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adv7850/7842 vtotal measurement accuracy

Question asked by jps3 on May 25, 2014
Latest reply on Jun 12, 2014 by GuenterL



I was doing some debugging with our other products that use the 7842 & noticed that on a particular VGA resolution(1920x1200@60hz), the measured vtotal was not the same.


In this case the vtotal measured were as follows:


product 1(7842)           1235*

product 2(7842)           1245

(Current project)7850   1242


* correct/expected value


These values come from the cp map(LCF in 7850, SCF in 7842). On product 2, its off enough such that its mis-detected as 1600x1200


I was not expecting these values to be that far off from product to product.


So couple questions:

  1. Can you tell me what would cause these values to vary from product to product?
  2. could this be reasonable or expected based on part tolerances, pcb layout, etc?