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Maximum Prop cyrstal speed — Parallax Forums

Maximum Prop cyrstal speed

PhilldapillPhilldapill Posts: 1,283
edited 2008-02-02 14:56 in Propeller 1
What is the maximum external crystal that the propeller can handle with no errors? I've seen OzStamp's DLP prop using a 6mhz, and at 16xPLL, that's 96MHZ... 18MHZ more than what is normally used. What's the deal?

Comments

  • James LongJames Long Posts: 1,181
    edited 2008-02-02 06:55
    Pdp,

    You can use much faster crystals, but you can not run the Prop much faster and have success. The 96 Mhz is about the fastest most people will push the Prop.

    Is there a reason you want to push one faster than 96 Mhz?



    James L

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  • PhilldapillPhilldapill Posts: 1,283
    edited 2008-02-02 07:00
    No, not really. Just curiousity as to why Parallax doesn't use a 6MHZ across the board. I assume it has to do with stability like overclocking a computer may cause errors?
  • stevenmess2004stevenmess2004 Posts: 1,102
    edited 2008-02-02 07:03
    The prop is designed to cover a very large temperature range. (Have a look in the data sheet) To get stable operation over the temperature range the PLL must be kept less than 160MHz (I think) and the clock speed less than 80MHz. They did some tests at one stage and had it operating over 100MHz at one stage but the counters and things start failing. Having said that, using the prop at 96MHz at room temperature seems to work fine.

    Steven
  • VIRANDVIRAND Posts: 656
    edited 2008-02-02 07:37
    Instead of 5 or 6 Mhz crystals you can use 10 or 12 or 20 or 24 Mhz ones at least. I use 10 because I have HYDRA.
  • GadgetmanGadgetman Posts: 2,436
    edited 2008-02-02 09:57
    No, you can't use 12, 20 or 40MHz Xtals.

    The PLL ALWAYS multiply the Xtal frequency by 16, and if that gets over 160MHz...


    Stick to 10MHz or less.

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  • deSilvadeSilva Posts: 2,967
    edited 2008-02-02 12:26
    Either you stick to the datasheet or you strive for the limits. We had very instructive discussions in the past I shall not repeat here.

    The PLL works well with 12 MHz crystals, but you should constrain yourself to a divided clock (= PLL8X); I in fact prefer this over 6 MHz/PLL16X).

    There might be reasons to not use the PLL, then 20 MHz crystals will do fine , also any input from an external oscillator.
  • RaymanRayman Posts: 14,162
    edited 2008-02-02 12:49
    I found·some 6.25 MHz crystals so I can run at 100 MHz.· This works fine.·

    You can use crystals up to 100 MHz or so as long as you don't use the PLL.· But, you have to be careful with part selection (as mentioned in earlier threads).
  • deSilvadeSilva Posts: 2,967
    edited 2008-02-02 12:57
    Crystals above 20 MHz use higher harmonics and might not work as you expect smile.gif
  • LeonLeon Posts: 7,620
    edited 2008-02-02 13:02
    I can get 40 MHz fundamental crystals.

    Leon

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  • deSilvadeSilva Posts: 2,967
    edited 2008-02-02 13:16
    All right then.. I can not :-(

    .. but I have not tried very hard smile.gif
  • hippyhippy Posts: 1,981
    edited 2008-02-02 14:11
    This Wiki Page seeks to give an objective overview of using the Propeller Chip beyond the ratings stated in the Propeller Chip Data Sheet ...

    propeller.wikispaces.com/Oscillator
  • LeonLeon Posts: 7,620
    edited 2008-02-02 14:56
    ACT makes them, they are available from Rapid Electronics in the UK. I got some to use in a ladder filter but haven't tried them.

    Leon

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