Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!dptg!mtunb!dmt
From: dmt@mtunb.ATT.COM (Dave Tutelman)
Newsgroups: comp.sys.ibm.pc
Subject: Re: How can I tell what monitor there is?
Message-ID: <1575@mtunb.ATT.COM>
Date: 31 Jul 89 13:53:06 GMT
References: <934@kosman.UUCP> <664@chyde.uwasa.fi> <1575@unccvax.UUCP> <666@chyde.uwasa.fi>
Reply-To: dmt@mtunb.UUCP (Dave Tutelman)
Organization: AT&T Bell Labs - Middletown, NJ
Lines: 37

In article <666@chyde.uwasa.fi> ts@chyde.uwasa.fi (Timo Salmi LASK) writes:
>In article <1575@unccvax.UUCP> cs75jmc@unccvax.UUCP (John Covington WN4BBJ) writes:
>>... [ can tell the mode but not the actual monitor -- in particular,
>>	can't tell CGA color from composite monochrome ] ...
>>  ..... my paraphrase .....
>
>Quite.  But I am given to understand that the fact remains that the
>mono/color-detection function is still very useful in programming,
>because if one uses direct writes to video memory, one needs to know
>where it starts.  And that differs between the mono/color screen
>types, which are hardware, not software related.  (B000 Hex and B800
>Hex actually).  Right?

Not to worry!  What John _meant_to_say_ was not "composite monochrome"
but "composite black-and-white".  A "monochrome display board"
   -	ALWAYS starts at B000.
   -	ALWAYS is in mode 7.
A CGA display board:
   -	ALWAYS starts at B800.
   -	May be in any of modes 0-3.
(This is true for character modes.  CGA and Hercules boards have
additional modes for bitmapped graphics.  However, these modes are
similarly unambiguous as to which board it is.)

A CGA board can support a composite monitor that gives black&white or
gray scale.  The program treats it indistinguishably from any other case
of CGA, but the human viewer doesn't see colors.  John's point is that you
cannot tell whether or not the viewer will see colors or just grays,
merely by probing the hardware from the software.  You can prompt the
user, if you REALLY need to know.

+---------------------------------------------------------------+
|    Dave Tutelman						|
|    Physical - AT&T Bell Labs  -  Middletown, NJ		|
|    Logical -  ...att!mtunb!dmt				|
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