DP83TC811S-Q1: Problems with communication

Prodigy 40 points

Replies: 4

Views: 96

Part Number: DP83TC811S-Q1

Hi Guys,

I'm working on a 100Base-TX to 100Base-T1 converter as an university project, which uses the DP83TC811S. I developed a prototype, that uses a direct connection with RMII between the two PHYs KSZ8081RNA (100Base-TX) and DP83TC811S (100Base-T1). I attached my schematic and the programming of the registers of the PHYs by using SMI over a STM32F107RC (with STM32CubeIDE). The Hardware seems to be working, the PHYs seem to communicate with each other and a communication between two converters with 100Base-T1 seems to be working too (synchronous LED_1 blinking).




My Problem with the project is that, when I connect two converter and use them as a bridge between my PCs, a communication cannot be achieved. I used Wireshark to see what's going on, but the only thing I see is that the PCs are trying to communicate, but cannot achieve a IP exchange. (I attached some screenshots)

What is the problem in this application and what needs to change at the prototype in order work properly. I can only think of a problem in the settings of the register of the PHYs or the communication between the PHYs.

I'm a student and I cannot think of any solution for the problem with my knowledge. I hope that somebody can solve the problem or at least explain what's wrong!

Thanks a lot!!

4 Replies

  • Hi Tobias,

    For RMII, the PHY will use CRS_DV and with that you see a toggle at the end of the frame.

    If you are using back-2-back method, that toggle cannot be used.

    Please either configure RMII to version 1.0 through register 0x17 or set register 0x47D bit[2] to 0 instead of 1.

    1 = CRS_DV

    0 = RX_DV

    Best regards,

    Ross Pimentel

    Ethernet - Applications Engineer

  • In reply to Ross Pimentel:

    Hi Ross,

    unfortunately your suggestion didn't solve my issue.

    I tried both variations and both don't seem to be working.

    Do you have other tips or possiblilities of a solution?

    Best regards,


  • In reply to Tobias Jehle:

    Hi Tobias,

    Can you please send me a register dump of 0x0 to 0x1F as well as 0x133, 0x467, 0x196 for the 811 devices please?

    Do you have an oscope on hand? I suggest you probe TX_EN, RX_DV and RX_ER to see if you see traffic on both media converters when sending pings.

    See if the length of those TX_EN and RX_DV assertions are the expected bit lengths of the frames transmitted.

    Best regards,

    Ross Pimentel

    Ethernet - Applications Engineer

  • In reply to Ross Pimentel:

    Hi Ross,

    I'm sorry it took me so long to answer. Our Highspeed-oscope was away for calibration.

    I did what you asked for. I measured TXEN, CRSDV, RXER and I created a register dump (files are in the .zip). I didn't use RXER in the application, so it's not connected to anything. I thought it was optional and not required.

    But I don't quite understand how I can check the expected lengths of the frames. I sended a 32 byte package per pinging and the Signals were asserted for about 8 microsecs. I would  be kind of you, if you can explain, how to do that. I'm a electrical engineering student and would like to know those things for my future;)

    Best regards,

    Tobias Jehle