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Hot!KSZ8041RNL REF_CLK outputting 25MHz

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AndyD
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2020/03/31 05:58:07 (permalink)
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KSZ8041RNL REF_CLK outputting 25MHz

Hi,
 
We have a design using the KSZ8041RNL, using an external 25MHz oscillator on pin 9 as per datasheet.  However, we get 25MHz out of pin 19 (REF_CLK), and believe it should be 50MHz.  We've been through the datasheet and design checklist, and all points look ok.
 
We have it set at PHY Add: 00011.  and CONFIG[2:0] 001 = RMII.
 
Has anyone seen this before? Or have any ideas?  Any suggestions would be gratefully received.
 
Thanks.
Andy
 
 

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    mbrowning
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    Re: KSZ8041RNL REF_CLK outputting 25MHz 2020/03/31 13:48:54 (permalink)
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    3.13

    The KSZ8041RNL is configured in RMII mode and outputs the 50-MHz RMII reference clock to the MAC on REF_CLK(pin 19) after it is powered up or reset with the following:• A 25-MHz crystal connected to XI (pin 9) and XO (pin 8), or a 25-MHz reference clock connected to XI (pin 9)/
    post edited by mbrowning - 2020/03/31 13:54:41
    #2
    ric
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    Re: KSZ8041RNL REF_CLK outputting 25MHz 2020/03/31 15:15:07 (permalink)
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    Doesn't that confirm what the OP said, that they should have 50MHz on pin 19?
     

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    AndyD
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    Re: KSZ8041RNL REF_CLK outputting 25MHz 2020/04/01 01:56:27 (permalink)
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    Thanks both for answering, but this is exactly the issue.  It seems it should output 50MHz on pin 19.
     
    The NL suffix states:
    Crystal/Oscillator/External Clock Input:MII mode: 25 MHz ±50 ppm (crystal, oscillator, or external clock)
    RMII mode: 50 MHz ±50 ppm (oscillator or external clock only)
     
    But we are using the RNL suffix which states:
    Crystal/Oscillator/External Clock Input: 25 MHz ±50 ppm
     
    This is consistent throughout the datasheet.
     
     
    We have checked the device marking for RNL version.
    #4
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