I2C setup for P1.11 and P1.12 nRF54L15-DK example?

[MarcelR]

Hi,

on my Debian 13 with nrfconnect 3.1.0 and nRF54L15-DK:

I am not able to get I2C/TWI running (the same sensor runs fine on nRF52840-DK).

1. Question: Is there any nRF54L15-DK based sample I could use to get a demo running?

I have tried P2.01 and P2.02 which didn't work, and some googling showed that this is probably not possible.

So I have changed to P1.11 and P1.12, I can measure 3.1V on SDA and SCL.

But no data flow is possible.

My .overlay is
```

&i2c21 {

status = "okay";

clock-frequency = <I2C_BITRATE_STANDARD>; /* 100 kHz */

pinctrl-0 = <&i2c20_default>;

pinctrl-1 = <&i2c20_sleep>;

pinctrl-names = "default", "sleep";

tmpsns_top: lm75@49 {

compatible = "lm75";

reg = <0x49>;

};

tmpsns_bottom: lm75@48 {

compatible = "lm75";

reg = <0x48>;

};

};

```

and my pinctrl is

```

&pinctrl {

/* with internal pull-ups to avoid external resistors on DK */

i2c20_default: i2c20_default {

group1 {

psels = <NRF_PSEL(TWIM_SDA, 1, 11)>, /* P2.01 -> P1.11 */

<NRF_PSEL(TWIM_SCL, 1, 12)>;

bias-pull-up; /* enable internal pull-ups */

};

};

i2c20_sleep: i2c20_sleep {

group1 {

psels = <NRF_PSEL(TWIM_SDA, 1, 11)>,

<NRF_PSEL(TWIM_SCL, 1, 12)>;

low-power-enable;

};

};
};

```

Thanks for some hints, or a working example.

(I have tried the i2c shell CONFIG_I2C_SHELL=y but could not get it running on /dev/ttyACM0 nor /dev/ttyACM1 - probably because DK blocks it - but I don't know)

[Vidar Berg]

Hello,

I am not able to get I2C/TWI running (the same sensor runs fine on nRF52840-DK).

Could it be the voltage difference? The IO voltage is 1.8 volts by default on the 54L DK while it's 3 volts on the 52840 DK. The IO voltage can be changed through the board configurator app: https://www.nordicsemi.com/Products/Development-tools/nRF-Connect-for-Desktop 

Please also note that there are dedicated clock pins that should be used: https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/pin.html#clock_pins, but I don't think that is the problem considering it's only running at 100khz.

Best regards,

Vidar

[MarcelR]

Hi Vidar,
thank you for taking care.

Voltage down to 1.4V is OK, so this was not the issue.

It is working now, after days of fiddling + try&error around.

Changing to &i2c21 with Ports
            psels = <NRF_PSEL(TWIM_SDA, 1, 10)>,  /* P1.10 */
                    <NRF_PSEL(TWIM_SCL, 1, 11)>;  /* P1.11 clock PIN */
fixed it.

Why? I don't know at all.
Interestingly, the DK LED1 on P1.10 (still lit) did not harm my SDA bus, probably it is nicely decoupled with a transistor.

Christmas wish: if nordic could supply working samples or having a clear table which PIN combination works (and why) would be very helpful.

best regards
Marcel

[Vidar Berg]

Hi Marcel,

Thank you for the update and feedback. It looks like the issue was indeed that you weren't using one of the dedicated clock pins earlier (P1.11 is a clock pin) and that I was wrong to assume it would be OK given the low frequency. For the 54L series it is important to read carefully through the Pin assignments chaper when planning the pinout for your design. We've also published a blog post on this topic here Essential pin planning guidelines for the nRF54L Series 

Best regards,

Vidar