利用反转法扫描键盘，程序简单，理解稍有难度，方便51学习者的学习。-Inversion method by scanning the keyboard, the program is simple, a little difficult to understand, easy 51 learners.

51单片机的一些实验设计，led灯的点亮，键盘扫描，蜂鸣器等-51 microcontroller design some experiments, led lamp lighting, keyboard scanning, buzzer, etc.