Marko Mäkelä wrote: > On the C128 MMU, EXROM and GAME are general purpose input/output pins. > In C128 mode, you can use them as outputs: the PLA doesn't care about > them. If you programmatically switch to C64 mode, you can set EXROM > and GAME as you wish, but you can't control them afterwards, since the > MMU won't be addressable in the C64 mode. > Nothing like a crash course in cart electronics. As I now understand it, if GAME or EXROM are grounded on powerup, the C128 moves right into 64 mode (after the Z80 sets all the stuff up). I found in my C128 PRG that if GAME or EXROM are *NOT* grounded on boot, then the C128 polls the various memory addresses for expansion ROMs, which is a "more flexible solution". I guess my question is: If EXROM and GAME are general purpose outputs in C128 mode, does that mean that the cartridge must fully decode the LO ($8000) and HI ($c000) bank memory addresses for any cartridge, or does the C128 drive EXROM low for LO and GAME low for HI banks? I looked at p627 and p473 of the C128 PRG, but it's still unclear to me. Jim Message was sent through the cbm-hackers mailing listReceived on 2009-03-30 09:28:33
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