nRF9151 DK GPIO 26/27 default state

[Konstantin Klitenik]

Hello,

I'm trying to figure out why GPIO 26 and 27 on the nrf9151 DK default to HIGH. I have my SALAE USB scope connected to several pins. When the board resets, only GPIO 26 and 27 go HIGH, before being set by my code to go LOW. GPIO 22, 23, 28, for example, are always LOW.

I tried adding pull down in the device tree `<&gpio0 27 (GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH)>;` but that doesn't seem to help.

I have nothing else in my device tree using GPIO 26 and 27. All my UARTs are off.

Note that I'm NOT using nrf9151dk board files (which does use pins 26 and 27 for UART). I have a custom dts which does not.

Best,

Konstantin

[Mariano Goluboff]

Hi Konstantin,

The nRF9151DK has those pins connected to the UART on the nRF5340 interface device, which shows them as virtual COM ports. It's possible that the nRF5340 is driving the pins. If you want to use the GPIOs for something other than UART, I would recommend that you cut the solder bridges to disconnect from the interface chip's UARTs:

Here's page 2 of the nRF9151DK's schematic which shows which solder bridges to cut:

Mariano

[Konstantin Klitenik]

You're right. When I briefly looked at the DK, I saw the solder bridge but thought it was disconnected by default. Thanks!