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DP83822IF: LED_1 and SD connection

Toshihiro Watanabe
Genius 10235 points
Part Number: DP83822IF

Hello,

I want to confirm about below note in datasheet.

---------------------

TI recommends connecting Signal Detect pin from the Optical Transceiver to the LED_1 pin and enable it using SD_EN bootstrap pin in 100BASE-FX mode. The LED_1 pin is not used in design and that, if the electrical link between the fiber module and the DP83822 is broken, disconnected or otherwise disrupted, the link will recover only by initiating a soft reset through MDIO/MDC interface.

---------------------

When SD signal doesn't connect LED_1 and link broken, RESET required for recovery link. DP83822 link status depends on SD signal status. This means above condition never occurs when SD signal connects to LED_1 even though bit error rate is worse as not maintain link condition. Because link status equals SD signal.

Does my understanding correct?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Genius 9920 points

    Hi Toshihiro,

    Signal detect is only used for the fiber transceiver so I am not sure you can say that it is equal to the link status.

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 10235 points

    Hello Cecelia-san,

    I understood below post says LINK status equals SD signal status, I mean LINK is established when SD is active, LINK is broken when SD is inactive.

    Do I understand incorrectly?

    Best regards,

    Toshihiro Watanabe

  • 0 in reply to Toshihiro Watanabe
    TI__Genius 9920 points

    Hi Toshihiro-san,

    Yes that is making more sense now. The SD depends on the link established. 

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 10235 points

    Hello Cecilia-san,

    Please let us discuss below note in datasheet.

    "TI recommends connecting Signal Detect pin from the Optical Transceiver to the LED_1 pin and enable it using SD_EN bootstrap pin in 100BASE-FX mode. The LED_1 pin is not used in design and that, if the electrical link between the fiber module and the DP83822 is broken, disconnected or otherwise disrupted, the link will recover only by initiating a soft reset through MDIO/MDC interface."

    1) Above notification is when SD signal does not connect to LED_1  -> The customer connects SD signal to LED_1

    2) DP83822 fiber mode link status = SD signal logic.

    [Question]

    1) The customer connect SD and LED_1. Is there any scenario the customer need to apply software reset as mentioned the NOTE?

      -> The customer worries below scenario and the system got frozen which link doesn't recover like NOTE case occurs.

          "Optical power of opto module got weak very much. In this condition, Opto module BER got worse like DP83822IF can't keep LINK connection. in this case, SD is still high,  showing link established. DP83822IF will understand LINK is still established but link is hard to keep in communication level.  In this mode, in this condition, optical cable was removed, LINK is re-established automatically?"

    The above is complex situation. It is OK we can know if we don't need to worry about NOTE case if SD signal connects to LED_1, never needed software reset. 

    Best regards,

    Toshihiro Watanabe

  • 0 in reply to Toshihiro Watanabe
    TI__Genius 9920 points

    I will have to confirm with our design team on your Question #1. 

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 9920 points

    Hello Watanabe-san,

    Thank you for your patience. It looks like there may have been a typo in the description for this Note. You will only need to do a soft reset if you do NOT connect SD pin to the fiber transceiver. This will recover the broken link. No reset is required if you have connected SD to PHY. 

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 11040 points

    Cecilia,

    Please let me follow up this and let me ask additional questions.

    Customer also has concerns that the link is disconnected when the optical signal quality is bad due to vibration, bad optical cable connection, bad eye pattern and bad bit error rate and so on. When disconnections happen like this, they are not sure how to detect the failures. Could you give any ideas to solve this concern?

    Regards,

    Noriyuki Takahashi 

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 9920 points

    Hello,

    Please refer to section 8.4.10 Cable Diagnostics for our cable diagnostic features.

    Thanks,

    Cecilia

  • 0 in reply to Cecilia Reyes
    TI__Genius 11040 points

    Cecilia,

    It seems that 8.4.10 Cable Diagnostics is for 100BASE-Tx. Customer system needs to support 100BASE-FX.

    So, in case of 100BASE-FX, how can they do to solve the link disconnection concern?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 11040 points

    Cecilia,

    This is a kind reminder. 

    Could you give any comments?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 9920 points

    Hello Takahashi-san 

    For fiber, we do not have a way to detect the cause for signal loss from the examples that you had mentioned above, we only have signal detect. You are also able to measure the RX_ER count to identify any packet errors.

    Thanks,

    Cecilia