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ADV7341 DAC - Setting levels for S Video

Question asked by DunbarB on Sep 24, 2013
Latest reply on Sep 26, 2013 by GuenterL

Hi, I'm using ADV7341.

Basic problem is I can't get levels correct for LumaChroma outputs in SVideo mode.

 

I have 525 YCbCr input with TRS timing method, and am wanting CVBS - Luma - Chroma on DAC1,2,3 outputs respectively.

I also want the CVBS and Luma output to have no pedestal, and be 714 mV full range for white-blanking.

I started with your Table 65 script in the datasheet, but modified it a bit like so:

Addr/Data writes follow:

1702 - same as yours

00FC - same

0100 -same

0210 - put out YPrPb instead of RGB

8010 - same

82C3 - change so we can get Luma on DAC2 and Chroma on DAC3

8810 - same

 

So in this setup my composite looks pretty good, but Luma and chroma need 'just a bit' of adjustment, they are within about 2% of where they need to be:

Luma is 980 mV, should be 1000.  Chroma is 890 mV, should be 903.

 

I write a 01 to reg87, which allows scaling control of 'Luma and Color Scale' according to datasheet.

I write a 82 to reg9D, and I can successfully get my Luma output levels where they should be.

But when I write gain values to reg9E, I can change Chroma levels but can't get them to where they need to be. 

The chroma levels seem to saturate at about 650 mV p-p...

They were higher than this before I wrote reg87

What am I missing?

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