Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: Clause 45: MDIO Electrical Specifications


As you correctly point out, the conclusion of the MDIO Electrical ad-hoc was to
recommend to IEEE P802.3ae that JEDEC JESD8-11 be adopted as the MDIO electrical
interface. This is what I reported at the opening IEEE P802.3ae Task Force
meeting in January and, as you point out, is recorded in the meeting minutes in
the General Presentations section
( - pages 15/16).

Please note however that this was a report of the recommendation of the Ad-Hoc
given at the start of the meeting. When the Clause 45 track met later in the
week to resolve comments, the track discussed the ad-hoc's recommendation in
relation to D2.0 comment #1115 and the conclusion of this discussion was a
decision to use electricals based on JEDEC JESD8-11. These electricals are a
1.2v instance of JEDEC JESD8-11 with some additional parameters.  This is
documented in the comment resolution database against comment #1115
( - Page 76) and was
also reported by Ben Brown in his Logic Track report at the close of the IEEE
P802.3ae Task Force meeting
( - Page 5).

In conclusion, while the ad-hoc made a recommendation, during comment resolution
this recommendation was modified and I am bound by the results on the comment
resolution process, which were approved by the Task Force, when preparing the
draft. You are therefore correct in saying that the changes that I made to the
draft do not match the report I gave of the Ad-hoc's recommendation at the start
of the meeting. This however is all part of the comment resolution process. Note
however, this is not to say that the work of the Ad-Hoc was ignored, it is the
basis of what appears in the draft today.

In relation to your new comment, I feel I have to put a 'proposed reject'
against it, citing comment #1115 from D2.0 - please don't take the reject
personally! I feel I have to do this as I believe that the current draft is
aligned to the consensus of the group. However, as with all comments, the actual
response will be discussed and decided at the upcoming meeting, in this case
during the Clause 45 track.

I do believe that the selection of a electrical specification for Clause 45 is a
most difficult task in particular in relation to selecting an approach that is
acceptable today, but will not become a burden to future implementations. I want
to thank you, and everybody else that has taken part in this, for the
contributions so far. As you will no doubt have noted there was another
suggestion for the Clause 45 electrical interface yesterday and I hope that now
there is wider interest we can all work together to come to a acceptable


"Jeff Porter (rgbn10)" <> on 01/03/2001 03:55:27

Sent by:  "Jeff Porter (rgbn10)" <>

To:   Edward Turner/GB/3Com@3Com
Subject:  Re: Clause 45: MDIO Electrical Specifications


I submitted a comment to D2.1 on this issue, included again at the bottom
of this note.  The comment is that D2.1 does not reflect the ad hoc
decision that was reported in Irvine, namely to adopt JEDEC JESD8-11
for MDC/MDIO. The suggested remedy is that we simply reference
JESD8-11 (, "Free Standards") as the MDIO interface.

For D2.2 (Friday?) and D3.0 (March meeting) I suggest leaving text as is,
"complete" in some sense, or accepting my comment and resetting to the
ad hoc recommendation and referencing JESD8-11 directly.  Additional
tweaks can wait for D3.0 comments.

FYI, my recollection of why JESD8-11 is proposed:

-- In earlier meetings, the consensus was that the Clause 22 electrical
   interface was no longer practical (voltages too high).

-- In earlier meetings, the consensus was that 10G did not want to
   spend energy defining new "logic families", that is, non-standard
   interfaces, for XGMII and MDIO, since there seem to be plenty of
   digital interface standards to reference. (We seem to be spending
   energy now). An ad hoc was formed to report a recommendation at Irvine.

-- Many comments were made that the new interface should last for
   many years, not just a solution for 10G only. (since MDIO
   may need to connect to phy's of different generations.  Changing
   addressing and electrical now, but not again for a long while
   since three generations of MDIO in one box is unthinkable.)

-- HSTL was repeatedly adopted/affirmed for XGMII interface.  As a practical
   matter, systems with XGMII interface will have a 1.5V supply available.
   No other P802.3ae interfaces infer a supply voltage.
   (OK, as a practical, practical matter, it seems that at least for 0.18um
   parts, the "HSTL" XGMII interface can be designed to be powered at
   either 1.5 or 1.8V, even though standard only says 1.5V.  In non-standard
   systems using 1.8V "HSTL", perhaps only 1.8V supply would be available,
   but then I would expect those systems to design MDIO to operate at
   either 1.5 or 1.8V, also outside standard.)

-- JESD8-11 provides two approaches for future proofing:

   ** If P802.3ae says nothing about "Normal Range" (Vdd 1.5+/- 0.1V)
      versus "Wide Range" (Vdd 0.9-1.6V), then every Clause 45 MDIO
      must support operation at interface Vdd=1.5V, insuring compatibility.
      Part vendors could choose to support wide range, and system
      implementers could select wide range parts, and operate the interface
      on any supply between 0.9 and 1.6V.

   ** If P802.3ae requires, in addition to JESD8-11, specifically
     "Wide Range" support, then compatibility is also assured, since every
      Clause 45 MDIO interface would operate with an interface supply between
      0.9 and 1.6V. (i.e. 1.5V+/-0.1V, down to 1.0V+/-0.1V).

-- XGMII spec came from JEDEC (JESD8-6), JESD8-11 was available and seemed to
   the consensus goals, it was proposed in ad hoc, and despite prodding from Ed,
   alternatives were proposed, recommendation (by default) was reported
   at Irvine.

From (unapproved) Irvine minutes, I only find:
"Mr. Turner gave a quick ad-hoc MDIO report. A number of individuals from both
802.3ae and 802.3af committees worked on the new electrical interface
specification and
they selected an interface with an expected long life. This interface will be
with lower voltage devices that emerge in the future. They recommended the JEDEC
standard JESD8-11 interface. The ad-hoc work is finished, Ed
these ad-hoc conclusions be added to the next version of the draft standard."

Do I think JESD8-11 is perfect "as is"?  No - while Normal Range
requires >2mA drive, Wide Range only requires an anemic 100uA (as does table in
Though 2.5MHz is slow, perhaps we should still say something about expected
desired range of edge rates, etc.  But I'm confident part vendors would make
guesses here.  For the standard, I'm just suggesting that we start back at
JESD8-11, and make any *needed* refinements as D3.0 comments.


Edward Turner wrote:
> Rick,
> I support your effort to bring forward these potential issues to the group at
> large.  I also encourage further reflector discussion if people feel there is
> something broken in the draft.  It is important that we make the correct
> decisions when these items come up for vote at the meeting.
> I was not sure if you were at the meeting and wanted to explain some of the
> background thinking that had gone on 'off the reflector' during the ad-hoc and
> at the Irvine meeting.
> I also encourage any of you who are attending the meeting and have points to
> raise on the MDIO electrical interface to come along to the Clause 45 sub
> so that we can hear your concerns when we discuss the electrical interface
> comments.
> Regards
> Ed

Clause: 45
Page: 45.222
Line: 15
CommentType: DISAPPROVE (Technical)
Resolution of Draft 2.0 Comment 1115 ""adopt[ed] an instance of the
JESD8-11 standard with a VDD of 1.2V""  JESD8-11 (, ""Free
Standards"") was selected by an apathetic ad-hoc.
However, JESD8-11 does not support 1.2v only operation.  The choices,
Normal and Wide range, are mentioned in the title of JESD8-11
2.2.1 Normal Range (1.4 to 1.6V Vdd)
2.2.2 Wide Range (0.9 to 1.6V Vdd)
In either case, the sending and receiving Vdd for this interface must
track within 0.1V (Note 1 in 2.3.1 and 2.3.2)
An MDC/MDIO implmenter could select to support either Normal or Wide
range since interoprability at 1.5V is maintained.  If all connected
parts in a system are wide range, a supply lower than 1.5V nominal
could be used.
When an XGMII (HSTL JESD8-6) is present, 1.5V will be available.
Change 45.4.1 to read
""The electrical characteristics of the MDIO interface are defined
in JESD8-11.  Pin input capacitance is limited to 10pF maximum.""
Retain NOTE, change to read ...""Vdd of 1.5V""
Delete Table 45-41.
Annex 45A, change 1.2V Vdd to 1.5V Vdd throughout.