/sys$common/syshlp/helplib.hlb FORTRAN, Format Specifiers, Z  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Zw[.m] (Hexadecimal Editing)

  On input, transfers w characters from the external field and
  assigns them, as a hexadecimal value, to the corresponding I/O list
  element (which can be any data type).  The input value must be in
  the form of a hexadecimal constant.  Each input character
  corresponds to four bits in the variable, high order to low order.
  If the input value contains more characters than specified by "w",
  an error occurs.  If the input value contains fewer characters, it
  is padded with zeros on the left before being converted.

  On output, transfers the number of hexadecimal characters specified
  by "w" from a variable or constant to the record.  The rightmost
  characters represent the low-order bits.  If the variable or
  constant contains more characters than "w" specifies, the value is
  set to all asterisks (an error occurs).  If the variable or
  constant contains fewer characters, the value is padded on the left
  with spaces.  "m" specifies the minimum number of characters (with
  zero padding) that the value can contain.  "m" must be an integer
  in the range 1 through 255.  "w" must be large enough to include a
  possible minus sign.  If "m" is present, the external field
  consists of at least "m" digits and, if necessary, is zero filled
  on the left.