Int 16 Fn 01  - Keyboard - Check For Keystroke                             [B]

   AH = 01h

Return: ZF set if no keystroke available
   ZF clear if keystroke available
       AH = BIOS scan code
       AL = ASCII character

Note:  if a keystroke is present, it is not removed from the keyboard buffer;
     however, any extended keystrokes which are not compatible with 83/84-
     key keyboards are removed by IBM and most fully-compatible BIOSes in
     the process of checking whether a non-extended keystroke is available
   some (older) clone BIOSes do not discard extended keystrokes and manage
     function AH=00h and AH=10h the same
   the K3PLUS v6.00+ INT 16 BIOS replacement doesn't discard extended
     keystrokes (same as with functions 10h and 20h), but will always
     translate prefix E0h to 00h. This allows old programs to use extended
     keystrokes and should not cause compatibility problems

See Also: AH=00h,AH=11h,AH=21h,INT 18/AH=01h