led.vhd

用VHDL编写的一个LED显示程序

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity led is
port(clkin:in std_logic;
     rst:in std_logic;
     q:out std_logic_vector(7 downto 0)
    );
end led;
architecture one of led is
type states is(s0,s1,s2,s3);
signal present:states;
signal clkout:std_logic;
signal clk1hz:std_logic;
signal q1:std_logic_vector(7 downto 0);
signal count:std_logic_vector(3 downto 0);
begin
process(clkin)
begin
clkout<=not clkin;
end process;
process(clkout)
variable m:integer range 0 to 12499999;
begin
if rising_edge(clkout) then
   if m=12499999 then
      clk1hz<=not clk1hz;
   else
      m:=m+1;
   end if;
end if;
end process;
process(clk1hz,rst)
begin
if rst='0' then
   present<=s0;
   q1<=(others=>'0');
elsif clk1hz'event and clk1hz='1' then
 case present is
   when s0=>if q1="00000000" then-------------------------s0模式：从左到右逐个点亮LED
                 q1<="10000000";
            else
                 if count="0111" then
                     count<=(others=>'0');
                     q1<="00000001";
                     present<=s1;
                 else
                     q1<=q1(0)&q1(7 downto 1);
                     count<=count+1;
                     present<=s0;
                 end if;
             end if;
   when s1=>if count="0111" then---------------------------s1模式：从右到左逐个点亮LED              
                 count<=(others=>'0');
                 q1<="10000001";
                 present<=s2;
            else
                 q1<=q1(6 downto 0)&q1(7);
                 count<=count+1;
                 present<=s1;
            end if;
   when s2=>if count="0011" then---------------------------s2模式：从两边到中间逐个点亮LED
                 count<=(others=>'0');
                 q1<="00011000";
                 present<=s3;
            else
                 q1(7 downto 4)<=q1(4)&q1(7 downto 5);
                 q1(3 downto 0)<=q1(2 downto 0)&q1(3);
                 count<=count+1;
                 present<=s2;
            end if;
   when s3=>if count="0011" then---------------------------s3模式：从中间到两边逐个点亮LED 
                 count<=(others=>'0');
                 q1<="10000000";
                 present<=s0;
            else
                 q1(7 downto 4)<=q1(6 downto 4)&q1(7);
                 q1(3 downto 0)<=q1(0)&q1(3 downto 1);
                 count<=count+1;
                 present<=s3;
            end if;
 end case;
end if;
end process;
q<=q1;
end one;