INT 14h,  01h    Transmit character with wait

      Entry:  AL         Character

              DX         Port number

      Exit:   AX         Port status (see function 03h)

    AL contains the character to be sent.   If there is room in the transmit
    buffer the return will be immediate,  otherwise it will wait until there
    is room to store the character in the transmit buffer.  On return, AX is
    set as in a status request (see function 03h).