VMS Help PASCAL, Predeclared Routines, Char Strng, BIN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The BIN function returns a character-string value  that  is  the
  binary  equivalent of the specified parameter.  The return value
  is compatible with all other string types.

  Syntax:

     BIN( x [[, length[[, digits]]]] )

  The parameter 'x' is  the  expression  to  be  converted.   This
  parameter  must  have  a  size that is known at compile time; it
  cannot be VARYING OF CHAR, a conformant parameter, or  a  schema
  type.

  Two optional  integer  parameters  specify  the  length  of  the
  resulting string and the minimum number of significant digits to
  be returned.  If you specify a length that is too short to  hold
  the  converted  value,  the resulting string is truncated on the
  left.

  If you omit the  optional  parameters,  the  bit  width  of  the
  converted  parameter  value determines the string length and the
  number  of  significant  digits.   By  default,  the  number  of
  significant digits is the minimum number of characters necessary
  to express all  the  bits  of  the  converted  parameter.   This
  default  length is one character more than the default number of
  digits, which causes a leading  blank  to  be  included  in  the
  resulting string when both parameters are omitted.