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ADV7181C Letterbox detection issue

Question asked by dbolshakov on Apr 19, 2013
Latest reply on May 31, 2013 by dbolshakov

Hi!

 

We are using ADV7181c to receive CVBS analog video (PAL) in our system.

 

And we should implement some kind of aspect ratio detection with ADV7181c yet...

It's described in ADV7181C_Manual.pdf (document revision: Rev0, date: 07/2008) p.183 that the chip is suitable for letterbox detection.

But we've got an issue with this function.

 

The values received by reading LB_LCT and LB_LCB registers (0x9B and 0x9D) are always 0x00. So letterbox black lines are not detected.

But we use 16x9 wide screen PAL video for tests and see this black lines on TV screen...

 

I've tried to play with the Letterbox Threshold Control increasing and also decreasing threshold, but it didn't help.

I've also tried to change Letterbox Start Line / End Line (register 0xDD), but also without any effect... 

By the way, please, can you explain how LB_SL and LB_EL should be coded in case of PAL (what means 0100 = 23/286 NTSC etc) and what values are valid for PAL?

 

So, please, can you advice something to get this function working...

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