Ripple Carry Adder Behavioral

Test Bench Program :-

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;


ENTITY tb_rca_Behavioral IS
END tb_rca_Behavioral;

ARCHITECTURE behavior OF tb_rca_Behavioral IS

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

    COMPONENT rca_Behavioral
    PORT(
         a : IN  std_logic_vector(3 downto 0);
         b : IN  std_logic_vector(3 downto 0);
         Cin : IN  std_logic;
         Cout : OUT  std_logic;
         s : OUT  std_logic_vector(3 downto 0)
        );
    END COMPONENT;
   

   --Inputs
   signal a : std_logic_vector(3 downto 0) := (others => '0');
   signal b : std_logic_vector(3 downto 0) := (others => '0');
   signal Cin : std_logic := '0';

  --Outputs
   signal Cout : std_logic;
   signal s : std_logic_vector(3 downto 0);


BEGIN

-- Instantiate the Unit Under Test (UUT)
   uut: rca_Behavioral PORT MAP (
          a => a,
          b => b,
          Cin => Cin,
          Cout => Cout,
          s => s
        );

   -- Stimulus process
   stim_proc: process
   begin
      -- hold reset state for 100 ns.
      wait for 100 ns; a<="0001"; b<="0001";cin<='0';
      wait for 100 ns; a<="0101"; b<="1001";cin<='0';
      wait for 100 ns; a<="1001"; b<="1101";cin<='0';
      wait for 100 ns; a<="0111"; b<="1011";cin<='1';
      wait for 100 ns; a<="0101"; b<="1111";cin<='0';
      wait for 100 ns; a<="0011"; b<="1101";cin<='1';
      wait for 100 ns; a<="1001"; b<="0101";cin<='0';
      wait for 100 ns; a<="1101"; b<="1001";cin<='1';
      wait;
   end process;

END;


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Ripple Carry Adder Behavioral (  VHDL  )  :-

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_unsigned.ALL;


entity rca_Behavioral is
    Port ( a : in  STD_LOGIC_VECTOR (3 downto 0);
           b : in  STD_LOGIC_VECTOR (3 downto 0);
           Cin : in  STD_LOGIC;
           Cout : out  STD_LOGIC;
           s : out  STD_LOGIC_VECTOR (3 downto 0));
end rca_Behavioral;

architecture Behavioral of rca_Behavioral is
signal q: std_logic_vector(4 downto 0);
begin

process(a,b)
begin
q<=('0' & a)+('0' & b)+cin;
end process;

process(q)
begin
s<=q(3 downto 0);
Cout<=q(4);
end process;