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DP83640 MDIO pull-up resistor

Carsten Hyldal
Prodigy 60 points


Hi

The datasheet specifies a 1.5k pull-up resistor at the MDIO pin. Is it very important to use this exact value or would e.g. 2.21k also be okay? Is it possible to specify a tolerance for the required pull-up resistor.

Thanks in advance for feedback.

  • 0
    TI__Mastermind 31600 points

    Carsten,

    IEEE 802.3 specifies the pull-up resistor for MDIO as 1.5 kOhm +/- 5% for applications in which the PHY is attached via the MII cable described in the spec.  The value of 1.5 kOhm was chosen to allow several PHYs to be bused together, i.e. to share the MDC and MDIO signals. 

    The overwhelming majority of implementations that I see these days connect MDC and MDIO in a point to point fashion between the PHY and the MAC.  In these cases, strict adherence to the specification is not required.  A 2.2 kOhm resistor with a tolerance of +/- 10% should be sufficient.

    Patrick