改变学习板上的2个电位器对应的2段模拟输入，实现模拟输入，学员观察数码管的数字变化情况,通过改D[4]的值，实现模拟输出.-Changing the learning board two potentiometers corresponding paragraph 2 analog inputs, analog inputs, digital tube digital trainees observe the changes, by changing D [4] value for analog output.