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I would like to know what is the fastest crystal that I could use with the prop — Parallax Forums

I would like to know what is the fastest crystal that I could use with the prop

jmbertoncelli@USAjmbertoncelli@USA Posts: 48
edited 2008-07-10 23:55 in Propeller 1
Hello,
I would like to know what is the fastest crystal that I could use with the prop proto board?

My current program setup is:

_clkmode = xtal2 + pll16x
_xinfreq = 5_000_000

what about:

_clkmode = xtal3 + pll16x
_xinfreq = 5_000_000


I tried to use xtal3 + pll16x but nothing work I guess that the crystal is not fast enough????

thanks a lot.

jm.

Comments

  • LeonLeon Posts: 7,620
    edited 2008-07-10 21:48
    This has been covered in previous posts.

    Leon

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  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2008-07-10 22:18
    Welcome to the forums!

    Here's a good link for Oscillator speeds and options that could work for you.

    propeller.wikispaces.com/Oscillator

    OBC

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    New to the Propeller?

    Getting started with the Protoboard? - Propeller Cookbook 1.4
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  • jmbertoncelli@USAjmbertoncelli@USA Posts: 48
    edited 2008-07-10 22:43
    Thank you for your help!

    jm.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2008-07-10 22:44
    Xtal1, 2 and 3 are the drive characteristic which has nothing to do with the speed of of the crystal. We have never found an instance where xtal3 was needed for correct crystal operation. It is the crystal which determines the speed of operation. In all your examples the crystal is 5MHz which with PLL16x will always generate 80 MHz.

    The fastest speed the Propeller can be clocked is determined by it's operating temperature. The datasheet shows the frequency vs temperature, please note the indicated line is the failure point, not an indication of an achievable speed (unless you don't care if you Propeller doesn't always work). So you will need to derate this value (lower the frequency to ensure the Propeller will always work). At room temperature the highest people have been able to get it to reliably operate is 7.3728 MHz crystal wound up by PLL16x.

    However, just like overclocking your computer, we make no guarantee of operation above 80MHz.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • johnfl68johnfl68 Posts: 72
    edited 2008-07-10 23:38
    In the Wiki that Oldbitcollector mentioned above, it states that a 6.25 MHz crystal will give you 100 MHz (PLL divided by 1).

    Anyone know where to readily get a 6.25 MHz crystal that works for the Prop??? No one seems to carry 6.25 MHz.

    Thanks!

    John
  • LeonLeon Posts: 7,620
    edited 2008-07-10 23:43
    It doesn't cost much to get crystals made for a particular frequency. I use these people:

    http://www.quartslab.com/

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • TimmooreTimmoore Posts: 1,031
    edited 2008-07-10 23:55
    http://www.electronicplus.com/content/ProductPage.asp?pagenum=2&lname=&maincat=cco&subcat=cry
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