INT 14h,  0Ch    Non-destructive read-ahead

      Entry:  DX         Port number

      Exit:                 AX         FFFFh - Character is not available
              AH         00h   - Character is available
              AL         Next character

    Return in AL the next character in the receive buffer.  If the receive
    buffer is empty,  return  FFFFh.  The  character  returned  remains in
    the receive buffer. Some applications call this "peek".