nrf5340 external lfclk test

[Август]

Hello,

I want to test nrf5340 external lfclk, but I don't how to test it.

sdk:1.5.0

board: nrf5340dk without  hfclk

I want to use external lfclk to generate 1khz waves, can you give me some suggestions?

Thank you

[ketiljo]

board: nrf5340dk without  hfclk

 Is this a typo? It won't work well without the HF clock.

The external LF clock must be a 32.768 kHz clock source. See the product specification for more: https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/oscillators/doc/oscillators.html#concept_32k_xosc

[Август]

Hi ketiljo,

Thanks for your quick reply.

We want to make sure only external lfclk so remmove the HF clock.

We use the following two projects to test.

app:v1.5.0\nrf\samples\nrf5340\empty_app_core

net:v1.5.0\nrf\samples\peripheral\radio_test

I set up a thread to control the led.

How to ensure that only low-speed crystals are working on boards with high-speed crystals? 

Thank you

[ketiljo]

The external HF clock is only needed by the radio, the CPU runs on a internal RC oscillator unless you change the config The HF and LF clock sources are used for different things. Typically, only the RTC and WDT are clocked from the LF clock.  https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/clock/doc/clock.html

Timers are clocked from the HF clock, so either the RC or the XO depending on the config.