Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!ames!attctc!chasm
From: chasm@attctc.Dallas.TX.US (Charles Marslett)
Newsgroups: comp.sys.ibm.pc
Subject: Using two graphics cards (one a VGA)
Summary: Snide remark by one twice bitten . . .
Keywords: VGA CGA COMPAQ 386 GRAPHICS
Message-ID: <10738@attctc.Dallas.TX.US>
Date: 25 Dec 89 06:38:44 GMT
References: <5209@arctic.nprdc.arpa> <354@vidiot.UUCP>
Distribution: na
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 34

In article <354@vidiot.UUCP>, brown@vidiot.UUCP (Vidiot) writes:
< In article <5209@arctic.nprdc.arpa> trejo@nprdc.arpa (Leonard J. Trejo) writes:
< <We're trying to use two graphics cards in a Compaq 386/25 computer
< <running MS-DOS 3.1.  One card is the Compaq Video Graphics Controller
< <(VGA-compatible) and the other is the Compaq Video Display Controller
< <(CGA-compatible).  We'd like to use, simultaneously, the VGA for 
< <graphics-only display purposes only and the CGA as a text-only 
< <console which echoes keyboard input.  Problem is that despite our 
< <best efforts, graphics always go to the CGA card.  I'm told that 
< <this is because VGA and CGA screen memory overlap, plus that 
< <whenever another graphics card is installed with the Compaq VGA, 
< <graphics are forced to go to the other card and the VGA runs in 
< <monochrome mode.

The VGA is configuring itself as a monochrome adapter -- only video modes
0x07 and 0x0F (of IBM's standard set) are monochrome modes, so only those
two will use the VGA adapter.  All the 640x480 modes are color (even though
one is a 2-color color mode ;^).

< You have been told correctly.  You can only run a monochrome and a color card
< in the same system.  Both the VGA and CGA use the same memory mapped space and
< control registers (CGA is a sub-set of VGA cards).

Not quite correct:  the VGA will be a monochrome VGA if a CGA is coresident
(that is, if the BIOS was written correctly -- I have done it wrong quite often!).

<                 harvard\     att!nicmad\
< Vidiot            ucbvax!uwvax..........!astroatc!vidiot!brown
<                 rutgers/  decvax!nicmad/
<         ARPA/INTERNET: <@spool.cs.wisc.edu,@astroatc:brown@vidiot>

Charles Marslett
STB Systems, Inc. <-- apply all standard disclaimers!
chasm@attctc.dallas.tx.us