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External Powering of NUCLEO-L031K6 HSI able to run?

Associate II

Hello All,

I would like some clarification as to how I can verify if the internal clock HSI will run based on what external power input is given.

I had originally found that running the board on external 3.3 v will not allow the HSI clock to be used, and the clocks would only run if I attached USB power. If I removed USB power from the board after power it briefly the clocks would still run even at 3.3 v external power. 

From this post I understand that the ST-link needs to be able on some nucleo board to run the HSI clock.

From the NUCLEO-L031K6 board documentation I found this table:


this shows that using a 5 v in will not run the ST Link, however reading further the following section is talked about:


The section doesn't include "running clocks", but I am not sure if the document would explicitly include "running clocks" since it might be an implicit understanding.

Given the above background I have the following questions:

1. Is it indeed that the non activation of an ST-Link is the cause of of the HSI clock not running?

2. How am I able to check if the HSI clock is dependent on something else to be active?

3. Will the HSI clock be active if I power the board using 5 V or only if I use the VIN pin?

4. If usb power is needed to run certain clocks, what clocks can I use with external power?

Any guidance to understand this would be much appreciated.


Edit: corrected references to HSI from HSE clock.





@Mike_ST wrote:

SB9 is the reset signal between the ST-LINK and the LSTM32L031.

^^^  This!  ^^^

If the ST-Link is not powered, it will drag NRST down - thus keeping the Target in reset!



Hey Andrew,

I am trying to output the HSI clock signal on a pin on a blank program so I can apply it to a main program, but I am not getting a reading. 

You stated use a "scope"/oscilloscope.

I am using a logic Analyzer that only has digital read pins. Will the digital logic analyzer not work?

In terms of my code, I use the stm32CubeMx tool to configure everything so i don't think I would be missing anything at this point.

I have attached my code file below.

Any thoughts as to what might be happening?

Hey Mike,

I have tried to power the board using a 5 v input and I am getting the same behavior despite the table above showing a 5V connection doesn't need and SB modified.


Stop waste time with this chaos. MCU clocks have nothing to do with powering. Use schematics and docu for MCU.

Every Nucleo have LED use it for show if your code is run . And measure if reset pin is ok ... no ... correct it.

Taking the SB9 jumper out was the solution.

I began to use 5 v input as well and this worked for that too despite the data sheet not alluding to taking out the SB9 jumper to run the board as normal.


Thanks Andrew.