Re: Two stage synchroniser,how does it work?

No. A "metastable" Q output from the first stage does not refer to a
"wrong" output value, such as it being a "1" when it should be a "0",
but
about the Q output getting stuck half-way or oscillating for a while,
which can happen if its D input was in transition when it was clocked.
If
that metastable Q output was fed to, for example, an incremental
counter,
then that counter could do something worse than incrementing or not
incrementing -- like making a big jump to a completely different value
because its own setup time was violated. *That* is why metastable
states
are considered so nasty.

Adding a second d-type with a short propagation delay from the first
means that there's a whole clock cycle for the first stage to come out
of
metastability and give a good setup time for the second D-type, so that
*its* Q output is either a secure 0 or 1 but not something between the
two. Thus it becomes a negligible source of error compared to a
system's
overall reliability. Understand now?

unfortunatley it is not convincing. it is ok for a discussion of
Metsatability per se but not data transfer.

the above argument states clearly that first Q output is not copy of D
input but is unstable halfway. So is the input to second flop. Now lets
look at value rather than stability at second Q output, stable yes but
correct who knows...

Sorry for being so microanatomical but history has other examples when
consensus doesn't fit reality

kadhiem


.

Relevant Pages

  • Re: Quantum Leap
    ... so one cannot say that an actual transition takes place. ... so some approximation to it must be used. ... is no "jump", just a continuous evolution. ... already brought up: Rabi oscillations. ...
    (sci.physics.research)
  • Re: Slow preload of source clip when render a Timeline
    ... > When i render my timeline I can see that the preload of media source ... > transition jump when this load occur. ...
    (microsoft.public.win32.programmer.directx.video)
  • Screen jumps when going from form to form
    ... or unloading seems to jump. ... The transition from one form to another is not ... DoCmd.OpenForm stDocName,,, stLinkCriteria ... The same jumping happens if I tab through controls on a form. ...
    (microsoft.public.access.formscoding)
  • Re: Traveller and jump drive malfunction
    ... it is possible that the protective bubble is ... there to stay and the jump drive is no longer strictly necessary once ... Transition is almost instantaneous and must be carefully controlled, for the entire fate of the voyage is determined at the critical transition instant... ... nothing the crew can do (short of destroying the ship) will prevent it from emerging at the point in space specified by the precomputed jump vector." ...
    (rec.games.frp.gurps)