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TM4C129ENCPDT: Adapting 100BASE Ethernet from RJ45 to SFP

Peter Johnson
Prodigy 50 points
Part Number: TM4C129ENCPDT
Other Parts Discussed in Thread: DP83849IF, , TM4C1292NCPDT, TM4C129DNCPDT

I'm hoping that there is a design guideline or that someone here has experience with adapting, for example, the evaluation kit design from the RJ45 connector and magnetics to an SFP connector/module. It seems like it should be as simple as taking the differential Tx and Rx from the SFP to the micro just like with the RJ45 but I have not found any information in the SFP documentation or in Tiva docs about the necessity of the magnetics and what, if any, terminations are needed. Also, I believe that the SFP will require at least the Rx LOS signal into the ethernet PHY but I would guess i would need to change some setting in the registers for the phy to point to whatever GPIO is used for that signal. Anyone able to help, thanks!

  • 0
    TI__Guru**** 191486 points

    Hi Peter,

      My limited knowledge for SFP is that it is mainly used for high speed (e.g. Gbit) while Tiva supports only 10BASE-T and 100BASE-TX. We have no such reference design and hardware design guideline for Tiva with SFP support. However, I find the below TI reference designs that may be helpful. This is all I can find. 

    https://www.ti.com/tool/TIDA-00088

    https://www.ti.com/tool/TIDA-00234

  • 0 in reply to Charles Tsai
    Prodigy 50 points

    Thanks for the reply, Charles. SFPs are also available in 100BASE-FX and an RJ45-converter and my application desires that we switch between the two. I may need to ask this on a different forum but I will start here because it's one half of the interface. 

    Because of the lack of the -FX support, I was looking into using a media converter IC to be able to go from the SFP interface to the micro. I was reading TIDU510B for Copper-to-Fiber 100BASE-FX or 1000BASE-X Media Converter Reference Design and thinking about using the DP83849 for this. But that IC uses the MII interface to interact which to my understanding is built in to the TM4C between the internal PHY and MAC. Is that understanding correct? Any suggestions for any alternate options?

    Should I cross-post this under the DP83849 Pn in that area? 

  • 0 in reply to Peter Johnson
    TI__Guru**** 191486 points

    Hi Peter,

    Peter Johnson said:
    Because of the lack of the -FX support,

    Correct. Tiva MCU's integrated PHY does not support -FX. 

    Peter Johnson said:
    I was looking into using a media converter IC to be able to go from the SFP interface to the micro. I was reading TIDU510B for Copper-to-Fiber 100BASE-FX or 1000BASE-X Media Converter Reference Design and thinking about using the DP83849 for this.

    I'm not an expert of DP83849 since I mainly support MCU side. However, reading TIDU510B document, it looks like DP83849IF can act as a media converter from RJ45 to SFP. Please open a new thread with part number for DP83849. The thread will automatically route to Interface Forum where the experts there can answer your questions about DP83849.

    Peter Johnson said:
    But that IC uses the MII interface to interact which to my understanding is built in to the TM4C between the internal PHY and MAC. Is that understanding correct? Any suggestions for any alternate options?

    Correct. Depending on which TM4C part number you refer to, some part numbers have the integrated PHY but there are also part numbers that expose MII/RMII that connect to an external PHY. 

    Peter Johnson said:
    Should I cross-post this under the DP83849 Pn in that area? 

    Yes, please create a new thread for DP83849. 

  • 0 in reply to Charles Tsai
    Prodigy 50 points

    Will do. Should i leave this open and hopefully provide a link in the future or should i resolve it and add that information when available?

  • 0 in reply to Peter Johnson
    TI__Guru**** 191486 points

    Hi Peter,

      This thread will automatically change the status to open when you post back with any updates within 30 days. The thread will automatically lock after 30 days if no activities. When that happens, you can create a new thread and link to this one. 

  • 0 in reply to Charles Tsai
    Prodigy 50 points

    Okay, sounds good. Just thought of another follow-up - you mentioned other PNs (presumably in the TM4C129 family) that have an externally available MII. Would you be able to provide some of those PNs that are the closest to my current TM4C129ENCPDT that either have the external MII or, even better, support 100BASE-FX with the built-in PHY. 

  • 0 in reply to Peter Johnson
    TI__Guru**** 191486 points

    Hi Peter,

    Peter Johnson said:
    Okay, sounds good. Just thought of another follow-up - you mentioned other PNs (presumably in the TM4C129 family) that have an externally available MII. Would you be able to provide some of those PNs that are the closest to my current TM4C129ENCPDT that either have the external MII

    Please use this TM4C production selection guide. TM4C1292NCPDT and TM4C129DNCPDT will have MII interface. I want to give you a heads up that we currently do not have any TI reference designs or EVM boards demonstrating the use of MII interface with an external PHY.

    Peter Johnson said:
    or, even better, support 100BASE-FX with the built-in PHY.

     As mentioned earlier, the integrated PHY does not support -FX.