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Use two DS80PCI402 as x8 lane PCIE3.0 redriver

Peng Feng1
Prodigy 25 points
Other Parts Discussed in Thread: DS80PCI402

Hello,

I use  two DS80PCI402  chips as x8 lane PCIE3.0 redriver. That's to say, each DS80PCI402 drives x4 lanes (4 TX & 4 Rx).

I placed the TI redriver chips in the middle of CPU(PCIE3.0 source) & PCIE x8 slot. The input/output PCIE3.0 trace is about 10inches.

That is, the length of the trace from CPU to PCIE x8 slot is about 20 inches.

The two DS80PCI402 control pins setting: ENSMB=0 (pin mode),  RATE=F, RXDET=F, LPBK=F, VDDSEL=0 (3.3V mode), SD_TH=F, PRSNT#=0.

The two DS80PCI402 EQ & DEM setting: EQA[1:0]=01, DEMA[1:0]=00, EQB[1:0]=01, DEMB[1:0]=00,

And the PCIE1.0/2.0/3.0 TX eye diagram are all passed.

But when I insert a PCIE3.0 x16 graphics card into the PCIE x8 slot, it can only be identified to X1 width. The right result should be x8 width. Because the PCIE x8 slot has x8 lane PCIE3.0 signals.

And when I change the PCIE width from "AUTO" to "FORCE x8" in the BIOS setup, it can recognize x8 PCIE3.0 width. Normally, the BIOS setting should be "AUTO" option.

Please help to see this issue. Thanks.

  • 0
    TI__Intellectual 1705 points
    Hi,
    The DS80PCI402 has the RX detection function, so when RXDET=Float the input impedance is high-z until a downstream 50 ohm receiver is detected on both the P/N. Also there maybe a timing issue which causes the CPU or end-point card to not see the 50 ohm input termination during the link training, so try to set the RXDET=1 which would disable the RX detection and force the input to be 50 ohms. Recommend to also check for good connection of the /PRSNT signal on the on the PCI bus for the x8 lanes.
    Regards,Michael