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AM335X - Ethernet using RMII at 1V8

Rodrigo Aznar Mendes
Prodigy 215 points

Hi all,

We are going to implement two ethernet ports 10/100 using two RMII interfaces. The phy we have chosen allow interface to AM335X at 1V8.

Does someone have implemented RMII at 1V8? 

Is there any additional care to be taken in the design or layout?

Thanks

Rodrigo

  • 0
    TI__Mastermind 27890 points

    Hello Rodrigo,

    Keep in mind that the RMII(1) and MDIO signalling interfaces share the same voltage supply/domain on AM335x; whichever PHY you select will need to support MDIO at 1.8v as well.

  • 0 in reply to -DK-
    Prodigy 215 points

    Thanks DK for remind us this detail.

    I have one special doubt. In this case using 1V8, would it be possible to use an 1V8 oscillator to source clock to the phy and also the RMII_REFCLK ?

    thanks once again

    Rodrigo

  • 0 in reply to Rodrigo Aznar Mendes
    TI__Mastermind 27890 points

    Rodrigo,

    Assuming RMII spec VIH(MIN) of RMII_REFCLK @ 1.4V and AM335x RMII(x)_REFCLK VIH(MIN) of (0.65*VDDSHVx (where VDDSHVx=1.8V) = (VIH@1.17V) ), I think this should not present a problem. Depending on the PHY you choose, RMII_REFLK VIH(MIN) can actually be as low as 1.3V @ 1.8V operation.

    There may be other AM335x-specific "gotchas" that I am missing, so I will revisit this subject with the team on Monday.