You can use this type of constant wherever numeric constants are
  allowed; it assumes a numeric data type according to its context.

  A hexadecimal constant has one of these forms:

    Z'd[d...]'
    Z"d[d...]"

    d   Is a hexadecimal (base 16) digit in the range 0 - 9,
        or a letter in the range A - F, or a - f

  You can specify up to 128 bits in hexadecimal (32 hexadecimal
  digits) constants.  Leading zeros are ignored.