VMS Help TCPIP Services, TELNET, TN3270 Keyboard Functions, PA Keys  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    VT100: PF4 , KP- , KP,      VT200: PF4 , KP- , KP,
    DEFINE_KEY Function: PA1-PA3

    These program access keys are defined by the program you are
    using. These keys request attention from the remote application
    program without sending any data. You should refer to the user's
    guide of your application program to learn how the PA keys are
    defined.