System oscillator will not start

[aune]

Using the FRDM-K22F ( MK22FN512VLH12 ), and trying to use the external crystall.

After setting up the HGO = 1, Range = 1 and EREFS = 1, and selecting CLKS = 2 I would assume that the oscillator should start, but nothing happens.

I have verified that R57 is not present on the PCB.

[aune]

If I don't set the HGO = 1, but leave this at 0, it works. ANyone got a good explanation why?

[jeremyzhou]

Hi,

In the External Crystal/Resonator Connections section, it illustrates the various external crystal/resonator connections of the corresponded oscillator mode.

And please refer to it in details.
Have a great day,
Ping

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[mjbcswitzerland · Accepted solution]

Hi

The gain setting must match with the HW.

If the crystal is not loaded (no loading capacitors or feedback resistor) the low gain is correct. Setting high gain will be wrong and not work.

If the crystal is loaded (with loading capacitors and a feedback resistor) the high gain is correct. Setting low gain will be wrong and not work.

Some Freescale boards require high gain and some require low gain.

If it is not clear from the circuit see which one works and use that.

Regards

Mark

[aune]

Thanks for the explanation, makes sense.

As you said, I have no external feedback resistor, so when setting HGO = 0, the oscillator started up just fine.