myled8.vhd

led跑马灯显示

entity myled8 is
  port (clk:in bit;
        y:out bit_vector(7 downto 0));
end myled8;
architecture bhv of myled8 is
 signal b:integer range 0 to 7;
  begin 
a1:process(clk)
   variable a:integer range 0 to 4000;
    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 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";
    else y<="10000000";
    end if;
  end process;
end architecture;