Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!zaphod.mps.ohio-state.edu!wuarchive!psuvax1!psuvm!hdk
From: HDK@psuvm.psu.edu (H. D. Knoble)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: Num Lock .com utility wanted
Message-ID: <90254.123515HDK@psuvm.psu.edu>
Date: 11 Sep 90 16:35:15 GMT
References: <25475.26e8c676@kuhub.cc.ukans.edu>
Organization: Penn State University
Lines: 44

Publications of NUMLKOFF codes that use special characters are bound to
fail because of they don't display consistently across systems. Such
a .COM file was published in PC Magazine. It follows here:

                                  NUMLKOFF.COM

From PC Tutor, PC Magazine, June 14, 1988, pp378-379, Vol 7, No. 11, by
H. M. Weingartner. The 8 byte program, which deactivates the NumLock function,
was created by entering the following commands to DEBUG:

N NUMLKOFF.COM
A 100
POP DS
AND BY [417],DF          <--417 enclosed in square brackets, ASCII 91 & 93.
INT 20
            <--Make sure you enter this blank line.
RCX
8
W
Q

METHOD AND DISCUSSION (PC Magazine, 8(1):373, January 17, 1989)

Very basically speaking, the BIOS uses 3 bits of a byte located at 0:417h to
keep track of the status of the NumLock, CapsLock, and ScrollLock functions.
The mapping of this byte follows:

 0040:0017h

  7   6   5   4   3   2   1   0    <---Bit positions
      I   I   I
      I   I   +---->  1=ScrollLock active
      I   +-------->  1=NumLock active
      +------------>  1=CapsLock active

If the bit is 1, then the corresponding function is on. NUMLKOFF simply sets bit
five to zero. {If the AND above used constant BF instead of DF, (and appropriate
name changed) then the CapsLock function would be turned off. Similarly, if the
DEBUG instruction AND BY were changed to OR BY and the mask(s) complemented,
then the function(s) would be (NUMLK)ON instead of OFF.}

As a note in passing, the function TOGGLE.COM, published in the May 31, 1988
Utilities column of PC Magazine, allows all three functions to be controlled
more generally.