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DS80PCI102 Configuration

Other Parts Discussed in Thread: DS80PCI102

Hello TI,

I have a customer who produced a pair of prototype boards using two TI DS80PCI102 (one on each board) to move 1 lane of PCI E over 12 inches of 100ohm twisted pair between them.

They set the configuration settings to what they believed would be the best setting for this application however they are experiencing issues.  Can TI advise us on the proper settings for this setup? 

Thanks,

Dan

  • Hi Dan,

    Can you provide us a block diagram of the system that includes the estimated amount of loss before and after the DS80PCI102? Our advise of the proper settings depends on several things:

    - What data rate is your customer primarily running? Do you need to support multiple PCIe generations? This will help us determine proper settings for the RATE pin.

    - What is the estimated amount of trace/cable loss (in dB) on either side of the system? This will allow us to determine whether the repeater is placed in an optimal location and what EQ, VOD, and DEM to recommend. Since cable quality varies among vendors, 12 inches of 100 Ohm twisted pair will not provide as much information as the amount of loss that the repeater is expected to compensate, and this loss is frequency dependent. If there is s-parameter (.s4p) data for the twisted pair, that would be ideal.

    - Is your customer running in pin mode or SMBus slave mode? SMBus slave mode will provide additional granularity when working with EQ, VOD, and DEM settings, but it will require programming capability.

    - What kind of signal conditioning capabilities does the Tx and Rx root complex/endpoint have? The more signal conditioning capabilities the root complex/endpoint has, the more flexibility we have when tuning the repeater.

    Thanks,

    Michael

  • Hello TI,

    No Block diagram yet.  

    We are looking for a good place to start. Could you please provide us with some generic settings that are “in the ball park”?

    Some answers to above questions below.  

    - What data rate is your customer primarily running? Do you need to support multiple PCIe generations? This will help us determine proper settings for the RATE pin.

    We need to support multiple generations.

    - What is the estimated amount of trace/cable loss (in dB) on either side of the system? This will allow us to determine whether the repeater is placed in an optimal location and what EQ, VOD, and DEM to recommend. Since cable quality varies among vendors, 12 inches of 100 Ohm twisted pair will not provide as much information as the amount of loss that the repeater is expected to compensate, and this loss is frequency dependent. If there is s-parameter (.s4p) data for the twisted pair, that would be ideal.

    ~7” of trace -> TI part -> ~1” of trace -> connector -> 6 inches of cable (we shortened this) -> connector -> ~2” of trace -> part. we do not has s-parameters.  

    - Is your customer running in pin mode or SMBus slave mode? SMBus slave mode will provide additional granularity when working with EQ, VOD, and DEM settings, but it will require programming capability.

    Pin mode

    - What kind of signal conditioning capabilities does the Tx and Rx root complex/endpoint have? The more signal conditioning capabilities the root complex/endpoint has, the more flexibility we have when tuning the repeater.

    Unknown

     

  • Hi Dan,

    Thanks for the details. This will definitely be helpful for getting us in the ball-park.

    1. To support multiple generations, leave the RATE pin floating so that the repeater will auto-select between limiting mode (Gen 1/2) and non-limiting mode (Gen 3).

    2. The amount of loss in the system seems well in the support range of the DS80PCI102. Although I do not have a model to reference for the 6-inch cable loss, I do have measurements TI has obtained in the past for typical 1", 2", and 7" FR4 trace:

    I will assume right now that we are not taking into account the 6-inch cable loss, but that at 6 inches, the loss is not significantly more. Given my estimates on the loss you are expecting around 4 GHz (assuming Gen-3), I'd recommend starting with VOD around 1.0-1.1V, DEM minimal, and EQ minimal as well. See the diagram below for recommended settings (Levels are based on DS80PCI102 datasheet Tables 1 and 2).

    Depending on the loss from the twisted pair, you may need to tweak DEMB and EQA, but I think the recommendations above should help you get started. All other parameter settings should be left as default, so RXDET = Float and RATE = Float.

    Thanks,

    Michael