Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hpcvlx!bill
From: bill@hpcvlx.cv.hp.com (Bill Frolik)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Sys Req - key.
Message-ID: <102760024@hpcvlx.cv.hp.com>
Date: 6 Dec 89 16:56:16 GMT
References: <187@nmtvax.nmt.edu>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 26


| This is probably a useless question, but there is a mysterious key on my 
| XT-keyboard called the 'Sys Req' key. I've seen this key on many other 

How you use the SYS REQ key is completely up to you.  I'm not sure
exactly WHY the key is there, or why IBM chose to call it SYS REQ.
I think it might have been derived from the old IBM minicomputer
consoles and/or their SNA terminals -- the microcomputer market was
just getting started, and I don't think anyone really knew what kinds
of special keys ought to be on the keyboards...

Anyway, SYS REQ has a scancode (54h), but doesn't stick anything the
keyqueue, so you generally can't detect it with Int 16h or your run-of-
the-mill CON driver.  The advertised method for detecting SYS REQ
being pressed/released is to intercept the SYS REQ hook in Int 15h
and examine AX.  The BIOS calls Int 15h with AH=85h whenever SYS REQ
changes state.  If AL=0, the key has been depressed.  If AL=1, it has
been released.

________________________________________

Bill Frolik	Hewlett-Packard Co.
hp-pcd!bill	Corvallis, Oregon