count30.vhd

四字路口交通灯管理器的设计（含波形输出）

LIBRARY IEEE; 
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY count30 IS
PORT(
       clk        :IN STD_LOGIC;
       enable     :IN STD_LOGIC;
	   c          :OUT STD_LOGIC);
END count30;
ARCHITECTURE a OF count30 IS
BEGIN
   PROCESS(clk)
	  VARIABLE cnt:INTEGER RANGE 30 DOWNTO 0;
   BEGIN
	  IF(clk 'EVENT AND clk='1')THEN
	         IF enable='1'AND cnt<30 THEN
                 cnt:=cnt+1;
             ELSE
                 cnt:=0;
             END IF;
      END IF;
   IF cnt=30 THEN
      C<='1';
   ELSE
      C<='0';
   END IF;
   END PROCESS;
   END a;