Well, I have not studied the structure of FFs enough to say one way or another whether I agree with your statement on the basis of structure. I will continue to think about that one. However, the following overview of metastability clearly shows it persisting for multiple clock events on a single FF (of course, this COULD be an error by the author): http://www.cs.gmu.edu/cne/pjd/PUBS/CACMcols/cacmNov07.pdf Moreover, a bigger reason why I am skeptical of your assertion is that it implies that it should be possible to make a totally metastable-free synchronizer as long as I make it have a delay of three clock cycles (i.e., give the input FF two clock cycles to stabilize and then latch its output). While 3 or even 2 stage synchronizers can make the probability of metastability very small, every solid source I've seen says that it is impossible to eliminate it totally. Sean On Fri, Jul 1, 2011 at 11:29 AM, Dave Tweed wrote: > Sean Breheny wrote: >> Well, first, metastable states can last for more than one clock cycle. > > No. If you look at the structure of any practical latch or master-slave > flip-flop, a new enable pulse or clock edge erases any previous state, > including metastable. > >> There is no absolute limit to the duration of the metastable state. > > That's true, in the absence of any more clock edges. > > -- Dave Tweed > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .