自动交通控制系统,设计一个具有主、支干道十字路口的交通灯自动控制芯片。

当主干道与支干道均无车辆要求通行时，主干道应保持畅通，亮绿灯，支干道亮红灯。

如果主干道无车，支干道有车，则允许支干道通行，主干道亮红灯，支干道亮绿灯。

如果主干道和支干道均有车要求通行，则两者应交替通行，并要求主干道每次通行30秒，支干道每次通行20秒，并显示剩余时间。

每次绿灯变红灯时，黄灯应先亮3秒钟，并显示绿灯和黄灯剩余时间。

-Automatic traffic control systems, to design a main, branch roads intersection traffic lights automatically control chip. When the trunk and branch roads requires no vehicle traffic, roads should be kept clear, bright green, red branch roads. If no car trunk, branch roads have a car, then the branch roads to allow access, main road red light, green light branch roads. If the car trunk and branch roads are required pass, then they should alternate access and request access roads every 30 seconds, 20 seconds pass each branch roads, and displays the remaining time. Each time the green light becomes red, yellow light should be 3 seconds and displays the time remaining green and yellow.