to each other but do not overlap.
I'm struggling a bit with getting the pulses compressed together though. Sorry, but I can't work out how to do this right now. I'll carry on trying different combinations on the scope.
Colin.
Quote:
Originally Posted by Mark1960
Hi Colin, that confirms the NOP test is running.
I think next is to check the prom chip selects again. First on the fast sweep time you should see the low pulses closer together than the last time you looked at them. Then slow down the sweep time until the pulses compress together and you should see a burst of 4K pulses, a larger gap, then another burst in a repeating pattern. If you look at two prom chip selects on different channels of the scope they should not both be active at the same time. Check for this on every possible pair of chip selects to make sure the address decoding is correct.
Then for each prom, while monitoring the chip select with one probe, check each data line at the 6502 socket. While chip select is low, every data line should be a good logic level before the chip select returns to a high level.
It’s a lot to test, so take it in steps and post results as you go along and we’ll add comments if we see any sign of problems.
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