Re: <Q> C64 ULTIMAX mode-

From: Marko Mäkelä (
Date: 1999-09-26 16:44:21

On Sat, 25 Sep 1999, Radioactive Warrior wrote:

> What decodes ULTIMAX addresses, the PLA?  Could someone list how the
> PLA behaves when /EXROM = 1 & /GAME = 0   ???

Have a look at the PLA equations.  You can get them from
<URL:>.  For
interpreting them, you should maybe also have the schematic diagram.

> The c64 PRG does a piss-poor job, as per usual, of explaining it
> saying only $1000-7FFF and $A000-CFFF is "OPEN" in ultimax mode.

Actually that description is surprisingly accurate.  No memory device will
catch accesses to that address space in the UltiMax mode.  It's similar to
$de00-$dfff in the I/O area when nothing has been connected there.

BTW, there's also something special about the video chip in UltiMax mode.
One block (I think it's $3000-$3fff) will be fetched from external memory
(ROMH or ROML, I don't remember).  If there's no ROM there, the video chip
will display what the processor fetched on the preceding cycle, similar
to what happens when you enable the screen in the 2 MHz mode of the C128.
Unfortunately the data lines are not stable enough to make both the
processor and the video chip run on open address space.  I've tried that
some times.

BTW, has anyone written any graphics demos for the C128's 2 MHz mode (I
mean with the VIC-IIe screen enabled and the CPU running at 2 MHz all the

And now something completely unrelated: I noticed someone complain that he
cannot view PDF files on a text terminal.  Try ps2ascii, which is part of
the Ghostscript tools.  A recent enough version of Ghostscript (at least
Aladdin Ghostscript 5.50) understands PDF.  The following .mailcap line
seems to work in Lynx:

application/pdf; ps2ascii '%s' | less


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