VHDL - Nor Gate

 nor_gate.vhd

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity nor_gate is
Port (
a: in std_logic;
b: in std_logic;
c: out std_logic);
end nor_gate;

architecture Behavioral of nor_gate is
begin
c<= not(a or b);
end Behavioral;

tb_nor_gate.vhd

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity tb_nor_gate is
end tb_nor_gate;

architecture Behavioral of tb_nor_gate is
component nor_gate is
Port(a: in std_logic;
b: in std_logic;
c: out std_logic);
end component;
signal tb_a,tb_b,tb_c : std_logic:=’0';

begin
uut : nor_gate port map(
a=>tb_a, b=>tb_b, c=>tb_c
);

stim_process: process
begin

tb_a<=’0' ; tb_b<=’0'; wait for 100ns;
tb_a<=’0' ; tb_b<=’1'; wait for 100ns;
tb_a<=’1' ; tb_b<=’0'; wait for 100ns;
tb_a<=’1' ; tb_b<=’1'; wait for 100ns;

end process;
end Behavioral;

The output waveform for nor gate will be as follows: