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DP83640: Optimized Layout by swapping TX/RX and polarities

Michael Wohl
Prodigy 240 points
Part Number: DP83640


Hello,

Background:  I am designing a custom PCB using the F28388D C2000 SOC with the DP83640 PHY and Pulse JKM-0201NL connector with embedded magnetics.

Question:  To optimize the layout (keeping Connector to Phy differential signals on top layer and not routing under connector), I would need to swap RX & TX differential pairs as well as reverse each pair's polarity (swapping diff + and - signals).

From what I read in the DP83640 data sheet, it seems that all of this is automatically handled and/or corrected by the PHY automatically and WITHOUT need to change PHY settings from their default.   

I was hoping you could you confirm this for me.   We expect to use this at 100M, but is there any operational differences in the PHY compensating for these "swaps" depending upon the link type itself?

Thanks for your support.

Mike

  • 0
    TI__Guru**** 202530 points

    Hello Mike

    Thank you for the query. Please see below. The function is enabled by default.

    Auto-MDIX

    When enabled, this function uses Auto-Negotiation to determine the proper configuration for transmission and reception of data and subsequently selects the appropriate MDI pair for MDI/MDIX operation. The function uses a random seed to control switching of the crossover circuitry. This implementation complies with the corresponding IEEE 802.3 Auto-Negotiation and Crossover Specifications.

    Auto-MDIX is enabled by default and can be configured through PHYCR (19h) register, bits [15:14].

    Neither Auto-Negotiation nor Auto-MDIX is required to be enabled in forcing crossover of the MDI pairs. Forced crossover can be achieved through the FORCE_MDIX bit, bit 14 of PHYCR (19h) register.

    If you do not have any additional questions, please click resolved button to close the thread.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 240 points

    Hello Sreenivasa,

    Thank you for the quick reply.

    Just to be clear,

    • does this (automatic handling) cover polarity swapping in addition to transmit/receive swapping?
    • also for future designs, is polarity reversal  handled automatically if it only occurs on one of the pairs (independent of whether TX and RX have been swapped)?

    Thanks again

    Mike

  • 0 in reply to Michael Wohl
    TI__Guru**** 202530 points

    Hello Mike, 

    Thank you for the reply. 

    Your under is correct. the below conditions are taken care.

    Polarity reversal • Cable swap (MDI vs MDIX) detection

    Regards,

    Sreenivasa