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From: ryders@watdcsu.waterloo.edu (Steve Ryder                                                                     Independent Studies)
Newsgroups: comp.sys.ibm.pc
Subject: TSR interrupt handlers
Message-ID: <4106@watdcsu.waterloo.edu>
Date: Wed, 11-Nov-87 20:35:20 EST
Article-I.D.: watdcsu.4106
Posted: Wed Nov 11 20:35:20 1987
Date-Received: Sat, 14-Nov-87 16:16:18 EST
Distribution: comp
Organization: U of Waterloo, Ontario
Lines: 64
Keywords: TSR interrupt handler

Anyone experienced with TSR programs and interrupts?

What I am trying to do is create a program to disable the PrtSc. This is
governed by int 21h function 05. So, the program assembles, and loads without
a hitch. A memory map shows it to be resident and the correct vector is hooked.
But when the actual PrtSc key is depressed, instead of getting the expected
'Print-Screen disabled.' message, unusual characters print to the screen and
then the machine hangs. Any help would be greatly appreciated. Please e-mail
replies.

;Print screen disabler (memory resident)
cr	equ	0dh
lf	equ	0ah

cseg	segment para public 'CODE'

	org	100h

	assume	cs:cseg,ds:cseg,es:cseg,ss:cseg

init	proc	near

	mov	dx,offset pscreen	;set interrupt vector
	mov	ax,2505h
	int	21h

	mov	dx,offset message	;display installation message
	mov	ah,9
	int	21h

	mov	dx,((offset pgmlen+15)/16)+10h	;TSR 
	mov	ax,3100h
	int	21h

init	endp


pscreen	proc 	near

	sti
	mov	dx,offset warning	;interupt request for PrtSc
	mov	ah,9			;and print 'disabled' message
	int	21h
	iret

pscreen	endp

message	db	cr,lf,'Print-Screen disabler installed.'
	db	cr,lf,'$'

warning	db	cr,lf,'Print-Screen is disabled.'
	db	cr,lf,'$'

pgmlen	equ	$-init

cseg	ends

	end	init


-- 
 ___ ___ __      __   Steve Ryder                     ryders@watdcsu.UUCP        | | | | \ \    / /   {allegra,decvax,ihnp4,utzoo}!watmath!watdcsu!ryders
 | |_| |of\ \/\/ /    I.S., University of Waterloo, Waterloo, Ont., N2L 3G1      |_____|   \_/\_/     (519)885-1211 x2352 x2345
                      <insert disclaimer or your choice here>                        "As much as thou hast, so much art thou worth." -CERVANTES, Don Quixote