Check oscillator/Xtal accuracy - how to?


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  1. #1
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    Default Check oscillator/Xtal accuracy - how to?

    Hi,

    What is the best way to check the oscillator's or the Xtal's accuracy?

    Setting a Pin HIGH then LOW and startover again seems clearly not a good way of doing.
    Roger

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    Wink Flotul is Back !!!

    Hello, Roger

    Last time I did that ( 15 days ago ...)

    I used my R/C Transmitter ( 1500µs neutral )... and placed a "PULSIN" command at the other end ...

    Result Was OscTune +6 and +9 @ 4 Mhz, for a couple of 16F88 in Int RC mode.

    You also can use a DIL canned Oscillator and a gang of dividers ( 4040 ??? ) to get a "readable" signal period.

    Alain
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    Frequency Counter! They're cheaper than a round of drinks at the pub nowadays... (even some DVM's go to 10MHz) but don't connect directly (it'll load the oscillator)... a couple of turns of enamelled copper wire around a small jar fed back with some coax to the Frequency Counter is enough to pick up a signal.

    If you must connect, always do it on OSC2 which is the drive-out pin.

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    Default ...

    Connecting an oscilloscope directly to the resonator or Xtal will allow me to check the oscillator only.

    To make a nice and clean measurement of the PIC itself allowing me to fine tune it (OSCTUNE register), how should I do?
    Roger

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    For the internal osc, just set your config option to output Fosc/4 on OSC2 and check it
    with a freq counter or O-scope.

    With a 4MHz internal osc, you should see a 1MHz output on OSC2 when it's spot-on 4MHz.
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

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    Default external?

    Thanks Bruce,

    What about measuring the PIC's accuracy with an Xtal?
    Roger

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