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CV format auto-detection appears to stop in ADV7441A

Question asked by rpdm on Jul 6, 2017
Latest reply on Jul 13, 2017 by rpdm

Hi,

 

We have an application with an ADV7441A (yes, NRND) that was altered to allow auto-switching of input sources - where the ADV7441A chip would be cycled through HDMI, VGA, CV, YC inputs (changing VID_STD, etc. as it went) until a valid source was found.

 

This worked fine, but after a while (perhaps an hour or so) the HDMI & VGA would work fine but not the CV or YC.  Those would be decoded into perhaps a grey-scaler variant or would be sensed as 60Hz even though 50Hz PAL was fed in.

 

It's as if the standard detection logic inside the chip had halted.  Meaning that it's left in a random state for when CV or YC is next selected - and is thus decoded wrongly.  So PAL might get decoded as if it's PAL-60, so the syncs from the ADV7441A chip are running at 60Hz, even though the video content is obviously 50Hz.

 

The only way around this is to reset the chip (via the reset pin, or reset register - both work).  I've tried re-sending the I2C register values that normally work fine, but this does nothing - nor does a power-save down/up do anything.

 

It does seem as though the standard identification for CV/YC is failing - possibly as a result of the chip being constantly switched between multiple modes.

 

Is there any way to 'poke' the standard identification logic back into life - or do you think something else is going on?

 

Obviously, we have a fix (a reset), but I'd prefer to know what the cause might be.

 

Thanks,

Richard

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