交通灯控制系统（8253定时）假设为某个十字路口设计一个交通灯控制系统。在十字路口的东西和南北两个方向都各有红、黄、绿三个信号灯。红、黄、绿交通灯的变化规律为： 1）南北方向的绿灯、东西方向的红灯同时亮20秒。 2）南北方向的绿灯灭、黄灯亮5秒，同时东西方向的红灯继续亮。 3）南北方向的黄灯灭、红灯亮，同时东西方向的红灯灭、绿灯亮，持续20秒。 4）南北方向的红灯继续亮，同时东西方向的绿灯灭、黄灯亮5秒。 5）转1）重复。--Traffic light control system (8253 regular) is assumed to be a crossroads in the design of a traffic light control system. At the crossroads of East and West and North-South in both directions, each of red, yellow and green three lights. Red, yellow and green traffic lights change as follows: 1) green north-south direction, east-west direction at the same time the red light 20 seconds. 2) North-South direction to eliminate the green, yellow light 5 seconds, while east-west direction of the red light continues to light. 3) The north-south direction to eliminate the yellow light, red light, while east-west direction out of the red light, green light, sustained 20 seconds. 4) North-South direction of the red light continues to shine, while east-west direction out of the green, yellow light 5 seconds. 5) to 1) repeat.