nRF54L15: UART pinout not working unless connecting the RTT viewer

[Pedro Sousa]

Hi everyone,

I am working with the new nRF54L15 and have connected UART21 to pins 2.07-2.08, which are capable of handling both Trace data and UARTE. However, I am encountering an unusual behavior with the UART RXD pin.

When I attempt to use the UART RXD pin, it only works fine when either:

• The JLINK is connected via SWD
• The RTT Viewer is connected

If neither of the above tools are connected, I am unable to use the UART RXD at all.

Has anyone else experienced a similar issue with the nRF54L15? Any ideas on what might be causing this behavior or suggestions on how to resolve it would be greatly appreciated.

Thank you in advance for your help!

[khelmutlord]

P2.07 is connected to the onboard debugger per the DK's schematic.

Could you try cutting SB24 or disabing the debugger connection in the board configurator?

docs.nordicsemi.com/.../index.html

[Pedro Sousa]

Hi khelmutlord,

Thank you for your answer, but I am not using the DK. I am using my prototype, without anything connected there.

The behavior is, if I connect to the board using JLinkExe => connect command the RX is available otherwise it doesn't work. I am testing with echo_bot sample. 

Also, if I use the config CONFIG_NRF_APPROTECT_LOCK=y I am not able to connect JLink and the RX never works. It seems that something happens when I connect JLink that allows the RX to receive data.

Any thoughts?