设计任务要求

控制器部分的状态转移图和流程图；交通灯控制器：用于十字路口的交通灯控制器。实验要求：

（1）东西方向各有一组红,黄,绿灯用于指挥交通，红，黄，绿的持续时间分别为25s,5s,20s 。

（2）当有紧急情况（如消防车）时，两个方向均为红灯亮，计时停止，当特殊情况结束后，控制器恢复原来状态，正常工作。

（3）两组数码管，以倒计时方式显示两个方向允许通行或禁止通行的时间。-Part of the design task requires the controller state transition diagrams and flow charts　traffic signal controller: the controller for the traffic light intersection. Experimental requirements: (1) east-west direction have a group of red, yellow, green light for directing traffic, red, yellow and green are the duration of 25s, 5s, 20s. (2) When there is an emergency situation (such as fire engines), the two directions are the red light, time stops, when the end of special circumstances, the controller to restore the original state of work. (3) two sets of digital control to display the countdown in both directions to allow access or prohibit the passage of time.