NRF52 Clock Issue

[AWUk]

Hi,

I have a board with a NRF52 (3rd party board), there is a 32MHz crystal with the correct load capacitors on, but the crystal is outputting 1MHz on a scope (Tektronix 100MHz), the code runs fine on the DK board, it has the 32KHz also on board, so the board powers up etc, but nothing is running on the NRF, no current is being pulled, am I missing something? It seem that the crystal goes to pin 34 and 35 on the NRF IC, and there are 18pF load capacitors fitted, which according to the datasheet of the crystal (Abracon ABMM2 series) is correct.

[AmbystomaLabs]

You are just looking at the alias of the signal. It's a nyquist theorem thing. Just turn the sample rate up (ie, horizontal scale to a minimum) to see the real signal. On your scope the minimum will be about 10nsec/div.

Normally, you will see a fairly square wave looking thing, but since your scope has only a 100MHz front end it will likely look like a distorted sine wave. The reason is all the harmonics that make it square are way beyond the capabilities of your scope so they will either be lost or alias back in band.

Also, the parasitic capacitance of the scope probes might pull the crystal a bit. So it may be a little outside of its ppm accuracy. A better approach is to use the ppi to buffer the clock and route it out gpio.

And remember the 32MHz has to be running. The SD always turns it on but normally your code will be executed with HFINT main clock for power savings. You actually have to request the 32MHz to be on in your code.