Library /sys$common/syshlp/latcp$help.hlb SET, PORT, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 port-name

    Specifies the name of the port. A port name must be in the form
    LTAn:, where n is a unique number from 1 through 9999.

                                   NOTE

       You cannot use the CREATE PORT and SET PORT commands,
       along with the DCL command SET TERMINAL, to change the
       characteristics of a DECserver port unless there is an
       existing LAT connection to that DECserver.