Subject: SE and diff drivers on same pin

From: "Barnes, Larry" <[email-masked]>
Date: Tue, 4 May 1999 15:37:31 -0600

I'm trying to construct a model of a SCSI-2 part.  SCSI-2 data pins are
either differential or single-ended depending on what bus is detected by the
part.  

I was planning on using the model selector to assign either the SE or diff
driver to the correct pin.  BUT I am in a quandary where to place the Diff
Pin definitions.  

Also the I-V curves of the differential pins are not exact mirrors of each
other, so I have set of data available for each side of the diff driver.

I guess I could defined two complete components in the file, one
single-ended usage and one for differential.  But I still have a question as
to how to implement the Diff Pin definitions

Any suggestions would be appreciated.

Regards,
Larry Barnes
[email-masked]

---

From: "Beal, Weston" <[email-masked]>
Date: Wed, 5 May 1999 08:50:44 -0500

Larry,

Defining the differential pins with different drivers is no problem.  You
just assign the appropriate model in the pin list and then define the pins
as differential in the diff pin block.  I think that IBIS allows you to use
model selector and diff pin on the same pins, but it is likely to confuse
half the simulators, or simple not be supported.  I've seen this type of
device before in IBIS and the manufacturer defined it as two different
devices.  This is your best bet, I think.

Regards,
Weston Beal
Signal Integrity Engineer
Compaq Computer Corp.

		-----Original Message-----
		From:	Barnes, Larry [mailto:[email-masked]]
		Sent:	Tuesday, 04 May, 1999 4:38 PM
		To:	[email-masked]'
		Subject:	SE and diff drivers on same pin

		I'm trying to construct a model of a SCSI-2 part.  SCSI-2
data pins are
		either differential or single-ended depending on what bus is
detected by the
		part.  

		I was planning on using the model selector to assign either
the SE or diff
		driver to the correct pin.  BUT I am in a quandary where to
place the Diff
		Pin definitions.  

		Also the I-V curves of the differential pins are not exact
mirrors of each
		other, so I have set of data available for each side of the
diff driver.

		I guess I could defined two complete components in the file,
one
		single-ended usage and one for differential.  But I still
have a question as
		to how to implement the Diff Pin definitions

		Regards,
		Larry Barnes
		[email-masked]

---

From: "Muranyi, Arpad" <[email-masked]>
Date: Wed, 5 May 1999 08:27:02 -0700

Larry,

It seems to me that you would like to use the [Model Selector] to be able to
switch between the differential and single ended mode of the buffer.  You
are
right, this would only be possible if the [Diff Pin] keyword (or a similar)
function could be inside the [Model Selector].  Unfortunately this can't be
done currently.  I would suggest to use the comment character before the
line
that defines the pins of interest as differential in the [Diff Pin] section
for
the single ended mode, and no comment character for the differential mode.

I am just curious, are there a lot of devices like this out there?  If so,
we
should probably find an IBIS solution for this case.  This could be brought
up
in one of the Open Forum meetings, if necessary.

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

-----Original Message-----
From: Beal, Weston [mailto:[email-masked]]
Sent: Wednesday, May 05, 1999 6:51 AM
To: [email-masked]'
Subject: RE: SE and diff drivers on same pin

Larry,

Regards,
Weston Beal

		-----Original Message-----
		From:	Barnes, Larry [mailto:[email-masked]]
		Sent:	Tuesday, 04 May, 1999 4:38 PM
		To:	[email-masked]'
		Subject:	SE and diff drivers on same pin

		Regards,
		Larry Barnes
		[email-masked]

---

From: Matthew Flora <[email-masked]>
Date: Wed, 05 May 1999 10:08:50 +0000

Dear Larry, Arpad,

>are right, this would only be possible if the [Diff Pin] keyword (or a
>similar) function could be inside the [Model Selector].  Unfortunately this
>can't be done currently.  I would suggest to use the comment character before
>the line that defines the pins of interest as differential in the [Diff Pin]
>section for the single ended mode, and no comment character for the
>differential mode.

As annoying as it is to build two separate models, I would advocate doing that
rather than commenting out various sections of the model depending on what
"mode" the user desires.

Would you, as a user, like being forced to modify a model file in order to use
it?  Sounds tedious and "unfriendly".  In my experience, many of the folks
using IBIS models know nothing about IBIS (and don't necessarily want to if
they don't have to).

I realize the maintenance burden goes up having to support two models, even if
they are in the same file.  But consider that the maintenance burden affects
only a couple of people in your organization for a limited time, while
potentially hundreds of users would be saved having to edit the model file(s),
perhaps multiple times each.  Remember that your models are likely to be in
use in the field much, much longer than it takes you to build/maintain them.

Regards,
Matthew Flora
Senior Engineer
HyperLynx
(425) 869-2320 PH
(425) 881-1008 FAX
[email-masked]
17641 NE 67th Court, Redmond, WA 98052 USA