GPIO configured as Input on STM32H563VGT6 does not work

[SRond]

Hey everyone,

I have an odd problem with a STM32H563VGT6.

I have configured several GPIO as inputs with no pull-up/ no pull-down. The pins are wired to an external 10k pull-down and a DIP-Switch which is directly connected to +3V3. (screenshot below).

When all switches are off, I read and measure +0V on my pins. If I set one switch to active so it connects +3V3 to the MCU-Pin this pin reads a high and I can measure +3V3 with an osciloscope. The weird thing is now that I can also measure something between +1.7V and 2.9V on the other lanes, even though thex should be low and pulled down by the 10k resitor. I tried to work with the internal pull down of the mcu with the same results. I tried to configure 3 of the pins to output and set them to low. The remaining pin was set as input. After I switched the respective switch to high I got the same result and even the pins which should drive the lanes active low got some voltage somewhere between 1.7V and 2.3V.

I work on a custom board but all other functions like DAC, ADC, USART work fine and I have never had the situation that GPIO was an issue. I have already checked the bare PCB without parts for possible wrong connections between GND and 3V3 or any wrong or missing connections in the area of the DIP-switch. Seems alright and values and open lines are what I would expect.

I have already seen in the documentation that there is an SMPS versions of my MCU but from everything I can see and from everything that is printed on the MCU it should be the STM32H563VGT6 and the PCB layout matches to this controller.

I configured with CubeMX Version 6.13 and worked with CubeIDE Versions 1.16 and 1.17. Maybe there are some known issues somewhere that I missed?

Thanks in advance for any help

[gbm]

Once again: are you sure that the "lower" terminal of your pulldown resistors is actually connected to the ground? What happens if you physically remove the resistors and use internal port pulldowns?

[SRond]

@gbmThe external pull-down resistors to ground are properly connected and they are the 10k. I double checked with a multimeter on two different PCB. And the whole ground and supply voltage network of the PCB seems ok as well. I checked with an oscilloscope. The levels of 3V3 and +15V look stable and the osci did not trigger any change of edge. I also measured GND to GND on several different places. It was all in the range of a few mV. Nothing out of the ordinary.To rule out the DIP switch we soldered it out and hard soldered a bridge to one of the paths, same problem.

Just as I am writing this there is one idea comming in my mind that we have not yet tryed: I am going to solder out the 10k resistors and the dip-switch so there really is only the one path with high and the other pins are let open with internal pull down. If I still can measure weird behavior it has to come from some internal connection between the pins on the port. If the beavior is right then there is a mayor problem on the schematics or the PCB.

@gbmI was just writing as you wrote yours ;)

@SofLitNow I have tried a firmware version where I set the internal resistors to pull up. The behavior is pretty much what I expectet but it does not make sense. If all switches are on I can measure 3V3 and the pins register high. That is ok. If all switches are off I can measure 0.7V and the pins register low. The 0.7 is around what I would expect with the internal pull up active so I think also OK. If only one of the switches is high and the others are low I get back to measuring something between 1.7V and 2.9V on the lines which should be at 0.7V. I do not understand were this voltage comes from.

[gbm]

Remove the resistors, keep the switch. For me it looks like 99% that some ground connection is missing, either for the resistors or one of MCU's GND pins.

[LCE]

What's the MCU's actual supply voltage?

I would never connect any supply voltage to a GPIO directly, I'd put at least serial 100R in there somewhere.

And I support gbm's idea about the missing / bad GND connection.
We once had a PCB where someone gave the wrong net names to all internal GND planes, that was a mess...

PS: If somehow that GPIO bank A is not running from 3.3V but any lower voltage, then your results might make some more sense