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TLK10x use without magnetics

Kyle Aven
Intellectual 950 points
Other Parts Discussed in Thread: TLK106

i am working on a design where i need to connect the MII interface of the AR6400 chipset with the ETH port on a TM4C1294. I was planning on using the TLK10x family of devices to make this connection. The question now is if magnetics are required for a IC to IC connections. These processors will be located on the same PCB. It seems that with no cable length needed, the ETH(RX,TX) from the TLK10x could be connected directly to ETH(TX,RX) of the TM4C1294 in a crossover manner. I have little to no experience with ETH PHY other than using magnetics and a RJ45 connector. Any help would be greatly appreciated.

Thanks

kyle

  • 0
    TI__Mastermind 31600 points

    Kyle,

    You can make this connection without transformers.  We have an application note on this functionality:

    http://www.ti.com/lit/pdf/slla327

    Patrick

  • 0 in reply to Patrick OFarrell
    Intellectual 950 points

    Patrick,

    A few concerns have come up after reading the application note:

    1. Are DC isolation capacitors needed if both the TLK106 and the TM4C1294 are powered from the same 3V3 supply?

    2. Are pull-up resistors necessary on the ETH TX/RX lines?

    3. Does a crossover need to be performed when connecting to the TM4C1294? I know that the TLK106 supports Auto-MDIX, but does it work properly if the TM4C1294 does not? Also does this increase link time or negotiation time?

    Thank you

  • 0 in reply to Kyle Aven
    TI__Mastermind 23675 points

    Hi Kyle,

    Here are the answers to your questions:

    1. Are DC isolation capacitors needed if both the TLK106 and the TM4C1294 are powered from the same 3V3 supply?

    You will need isolation capacitors even if the two devices are powered from the same 3V3 supply. The reason being is that you can and most likely will have grounds that are offset from each other. It is important to isolate so that these imbalances do not affect the signal. It is also an IEEE standard to have an isolated interface.

    2. Are pull-up resistors necessary on the ETH TX/RX lines?


    Yes, the termination resistors connected to 3V3 supply are necessary for proper operation.

    3. Does a crossover need to be performed when connecting to the TM4C1294? I know that the TLK106 supports Auto-MDIX, but does it work properly if the TM4C1294 does not? Also does this increase link time or negotiation time?

    The PHY will automatically cross if during its auto processes it senses the lines are crossed. If you know what the link partner is configured for (TM4C1294) you can force the TLK106 into a specific mode by writing to the following register:

    Register 0x0019 (PHYCR)

    Force MDIX - write 0x4001 (Disables auto-mdix)

    Force MDI - write 0x0001 (Disables auto-mdix)

    Regards,

    Ross