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DP83TC812EVM-MC: DP83TC813EVM connection as bridge

Robert Reichert
Prodigy 20 points
Part Number: DP83TC812EVM-MC


I have connected a DP83TC812EVM and a DP83TC813EVM as shown in the following figure. I have adjusted the MDIO addresses by removing the resistors as follows to get by with only one USB connection:

  • DP83TC812 on DP83TC812EVM = 10
  • DP83867 on DP83TC812EVM = 1
  • DP83TC813 on DP83TC813EVM = 0
  • DP83867 on DP83TC813EVM = 3

The power is supplied via USB.

Now let's talk about my problem:

  • A ping via this connection is not possible. (if only the ethernet ports are connected, the ping works, so it cannot be due to a firewall)
  • If the DP83TC812EVM register 0624 is set to 55BF and 0619 to 1555 via MDIO, there seems to be a data stream via the SPE connection. The LED1 of the DP83TC812EVM flashes and the LED of the Ethernet port also flashes. However, no packets can be detected using the network sniffing tool (Wireshark).

What could be the reason for this? I have already checked the registers of the DP83867 and they should actually fit like this.

  • 0
    TI__Genius 14006 points

    Hi Robert,

    I'm a litte confused by the MDIO and VCC connection between the 2 DP83TC812EVMs. Could you provide a more detailed block diagram or picture?

    1. Try pinging from port 1 to 2, and after link up and reading registers 0x639, 0x63A, 0x63B, 0x63C, 0x63D, 0x63E in order three times (no configuration on PHY) on the DP83TC812 and DP83TC813. 

    Then, try pinging from port 2 to 1 and reading the same registers. 

    2. Try writing 0x0624 = 0x55BF,  0x0619 = 0x1555  in that order on both PHYs and see if wireshark detects any packets.  

    3. Also check that the DP83867 is configured correctly for 100 Mbps and also seeing link. You can set the speed by setting 0x0=0x2100. You can check for link in register 0x1. 

    Here is a debug guide you can look at for reference:

    https://www.ti.com/lit/ug/snla431/snla431.pdf?ts=1706134109795&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDP83TC812S-Q1

    https://www.ti.com/lit/an/snla246b/snla246b.pdf?ts=1706134144294 

    Best regards,

    Melissa

  • +1 in reply to Melissa Chang
    Prodigy 20 points

    Hi Melissa,

    First the MDIO and VCC connection, but doesn't matter it works fine like this:

    1) Register values after pinging:
    For DP83TC812 Ping 1-> 2:
    Register 0639 is: 0078
    Register 063A is: 0000
    Register 063B is: 0078
    Register 063C is: 00de
    Register 063D is: 0000
    Register 063E is: 00de
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000

    For DP83TC813 Ping 1-> 2:
    Register 0639 is: 00c1
    Register 063A is: 0000
    Register 063B is: 00c1
    Register 063C is: 008d
    Register 063D is: 0000
    Register 063E is: 008d
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000

    For DP83TC813 Ping 2-> 1:
    Register 0639 is: 0010
    Register 063A is: 0000
    Register 063B is: 0010
    Register 063C is: 0004
    Register 063D is: 0000
    Register 063E is: 0004
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000

    For DP83TC812 Ping 2-> 1:
    Register 0639 is: 000b
    Register 063A is: 0000
    Register 063B is: 000b
    Register 063C is: 001a
    Register 063D is: 0000
    Register 063E is: 001a
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000
    Register 0639 is: 0000
    Register 063A is: 0000
    Register 063B is: 0000
    Register 063C is: 0000
    Register 063D is: 0000
    Register 063E is: 0000

    2) Wireshark didn't see anything after setting registers at desired values. But if I set DP83867 register 0x16 = 0xF000 there is a massage stream.

    3) The DP83867 have been in Auto-Negotiation (0x0 = 0x1140) and there have been a link, but after fixing it to 100Mbps there isn't a link anymore.

    Now I tried to fix the PC Port to 100Mbps, and I get a ping, even in Auto-Negotiation mode. But there are a lot of timeouts.

    Best regards Robert

  • +1 in reply to Robert Reichert
    Prodigy 20 points

    Even the Timeouts have been fixed now. The power supply hasn't been enough via the previous setup now if each board is connected to a barrel connector and an external supply everything works fine.

    Best Regards

  • 0 in reply to Robert Reichert
    TI__Genius 14006 points

    Hi Robert,

    Glad to hear it works now. I am going to close this thread for now. 

  • 0 in reply to Robert Reichert
    Prodigy 20 points

    If setting Reg 0x0 = 0x1140 and 0x9 = 0x0 no setup at PC is necessary.

  • 0 in reply to Robert Reichert
    TI__Genius 14006 points

    Understood. Thank you for updating us.