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From: lisa@phs.UUCP (Jeff Gillette)
Newsgroups: net.micro.pc
Subject: Custom Interrupt 10h ???
Message-ID: <994@phs.UUCP>
Date: Tue, 5-Feb-85 23:05:06 EST
Article-I.D.: phs.994
Posted: Tue Feb  5 23:05:06 1985
Date-Received: Sat, 9-Feb-85 08:08:34 EST
Organization: Duke Physiology
Lines: 23

<>

I have a Hercules graphics card in my XT, which allows me to use a number of
special fonts and foreign alphabets (which I have written) by bit-mapping the
screen of the PC.  All of this works very well in my applications programs, 
but ...

I would like to substitute my own video interrupt (10h), which would allow me
to use special fonts and alphabets with any [commercial] application making
standard DOS calls.  I have imitated the inputs/outputs for interrupt 10h
calls in the PC technical manual, and the scheme works well when I set the
8088's registers and execute an interrupt 10h from an application program,
but ...

The operating system crashes when it tries to output a character to the screen
through my custom interrupt.  Is anyone aware of some special quirk of MS-DOS
2.1 that depends on a special variable or an undocumented value returned in a 
register?  I think I am following all the specifications of the PC technical 
manual, but ...

	Jeffrey William Gillette	...!duke!phs!lisa
	The Divinity School
	Duke University