Subject: RE: True or False?

From: "Muranyi, Arpad" <[email-masked]>
Date: Fri, 9 Oct 1998 15:17:00 -0700

Chris,

I don't know what it feels like to be an attorney, because I have never been

one.  I wonder about the same question...

Regarding A) The device has a differential input, so I DO HAVE TO use the
             [Diff Pin] keyword.  The die has a direct connection between
the
             pads which do the loopback, so I must have a way to describe
the
             series properties of those connections.  The only model type
that
             is allowed in the IBIS spec with the series models is the
             "non-sensing" Terminator model type.  Do you have a suggestion
for
             how to model this other than the way I did it?  I am willing to
             make changes if it makes sense...

Regarding B) I have to make a model now, since the customer wants to use it
             immediately.  Even though I would prefer this, I can't wait for
a
             new IBIS spec version.

I don't see why my model is "debatebly" legal because nothing I did in it is

illegal according to the spec.  The model makes sense if you think about
what it
describes and not about what the comments in the spec say regarding what the

Terminator models could be used for.

So we have a choice of fixing the spec, make legal (but "senseless"?
models), or
not have any models.  Which one would you choose when the customer wants to 
simulate and is pounding on the door for models?

Remember, this is an existing device and we should both be interested in
finding
a way to model it.

Arpad
============================================================================
====

Arpad,

I wonder if this is what it feels like to be an attourney?...

> In my opinion then, it would be perfectly legal (even if it makes no
sense) 
> to have two pins in the pin list defined as "NC" while defining them as
> differential pairs in the [Diff Pin] section.

"EVEN IT MAKES NO SENSE" -- Abusing the spec in a insensible manner 
promotes confusion and indicates that the spec should be revised to 
either:

      A) eliminate the insensible use

          - don't use [Diff Pin] to assign a vdiff to a pair
            of "non-sensing" (excuse the pun) terminators.

      B) make the use sensible

          - Allow [Series Mapping] to be applied to a receiver
            as well as a terminator.

I don't think you should release a model that makes no sense even if 
it's debatably "legal."

Chris

Muranyi, Arpad wrote:
>
> Chris,
>
> Thanks for the clarification.  I reread the section you pointed out to me
> (several more times) and I believe I am starting to understand the
problem. 
>
> It seems to me that the problem is not that I am using the series model 
> together
> with a terminator model, but that these were "coupled" as a differential 
> pair.
>
> You made a statement that "the Diff Pins had to be NON-terminators" (I
guess 
>
> Input, I/O, etc...).  Looking at the [Diff Pin] section of the spec, 
> however, I
> could not find anything that suggests that differential pins had to be a 
> certain
> type of a model.  Also, I don't see anything in the [Diff Pin] section
that 
> calls a [Model](s) for the pins it defines as differential.  The [Model]
> keywords are still referenced only by the pin list section (some times 
> through
> the [Model Selector] keyword) even if we have a [Diff Pin] definition for 
> them.
> In my opinion then, it would be perfectly legal (even if it makes no
sense) 
> to
> have two pins in the pin list defined as "NC" while defining them as
> differential pairs in the [Diff Pin] section.  If this is legal then
calling 
>
> Terminator type models in the pin list and defining them as differential 
> pairs
> should also be legal.
>
> Using this argument I would summarize that the model we made is NOT 
> violating
> the spec. because
>
> 1)  The pin list calls a model that is type Terminator 
> 2)  Terminator model types are legal with Series models
> 3)  Applying the [Diff Pin] keyword does not change the model type 
>     already defined on the pin list to anything else
> 3)  Applying the [Diff Pin] keyword does not add models of any type 
>     to the models already defined on the pin list
> 4)  There are no restrictions for what model types can be associated 
>     as differential pair in the [Diff Pin] section
>
> Please let me know whether this argument is acceptable or not. 
>
> Sincerely,
>
> Arpad
>

---

From: Chris Rokusek <[email-masked]>
Date: Fri, 09 Oct 1998 18:29:12 -0700

Arpad,

Since you must have the [Series Map] to connect IN to OUT and therefore
must have terminators on those pins to stay "legal" for the time being,
I urge for you to leave out the [Diff Pin] relationship and rely on
another device within the board to associate the nets since you can't
legally put an actual sensing receiver at the series pin locations
anyway.

As a temporary solution, this method would result in the proper
connectivity for our customers...any other vendors care to comment?

If you want to leave it in that is your choice as I must surrender that
your model may actually be legal--perhaps due to an oversight in the
[Diff Pin] specification (noticed I used the word "may"!!).  We will
instruct our customers to delete the [Diff Pin] lines until we are able
to support it with a patch (yuck!).

Viewlogic will endorse a proposed BIRD allowing other types of models on
the series pin nodes.

Chris

P.S.  I will be out of the office all next week so am defenseless to
your reply :) !!

---

From: Scott McMorrow <[email-masked]>
Date: Fri, 09 Oct 1998 19:24:21 -0700

All,

I believe the more appropriate solution is to model the
device using an ebd model.  In this way a differential
receiver can be place on the pass-thru between the
input and output pins of the device.

Ebd models work quite well for complex package
situations, such as this one.

Regards,

Scott

--
___________________________
Scott McMorrow
Principal Engineer
SiQual

mailto:[email-masked]
___________________________

---

From: Kellee Crisafulli <[email-masked]>
Date: Mon, 12 Oct 1998 11:01:26 -0700

Hi Arpad, Chris, IBIS

  I have 2 points which seem important in the context of your
question:

1) Why not use .ebd it seems perfect for what you are doing.

2) I thought terminators are stand alone key words.  That is
   not used in the context of an IC model but rather used to
   create and define a terminating component.

---------------------------------------------------------
Have a great day....
Kellee Crisafulli at HyperLynx
SI,EMC,X-talk and IBIS tools for the Windows platform
E-mail: <mailto:[email-masked]>
web:    <http://www.hyperlynx.com>
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