led.vhd

用一个按钮开关循环控制四个led灯的闪烁方式

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity led is
	port(	a_in:	in	std_logic ;
			clk_in:	in	std_logic ;
			b_out:	out std_logic_vector(3 downto 0)
		);
end led ;
--============================================================
architecture behave of led is
	signal	state: std_logic_vector(1 downto 0) :="00";
	signal	period: std_logic_vector(23 downto 0) :="000000000000000000000000" ;
	signal		clk: std_logic :='0';
begin
---------------------=========================================
	sec_get:process(clk_in)
	begin 
		if(clk_in'event and clk_in='1') then
			if(period="100110001001011010000000") then
				clk<=not clk;
				period<="000000000000000000000000";
			else 
				period<=period+1;
			end if;
		end if;
	end process ;
--------------------==========================================
	state_change:process(a_in)
	begin
		if(a_in'event and a_in='1') then
			state<=state+1;
		end if;
	end process;
---------------------==========================================
	light:process(clk)
	begin
		case state is
		when "00" => if(clk='0') then
						b_out <= "0000";
					else
						b_out <= "1111";
					end if;
		when "01" => if(clk='0') then
						b_out <= "0011";
					else
						b_out <= "1100";
					end if;
		when "10" => if(clk='0') then
						b_out <= "0101";
					else
						b_out <= "1010";
					end if;					
		when "11" => if(clk='0') then
						b_out <= "1001";
					else
						b_out <= "0110";
					end if;
		when others => b_out <= "0000";
	end case;
	end process;
end behave;