Re: Commodore 8296GD

From: Michał Pleban <>
Date: Tue, 02 Oct 2012 22:30:15 +0200
Message-ID: <>

A.Fachat wrote:

> That brings me to the question - what is the memory layout of the hires
> mode? That should give us some more hints...

OK, here are first results of my ROM disassembly. So far I looked at a
routine at $883F which apparently is used to perform various graphics

First of all, the routine banks out the ROMs with these instructions:

lda #$83
sta $E888

The address $E888 is in the CRTC register space. Apparently the board
intercepts this address with some latch on its own. This latch most
probably drives the values of jumpers JU1-JU7 (as you can see on my
photo, these jumpers are replaced with a connector that goes to the
video board).

The routine then reads a command number that is apparently stored at
$03A0, and depending on that it does different things. The number #$07
is apparently an initialization code, which stores zeroes in
$A000-$DFFF. So this is most probably where the video data resides.

Finally the procedure restores ROMs with these instructions:

lda #$0F
sta $E888

These are the only accesses to the $E888 register in the whole ROM.

I will proceed with analysis on how the actual video data is organized.


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Received on 2012-10-02 21:00:06

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