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From: APratt.osbunorth@XEROX.ARPA
Newsgroups: net.micro
Subject: Re: Scroll lock on Tandy 1000 and IBM PC
Message-ID: <694@brl-tgr.ARPA>
Date: Wed, 14-Aug-85 16:08:15 EDT
Article-I.D.: brl-tgr.694
Posted: Wed Aug 14 16:08:15 1985
Date-Received: Mon, 19-Aug-85 06:02:29 EDT
Sender: news@brl-tgr.ARPA
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ScrollLock is a very special key on the PC keyboard. It's so special, MS-DOS
doesn't know it exists. The result is that striking the key normally DOES
NOTHING. Some programs, like SideKick, pay attention to it, though.

At a more technical (BIOS) level, Scroll Lock acts like Num Lock and Caps Lock:
striking it once sets a bit in the BIOS data area (beginning at 00400 absolute),
and striking it again clears the bit. You can get these "shift state" bits
from the BIOS with a call to the keyboard interrupt (check the Technical
Reference manual). Since it's not a "key" the way the spacebar and the
letter "A" are keys, it would be hard to simulate it on a Tandy keyboard,
unless Tandy had that in mind when they designed their keyboard software.

The intended use of Scroll Lock, of course, is to let you read text before it
scrolls away. It's a toggle, so you hit it once to "lock" scrolling and read
the text, then hit it again to "unlock" scrolling and proceed.

There are some public-domain utilities, probably available from Simtel-20,
which make the Scroll Lock key do its thing in normal MS-DOS operation. I 
couldn't name one, but maybe someone else can.

It's important to know that the ScrollLock key is also the Break key: Ctrl-
ScrollLock causes "break" processing in a more catastrophic way than Ctrl-C.
I expect the Tandy keyboard has something similar to this, but I don't know.

						-- Allan Pratt