light.vhd

用PLC程序编写十字路口的交通灯

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity light is
port(clk1:		in		std_logic;
	 light:		buffer	std_logic_vector(7 downto 0));
end light;
architecture behv of light is
	constant 	len:		integer:=7;
	signal		banner:		std_logic:='0';
	signal		clk,clk2:	std_logic;
begin
	clk<=(clk1 and banner) or (clk2 and not banner);
	process(clk1)
	begin
		if clk1'event and clk1='1' then
			clk2<=not clk2   ;
		end if;
	end process;
--	process(clk1,clk2,banner)
	process(clk)
		variable	flag:	bit_vector(2 downto 0):="000";
	begin
--		clk<=(clk1 and banner) or (clk2 and not banner);
		if clk'event and clk='1' then
			if flag="000" then
				light<='1' & light(len downto 1);
				if light(1)='1' then
					flag:="001";
				end if;
			elsif flag="001" then
				light<=light(len-1 downto 0) & '0';
				if light(6)='0' then
					flag:="010";
				end if;
			elsif flag="010" then
				light(len downto 4)<=light(len-1 downto 4)&'1';
				light(len-4 downto 0)<='1'&light(len-4 downto 1);
				if light(1)='1' then
					flag:="011";
				end if;
			elsif flag="011" then
				light(len downto 4)<='0'&light(len downto 5);
				light(len-4 downto 0)<=light(len-5 downto 0)&'0';
				if light(2)='0' then
					flag:="100";
				end if;
			elsif flag="100" then
				light(len downto 4)<='1'&light(len downto 5);
				light(len-4 downto 0)<='1'&light(len-4 downto 1);
				if light(1)='1' then
					flag:="101";
				end if;
			elsif flag="101" then
				light<="00000000";
				flag:="110";
			elsif flag="110" then
				banner<=not banner;
				flag:="000";
			end if;
		end if;
	end process;
end behv;