VHDL Code for Full Adder

Full Adder

The VHDL Code for full-adder circuit adds three one-bit binary numbers (A B Cin) and outputs two one-bit binary numbers, a sum (S) and a carry (Cout). Truth Table describes the functionality of full adder. sum(S) output is High when odd number of inputs are High. Cout is High, when two or more inputs are High. VHDL Code for full adder can also be constructed with 2 half adder Port mapping in to full adder.

Full Adder Truth Table

Full Adder Logic Circuit

VHDL Code for Full Adder

 library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity full_adder_vhdl_code is
 Port ( A : in STD_LOGIC;
 B : in STD_LOGIC;
 Cin : in STD_LOGIC;
 S : out STD_LOGIC;
 Cout : out STD_LOGIC);
end full_adder_vhdl_code;

architecture gate_level of full_adder_vhdl_code is

begin

 S <= A XOR B XOR Cin ;
 Cout <= (A AND B) OR (Cin AND A) OR (Cin AND B) ;

end gate_level;

Testbench VHDL Code for Full Adder

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

ENTITY Testbench_full_adder IS
END Testbench_full_adder;

ARCHITECTURE behavior OF Testbench_full_adder IS 

 -- Component Declaration for the Unit Under Test (UUT)

 COMPONENT full_adder_vhdl_code
 PORT(
 A : IN std_logic;
 B : IN std_logic;
 Cin : IN std_logic;
 S : OUT std_logic;
 Cout : OUT std_logic
 );
 END COMPONENT;

 --Inputs
 signal A : std_logic := '0';
 signal B : std_logic := '0';
 signal Cin : std_logic := '0';

 --Outputs
 signal S : std_logic;
 signal Cout : std_logic;

BEGIN

 -- Instantiate the Unit Under Test (UUT)
 uut: full_adder_vhdl_code PORT MAP (
 A => A,
 B => B,
 Cin => Cin,
 S => S,
 Cout => Cout
 );

 -- Stimulus process
 stim_proc: process
 begin
 -- hold reset state for 100 ns.
 wait for 100 ns; 

 -- insert stimulus here
 A <= '1';
 B <= '0';
 Cin <= '0';
 wait for 10 ns;

 A <= '0';
 B <= '1';
 Cin <= '0';
 wait for 10 ns;

 A <= '1';
 B <= '1';
 Cin <= '0';
 wait for 10 ns;

 A <= '0';
 B <= '0';
 Cin <= '1';
 wait for 10 ns;

 A <= '1';
 B <= '0';
 Cin <= '1';
 wait for 10 ns;

 A <= '0';
 B <= '1';
 Cin <= '1';
 wait for 10 ns;

 A <= '1';
 B <= '1';
 Cin <= '1';
 wait for 10 ns;

 end process;

END;

Output Waveform for full adder VHDL Code