Post by thread:Crystal ???

Hi: Can somebody explain me why the crystal used in PIC's must be with parallel resonant frequency ? Which would be the result is I use a crystal with series resonance ? Which is the difference ? Thank you. -- | ~~ ~~ /^\ | Jose Pineda | ~~ /^\ / \ ~~ | Fax : +58 2 2426039 | /_ \/ _ \ ~~ | E-mail : spam_OUTjpinedaTakeThisOuTdino.conicit.ve | / # _ # _ # _ _ \ | Caracas, D.F. | / # # _ # # # # # _ \ | Venezuela |_/______#_#_#_#_#_#_#_#_#_____\_|

> Can somebody explain me why the crystal used in PIC's must be > with parallel resonant frequency ? > > Which would be the result is I use a crystal with series > resonance ? > > Which is the difference ? The difference, from what I understand, is usually just this: one type of oscillator will run a little faster than the crystals fundamental; the other will run a little slower than the fundamental [I think parallel is faster but I'm not sure--the following may be backwards]. Ergo, to get a 1,000,000 Hz oscillator in a series resonant circuit you need about a 1,003,000Hz crystal and to get 1,000,000Hz in a parallel circuit you need a 997,000Hz crystal. Note that both of the above crystals would be called 1,000,000Hz since that's the "intended" oscillation speed, but using a series crystal in a parallel circuit would result in an oscillator that ran about 0.6% fast. NOTE: This is reproduced from memory from a magazine Q&A I saw ages ago and may bear no resemblance to reality--use at your own risk.

> Can somebody explain me why the crystal used in PIC's must be > with parallel resonant frequency ? Yes, but it would be better if you read about it in AN588 PIC Oscillator design guide, or Intel's application note AP-155 Oscillators for Microcontrollers.