How hard can you drive typical 32K watch crystal?

How hard can you drive typical 32K watch crystal?

Postby melbourne » Mon Oct 25, 2021 12:12 am

We've been having some crystal oscillator problems wit a PIC16F946, (probably board leakage), and I've looked at the LP oscillator waveforms. I've got about 1.1Vpp at each end.(2.3Vpp across). Isn't that rather a lot for a typical watch crystal?

(The documentation for PIC16F946 is still 'preliminary' after 10 years, missing AC information, says that the driver circuit is new, and the logic diagram for the LP oscillator is clearly wrong, so I have a lack of confidence in the oscillator driver circuit.)
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Re: How hard can you drive typical 32K watch crystal?

Postby ric » Tue Nov 02, 2021 9:55 am

"FIGURE 4-3:" on page 90 does show a series resistor between OSC2 and the crystal, with a note saying "A series resistor (RS) may be required for quartz crystals with low drive level.".
Do you have one there?
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Re: How hard can you drive typical 32K watch crystal?

Postby ric » Tue Nov 02, 2021 9:59 am

melbourne wrote:The documentation for PIC16F946 is still 'preliminary' after 10 years,

Which version do you have?
Version "F" was released in 2007, and only mentions "Preliminary" in the "DATA SHEET REVISION HISTORY" appendix.
https://www.microchip.com/content/dam/m ... 41250F.pdf
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