单片机学习100实例，函数的使用和熟悉，实例3：用单片机控制第一个灯亮 实例4：用单片机控制一个灯闪烁：认识单片机的工作频率-100 instances of single-chip learning, a function of use and familiarity, Example 3: The single-chip control of the first instance of four lights: flashing lights with a single-chip co