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1989-04-19
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From: asickels@bonnie.ics.uci.edu (Alan Sickels)
Subject: Re: Reverse Num-Lock problems
Date: 19 Apr 89 23:52:10 GMT
Summary: It's internal
bobc@killer.Dallas.TX.US (Bob Calbridge) writes:
>Here's a problem that has started to pop up lately at our school district.
>Under certain circumstances the numeric key pad acts contrary to what the
>numlock light says. We suspect anything from the keyboard to the software.
I've got an XT clone and it happens quite frequently to me. This is what
is happening: The true NUM-LOCK state on PC/XT's and clones is stored in
memory in bit 5 of byte 0040:0017H. With the AT and 386's, the keyboard
communication is two way and the keyboard lights reflect the true state
of the memory location. The PC/XT's can't do that so it's kept track of
independent of the true state. This also annoyed me so I wrote a quick
assembly program to turn all the indicator bits off (i.e. NUM-LOCK,
CAPS-LOCK, and SCROLL-LOCK) and just make sure all the lights are off
when I run it. Source code included.
MOV AX,0040H
MOV DS,AX
MOV BX,0017H
AND BYTE PTR [BX],8FH
MOV AH,4CH
INT 21H
Alan Sickels