设计任务：模拟十字路口交通信号灯的工作过程，利用实验板上的两组红、黄、绿LED作为交通信号灯，设计一个交通信号灯控制器。要求：

（1）　　交通灯从绿变红时，有4秒黄灯亮的间隔时间；

（2）　　交通灯红变绿是直接进行的，没有间隔时间；

（3）　　主干道上的绿灯时间为40秒，支干道的绿灯时间为20秒；

（4）　　在任意时间，显示每个状态到该状态结束所需的时间。

-The design task: simulate the crossroads of the working process of the traffic lights, the use of the experimental board two sets of red, yellow and green LED traffic lights, to design a traffic signal controller. Requirements:

(1) traffic lights from green to red, four seconds of yellow light interval

(2) traffic lights red to green directly, there is no interval

(3) on the main road green time of 40 seconds, the branch roads of the green time of 20 seconds

(4) at any time, each state to the state to the end of the time required.