说明：  利用DAC0832产生的正斜率斜波接到运放的正输入端，可调电位器的输出电压接到运放的负输入端，运放输出端信号引到CPLD器件所对应的输入检测管脚。最后通过CPLD将被测电压显示到数码管上
(DAC0832 to produce a positive slope ramp receiving the output voltage of the op amp positive input terminal of the adjustable potentiometer received negative input of op amp, op amp output signal lead to the detection of the corresponding input pin CPLD devices. Finally, through the CPLD, the measured voltage to the digital tube)