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Re: 64/66 system benifits and ad-hoc agenda

Dear Kamran,

> is the 64b/66b a proposal for line code in serial link, or could be a
> replacement of 8b/10b also in the Hari interface?  It seems like the
> 8b/10b code is well accepted as the right choice for Hari.  Is this
> still flexible or set in stone (because many companies have already
> started designing their high-speed I/O)? 

The 64b/66b code is motivated by the relative difficulty of pushing
existing lasers system to run at 12.5 Gbaud vs 10.3 Gbaud.  At the
higher speeds we have difficult technical challenges in many areas such
as skin loss, dielectric loss, laser relaxation-oscillation time
constants, etc. 

The 8b/10b code has a 25% overhead rather than the 3.125% of the
64b/66b, but in return has better control over transition density and
disparity.  At speeds below ~5 Gb/s the overhead of the 8b/10b code can
be ignored with little practical consequence. 

Although a code like 64b/66b could be substituted for the 4x 2.5Gb/s
HARI links, there is little incentive because the 3.125 Gbaud
transmission of 8b/10b is easily supported both by CMOS and by the FR-4
PCB infrastructure. 

Best regards,
Rick Walker