Differential ADC vs Single Ended ADC

[darrenweinhold]

Is there a way to configure ADC channels as differential instead of single ended? I can't find any mention of it in the documentation and don't see anything in the source code for it.

[davefes]

Which bit of hardware?

[darrenweinhold]

I'm looking specifically at the Portenta H7. But I was thinking more generally that there would likely be a way to do this for hardware that supports it.

[rkompass]

The processor of Portenta H7, the STM32H747 as an ADC that provides differential inputs: Can manage Single-ended or differential inputs (programmable per channels). This is stated on page 962 of the reference manual. The assignment of (the 20 relevant) pins to positive and negative input channels is fixed and can be seen at page 968. Apparently you just have to set a bit in the ADC differential mode selection register (ADC_DIFSEL) to activate the differential mode for a channel (should be done with inactive ADC), see page 1075.
This you may achieve with a mem32() instruction from micropython. Address offset: 0xC0, didn't find the base address yet.
It is unlikely that such a feature will be incorporated into MP soon, as there are lots of other features in different processors that would have to be coordinated before, to have a common api. But you might write an adc class especially for this processor.

[darrenweinhold]

Thanks for the feedback. I missed the note on page 1075. I will do some more digging to see about setting the register. It would be great to have some defined way of using differential mode, but I understand the challenges with some much different hardware to support.

I really appreciate the thoroughness of this answer and how great answers like this are to the community. Thanks!

[rkompass]

Not on the Pyboards, not on RPi2040 (the hardware does not allow this). There are external ADCs with drivers for micropython like for example the ads1115 which allow to configure differential inputs.

[darrenweinhold]

That is very good to know for that hardware. I am looking at an ADS1115 as a backup :)