Connect cross power-domain to UART00 on P2 of nRF54L15 DK

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Wed, 05 Nov 2025 08:11:12 GMT

I am sorry that this wasn't picked up earlier.

Yes, there are some more limitations on the pin selection, compared to the nRF52 and nRF53 series. Also, it is unfortunate that the build system doesn't pick up these kinds of mistakes. We have reported this internally.

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

papatel — Mon, 03 Nov 2025 20:40:56 GMT

Yes, this was our mistake and every LLM we tried also made the same mistake in assuming that UART pin assignments (TX vs RX) were not restricted, only the peripheral itself within P2. This was an unexpected limitation and a HUGE step backward in terms of ease of integration.

This severe limitation is documented but Nordic should probably make that more clear as anyone familiar with the NRF52 series would never make the assumption that pin assignments for UART are completely restricted for any port.

Nordic engineers also missed this in our private schematic review.

Lastly the build environment doesn't complain at all when we selected incompatible TX/RX pins on port 2 or assigned the wrong peripheral. Compiles just fine and fails completely silently during testing no matter what logs/traces/debugging you turn on. That should be fixed in parallel with more clarity on the documentation.

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Fri, 31 Oct 2025 07:38:12 GMT

Make sure P2.07 is RX and P2.08 is TX.

Source: https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/pin.html#ariaid-title4

BR,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

papatel — Fri, 31 Oct 2025 06:23:55 GMT

I'm on 3.1.1 and I can't get uart00 working with P2.07 and P2.08 for TX/RX. Everything compiles just fine but TX line doesn't toggle when I write out to UART and nothing can be received either. Did something break in the latest SDK for P2 + uart?

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Tue, 01 Apr 2025 20:18:36 GMT

Thank you for the update. Yes. It will be part of the 3.0.0 release, and therefore also part of the preview/release candidates.

BR,
Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

pauleffect — Tue, 01 Apr 2025 16:58:03 GMT

I just checked ncs version 3.0 preview. The fix is there (along with higher baud rates). Thank you anyway!

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Tue, 01 Apr 2025 13:55:45 GMT

[quote user="pauleffect"]

Would you kindly share the fix? I'm guessing that, under the hood, before calling the following function,

[/quote]

I don't have the details. Just got an update saying this was fixed for future releases.

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

pauleffect — Tue, 01 Apr 2025 13:32:05 GMT

if you've already done the PCB (which I'm guessing to be the case), why not use the coprocessor to emulate an uart? It's a dead-simple to implement peripheral. Especially if you work with a fixed baud rate. Detect the start bit (falling edge), wait for X nanoseconds, read 8th bit, wait for X nanoseconds [... repeat], check stop bit (high), you have a valid byte.

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

pauleffect — Tue, 01 Apr 2025 13:28:55 GMT

Would you kindly share the fix? I'm guessing that, under the hood, before calling the following function,

nrf_uarte_baudrate_set(get_uarte_instance(dev), nrf_baudrate);

the correct baud rate must be calculated, while taking into account the clock source of the peripheral.

In zephyr's repo, if the peripheral is clocked higher than 16Mhz, the below macro is used to calculate a "custom" baud rate:

#define UARTE_GET_CUSTOM_BAUDRATE(f_pclk, baudrate) ((BIT(20) / (f_pclk / baudrate)) << 12)

Which I think is ok, because for an f_pclk of 16M and a baudrate of 1M, it produces a reg value of exactly 0x10000000 (as referenced by the docs to be 1Mbaud for a 16Mhz clock).

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Mon, 17 Mar 2025 12:59:14 GMT

I don't know. If you want roadmap details, you should contact our Regional Sales Manager (RSM) for your area. If you don't have their contact details, please send me a DM here on DevZone, and link to this ticket.

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Mon, 17 Mar 2025 12:52:04 GMT

Nice!

May I know when will the next NCS be available?

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Mon, 17 Mar 2025 12:44:48 GMT

The baudrate issue is fixed, and the fix will be included in future versions of NCS.

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Mon, 10 Mar 2025 08:55:08 GMT

[quote user="Archiet"]Is there any chance to use P2.06 on UARTE00?[/quote]

That doesn't seem to work.

I will update you when I know more about the baudrate issue.

BR,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Fri, 07 Mar 2025 05:05:19 GMT

Hi there!

Thanks for the reply.

Is there any chance to use P2.06 on UARTE00? I understand this pin is not dedicated pin on P2 but P1.04 and P1.05 are also not dedicated ones on P1 which they can still be used as UARTE20 in UART sample code. My point is all mentioned pins are not dedicated ones based on the pin assignment table but why there is freedom on P1 but P2?

Regarding the baud rate problem, please kindly update to me when there is feedback from the developer

Thanks a lot!

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Thu, 06 Mar 2025 09:42:03 GMT

Sorry. I missed that part.

You can't use P2.06 for UARTE00. You can look in the pin Assignment (Table 3) on this site what pins you can use for UARTE00. On P2, you can use:

P2.00
P2.02
P2.04
P2.05
P2.07
P2.08
P2.09
P2.10

I tested just now, and it worked only replacing this line:

psels = <NRF_PSEL(UART_TX, 2, 8)>, <NRF_PSEL(UART_RX, 2, 6)>;

with e.g.

psels = <NRF_PSEL(UART_TX, 2, 8)>, <NRF_PSEL(UART_RX, 2, 7)>;

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Wed, 05 Mar 2025 14:32:42 GMT

Hi there!

Thanks for the hint regarding overlay file.

On the other hand, are you able to use P2.06 as Rx? If yes, could you share what you have made with me so I could follow? Thanks!

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Wed, 05 Mar 2025 14:01:15 GMT

Thank you for uploading!

Hmm... Yes, I see that it uses 921600 baudrate.

I also noticed that it says in the top row from here:

https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/uarte.html#d1900e814

That the core frequency scales with the CPU frequency, which happens to be 8 times faster than the frequency of the other UART instance. So there is probably the reason. This however, in my opinion, should be compensated for when setting the baud rate in DeviceTree (your DTS file).

I will ask our developers if this is the intended behavior.

By the way, I see that you modified the .dts file directly. While it works, it is not the intended way to change something in devicetree. The intended way is to copy whatever you want to change from the .dts or .dtsi files, create your own file called <board_name>.overlay, and place it in your application folder. (in this case, that would be nrf54l15dk_nrf54l15_cpuapp.overlay), and paste whatever you want to modify into that file. Then, in the overlay file, you can change whatever you want to. I'll attach your modified project, including the .overlay file, for reference.

devzone.nordicsemi.com/.../8270.UART_5F00_TEST.zip

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Wed, 05 Mar 2025 07:03:02 GMT

devzone.nordicsemi.com/.../1581.UART_5F00_TEST.zip

Hi there!

Here is the zip folder of my application.

I am using P2.08 and P2.07 as Tx and Rx of UARTE00 with pre set baud rate 115200. In this application, you should be able to use UARTE00 without problem except the actual baud rate is 921600.

Based on this application , you will find Rx is not working if you change Rx from P2.07 to P2.06.

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Tue, 04 Mar 2025 15:11:50 GMT

Hi there!

My computer is not with at the moment but I will do it.

Meanwhile, you can also build it by copying the sample in the link below but with UARTE00 assigned to P2.06(Rx) and P2.08(Tx) with baud rate 115200. It could be an faster alternative for your debugging. Thanks.

github.com/.../l5_e1_sol

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Tue, 04 Mar 2025 14:52:27 GMT

[quote user="Archiet"] Or should I zip the project folder and share here?[/quote]

Preferably, yes. If I don't need to create my own application on top of a CMakeLists file and a couple of scattered files, it will be a lot easier for me to reproduce, meaning I will be able to do it sooner.

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Tue, 04 Mar 2025 09:54:19 GMT

Hi there!

I have attached my main.c, conf file, Cmake list and DTS file here.May I know what other files you need? Or should I zip the project folder and share here?

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Edvin — Tue, 04 Mar 2025 09:51:36 GMT

Hello,

Can any of you please upload the application that you are using to reproduce this. It is easier, and quicker, for me to reproduce, and potentially forward to our developers if I have something that I can just build and flash.

Best regards,

Edvin

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

jing — Tue, 04 Mar 2025 06:04:09 GMT

I have the same experience.

for uart00, it works only with the dedicated pin function. not able to use P2.06 for rx. try changing to P2.07.

also observed that the baud rate on the terminal program must be 8x of the uart current-speed.

not sure if has anything to do with the peripheral clock frequency being 128 MHz in mcu domain?

jing

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Mon, 03 Mar 2025 09:52:16 GMT

Hi again,

I just changed the baud rate to 921600 in my serial port tool, then Tx of UARTE00 becomes readable text but it should be 115200 according to device tree I attached above . For Rx, it still cannot control LED of DK until I change it to P2.07 with baud rate 921600. Do you know why the actual baud rate is different from my setting and why Rx as P2.06 is not working but P2.07? Look forward to hearing from you. Thanks!

RE: Connect cross power-domain to UART00 on P2 of nRF54L15 DK

Archiet — Mon, 03 Mar 2025 08:37:17 GMT

Hi there!

I have tried to add UARTE21 to P1 and UARTE00 to P2 respectively.

UARTE21 works well but TX of UARTE00 only shows garbled code and RX of UARTE00 is not able to toggle LED of the DK. Could you give me some hints what did I miss?

Here is the sample I follow

https://github.com/NordicDeveloperAcademy/ncs-fund/tree/fc73a4be8bea67d306d015929546275a95ea909a/v2.8.x-v2.7.0/l5/l5_e1_sol

Following is the application I have, including main.c, CMakelist, cong and dts I am using.

devzone.nordicsemi.com/.../02441.main.c devzone.nordicsemi.com/.../5327.CMakeLists.txt devzone.nordicsemi.com/.../1643.prj.conf devzone.nordicsemi.com/.../nrf54l15dk_5F00_nrf54l15_5F00_cpuapp.dts