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TM4C129ENCPDT: Reset issue when connecting Ethernet cable between two controllers

RAGHUL N M
Intellectual 490 points
Part Number: TM4C129ENCPDT

We have developed our own controller board using TM4C129ENCPDT microcontroller IC. Two similar controller boards will be connected using an ethernet cable between the two RJ45 connectors in each controller board. We are facing an issue like, when connecting the two controller boards using an ethernet cable and a code to transfer data through ethernet between the controller boards is running,  the controller starts resetting continuously. The reset issue starts as soon as the controller starts establishing the link between the two controllers. Due to the continuous reset, the ethernet connection is also not establishing. This issue is not occurring always and so, sometimes, once if the link between the two controllers is established, then it is not resetting. The reset occurs only when we try to establish the connection between the controllers. 

The two controller boards are operating with different power supplies. And so, connecting an ethernet cable between them also connects the ground reference of the two controllers together. I suspect that may be the problem but not sure.

It also looks like the 3.3V supply to the controller drops due to a high current drawn by the controller board as we try to establish a connection between them by running an ethernet code. The code running in the controller has a UART, two SSI, Ethernet communication and some GPIO operations. 

Even if the two controllers are connected by an ethernet cable and if the code running in each controller boards is not an ethernet communication code, then this problem is not occurring.

Thank You for your time.

  • 0
    TI__Guru**** 191886 points
    Hi,
    Can you first check the RESC (Reset Cause) register and find out what exactly caused the reset to happen. You may have a brown out event that caused the MCU to reset. You need to monitor the power supply VDD and VDDC and see if they are out of regulation when establishing an Ethernet connection. It is also possible you have experienced some ESD event. Please review and compare the TM4C129 system design guideline (section 4.1) on the recommended Ethernet PHY interface against your board design.
  • 0 in reply to Charles Tsai
    TI__Guru**** 191886 points
    Here is the system design guideline incase you haven't reference it before. www.ti.com/.../spma056.pdf
  • 0 in reply to Charles Tsai
    TI__Guru**** 191886 points
    Hi,
    I have not heard back from you. I hope you are able to reference the system design guideline and compare the recommended PHY interface against your own. You might want to also check the recommended decoupling capacitors on the power supply in section 4 of the user's guide. I will close this thread for now. If you still have question on the same topic you can reopen this thread by replying to the thread or open a new thread for new questions.
  • 0
    Guru 55913 points

    Hi,

    RAGHUL N M said:
    The two controller boards are operating with different power supplies. And so, connecting an ethernet cable between them also connects the ground reference of the two controllers together. I suspect that may be the problem but not sure.

    Perhaps first mistake assuming common ground exist between two Ethernet isolated transformers. Should not typically share common ground, not required for Ethernet IP also being the magic pact of Internet communications. Also be sure the cable is cross over not straight through or network CSMCAD (collision avoidance) physical link layer will behave oddly if not.

  • 0 in reply to Charles Tsai
    Intellectual 490 points

    Thank You.

    Actually, our design and the standard design is slightly different. In the standard design hx118nl pulse transformer, IC is used. We have used an RJ45 connector with build in magnetics. So we didn't use that IC. The RJ45 connector is in the link below.

    https://www.digikey.com/products/en?keywords=1419-1021-ND

    We have also pulled up the termination resistors at the end as in the standard design.

    So I hope that doesn't make much difference. Other than that everything else is the same.

    I hope if I power both the controller with the same power source, the problem may resolve. I have to check that.

    Thank you for your time.

  • 0 in reply to RAGHUL N M
    TI__Guru**** 191886 points
    Hi,
    I will suggest you take a look at the schematic below for a TI design where the RJ45 with built-in transformer is used. Please note that the ESD protection diodes are placed between the PHY and the connector. This is really important. Not sure if your design has the diodes.

    www.ti.com/.../tidrm69.pdf
    www.ti.com/.../tidm-tm4c129poe
  • 0 in reply to Charles Tsai
    Intellectual 490 points
    Thank You very much Charles.
    We missed that ESD protection diodes in our design. Hope that resolves my issue.
    We need to re design our board. Only then I can confirm it.

    Thank You once again.
  • 0 in reply to RAGHUL N M
    Guru 55913 points

    You don't need the ESD protection diodes for Ethernet to work, as stated earlier common ground is not required nor needed!