We have encountered a particular DVI signal that causes the DE (DataEnable) signal from the ADV7842 to be erratic. We have not seen this error on any other DVI or HDMI signal we have encountered, at any resolution. The captured image moves up and down and some scan lines will shift horizontally. The signal is 1280x1024, HF=63982Hz, VF=60.02Hz, Pixels Per Line=1688, Lines Per Frame=1066, PF=108.001616MHz. The signal looks like a standard DMT1260G format from a Quantum generator with a minor adjustment to the horizontal frequency. I have tried other video capture products with no problems, including one of our own that uses the ADV7441. I cannot reproduce the problem with any video generator, even by changing timing parameters. On the problem signal I have tried different cables, buffering with splitters and transmitting with an optical HDMI cable, with no change to the errors, so I don't think it's an equalization or TMDS signal integrity problem. If I put a 1:1 video scaler device between the source and our input, the problem goes away. So, receiving and re-transmitting does not pass the error through. The signal comes from a medical imaging system in a hospital so access to the signal for debugging has been difficult. There's something about the signal the 7842 doesn't like. The DE regeneration and vertical filters are locked according to the status registers. The odd thing is it seems to only affect the DE output, the vertical and horizontal sync outputs look stable.
I have attached scope pictures of the DE output (blue) with respect to VS (yellow) as the trigger. The first one shows where sometimes there is no DE after vertical sync (faint blue trace). The second one shows where sometimes DE occurs inside vertical sync (faint blue trace). The scope inputs come directly from the 7842 outputs so no contribution from any other on-board logic.
Any suggestions as to what could be causing this and if there is any possible solution, would be greatly appreciated. Since there is no documentation showing any of the HDMI PLL etc. registers I was not able to experiment with any settings.
Thanks.
