说明：   利用80C196片内的A/D转换模块，进行A/D转换实验，模拟量输入选用板提供的电位器，改变电位器值，观察AX寄存器中每次转换结果。将高8位AD结果用8255的PA口输出到LED灯上。
(80C196 chip to use the A/D converter module, for A/D conversion experiments, Analog Input selection board provided by potentiometer to change the potentiometer value to observe the AX register in the results of each conversion. High-8 AD results with 8255 output to the PA port LED lights on.)