Program not running when powering from external source

DavidL_ · ‎2024-09-23

I have an L432KC and to test it, I created a simple blinking program which I uploaded via USB, which works just fine. When connecting my MCU to my external 5V power supply though, my program does not run. Looking at some posts, I found people suggesting to pull down the Boot0 pin to ensure that it loads the user program, I am not able to find the Pin name on the board of the Boot0 pin of the L432KC though.

I'd appreciate it if someone could help me out.
Thanks in advance!

Andrew Neil · ‎2024-09-24

@DavidL_ wrote:
How would I „break“ this link? What exactly does that mean?

It's here:

The photo in the UM shows a zero-ohm resistor fitted:

To break the link, you need to remove that zero-ohm link.

There's no need to be particularly careful with it - you don't need to keep it - so just heat it up with a soldering iron until it comes off.

@SofLit @STTwo-32 I've noted before that this needs to be better documented:

https://community.st.com/t5/stm32-mcus-products/docmentation-of-solder-bridges/m-p/689362

#BreakSolderBridge #SolderBridge #SB

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TDK · ‎2024-09-23

You're connecting 5V to CN4 pin 4 and GND to GND somewhere?

Are you relying on the clock from the ST-Link chip? Use HSI instead.

Unlikely BOOT0 is the issue here as it is pulled down by default, unless you've modified solder bridges.

If you feel a post has answered your question, please click "Accept as Solution".

DavidL_ · ‎2024-09-24

I see no CN4 pin on the boar, I have a "5V" pin that i connect my external power source to.

TDK · ‎2024-09-24

The user manual has instructions for powering the board externally. I suggest following those. Perhaps a picture of what you're doing would help. All connectors are named.

If you feel a post has answered your question, please click "Accept as Solution".

Andrew Neil · ‎2024-09-24

@DavidL_ You haven't said what board you're using!

@TDK wrote:
Are you relying on the clock from the ST-Link chip? Use HSI instead.

Also, if the on-board ST-Link is not powered, it's likely to pull the Target's NRST pin down - which will hold the target in Reset ...

DavidL_ · ‎2024-09-24

I am simply connecting my power supply to the „5V“ pin and ground to GND.

I read through the section in the pdf i found for the board, but these weren’t exactly instructions, more like infos.

DavidL_ · ‎2024-09-24

I mentioned in my first comment that I have a L432KC board.

I tried erasing everything from the MC via the STM Programmer, but i got an error indicating that the reset is pulled down, so that seems plausible.

Does the ST-Link chip need to be powered individually?

Andrew Neil · ‎2024-09-24

@DavidL_ wrote:
I mentioned in my first comment that I have a L432KC board.

That's just a chip part number - it doesn't identify a board.

Do you mean a Nucleo-L432KC board?

https://community.st.com/t5/stm32-mcus-products/communication-between-nucleo-f411re-and-raspberry-pi-using-st/m-p/721506/highlight/true#M261161

@DavidL_ wrote:
Does the ST-Link chip need to be powered individually?

The thing is, the ST-Link on Nucleo boards provides two things to the Target microcontroller:

The clock signal
The NRST signal

So, if the ST-Link is not powered, the Target will get no clock, and its NRST line will be pulled low.

There should be a link you can break to disconnect the NRST signal.

~~You can also break-off the ST-Link section of the board~~. <-- Sorry, not on this board - that only applies to Nucleo-64

https://community.st.com/t5/stm32-mcus-products/measuring-ground-current-does-not-seem-to-match-datasheet-on/m-p/716720/highlight/true#M259890

Andrew Neil · ‎2024-09-24

@Andrew Neil wrote:

There should be a link you can break to disconnect the NRST signal.

It's SB9:

DavidL_ · ‎2024-09-24

Thanks for the clarification, I have a Nucleo-32 L432KC.

Do i want the NRST to be low or high if I want my user code to be run at startup (or does it even matter)?

After some errors, I tried to erase the contents of the chip, the STM32CubeProgrammer application can recognize the chip, but any flashing attempt fails with a "dev_target_held_under_reset" error.

There is a physical jumper from GND to NRST, do i want to keep it on?