以单片机为核心，设计一个简单交通灯控制系统，设A车道与B车道交叉组成十字路口，A是主道，B是支道。设计要求如下：

（1）　　用发光二极管模拟交通信号灯、两个方向分别设置红、绿、黄3种通行指示灯，用按键开关模拟车辆检测信号。

（2）　　正常情况下，A、B两车道轮流放行， A车道放行40秒，其中5秒用于警告，B车道放行25秒，其中5秒用于警告。有计时牌显示路口通行转换剩余时间。

（3）　　在交通繁忙时，交通信号灯控制系统应有手控开关，可人为地改变信号灯的状态，以缓解交通拥挤状况。在B车道放行期间，若A车道有车而B车道无车，按下开关K1使A车道放行15秒；在A车道放行期间，若B车道有车而A车道无车，按下开关K2使B车道放行15秒。

（4）　　有特种车辆如119、120通过路口时，系统可转为特种车辆放行，其他车辆禁止通行的状态，15s后系统恢复正常管理。

（5） 两个方向放行的时间可以通过键盘设置。

-Based on the single chip computer as the core, to design A simple traffic light control system, set up A lane and B lane cross composition crossroads, where is A, B is A way. The design requirements are as follows:



(1) using light-emitting diode simulation of traffic signal lamp, two direction set respectively red, green, yellow three traffic light, with key switch simulation vehicle detection signal.



(2) under normal circumstances, A, B two lane in turn release, A lane release forty seconds, of which 5 seconds for warning, B lane release 25 seconds, of which 5 seconds for warning. A timing brand display intersection traffic conversion time remaining.



(3) in the heavy traffic, traffic light control system should be hand control switch, can change the state of artificial light, in order to ease traffic congestion. In the B lane release period, if A lane car and B lane car free, press the switch K1 make A lane release 15 seconds　In A lane release period, if B lane have A car an