Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!newstop!sun!amdahl!netcom!ergo
From: ergo@netcom.UUCP (Isaac Rabinovitch)
Newsgroups: comp.lang.pascal
Subject: Re: Scan codes in TurboPascal
Message-ID: <13295@netcom.UUCP>
Date: 17 Sep 90 04:45:06 GMT
References: <1561.26f20a24@waikato.ac.nz>
Organization: UESPA
Lines: 59

In <1561.26f20a24@waikato.ac.nz> iam@waikato.ac.nz (Ian McDonald) writes:

>How do you pick up Scan codes in TP 5.5?  From my reading of the manuals you
>have to resort to machine code.  I am after picking up Ctrl-ESC as well as just
>Esc as ReadKey doesn't differentiate.

Correction:  ReadKey *does* know about scan codes.  (I gather you knew
that, but your writing style makes precise interpretation a
nondeterministic procedure.)  You're right about ReadKey treating
CTL-ESC the same as ESC, but that's not ReadKey's fault -- it
sends a signal to the BIOS saying it wants a key, and reports what it
gets.

One way around this is to talk to the BIOS yourself.  Now, this is
indeed a low-level function, but you can do it in a high-level
language if you've got the right function libraries -- and as it
happens, the Turbo Pascal DOS Unit is such a library.  With the INTR
function, you can send arbitrary software interrupts almost as easily
as any assembly-language hacker.  The following function uses INTR to
invoke interrupt 16h, function 2h:  interrogate shift status byte.

	uses dos;

	function shifts : byte;
		var
			r : Registers;
		begin
			r.ah := $02;
			intr($16, r);
			shifts := r.al;
		end;

The word returned by shifts is the sum of the following values:

	1 -- right shift key depressed
	2 -- left   "     "    "
	4 -- ctrl key depressed
	8 -- alt   "     "
	16 -- scroll lock on
	32 -- num     "   "
	64 -- caps    "   "
	128 -- insert mode on

Note that this gives you the shift status *now*, which is not
necesarily  what the shift status was when ReadKey returned; you'll
want to interrogate shifts *very* soon after calling ReadKey.
-- 

ergo@netcom.uucp			Isaac Rabinovitch
{apple,amdahl,claris}!netcom!ergo	Silicon Valley, CA

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