VMS Help PASCAL, Predeclared Routines, Low Level, SET_INTERLOCKED  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The SET_INTERLOCKED function  assigns  the  value  TRUE  to  the
  parameter and returns its original Boolean value.

  Syntax:

     SET_INTERLOCKED( b )

  The variable 'b' must  be  a  variable  of  type  Boolean.   The
  variable  does  not  have  to be aligned; therefore, it can be a
  field of a packed record.