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DS92LX2121 - Is it possible to run 2 displays from from one HS Interface driver?

Other Parts Discussed in Thread: DS92LX2121, DS92LX2122, DS90UB904Q-Q1, DS90UB903Q-Q1

Can two deserializers (DS92LX2122) be driven from one DS92LX2121

  • Hi Lee,

    This is an interesting idea. This SerDes pair is not typically meant to be interfaced with multiple deserializers at the same time.

    Can you provide a block diagram and application for your idea? Are you trying to create a fan-out where you drive two CML-input deserializers simultaneously, and if so, are they displaying the same data or are they displaying different information? Or, are you thinking of muxing one deserializer at a time to the serializer?


  • sorry don't have a block diagram at this point but I am trying to do exactly what you are suggesting.

    Fan out of the serializer to two different deserializers that would be displaying the same data at the same time.

    If I have to mux to get it to work I would certainly entertain that idea but my preference would be to do a basic fan out as you suggest.

  • Hi Lee,

    Thanks for your patience as I looked at some of the possibilities for situating the DS92LX2121 and DS92LX2122 as you suggested.  The big question that you will need to determine is whether back-channel communication is necessary for your application. The CML differential pair coming from the DS9XL2121 is made to communicate high speed data from serializer to deserializer and low-speed communication data from deserializer to serializer via backplane connection. Since you are planning to run a DS92LX2121 and DS92LX2122 in a fan-out application, there is possibility of problematic line contention in the back-channel direction if two DS92XL2122 deserializers are connected to the same DS92LX2121 serializer.

    There is one possibility for creating a fanout, but this would involve that one of the DS92LX2122 deserializers does not have back-channel communication capability with the DS92LX2121. The idea is to use Reg 0x3F to enable CMLOUT P/N, then use the CMLOUTP (Pin 38) and CMLOUTN (Pin 39) outputs of one DS92LX2122 to send into the second DS92LX2122. The CMLOUTP/N outputs are originally intended to via the eye diagram of the CML signal coming into the deserializer after it has been processed by the internal EQ and reclocked. However, it can also be used as a secondary output that holds data identical to the data received by the first DS92LX2122. The system would look similar to the following:

    We have tried this in the lab previously and have found that it is capable of driving two displays in this configuration at the expense of a "passive" second DS92LX2122 that does not communicate back-channel information back to the DS92LX2121.

    The DS92LX2121/22 datasheet does not contain much description about the CMLOUTP/N functionality, but more detailed description can be found by referencing the automotive equivalent of this SerDes pair (DS90UB903Q-Q1 and DS90UB904Q-Q1).