What is up with STM32H563 ADC INP0?

[Dimlite]

Hi,

I am not able to get a correct reading from ADC1 INP0 (PA0). All the other analog channels works fine.

The datasheet mentions this:

ADC option register (ADC_OR), option bit 0 (OP0)

For ADC1:

0: INP0/INN1 GPIO switch control disabled

1: INP0/INN1 GPIO switch control enabled

Note:This option bit must be set to 1 when ADCx_INP0 or ADCx_INN1 channel is selected.

The expected value is 2048, but I get 4095 when OP = 1, and 3433 with OP0.

The input has a 2 k resistor in series, and I measure 1.5 V (correct) on the far side, and 1.3 V on the side directly connected to the input.

Please see attached file, which is from the datasheet for RGT6. I don't know how to interpret the table. Is option register implemented or not regarding ADC1?

What is the purpose of the option bit, and what am I missing here?

[Andrew Neil]

What board(s) are you using?

See: https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[Dimlite]

It is a custom board.

[Andrew Neil]

The show the schematic - which was point #3 in the posting tips:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[Dimlite]

Though I doubt this is related to the external HW, please see attached file.The schematic consists of multiple pages that I can not share. To the right you see the LP-filter mentioned above (2k + cap). This is connected to PA0, though not on this page.