[atari7800] AW: Re: DMA TIMING
- From: "Matthias" <matthias@xxxxxxxxxxxx>
- To: <atari7800@xxxxxxxxxxxxx>
- Date: Tue, 9 Nov 2004 23:40:49 +0100
Ok, if I understand it correctly than you have a max. of 8 colors in 320b
mode, right?
How do I have to handle the color registers than?
> -----Ursprüngliche Nachricht-----
> Von: atari7800-bounce@xxxxxxxxxxxxx [mailto:atari7800-
> bounce@xxxxxxxxxxxxx] Im Auftrag von Eric Ball
> Gesendet: Dienstag, 9. November 2004 13:29
> An: atari7800@xxxxxxxxxxxxx
> Betreff: [atari7800] Re: DMA TIMING
>
> > > FWIW, MESS doesn't work according to spec, it reads all three palette
> bits
> > in 320B mode not just the high bit.
> >
> > Whoops. Let me verify that with the CC2, then I can fix
> vidhrdw/a7800.c
>
> I just had an AH-HH! moment about this. MARIA has two 800 bit line RAMs,
> so
> each 160H pixel has 5 bits as a color LUT index. The 320H modes don't
> change how the line RAM is written to, just how it is read. Which,
> unfortunately, means there are only 2.5 bits per 320H pixel, or max 8
> colors
> per pixel with one bit shared between the two half pixels.
>
> It's unfortunate that the MARIA designers didn't have enough transistors
> for
> 320x5 (or even 320x6) bit line RAMs, but there is a little bit of genius
> in
> how they did manage to squeeze the 320H modes out of the 160H line RAM.
> I
> also wonder whether this means there are a couple more 160H modes hidden
> in
> there.
>
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