TTY_DEFPORT provides flag bits for port drivers. Bit 0 set
    to 1 indicates that the terminal controller does not provide
    automatic XON/XOFF flow control. This bit should not be set for
    VSI Controllers, but it is needed for some foreign controllers.
    Currently only the YCDRIVER (DMF32, DMZ32) uses this bit.
    The remaining bits are reserved for future use. This special
    parameter should be modified only if recommended by VSI.