• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 592 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS90UB954-Q1: Can I disable the Back-Channel on the FPD Link

Tim Webber
Prodigy 50 points
Part Number: DS90UB954-Q1
Other Parts Discussed in Thread: DS90UB953-Q1

We are having some data transport issues between the FPD Link serialiser and de-serialiser ICs (DS90UB953-Q1, DS90UB954-Q1) where video frames are lost when the connecting cable is trodden on. To try and see what is happening to the actual signal when the cable is stepped on, I wish to view the eye diagram of the signal as it arrives at the deserialiser IC using a high performance scope. The problem is that the back-channel data being ‘overlaid’ onto the 4Gbps data makes it almost impossible to take an eye diagram on a high speed scope as the signal is jumping up and down with the back channel data as it is sourced from the deserialiser back to the serialiser.

So is there anyway of disabling the back-channel data or any other way you can recommend whereby we can observe the eye-diagram of the incoming signal at the deserialiser pins (or probably more accurately, across the DC blocking caps)?

  • 0
    TI__Guru** 107510 points

    Hello Tim,

    you can disable the BC in the correspondent reg 0x58 for that port.

    But why are you not using the CMLOUT pins to measure the incoming Forward channel signal without BC signal?

    You just need to have 33nF to 100nF soldered at each CMLOUT pin and terminated with a differential 100 ohm resistor if your scope requires that.

  • 0 in reply to Hamzeh Jaradat
    Prodigy 50 points

    Thanks Hamzeh for your suggestion.

    The reason we don't want to use the CMLOUT pins to observe the eye is that these outputs come after the input equalisation circuit for the Link. This means that the eye observed at the CMLOUT pins will not actually be the same as the signal as received by the DS90UB954-Q1 RIN0_P/N pins. The equalisation circuit will undoubtedly mask to a degree the effect of standing on the cable.

    I will however pursue disabling the back channel via register 0x58 and add a free running crystal to the CLKIN pin of the DS90UB953-Q1. Hopefully in this way we can retain data transmission without the need for the back channel.

    Kind regards,

    Tim

  • 0 in reply to Tim Webber
    TI__Guru** 107510 points

    Tim,

    understood, but the 954 is processing and forwarding the equalized data not the "raw" received data.

    once you place a crystal on the 953 side, please do not forget to change the working modes on both sides to Non-Synch mode instead of Synch Mode.

    please refer to 953 table 8 and 954 table 2.

  • 0 in reply to Hamzeh Jaradat
    Prodigy 50 points

    Thanks Hamzeh,

    Indeed, the 954 is processing the equalised data, but we wish to understand what is happening to the signal as a result of the cable being stepped on.

    Thanks for the top tips re the updated setup with external crystal .... notes taken.

    Kind regards,

    Tim