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From: eli@aspasia.gang.umass.edu (Eli Brandt)
Newsgroups: comp.lang.pascal
Subject: Re: Keyboard lights
Message-ID: <22707@dime.cs.umass.edu>
Date: 16 Nov 90 17:59:21 GMT
References: <2526@oucsace.cs.OHIOU.EDU>
Sender: news@dime.cs.umass.edu
Reply-To: eli@aspasia.CS.UMASS.EDU (Eli Brandt)
Organization: University of Massachusetts, Amherst
Lines: 60

In article <2526@oucsace.cs.OHIOU.EDU> rsandfor@oucsace.cs.ohiou.edu (Robert Sandford) writes:
>on or off. It seems to work only on 101 keyboards though. Others
>it will just set either the num lock on or off but the light will
>not change. If anyone knows how to make the lights flash please E-mail
>the info, I probably need to reset something, because when I put the 
>capson and capsoff i can't get it to flash on and off. So any ideas on how
>i would aprreciate it.
> 
>PROGRAM Key_lights;
>USES CRT;
>
>VAR s:string;
>
>PROCEDURE CapsOn;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] OR $40
>END;
>
>PROCEDURE CapsOff;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] AND $BF
>END;
>
>PROCEDURE NumOn;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] OR $20
>END;
>
>PROCEDURE NumOff;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] AND $DF
>END;
>
>PROCEDURE ScrollOn;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] OR $10
>END;
>
>PROCEDURE ScrollOff;
>BEGIN
>  Mem[$40:$17]:=mem[$40:$17] AND $EF
>END;
>
>BEGIN
>  CapsOn;
>  Scrollon;
>  Numon;
>END.

On my keyboard, at least (an IBM "enhanced" eight-pounder), there are two
different sets of bits.  There is the one you're using, which flips
both the keyboard state and the LED, and there's another which flips just
the LED's.  If you use the second one it's very easy to get the true
state out of sync with the indicator light, which can be annoying.  The
problem is that many "compatible" BIOS's/keyboards don't seem to implement
this properly.  Try playing around with the other byte, which I think is
located at $84.  (For God's sake don't just write to that location without
seeing what it is; I've probably got it wrong)

Eli