Why do the ADC value only increase?



I use the AUXV0 of Q24PL samples one input.

When I input “AT+ADC?”, the value of the input is given (such as: “+ADC: 4248, 233”)
And when the volt of the input increases, the ADC value increases (such as: “+ADC: 4248,1223”).
When the volt increases again, the ADC value increases again (such as: “+ADC: 4248,2023”).

But when the volt decreases, the ADC VALUE does not decrease, and has not any change (also :"+ADC: 4248,2023").
And when the volt of the input is 0V (tied to GND), the ADC VALUE hasnot any change (also :"+ADC: 4248,2023").

Again, if I reset the Q24PL, the ADC VALUE just changes to “+ADC: 4248,0”.


can sb. help me?