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DS90UB927Q-Q1: Patterns present when video disconnected

Ryan.Bishop
Expert 3900 points
Part Number: DS90UB927Q-Q1
Other Parts Discussed in Thread: ALP

Hello,

We can use external video source and feed 927 serializer EVM through to 928 deserializer EVM and on to LCD.  Can also generate patterns using serializer or deserializer.

Do still have one funny behavior. With everything hooked up, and with pattern generators disabled in ALP Pattern Generator tab, if driven with external video source and then turn off the external source, I still see a scrolling of patterns.  This is not the scrolling pattern I have set up in pattern generator. I see R, G, B, BLK, WHT, checkerboard (looks to be scaled by 16 since squares are good sized), [probably] vertical lines (one pixel wide), and then horizontal lines (one pixel wide).

Have looked through the registers, and don’t see anything that I think would get the EVMs in this mode. It will do this with cable from external video source disconnected (I can power off the drive and disconnect cable while it is in this mode) and it continues this scrolling pattern, so the external source would not seem to be the problem, and I can disconnect cable from serializer to deserializer and it stops, so probably not the deserializer.

Might there be some register setting in the serializer that I have inadvertently left set that puts it in this mode? 

In serializer register 0x03 I can disable PCLK_AUTO to kill this behavior, but why is it scrolling?

Thank you,
Ryan B.

  • 0
    TI__Genius 11340 points
    Hi Ryan,

    When you disable pat gen from ALP, is the ALP connected to the 927 or 928?

    It's possible you have the pat gen for 928 disabled but not the pat gen from 927.

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    TI__Expert 3900 points
    Hi Jiashow,

    We have verified that the pat gen is off for the 927.

    We think it has something to do with the PCLK_AUTO (Serializer register 0x03, General Configuration, bit 1). If I have that set to H (auto-switch) and have Pattern Generator (set for external timing source) and external video source running, I can override the external video by selecting pattern generator (and go back and forth between pattern generator and external source) but if I turn off external source, then it gets into this scroll pattern (8 patterns - R, G, B, BLK, WHT, checkerboard, vertical one pixel lines, horizontal one pixel lines), and of course it doesn’t seem to matter about Pattern Generator Enable since external source selected. If Pattern Generator timing source set for internal, and PCK_AUTO = H, I can switch between Pattern Generator and external source, as long as external source stays on, but if I turn that off, with pattern generator on, and then turn off pattern generator, I get the eight scroll pattern described about (it is not the same as the scroll pattern used by Pattern Generator).

    Is there something more I need to know about PCLK_AUTO?

    Thank you,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Genius 11340 points
    Hi Ryan,

    If you have PCLK_AUTO enabled, it switches to the internal clock and supplies it to the pat gen path.

    Is there a reason why you are switching between external source and pat gen? You should switch pat gen off before you turn off the external source.

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    TI__Expert 3900 points

    Hi Jiashow,

    Right now they are simply running tests on the EVMs, so I don't think switching between external source and pattern generation is part of their application.

    So can you confirm that the pattern generator must always be turned off before the external source is turned off? Aren't there applications where the user could disconnect the cable while the pattern generator is on?

    Is there any reason why turning off the video source and then turning off the pattern generator is resulting in a completely different pattern?

    Regards,
    Ryan B.

  • 0 in reply to Ryan.Bishop
    TI__Genius 11340 points
    Hi Ryan,

    We actually haven't seen something like this before; typically if you disable pat gen, you shouldn't see any patterns on the display. But I'm suspecting this is because when you remove the external source, PCLK_AUTO is supplying an internal clock to display the scrolling patterns.

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    TI__Expert 3900 points
    Hi Jiashow,

    Update on this:
    Currently we have external source for video going to the serializer (and then over cable to deserializer and LCD).

    No pattern generator enabled in either SER or DES, just the external source driving the SER.

    If I reset the video source (without doing anything to the SER or DES) therefore interrupting the video, I do see the repeating pattern I described above (R full screen, G full screen, B full screen, BLK full screen, WHT full screen, checkerboard, vertical one pixel lines, horizontal one pixel lines).

    Not writing anything to the SER over I2C to configure it, so using default settings there. On DES end, we have it set up so that if we see LOCK, we put up whatever video is there.

    Are there any tests or troubleshooting steps you can recommend to identify the cause of this 'rouge pattern'?

    Regards,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Genius 11340 points
    Hi Ryan,

    Could you verify that reg 0x64 bit 0 pat gen is off, and 0x65 bit 0 auto-scrolling is off?

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    TI__Expert 3900 points
    Hi Jiashow,

    Yes, both the PatGen and Auto-scrolling are off. They are never changed from their default setting of 0.

    Let me know what else we can try that might shed some light on this.

    Regards,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Genius 11340 points

    Hi Ryan,

    Have you tried it with a different part and see if the same issue occurs?

    Can you also check the auto-scrolling  time slot and see if the scrolling pattern changes (check app note AN-2198 on auto-scrolling)? I would like to see if the scrolling pattern is due to auto-scrolling.

    Best,

    Jiashow