traffic.vhd

该程序是用VHDL实现的交通灯模拟程序

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;

ENTITY traffic IS
	PORT(	en:		IN	STD_LOGIC;
			clk:	IN	STD_LOGIC;
			rst:	IN	STD_LOGIC;
			q:		OUT	STD_LOGIC_VECTOR(11 DOWNTO 0)
		);
--	Set the time of the yellow light according to the clock
	CONSTANT number1 : INTEGER := 2;
--	Set the time of the green light according to the clock
	CONSTANT number2 : INTEGER := 5;
END traffic;

ARCHITECTURE func1 OF traffic IS
BEGIN 
	PROCESS(clk)
	VARIABLE temp1:	INTEGER RANGE 0 TO 20;
	VARIABLE temp2:	INTEGER RANGE 0 TO 2;
	BEGIN
		IF(rst = '0') THEN
			q<="000000000000";
		ELSIF(clk'EVENT AND clk='1')THEN
			IF(en = '1') THEN
				temp1 := temp1 + 1;
				IF(temp1 = number1 AND temp2 = 0) THEN
					q<="001100100001";  -- Direction A
					temp2 := temp2 + 1;
				ELSIF(temp1 = number2 AND temp2 = 1) THEN 
					q<="001010010001";  -- Direction A to Direction B
					temp1 := 0;
					temp2 := temp2 + 1;
				ELSIF(temp1 = number1 AND temp2 = 2) THEN
					q<="100001001100";  -- Direction B
					temp2 := temp2 + 1;
				ELSIF(temp1 = number2 AND temp2 = 3) THEN
					q<="010001001010";  -- Direction B to Direction A
					temp1 := 0;
					temp2 := 0;
				END IF;
			END IF;
		END IF;
	END PROCESS;
END func1;