INT 14h,  0Bh    Transmit no wait

      Entry:  DX         Port number

      Exit:   AX         0001h - Character was accepted
                         0000h - Character was not accepted

    This is exactly the same as the "regular"  transmit call, except that if
    the driver is  unable to  buffer the character  (the buffer is full),  a
    value of 0000h is returned in AX. If the driver accepts the character
    (room is available),  0001h is returned in AX.