Q35919: How to Force CAPS LOCK On or Off with PEEK and POKE

Article: Q35919
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom B_GWBasicI | mspl13_basic
Last Modified: 12-DEC-1989

This article describes how to programmatically force the CAPS LOCK key
on or off without actually pressing the CAPS LOCK key.

This information applies to Microsoft QuickBASIC Versions 1.00, 1.02,
2.00, 2.01, 3.00, 4.00, 4.00b, and 4.50 for MS-DOS, to Microsoft
GW-BASIC Versions 3.20, 3.22, and 3.23 for MS-DOS, to Microsoft BASIC
Compiler Versions 6.00 and 6.00 for MS-DOS, and to Microsoft BASIC PDS
Version 7.00 for MS-DOS.

You can determine the state of the CAPS LOCK key with the following
PEEK command:

   DEF SEG = 0
   X = PEEK(1047) AND 64

If CAPS LOCK is off, the value of "X" will be "0". If CAPS LOCK is on,
the value will be 64.

To force the CAPS LOCK off, use the following command:

   DEF SEG = 0
   POKE 1047, PEEK(1047) AND 191

To force the CAPS LOCK on, use the following:

   DEF SEG = 0
   POKE 1047, PEEK(1047) OR 64

Each bit of location 1047 reflects the status of a keyboard flag. This
includes NUM LOCK, SCROLL LOCK, CAPS LOCK, INSert mode, and whether or
not the LEFT SHIFT and RIGHT SHIFT keys, the ALT key, or the CTRL
(Control) key is currently pressed or not. See the following table:

Bit No.         Decimal value           Keyboard flag

0               1                       RIGHT SHIFT
1               2                       LEFT SHIFT
2               4                       CTRL (Control)
3               8                       ALT
4               16                      SCROLL LOCK
5               32                      NUM LOCK
6               64                      CAPS LOCK
7               128                     INSert mode

To determine the state of any flag, the following statement will
return "0" if the flag is clear (off or not pressed), and will return
<bval> if the flag is set (on or pressed):

   PEEK(1047) AND <bval>
   (where <bval> is the decimal value of the bit that represents
   the flag you want)

To force the flag on (which applies only to the LOCK keys and the
INSert mode), you need to set the appropriate bit. You can do this
with the following POKE statement:

   POKE 1047, PEEK(1047) OR <bval>
   (where <bval> is the decimal value of the flag you want to set)

To force the flag off, you can use the following similar statement:

   POKE 1047, PEEK(1047) AND (255 - <bval>)

Note that simply poking the bit value into 1047 would effectively set
the flag, but would also clear all other flags. Thus, be sure to
retain the previous values of the other flags by using the above
strategies.

This information is outlined in the book "Advanced MS-DOS" by Ray
Duncan (Copyright 1986 by Microsoft Press).

Note that instead of using PEEK, you may also get the status of
keyboard flags with IBM ROM BIOS interrupt 16 hex, using function
number 2. This interrupt returns the ROM BIOS flags byte that
describes the state of the following keyboard toggles and SHIFT keys:
RIGHT SHIFT or LEFT SHIFT key down, CTRL key down, ALT key down,
SCROLL LOCK on, NUM LOCK on, CAPS LOCK on, INSert on. QuickBASIC and
the BASIC Compiler have a CALL INTERRUPT statement (not found in
GW-BASIC) which can call this interrupt.

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