XORing bits to eliminate skew

Sarad AV jtrjtrjtr2001 at yahoo.com
Fri Oct 18 06:37:14 PDT 2002

--- Sandy Harris <pashley at storm.ca> wrote:
> georgemw at speakeasy.net wrote:
> >BTW, if the bits are assumed to be independent of
> >each other and you're only concerned with
> eliminating skew,
> >there's a well known simple scheme to eliminate it
> >entirely:
> >
> >group the bits into pairs
> >if the pair is 00 or 11 toss it
> >if the pair is 01 map it to zero
> >if the pair is 10 map it to 1
> >
> >this method gets you a fourfold reduction
> >in the number of bits in the best case.
> >
> I read that Intel chipsets use something similar,

its given in rfc 1750

5.2.2 Using Transition Mappings to De-Skew

 Another technique, originally due to von Neumann [VON
NEUMANN], is to   examine a bit stream as a sequence
of non-overlapping pairs. You   could then discard any
00 or 11 pairs found, interpret 01 as a 0 and   10 as
a 1.  

Regards Sarath.

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