For the oscillator the configuration is like the capacitors are connected "serially".The load capacitors are connected in parallel so one of its lead connected to the crystal and another lead connected to the reference ground.
Hi,
For the oscillator the configuration is like the capacitors are connected "serially".
So if you find a "load capacitance" in the crystal's datasheet you need to use "twice" this value for each capacitor with your configuration.
But i don't think this is the problem here.
Klaus
Hi,
Try to use a series resistor on positive side of the crystal.
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Hi,
Try to use a series resistor on positive side of the crystal.
When I was playing with a 32 kHz crystal, I got it working in a simple circuit. It required a lot of adjusting of component values. Evidently crystals can only operate within a narrow environment.
Later I must have overdriven it, because its frequency is not always stable, and it no longer starts to oscillate so easily. I believe my mistake was that I applied supply voltage through a low resistance. It was just a few V but that was apparently enough to alter the crystal's performance.
I don't know that this is the same as your problem but it tells how we need to be mindful of a crystal's fragility.
Could also be a dry joint that makes intermittent contact or heat-related disconnections.
To see if you are getting some strange interaction with the firmware, try creating a program that turns on the 32kHz oscillator and then effectively does nothing - perhaps using the oscillator to flash a LED. IF that stops then the problem is likely to be with the oscillator/crystal; if not the there is some other interaction with the firmware.
Susan
Yes. Correct.So my calculated value is 18pF. Is that correct?
Now I am thinking that it may be I am using a wrong load capacitor. Reviewing the microcontroller's latest datasheet, it has a remark that if a crystal which is recommeded a 12.5pF load capacitance, I do not need to connect any external capacitor to it. From the datasheet, the microcontroller internal capacitance is 3.05pF or 3.29pF. Why it suggests that I do not need to connect any external capacitor? (My crystal is 12.5pF load capacitance)
One weird observation: When I pull down the hardware reset pin of the MCU to reset the MCU, a longer pull-down time (or reset time) will result a longer pause time of the crystal.
For example, if I just pull down the reset pin for about 1 secound, the MCU reset and the crystal did not pause. If I pull down the reset pin for 5 sec, after reset, the crystal pause for 10sec. Then if I pull down the reset pin for 15sec, the crystal pause for 20sec after reset.
I presume that the datasheet specifies the oscillator circuit clearly and that no external bias resistor is required according to the datasheet. The case that a bias resistor is required though should be considered as silicon and/or documentation bug.
If the oscillator is not running due to crystal quality, we can expect a too high ESR. It can't be fixed by an external circuit. Us a known good crystal.
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