nRF52833 Unable to Use External 32 MHz Crystal

[ge90114b]

Hewy there:

I have a custom nRF52833 board with NCS v3.1.0, using ESB and USB CDC ACM. The external 32 MHz crystal is oscillating fine — we see a clean 32 MHz sine wave at 700 mVpp on the scope. Crystal is X201632MOB4SI (YSX211SL, CL=12 pF), with 12 pF caps on both pins.

But EVENTS_HFCLKSTARTED never fires. HFCLKSTAT still shows SRC=0 (internal RC). We also tried setting HFXODEBOUNCE to 0x40 before starting the task, no change.

The app hangs in lfclk_spinwait() when using CONFIG_CLOCK_CONTROL_NRF_K32SRC_SYNTH=y. With RC everything runs but USB fails (Windows error code 43) and ESB doesn't work.

Why would EVENTS_HFCLKSTARTED not trigger when the crystal is clearly oscillating at the right frequency and amplitude?

Thank you.

[Turbo J]

Oscilloscope probes puts a BIG load on the crystal - so big that it may not run once you remove the probes again.

Usage of 12pF loading caps with a 12 pF crystal is almost surely wr0ng. You need to use the formula to calculate them, they should be close to twice as big IMHO. That would also explain why it only works with the scope attached...

[ge90114b]

I think so too, so I bought a capacitor with a larger capacity to prepare for testing. Thank you for your reply