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Original question:

DP83869HM: DP83869HM RGMII delay

DP83869HM: RGMII delay figure understanding

Thierry HAUSER
Intellectual 400 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83TG720R-Q1, DP83869

I try to understand precisely RGMII delay, and check RGMII timing.

Figure 8.6 of SNLS614B_dp83869hm_Datasheet.pdf show only TskewT and TskewR : 

Many questions : 

  1. Why TskewT show in figure Transmit, is specifed into table 8.6 RGMII output timing? Shouldn't it be located into table  RGMII input timing?
  2. Why there is no setup or hold figure into Figure 8.6 ? ( I would expect setup&hold at receiver side)
  3. For output timing , why is there some setup&hold specification ? shouldn'y it be only skew & delay specifications?
  4. Concerning Tcyc for input timing, is there any specifcation? (same fo dutycycle)
  5. Is there any big RX/TX inversion in fact?

Thanks for your feedback

N.B:  I've check DP83TG720R-Q1 datasheet for instance, and it's all very clear to understand

  • 0
    TI__Mastermind 19250 points

    Hi Thierry,

    You can refer to the following application note https://www.ti.com/lit/an/snla243/snla243.pdf  and check if this gives you more information.

    The image above is very similar to the one in the RGMII v2.0 standard. The image in the standard is referenced with respect to MAC and not PHY. Hence, it would look like RX and TX are inversed.

    RGMII standard mentions that TskewT is the skew at the output of transmitter. This means that TskewT is the skew between TX_CLK and TX_D* at the output of the MAC. Also, it means that TskewT is the skew between RX_CLK and RX_D* at the output of the PHY. Hence, the parameter is mentioned in the output timing in our datasheet.

    The setup and hold time are mentioned in Figure 8-7 where there are mentioned for RX_* pins. From PHY perspective, they are valid for TX_D* pins, where they are inputs to the PHY.

    --
    Regards,
    Gokul.

  • 0 in reply to Gokul Koraganji
    Intellectual 400 points

    Thanks Gokul for this link to snla243pdf !

    But according to snla243 I've got some questions /remarks : 


    • I was not able to find these informations into DP83867 datasheet. Where are they come from?
    • Where could I found all these informations for DP83869 ?

    Thanks for you feedback

  • 0 in reply to Thierry HAUSER
    TI__Mastermind 19250 points

    Hi Theirry,

    I am not sure if I can get the same data for DP83869. I will check with our team and get back to you.

    --
    Regards,
    Gokul.