if it so ,how much the maximum clock rate?
DDR mode doesn't change the overall performance of the part-- DDR mode maximum would be half the SDR mode maximum. It's really no different than SDR mode-- just half the pixel clock rate since you are getting pixels on each edge instead of every other edge.
I would not recommend you use DDR modes, they are not widely used or tested in comparison to SDR modes. This is especially true on an older part like ADV7441A.
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