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ADV7842 and VBI

Question asked by JeffMcD on May 26, 2011
Latest reply on Jun 1, 2011 by JeffMcD

Maybe I don't understand what VBI is all about, but I'm struggling to understand the following issue.

 

Using the ADV7842-ADV7511 Eval kit, start with editing ADV7842-VER.5.9c.txt, and copy script 5-8b. Paste it and change the name so you can find it. In the new script delete the 3 lines below:

 

44 A5 45 ; NOM START VBI
44 A6 50 ; NOM START VBI (part) NOM END VBI (part)
44 A7 1D ; NOM END VBI

 

Save the file.

 

Now connect a 1920 x 1080 x 60 reduced blanking input with an image that has one or more horizontal lines.

Run the original 5-8b script. Use a piece of tape or whatever to mark the location on the monitor of one of the horizontal lines.

Now run the version of the script that has the 3 lines removed. Notice that the image has shifted down by about 6 lines.

 

As I understand it, the VBI regs are used to define the vertical blanking interval. I don't understand why removing the three lines above moves the image.

 

Also note that manually changing the registers (using AVES) to the values of the 3 lines does not move the image up 6 lines.

 

What am I missing?

 

 

Thanks in advance,

 

Jeff

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