Subject: Cannot use GPIO P0.19 on nRF9160 as UART TX pin

[thwcs7]

Hi everyone,

I'm working with the nRF9160 and trying to configure P0.19 as the UART TX pin using Zephyr.
Here's the configuration I used in the device tree:

uart1_default: uart1_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 19)>; // TX in board = P0.19
// nordic,drive-mode = <NRF_DRIVE_H0D1>;
};
group2 {
psels = <NRF_PSEL(UART_RX, 0, 20)>; // RX in board = P0.10
bias-pull-up;
};
};

uart1_sleep: uart1_sleep {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 19)>,
<NRF_PSEL(UART_RX, 0, 20)>;
low-power-enable;
};
};

However, the UART does not transmit any data. When I change to another pin like P0.11, it works fine.

• Is there any hardware limitation that prevents using P0.19 as a TX pin?

• Does Zephyr or the modem firmware restrict certain GPIOs from being used for UART?

• Any way to check if the pin configuration is being applied correctly at runtime?

Thanks in advance!

[runsiv]

Hi

Are you using the 9160DK? 

As you can see here and at the bottom side the DK. P0.19 is connect to the 52840 and I suspect this is what it causing issues for you

Regards

Runar

[thwcs7]

I don't think so. I'm using a custom board for my specific application, based on the nRF9160-SIxA.

[runsiv]

Interesting, it should not be anything stopping you from using P0.19. Have you created your own custom board? 
If so could you upload the board files and the full overlay so I can have a look at it

Regards

Runar

[thwcs7]

It's just as simple as this.

[thwcs7]

[runsiv]

Sorry I was a bit unclear in my wording. Let me rephrase. In VScode are you using a custom board you have created yourself as the board target? If you are using the DK as your board target you would need to disable in your overlay the peripherals used to communicate with nrf52840 in the dk. This you would find in the board files for the dk, and just disable in the overlay files

Regards

Runar

[thwcs7]

"Ohh, I'm using nrf9160_nrf9160_ns as the target for my board. After building, I checked the zephyr.dts file and noticed that there are some references to the nRF52840. I think I should either remove or comment them out. In your opinion, which approach would be better?"

[runsiv]

In general if you are using a custom board I would create a custom board target. We have a pretty great guide on how to do it here

Regards

Runar