How to measure nRF52832 32Mhz Crystal frequency by counter ??

[jasonchiang]

Sorry for disturbing!

I have some questions about measuring nRF52832 32Mhz Crystal frequency.

I use an active probe(Tektronix P6243) to catch the signal and the test result is below.

Question1. Do we need to key any code for Crystal oscillates stably??

Question2. Why the front end of waveform has some distortion??  Is this correct? 

Question3. How to measure crystal by a counter (Agilent 53210A) ?? When I use the probe to measure crystal output pin, the value shows unstable on the counter. Does this situation related to the front end of waveform??

[Håkon Alseth]

Hi,

 

 

Question1. Do we need to key any code for Crystal oscillates stably??

The crystal is stable after the EVENTS_HFCLKSTARTED event is set.

Here's an example in C:

NRF_CLOCK->TASKS_HFCLKSTART = 1;
nrf_gpio_pin_set(TEST_GPIO);
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
nrf_gpio_pin_clear(TEST_GPIO);
NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

 

Question2. Why the front end of waveform has some distortion??  Is this correct? 

Are you thinking of the amplitude change after stabilizing or the "noise" in the actual sinus, ie: picture nr. 2?

The amplitude change is due to the stabilisation, while the noise on the zoomed in sinus is likely picked up by noise from the probe or the grounding. Does not look that bad.

Question3. How to measure crystal by a counter (Agilent 53210A) ?? When I use the probe to measure crystal output pin, the value shows unstable on the counter. Does this situation related to the front end of waveform??

You'll have to contact the supplier of this instrument in order to set it up to count clocks on a crystal. I do not have any experience with this specific frequency counter.

 

Kind regards,

Håkon 

[jasonchiang]

About Question2

I zoom out the horizontal scale on my oscilloscope

It looks like crystal oscillates for a period of time then stops oscillating  and oscillates again.(repeat and repeat)

Is this situation normal or can it be always oscillating ?(sorry i don't know about 32M crystal operation of this chip)

I try to confirm if 32M crystal accurate or not. Do you have any suggestion about measuring 32M crystal frequency??

Thank you for your reply !!

[Håkon Alseth]

Hi,

 

If your firmware is running a bluetooth example using the SoftDevice, then this is normal. For power consumption reasons, the external HFCLK is only started when it is needed by the radio.

If you have access to a spectrum analyzer, you can check the crystal accuracy by outputting a unmodulated signal at a given frequency (let's say 2.440 GHz), then see how much the RF signal deviates from this expected frequency.

 

Kind regards,

Håkon