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DP83TC811R-Q1: What is the TX_TCLK clock based off?

user5876804
Prodigy 60 points
Part Number: DP83TC811R-Q1
Other Parts Discussed in Thread: DP83TC811

I am working on an application that uses DP83TC811R-Q1. The devices will be connected to an RMII MAC and operate as RMII slaves. The datasheet states that it's possible to configure the slave to emit the TX_TCLK clock that is synchronized with the master's transmit clock on a GPIO pin. I have questions about this clock:

1. Is this clock 66.667MHz? I have seen this in other documents about 100BASE-T1, but I don't see it stated in the DP83TC811R-Q1 datasheet.

2. What is the TC_TCLK clock based on? Is it derived from the RMII reference clock input provided to the 100BASE-T1 master PHY on its XI pin? Or is it sourced from an internal oscillator that is separate from external clock signals provided to the chip?

Thanks!

  • 0
    TI__Genius 9920 points

    Hello,

    Thanks for reaching out!

    1. Yes you are correct the DP83TC811 follows these standards but we have not mentioned this specifically in our datasheet. Thanks for pointing this out we will add this in our next datasheet refresh

    2. The TX_TCLK is based on the signal given by the master, essentially a slave clock recovery for measuring jitter on slave

    Hope that gave you some more clarity. 

    Thanks!

    Cecilia

  • 0 in reply to Cecilia Reyes
    Prodigy 60 points

    Thanks Cecilia for the response!

    This didn't quite answer my question #2, let me try to clarify what I meant:

    I know that the 100BASE-T1 slave recovers its TX_TCLK clock from the signal sent from the 100BASE-T1 master. What I would like to know is where the 100BASE-T1 master sources this clock from? Is it generated internally by an independent oscillator in the PHY chip, or is it derived from an external clock reference (for example the 50MHz clock delivered to its XI pin when the device operates in RMII slave mode)?

    I am interested in seeing if it is possible to use this mechanism to synchronize a clock on the 100BASE-T1 slave side to a clock that I control on the 100BASE-T1 master side.

    Thank you,

    Per

  • 0 in reply to user5876804
    TI__Genius 9920 points

    Hi Per - thanks for the clarity. 

    It is not generated from an independent oscillator. It is a clock recovered the transmitter and occurs in the PMA layer.

    We expect this clock to be aligned with the master clock from its source however this was an item that we did not validate so we cannot guarantee the synchronicity. 

    Thanks,

    Cecilia