RE: [IBIS-Users] ibis version4 query

From: Mirmak, Michael <michael.mirmak_at_.....>
Date: Tue Jun 07 2005 - 09:41:19 PDT
Arnab,

Thanks for your interest in IBIS.  Explaining all the details in
implementing [External Model] would be difficult to do in a single
e-mail.  :)  An IBIS Cookbook update for version 4.1 will be considered
once the 4.0 edition is finalized and issued.

The example you cite is actually a differential model, which has
additional options not shown in the text of your original message.
There are also port mapping and other required keywords in the
specification example.

Simply put, diffio.spi should be a separate file containing a Berkeley
SPICE model of the buffer you would like to analyze.  This model should
contain a number top-level or externally-accessible subcircuit nodes
(the nodes are dependent on the ports required by your Model_type; see
pages 95-96 of the IBIS 4.1 specification in PDF for the table
explaining which ports are required).  These nodes correspond to the
power and ground connections for your buffer; the output(s) to "the
outside world"; and digital connections between the buffer and a logic
core.  Depending on Model_type, these "digital" connections might
include a buffer enable, an input to toggle the buffer and/or an output
from the buffer.  

As SPICE cannot process truly digital signals, we assume these "digital"
signals are converted to analog format before being used by the buffer.
Similarly, the tool may require digital signal outputs from the buffer.
The specification therefore includes language to define how digital
signals supplied or needed by the tool are converted to analog signals
compatible with the SPICE model.

The D_to_A line specifies the parameters of the digital-to-analog
converter the simulation tool should create to connect digital signals
from the simulator to analog signals needed by the SPICE model.  The
trise and tfall parameters signify the rise and fall times, from 0 to
100%, the simulation tool should use for the outputs of the D_to_A
converters.

Per the specification, [Model]s which use [External Model] may omit the
[Pulldown], [Pullup], [POWER Clamp] and [GND Clamp] keywords.  However,
I should note that any [Model] which uses [External Model] *must*
contain the following subparameters and keywords:

- Model_type
- Vinh, Vinl (as appropriate to Model_type)
- [Voltage Range] and/or [Pullup Reference],
- [Pulldown Reference], [POWER Clamp Reference],
- [GND Clamp Reference], [External Reference]
- [Ramp]

I hope this helps!

- Michael Mirmak
  Intel Corp.
  Chair, EIA IBIS Open Forum


________________________________

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Arnab Hazarika
Sent: Tuesday, June 07, 2005 3:18 PM
To: ibis-users@eda.org
Subject: [IBIS-Users] ibis version4 query


Hi all,
We are trying to incorporate the [External Model] parameter in ibis
models version 4.1.The pdf IBIS ver4.1 example shows an example 
 
[Model]Ext_spice_diff_buff
[External Model]
Language SPICE
Corner  Typ  diffio.spi  diff_io_typ
 
Ports A_signal _pos  A_signal_neg my_receive my_drive my_enable
| D_to_A d_port    port1          port2      vlow  vhigh trise  tfall
corner_name
D_to_A   d_drive  my_drive    my_ref    0.0   3.3    0.5n  0.3n  Typ
|
[End Model]
 
We had doubt regarding  what diffio.spi should contain?
 
Also what does the trise and tfall parameters signify?
 
Moreover if we include [External Model]  do we not have to contain the
pull up/down,GND/Power clamp? 
 
Could someone throw light on this ....Better if someone refers new ibis
models where this has been used?
 
Thanks in advance. 
 
Best regards
arnab hazarika
 

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Received on Tue Jun 7 09:41:22 2005

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