lesson17_3 - 单个字符

代码说明：

说明：  接到单片机上后，输出到示波器可以看到一定频率的方波，通过按键可以调节波形的频率，同时在显示屏上也可以产生对应的周期和频率，外加信号发生器，可以得出对应的周期频率(After being connected to the single chip computer, the square wave of a certain frequency can be seen when it is output to the oscilloscope. The frequency of the waveform can be adjusted by keystrokes. At the same time, the corresponding period and frequency can be generated on the display screen, and the corresponding periodic frequency can be obtained by adding a signal generator.)