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Yet another lockup latch question

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mhdft

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I tried to find an answer to my question, but no threads seem to have the complete answer.
So, here is the question:

Assume that we have the following cases:
CLK1+ : Posedge CLK1 scan flop
CLK1- : Negedge CLK1 scan flop
CLK2+ : Posedge CLK2 scan flop
CLK2- : Negedge CLK2 scan flop

Which of the following scan chain connection cases requires a lock-up latch and why?

CLK1+ ---> CLK2+
CLK1+ ---> CLK2-
CLK1- ---> CLK2+
CLK1- ---> CLK2-

Thanks!
 

In test mode, all flops should be clocked by the same clock. Needing lockup or not depends if there is hold time between two flops.
 

Thanks for your response. Yes, CLK1 and CLK2 are irrelevant, I tried to show that there is considerable skew between these clock ports of these flops. The real question is + => - or - => + transitions.
I would think + => - should not need a lockup latch. How about - => + ?
 

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