用8255做输出口，控制十二个发光二极管亮灭，模拟交通灯管理。十字路口东西南北走向。初始状态0为东西红灯，南北红灯。状态1（10s），东西绿灯通车，南北红灯；状态2（3s），东西绿灯灭，黄灯闪几次，南北红灯；状态3（10s），东西红灯，南北绿灯通车；状态4（3s），东西红灯，南北绿灯灭，黄灯闪几次。依次循环-Done by 8255 output, controlling 12 out bright light-emitting diodes to simulate the management of traffic lights. East-west north-south crossroads. Initial state 0 for the east-west red lights, red lights north and south. State 1 (10s), something the green light opened the North-South red　state 2 (3s), green things out, yellow light flashing several times, the North-South red　state 3 (10s), what a red light, green light to the opening of the North and the South　state 4 (3s), what a red light, green light to eliminate the North and the South, yellow light flashing several times. Followed by cycle