Path: utzoo!attcan!ncrcan!ziebmef!stephen
From: stephen@ziebmef.uucp (Stephen M. Dunn)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Mono-monitors at colour-adapters ?
Summary: A couple of notes
Keywords: CGA,EGA,VGA,Monochrome
Message-ID: <1989May20.125018.4807@ziebmef.uucp>
Date: 20 May 89 16:50:17 GMT
References: <5003@uklirb.UUCP>
Reply-To: stephen@ziebmef.UUCP (Stephen M. Dunn)
Organization: Ziebmef Public Access Unix, Toronto, Ontario
Lines: 48

In article <5003@uklirb.UUCP> kirchner@uklirb.UUCP (Reinhard Kirchner) writes:
$How can a monochrome monitor be used at a colour adapter ?

   Well, there must be a very easy way, because at the university I attend, 
we have room after room of IBMs and clones with mono monitors attached to
CGA cards.  I don't know how it works (I have a Herc-clone in my AT-clone),
but it's probably something as simple as there being a monochrome output on
the CGA card, or a monochrome monitor just ignoring the chroma signal and 
relying solely on the luma signal.

$and the rationale behind: How to run programs which insist on CGA, EGA, VGA-
$ colour if you only can afford a mono-monitor.

   If you only need CGA compatibility, try getting SIMCGA (or similar) ...
many BBSs have it, and so do most of the PD/shareware distribution houses.
It looks kinda weird sometimes, but it works.  What it does, in case you
don't know, is simulates a CGA on a Herc-compatible monochrome board.  It
seems to be able to handle both BIOS calls and direct memory writes somehow.

$2. Use the mono-monitor at a hercules adapter and convert by software.
$   I have seen such converters for CGA->hercules, but not for EGA or VGA.
$   Are those existing or for some ( which ) reason impossible?

   A full VGA simulator on a Herc would be impossible, as the VGA allows for
higher resolution than the Herc does.  However, an EGA emulator should be
possible, as the Herc has better resolution than the EGA and could therefore
display EGA output.  The problem is that you would have to decide which out
of the EGA's colours would appear as a dot on the screen and which would
appear as a space.  This is not a problem in CGA simulation.  In the CGA, you
either have four colours with 320 pixels across the screen (which can
be represented on a Herc by using two adjacent pixels for each dot, as the
resolution is more than twice this), or two colours with 640 pixels (which is
really kinda monochrome, anyway).

$3. Some intelligent graphic adapter could do the conversion by itself.
$   I know that VGA-adapters my drive mono-monitors, but
$   - does this work even if the software uses a colour mode or must the
$     software use the VGA-mono-mode ?

   Well, EGA is a superset of CGA and VGA is a superset of EGA, so anything
that runs on a lower adapter will run on a higher one.  Also, some VGAs
will run Herc softwaare (maybe it's part of the VGA standard; I don't know).
As for connecting them to monochrome monitors, ask a computer dealer or two.
-- 
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! Stephen M. Dunn              stephen@ziebmef.UUCP ! DISCLAIMER:  Who'd ever !
! Take off to the Great White North eh, ya hosehead ! claim such dumb ideas?  !
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