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ADV7180 > ADV7171 Fails to produce PAL ColorBars in Free-Run

Question asked by VACBrick on Feb 22, 2012
Latest reply on Mar 5, 2012 by DaveD

System block involves the ADV7180 feeding an ADV7171 producing composite output. When the ADV7180 is in free-run (no PAL input signal) the result is the ADV7171 does not produce Color Bars with color. If a PAL signal is applied to the input of the ADV7180 as a reference, the 27MHz clock "trues up" and color is produced. I should also mention that the ADV7171 is in master mode. This is best duplicated on an analog TV, as LCD or any other device that does AtoD sampling has enough slop and/or processing to allow it to work, or it would appear so. The ADV7171 is NOT the problem as a clean 27MHz clock input has no issue generating the PAL Color Bars. ADV7180 has been configured as both NTSC and PAL in free run yet the clock is not exactly 27MHz.. NTSC did appear to be a bit tighter, but 27.0123MHz is far enough off that the color is gone.

 

This ties into a second issue we have seen whereby no blue screen output is available from the ADV7180 after a power on reset sequence until any selected input has received a taste of active video signal. This does not appear to be an issue of the reset sequence be it hardware or I2C. So the September 21 thread/posting does not apply.

 

Dave

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