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Old 27 July 2021, 01:24   #3
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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.

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...

hjalfi is offline  
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