INT 16 - KEYBOARD - GET KEYSTROKE
        AH = 00h
Return: AH = BIOS scan code
        AL = ASCII character
Notes:  on extended keyboards, this function discards any extended keystrokes,
          returning only when a non-extended keystroke is available
        the BIOS scan code is usually, but not always, the same as the hardware
          scan code processed by INT 09.  It is the same for ASCII keystrokes
          and most unshifted special keys (F-keys, arrow keys, etc.), but
          differs for shifted special keys.
SeeAlso: AH=01h,AH=05h,AH=10h,AH=20h,INT 18/AH=00h

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