Re: <Q> C64 ULTIMAX mode-

From: MagerValp (
Date: 1999-09-26 00:29:32

>>>>> "Zak" == Radioactive Warrior <> writes:

Zak> Hi all, I am trying to find out what the 6510 sees at addresses
Zak> $1000 - $7FFF in "ultimax mode". My code kept crashing when I
Zak> tried switching into ultimax mode (I had the ML at $2000)

Makes sense. Switching to ultimax mode makes everything between $1000
and $7FFF disappear.

Zak> and as soon as I moved the ML to $0F00 (toggling /EXROM & /GAME
Zak> with an external latch at $DE00, ala super snapshot) it worked on
Zak> the first go... What decodes ULTIMAX addresses, the PLA?


Zak> Could someone list how the PLA behaves when /EXROM = 1 & /GAME =
Zak> 0 ??? The c64 PRG does a piss-poor job, as per usual, of
Zak> explaining it saying only $1000-7FFF and $A000-CFFF is "OPEN" in
Zak> ultimax mode.

Open means that nothing is answering at these addresses and you'll
only get bus noise if you try to read from it, like $DE00-$DFFF
behaves if you don't have a cartridge plugged in. So in ultimax mode
you have

4K of ram at $0000-$0FFF
8K of cartridge rom at $8000-$9FFF
4K of I/O registers at $D000-$DFFF
8K of cartridge rom at $E000-$FFFF

The rest of the address space is unusable (unless you're Marko Mäkelä :).

    ___          .     .  .         .       . +  .         .      o   
  _|___|_   +   .  +     .     +         .   .  Per Olofsson, konstnär
    o-o    .      .     .   o         +
     -       +            +    .
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