[Coco] High Color Display Mod for MM/1?

[Bob Devries]

Joel,
It's certainly an interesting prospect. As well as that, there's the so 
called VGA mode that the MM/1 is supposed to have, but no-one seems to have 
knowledge of.

It would be good to collect data sheets of all the major chips in the MM/1 
and upload them to maltedmedia. I have a PDF file of the SCC66470B which I 
can upload.

It could also be advantageous to upload the disk images of the original 
distribution disks.

My own MM/1 is a CPU board with an IO board mounted on a non-active 
backplane (no memory provision), and I have the MIDI paddle board.

--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Joel Ewy" <jcewy at swbell.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Friday, September 05, 2008 3:58 PM
Subject: [Coco] High Color Display Mod for MM/1?


> Ok, you've all gotten me thinking about the MM/1 again.  I've long
> wanted to experiment with restuffing all, or more likely only part of
> the palette registers on the MM/1 to get more colors per line, like
> what's already been done for high color displays on the CoCo.  So I
> needed to know the address of the RAMDAC.  I was looking at the
> schematics Bob uploaded instead of falling asleep, and then got curious
> and went searching for a datasheet for the Brooktree BT478.  Before I
> found it, I came across a datasheet for the Brooktree BT481, which
> appears to be an updated, pin-compatible replacement for a number of
> RAMDAC parts, including the BT478.  What intrigues me about this chip is
> that it has high-color and true-color modes where it latches serial
> bytes to feed the video DACs directly, bypassing the palette.  There is
> one 15-bit (5-5-5) mode that looks particularly promising.
>
> Now the problem with this is that, at the very least, the horizontal
> resolution would be halved.  So the interlaced overscan 384x480 8-bit
> mode would become a rather odd 192x480 15-bit color mode.  Would it be
> worth doing?  I don't know.  Probably not, but it's certainly
> interesting to think about, and I'm definitely going to keep my eyes
> open when I next look through my boxes of old video cards to see if
> there's a BT481 out there that can be liberated from a socket or gently
> heat-gunned off its board.
>
> Any thoughts?
>
> JCE
>
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