NUCLEO-WL55JC reset when laptop attached to it.

[HOPilsan]

I use the NUCLEO-WL55JC STM32WL Nucleo-64 board, which I supply with an external power supply.

Each time I attach my laptop in order to view the console, the WL55JC is reset. I assume the STLINK-V3E issues a reset to the WL55JC.

Is there a possibility to avoid that?

I tried to take away the jumper that allows T_NRST to be connected to ST-LINK, but then, when I attach my laptop the board, the WL55JC enters an unusual state (it neither continues normal operation nor does a reset). Except for this I did not find any other ideas how to change the behavior. Is there any?

[Andrew Neil]

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@HOPilsan wrote:

I attach my laptop in order to view the console

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What "console" are you using?

[HOPilsan]

It is LPUART1 which is tunneled by the ST_LINK through USB to my laptop.

[Andrew Neil]

Does the board have jumpers/solder-bridges to disconnect the NRST from the ST-Link to the target?

Or use a separate USB-to-UART adaptor.

[HOPilsan]

Does the board have jumpers/solder-bridges to disconnect the NRST from the ST-Link to the target?

It does. But as mentioned in the text above I did not get the desired result by removing the jumper. I have no idea why, since this is the obvious approach.

Sure another USB-to-UART adapter could be a solution …

[Andrew Neil]

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@HOPilsan wrote:

as mentioned in the text above I did not get the desired result by removing the jumper. …

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Sorry - missed that.

Did you leave SWDIO and/or SWCLK connected? Any other connections to the ST-Link?

Do you have a scope to see what's happing on the power lines? Maybe some glitch with power being applied from 2 different sources ... ?

[HOPilsan · Accepted solution]

First I left SWDIO and SWCLK, then I removed them. No change.

Yep, a good idea o check the voltages. I'll do that.

[Sco]

You mentioned you " take away the jumper that allows T_NRST to be connected to ST-LINK", would you confirm which jumper you removed?

BTW, if you assume it's impacted by the NRST, another way is to monitor this signal to see if there is a drop when the reset happens.

[HOPilsan]

It was jumper JP8 position 9-10. I'll check both NRST and the voltages and give feedback.

[Andrew Neil]

Have you checked the RCC_CSR register? It has some bits which identify the cause of a reset...

https://www.st.com/resource/en/reference_manual/rm0453-stm32wl5x-advanced-armbased-32bit-mcus-with-subghz-radio-solution-stmicroelectronics.pdf#page=341