Problem with UARTE in direct supply mode

[TSonono]

Hello,

I encounter a problem when I am trying to measure the current consumption of the nRF52840 on the nRF52840-DK. I have set the board in direct supply mode as described here. I am feeding the external supply pins with 3.3V using an otii arc. However, it seems that if I do not connect a USB cable to the J2 connector, I cannot send data over the UART pins I have configured (0.27 and 0.26). What could be the cause of this? The application works fine when I'm not measuring current OR when I'm measuring current as long as there is also a USB cable connected from my PC to J2.

Best regards,
Tofik

[Simonr]

Hi Tofik

What are these pins (P0.26 and P0.27) connected to? What UART instance are you using in your application? It might be a conflict between the UART backend and your application causing this. Are you measuring current using a PPK or some other device? If you are using a PPK, it will need a DK's MCU in order to communicate with the nRFConnect application. Please see the PPK user guide for alternative ways to measure current without the onboard MCU (you will need a second DK in that case).

Best regards,

Simon

[TSonono]

Hi Simon,

The uart pins are connected to another nRF52840-DK (which I’m not doing any measurements at). The two DK:s communicate over uart essentially. I’m not using a PPK, I’m using an otii arc. However, a colleague is using a PPK and is experiencing the same problem.

The uart instance is UARTE0 enabled by NRF_LIBUARTE_DRV_UARTE0 in sdk_config.h.