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Testing Ethernet..

Andrew Frazer
Expert 2305 points


i want to more accurately test ethernet based circuits, to check that things behave like i expect..   

One of the things i think woudl be useful woudl be to create eye diagrams and see what is going on...

This is quite new to me.. What test equipment and process's woudl be helpful

  • 0
    TI__Mastermind 23675 points
    Hi Andrew,

    All of our devices can be put into test modes through the SMI or you can observe their operation by using external test fixtures. There are a range of fixtures from companies like Tektronix that will have an Ethernet Test Suite.

    The Tektronix one is called TDSET3.

    You can also use a scope and use a termination cable on the cable side of the device to observe the signaling.

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Expert 2305 points
    Thanks for this, can you tell me how you put it into Test mode? Do you set some register?

    what does the termination cable look like ( ie, hows it wired )..

    At this stage, what id like to be able to do is create some eye digagrams so i can check my designs are not doing crazy stuff before sending out for more extensive testing.
  • 0 in reply to Andrew Frazer
    TI__Mastermind 23675 points
    Hi Andrew,

    Each of our PHYs has a datasheet with register descriptions at the end that talk about what to do to configure each mode. For instance, if you want to view the eye diagram for one of our PHYs at 100Mbps you will need to force the PHY into 100Mbps mode. Set register 0x0000 to 0x2100. This will disable auto-negotiation and configure it for 100Mbps. You can then specify if you want to change what channel you want to check by forcing either MDI or MDIX using register 0x0019.

    Please look at this post for how to make a termination cable:
    e2e.ti.com/.../372898

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Expert 2305 points

    Thanks Ross, 

    The cable terminations make snese, i'm assuming that you'd need a differential probe on your scope to to use that setup.    I dont'  at the moment have a differential probe, ( I am in the process of working out which scope i want to buy )..    I was thiking however it might be possible to use a Ethernet transforer to get a single ended signal?     

    I need to look at our ethernet driver code but it seems that it wont' be too hard to get it into a test mode.

  • 0 in reply to Andrew Frazer
    TI__Mastermind 23675 points

    Hi Andrew,

    Technically the spec allows you to measure either between the IC and magnetic or after the magnetic on the cable side. It is generally easier to use a diff probe and use the termination cable, but since you have only single ended probes what you could do is have one probe connected to the TD+ pin and another connected to TD- pin. On your scope just use the MATH function to subtract the two signals. Do add 100 ohm termination on the cable side of the magnetic so you do not get reflections though. 

    Kind regards,

    Ross