Subject: Capslock status and toggling

77. *****
 Q: How do I detect the CapsLock status, how do I turn it on/off?

 A: Here are the relevant Turbo Pascal routines in answer to these
questions.
  {}
  Uses Dos;  { The Dos unit is needed }
  {}
  (* Is CapsLock on *)
  function CAPSONFN : boolean;
  var regs      : registers;
      KeyStatus : byte;
  begin
    FillChar (regs, SizeOf(regs), 0);
    regs.ax := $0200;      { Get shift flags }
    Intr ($16, regs);      { The keyboard interrupt }
    KeyStatus := regs.al;  { AL = shift status bits }
    if (KeyStatus and $40) > 0 then         { bit 6 }
      capsonfn := true
    else
      capsonfn := false;
  end;  (* capsonfn *)
  {}
  (* Set CapsLock. Use true to turn on, false to turn off *)
  procedure CAPS (TurnOn : boolean);
  var keyboardStatus : byte absolute $0040:$0017;
      regs           : registers;
  begin
    if TurnOn then
       keyboardStatus := keyboardStatus or $40
     else
       keyboardStatus := keyboardStatus and $BF;
    { Interrrupt "check for keystroke" to ensure the LED status }
    FillChar (regs, SizeOf(regs), 0);
    regs.ah := $01;
    Intr ($16, regs);
  end;  (* caps *)
  {}
As you see, CapsLock is indicated by bit 6. The other toggles can be
handled in an equivalent way using this information about the memory
location Mem[$0040:$0017]:
  ScrollLock = bit 4      $10  $EF
  NumLock    = bit 5      $20  $DF
  CapsLock   = bit 6      $40  $BF
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