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DP83826E: Polarity SWAP RX +/- and TX +/-

DAVID SABALESKY
Prodigy 225 points
Part Number: DP83826E

Tool/software:

I would like to know if it i permissible to have only one MDI channel namely the RX +/-  with pin polarity swap.

The TX +/- channel is fine. I like to always route my pairs without vias. The run is extremely short since we are using Magic Jack Ethernet Ports, aka built in magnetics.

Running at 100Base.

From page 41 of data sheeet,

9.3.13.4 Active Link Polarity Detection and Correction Swapping the wires within the twisted-pair causes polarity errors.

Wrong polarity affects 10BASE-Te connections. 100BASE-TX is immune to polarity problems because it uses MLT-3 encoding.

10BASE-Te receive block automatically detects reversed polarity

I am uncertain of  this mention and if it covers 100Base-RX, I believe that it does.

Please advise on polarity pin swap on only the RX channel.

Your advice is greatly appreciated.

Sincerely,

David

  • 0
    TI__Mastermind 19621 points

    Hi David!

    Yes, you can polarity swap only the RX channel, if the intent is to only operate at 100Mbps. As you read in the data sheet, this would cause problems with 10BaseTe but not with 100Base-TX. The reason being MLT-3 does not care about the voltage level of the signal, instead it interprets '1s' and '0s' based on when the voltage level transitions.

    Regards,

    Alvaro