NRF52840 Clock Configurations

[Nivethitha]

Hi,

In NRF52840, We use LFXO Oscillator (KJ3270001). We did not connect any crystal or Oscillator for HFCLK. 

1) What will be the clock source for SPI and I2C communications, if no HFCLK source is selected in Code?. in data sheet it is given like Accuracy for SPI and I2C depends on HFCLK Frequency?

2)Is the HFCLK is HFINT by default or the frequency will be derived from LFXO?

3) What will be the clock for the other peripherals? Where should it be changed?

4)PCLK32KI-> what is this clock used for? 

Please explain in detail about the clock tree in NRF52840.

[Simonr]

Hi

Please check out the HF clock controller section of the product specification for more details on the HF clock sources. The HF clock controllerwill automatically provide the clock(s) requested by the system. If the system does not request any clocks from the HFCLK controller, the controller will enter a power saving mode. The HFINT source will be used when HFCLK is requested and HFXO has not been started.

Best regards,

Simon

[Hyun-Young]

Can you give me an example, how I can use HFCLK?

[Simonr]

Hi

The HF clock will automatically be called by drivers/libraries requiring it. Any example using the radio peripheral for example will use the HF clock. I'd recommend checking out the Radio Test example in that starts with enabling the HF crystal and then configuring CLI.

Best regards,

Simon