-- FILE: x_or.adb
-- DATE: 7/98
-- AUTHOR: Sy Wong
-- AIM: Implementation of exclusive or function

with NOR, NAND, INVERT;
package body X_OR is
  procedure update (d: in out device) is
    unit1: NOR.device;
    unit2, unit5: INVERT.device;
    unit3, unit4: NAND.device;
  begin
    -- d.data_out:= (d.input1 or d.input2) and not (d.input1 and d.input2);
    unit1.input1:= d.input1;
    unit1.input2:= d.input2;
    NOR.update (unit1);

    unit2.data_in:= unit1.data_out;
    INVERT.update (unit2);    -- invert NOR function to OR

    unit3.input1:= d.input1;
    unit3.input2:= d.input2;
    NAND.update (unit3);      -- not (d.input1 and d.input2)
                         
    unit4.input1 := unit2.data_out;
    unit4.input2 := unit3.data_out;
    NAND.update (unit4);
    unit5.data_in:= unit4.data_out;
    INVERT.update (unit5);     -- make NAND into AND

    d.data_out:= unit5.data_out;
  end update;
end X_OR;