INT 16 - KEYBOARD - CHECK FOR ENHANCED KEYSTROKE (enh kbd support only)
        AH = 11h
Return: ZF set if no keystroke available
        ZF clear if keystroke available
            AH = BIOS scan code
            AL = ASCII character
Notes:  if a keystroke is available, it is not removed from the keyboard buffer
        unlike AH=01h, this function does not discard extended keystrokes
SeeAlso: AH=10h,AH=21h