The optional Communications Mode argument specifies the
    communications method used on the link.  Possible comm-mode
    values are:  asynchronous and synchronous.  The default
    value is taken from the device capability.  If that is
    unknown, the default is synchronous.

    Example:

    create modem connect line DSY-0-0 -
         communication port DSY-0-0, -
         communications mode synchronous