/sys$common/syshlp/helplib.hlb FORTRAN, Character Sets, Nonprintable Characters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  If nonprintable characters appear anywhere in a Fortran source line
  or comment, the compiler issues a warning diagnostic and the
  nonprintable character is replaced with a blank in both the
  compiled source and the listing, except for the following special
  cases:

   o  The form-feed character (0C hex) is treated as a blank without
      causing a diagnostic message to be issued.  In addition, a
      source record of length 1 containing a form-feed character
      causes the compilation source listing to begin a new page.

   o  A source record of length 1 containing a Ctrl-Z character (1A
      hex) is treated as a blank line.  Such a record is created by
      the ENDFILE statement.

  If you must use a nonprintable character in a character constant,
  use the CHAR intrinsic function (with the concatenation operator,
  if necessary).  For example:

     CHARACTER*(*) ESC_BRACKET
     PARAMETER (ESC_BRACKET = CHAR(27)//'[')