/sys$common/syshlp/helplib.hlb SET, TERMINAL, Qualifiers, /TTSYNC  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /TTSYNC (default)
       /NOTTSYNC

    Controls whether transmitting to the terminal is stopped when
    Ctrl/S is pressed and resumes transmission when Ctrl/Q is
    pressed.