[SI-LIST] Re: Ring back

  • From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 23 May 2006 10:16:55 -0700

Andy,

A disclaimer first:  The following comments are my private opinion
which is not an official representation of Intel's position on this
subject in any way.

1)  As far as I know, most IEEE specifications are only available for
money to non IEEE members, and I checked, this one goes for $ 79.00:
http://webstore.ansi.org/ansidocstore/product.asp?sku=3DIEEE+181-2003

As far as I know, a fairly high percentage of the employees of non
academic institutions are not IEEE members.  For whatever reasons,
I would most likely not get reimbursed by my employer if I wanted
to purchase one, and I am not inclined to pay for it out of my own
pocket.  If IEEE wants to be useful to the engineering community in
general, they should make such documents available free of charge.

2)  I find it equally odd that more important documents, such as the
VHDL-AMS language reference manual is only available for money.  What
do you think software engineers would say if the C++ (or any other)
language definitions would not be freely available on Microsoft's
support pages?

3)  The IEEE definition for undershoot itself is a little gray to me.
Quoting from Art Porter's posting:

"3.1.49 undershoot: A waveform aberration within a post-transition
aberration region or pre-transition aberration region that is less
than the lower state boundary for the associated state level."

What does "lower state boundary" stand for?  I don't think it means
the nominal low voltage level of the signal, such as 0 V in a normal
5 V CMOS environment, because that would seem to be the "associated
state level".  Then does it refer to the lowest allowable voltage
below the GND supply rail, such as -2 V?  Hmmm, could someone shed
some light on this for me please?

Also, what does "...less than the..." mean?  In the above case,
when the logic low is 0 V, does less than mean the negative voltage
values (below 0 V), or the positive voltage values (above 0 V) due
to the transition not having reached its target, i.e. an amplitude=20
that is less than its desired value?

4)  I don't think I can or should defend Intel, but I find your
anger against Intel as a company for "perpetuat[ing] confusion
and misunderstanding" a little too much.  For one, "Intel", whoever
it is, does not tell its employees to do this deliberately, it just
happens.  It could, or does happen at other companies too.  Not
because they want to generate confusion, but simply because most
of the engineers use a vocabulary that they are familiar with.  May
I suggest that perhaps educational institutions should take a bigger
responsibility in promoting a "standard" vocabulary, and proper
spelling?  I can't hold myself back to not mention one of my pet
peeves, the incorrect spelling of units, such as "nS" which is
meant to indicate nano-seconds, yet it means nano-Siemens, a unit
of conductance, not time...

This is not to say that agree with the incorrect usage of the
terms overshoot and/or undershoot by my colleagues at Intel and/or
any other company, whatever the correct usage is.  (Of course the
correct way is my own interpretation, which I will keep a secret
for now).  :-)

5)  I also have a problem with the terms "positive overshoot" or
"negative overshoot" because they do not specify whether they
refer to the direction of the transition, or the voltage values
of the waveform.  In today's low voltage signaling I can imagine
a waveform that has only positive voltage values, yet it has
overshoot on both rising and falling edges, i.e. the waveform
goes over its target value in either direction.  Would the
undershoot(?) after the falling edge then be called "negative
overshoot" even if the waveform will never have negative voltage
values?  Or better yet, what about ECL where the waveforms are
always in the negative voltage range?

6)  I agree this subject is a very confusing one, because there
are supporting arguments for either usage of these words.  I would
suggest that instead of blaming a certain company for doing wrong
we should collectively come up with the best terminology and figure
out how to promote it the best way.  I must warn you though, it will
take some time to get the new terminology accepted universally.
As they say, old habits die hard.

Sincerely,

Arpad Muranyi
Intel Corporation
------------------------------------------------------------------

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Andrew Ingraham
Sent: Tuesday, May 23, 2006 6:54 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Ring back

> In Intel FSB specs ...
...
> I first hit this several years ago doing slot 2 designs and it's =
always
> been counter-intuitive to me - I would prefer the terms "positive
> overshoot" and "negative overshoot" instead of "overshoot" and
> "undershoot".  But, there was too much momentum behind the existing
> terminology to change it.  So, I've adapted my terminology =
accordingly.

Indeed, Intel was the large semiconductor company I referred to earlier,
that consistently uses 'undershoot' incorrectly.

> To me, the bottom line is that these terms, like many in our =
discipline,
> are merely conventions, and ambiguous ones at that.

Not necessarily.  The IEEE, at the least, has actual definitions for
overshoot and undershoot.  Intel chooses to ignore IEEE's definitions =
and
use undershoot to describe overshoot.  Which has helped a whole =
generation
of engineers to use those words incorrectly and perpetuate confusion and
misunderstanding.

>  It's best to very
> carefully spell out exactly what we mean when using these terms (which
> this spec does).

Yes, but it would be better to also use them correctly.

I'm sure we all use the wrong terms sometimes.  I don't carry an IEEE
dictionary and I know I am frequently wrong.  I just get annoyed by =
Intel's
misuse of 'undershoot' because the error is so glaring, being so =
frequently
used and exactly opposite to its correct meaning.

(Climbing off my soapbox now...)
...
...
...

Regards,
Andy
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: