led.vhd

该程序实现跑马灯效果,跑马灯共4个状态循环显示

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY led IS
 PORT(clk:IN STD_LOGIC;
      rst:IN STD_LOGIC;
      q:OUT STD_LOGIC_VECTOR(3 DOWNTO 0)
     );
END led;

ARCHITECTURE one OF led IS
 TYPE STATE IS(s0,s1,s2,s3);
 SIGNAL present :STATE;
 SIGNAL q1:STD_LOGIC_VECTOR(3 DOWNTO 0);
 SIGNAL count:STD_LOGIC_VECTOR(3 DOWNTO 0);
BEGIN
PROCESS(clk,rst)
 BEGIN
  IF rst='0'then
     present<=s0;
     q1<=(OTHERS=>'0');
  ELSIF clk'event AND clk='1'THEN
    CASE present IS
     WHEN s0=>IF q1="0000"THEN
                 q1<="1000";
              ELSE
                 IF count="0011"THEN
                    count<=(OTHERS=>'0');
                    q1<="0001";
                    present<=s1;
                 ELSE q1<=q1(0)&q1(3 DOWNTO 1);
                    count<=count+1;
                    present<=s0;
                 END IF;
              END IF;
     WHEN s1=>IF count="0011"THEN
                 count<=(others=>'0');
                 q1<="1001";
                 present<=s2;
              ELSE q1<=q1(2 DOWNTO 0)&q1(3);
                 count<=count+1;
                 present<=s1;
              END IF;
     WHEN s2=>IF count="0011"THEN
                 count<=(others=>'0');
                 q1<="0110";
                 present<=s3;
              ELSE q1(3 DOWNTO 2)<=q1(2)&q1(3);
                   q1(1 DOWNTO 0)<=q1(0)&q1(1);
                 count<=count+1;
                 present<=s2;
              END IF;
     WHEN s3=>IF count="0011"THEN
                 count<=(others=>'0');
                 q1<="1000";
                 present<=s0;
              ELSE q1(3 DOWNTO 2)<=q1(2)&q1(3);
                   q1(1 DOWNTO 0)<=q1(0)&q1(1);
                 count<=count+1;
                 present<=s3;
              END IF;
    END CASE;
   END IF;
 END PROCESS;
 q<=q1;
END;