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Path: utzoo!mnetor!uunet!husc6!bu-cs!acm
From: acm@bu-cs.BU.EDU (ACM)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Screen Base Address
Message-ID: <14253@bu-cs.BU.EDU>
Date: Mon, 12-Oct-87 19:47:08 EDT
Article-I.D.: bu-cs.14253
Posted: Mon Oct 12 19:47:08 1987
Date-Received: Wed, 14-Oct-87 00:53:39 EDT
References: <5326@jhunix.UUCP> <2789@bnrmtv.UUCP> <1664@homxc.UUCP>
Reply-To: madd@bucsb.bu.edu
Followup-To: madd@bucsb.bu.edu
Organization: Boston University ACM
Lines: 31
Keywords: DOS Video address

In article <1664@homxc.UUCP> djs@homxc.UUCP (D.SPATHIS) writes:
>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
>
>
>One thought for finding the screen address goes something like this:
>
>IF one possible place for the screen buffer is B000:1000 then read this
>absolute memory location saving the data byte that is there.  Now write
>some other non-blank value there.  Call a BIOS clear screen function.
>Lastly, check the location again - if blank it's part of the active
>screen buffer.  Repeat with more gueses for screen address until happy.

Yea, that works ok but it's not too reliable.  The way that I usually
do it is to ask the BIOS what the default screen mode is; if it's
color, I use $B800:0000 and if it's mono I use $B000:000.  Now, this
isn't completely reliable but it very, very seldom fails.  It would be
better to ask the board where its buffer is but I never did figure out
how to do that.

jim frost
madd@bucsb.bu.edu