ADC1 behaving strangely on a STM32L496AGI6.

kvresto · ‎2020-06-19

Hi forum.

I have a question regarding the STM32L496G-discovery board. I want ADC1 to sample PC4 located on the on board Arduino connector, take 10 samples for this example and have the DMA xfer these to memory.

I have a CubeIde project set up and have set up all the ADC and DMA components to work. This same project works as expected when I use the NUCLEO-L496ZG which is fitted with the STM32L496ZGT6U, but when I run the same code on the STM32L496G-discovery board which is fitted with a STM32L496AGI6, I find the output from the ADC sits about mid point.

Then when I take the analog pin PC4 to ground or 3V, nothing happens.

I have looked into the ref manual, and in fact this was the same data I used when setting this example up for the NUCLEO-L496ZG, but I cannot find anything that may be specific to the STM32L496AGI6.

Has anyone had the same experience. Is there something strange about the

STM32L496G-discovery board, or is the problem with my understanding. I have posted my setup code, I hope that helps clear up what I talking about.

By the way the only ADC sampling I can see in the STM32L496G-discovery boards schematic is for the IDD measure which feeds in to on board MFX_V3, a STM32L152CCT6, so there seems to be no other ADC use.

Thanks.

waclawek.jan · ‎2020-06-20

Isn't the given pin connected to any other onboard peripheral on the Disco board?

Can't the difference be in how VREF pins are connected?

JW

kvresto · ‎2020-06-20

right on JW. I made an assumption based on other ST boards I have used, and didn't go back and double check.

Thanks

waclawek.jan · ‎2020-06-21

Thanks for coming back with the information.

Can you please be more specific what did you do, for others who come across this thread? I don't use the 'L496 Disco.

Thanks,

JW

kvresto · ‎2020-06-25

JW, R18 that feeds into VREFP pin of the L496 is not populated. This is actually documented, but I didn't even think at the time to check. I assumed VREF was connected to something, as are most if not all other demo boards, at least the ones I have used, so your reference to VREF although a bit confusing led me to go back and double check.

Thanks.

EDIT: Also the other problem was my experience here.

waclawek.jan · ‎2020-06-26

Thanks for coming back with the information. This indeed may be confusing if you don't look very carefully... :)

JW