The AT attribute specifies that VSI Pascal allocates no  storage
  for  the object (storage has already been allocated) and that it
  resides at the exact, specfied address.

  Syntax:

     AT( n )

  The exact address is specified by  the  constant  expression  n.
  Variables representing machine-dependent entities are frequently
  given the AT attribute.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the AT attribute.