need dft help - slow cells commands and capture masks

need dft help

how can we decide that for which cells we should use add slow cells command? from where we get dese cells?

how can we deicde that for which inputs we should use add capture masks???

Re: need dft help

Hi Badola,

You will put the add slow cells to those flops which are the startpoint s of "false path" and "multicycle paths". During STA you dont do an analysis for the false and the multicycle paths, so you will not want to use these paths for detecting faults. So you put a "add slow cell" on these flops , what this command does is that if there is any change on the Q pin of one of these flops and if that transition is able to reach some flop then it will be masked on the end point. If the transition gets gated at some place then it will be a valid transition.

For the "add capture masK", the only difference is that it is more pessimistic and at the end points of the false and multicycle paths. In case of "add slow cell" only when there is change on the Q pin of the flop and and that transition reaches a flip flop then the value captured is X , but for "add capture mask" if the clock is pulsed for then an X will be captured even if there is no change in the D pin.

There is another similar command you will like to see is "add slow path".

-cheers
vlsi_eda_guy