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DP83867ERGZ-S-EVM: Can I use this EVM to run serial data on independent media at less that 1.25 Gbps?

Shaun viola
Prodigy 90 points
Part Number: DP83867ERGZ-S-EVM

Hi All,

I am interested in using the DP83867ERGZ-S-EVM to go from computer to independent media for transmission then use another EVM at receiver to go back to computer. The issue is I'm not sure the bandwidth capability of the independent media. Therefore, I want the capability to run 10 Mbps, 100 Mbps and up to 1 Gbps (Which I think is 1.25 Gbps with 8b/10b encoding). My concern with this EVM is I don't think it can run slower than 1.25 Gbps, I think it repeats the lower data rates to get up to that speed for transmission, is that correct? And is there a solution for my requirements, even happy to buy multiple EVMs that output at different serial speeds if need be.

Thanks for your help,

Shaun

  • 0
    TI__Expert 5425 points

    Hi Shaun,

    The DP83867 supports auto-negotiation, which is an IEEE standard that allows the PHY to link down to 10/100 Mb depending on the capabilities advertised by the PHY and link partner. In addition, let's say that the PHY and the link partner currently established a forced link of 1Gb. If the link partner starts sending data at 10/100 Mb instead, idle frames will be sent along with the data to reach 1Gb, but the idle frames will not be sent from the PHY to the MAC.

    Does this information help with your questions?

    Regards,

    Adrian Kam

  • 0
    Prodigy 90 points

    Hi Adrian,

    This is really helpful thanks, I'm actually looking to send data in one direction only. Do you know if it is possible to setup one EVM as a transmitter and one as a receiver and force ethernet data at 10/100/1G as auto negotiation isn't possible. And if so is this easy enough to achieve with the EVM i.e. can we interface with the chipset easily to do this?

    Cheers,

    Shaun

  • 0 in reply to Shaun viola
    TI__Expert 5425 points

    Hi Shaun,

    There is no way to set the PHY to be capable of transmitting at 10/100/1G adaptively without auto-negotiation. You potentially can generate software to perform register writes to force the PHY to a specific speed when the application requires it, although this could cause issues if the speed change happens while in the middle of transmitting/receiving. If you do decide to go this route, you would have to pause transmit/receive for a bit while you change speeds manually. Is there a reason auto-negotiation is not possible? The DP83867 does support parallel detection, which allows the PHY in auto-negotiation mode to link-up with a link partner without auto-negotiation, but this only works for 10/100.

    Regards,

    Adrian Kam

  • 0 in reply to Adrian Kam
    Prodigy 90 points

    Hi Adrian,

    This set up has a transmitter at one end of the link and a receiver at the other end of the link i.e. there are not transceivers at both ends of the link (I think this makes auto negotiation impossible as it's only transmitting in one direction.) If I can set the data rate of the application and set the transport layer to UDP is it possible to use this chip to go from ethernet to serial PHY data and then at the receiver do the reverse, go serial PHY back to Ethernet? Or is there another EVM that would allow this?

    Thanks in advance,

    Shaun

  • 0 in reply to Shaun viola
    TI__Expert 5425 points

    Hi Shaun,

    Through software, you can ensure that the transmitter never receives data, and the receiver never transmit data. However, there is no way to just shut off the transmitter or receiver circuitry of the PHY because the PHY will need to send/receive idle frames in order to maintain link. Is there a reason you cannot use transceivers? Other than this, it seems like the EVM should be able to do what you describe, as going from ethernet to serial PHY data and the reverse is a standard setup.

    Does this information help?

    Regards,

    Adrian Kam

  • 0 in reply to Adrian Kam
    Prodigy 90 points

    Hi Adrian,

    Ok that's what my concern was that in order to maintain the link it needed something going in both directions. I've used these boards in non standard applications before but they have been duplex comms systems so that's why they have been able to work. In this application the transmitter node has no receiver components and the receiver node has no transmitter components and they are remote from one another. I'm looking to establish ethernet to serial and serial to ethernet simplex link with the transmitter sending and forgetting. Is it possible to have some kind of loop back or a local node to send idle frames to the transmitter?

    Or do you know of another way of achieving this? i.e. a different send and forget simplex serial protocol that can be used with computers?

    Thanks in advance,

    Shaun

  • 0 in reply to Shaun viola
    TI__Expert 5425 points

    Hi Shaun,

    What parameter or spec are you trying to reduce/save with this one-way ethernet application? If you are trying to cut cable costs or power consumption, then what you are looking for is not possible with our ethernet PHYs. As I have stated in the previous reply, it can be done through software. If you are concerned about having to manage the idle frames through software, then that is not an issue since the idle frames are handled by the PHYs.

    Regards,

    Adrian Kam