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DP83867IS: RX_D0 as a strap-pin,its amplitude will change during power-up reset.

user6478535
Prodigy 30 points
Part Number: DP83867IS

About the sampling of power-up reset,

It is mentioned in the datasheet at page 12:

（image 1）

and page 14:

（image 2）

When I test the RX_D0 waveform，I found:

（image 3）

When power-on reset,the rx_d0's value will change:from 3.3V to 0V;

I want support:

1）What is the value of T2_MIN（image 1）？

2）What is the sampling value in the waveform（image 3）？

  • 0
    TI__Expert 3595 points

    Hi,

    1. The T2_MIN value is considered device internal information that should not affect the functionality of the PHY. But, please let us know the application and if this is critical information.

    2. The sampling value is listed on the waveform image as 2.0 us/div.

    Thanks!

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    Thank you for your reply！

    About the point 2，I wonder which mode did it sampled？（mode 1 or 4）

  • 0 in reply to user6478535
    TI__Expert 3595 points

    Hi,

    Using the information from the timing diagram from the datasheet, it looks like it should be strapping mode 1. But, this can be verified by checking the strap on reset register 0x6E. The bottom 4 bits will tell you which PHY ADDR value was strapped. 

    Please let me know if the device did not strap mode 1.

    Thanks,

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    Hi,

    The register 0X6E's value is 0x080F；The result looks like mode 4；

    The schematic design is as follows：

    On the other side is Mac：

    I tried to get rid of C240/C241/C242/C243，but the result is the same as before.

    Please check it for me,thank you！

  • 0 in reply to user6478535
    TI__Expert 3595 points

    Hi,

    In the first image I see a pullup line to 3.3V. Was there a reason you added this? This should not be needed and will cause the strapped value to be "HIGH". 

    Thank you though for identifying the timing inconsistency. I will make a note of this.

    Thanks,

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    Hi，

    I need the phy address is 0XF，so i add this pullup.

    I want to know why the actual test results（image 3）are different from those in the datasheet（image 2）.

  • 0 in reply to user6478535
    TI__Expert 3595 points

    Hi,

    So after reviewing the image and the scope shot. The test results look different from the datasheet because the datasheet image is not "drawn to scale" the datasheet is representing both us and ns intervals. The most appropriate change for the image is that the initial T2 start line should be moved to be along the rising edge of the RESET_N signal. If the scope shot you captured was taken using a ns interval instead of us, I believe that it would show more precisely the point at which the high signal is latched.

    Also, I wanted to copy and paste this line from the datasheet just as a reminder if using SGMII. "For SGMII Mode 4 strap, TI recommends using Rhi = 4 kΩ and Rlo = 10 kΩ on RX_D0 and RX_D1 , RX_D2 and RX_D3"

    Thank you!

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    Hi,Lysny:

    on datasheet:

    The sample point is not on the Edge of reset_N;

    on test result:

    Maybe I got it wrong？（the sample point shouldn't be on the edge）

    By the way,thank you for your remind;

    But after I replaced the resistor, the situation was similar;

  • 0 in reply to user6478535
    TI__Expert 3595 points

    Hi,

    Yes, I was saying that the previous image in the datasheet should be edited to best reflect the scope shot. The scope shot and the second image you have shown reflects the expected behavior. The timing is a range, so we could see the latch on the ramp up or at any time after, but within the datasheet spec.

    Does this make sense?

    Thanks,
    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    OK,thank you for your patience！