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RE: XGMII electricals -> MDIO electricals

If we change anything on MDIO electricals, lets do it right.  The current
voltage levels and speed cover three decades of MAC speed (10, 100 and
1000Mb/s).  If we change them, I believe we need to look forward to
something that will at a minimum be friendly for the next decade of speed.
I think a change to both the frequency and voltage levels is appropriate.

--Bob Grow

-----Original Message-----
From: Devendra Tripathi [mailto:tripathi@xxxxxxxxxxx]
Sent: Friday, November 03, 2000 9:54 AM
To: Edward Turner; 'stds-802-3-hssg@xxxxxxxx'
Subject: Re: XGMII electricals -> MDIO electricals

I would retain the current MDC/MDIO electrical specification. Timing wise, 
the clock
frequency could be multiplied by a factor of 10.


At 01:48 PM 11/3/00 +0000, Edward Turner wrote:

>I'd like to pick up your last point : "...what about MDC/MDIO levels?".
>For D1.1 I inserted an editors note under an "Electrical interface" 
>section as a
>place holder for an interface to be approved by the Task Force.  At the
>meeting I intend to propose that we just adopt the logic family that the
>uses (we might have to put a note in about termination schemes as the MDIO
>If anyone has any specific concerns with this I encourage them to voice 
>them and
>bring bring forward an alternative proposal to the meeting.
>"Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx> on 02/11/2000 22:18:44
>Sent by:  "Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx>
>cc:   "'stds-802-3-hssg'" <stds-802-3-hssg@xxxxxxxx> (Edward
>       Turner/GB/3Com)
>Subject:  Re: XGMII electricals
>In an effort to get us all on the same page, here are links to
>the standard XGMII interface proposals, SSTL-2 and HSTL Class 1
>on the JEDEC site under "Free Standards":
>HSTL Class 1
>SSTL_2 Class 1 (per page 9,
>First, I also discourage the development of a new 1.8V interface definition
>for XGMII for many of the reasons already on the reflector.
>I regret not making a larger issue in New Orleans about the fact
>that HSTL is a 1.5V specification.  I thought there was consensus on
>the idea of saving power by going to HSTL, and was (too) willing to
>go along with voting on HSTL and 1.8V at the same time based on
>claims that there was another standard out there, and assuming that
>lacking a standard, we would still go to real (1.5V) HSTL.
>The very valid point has been made that interface variations outside
>of the IEEE standard often become popular, and that may also
>become true with XGMII.  So the question is where the standard
>should point, what guidance should we give implementers?  Since HSTL is
>available, standardized, and lower power, this makes a better *standard*
>interface than SSTL_2 (similar attributes, but higher power).
>That is, guide implementers toward a lower power solution.
>It has been stated that 2.5V SSTL_2 interfaces are implemented on
>early XGMII interfaces.  There was discussion at New Orleans that at
>least some of these interfaces also work down to 1.8V. Even if we select
>(i.e. 1.5V), as a practical matter, many 0.18um HSTL interfaces may also
>up to 1.8V, which may be more convenient in systems at first than a 1.5V 
>If XGMII lives long enough for some reason, the market might go to even
>"1.5V tolerant" interface (e.g. 0.9-1.6V range specified in jesd8-11.pdf,
>October 2000, but with 50 ohm drive level).
>Perhaps a bigger question is, what about MDC/MDIO levels?
>"Grow, Bob" wrote:
> >
> > Implementing the XGMII concensus of the Task Force expressed through
> > polls in New Orleans is a problem. In fact, I would characterize the 
> actions
> > we took in New Orleans to be an example of group think gone wild.  We
had a
> > comprehensive SSTL specification in the draft, but made the straw poll 
> votes
> > to change on concepts, not proposed specifications.
> >
> > There is no standard for HSTL at 1.8 volts (the preferred voltage per
> > poll), nor did the TF select any other parameters of the electrical
> > specifications.  (Class I, 1.5 volt  HSTL as specified in EIA/JESD8-6 
> is the
> > closest standardized alternative that the team working on clause 46
> > find).  Because we couldn't find a standard to reference and the Task
> > didn't endorse a complete set of 1.8 volt specifications, there was no
> > an HSTL electrical specification could be inserted into the draft
> > adding a lot of technical material that hadn't been endorsed by the
> > committee.  Therefore, all you will find in Draft 1.1 on HSTL is an 
> editor's
> > note describing the situation.
> >
> > Most discussion supports the idea that the XGMII electrical interface 
> is for
> > near term usage (with continued use as an module to module logic
> > within a chip). Implemeters expect the electrical interface to be
> > by I/O devices in quick turn silicon libraries.  Some participants in
> > editorial session thought ASIC vendors might have a 1.8 volt HSTL
> > from the above referenced specification, but weren't sure of any vendors
> > supporting it (for inclusion in the standard it should be supported by
> > vendors).
> >
> > We have a similar problem with the clock alignment were the straw poll
> > endorsed a change without any specifications to implement the change
> > skew specifications).
> >
> > As it now stands, I would vote against going to Task Force ballot.  It 
> would
> > be a shame for TF ballot to be delayed because of the absence of XGMII
> > electricals.  I see three alternatives that would allow us to go forward
> > TF ballot.
> >
> > 1.  Return to the SSTL specifications of Draft 1.0
> > 2.  Reference HSTL at 1.5 volts per EIA/JESD8-6 and select from the
> > within that specification.
> > 3.  Someone presents a detailed proposal including all appropriate
> > specifications (timing, thresholds, AC and DC characteristics,
> > etc.)
> >
> > As the clause editor, I will be proposing alternative 1 in Tampa unless
> > participants come through with presentations (sufficiently detailed to 
> go to
> > TF ballot), and the Task Force endorses the specifications presented.
> >
> > Bob Grow
> > Editor Clause 46

Best Regards,

Devendra Tripathi
Vitesse Semoconductor Corporation
3100 De La Cruz Boulevard
Santa Clara, CA  95054
Phone: (408) 986-4380 Ext 103
Fax:	(408) 986-6050