[time-nuts] Metastability (was Brooks Shera)

David davidwhess at gmail.com
Mon Mar 25 18:20:06 EDT 2013

On Mon, 25 Mar 2013 14:56:25 -0700, Hal Murray
<hmurray at megapathdsl.net> wrote:

>n1hac at alum.dartmouth.org said:
>> S/LS logic was introduced in the mid 70's, F/AS/ALS around 1980, HC was
>> early 80's.  By the third 7400 generation (F/AS/ALS) the problem was well
>> known with parameters available and the logic fairly hard to it.
>The problem is well understood in the right circles, but we wouldn't be 
>having this much of a discussion if it really was widely understood.
>The parameters are not readily available.  I've never seen them in data 
>sheets.  Sometimes you can find them in app-notes, but those are usually just 
>typicals.  I don't remember seeing any worst-case test results.  Peter Alfke 
>from Xilinx did a lot of good work in this area.

Besides the rare application note, I have seen metastability data in
ECL datasheets and in datasheets from other logic families when the
part was specifically described as hardened against metastability.

It would be fun to build a test fixture to characterize metastability
in some popular logic families from various manufacturers.  I lack the
right kind of oscilloscope to do it the easy way but maybe there is a
more sophisticated way.

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