3-to-8 line Decoder VHDL Code (with-select-when)

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A binary decoder is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2^n unique outputs. 


VHDL Code:


library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity decoder38 is
    Port ( A : in  STD_LOGIC_VECTOR(2 downto 0);
           G1,G2b,G3b : in  STD_LOGIC;
           Y : out  STD_LOGIC_VECTOR (7 downto 0));
end decoder38;

architecture Behavioral of decoder38 is

signal en : std_logic_vector (5 downto 0) ;
begin
en <= (G1 & G2b & G3b) & A ;
with en select 
y <= "00000001" when "100000",
"00000010" when "100001",
"00000100" when "100010",
"00001000" when "100011",
"00010000" when "100100",
"00100000" when "100101",
"01000000" when "100110",
"10000000" when "100111",
"00000000" when others;
end Behavioral;


Testbench:

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
 
ENTITY decoder38_tb IS
END decoder38_tb;
 
ARCHITECTURE behavior OF decoder38_tb IS 
 
    -- Component Declaration for the Unit Under Test (UUT)
 
    COMPONENT decoder38
    PORT(
         A : IN  std_logic_vector(2 downto 0);
         G1 : IN  std_logic;
         G2b : IN  std_logic;
         G3b : IN  std_logic;
         Y : OUT  std_logic_vector(7 downto 0)
        );
    END COMPONENT;
    

   --Inputs
   signal A : std_logic_vector(2 downto 0) := (others => '0');
   signal G1 : std_logic := '0';
   signal G2b : std_logic := '0';
   signal G3b : std_logic := '0';

  --Outputs
   signal Y : std_logic_vector(7 downto 0);
  
BEGIN
 
-- Instantiate the Unit Under Test (UUT)
   uut: decoder38 PORT MAP (
          A => A,
          G1 => G1,
          G2b => G2b,
          G3b => G3b,
          Y => Y
        );

   -- Stimulus process
   stim_proc: process(A,G1,G2b,G3b)
   begin
G1 <= '1' after 30 ns;
G2b <= '0';
G3b <= '0' after 40 ns;
A(2) <= not A(2) after 80 ns;
A(1) <= not A(1) after 40 ns;
A(0) <= not A(0) after 20 ns;
   end process;
END;


Output:



The above code is tested on Xilinx ISE Design Suite 14.7 Webpack.
It is intended only for educational purpose.

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