D FLIP-FLOP ASYNC

-- design.vhd

library IEEE;
use IEEE.std_logic_1164.all;

entity d_flipflop_async is
    port(C, D : in std_logic;
         Q, Qn : out std_logic);
end entity d_flipflop_async;

architecture d_flipflop_async_arch of d_flipflop_async is
begin
    process(C, D)
    begin
        if(C = '0' and D = '0') then
            Q <= Q;
            Q <= Qn;
        elsif(C = '0' and D = '1') then
            Q <= Q;
            Qn <= Qn;
        elsif(C = '1' and D = '0') then
            Q <= '0';
            Qn <= '1';
        elsif(C = '1' and D = '1') then
            Q <= '1';
            Qn <= '0';
        end if;
    end process;
end architecture d_flipflop_async_arch;


-- testbench.vhd

library IEEE;
use IEEE.std_logic_1164.all;

entity d_flipflop_async_tb is
end entity d_flipflop_async_tb;

architecture d_flipflop_async_tb_arch of d_flipflop_async_tb is
    signal C1, D1, Q1, Qn1 : std_logic;
begin
    DUT1 : entity work.d_flipflop_async(d_flipflop_async_arch)
           port map(C1, D1, Q1, Qn1);

    STIMULUS : process
    begin
        C1 <= '0'; D1 <= '0'; wait for 10ns;
        C1 <= '0'; D1 <= '1'; wait for 10ns;
        C1 <= '1'; D1 <= '0'; wait for 10ns;
        C1 <= '1'; D1 <= '1'; wait for 10ns;
        C1 <= 'X'; D1 <= 'X'; wait for 10ns;
    end process;
end architecture d_flipflop_async_tb_arch;