Library /sys$common/syshlp/dbg$help.hlb DEBUG, CALL, Qualifiers, /AST  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /AST (default)
       /NOAST

    Controls whether the delivery of asynchronous system traps
    (ASTs) is enabled or disabled during the execution of the called
    routine. The /AST qualifier enables the delivery of ASTs in the
    called routine. The /NOAST qualifier disables the delivery of
    ASTs in the called routine. If you do not specify /AST or /NOAST
    with the CALL command, the delivery of ASTs is enabled unless you
    have previously entered the DISABLE AST command.