Using nRF5340-PDK at 3.3V instead of 1.8V

[DBT]

I want to interface the nRF5340-PDK board to a different vendor's board that runs at 3.3V.

I'm using the SPI bus to communicate between the two boards

Using the nRF5340-PDK board in its default state as it comes from the factory, the SPI bus signals are 1.8V

What changes do I need to make to the switch settings, power connections, modifications, etc to make the nRF5340-PDK produce SPI signals at 3.3V?

What software changes are needed?

I've already tried figuring it out on my own.

I've already tried changing some UICR registers using nrfjprog, and I've already tried doing several things with switch positions and power connections, but the board appears to have lots of options for configuring the power and I may have missed something.  

[Jørgen Holmefjord]

Hi,

It should be sufficient to write the VREGHOUT UICR register:

nrfjprog --family nrf53 --memwr 0x00FF8010 --val 5

I tested this on the DK, and it sets the GPIO output to 3.3V when running from 5V power source.

Note that if you have previously written 0 to this register, you need to do an eraseall operation before you can write it again:

nrfjprog --family nrf53 --memwr 0x00FF8010 --val 5
Parsing parameters.
Writing.

nrfjprog --family nrf53 --memrd 0x00FF8010
0x00FF8010: 00000005                              |....|

nrfjprog --family nrf53 --memwr 0x00FF8010 --val 7
Parsing parameters.
ERROR: The area to write is not erased.

nrfjprog --family nrf53 -e
Erasing user available code and UICR flash areas.
Applying system reset.

nrfjprog --family nrf53 --memwr 0x00FF8010 --val 5
Parsing parameters.
Writing.

Best regards,
Jørgen

[DBT]

OK that works if I connect a 5V power supply to P27 (Li-Po) and change SW9 to Li-Po.

Is there a way to do it using only the power from the micro-USB connector J2?