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Path: utzoo!linus!decvax!mcnc!duke!phs!lisa
From: lisa@phs.UUCP (Jeffrey William Gillette)
Newsgroups: net.micro.pc
Subject: AT, Xenix, EGA question
Message-ID: <1037@phs.UUCP>
Date: Sat, 10-Aug-85 20:40:47 EDT
Article-I.D.: phs.1037
Posted: Sat Aug 10 20:40:47 1985
Date-Received: Mon, 12-Aug-85 23:30:08 EDT
Organization: Duke Physiology
Lines: 28

[]

I have been asked this by a colleague at the Duke Medical Center, and since
I do not have the relevant hardware, I submit it for your suggestions.

My friend has an AT, Xenix, an Enhanced Graphics Adapter, and the enhanced
color graphics monitor.  He has discovered that Xenix will boot happily with
the EGA set for a normal (poor resolution) color character set, but will not
boot with the EGA set for the high resolution font (which is, after all, the
whole purpose of the expensive monitor).

Evidently initializing the EGA for enhanced color is more complex than for my
monochrome monitor - it is reported to involve rewriting a table pointed to 
by one of the "reserved" interrupts.  My friend immediately tried to write a
short assembly language program (patterned after his successful MS-DOS 
program) that does the required work.  Obviously he ran into problems with
the protected memory scheme.  There is no obvious way to write to an absolute
memory address on the 80286 in protected mode.

Thus the question.  1) is there an easier way to initialize the enhanced
color text mode for the EGA - one that will work within the constraints of
Xenix and the 286?  or 2) is there a simple way to get at an absolute address
in Xenix and modify it?

Jeffrey William Gillette		uucp: ...!duke!phys!lisa
The Divinity School
Duke University