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Crystal oscillator questions — Parallax Forums

Crystal oscillator questions

JDatJDat Posts: 103
edited 2014-01-02 13:43 in Propeller 1
Hello!

Newbie question.

Why Propeller don't need 18-22 pF capacitors for external crystal oscillator? Usually Pierce oscillator (used on most MCUs) need external capacitors. How this is solved on Propeller 1 (and maybe Propeller2)? Did I missed something in datasheet?

Comments

  • LeonLeon Posts: 7,620
    edited 2014-01-02 12:58
    The chip includes the capacitors, it's in the documentation.
  • JDatJDat Posts: 103
    edited 2014-01-02 13:01
    Can You, please, give me additional information regarding this? Seems that I am little bit blind after beer :D and can not find information in datasheet.
  • LeonLeon Posts: 7,620
    edited 2014-01-02 13:04
    Page 4 of the datasheet says that no Cs are needed. Page 25 specifies the input capacitance as 6 pF.
  • JDatJDat Posts: 103
    edited 2014-01-02 13:10
    Will that be sufficient to launch propeller into space (on cubesat)?
  • LeonLeon Posts: 7,620
    edited 2014-01-02 13:14
    Will what be sufficient?
  • PublisonPublison Posts: 12,366
    edited 2014-01-02 13:15
    Page 14 of the Data Sheet shows tthe specs:

    http://www.parallaxsemiconductor.com/sites/default/files/parallax/Propeller-P8X32A-Datasheet-v1.4.0_1.pdf
  • JDatJDat Posts: 103
    edited 2014-01-02 13:19
    Thank You very much for this information!
  • jmgjmg Posts: 15,173
    edited 2014-01-02 13:43
    JDat wrote: »
    Will this be sufficient to launch propeller into space (on cubesat)?

    You can check the oscillator margin with a series resistor on the crystal, and you may want to check temperature extremes.
    Osc startup is usually 'harder' than run, so cycle the power at each test.

    If precision matters, (ppm levels) you may need some additional external C, as well as the on-chip C's, in order to match the Xtal's test/Cal C value.
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