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DS90UB953A-Q1: DS90UB953 Forced switch between Coax and STP mode

Patrick Thomas
Prodigy 20 points
Part Number: DS90UB953A-Q1
Other Parts Discussed in Thread: USB2ANY, ALP

Dear TI Team,

I encounter a problem with the SERDES pair DS90UB935-DS90UB936.

They are linked by 100Ohms STP, 2 meters long. In the USB2Any -Analog Launch Pad GUI I can set the DESER to go into twisted pair or coax mode by register 0x6D (interestingly the description here talks about strapping this mode via MODE Pin witch from my recherche is not documented in the datasheet). 

Now for the Serilizer I cannot find such a register or strapping hint to force it into STP mode. In the Landingpage of the GUI it still says COAX mode and I can`t even find a status register wher the GUI can find this information.

So my question is

1: how does the SER decide ehether to use COAX or STP as cable mode? Is ist by measuring impedance, just trying out or configured somehow? And how is it intended to be altered?

Best Regards,

Patrick

  • 0
    TI__Mastermind 18991 points

    Hi Patrick,

    Thanks for your inquiry. For questions about ALP, I would recommend taking a look at the EVM user guides for the DS90UB954 and DS90UB953. There is some information here about the configuration of our devices using ALP.

    With regards to the serializer side, is it a non-TI board which you are using here? I believe it's just the desierlizer EVM that's set up for use as STP.

    The port config register (0x6D) should also be port specific (set in register 0x4C to select RX0 or RX1). Could you confirm that we're selecting the correct RX port to set as STP mode?

    Best,

    Thomas

  • 0 in reply to Thomas Bejin
    Prodigy 20 points

    Hi Thomas,

    thank you for the general advices regarding the documentation.

    I have custom boards here based on your devboards and yes on the DESER side I can select the STP or Coax mode (and RX0 is selected, i can see and communicate with the slaves at the SER side from DESER).

    It seems that with the SER, ALP shows always the "coax mode" it changes only to TP when the SER is not present at all- this is misleading for the developer and seems an issue with the interpretation in ALP as there isn`t any SER register telling ALP wich mode is has chosen.

    For my issue there was a manufacturing problem on one of my boards letting just one of the diff pairs trough. The other boards work just fine in STP mode so I guess we can close this thread.

    Have a nice weekend,

    Patrick

  • 0 in reply to Patrick Thomas
    TI__Mastermind 18991 points

    Hi Patrick,

    Thanks for confirming that this issue was due to a manufacturing issue on one of your boards. If you ever have questions in the future please don't hesitate to reach out!

    Best,

    Thomas