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Original question:

DS160PR410: Difference between SN65LVPE504 and DS160PR410

SN65LVPE504: Difference between SN65LVPE504 and DS50PCI402

Amy Chen
Prodigy 20 points
Part Number: SN65LVPE504
Other Parts Discussed in Thread: DS50PCI402,

Hi


The situation I encountered was a PCIe root port with X8 GEN3 signal, and the downstream device had X4 GEN2 bandwidth. We found that sometimes the device can only recognize the X1 GEN2 bandwidth.
We hope to place a redriver between the root port and the device to improve compatibility.

These are my questions.
1. In this case, which redriver is recommended?
2. In this case, is a limited redriver or linear redriver a better choice?
3. If we use a GEN3 redriver, then the GEN3 signal is still after the redriver? At this time, will there be speed and bandwidth negotiation between the redriver and the device? Otherwise, will the negotiation return to the root port?
4. If using GEN2 redriver, the signal after redriver will become GEN2 signal?
5. I found that SN65LVPE504 and DS50PCI402 are GEN2 redrivers. What is the difference between these redrivers? According to my requirement, which one is recommended? DS50PCI402 is an 8-channel redriver, I can use DS50PCI402 instead of two SN65LVPE504 to achieve bidirectional mode.

Thanks

  • +1
    TI__Guru* 93670 points

    Hi Amy,

    Please note responses to your questions below:

    1). DS50PCI402 has higher EQ gain and it is 8 channels so it could be a better option.

    2). For Gen1/2 a limited redriver could be a better option since there is no link training that needs to go through. Also, a limited redriver has higher gain thus it can handle more loss on its input.

    3). Yes Gen3 signal would be present after the linear redriver and there is link training and protocol negotiation between root port and end point.

    4). Yes when using Gen2 redriver we are operating in limited mode and the signal becomes Gen2 data rate.

    5). DS50PCI402 has higher equalization gain. Further it has 8 channels and could be better suited for this application.

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser
    Thank you very much. It completely solved my problem.
    I have another question below.

    According to your answer.
    "4). Yes when using Gen2 redriver we are operating in limited mode and the signal becomes Gen2 data rate."

    1. I just want to know, because the redriver does not participate in the link training and protocol negotiation process, how does the redriver convert GEN3 to GEN2 data rate?
    2. Operating in limited mode means that the signal is limited to the GEN2 signal, right? Or is it just that the electrical characteristics have changed?
    Can you describe these transfer processes in more detail?
    Thank you.

  • 0 in reply to Amy Chen
    TI__Guru* 93670 points

    Hi Amy,

    In limited mode, this is true for both LVPE504 and PCI402 - device does not transfer link training information such as pre or post de-emphasis or VOD. These are controlled by these two device settings. 

    Redriver does not convert Gen3 to Gen2 data rate. PCIe protocol negotiates and determines Gen3 or Gen2.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser
    To my understanding I think this means that regardless of whether there is a redriver in the system or not, the host will first get link training and protocol negotiation with the device. At this time, there may be only the GEN1 signal, and when they reach an agreement, it will get the GEN2 signal. Then, redriver involved in GEN2 signal processing, such as equalizer, de-emphasis, etc.
    Is this correct?
    Many thanks.

  • +1 in reply to Amy Chen
    TI__Guru* 93670 points

    Hi Amy,

    Your understanding is correct. Redriver does not have the intelligence to get involved into the protocol negotiation.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser

    Thank you very much for solving my problem.
    So, back to my situation I mentioned first, in my opinion, I ran into trouble during the link training phase.
    After I put a redriver between the root port and the end device, do you think it would be better?
    It may be that the redriver improves the signal quality and then they will retrain again to get the correct ×4 bandwidth, right? Could this be happening?
    If it is feasible or getting more correct accuracy, then I think it may be valuable to place a redriver in my structure.
    Thank you.

  • +1 in reply to Amy Chen
    TI__Guru* 93670 points

    Hi Amy,

    Agreed. Redriver between root port and the end point can enable X4 Gen2 you were trying to achieve.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser 

    Thank you very very much.
I will try it on my design.
We just ran out of methods and don't know how to solve it.
Hope it can really solve the problem.
Maybe in the future I will bring you good news.
Thank you for your detailed explanation.