Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!van-bc!rsoft!mindlink!a780
From: Mike_Benna@mindlink.UUCP (Mike Benna)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Dual Monitor hook up & 16-bit VGAs
Message-ID: <4738@mindlink.UUCP>
Date: 8 Feb 91 21:41:27 GMT
Organization: MIND LINK! - British Columbia, Canada
Lines: 33

Here are a few more tidbits of information which I haven't seen
mentioned yet:

1) The Trident 8800CS chip set works fine in 16-bit mode, even with an
8-bit MDA card installed.  I do not know how they do this but I can tell
you that it works fine.  At one point I thought it was my motherboard
but since the Trident VGA cards works in 16-bit mode on at least 4
different motherboards I suspect it is the 8800CS which makes the
difference.

2) Many 16-bit VGA cards can be forced into 16-bit mode by setting a bit
in their extended VGA registers.  For instance the Paradise cards
(PVGA1A and PVGA1B) can be set to 16-bit mode by setting bit 2 of port
$3CE, index $09.  This renders the MDA card useless but the VGA runs at
full speed in 16-bit mode.  This solution is far more preferable to the
hardware modifications I saw mentioned earlier.

3) Most 16-color graphics modes use the latch registers which are
compatible with the EGA.  Since these latch registers are only 8-bits
wide, most VGA cards (even 16-bit cards) run in 8-bit mode when doing
any 16-color graphics.

Text modes and 256-color graphics modes almost always run in 16-bit
mode.  Properly coding the alignment of your video memory writing can
result in a 2:1 increase in speed when using 16-bit VGA cards (believe
me - I've done lots of this type of optimization - it can make a big
difference).

        ---> Mike
--
   ---> Mike Benna, Vancouver, B.C., Canada
        MindSpan Technologies Corp - Video Game Design and Development
  UUCP: Mike_Benna@mindlink.UUCP  or  uunet!van-bc!rsoft!mindlink!Mike_Benna