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--******************************************************************************
--*                                                                            *
--*                             4 - 16 Decoder                                 *
--*                                                     Device : XC9536-PC44   *
--*                                                     Author : Seiichi Inoue *
--******************************************************************************

library ieee;                                    -- Defines std_logic types
use ieee.std_logic_1164.all;

entity Decoder2 is
  port ( A, B, C, D : in std_logic;              -- Defines ports
         Q : out std_logic_vector(15 downto 0));
end Decoder2;

architecture Decoder2_arch of Decoder2 is
  signal IN_DATA : std_logic_vector(3 downto 0); -- Defines internal signals
begin
  IN_DATA <= D & C & B & A;                      -- Binding vector
  process( IN_DATA ) begin
    case IN_DATA is                              -- Decode with input data
      when "0000" => Q <= "0000000000000001";
      when "0001" => Q <= "0000000000000010";
      when "0010" => Q <= "0000000000000100";
      when "0011" => Q <= "0000000000001000";
      when "0100" => Q <= "0000000000010000";
      when "0101" => Q <= "0000000000100000";
      when "0110" => Q <= "0000000001000000";
      when "0111" => Q <= "0000000010000000";
      when "1000" => Q <= "0000000100000000";
      when "1001" => Q <= "0000001000000000";
      when "1010" => Q <= "0000010000000000";
      when "1011" => Q <= "0000100000000000";
      when "1100" => Q <= "0001000000000000";
      when "1101" => Q <= "0010000000000000";
      when "1110" => Q <= "0100000000000000";
      when "1111" => Q <= "1000000000000000";
      when others => Q <= "XXXXXXXXXXXXXXXX";    -- Illegal condition
    end case;
  end process;
end Decoder2_arch;

--******************************************************************************
--*                            end of 4 - 16 Decoder                           *
--******************************************************************************