VMS Help SET, TERMINAL, Qualifiers, /MANUAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Indicates manual switching of terminal lines to dynamic
    asynchronous DDCMP lines when your local terminal emulator does
    not support automatic switching. The /MANUAL qualifier should be
    specified with the /PROTOCOL=DDCMP and /SWITCH=DECNET qualifiers.