LockedGuidelines: Crystal oscillator FAQ and manuals.

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2004/08/11 13:09:05 (permalink)
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Guidelines: Crystal oscillator FAQ and manuals.

Read this page:

It was written by a great hacker and translated to many languages.
Read it please.

- Application notes, basic information:
1) Be sure to know your PIC's datasheet well and read ALSO the notes with small letters under the text, because they are important. Many questions are answered there.
2) Maybe your problem is already described in the errata: http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1433

3) There are more application notes that describe the crystal oscillator operation:


Almost the same as above, updated, but some information is missing.

Basic PICmicro Oscillator Design, 24 pages of technical explanation and oscillographs from real oscillator circuits.
This is an advanced paper.

Crystal Oscillator Basics and Crystal Selection, 11 pages, explanation of technical terms and deeper look at the physical hardware.

http://ww1.microchip.com/downloads/en/AppNotes/00949a.pdf (Making your oscillator work)
Nothing much to read, but contains a FAQ which the other app. notes don't.

Something new:
Finally! Some good theory and simulation now at Microchip also!
Beware that this app. note says that you have to read AN826 (FACT001, AN838 are also good) and AN849 first!

4) If you still don't have enough, there are some other application notes, you are advised to search for them on your own, so only two more:

Internal RC Oscillator Calibration:

"OSCILLATOR SELECTION FOR ST62", datasheet number 2501, available at STMicroelectronics.

Be sure to know how crystal operation works before you ask that :). Because you would be asked to read the above mentioned documents.

- What to do and what not to do.
1) Do place decoupling capacitors near each pair of power supply pins (usually the cheapest 100nF multilayer ceramic types).
2) If possible, avoid using breadboards. Keep tracks from PIC to crystal short, the same applies to capacitors.
Breadboards are a real nightmare to HF circuits... It adds so much L,C, and R (it may add unwanted inductance, capacitance and resistance) to the circuit that it's hard to predict how it will act.

- What to write in your post:
What PIC you are using, __CONFIG bits setup, value of capacitors in the crystal oscillator, supply voltage.

- What more?:
If you do not seem to find the information you were looking for in 5 minutes, please take another 55 minutes searching for that. Still no results? It is possible that there is no such information, try using the closest alternative datasheet of similat technology.



Good luck!
< Message edited by mfb -- Jan. 20, 2005 11:37:47 AM >

5 Replies Related Threads

    New Member
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    RE: Guidelines: Crystal oscillator FAQ and manuals. 2004/11/17 15:27:10 (permalink)
    Need a circuit wiring diagram of a variable RC RC external oscillator and frequency calculations for PIC 16F870.

    |_____ pin2(POT)__CLKIN
    == C

    f = 1/(2*pi*R*C) Hertz ?

    Please help ??

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    Quartz crystal resonator frequency 2006/03/23 14:32:10 (permalink)
    mfb, am I understaning you correctly that 40MHz crystals are unreliable and "black magic". Funny, we had run about 125 boards with the 40MHz crystals on them, no failures, and timing well within the 50ppm spec.

    No, you don't understand me :). Again. Take a crystal of quartz. Cut it precisely in a very precise angle trough one of the crystal mesh axes (I forgot the precise term, sorry), cut it to some unbelieveable thickness, so that it becomes very brittle, etch it to make it even thinner, much thinner than paper, metallize the sides with extremely precise amount of silver and pack it, make some contacts that will influence the frequency by a precise amount of energy absorbed, so that a sufficient resonance factor Q will remain for practical use. O.K. Now you have a 40MHz crystal. I believe that some japanese companies made that possible, but it surely it wasn't some 10 or 5 years ago. And quartz resonators are being used much longer than transistors!

    Quartz crystals sorted by cut angle:

    X - 10-200 kHz
    NT - 1-100 kHz
    CT 300-1000kHz
    BT 1-30 MHz
    AT 1-250 MHz

    Mostly used resonators are made from AT cut quartz crystals (80%). The cut type also guarantees temperature related frequency shifts, and different cuts have freq. maximum at different frequencies. The TTC cut quartz resonators have maximum at 90 deg. C, and the top is very, very flat, thus suitable for high stability clock sources.

    The fundamental resonator frequency is inversely proportional to resonator plate thickness. Usually manufactured pieces are up to 30MHz. Most of them is under 26MHz. (25MHz is used in LAN NIC) Higher frequencies are easily achieved by controlled crystal overdrive that causes it to resonate at 3rd, 5th 7th or 9th overtone (odd harmonic)

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    RE: Guidelines: Crystal oscillator FAQ and manuals. 2007/07/26 15:54:47 (permalink)
    there are many details illustrated for which nowadays knowledge has been lost again.
    actually it was possible to build a one-MOSFET oscillator after reading this document.
    FYI: This simple circuit practice is far from lost! It is often used in price sensitive equipment as the basis for very cheap PWM generators & driver.
    ...they needed to consult a technical dictionary
    ...hmmm, so does the forum when trying to understand the noise you inject here in the forum...[joke!][8D]
    Hope it helps
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    RE: Guidelines: Crystal oscillator FAQ and manuals. 2008/05/10 20:22:24 (permalink)
    ORIGINAL: nikemoto2511

    here a literature from intel, dated 1983. title is "quartz oscillators for microprocessors" . . . the file is around 1 megabyte in size, http://mio5.net/htm1/pic_prj/intel_oscillators_1983.pdf
    Your link seems to be broken. 

    Intel Application Note AP-155, "Oscillators for Microcontrollers" can be found at Some of These Links.

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    RE: Guidelines: Crystal oscillator FAQ and manuals. 2008/05/11 01:55:33 (permalink)
    Side comment:
    Interesting to see how long it takes between posts to keep this thread alive! Truly amazing.

    Agustín Tomás

    In theory, there is no difference between theory and practice. In practice, however, there is.

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