First post, by T-Squared
I was able to get a clone system to work with chips it normally doesn't use (256kbit, along with the normal 64kbit memory), and everything seems to be in-place for it to work properly (I've traced a bit of the system using the original 5160 schematics, and a multimeter). But the system is not detecting the full 640k I want to use. I am not sure where to go from here, though.
The one reason I'm assuming that the system isn't seeing the extra 384k of memory is that the A8 line (Pin 1 on the 256kbit memory) isn't being driven (I don't have an oscilloscope), even though it's connected to the relevant similar components that it uses in-place of the ones on the original 5160 schematic.
I'm also assuming that the system is detecting the basic structure of the memory (somewhat) correctly, and that the logic for multiplexing the memory is working too, because if it weren't, the system wouldn't even start up.
i.e. it sees only 256kBYTE because that's is all that is being activated and run-through by the POST because of the not-working A8 switching pin, but neither type group of memory individually adds up to 256kBYTE (2 banks of 256kbit; 512kBYTE total, 2 banks of 64kbit; 128kBYTE total = 640kBYTE)
Should I go farther down the A8 Line to make sure that it's connected properly, or am I on a wild goose chase and should check the multiplexing logic instead?