Musings on BabyVAX video

From: Michael Sokolov <msokolov_at_ivan.Harhan.ORG>
Date: Fri Jan 17 14:33:00 2003

Hi again folks,

Thinking about the VS3100/VT1300/VXT matters brought up another question that
has nagged me for a while. How much compatibility is there between KA410
(VS2000), KA42 (VS3100 M30/38/40/48), and KA43 (VS3100 M76) as far as video
boards go? I mean GPX and SPX. (Were there others?)

I know that the 4-plane and 8-plane GPX boards were originally designed for
VS2K, and I'm pretty sure that the VS3100 ones are the same as the VS2000 ones,
which implies that the video option connector on KA42 has to be identical to
the one on KA410.

But now comes SPX. I have seen many VS3100 M76 SPX machines, and SPX appears to
have been pretty standard on these machines. But I have questions. Does the SPX
board also work on earlier VS3100s and on VS2000? I seem to recall from
somewhere that the answer is yes for VS3100 and no for VS2000. Could someone
confirm? And how about the other way around? Can M76 use GPX? No video option
at all? (I seem to recall that base mono video was removed on KA43.)

This makes me wonder about the nature of interface between the system board and
the video option. Since it originates from VS2K, common sense says that it has
to be 16-bit EDAL, since that's all VS2K had. But then there is the DTJ article
about the design of VS4000 M90 where they've used a version of SPX that
attaches directly to 32-bit CDAL. Furthermore, they just lifted their SPX
design from the VXT2000 where it also attached directly to CDAL. Hmm. Did the
original SPX used in all these VS3100 M76s also attach to CDAL? Then how can
the video option connector, which at least mechanically hasn't changed since
KA410, be sometimes EDAL and at other times CDAL? Were there a lot of unused
pins on the original KA410 connector that were made into upper 16 bits which
are used sometimes but not at other times? But then if turning CDAL into EDAL
were only a matter of using only lower 16 bits, why did they design a much more
complex chip (SEAC) for this very purpose in VS4000 M90 (see the DTJ article)?

Just a hardware-minded hacker being curious.

MS
Received on Fri Jan 17 2003 - 14:33:00 GMT