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

       /HOSTSYNC
       /NOHOSTSYNC (default)

    Controls whether system transmission from the terminal is stopped
    (by generating a Ctrl/S) when the input buffer is full and
    resumed (by generating a Ctrl/Q) when the input buffer is empty.