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.

 

 

Four legs good, two legs bad, three legs stable.

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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.

 

Four legs good, two legs bad, three legs stable.

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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.
.
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

 

Four legs good, two legs bad, three legs stable.

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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.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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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...