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DP83867IR: RGMII pins used as strap pins also.

Stephen Gilbert52
Prodigy 140 points
Part Number: DP83867IR
Other Parts Discussed in Thread: AM3358

We have a design using dual DP83867IRRGZRs for dual GB ethernet on the same PCB with an Octavo AM3358 processor. Communications between the Physical device and MAC is using the RGMII configuration. Some of the RGMII pins of the DP8367s are also used as strap configuration pins for each device and are set using the data sheet resistor values for the addresses and modes that we want to operate in (used as a managed Physical Device).

I am doing the PCB layout for the project now and have the design constraints set to match the lengths of the set of RGMII RX pins and to match the lengths of the set of RGMII TX pins. All of the RGMII pins have been constrained to 50 ohms single ended. 

My question is: Will the RGMII pins that are also used as strap pins (pull-up and pull-down resistors added) have to have special consideration when routing?  Will the RGMII traces that have the pull-up and pull-down resistors for strapping have to be compensated for in a special way as referenced to the RGMII traces that are not used as strap pins and have no resistors? If special handling or compensation is required, what would need to be done?

I have studied all of the reference material regarding the DP83867 and AM3358 and also as much Sitara information as I can find and I do not see this question addressed.

Thank you for your consideration.

Stephen

  • 0
    TI__Genius 9920 points

    Hi Stephen,

    The extra length from the strap resistors will have to be considered in the routing. We suggest keeping those resistors as close to the PHY as possible or on the path of the RGMII traces to minimize extra lengths. But as long as you stay within the maximum RGMII trace lengths and within the delta of length matching of the RX and TX lines your layout should be ok. 

    We have our DP83867 EVM design files available on the web. You can review how our straps and traces were designed. 

    Thanks,

    Cecilia