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ADV7842 Digital Clamp on digital sources

Question asked by Elastino on Nov 20, 2011
Latest reply on Dec 9, 2011 by mattp

This is a useful note for public sharing. (UNOFFICIAL;User Provided Information)

 

Symptom :

Clamping error with digital sources

unexpected clamping effect on digital sources

A screencapture is attached.

 

Causes :

1. Digital fine clamp is enabled by default script.

2. With following conditions, clamping will affect unexpectedly.

   non-standard timing such as wider positive tri-level in digital source. (in case of 1080/60i from DVI)

   non-standard pedestal such as filled with 0 or 255 during blanking period

 

Workaround :

Disable digital fine clamping by set 0x6C[4] = 0 in CP block.

 

See also:

ADV7842 UG-214 Hardware User Guide 10.2 CLAMP OPERATION

 

Note:

Normally, digital fine clamp has no effect on digital sources such as DVI or HDMI, since these signals come with stable digital pedestal.

In Hardware User Guide, there is NO speicific information regarding bit4 of 0x6C, which should be explained by Analog Devices.

 

Applys to :

ADV7842 (CP 0x6C)

ADV7611 (CP 0x??)

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