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'crystal'
1996\04\01@063500 by Sipke de Leeuw

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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 ...

1996\04\01@082317 by terogers

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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.


'crystal'
1996\07\21@191127 by Brad Pousland
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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_OUTbpouslanTakeThisOuTspammole.uvm.edu
University of Vermont                   656-2604

1996\07\21@205238 by Reginald Neale

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>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  .....bpouslanKILLspamspam@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

1996\07\22@143024 by David E. Queen

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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  bpouslanspamKILLspammole.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.

1996\07\22@220704 by Brad Pousland

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>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  .....bpouslanKILLspamspam.....mole.uvm.edu
University of Vermont                   656-2604

1996\07\23@015624 by David E. Queen

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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_OUTspamTakeThisOuTmole.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.


'Crystal'
2000\02\07@065119 by Thomas Thorsen
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<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


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</x-flowed>

2000\02\07@111520 by jkitchen

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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}

2000\02\07@130043 by Robert A. LaBudde

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<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: ralspamspam_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"
================================================================

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2000\02\07@155423 by Sean Breheny

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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

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2000\02\07@165436 by Robert A. LaBudde

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<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: KILLspamralKILLspamspamlcfltd.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>

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