Re: VXS & Signal Distribution

[Gerard Visser <gvisser@indiana.edu>]

Hall D Electronics:

Hi Ben,
	I agreee, it can't possibly be 22 ns! I don't know what document this 
is from, but it is probably RapidIO specific. That's not really 
applicable here. I would certainly hope/expect that the skew and maybe 
even propagation delays are specified in ANSI/VITA 41.0-2006, the base 
physical specification for VXS. I don't have that standard (yet). I hope 
you guys do - can you take a look at what it says. (Don't send out the 
whole standard document, that's probably a violation of its copyright 
terms, I should spend the $25 to buy it. But if you see a skew 
specification, I presume you could just restate it in an email, will be 
helpful for the meeting tomorrow.)
	Thanks,

	Gerard

Benjamin Raydo wrote:
> Gerard/Ed,
> 
> The attached image may be of use for tomorrow's discussion (this is the skew
> spec referenced by VITA 41.2/VXS). Doesn't say much other than that we must
> manually measure pair-to-pair skew on each slot of the backplan if we are to
> guarentee a setup relationship between trigger and clock. I think the large
> pair->pair skew (22ns max) in the spec comes from fiber links that
> eventually get translatted into VXS copper pairs (I don't see how such a
> large skew can develop on our "small" 20 slot backplane alone).
> 
> Have fun,
> Ben