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BIRD ID#:        106
ISSUE TITLE:     Clarification on Signal_pin Parameters
REQUESTER:       Arpad Muranyi, Mentor Graphics Corp.
DATE SUBMITTED:  February 26, 2007
DATE REVISED:    
DATE ACCEPTED BY IBIS OPEN FORUM:  May 16, 2008

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STATEMENT OF THE ISSUE:

An ambiguity in the IBIS specification was discovered regarding the usage
rules of the Signal_pin, Diff_signal_pins and Series_pins subparameters
under the [Circuit Call] keyword.  The following sentence can be interpreted
in several ways:

|                                                 ... Only one of
| the three subparameters is permitted in a given [Circuit Call]
| keyword.  ...

The intent of the specification was to allow only one instance of any one of
these subparameters under a [Circuit Call] keyword.  However, the above
language may be interpreted to mean that, while these subparameters may not
be mixed, multiple instances of the same subparameter are still allowed.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

The following paragraph:

| The purpose of these subparameters is to identify which
| [External Circuit] needs to be stimulated in order to obtain
| a signal on a certain pin. These subparameters must be used
| only when the [External Circuit] that is referenced by the
| [Circuit Call] keyword has an effect on a pin. Only one of
| the three subparameters is permitted in a given [Circuit Call]
| keyword. The subparameters are followed by one or two pin
| names which are defined by the [Pin] keyword.

shall be modified as follows:

| The purpose of these subparameters is to identify which
| [External Circuit] needs to be stimulated in order to obtain
| a signal on a certain pin. These subparameters must be used
| only when the [External Circuit] that is referenced by the
|* [Circuit Call] keyword makes use of the stimulus signal of
|* the simulator. Any given [Circuit Call] keyword must contain
|* no more than one instance of only one of these three subparameters.
|* The subparameter is followed by one or two pin names which must
|* be defined by the [Pin] keyword.

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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

The above proposal is based on a discussion which was a result of the
discovery of an incorrect behavior of the v4.2.2 parser.  The parser will
issue error messages based on how many pins are referenced by these
subparameters, the limit being no more than two pins.  This behavior of the 
parser allows two Signal_pin subparameters under a [Circuit Call] keyword,
which was not the intention of the specification.

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ANY OTHER BACKGROUND INFORMATION:


The thoughts captured in this BIRD were discussed at the February 22, 2008
IBIS Open Forum Teleconference.

Approved at the May 16, 2008 IBIS Open Forum teleconference.

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