Post by thread:crystal

Hello all, I think someone else has ask this question before, but I didn't read any answers. What kind of crystal do we need for building the extern part of the oscillator for a PIC: serial or parallel ?? I am using a 8 MHz crystal, with two C's of 15 pF to ground as described in the databooks of MicroChip, now for one of my applications, but the crystal seems to run at a slightly higher frequence. For getting the correct frequence I have to increase the C's value to about 40 pF. Does someone can help me? Buy, ... Sipke de Leeuw ...

Sipke de Leeuw wrote: > > Hello all, > > I think someone else has ask this question before, but I didn't read any > answers. What kind of crystal do we need for building the extern part of the > oscillator for a PIC: serial or parallel ?? > (&etc.) I didn't see any answers, either, so try this: Basicly, a crystal is a crystal. Size & cut changes the LC model numbers to a degree, but there is really no major physical difference between series and parallel parts. What is different is the circuit used to oscillate the crystal during calibration (or at least the type intended when in use). I usually think of most common ic oscillator architectures as being series, but the truth is that for microprocessor use I don't think I've ever seen a frequency difference, which is subtle in any case. Almost any modern small crystal will oscillate just fine with almost any modern ic, so you can pretty well relax and follow the manufacturers' suggestions for external parts. Tom Rogers VP - R&D Time Tech, Inc.

Does the ECS-40-s-4 in parallel with the PIC16C84 need to have it's shell grounded? Brad _____________________________________________________________________ Brad Pousland http://mole.uvm.edu/~bpouslan Computing and Information Technologies spam_OUTbpouslanTakeThisOuTmole.uvm.edu University of Vermont 656-2604

>Does the ECS-40-s-4 in parallel with the PIC16C84 need to have it's shell >grounded? > Brad >_____________________________________________________________________ >Brad Pousland http://mole.uvm.edu/~bpouslan >Computing and Information Technologies .....bpouslanKILLspam@spam@mole.uvm.edu >University of Vermont 656-2604 Probably not from a functional standpoint. It could have a small effect on stability and startup time. But it might make a major difference in EMR test results, if that's significant in your application. Reg Neale Usual disclaimer applies "Ignorance is a renewable resource." . . . P. J. O'Rourke

At 08:46 PM 7/21/96 -0400, you wrote: >>Does the ECS-40-s-4 in parallel with the PIC16C84 need to have it's shell >>grounded? >> Brad >>_____________________________________________________________________ >>Brad Pousland http://mole.uvm.edu/~bpouslan >>Computing and Information Technologies bpouslanKILLspammole.uvm.edu >>University of Vermont 656-2604 > >Probably not from a functional standpoint. It could have a small effect on >stability and startup time. But it might make a major difference in EMR >test results, if that's significant in your application. > > Reg Neale Usual disclaimer applies >"Ignorance is a renewable resource." . . . P. J. O'Rourke > Forgive the question but isn't an ECS-40-s-4 a series crystal and the preferred type is parallel? Some of the books list a series crystal as tested but still say you need parallel.

>Forgive the question but isn't an ECS-40-s-4 a series crystal and the preferred >type is parallel? Some of the books list a series crystal as tested but still >say you need parallel. > What book is it that says you need parallel? I don't know enough about it. If anyone has further recommendations as to the clock circuit, I would be much obliged. Brad _____________________________________________________________________ Brad Pousland http://mole.uvm.edu/~bpouslan Computing and Information Technologies .....bpouslanKILLspam.....mole.uvm.edu University of Vermont 656-2604

At 10:05 PM 7/22/96 -0400, you wrote: >>Forgive the question but isn't an ECS-40-s-4 a series crystal and the preferred >>type is parallel? Some of the books list a series crystal as tested but still >>say you need parallel. >> > >What book is it that says you need parallel? I don't know enough about it. >If anyone has further recommendations as to the clock circuit, I would be >much obliged. > >Brad >_____________________________________________________________________ >Brad Pousland http://mole.uvm.edu/~bpouslan >Computing and Information Technologies EraseMEbpouslanspam_OUTTakeThisOuTmole.uvm.edu >University of Vermont 656-2604 > Well for one spot its in the PIC 16C84 data book section 8.2.2 The PIC16C84 oscillator design requires the use of a parallel cut crystal. Use of a series cut crystal my give a frequency out of the crystal manufacturers specifications. The PIC16C7X book says that true for all 16CXX oscillators in section 14.2.2 The odd thing is after saying that in a PIC16C84 data book table 8-2 the list the series crystal you were talking about the ECS ECS-40-S-4 as being one of the crystals tested. I wish someone at Microchip would say either that the ECS series parts test do work or someone make a mistake and should have used the parallel part numbers in the chart. I will use the parallel parts from now on, my first design was using the same crystal as discussed about and it was 4% off freq.

<x-flowed>Hello I'm just wondering if the capacity of the two capacitors in the crystal oscilator is important. i have two 22pF for my 4 Mhz crystal. Some projekts use different values. Does that make a difference? Yours sincerely Thomas Thorsen ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com </x-flowed>

If you need the 4 MHz crystal to be exactly on 4.000 000 MHz, then the value(s) of the caps does make a difference. Thomas Thorsen wrote: {Quote hidden}> Hello > > I'm just wondering if the capacity of the two capacitors in the crystal > oscilator is important. i have two 22pF for my 4 Mhz crystal. Some projekts > use different values. Does that make a difference? > > Yours sincerely > Thomas Thorsen > > ______________________________________________________ > Get Your Private, Free Email at http://www.hotmail.com

<x-flowed>At 12:49 PM 2/7/00 +0100, Thomas wrote: >I'm just wondering if the capacity of the two capacitors in the crystal >oscilator is important. i have two 22pF for my 4 Mhz crystal. Some projekts >use different values. Does that make a difference? 1. Sometimes the oscillator won't work if you don't have enough capacitance, although > 15 pF and < 100 pF should work at 4 MHz. 2. The size of the capacitors used will increase with increasing frequency. 3. About 27-33 pF seems to work best (i.e., give closest to exact frequency) for 4 MHz. About 22 pF works for 8 MHz. About 15-22 pF for 20 MHz. 4. You can pull the crystal frequency about +/- 0.01% by adjusting the capacitors used, particularly the OSC1 capacitor. You would do this to get the exact frequency 4.00000 MHz. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ralspam_OUTlcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causae scire" ================================================================ </x-flowed>

At 12:58 PM 2/7/00 -0500, you wrote: >2. The size of the capacitors used will increase with increasing frequency. > Do you mean "decrease" with increasing frequency? I haven't really done any math on this, but it seems that they should decrease. Also, in your example, you give smaller values for 8MHz than for 4MHz. Sean | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 @spam@shb7KILLspamcornell.edu ICQ #: 3329174

<x-flowed>At 03:54 PM 2/7/00 -0500, you wrote: >At 12:58 PM 2/7/00 -0500, you wrote: > >2. The size of the capacitors used will increase with increasing frequency. > > > >Do you mean "decrease" with increasing frequency? > >I haven't really done any math on this, but it seems that they should >decrease. Also, in your example, you give smaller values for 8MHz than for >4MHz. > >Sean Sorry, yes. You will note that the numbers I gave showed this. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: KILLspamralKILLspamlcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causae scire" ================================================================ </x-flowed>