-- Simulation Tutorial
-- 1-bit Adder

-- This is just to make a reference to some common things needed.
LIBRARY IEEE;
use IEEE.STD_LOGIC_1164.ALL;

-- We declare the 1-bit adder with the inputs and outputs
-- shown inside the port().
-- This will add two bits together(x,y), with a carry in(cin) and 
-- output the sum(sum) and a carry out(cout).
entity BIT_ADDER is
        port( a, b, cin         : in  STD_LOGIC;
              sum, cout         : out STD_LOGIC );
end BIT_ADDER;

-- This describes the functionality of the 1-BIT adder.
architecture BHV of BIT_ADDER is
begin
        
        -- Calculate the sum of the 1-BIT adder.
        sum <=  (not a and not b and cin) or
                        (not a and b and not cin) or
                        (a and not b and not cin) or
                        (a and b and cin);

        -- Calculates the carry out of the 1-BIT adder.
        cout <= (not a and b and cin) or
                        (a and not b and cin) or
                        (a and b and not cin) or
                        (a and b and cin);
end BHV;