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DS250DF810EVM: DS250DF810EVM will not fanout unless CDR is locked

Tom Roe68
Prodigy 140 points

Part Number: DS250DF810EVM
Other Parts Discussed in Thread: DS250DF810

I cannot get the DS250DF810 to fanout when the CDR is not locked. I need to use this part some of the time when the CDR is not locked for one bit rate we are using. I know you have to set all the registers up to pass data when not re-timed and I do that. x09 to 00, 1E to 00 etc. Also played with equalization and CTLE boost levels. went through the programmers manual and tried all the settings for fanout. 

It does do a lane crossing when the CDR is not locked so I know the signal is good enough to get through the lane and the registers are set. Also it gives <1E-13 BER on the one channel that passes through.

When you go from lane crossing to fanout or default to fanout the secondary channel goes mute. I have a scope on it, so I see the signal go away.

Does anyone know if the part can do a Fanout from A to A, B when the CDR is not locked?

Thanks

Tom 

  • 0
    TI__Mastermind 19235 points

    • Try settings the channels to adapt mode 0 and manually force a CTLE boost setting. You may start with CTLE = 0x00, and subsequently increment the CTLE setting if necessary to open the retimer output eye

    Table. Set CTLE Boost Value

     

    STEP

    SHARED/ CHANNEL REGISTER SET

    OPERATION

    REGISTER ADDRESS [HEX]

    REGISTER VALUE [HEX]

    WRITE MASK [HEX]

    COMMENT

    1

    Channel

    Write

    31

    00

    60

    Set Rx Adapt Mode = 0

    2

    Channel

    Write

    2D

    08

    08

    Enable CTLE boost override

    3

    Channel

    Write

    03

    00

    FF

    Set CTLE boost to 0x00. Different input channel loss will require different CTLE settings.

     

    • Try force signal detect high on all the channels by setting 0x14[7]=1

    • Try forcing eq_enable high by setting 0x95[3]

    • My assumption here is that the CDR bypass mode being used is the “CDR bypass when unlocked” setting via channel register 0x1E[7:5]

  • 0 in reply to Rodrigo Natal
    Prodigy 140 points

    Rodrigo,  I got this reply from Carlos Venturo. I tried all of these settings. It really looks like the channel is muted because when I leave it open in a working mode it passes noise through (since I have no input on that channel except 50 Ohms to ground) but in fanout it is off, not much noise, the same as it is when I mute it. I know to set 09 =x00 and 1E = x00 for both channels and the lane crossing setting works fine. 

    Do you know of any other registers that would mute the output when in fanout except when the CDR is locked?

  • 0 in reply to Tom Roe68
    TI__Mastermind 19235 points

    Can you email me the full set of channel register write operations you are performing to configure two adjacent channels to crosspoint fanout mode? I'd like to quickly review as a sanity check.

    Cordially,

    Rodrigo Natal

    HSSC Applications Engineer

  • 0 in reply to Rodrigo Natal
    Prodigy 140 points

    Total repower then

    I get a signal detect on Ch0, No output because there is no lock.

    Check that x09 is 0's on both channels

    Set ch0 to 1E to x09. the 09 is a default, I have tried all 0's truns on ch0

    Ch1 1E to x09 no output because there is no input

    Ch0 x96 to x0C set for fanout ch0

    Ch1 x96 to x03 set for fanout from ch0

    Then I tried a bunch of the settings you sent to me with CTLE and adaptation. Nothing works, output Ch1 is muted in fanout mode, not even noise.

    When I set to lane crossing it works. This is 2.125 gbps also tried at 10 gbps where I could get a CDR lock. When locked it worked.

    Thanks

    Tom

  • 0 in reply to Tom Roe68
    TI__Mastermind 19235 points
    • Can you triple confirm that you have 0x14[7]=1 and 0x95[3]=1 for your latest evaluation?
    • Additionally, do ensure that 13[6]=0, 0x14[6]=0, and 15[3]=0 (these are their default values and not likely that you changed them, but I just want to make sure)

    Your settings for 0x96 do look correct for both channels. 0x1E should be 0x09 for both channels, which looks to be your case. 0x09 should be 0x00 for both channels, which looks to be your case. Typically for this type of issue I would go in the lab and attempt to reproduce it on the bench at the evaluation board level. Unfortunately though I don't currently have that option, as I'm based in California Bay Area and we are in home lock down mode because of COVID-19. I will follow up with our digital design team and seek their input on this DS250DF810 crosspoint application case given your reported observations.

    Regards,

    Rodrigo