Power Supply and Crystal Configuration

[DaveS]

I am using the nRF51822.  I am using the regulator (not the DC/DC) connection and am not using the low-power (1.2V) mode.  All supplies are 3.3V.

Additionally, I am only using the 32MHz crystal and not a 32kHz crystal.  I will use the internal RC oscillator for 32kHz.  

How do I this up in the software.  Is there a tutorial which goes over the initiation of the device within the software?

Thanks,
Dave

[Andreas]

Hi,

 

No changes are needed for LDO (non-DC/DC) operation, this is done by default. For 32 kHz you need to modify nrf_clock_lf_cfg_t  used when enabling the softdevice. E.g. for SDK 12.3

nrf_clock_lf_cfg_t clock_lf_cfg = NRF_CLOCK_LFCLKSRC;

#define NRF_CLOCK_LFCLKSRC      {.source        = NRF_CLOCK_LF_SRC_RC,            \
                                 .rc_ctiv       = 16,                                \
                                 .rc_temp_ctiv  = 2,                                \
                                 .xtal_accuracy = NRF_CLOCK_LF_XTAL_ACCURACY_20_PPM}

 

For the 32 MHz  crystal you need to update the XTALFREQ register before the oscillator is started by the application, e.g.

 

// Set the external high frequency clock source to 32 MHz
    NRF_CLOCK->XTALFREQ = 0xFFFFFF00;

 

The other option is to change the reset value of NRF_CLOCK->XTALFREQ to 32 MHz. Reset value is defined by NRF_UICR->XTALFREQ 

 

Best regards,

Andreas