Question about 32Mhz High Frequency Clock configuration

[alan.kim]

Hello, community. I have a question about hardware and software setting for using 32Mhz.

(1) Software setting in sdk_config.h

#ifndef CLOCK_ENABLED
#define CLOCK_ENABLED 1
#endif
#if CLOCK_ENABLED
// <o> CLOCK_CONFIG_XTAL_FREQ - HF XTAL Frequency

// <0=> Default (64 MHz)
// <255=> Default (16 MHz)
// <0=> 32 MHz

#ifndef CLOCK_CONFIG_XTAL_FREQ
#define CLOCK_CONFIG_XTAL_FREQ 255
#endif

(2) Hardware setting 

We are utilizing nrf51822 with external 32Mhz xtal.

we have not been experienced any problem directly until now.

I wonder about that if we use the above software and hardware setting, whether there is any expected problem or not.

Also, when we use 32Mhz high frequency clock, Must CLOCK_CONFIG_XTAL_FREQ be 0?

[Kenneth]

Hi,

There is an anomaly regarding using 32MHz that you should read:
https://infocenter.nordicsemi.com/pdf/nRF51822_pan_v3.3.pdf?cp=4_4_1_0 

The registers you are referring to I believe are related to the nRF52-series. In your case you have two ways of enable 32MHz:

Either write to the XTALFREQ register in UICR (page 26 in reference manual), this way can be done during production programming.

Or write to the XTALFREQ in the CLOCK peripheral (page 55 in reference manual), this way can be done during code execution in firmware.

https://infocenter.nordicsemi.com/pdf/nRF51_RM_v3.0.1.pdf?cp=4_2_0 

Best regards,
Kenneth