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DP83822IF: specific length requirements for SMI communication and RMII communication

Lillian Liu(SH)
Expert 3300 points
Part Number: DP83822IF

Hi team,

The manual for DP83822IF mentions the equal length requirements for layout:

What are the specific length requirements for SMI communication and RMII communication? How much can't the difference be? please reply as soon as possible, thanks!

Best regards

Lillian

  • 0
    TI__Genius 14262 points

    Hi Lillian,

    Total RMII/SMI trace length should be less than 6 inches.

    RMII trace length matching will depend on speed:

    For 1G, match RMII traces within 50mils.

    For 10/100M, match RMII traces within 100mils.

    Please refer to this layout checklist for more information:

    SNLR048.xlsx

    SMI traces are slightly less strict, matching MDC/MDIO within 100mils is acceptable.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    TI__Expert 3300 points

    Hi Evan,

    Thanks very much for your reply!

    In the checklist you provided I found for MDI traces:

    Total Length recommend to be < 3 inches from PHY to magnetic

    While in the datasheet for RMII traces:

    Keep trace lengths as short as possible, less than two inches is recommended and less than six inches maximum

     

    As our Mac is on CPU board and PHY with magnetics is on COM board, I cannot satisfy the two requirements simultaneously. Which one is of higher priority for my condition?

    Thanks very much and looking forward to your reply!

    Lillian

  • 0 in reply to Lillian Liu(SH)
    TI__Genius 14262 points

    Hi Lillian,

    I unfortunately cannot comment on this, as we have not validated the behavior for MDI/MAC trace layout violations.

    Thank you,

    Evan