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DP83822I: What does table 4 indicate?

Toshihiro Watanabe
Genius 10235 points
Part Number: DP83822I

Hello,

We couldn't understand how to read/use table 4 of datasheet?

Could you explain how to use it? Example may be helpful to understand the meaning of table 4.

Could you support this?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Genius 9920 points

    Hi Toshihiro,

    Depending on your clock accuracy or the maximum packet size you plan to be using on your application, that is the threshold RBR you would want to use.

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 10235 points

    Hello Cecilia-san,

    I think there is a formula to calculate table 4. I can't see the formula. Could you explain this?

    I don't know RBR meaning. What does it mean?

    Best regards,

    Toshihiro Watanabe

  • 0 in reply to Toshihiro Watanabe
    TI__Genius 10235 points

    Hello Cecila-san,

    Could you share the information for we understand about table 4 information?

    Table 4 is assumed clock accuracy of Tx and Rx are same. In real world, this condition will be very rare. If Tx and Rx accuracy are different, how to calculate?

    Best regards,

    Toshihiro Watanabe

  • 0 in reply to Toshihiro Watanabe
    TI__Genius 9920 points

    I will see if I can find the formula for you. Will need to discuss with my team on how we can provide that for you.

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 9245 points

    Hi Cecilia,

    I am following up this instead of Watanabe-san.

    Please let me confirm below things.

    1. START THRESHOLD RBR[1:0] is RMII and Status Register[1:0], right?

    2. In the table 4, what does LATENCY TOLERANCE mean?

    3. In the table 4,  the accuracy like +/-50ppm, 100ppm is for 50-MHz Reference Clock in Figure 25 & 25-MHz Reference Clock in Figure 26?

    4. In the description "It assumes that the RMII reference clock and the far-end transmitter clock have the same accuracy." , what is the far-end transmitter?
        And if the far-end transmitter means MAC, users don't need to care about the accuracy in case of Figure 25, 26? This is because the same clock is used for PHY and MAC.

    5. Users should write RMII and Status Register[1:0] by using Table 4 based on their clock accuracy(50-MHz Reference Clock  or 25-MHz Reference Clock) and packet size what they need in their application, right?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 9245 points

    Hi Cecilia

    Could you give any comments?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 9920 points

    Hello Noriyuki,

    Apologies on the delay for these questions. Please expect a response from me in 3-5 days times due to extraneous circumstances 

    I will try my best to answer these questions for you:

    1. START THRESHOLD RBR[1:0] is RMII and Status Register[1:0], right?

    Correct, this is from the RCSR register 0x0017. Thank you for pointing that out. We will make it more clear for readers in our datasheet.

    2. In the table 4, what does LATENCY TOLERANCE mean?

    Latency tolerance is the variation in frequency between the 50MHz RMII clock and the recovered data. You are able to adjust this tolerance in the registers you mentioned above in #1

    3. In the table 4,  the accuracy like +/-50ppm, 100ppm is for 50-MHz Reference Clock in Figure 25 & 25-MHz Reference Clock in Figure 26?

    Correct, it is the reference clock used for RMII and the clock source depends on whether you are using Master or Slave mode

    4. In the description "It assumes that the RMII reference clock and the far-end transmitter clock have the same accuracy." , what is the far-end transmitter?
        And if the far-end transmitter means MAC, users don't need to care about the accuracy in case of Figure 25, 26? This is because the same clock is used for PHY and MAC.

    Far-end transmitter is the link partner's transmitter clock. It can be assumed to have the same accuracy because they are sharing the same clock in this case.

    5. Users should write RMII and Status Register[1:0] by using Table 4 based on their clock accuracy(50-MHz Reference Clock  or 25-MHz Reference Clock) and packet size what they need in their application, right?

    Correct, this is based on application and how large of a frequency tolerance your customer needs.

    Please let me know if you need more clarity on these items.

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 9245 points

    Hi Cecilia,

    Regarding 4, I am still not sure yet.

    DP83822I assume that RMII reference clock and the far-end transmitter clock have the same accuracy, but how the same accuracy is achieved?

    The customer product doesn't know whether the far-end transmitter have the same accuracy with RMII reference clock.

    Could you tell the supplemental explanation?

    Customer goal is to achieve no data loss. However, they have concern that it is impossible to make the same accuracy RMII reference clock and the far-end transmitter clock as the total system, because the far-end transmitter is not their products.

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 9920 points

    Hello Noriyuki,

    You will have to ensure that the clock and the far end transmitter have the same PPM variation which should be in the product's specifications. That should be suffice for having the same accuracy.

    Thanks,

    Cecilia