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ADV7188 Free-running problems

Question asked by Eugene on Jan 5, 2011
Latest reply on Jul 8, 2013 by jansen

Hi

 

I've designed a board using a ADV7188, interfacing to a ADV7341 through an FPGA. The design generates a single PAL CVBS output.

 

The design is completely functional whereby I can succesfully select an input channel to sample, and successfully output the selected channel again. The problem is that I can't get the free-running mechanism (the default blue-screen) of the ADV7188 up and running.

 

When I start the board without a video source connected, the ADV7188 outputs HSYNCs at 60.3us intervals and VSYNCs at 53Hz. This does not relate to any NTSC or PAL standard. The ADV7341 does not recognise the format either. The LLC generated by the ADV7188 is a constant 26.9128 MHz.

 

When I start the board with a video source, and then remove the source, the ADV7188 generates PAL timing signals and the ADV7341 recognises the format. However, the video displayed is monochrome, and not blue as it should be.

The LLC generated by the ADV7188 is a constant 27.0102 MHz. If I manually change the subcarrier frequency registers of the ADV7341 to compensate for the LCC frequency, the blue color returns. This is however not an acceptible solution for my application.

 

Next, I enabled the SFL datastream between the ADV7188 and ADV7341. This did not resolve any of the two problems stated above.

 

For my application it is important that stable video is displayed if no input video is available.

 

I'll appreciate any suggestions to address my problems

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