Subject: SPICE to IBIS

From: [email-masked]
Date: Fri, 21 Jul 1995 17:48:07 -0400

Hi All,

I'm a having a bit of difficulty with my understanding of the syntax for s2ibis.
I don't seem to understand how the [pin] syntax ties into the SPICE 
model. Its not in the docs I have.

Take a simple example.

For a single transceiver (I/O). I would have 2 pins, power, ground and one
spice model. Lets ignore package parasitics for now.

Say my SPICE subcircuit looks like

.SUBCIRCUIT MYIO internal_data_out_pin io_pin VDD VSS
...

i.e.
                         |\
                     ____|  \_____
                         |  /
                         |/
  internal_data_out_pin       io_pin

How do I tell s2ibis that the internal_data_out_pin is used for controlling
Vol pull up data and Voh pull down data when io_pin is an output?

How can I tell s2ibis to use a particular CMOS model (representative of
process) to be associated with a certain temperature at a specified
voltage. It would seem I would need to do this to get accurate min/max
numbers.

---------------------------------------------------------------------
Richard Mellitz              |
AT&T                         |
Global Information Solutions | [email-masked]
3325 Platt Spring Road       | Phone: (803)-939-6240
West Columbia, SC 29170      | Fax:   (803)-939-7317
---------------------------------------------------------------------

---

From: [email-masked] ( Bob Ross)
Date: Tue, 25 Jul 95 12:38 PDT

Richard:

I am not sure I understand fully the problem, but here is an attempt at some
answers.

Regarding the I/O pin in output mode, controlled by an "input" which itself
is an internal output, you somehow may have to break the connection for the
internal_data_out_pin inside the subcircuit so that this node is just an
input connection.  Then a phantom input can be created, but would not show
up in the IBIS model if the "**NoModel" option is used with an artifical
pin number.  The "**NoModel" option was created for this type of problem
where the external pin modeled by a Spice circuit is controlled by an internal
input.  The syntax for the I/O pin would reference this internal pin number as
the "input_pin".

Regarding the second point where min (or weak, slow) and max (or strong, fast)
process models are available, s2ibis to was not set up to deal with this
very practical problem.  IBIS itself does not put constraints on the stategy.
Currently s2ibis could be used in a cumbersome manner by using the **Iterate
option.  First the deck would be set up with the "typ" models and executed.
Then the "min" *.spi files would be edited by substituting the "min" models.
Similarly for the "max" *.spi files.  These modified files would be executed
manually to produce *.out files.  Then s2ibis is reinvoked to generate the
IBIS file.  The **Iterate option prevents generating new *.spi  and *.out
files where *.out files already exist.

An updated version of s2ibis for version 1.1 is planned to have an option 
that will support separate "min", "typ" and "max" Spice models.  When this
is implemented, you will not need to do any manual execution.

Bob Ross,
Interconnectix, Inc.