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

       /DISCONNECT=disconnect-character

    Defines the character that you can use to disconnect from a
    remote session. To generate a disconnect, press the Ctrl and
    disconnect-character keys together. The default disconnect-
    character is the backslash (\).

    You can select any ASCII character from @ through Z, except C, M,
    Q, S, Y, and the left bracket ([). For example, if you specify
    /DISCONNECT=A, Ctrl/A will be the disconnect character. You
    cannot select a character that is already defined as the break
    character.