We described an approach suitable for obtaining an analytical expression for the energy of an antiphase boundary in an ordered alloy in the hard sphere model using pair interatomic interaction potentials. Depending on the orientation of the antiphase boundary, the crystal is subdivided into two-dimensional monatomic packings parallel to the defect, and its energy is determined by the sum of the energies of the two-dimensional packings. The results of the calculations for antiphase boundaries of different orientations are given in the form of matrix expressions for each of the considered superstructures.