Re: Commodore 8296GD

From: Michał Pleban <*lists_at_michau.name*> Date: Thu, 04 Oct 2012 10:56:16 +0200 Message-ID: <506D4F30.5020004@michau.name> · lists_at_michau.name

Hello!

The second portion of wisdom from the ROM disassembly :-)

The routine at $8C1A initializes the CRTC into graphics mode by
modifying some of its registers. The modifications are as follows:

* Register $01 (horizontal displayed) = #$20
* Register $02 (horizontal sync position) = original + #$02

* Register $06 (vertical displayed) = #$20
* Register $07 (vertical sync position) = original + #$04

* Register $0C (RAM address high) = #$02

As you can see, the registers are set up for a 512x256 bitmap (because
the CRTC "characters" are 16x8), sync pulse positions are shifted to
better position this bitmap on the screen, and display address is
changed. I suspect this change also turns on graphics display - I will
verify it in the afternoon because right now I don't have access to the
machine.

Regards,
Michau.

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