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XT and HS

Discussion in 'Microcontrollers' started by gramo, Mar 17, 2007.

  1. gramo

    gramo New Member

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    What exactly is the difference between these too fuses on PIC micro's, i.e. how do you know what option too pick for the Crystal speed in use?

    :eek:
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's a VERY vague distinction - but HS (High Speed) gives more drive to the crystal.

    There's no specific changeover point - but 4MHz would be XT, and 20MHz would be HS. Often either will work, but perhaps a reasonable changeover would be 10MHz?, or even 4MHz and below is XT, and anything higher is HS?.
     
  3. gramo

    gramo New Member

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    Hehe. that’s the vaguest explanation I’ve seen you give to date Nigel!
     
  4. dave

    Dave New Member

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  5. gramo

    gramo New Member

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    So running HS for 4Mhz+ is safe and accurate?
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi gramo,

    From datasheet.

    EDIT: part2

    Eric
     
    Last edited: Jul 7, 2008
  7. gramo

    gramo New Member

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    Great find, thanks for clearing that up!
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's a very vague subject! - notice that the chart posted says 'guidance only'.
     
  9. eng1

    eng1 New Member

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    The application note AN588 says something about the power consumption:

     
  10. gramo

    gramo New Member

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    Soo, by running HS, I will have the best frequency response, would that make timing more accurate?
     
  11. blueroomelectronics

    blueroomelectronics Well-Known Member

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    If you need accurate timing use a 32768Hz crystal on TMR1 osc. These are more accurate than most high speed crystals.
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, it will make no difference.
     

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