NRF5340 Reset Pin Low

[alex_curtiss]

We're developing firmware for a custom board that uses the NRF5340. Today one of the developers reported that they were no longer able to communicate with the board over SWD. As far as they are aware, nothing unexpected or exceptional happened before this occurred. After some debugging it was found that the reset line (normally HIGH thanks to the internal pullup on the NRF5340) is hovering around 0.478V when the device is powered on (voltage rails are stable at 3V). When we pull the reset line up to 3V the device works as expected.

I'm wondering if you have any insight into why the reset line might be lower than expected, and if there's anything I can do to recover this board through software. It seems there is no PINRESET register for the NRF5340? Thanks in advance.

[Jared]

Hi,

Is there anything else connected to the reset line? Have you seen this on multiple devices, or only on one sample so far? How frequent does this happen?

The nRF5340 has a dedicated Reset pin so there isn't any need for such register as on the nRF52 series.  

regards
Jared 

[alex_curtiss]

nothing else is connected, it's a straight shot from the debug pin to the module pin. this has only happened on one sample. perhaps some ESD damage?

[Jared]

Hi,

It could be, but it's difficult to tell for sure. How frequently do you see this issue on the faulty sample? Has it happen again after you pulled up the Reset line? Could you tell anything about the state of the nRF5340 based on the flashed application? For example by looking at the state of any connected LEDS, BLE advertisements, Connections etc, does the CPU continue to run the program?

Also what supply source was used when this happened? 

regards

Jared