From: Marko Mäkelä (Marko.Makela_at_HUT.FI)
Date: 2002-08-22 08:47:25
Niklas Ramsberg <niklas.ramsberg@swipnet.se> wrote:
> the text says something about the GAME and EXROM pins on the
> expansion port (read: internal or external function ROM) being used
> as output lines
True, they can be used as outputs, just like the 40/80 column key line
can be used.
In my C128, I've misused the 40/80 line for selecting the C64 mode
KERNAL. When the line is low, I get the original -03 version. When
it is high, the C64 mode starts up with a different KERNAL. I can
select the stock ROM either by pressing the 40/80 key down or by using
a simple program (actually the cbmlink boot sector) that switches the
computer to C64 mode with the 40/80 line set '0'.
The document kernal-switch.html at
http://www.funet.fi/pub/cbm/documents/projects/memory/ describes yet
another modification: misusing the -GAME line for selecting the C128
mode KERNAL. The document also tells which KERNAL and Z80 BIOS
locations you need to modify in order to disable the "go 64 when -GAME
or -EXROM is low" misfeature.
Marko
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