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DP83848T CRS_DV pin

Johan Wallström
Intellectual 335 points
Other Parts Discussed in Thread: DP83848T

Hello,

I have an stm32f407 connected by RMII to a DP83848T.
Due to some problem, ~90% of incoming ethernet messages are missed by the stm. 
When I put a probe on the CRS_DV pin, the stm can receive every incoming message.
So, it seems to be an issue of a missing capacitor, pullup or similar. But I can't seem to find any 
information on how I am supposed to connect this pin? Any pointers?

best regards
Johan

  • 0
    TI__Mastermind 19780 points

    Hi Johan,

    You can review the DP83848 RMII app note here: www.ti.com/.../snla076a.pdf

    Note for CRS_DV you have to ensure your MAC and PHY are using the same RMII revision. I'd check this first. 

    RMII rev can be checked in register 0x17. See the DP83848 register map in the datasheet.

    Best Regards,

  • 0 in reply to Rob Rodrigues
    Intellectual 335 points

    Thanks!

    I have selected 1.0 in the 0x17 (value 0x31), which seems to work with my stm32f407, although I couldn't find a specific specification of that in the stm ref manual.

    Putting a 1nf capacitor removed the symptoms.

    On my second prototype I had the same issue, but in contrast the measurement probe would not remove the issue, but I wasn't able to see anything wrong with the signal. Still, a capacitor added removed the issue, and I wasn't able to see any difference on the scope, although it must be something there.

    I wasn't able to find any specific requirement for capacitor in any datasheet. 

    We will probably just put a space for a capacitor there for the next hardware revision and see what works as a value.