Re: XAUI AC coupling
All,
By my count, I have 4 votes for allowing XAUI DC-coupling against 0
votes for requiring only AC-coupling. The 4 votes are:
Ed Grivna - Cypress
Dawson Kesling - Intel
Jeff Porter - Motorola
Rich Taborek - nSerial
Any other opinions out there?
Best Regards,
Rich
--
"Jeff Porter (rgbn10)" wrote:
>
> Folks,
>
> I feel consensus emerging here.
>
> Rich writes
>
> > a) A XAUI implementer can always get away with AC-coupling and
> > AC-coupling details for XAUI are readily available;"
>
> and
>
> > That said, I'd be happy to go with (1) or (2).
>
> Dawson writes
>
> > An alternative is to mandate CAPABILITY for AC coupling. This allows DC
> > coupling where compatible implementations permit, but ensures that ALL
> > implemenations will interoperate via AC coupling.
>
> I agree. Specify the differential signal. Require the receiver
> to function *when* driven by ac coupled signals to provide a method
> that insures interoperability. After all, we've increased baud rate, among
> other reasons, to permit ac coupling as an approach to interoperability.
> Do not require ac coupling since dc coupling will often work, and we've
> left a way to interoperate.
>
> The remaining technical work is to include in an (informative) XAUI link
> budget (if we choose to explain how this could work) the attenuation,
> skew, and jitter, etc. budgeted for ac coupling.
>
> Proposals and justification for this budget item?
>
> Jeff
>
> Rich Taborek wrote:
> >
> > Dawson,
> >
> > In terms of specsmanship, I believe that we have two alternatives with
> > regard to coupling for XAUI:
> >
> > 1) Leave coupling out altogether as an implementation detail;
> > 2) Specify detail for both AC-coupling and DC-coupling.
> >
> > It sound like you're leaning towards (2) where I'm leaning towards (1).
> > My argument is that (2) is a whole heck of a lot more work than (1) and
> > may be more costly since compliance verification has some non zero cost.
> > I believe that (1) works and is interoperable because:
> >
> > a) A XAUI implementer can always get away with AC-coupling and
> > AC-coupling details for XAUI are readily available;
> > b) A savvy XAUI implementer may save $$$, increase reliability (fewer
> > components), increase signal fidelity (fewer vias), etc. by going with
> > DC-coupling if possible given their component selection.
> >
> > The only other possibilities are not palatable to me:
> >
> > 3) Mandate AC-coupling;
> > 4) Mandate DC-coupling.
> >
> > That said, I'd be happy to go with (1) or (2).
> >
> > Best Regards,
> > Rich
> >
> > --
> >
> > "Kesling, Dawson W" wrote:
> > >
> > > Rich and all,
> > >
> > > I agree that it would be nice to avoid AC coupling if we can still ensure
> > > interoperability.
> > >
> > > If we remove reference to coupling altogether, we must add a common mode
> > > specification or definite logic levels; we cannot only specify peak-to-peak
> > > swing as we are now doing and expect interoperability. (All chip-to-chip
> > > interconnect spec's I know of specify either DC-referenced logic levels or
> > > common mode and differential mode levels. Is there an exception? We have
> > > avoided this by mandating AC coupling up to this time.)
> > >
> > > An alternative is to mandate CAPABILITY for AC coupling. This allows DC
> > > coupling where compatible implementations permit, but ensures that ALL
> > > implemenations will interoperate via AC coupling.
> > >
> > > -Dawson Kesling
> > > Intel Corporation, NCD
> > > 916 855-5000 ext. 1273
> >
> > -------------------------------------------------------
> > Richard Taborek Sr. Phone: 408-845-6102
> > Chief Technology Officer Cell: 408-832-3957
> > nSerial Corporation Fax: 408-845-6114
> > 2500-5 Augustine Dr. mailto:rtaborek@xxxxxxxxxxx
> > Santa Clara, CA 95054 http://www.nSerial.com
-------------------------------------------------------
Richard Taborek Sr. Phone: 408-845-6102
Chief Technology Officer Cell: 408-832-3957
nSerial Corporation Fax: 408-845-6114
2500-5 Augustine Dr. mailto:rtaborek@xxxxxxxxxxx
Santa Clara, CA 95054 http://www.nSerial.com