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Old 27 July 2021, 01:24   #3
hjalfi
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Join Date: Feb 2019
Location: Zurich
Posts: 26
Hey, keirf! I know that name!

After copying the ADF to a floppy using his GreaseWeazle hardware (but my FluxEngine software!) and finding the memory tester, I see the following.

https://imgur.com/a/IKJCLBz

I'm going to guess that whichever chip is handling bits 12-15 isn't getting selected properly when address bit 0x080000 is asserted.

Unfortunately it's DRAM, which means the 20-bit address is split up into row and column and probably divided by two anyway to allow 16-bit accesses, so actually figuring out what line is causing problems is going to be non-trivial. I don't know yet whether the eight 4-bit RAM chips are divided into upper-half-megabyte/lower-half-megabyte, which might mean a bad chip, or if they represent even and odd 32-bit words, which means the chips would have to be fine for the low half megabyte to test correctly.

Looks like it's back to the continuity tester tomorrow...

Thanks!
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