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DS90UB913A-CXEVM configuration

Joe Rule
Intellectual 330 points


Hello,

     We have a DS90UB913A/914A EVM and we can get the setup to "lock" when no camera is connected but we see no data when probing the LVDS serial transmission lines between the 2 boards.  We have it configured to use the SMA connector interfaces, not the 4-wire interface.

Additionally, we do not see the lock LED come on when we connect our camera front end.  We have attempted to setup the EVM according to the User's Guide.  Is there something we're not considering or should look for?

Thanks,

Joe

  • 0
    TI__Genius 13475 points

    Joe

    If there is no camera or PCLK input to the serializer, it will switch over to an internal clock, so it is normal to be able to achieve lock even when there is no signal present on the input.  By configuring the boards appropriately, you can use this mode to put the pair of boards into BIST mode to confirm that you have a solid link before applying a signal to the serializer.

    Because of the way the backchannel works, you won't be able to see a signal by probing the FPD-III link, it will just look like noise.  If you want to observe the eye diagram, use the CML out connection from the '914 and enable this via the 914 registers.

    A few things to check:

    Make sure that the 913 and 914 are both set to the same mode.

    If you have I2C access to the 914, you will be able to monitor things such as if there is a signal present at the inptu to the device, if it is locked etc.  This may help in debug.

     

    Do you have I2C access to the '914? -

  • 0 in reply to Mark Sauerwald88474
    Intellectual 330 points

    Mark,

         We don't have an easy way to use I2C right now but I think we figured out the problem.  I believe our EVK was modified from the default configuration before we received it.  We had some components (mostly resistors) populated that were shown not to be in the schematic and vice versa.  It is now working.  However, we did remove the 49.9 Ohm (that was not actually 49.9 ohm when we checked it) from the LVDS line.  It seemed to be pulling the signal down to result in it not being at the same level as the opposing differential line.  Is there a reason for this 49.9 Ohm resistor that does not exist on the other differential line?

    Thanks,

    Joe

  • 0 in reply to Joe Rule
    TI__Genius 13475 points

    Joe

     

    When the board is configured to drive a coax cable, DOUTP goes to J2, and is terminated by a 50 Ohm termination resistor at the far end of the cable.  DOUTN is unterminated, so we provide R80, which is a 50 Ohm termination resistor so that the load is balanced.   If the output is going to the differential connector, then R29 and R80 are both removed, and C17 and C18 are put in, so the signal goes through the common mode choke (L5) and on to the differential connector.

    Mark

     

  • 0 in reply to Mark Sauerwald88474
    Intellectual 330 points

    Mark,

         Thanks for the help.  We now have our system up and running.  We would still like to understand how prone we are to losing the connection between the 913/914 during operation.  We have used BIST mode and observed long periods of time with no errors and then other times with an error after 20 minutes.  We have yet to ever lose our video stream.  Is there a recommended equipment setup to observe an eye diagram?  Is there a benchmark for CRC error frequency that would lend itself to knowing the system is close to losing the data stream completely due to too many errors?

    Thanks,
    Joe

  • 0 in reply to Joe Rule
    TI__Genius 13475 points

    Joe

    To look at the eye diagram, you have to use the CML out pins on the DS90UB914.   I like to use a high speed scope with a differential input - in my lab I use a Tek TDS7404 real time scope with a P7313 Differential SMA probe attached to the CML output pins.

    If the link is stable, there should be no CRC errors, things that might have you on the edge would include using a very long cable, being in an environment where there might be a lot of interference, or if the cable is being disturbed - for example a coax cable being bent sharply to generate a kink in it.

    Mark