VHDL for FPGA Design/4-Bit Adder

4-Bit Adder with Carry Out VHDL Code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
 
entity Adder is
   port
   (
      nibble1, nibble2 : in unsigned(3 downto 0); 
 
      sum       : out unsigned(3 downto 0); 
      carry_out : out std_logic
   );
end entity Adder;
 
architecture Behavioral of Adder is
   signal temp : unsigned(4 downto 0); 
begin 
   temp <= ("0" & nibble1) + nibble2; 
   -- OR use the following syntax:
   -- temp <= ('0' & nibble1) + ('0' & nibble2);
 
   sum       <= temp(3 downto 0); 
   carry_out <= temp(4);
end architecture Behavioral;

Simulation Waveform