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



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