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DP83826E: signal energy detect disable

Masakazu Adachi
Intellectual 2500 points
Part Number: DP83826E

Hello team,

I received 2 questions from the customer.

[Question 1]

The following statement is made on p. 45 of the data sheet,


Signal energy detect disable is recommended for EtherCAT. The customer assumes that the device is to be operated in RMII mode using Bootstrap, and Figure 9-11 shows that if RMII mode is selected, signal energy detect disable cannot be set. In this case, we will set "signal energy detect disable" in the PHY register setting after startup, but is the function the same as when "signal energy detect disable" is set in the Bootstrap above?

[Question 2]

This is a rudimentary question, but can you tell me why it is recommended for EtherCAT to disable signal energy detect for study purposes?

Regards,

Masa

  • +1
    TI__Mastermind 39795 points

    Hello Masa,

    For EtherCAT, RMII is not a recommended interface due to the latency requirements. This is why the right side of the flowchart is strictly MII.

    For EtherCAT, signal energy detect is recommended to be disabled as the EtherCAT topology is essentially a chain. If one of the nodes on the lines loses link due to idleness, then the entire application falls apart. There is more information on EtherCAT from Beckhoff.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2500 points

    Hello Gerome,

    Thanks. I understand.

    Regards,

    Masa

  • 0 in reply to Masakazu Adachi
    TI__Intellectual 2500 points

    Hello Gerome,

    I received an additional questions from the customer.

    Gerome Cacho said:
    For EtherCAT, RMII is not a recommended interface due to the latency requirements. This is why the right side of the flowchart is strictly MII.

    Are you referring to the following on p.18 of the datasheet?

    For example, while MII has a maximum TX delay of 40 ns and RX delay of 170 ns, RMII has a maximum TX delay of 96 ns and RX delay of 270 ns. Conversely, if this is acceptable, does it mean that RMII is acceptable?

    Gerome Cacho said:
    For EtherCAT, signal energy detect is recommended to be disabled as the EtherCAT topology is essentially a chain. If one of the nodes on the lines loses link due to idleness, then the entire application falls apart. There is more information on EtherCAT from Beckhoff.

    The customer thinks that when a link is not established, EtherCAT automatically forwards packets to another port instead of sending them to the corresponding port in the communication IC, so the entire application does not break down, right?
    DP83826 lists six criteria for determining that a link is not established as shown in the table below, but why is "determination by signal energy detect (disable)" recommended for EtherCAT?
    As in Q2, does "disable signal energy detect" = "go to the right side of Figure 9-11" = "MII (not RMII) is recommended"?

    Regards,

    Masa

  • 0 in reply to Masakazu Adachi
    TI__Mastermind 39795 points

    Hi Masa,

    Yes, I am referring to these latency specifications. If customer is okay with this, then they may proceed with their desired mode.

    The topology question would be a system implementation question, and Beckhoff would be the better advisor for this.

    Regarding direction on flowchart, going (Strap1 = '0', Strap7 = '1', and Strap 8 = '0') would be the plan.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2500 points

    Hi Gerome,

    Thanks for the support. Let's put the question in perspective. 

    Q1: The customer has a question about your answer, could you please answer it? You said "If one of the nodes on the lines loses link due to idleness, then the entire application falls apart. But the customer says that if the link is no longer established, it is automatically forwarded to another port, so the entire application does not fall apart. Which is correct?

    Q2: Why did you decide to plan (Strap1 = '0', Strap7 = '1', and Strap 8 = '0') ? Does this mean that signal energy detect should still be enable?

    These questions are about what is described in the TI datasheet, not about the EtherCAT system configuration. Please change to the Internal thread if necessary.

    Regards,

    Masa

  • +1 in reply to Masakazu Adachi
    TI__Mastermind 39795 points

    Hi Masa,

    In your topology, this is a valid use case, and thus if port forwarding upon loss of link is possible, then the entire application will not fall apart.

    However, Beckhoff Ethercat standard says to disable signal energy detection. Thus, if you are using their systems, then it is imperative to follow their guidance.

    Sincerely,

    Gerome

  • +1 in reply to Gerome Cacho
    TI__Intellectual 2500 points

    Hello Gerome,

    I understand. Thank you.

    Regards,

    Masa

  • 0 in reply to Masakazu Adachi
    TI__Intellectual 2500 points

    Hello Gerome,

    Could you please tell me where in the Beckhoff Ethercat standard it says "disable signal energy detection"?
    I can't find it on the web browse and I can't convince my customer...

    Regards,

    Masa

  • +1 in reply to Masakazu Adachi
    TI__Mastermind 39795 points

    Hi Masa,

    Its a little indirect, but if you see SNLA344B:

    "Baseline wander should be compensated (the PHYs should cope with the ANSI X3.263 DDJ test pattern for baseline wander measurements at maximum cable length)

    – Testing has been performed on this parameter and the DP83826 shows excellent performance compensating the baseline wander.

    – It is recommended that the register 0xB has bit 0 set to 0, otherwise the Baseline wander test will fail because the phy drops the link due to the Energy detection is seeing this test pattern as a link drop."

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2500 points

    Hello Gerome,

    Thanks! I understand.

    Regards,

    Masa