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                    BUFFER ISSUE RESOLUTION DOCUMENT (BIRD)

BIRD ID#:       92.1
ISSUE TITLE:    Multiple Terminator and Series Elements under [Model]
REQUESTOR:      Michael Mirmak, Intel Corp.
DATE SUBMITTED: November 2, 2004
DATE REVISED:   November 21, 2004
DATE ACCEPTED BY IBIS OPEN FORUM: January 28, 2005

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STATEMENT OF THE ISSUE:

At present, the IBIS 4.1 specification does not clearly prevent terminator 
keywords such as [Rac] from appearing multiple times within the same
[Model] keyword's scope.  Similarly, the specification does not explicitly 
prohibit multiple instances of, for example, [L Series] under the same [Model] 
keyword for Series types, or under the same [On] or [Off] keywords for the same
[Model]s of type Series_switch.

The IBIS 4.0 parser already issues warnings for multiple instances as 
described above.  The changes below will align the specification with parser 
behavior.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

Changes in BIRD92 are denoted by |*.
Changes in BIRD92.1 are denoted by |**.

Under Section 6, in the [Model] keyword description, replace the following
paragraph:

| Other Notes:  A complete [Model] description normally contains the following
|               keywords:  [Voltage Range], [Pullup], [Pulldown], [GND Clamp],
|               [POWER Clamp], and [Ramp].  A Terminator model uses one or
|               more of the [Rgnd], [Rpower], [Rac], and [Cac] keywords.  
|               However, some models may have only a subset of these keywords.
|               For example, an input structure normally only needs the 
|               [Voltage Range], [GND Clamp], and possibly the [POWER Clamp]
|               keywords.  If one or more of [Rgnd], [Rpower], [Rac], and 
|               [Cac] keywords are used, then the Model_type must be 
|               Terminator.

with the paragraph:

| Other Notes:  A complete [Model] description normally contains the following
|               keywords:  [Voltage Range], [Pullup], [Pulldown], [GND Clamp],
|*               [POWER Clamp], and [Ramp].  A Terminator model may use
|*               the [Rgnd], [Rpower], [Rac], and [Cac] keywords.  
|               However, some models may have only a subset of these keywords.
|               For example, an input structure normally only needs the 
|               [Voltage Range], [GND Clamp], and possibly the [POWER Clamp]
|*               keywords.  If any of [Rgnd], [Rpower], [Rac], and 
|*               [Cac] keywords is used, then the Model_type must be 
|               Terminator.

In the [Rgnd], [Rpower], [Rac], [Cac] keyword description, add the following 
sentence under "Usage Rules":

|* Note that only one instance of any one of these keywords is permitted
|** within any single [Model].  For example, [Rgnd] may not be used twice under
|* the same [Model] description.

In the [R Series], [L Series], [Rl Series], [C Series], [Lc Series], [Rc Series] 
keyword description, add the following sentences under "Usage Rules":

|* Note that only one instance of any one of these keywords is permitted
|** within any single [On] or [Off] keyword for [Model]s of type Series_switch.  
|** For example, [L Series] may not be used twice under the same [Off]
|** description.  Similarly, only one instance of any one of these keywords 
|** is permitted within any single [Model] of type Series.


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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

The IBIS 4.1 specification, as worded, could be interpreted to allow a [Model]
keyword to contain more than one [Rac] and more than one [Cac] keyword.  As 
the specification assumes that [Rac] and [Cac] are connected in series between 
the pad and ground, multiple [Rac] and [Cac] keywords could not be
unambiguously connected by simulation tools.  In other words, should the first
[Rac] to be defined connect to the first [Cac] to be defined, or the second?

A similar problem exists with [R Series] and related keywords.  As [Rc Series]
and [C Series], for example, are assumed to be connected in series between
pins as defined under [Series Pin Mapping], multiple [Rc Series] and 
[C Series] keywords under the same [Model] could not be unambiguously 
connected.  
               
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ANY OTHER BACKGROUND INFORMATION:
Note that the specification does not prohibit combining [Series Current]
with [R Series] or other passive series element keywords under the same
[Model].

BIRD92.1 is issued with minor typographical corrections, a reordering of 
the [R Series], etc. usage rules and with the addition of an Analysis section.

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