RE: XAUI AC coupling
I also agree that XAUI has chip to chip or internal to a box applications
where AC coupling would not be required and the decision should be left to
the designer. AC-coupling should not be a requirement.
Sharam Hakimi
> Hi Rich,
>
> I wholeheartedly agree. AC-coupling should be ALLOWED, but
> not REQUIRED. It is required in 1000Base-CX because the signals
> leave the box and are subject to alternate ground domains.
>
> -Ed Grivna
>
>
> > All,
> >
> > I'd like to propose that clause 49, XAUI, remove any requirement for
> > coupling, AC or DC. The basis of this proposal is as follows:
> >
> > 1) XAUI is a chip-to-chip interconnect. As such, DC-coupling is clearly
> > appropriate and advantageous from an implementation perspective, an
> > example is when interfacing chips from like logic families utilizing the
> > same power supplies. This is likely to be the case in many
> > implementations. Therefore, the standard should not dictate AC-coupling
> > when DC-coupling is adequate to achieve interoperability.
> >
> > 2) I've reviewed all instances of the use "coupling" including fuzzy
> > variants in the 802.3 standard. There is no precedent for dictating a
> > specific coupling method for a chip-to-chip interconnect in the
> > standard.
> >
> > 3) Absolutely nothing will be taken away from the standard by removing a
> > requirement for AC-coupling. If AC-coupling is either desired when not
> > required or required for a specific implementation, then the details for
> > AC-coupling including the determination of specific capacitor values,
> > the frequency spectrum of 8B/10B transmission code, etc. are all well
> > documented and readily available. 8B/10B transmission code is far and
> > away the most commonly used and well understood code in serial gigabit
> > links including chip-to-chip interconnects. From a signal coupling
> > perspective, except for proportionally higher signaling frequency, there
> > is no difference between a single XAUI lane and a 1000BASE-X link. Note
> > that for 1000BASE-X, both AC and DC coupling is available from
> > transceiver module vendors.
> >
> > AC coupling was proposed as a requirement for the Hari interface which
> > was effectively renamed as XAUI. It has been carried into the baseline
> > proposals for P802.3ae. Now is the time to decide whether AC-coupling is
> > an interoperability REQUIREMENT. I challenge anyone to argue and prove
> > that AC-coupling is required for XAUI interoperability. If such proof is
> > not forthcoming, clause 49 should be modified to remove any requirement
> > for AC-coupling.
> >
> > --
> >
> > Best Regards,
> > Rich
> >
> > -------------------------------------------------------
> > 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@nSerial.com
> > Santa Clara, CA 95054 http://www.nSerial.com
>