Hi, I will input a differential clock to DCM, how should I set contraints? Should I set constraint on IBUFGDS input or should I set constraint on its output? And should I set constraints on DCM outputs? Thanks.
Normally for pin-to-pin constraints you just use the positive pin of the differential input and the constraints otherwise work as they would for a single-ended clock. If you put constraints on a DCM input or on the input pin that feeds the DCM, you shouldn't need constraints on the output of the DCM as well. In fact often constraints on the outputs of DCM's are ignored in this case, because the timing analyzer uses the input constraints that were "pushed through" the DCM instead.
HTH, Gabor
thanks.
"Gabor =D0=B4=B5=C0=A3=BA "
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