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Original question:

DS90UB954-Q1: GPIOx Output Function Programming

What does fram valid signal for ds954 represent for?

xn x
Intellectual 340 points


Hi,

It seems that the frame valid output of DS954 is the valid signal of one frame for the sensor. But why for some sensors like ov10635 with normal vtotal/htotal settings have very short low level of less than 1ms?

How can I enlarge it? 

  • 0
    TI__Guru** 103215 points

    Hello,

    The frame valid signal is similar to the vertical sync signal from RGB video interface. It denotes time between consecutive frame start and frame end packets. The portion where it drops low periodically is equivalent to the vertical blanking for the input source which varies from imager to imager depending on the blanking requirements. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Intellectual 340 points

    Thanks for your reply,

    Take ov10635 as example, I set the Htotal/Vtoal as 1782/897 which outputs 1280/720/30fps frames. The blanking is much longer than the actual measures frame valid low period, why? I'm still confused.

  • 0 in reply to xn x
    TI__Guru** 103215 points

    Hello,

    Can you please try measuring the VS signal at the imager side? I think it should be equivalent to the FrameValid signal at the 954. Actually I believe that the FrameValid pulse with does not denote the entire vertical blanking, just the vertical sync width. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Intellectual 340 points

    Your are right!

    For some sensors, it does so. For some others, it doesn't.

    So, is it possible to change the frame valid to denote the entire vertical blanking, and how?

    Why there are difference of frame valid singal source between the sensors?

  • 0 in reply to xn x
    TI__Guru** 103215 points

    There is no way to adjust it from the 954 side. The signal is extracted directly from the VS signal of the imager. Different imagers may have different sync widths for the same overall vertical blanking. You can try measuring the VS signal at the imager side to confirm it. There is no way to make FrameSync equal the vertical blanking time - it is designed to equal the vertical sync time only. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Intellectual 340 points

    OK! I know!

    Thanks very much!