External Clocks

RE: External Clocks

webzoid — Thu, 21 Jun 2018 13:15:10 GMT

Ok, my understanding there then is that the 32MHz is probably working if the radio stack is active.

Thanks for your help

RE: External Clocks

Håkon Alseth — Thu, 21 Jun 2018 13:10:46 GMT

If you scope XC1/XC2, you change the load (impedance), thus reduce the amplitude. A normal low-voltage swing on these pins is only a couple of hundred millivolts.

Cheers,

Håkon

RE: External Clocks

webzoid — Thu, 21 Jun 2018 13:04:15 GMT

This is quite strange because I have had the SparkFun nRF52832 board running (using Arduino BLEPeripheral code) and when checking the 32M clock, there was barely any output.

RE: External Clocks

Håkon Alseth — Thu, 21 Jun 2018 13:01:09 GMT

32M crystal is required for the radio to work. This one you cannot get around if you want to use the radio.

32k can be sourced from either an external 32k crystal, or using the internal 32k RC oscillator. Using the RC oscillator will give a penalty on power consumption (you need to calibrate regularly), but reduce BOM cost.

RE: External Clocks

webzoid — Thu, 21 Jun 2018 12:59:18 GMT

Thanks for your code sample. I will try this shortly.

Is there any benefit in using the external 32MHz and 32.768kHz crystals over using the internal ones?

Obviously a reduction in BOM component cost is very beneficial.

RE: External Clocks

Håkon Alseth — Thu, 21 Jun 2018 11:35:07 GMT

Hi,

Most examples uses the external LFCLK by default. The external HFCLK is started on-demand (automatically by the softdevice) for power consumption reasons.

Use this code snippet to test your clock sources (add them to the blinky example for instance):

NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
    
NRF_CLOCK->LFCLKSRC = CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos;
NRF_CLOCK->TASKS_LFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0);

If your code hangs in one of the while-loops, then there's an external problem with your clock source (loading caps incorrect, soldering issue, or similar)

Note: if adding this to a SoftDevice example, be sure to run this _prior to the softdevice enable_

Cheers,

Håkon