Posted By
TLC
on 2023-03-17
07:20:31
|  Re: New Project: Hannes-compatible 256k RAM Expansion
A late note, addition, whatever, to this topic...
Story: I've been playing around a bit with my old H/S/Cs controller prototype plus Csory's version of Bard's Tale III, and I think I've found something relevant. Long story short, there happens to be a typo in Solder's ramregs.TXT file included in his 256K RAM (Hannes) document archive, ram256kb.zip . This says, the Csory expansion is activated by Bit4 = 0 and Bit5 = 1 of the $FD16 register. Actually, this would be the other way around. Bard's Tale III at least writes $DF to $FD16 to activate the Csory expansion logic, which, with respect to the register description, is a clear miss. The (maybe early) hand-drawn Csory expansion schematics in 05.PCX shows the thing to be activated by an XOR gate, so, which combination out of 01 or 10, it would not care. But the logic equations of the latest issue (20V8 GAL, 256KB_3.PLD) would finally tell the truth, that is, they clearly show that the right combination is in fact Bit4 = 1, Bit5 = 0 (which now coincides with what Bard's Tale III is actually doing). TL;DR: if you happen to be reimplementing Csory's RAM expansion schema, be absolutely sure to use P4=1 / P5=0 as activation.
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