-------------------------------------------------------------------------------
-- Module     : mux2to1
-------------------------------------------------------------------------------
-- Author     : Johann Faerber
-- Company    : University of Applied Sciences Augsburg
-------------------------------------------------------------------------------
-- Description: 2-to-1 multiplexer
--              function modelled as structure of basic logic gates
-------------------------------------------------------------------------------
-- Revisions  : see end of file
-------------------------------------------------------------------------------
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;

ENTITY mux2to1 IS
  PORT (a_i   : IN  std_ulogic;         -- data input a
        b_i   : IN  std_ulogic;         -- data input b
        sel_i : IN  std_ulogic;         -- select which input is connected to y
        -- sel = '1': a -> y
        -- sel = '0': b -> y
        y_o   : OUT std_ulogic          -- data output y
        );
END mux2to1;

ARCHITECTURE structure OF mux2to1 IS

  COMPONENT invgate
    PORT (
      a_i : IN  std_ulogic;
      y_o : OUT std_ulogic);
  END COMPONENT;

  COMPONENT and2gate
    PORT (
      a_i : IN  std_ulogic;
      b_i : IN  std_ulogic;
      y_o : OUT std_ulogic);
  END COMPONENT;

  COMPONENT or2gate
    PORT (
      a_i : IN  std_ulogic;
      b_i : IN  std_ulogic;
      y_o : OUT std_ulogic);
  END COMPONENT;

  SIGNAL p0, p1  : std_ulogic;
  SIGNAL p2 : std_ulogic;
  
BEGIN

  inv_gate_1 : invgate
    PORT MAP (
      a_i => sel_i,
      y_o => p2);

  and2_gate_1 : and2gate
    PORT MAP (
      a_i => a_i,
      b_i => sel_i,
      y_o => p0);

  and2_gate_2 : and2gate
    PORT MAP (
      a_i => b_i,
      b_i => p2,
      y_o => p1);

  or2_gate_1 : or2gate
    PORT MAP (
      a_i => p0,
      b_i => p1,
      y_o => y_o);

--  inv_gate_1 : invgate PORT MAP (sel_i, p2);

--  and2_gate_1 : and2gate PORT MAP (a_i, sel_i, p0);

--  and2_gate_2 : and2gate PORT MAP (b_i, p2, p1);

--  or2_gate_1 : or2gate PORT MAP (p0, p1, y_o);

END structure;

-------------------------------------------------------------------------------
-- Revisions:
-- ----------
-- $Id:$
-------------------------------------------------------------------------------