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tibs
Joined: 29 Nov 2001
Posts: 23
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 05 Oct 2004 10:45 questions about crystals |
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Hi all,
I have a problem with a microcontroler board wich seems to be out of order.
I don't have any Clock Output signal whereas the chip is well powered.
This board were fully functional there are 2 days. I have changed the crystal with an another and the board was repaired.....
My question is : could the microcontroller be started with a serial crystal?
I don't know wether a serial or paralell crystal had been soldered....
Tkx,
TIBS.
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Fom
Joined: 10 Mar 2004
Posts: 758
Helped: 56
Location: Taiwan
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| 05 Oct 2004 11:06 Re: questions about crystals |
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| It should be OK. Serial or parallel resonance is used depend on oscillator circuit not crystal itself. Every cristal has both serial and parallel resonance. So you can't say that is serial crystal another is parallel. You can say only this oscillator circuit uses serial resonance another uses parallel. Oscillator always work in the frequency range between these serial and parallel resonance. But for serial circuit it works very close to serial resonance. Parallel circuit is very close to parallel resonance.
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tutx
Joined: 04 Mar 2004
Posts: 149
Helped: 16
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| 05 Oct 2004 12:58 questions about crystals |
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In my opinion, It is possible to use a serial crystal. Do not worry about this issue!
Maybe you should verify your microcontroller.
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M!k
Joined: 22 Apr 2002
Posts: 812
Helped: 68
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| 05 Oct 2004 13:30 Re: questions about crystals |
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Most of all it's a question of accuracy. The oscillators frequency is closest to the specified frequency if the type of oscillator meets the crystals specification (serial or parallel resonance). This effects also the specified capacity for a parallel resonant crystal: the oscillator has to provide this capacity for a closest match to the specified frequency of the crystal (e.g. +-50ppm). If used in an other environment the frequency will drift up to some hundred ppm. Very often it will oscillate. But it could be critical if the oscillators capacity is too high for the crystal. This can cause startup problems.
Mik
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crystalguy
Joined: 14 Sep 2004
Posts: 13
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| 08 Oct 2004 22:33 Re: questions about crystals |
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| "series" or "parallel" from the crystal standpoint, is only a frequency calibration issue. 99.99% of the crystal oscillators integrated onto micro. is of the Pierce configuration which will have a load that appears in series with the crystal to form the final frequency. the load is usually on the order of 10pF to 30pF. the effect of this load is threefold (at least) it affects the oscillator frequency(smaller load capacitance means higher frequency), Gain margin (higher the load capacitance the lower the margin), crystal power dissapation (higher the load capacitance the higher the crystal power dissapation will be). Generally for microcontroller applications(or similar) a very lite load(small caps) is desirable since frequency stabiality is not real important and reliable operation is. hope this helps
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