内容：1、程序目的：使用定时器学习 倒计时 红绿灯原理

主要程序与倒计时相同

2、硬件要求：数码管、晶振12M

　　　　3、P1口连接至LED用于显示红绿灯(p1接锁存器，八段数码管的位信号和断信号都通过p1口锁存起来，这样可以节省端口)

　　　　4、数码管用于显示时间-Contents: 1, the program purpose: to learn to use the countdown timer with countdown traffic light principle the same as two major programs, hardware requirements: digital, crystal 12M 3, P1 port is connected to the LED lights for display (p1 pick latch, eight digital bit signals and off signals are latched by p1 tube mouth up, it saves port) 4, the digital display for time