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[802.3ae] RE: Clause 45: MDIO Electrical Specifications

 Edward Turner: 

I have a few questions concerning the MDIO Electrical Specifications.

The table in the PICS proforma section isn't all that explicit
on measurement conditions. As long as the measurements are taken by
humans we can quite easily understand the underlying meaning of the
specifications and overlook inconsistent current direction
specifications and trouble with inequalities and mins and maxes for
negative numbers etc., but there are a few aspects beyond that which are


Spec points: 

The best guess for a voltage to use for this measurement would be the
highest allowed VOL voltage 0.3V (EC2)

For push pull drivers, the corresponding choice for an IOH measurement
voltage would be the lowest allowed VOH voltage 1.0V (EC1)

For the option with open drain drivers and a resistive pull-up however
the same test condition would dictate a resistance that would overload a
driver trying to pull it low.

EC6 Bus Loading
interoperability but for ensuring a performance level of a collection of
units with MDIO interfaces joined with some network. Therefore I assume
it is not mandatory or even applicable to components.

EC5 Input capacitance for MDIO
The 10pF limit can be difficult to support both for MDC and for the MDIO
wire of MDIO in particular, given the wide variety the wide variety of
mechanical design and subassemblies possible, sometimes with several
devices connected to MDIO. 

 I would appreciate some comments and guidance on how to interpret the


Best regards Tord Haulin

	-----Original Message----- 
	From: Edward Turner 
	Sent: Thu 3/1/2001 4:23 PM 
	To: stds-802-3-hssg@xxxxxxxx 
	Subject: 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
	( -
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
	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


	"Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx> on 01/03/2001

	Sent by:  "Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx> 

	To:   Edward Turner/GB/3Com@3Com 
	cc:   stds-802-3-hssg@xxxxxxxx 
	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
	decision that was reported in Irvine, namely to adopt JEDEC
	for MDC/MDIO. The suggested remedy is that we simply reference 
	JESD8-11 (, "Free Standards") as the MDIO

	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.
	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
	   interface was no longer practical (voltages too high). 

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

	-- Many comments were made that the new interface should last
	   many years, not just a solution for 10G only. (since MDIO 
	   may need to connect to phy's of different generations.
	   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
	   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
	   systems using 1.8V "HSTL", perhaps only 1.8V supply would be
	   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+/-
	      versus "Wide Range" (Vdd 0.9-1.6V), then every Clause 45
	      must support operation at interface Vdd=1.5V, insuring
	      Part vendors could choose to support wide range, and
	      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,
	     "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
	   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
	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
	JESD8-11 standard with a VDD of 1.2V""  JESD8-11 (,
	Standards"") was selected by an apathetic ad-hoc. 
	However, JESD8-11 does not support 1.2v only operation.  The
	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
	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
	range since interoprability at 1.5V is maintained.  If all
	parts in a system are wide range, a supply lower than 1.5V
	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
	in JESD8-11.  Pin input capacitance is limited to 10pF
	Retain NOTE, change to read ...""Vdd of 1.5V"" 
	Delete Table 45-41. 
	Annex 45A, change 1.2V Vdd to 1.5V Vdd throughout.