Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Vidar Berg — Fri, 28 Nov 2025 07:51:14 GMT

So you were able to use the NFC pins now after you switched to new board, or is it still the same board? If you suspect the driver, you may consider reading out the TWIS PSEL registers and GPIO CFG registers to confirm the pins are configured correctly and according to the product specification. You can also add logging for the TWIS error events in the TWIS callback.

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Luis Santos — Wed, 26 Nov 2025 15:19:32 GMT

During testing, I observed the following:

Successful Configuration: The nRF5340 operates correctly as an I2C master when using P0.03 for SDA and P0.02 for SCL on my new board design.
Failed Configuration: On an older board, a previously working configuration (SDA on P0.03, SCL on P0.30) fails when the pins are swapped in the device tree:
- Working: psels = <NRF_PSEL(TWIS_SDA, 0, 3)>, <NRF_PSEL(TWIS_SCL, 0, 30)>
- Failing: psels = <NRF_PSEL(TWIS_SDA, 0, 30)>, <NRF_PSEL(TWIS_SCL, 0, 3)>

The issue suggests a problem on I2C slave driver.

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Luis Santos — Wed, 26 Nov 2025 13:35:45 GMT

Thank you for your response, Vidar.

Yes, I can confirm that I'm able to successfully toggle the pins between high and low states using the debug code I developed.

I can also verify that the signals are transmitting correctly. When using the same I2C bus with another slave device (my other custom board that uses P0.30 for SCL), the communication works properly.

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Vidar Berg — Wed, 26 Nov 2025 13:28:40 GMT

Thanks for confirming. The reason I asked what board you were using was because of on the DK the the NFC pins are not routed to the pin headers by default. In the DT overlay you can omit the drive strength setting ('E' drive is not available either) as Turbo said, but you need to keep the bias pull up property if you want to enable the internal pull ups.

Have you confirmed that you are able to drive these pins on your board? For example, by measuring if the pull-up is applied or by using a logic analyser?

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Luis Santos — Wed, 26 Nov 2025 12:53:49 GMT

Thank you for your support, Turbo J.

Even though I'm using the following configuration:

```dts
i2c2_default: i2c2_default {
group1 {
psels = <NRF_PSEL(TWIS_SDA, 0, 3)>,
<NRF_PSEL(TWIS_SCL, 0, 2)>;
};
};

i2c2_sleep: i2c2_sleep {
group1 {
psels = <NRF_PSEL(TWIS_SDA, 0, 3)>,
<NRF_PSEL(TWIS_SCL, 0, 2)>;
low-power-enable;
};
};

I'm still experiencing the same behavior.

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Turbo J — Wed, 26 Nov 2025 12:41:44 GMT

P0.03 does not support E drive modes AFAIK. Its also wrong to use a mode that actively drives "high" level with I²C bus lines - that is what the pullup resistors are there for.

Try omitting the "nordic,drive-mode" line or set it to "H0D1".

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Luis Santos — Wed, 26 Nov 2025 12:34:01 GMT

Thank you for your response, Vidar.

While I don't have an nRF5340DK available for testing with this specific pin configuration, I can confirm that my I2C slave implementation works correctly on a custom board using the following configuration:

```dts
i2c2_default: i2c2_default {
group1 {
psels = <NRF_PSEL(TWIS_SDA, 0, 3)>,
<NRF_PSEL(TWIS_SCL, 0, 30)>;
bias-pull-up;
nordic,drive-mode = <NRF_DRIVE_E0E1>;
};
};

The only modification from my working custom board design is changing the SCL pin to P0.02.

In my zephyr.dts file, I currently have:

RE: Issue Using NFC Pins (P0.02/P0.03) as I2C Slave on nRF5340

Vidar Berg — Wed, 26 Nov 2025 12:10:35 GMT

Hello,

I see you have correctly included the uicr node with the nfct-pins-as-gpios; property in your overlay, so provided the overlay is being applied to the build, I would have expected this to work (you can verify that it's applied by looking at the generated zephyr.dts). Are you testing this on a custom board or the nRF5340 DK?

Best regards,

Vidar