TVP7002: Distorted video, potentially heat related

Most often issues like this are really IO timing issues. Can you look at the clock signal entering your target device on one channel then each of the data lines in turn with persistence enabled.

This will allow you to generate an eye diagram for each of the data lines hence allow you to make sure that you are meeting the setup/hold timing requirements for the DM81xx.

Try adding a small capacitance to the TVP7002 PCLK output. If this makes ANY difference to the video captured (either makes good video turn bad, or make bad video better/worse/any visible change at all) then you most certainly have a setup/hold violation. As a first order test the 'capacitor' can simply be your finger :) Touching the clock can often be enough to highlight timing issues.

As both devices heat up their IO timings will change very slightly, so this could be temperature related, but this is a red herring and is really a timing issue.

You can also try inverting the clock polarity on both the TVP (register 0x18, bit 0) and on the DM81xx port (don't recall this register address off hand). Changing this will change how things look and might give more insight as to the root cause.

Based on the eye diagrams you may need to invert the clock, add a delay buffer or tune your clock signal trace length.

BR,Steve

Hi Steve,

Thanks for the response I'll look into what you suggested.  We are experiencing several other issues with other boards (same design and layout, just a different board), are these also timing related as well?  The TVP7002 output clock goes through a 10R resistor right next to the clock pin, then through a 2000.3mil trace length and one via to the input to the DM81xx.  The VOUT traces range from 1584 to 2094mils with the majority of them ~1900mils.

#1 Blue/Red Image - intermittent, sometimes fixed with power cycle.  Once it is a good image, it will work indefinitely until a power cycle.

#2 - Pixelated, lack of color depth - always present, regardless of power cycle

#3 - Green lines - can be resolved by disconnecting input signal to TVP7002, then reconnecting.

Thanks,

Aaron

Aaron,
#2 definitely looks like a timing issue.
Try bypassing the resistor as a test. Again the intent here is not to fix things but more see what causes any form of change. If anything you do results in any visible change at all then timing is most likely.
With good timing the display will be rock solid, not necessarily correct, but stable.
If things are stable but wrong then the issue is likely something else.
Certainly need to verify timing margins are correct first though.
BR
Steve

Update:
The TVP7002 RESET was pulled high during power up and initialization of the DM81xx. I modified the DM81xx startup script to put the TVP7002 into reset for 1ms, and now am getting good results. Issues #1 and #3 are no longer seen, issue #2 is still to be tested.