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DP83822I: Inquiry Regarding RGMII Line resistor Connection

deukki shin
Prodigy 30 points
Part Number: DP83822I


Tool/software:

Hello!

I am currently using the DP83822I product with EtherCAT communicaion.

 - I/O Voltage: 1.8V

 - RGMII Mode

I placed 33Ω series resistor on the RGMII lines.

However, I observed intermittent frame loss during operation.

After replacing the 33Ω resistors with 0Ω, the issue was improved.

Due to this result, I am considering removing the 33Ω resistors from the RGMII lines.

Before proceeding, I would like to ask if there could be any potential issues or side effects from this change. (33Ω → 0Ω)

Thank you for your support.

Best Regards,

  • 0
    TI__Guru**** 178926 points

    Hi,

    When you say after replacing the 33Ω resistors with 0Ω, the issue was improved -> Are you still seeing the frame loss?

    Have you tried the Reverse Loopback? The Far-End (Reverse) loopback is a special test mode to allow PHY testing with a link partner. In this mode, data that is received from the Link Partner passes through the PHY’s receiver, is looped back at the MAC interface and then transmitted back to the Link Partner. With this mode, we verified the PHY and MDI interface design. If you do not see frame loss with reverse loopback, then the issue is more likely the MAC interface or the MAC itself. 

    All MAC output pins have series termination resistors. And you should be able to alter the value through register writes upon power up.

    Have you had a chance to measure the signal using a scope between the 33ohm and 0ohm? I would recommend you perform either a scope measurement or IBIS simulation to determine if internal terminating resistors are good enough for you application.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 30 points

    Hi,

    I have performed the loopback test, and when I changed the resistors to 0 Ω, no frame loss occurred.

    Therefore, I am considering using 0 Ω instead.

    As for IBIS simulation, I plan to look into it later.

    Could you explain how to perform an IBIS simulation?

    Thank you.

  • 0 in reply to deukki shin
    TI__Guru**** 178926 points

    Hi,

    For IBIS simulation, please see this app note, https://www.ti.com/lit/ug/snlu313/snlu313.pdf.

    But with DP83822 output having default series termination of 58.07ohm, and then with the external 33ohm resistance, the total resistance is probably not matching with your MAC trace impedance. Impedance mismatch will create reflection, that impacts the MAC set and hold timing, create the frame loss issue.

    Thanks

    David