VHDL Code for 2 to 4 decoder

Binary decoder

2 to 4 Decoder design using logic gates

Truth Table for 2 to 4 Decoder

Similar to Encoder Design, VHDL Code for 2 to 4 decoder can be done in different methods like using case statement, using if else statement, using logic gates etc. Here we provide example code for all 3 method for better understanding of the language.

library IEEE;
use IEEE.STD_LOGIC_1164.all;

entity decoder is
port(
a : in STD_LOGIC_VECTOR(1 downto 0);
b : out STD_LOGIC_VECTOR(3 downto 0)
);
end decoder;
architecture bhv of decoder is
begin

process(a)
begin
case a is
when “00” => b <= “0001”; when “01” => b <= “0010”; when “10” => b <= “0100”; when “11” => b <= “1000”;
end case;
end process;

end bhv;

VHDL Code for 2 to 4 decoder using if else statement

library IEEE;
use IEEE.STD_LOGIC_1164.all;

entity decoder1 is
port(
a : in STD_LOGIC_VECTOR(1 downto 0);
b : out STD_LOGIC_VECTOR(3 downto 0)
);
end decoder1;

architecture bhv of decoder1 is
begin

process(a)
begin
if (a=”00″) then
b <= “0001”;
elsif (a=”01″) then
b <= “0010”;
elsif (a=”10″) then
b <= “0100”;
else
b <= “1000”;
end if;
end process;

end bhv;

VHDL Code for 2 to 4 decoder using logic gates

library IEEE;
use IEEE.STD_LOGIC_1164.all;

entity decoder2 is
port(
a : in STD_LOGIC_VECTOR(1 downto 0);
b : out STD_LOGIC_VECTOR(3 downto 0)
);
end decoder2;

architecture bhv of decoder2 is
begin

b(0) <= not a(0) and not a(1);
b(1) <= not a(0) and a(1);
b(2) <= a(0) and not a(1);
b(3) <= a(0) and a(1);

end bhv;