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Path: utzoo!utgpu!water!watmath!watcgl!watmum!smvorkoetter
From: smvorkoetter@watmum.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Screen Base Address
Message-ID: <2020@watcgl.waterloo.edu>
Date: Tue, 13-Oct-87 14:32:33 EDT
Article-I.D.: watcgl.2020
Posted: Tue Oct 13 14:32:33 1987
Date-Received: Sat, 17-Oct-87 13:03:52 EDT
References: <5326@jhunix.UUCP> <2789@bnrmtv.UUCP> <1664@homxc.UUCP>
Sender: daemon@watcgl.waterloo.edu
Reply-To: smvorkoetter@watmum.waterloo.edu (Stefan M. Vorkoetter)
Organization: U. of Waterloo, Ontario
Lines: 25
Keywords: DOS Video address

In article <2789@bnrmtv.UUCP>, perkins@bnrmtv.UUCP (Henry Perkins) writes:
> In article <5326@jhunix.UUCP>, ins_agwa@jhunix.UUCP (Gunther Wil Anderson) writes:
> > Does anyone know how to determine the screen base address from
> > within DOS, independent of screen type (i.e. not by determining
> > the screen type and then assuming that the base address is what
> > it should be for that type)?
> 
> The screen base address isn't dependent on DOS; it's dependent on
> the display board you're using, and the BIOS which supports it.
  . . . . .  
> {hplabs,amdahl,ames}!bnrmtv!perkins         --Henry Perkins

The way I do it in a terminal emulator I wrote is to write the string "AZ"
in the top left corner of the screen using the appropriate BIOS calls.  I
don't know what these are since I let the compiler worry about it.  I then
read all the possible places where this could have been written to see 
where it is.  This has yet to fail me.  The only way it could fail is if
one of the places I check already has A in the first byte, and Z in the
third (the second and fourth are attributes).  Since I only check likely
possibilities, such as B000:0 and B800:0, this won't happen.



Stefan Vorkoetter
University of Waterloo