Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!bellcore!texbell!killer!chasm
From: chasm@killer.DALLAS.TX.US (Charles Marslett)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Original IBM AT and VGA
Summary: Rumors, rumors, rumors
Keywords: IBM AT VGA
Message-ID: <8466@killer.DALLAS.TX.US>
Date: 25 Jun 89 18:47:27 GMT
References: <7244@ecsvax.UUCP> <239@helens.Stanford.EDU>
Distribution: usa
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 75

In article <239@helens.Stanford.EDU>, mike@relgyro.stanford.edu (Mike Macgirvin) writes:
> In article <7244@ecsvax.UUCP> mvolo@ecsvax.UUCP (Michael R. Volow) writes:
> >
> >                                 . . . It worked once when we moved it
> >to an 8-bit slot but then mysteriously went back to mono. It will 
> >display, but in monochrome only. Any help would be appreciated. If you

> 	The 'mysteriously went back to mono' caught my eye. I have at
> home a Paradise VGA-Plus and a Sony 1302. These two interact very strangely.
> This might have something to do with what you're seeing... If I turn on
> the computer power BEFORE the monitor power, the VGA card is not able to
> poll the monitor for its type, and it boots up B/W. If I turn on the monitor
> power BEFORE the computer power, I get no display at all (still can't figure
> out why) UNTIL I turn the monitor back OFF and then ON again (After the
> computer BIOS has initialized the display), then everything works in color. 
> This is a generic XT clone. I would recommend setting the computer to
> color, and experiment with the timing of turning these things on. If
> somebody could explain why mine won't display until I reset the monitor
> power, I'd love to know.... it's a real hassle to not be able to just turn
> on ONE switch and go...

Two problems seem to be appearing here: the monitor latches up in a no-display
mode in one case, and the adapter fails to recognize the monitor in the other.

Try this:

   Boot up normally (with the monitor turned on at the same time or after the
computer is).  Then when the VGA comes up in monochrome run a short program
to turn off bits 1 and 2 of memory location 0040:0089.  "MODE CO80" will
now get you into a normal color mode (with most VGA cards).  There is a BIOS
call that turns off or on one of the two bits, but the other is intended to
tell the software that a real monochrome VGA monitor is out there, so do
everything in gray-scale.  The program just overrules the original test
the VGA BIOS did on the monitor

/* No warranty on this code: */

#include <stdio.h>
main()
   {
   unsigned char far *ptr = 0x00400089L;
   unsigned int k, m;

   k = *ptr;
   m = k & 0xF9;
   *ptr = k;
   printf("Original VGA flag byte = %02x, replaced with %02x\n", k, m);
   }


The problem with the monitor remaining off if it is turned on before the
computer may be related to a safety feature in the monitor (many do not
like being on and not seeing a horizontal sync signal on the input).  If
this is the case, the monotor will be subject to unhealthy stress if it is
turned on first (if the time is not long, it is unlikely to damage it, but
it's better to be gentle to expensive electronic toys).

> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +            These views are my own, and may not be correct.                +
> +  Mike Macgirvin                                                           +
> +  - Systems Administrator  Stanford Relativity Gyroscope Experiment        +
> +  - Internet:              mike@relgyro.stanford.edu (36.64.0.50)          +
> +  - Bitnet:                mike%relgyro.stanford.edu@stanford              +
> +  - Uucp:                  uunet!relgyro.stanford.edu!mike                 +
> +  "There must be some kind of way out of here." - Dylan (w/help from Jimi) +
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


On the other hand, these views are my own, and may not be correct, but I'll
never admit it!!!!
===========================================================================
Charles Marslett
STB Systems, Inc.  <== Apply all standard disclaimers
Wordmark Systems   <== No disclaimers required -- that's just me
chasm@killer.dallas.tx.us