How to properly use VADC port to read value from an external potential meter?

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Hi there,

I have a PMSM motor which is controlled by XMC1302T038 mcu with sensorless FOC and now I want to control its speed by connecting an external potential meter to pin 2.5 of XMC1302. However I am running into two problems when read pot value from this P2.5 VADC port:
1. the values I got are not stable. They are bouncing always even if I set pot meter to a fixed position. I searched around and seems I need some special code to filter the sampled values. I am new to this VADC area. Could some one please give me some guide?
2. the values I got don't match the 3.3v reference voltage. I am using 3.3v to power on the whole system including the mcu and the related VADC configuration register is configured to "AREF = 00" which means "VAREF = VDD".
when the pot meter is set to 1.454v, I got value around 1369, when the pot meter is set to 2.193v, I got value around 2030, those values do suggest the reference voltage is around 4.4v, this is strange because the reference voltage should be 3.3v.

Appreciate any help.
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