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[DP83867] RJ45 connection by reversed channel & compliance test

Takahiro Ogo
Genius 5940 points

Hi,

I know the DP83867 automatically detects and corrects polarity of the channel.
So, DP83867 can connect to RJ45 as bellow.
[RJ45 connector]              [DP83867]
TD_x_P(Positive)    ---      TDx- (Negative)
TD_x_N(Negative)    ---     TDx+ (Positive)

This is very good feature for PCB design. But my customer are worried about compliance test.
They think the compliance test is output from Ether PHY. So, if the channel polarity is reversed at RJ45, the compliance test will be failed.
Is their understanding correct?  Do we need to care anything for compliance test when the channel polarity signals are reversed ?

Best Regards,
Taka

  • 0
    Genius 5940 points
    Hi,

    Can anybody tell me?
    My customer are waiting for the reply.

    Best Regards,
    Taka
  • 0 in reply to Takahiro Ogo
    TI__Mastermind 23675 points
    Hi Taka,

    You will need to consider polarity for 1G and 10M compliance testing.
    For 100M, there is no need.

    You have to configure the PHY for 1G compliance testing in the register map, so if you are concerned you can also configure the polarity since you will already have register access.

    The other option is to change the polarity on the cable.

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Genius 5940 points

    Hi Ross,
    Thank you for your reply.

    Ross Pimentel said:
     
    You have to configure the PHY for 1G compliance testing in the register map, so if you are concerned you can also configure the polarity since you will already have register access.
    I understand that the polarity detection and correction feature of DP83867 does not have to be managed.
    It means that I can't configure the polarity. Is my understanding correct?
    If so, we have to change the polarity on the cable for the compliance test.

    Best Regards,
    Taka
  • 0 in reply to Takahiro Ogo
    TI__Mastermind 23675 points

    Hi Taka,

    You are correct. You will need to change the polarity on the cable since the DP83867 does not allow you to override the polarity. 

    Kind regards,

    Ross

  • 0 in reply to Ross Pimentel
    Genius 5940 points

    Hi Ross,

    I have received some questions from my customer yet. They placed importance on the compliance test.
    Sorry to trouble you. Thank you for taking care of it.



    (1) If the polarity channel are changed on the cable, is there no problem to pass the compliance test?Is it permitted? 
    Also, they are saying the characteristic is changed by this special cable. (in comparison to standard cable)

    (2)When DP83867 just transmit the data, can DP83867 detect the polarity? So, how does DP83867 detect the polarity?

    (3)For DP83867ERGZ EVM, the channel polarity is reversed. Have the EVM passed the compliance test?
       
    (4)My customer found the following register which is setting for Line Inversion.
    For this reversing connection, can they use this register setting to pass the compliance test?
    [PHY Control Register (PHYCR), Address 0x0010]
    BIT : 1
    BIT NAME : LINE_DRIVER_INV_EN

    <DESCRIPTION>
    Line Driver Inversion Enable:
    1 = Invert Line Driver Transmission.
    0 = Normal operation


    Best Regards,
    Taka

  • 0 in reply to Takahiro Ogo
    TI__Mastermind 23675 points

    Hi Taka,

    The 867 does not output opposite polarity by default. If their layout is incorrect with routing to the RJ45 they really have no other option than to change the polarity of the cable or to enable inverted polarity of the line driver. There is no rule that says you cannot do this in compliance testing.

    They should still pass compliance. If they are using a special cable then i cannot guarantee compliance. 1G PHYs are meant to work with the characteristic impedance of CAT5 and CAT6 cable. If the cable quality is worse than CAT5 you might not pass because you are exceeding the max data rate of that cable.

    The 867 has an internal polarity detection circuit. For competitive reasons we will not discuss the details on how it is implemented.

    The EVMs have passed compliance.

    Yes, they can use that bit to invert the driver. If they use that then they should not change the polarity of the cable.

    Kind regards,

    Ross

  • 0 in reply to Ross Pimentel
    Genius 5940 points

    Hi Ross,
    Thank you for the detailed explanation. I appreciate it!

    I just have a question. Wheh EVM passed the compliance test, which method did you use?
    (to change the polarity of the cable? or to enable inverted polarity of the line driver?)

    Best Regards,
    Taka
  • 0 in reply to Takahiro Ogo
    TI__Mastermind 23675 points
    Hi Taka,

    I do not have that information on what method was used.
    Both should result in a PASS.

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Genius 5940 points

    Hi Ross-san,
    Thank you very much for your kind support, always!
    I explained that to my customer. They will use  LINE_DRIVER_INV_EN bit to pass the compliance test.

    Thank you again for all your help.
    Taka