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

       /EIGHT_BIT
       /NOEIGHT_BIT

    Controls whether the terminal uses the 8-bit ASCII protocol
    rather than the 7-bit ASCII protocol. You can use the Terminal
    Fallback Facility (TFF) to set the 8-bit characteristic on
    terminals. If the terminal you specify has the TFF enabled,
    the /EIGHT_BIT qualifier has no effect. For more information on
    terminal fallback, refer to the OpenVMS Terminal Fallback Utility
    Manual (available on the Documentation CD-ROM).