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  Like services 10H and 11H, service 12H (decimal 18) provides additional
  support for the 101/102-key keyboard. Service 12H expands the function of
  service 02H to provide information on the extra shift keys provided on the
  101/102-key keyboard. This service returns the same value in register AL
  as service 02H (Figure 11-2), but it also returns an additional byte of
  flags in register AH (Figure 11-5).

  This extra byte indicates the status of each individual Ctrl and Alt key.
  It also indicates whether the Sys Req, Caps Lock, Num Lock, or Scroll Lock
  keys are currently pressed. This information lets you detect when a user
  presses any combination of these keys at the same time.

        Bit                Meaning
  7 6 5 4 3 2 1 0
  --------------------------------------------------------------------------
  X . . . . . . .          Sys Req pressed
  . X . . . . . .          Caps Lock pressed
  . . X . . . . .          Num Lock pressed
  . . . X . . . .          Scroll Lock pressed
  . . . . X . . .          Right Alt pressed
  . . . . . X . .          Right Ctrl pressed
  . . . . . . X .          Left Alt pressed
  . . . . . . . X          Left Ctrl pressed
  --------------------------------------------------------------------------

  Figure 11-5.  Extended keyboard status bits returned in register AH by
  keyboard service 12H.