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DP83867E: Bootstrapping Resistors for SGMII vs RGMII and Pin Requirements

Ross Ferens
Prodigy 40 points

Part Number: DP83867E

Our design is utilizing two of these PHYs.  One is acting as an SGMII to 1000Base-T transceiver and the other is a RGMII to 1000Base-T transceiver.

In the schematic currently, we have 0 ohm resistors drawn as Do Not Installs on all the pins that are used for Tx and Rx skew control via bootstrapping.

Referring to this note in the Data Sheet:

image.png

Does this mean we should add hooks in the design via 0 ohm resistors on the RX_D3 and RX_D1 pins as well?  Does this not apply to RGMII and only to SGMII?

Also, given this note from the Data Sheet:

"Strap modes 1 and 2 are not applicable for RX_CTRL. The RX_CTRL strap must be configured for strap mode 3 or strap mode 4. If the RX_CTRL pin cannot be strapped to mode 3 or mode 4, bit[7] of Configuration Register 4 (address 0x0031) must be cleared to 0. Autoneg Disable can always be set to 0 when using gigabit Ethernet."

Does this mean that we can not have these 0 ohm resistors as Do Not Install placeholders on the RX_CTRL pin?  

 

Finally, for the SGMII circuit, we have strap resistors on RX_DR/SGMII_SOP which is being utilized as an output.  Should we not use strap resistors on any outputs that are in use?

  • 0
    TI__Mastermind 26771 points

    Hi Ross, 

    Ross Ferens said:
    Does this mean we should add hooks in the design via 0 ohm resistors on the RX_D3 and RX_D1 pins as well?  Does this not apply to RGMII and only to SGMII?


    The notes in the datasheet is to match skew and impedance for the SGMII differential pair. This is not needed for RGMII and only needed for SGMII because SGMII utilizes differential pair for communication. So yes, it only applies to SGMII. 




    Ross Ferens said:
    Does this mean that we can not have these 0 ohm resistors as Do Not Install placeholders on the RX_CTRL pin?  

    Yes, please strap RX_CTRL to mode 3 or 4. 


    Ross Ferens said:
    Finally, for the SGMII circuit, we have strap resistors on RX_DR/SGMII_SOP which is being utilized as an output.  Should we not use strap resistors on any outputs that are in use?

    It is fine to use strap on SGMII output. These straps are necessary to set the PHY address. 

    Best,
    J