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  1. #1
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    clock input pins signal integrity

    I am using a external crystal as a clock source. the clock freq is 27MHz.

    Using a scope and probing x1 and x2 input pins(crystal). The signal across the
    crystal are very different. One is sinusoidal while the other is distorted.

    your thoughts

    thnaks cool

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    Re: clock input pins signal integrity

    You don't say what the chip is, but it sounds normal. The crystal is not a "clock source" - it is the resonant component in an oscillator. The oscillator if formed with the two chip pins. One pin will be an input, the other will be the output. The signals will be very different.

    Does it work?

    Keith.


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    Re: clock input pins signal integrity

    it seem to, but it looks much differnt than what I seen before

    cool



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    Re: clock input pins signal integrity

    The XIN signal would always be near to a sine, the XOUT may be different depending on the clock oscillator design. A "simple" clock oscillator is CMOS inverter with excess gain, that drives the crystal with a more or less rectangular waveform at XOUT. A modern EMC optimized oscillator uses a lower drive level. XOUT looks more like a sine in this case.



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    Re: clock input pins signal integrity

    I would expect a sine wave with a voltage level dependent on the cpu core requirerments



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