myled.vhd

利用if语句实现流水灯设计。工具：Quartus ii 6.0 语言：VHDL

library ieee;
use ieee.std_logic_1164.all;
entity myled is
	port(clk:in std_logic;
	       y:out std_logic_vector(7 downto 0));--8位流水灯输出
end myled;
-------------------------------------------------------------------
architecture bhv of myled is
	 signal b:integer range 0 to 7;
begin
	a1:process(clk)
	variable a:integer range  0 to 4000;--1秒计数，时钟频率4000Hz
	begin
	if clk'event and clk='1' then
	     if a<4000 then
	      a:=a+1;
	     else 
	      a:=0;
	      b<=b+1;
	    end if;
	end if;	
end process;
-------------------------------------------------------------------
a2:process(b)
   begin
		  if b=0 then     --高电平亮，轮流亮过去
		    y<="00000001";
		  elsif b=1 then 
		    y<="00000010";
		  elsif b=2 then 
		    y<="00000100";
		  elsif b=3 then
		    y<="00001000";
		  elsif b=4 then 
		    y<="00010000";
		  elsif b=5 then 
		    y<="00100000";
		  elsif b=6 then 
		    y<="01000000";
		  elsif b=7 then  
		    y<="10000000";
		 end if;
		end process;
end bhv;