I finally got around to looking at this project, which I am calling the Clulow-Guion_32K upgrade, located http://www.mainbyte....32kconsole.html
WOW! That was quite a project. That's going to take some time to figure out.
Actually not that hard to figure out once you get the pin #'s on those piggy-backs straight. I initially had almost half of them bass ackward . Figuring out where the 2-input AND on U613, pin 13 for the wait state bypass defeat switch was a bit confusing, but I think I got it now.
Your mod has 64K RAM and only 32K is used? Did they put some of the extra memory into that space, or do you still only have 256 bytes in the >8000 to >83FF address area?
It only has 256 bytes. There may be enough unused logic gates in there now to implement a 1024 byte scratch pad, though. There's certainly enough memory.
There is no attempt to accelerate Video, Cart, or GROM access. That, in part I think, would explain the lack of acceleration when running console BASIC, or XB.
When I'm certain of the placement of that AND gate I'll post a revised schematic. And, if I can figure it out quickly, maybe a way to mod this mod for the 1024 byte Scratch PAD (not a high priority for me at the moment since the 32K expansion would be just as quick w/ this mod).
Edited by hhos, Tue Jan 15, 2019 3:06 PM.