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SN65LVDS822: rgb display problem

GerhardJL
Prodigy 90 points
Part Number: SN65LVDS822
Other Parts Discussed in Thread: SN65DSI84,

Good day,

I am using a SOM manufactured by variscite  using a nxp procc

 Part of the SOM is using a SN65DSi84 mipi dsi >> lvds bridge

On my carrier brd, interfacing to this SOM, I use a SN65LVDS822  lvds >> 24b rgb converter.

I use the suggested 100R imp on the 4xlane lvds and configured the device as 'std'  4-lane lvds traffic.

(Clock : 33mhz)

Problem -

I have that from to time after Power re-cycle, the

rgb displays a roll-down event every 12seconds.

At other time, after power re-cycle, the display is stable.

I am unable to trace this fault

Any suggestions?

Thank you

Gerhard

  • 0
    TI__Guru** 103215 points

    Hello Gerhard,

    Have you been able to trace the problem to either SN65LVDS822 or SN65DSI84? i.e. when you experience the problem can you try checking the error registers in SN65DSI84? Also are you following the init sequence for SN65DSI84 in table 2?

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Guru** 103215 points

    Hello Gerhard,

    Any feedback?

    Thanks,

    Casey 

  • 0 in reply to Casey McCrea
    Prodigy 90 points

    Hi Casey,

    Unfortunately the 12s cadence is still peristant, as described.

    At this time the dsi84 is mounted on SOM from Variscite (DART MX8M)

     which connects to a lvds (3-lane) LCD on their eva-kit, which works fine.

    In our use-case carrier brd, we have the lvds822 wired to the dsi84 on the SOM

    In the .dts minimal settings are available, but to set the format to 4 lanes,

    instead of 3 lanes.

    I notice that on the dsi84,  the single channel format (4 lanes) only make provision for the

    2 x lsb to be on the 4th lvds lane.  Unless one use the dsi84 in dual channel,

     where the  2x msb is then output on lvds lane4.  But in this mode only Odd/Even pixel are then available on chn0/1.

    so one would loose colour granularity, imho.   I am using it however in this mode, just to at least test.

    However, using it in this moded (dual-ch output) does not solve the 12s cadence,

     it has no impact on the 12s cadence, I have initially on 3-chn lvds, where the same fault state was observed.

    This quite a large scale project, used in the nfc card payment industry, so, I am a bit stuck.

    Yet, no resolution yet. /:)

    Do you have any pointers?

    Are the DSi84 actually compatible to to the 822lvds?

    Thanks!

    Gerhard

  • 0 in reply to GerhardJL
    TI__Guru** 103215 points

    Hello Gerhard,

    The two devices should be compatible. I don't see any immediate reason for a problem to occur every 12 seconds. Can you please check the DS65DSI84 error registers as I mentioned? Is there anything else in the signal path which could contribute to the periodic error? Maybe power supply glitch or something else? SN65LVDS822 is a fairly simple device. It simply passes through the LVDS data into a new format so it doesn't have much smarts. I would imagine the problem lies elsewhere in the signal path or potentially even in the TCONN. Maybe the timings are not exactly correct for the display being used with the new carrier board? 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Prodigy 90 points

    Hi Casey,

    Follow-on steps - (without solution) -

    At this time I have dissected PSU's to eliminate issues.

    Change timing params in the .dts

    Observed that timing changes are correct, observing the 822 output sync, clk, de - using scope.

    Follow-on question -

    Would it help if I post a video of the problem

    Post a sch clip

    Are there other lvds>24bRGB converter ic's to consider, with eval-boards/kits?

    Are the 822 the latest offering from ti?

    Thank you for responding to my post here.

    Regards,

    Gerhard

  • 0 in reply to GerhardJL
    TI__Guru** 103215 points

    Hello Gerhard,

    If you have probed the output syncs, PCLK and DE from 822 and they look as expected, then I don't believe the problem is from 822. Unfortunately I'm not really sure what could be happening. Maybe the power sequence just needs to be adjusted between enabling the display TCONN or the 822 or the DSI converter?

    Best Regards,

    Casey