Simple 4 : 1 multiplexer using case statements

Here is the code for 4 : 1 MUX using case statements.The module contains 4 single bit input lines and one 2 bit select input.The output is a single bit line.

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity multiplexer4_1 is
port (
      i0 : in std_logic;
      i1 : in std_logic;
      i2 : in std_logic;
      i3 : in std_logic;
     sel : in std_logic_vector(1 downto 0);
     bitout : out std_logic
     );
end multiplexer4_1;

architecture Behavioral of multiplexer4_1 is
begin

process(i0,i1,i2,i3,sel)
begin
case sel is
  when "00" => bitout <= i0;
  when "01" => bitout <= i1;
  when "10" => bitout <= i2;
  when others => bitout <= i3;
end case;
end process;

end Behavioral;

The testbench code used for testing the code is given below:

  LIBRARY ieee;
  USE ieee.std_logic_1164.ALL;

  ENTITY testbench IS
  END testbench;

  ARCHITECTURE behavior OF testbench IS
          SIGNAL i0,i1,i2,i3,bitout :  std_logic:='0';
          SIGNAL sel :  std_logic_vector(1 downto 0):="00";
  BEGIN
    UUT : entity work.multiplexer4_1 port map(i0,i1,i2,i3,sel,bitout);

     tb : PROCESS
     BEGIN
            i0<='1';
            i1<='0';
            i2<='1';
            i3<='0';
            sel <="00";
            wait for 2 ns;
            sel <="01";
            wait for 2 ns;
            sel <="10";
             wait for 2 ns;
             sel <="11";
              wait for 2 ns;
            --more input combinations can be given here.
     END PROCESS tb;

  END;

     The simulated testbench waveform is shown below:

  The code was synthesized using XILINX ISE XST . The RTL schematic of the design is shown below.

Note :- Use RTL Viewer to get a closer look on how your design is implemented in hardware.