What voltage would you expect to see on a ceramic resonator?

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I have a 24mHz resonator on a micro(not AVR, actually Kinetis) and the waveform is roughly 480mV peak to peak. Is this what you'd expect? I'm having trouble whereby as soon as I switch the clock source from internal to external, the next read of an SFR crashes the system.

 

 

Quebracho seems to be the hardest wood.

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Surely you would expect 3.3V pk-pk on XTAL2 pin.

 

And any probe on XTAL1 will generally kill the oscillations.

 

24MHz seems rather high for a chip with a PLL.   (I assume 24mHz was a typo)

 

David.

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Sorry, yes meant MHz.

Yes, it's a bit high. Client using existing stock! Not really sure if a ceramic reso will be accurate enough for USB...

Works now, I stupidly assumed my client had copied the dev PCB, which has 8MHz, so my processor was trying to run 3 time faster than it's supposed to.

 

Quebracho seems to be the hardest wood.

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I am sure that it will be accurate enough for USB.
Just as long as there is sufficient "drive" from the Freescale oscillator silicon.
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It always seems wise to copy a working design than to start from scratch. e.g. 8MHz or 12MHz crystals / resonators.

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It's within spec. Upper limit is 32MHz

 

Quebracho seems to be the hardest wood.

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John_A_Brown wrote:

It's within spec. Upper limit is 32MHz

 

 

But not when mistakenly multiplied by 3. See above.

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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david.prentice wrote:

Surely you would expect 3.3V pk-pk on XTAL2 pin.

 

These days, not always....

In the old days of CMOS inverter Oscillators, the classic expectation was ~50% Vcc bias, and full swing.

A problem with such inverters, is while they are simple, they have widely varying Icc with Vcc.

 

A more modern Xtal Oscillator uses a current source, driving a N-FET. Icc no longer varies greatly with Vcc.

 

This self-biases somewhere under 1V, and may have 1.3v p-p swings. 

 

See the threads around newer AVRs losing the full-swing oscillator, and taking a hit in the MHz department at the same time...