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                       Buffer Issue Resolution Document  (BIRD)

BIRD ID#:      81.1
ISSUE TITLE:   Clarify Usage Rule for [Pin] I/O Model Assignment
REQUESTOR:     Lance Wang, Cadence Design Systems, Inc.
DATE SUBMITTED:  December 23, 2002; January 10, 2003
DATE ACCEPTED BY IBIS OPEN FORUM:  February 14, 2003

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STATEMENT OF THE ISSUE:

IBIS model makers/users often mistakenly assign a Series/Series_switch 
model to pins in [Pin] section. Series/Series_switch type model or a 
[Model Selector] which contains Series/Series_switch models should not 
be assigned directly to a single pin by its definition. It should be only 
assigned in [Series Pin Mapping] for a pin pair. 

A little description in [Series Pin Mapping] Notes is not enough to drive
the better quality IBIS models. 

Clarification is necessary in the usage rules of [Pin] section.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

The [Pin] keyword from the Draft Version 4.0 document is modified to 
clarify the usage rules for Series/Series_switch type model.

Changes are shown by |* lines, and the new ones by |** lines.

|=============================================================================
|     Keyword:  [Pin]
|    Required:  Yes
| Description:  Associates the component's I/O models to its various external
|               pin names and signal names.
|  Sub-Params:  signal_name, model_name, R_pin, L_pin, C_pin
| Usage Rules:  All pins on a component must be specified.  The first column
|               must contain the pin name.  The second column, signal_name,
|               gives the data book name for the signal on that pin.  The
|               third column, model_name, maps a pin to a specific I/O buffer
|               model or model selector name.  Each model_name must have a  
|               corresponding model or model selector name listed in a [Model] 
|               or [Model Selector] keyword below, unless it is a reserved
|               model name (POWER, GND, or NC).
|
|**          The model_name column cannot be used for model or model selector
|**          names that reference Series and Series_switch models.
|*
|               Each line must contain either three or six columns.  A pin
|               line with three columns only associates the pin's signal and
|               model.  Six columns can be used to override the default
|               package values (specified under [Package]) FOR THAT PIN ONLY.
|               When using six columns, the headers R_pin, L_pin, and C_pin
|               must be listed.  If "NA" is in columns 4 through 6, the
|               default packaging values must be used.  The headers R_pin,
|               L_pin, and C_pin may be listed in any order.
|
|               Column length limits are:
|                   [Pin]         5 characters max
|                   model_name   20 characters max
|                   signal_name  20 characters max
|                   R_pin         9 characters max
|                   L_pin         9 characters max
|                   C_pin         9 characters max
|-----------------------------------------------------------------------------
[Pin]   signal_name     model_name      R_pin   L_pin   C_pin
|
  1     RAS0#           Buffer1         200.0m  5.0nH   2.0pF
  2     RAS1#           Buffer2         209.0m  NA      2.5pF
  3     EN1#            Input1          NA      6.3nH   NA
  4     A0              3-state
  5     D0              I/O1
  6     RD#             Input2          310.0m  3.0nH   2.0pF
  7     WR#             Input2
  8     A1              I/O2
  9     D1              I/O2
 10     GND             GND             297.0m  6.7nH   3.4pF
 11     RDY#            Input2
 12     GND             GND             270.0m  5.3nH   4.0pF
|  .
|  .
|  .
 18     Vcc3            POWER
 19     NC              NC
 20     Vcc5            POWER           226.0m  NA      1.0pF
|
|**21     BAD1           Series_switch1     |   Illegal assignment
|**22     BAD2           Series_selector1   |   Illegal assignment

|=============================================================================


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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:

Series and Series_switch models are designed for a pair of pins. When assign 
Series/Series_switch model to a single pin, the EDA tools can not correctly
build the connections with pins and Series/Series_switch models.  We
found many cases of bad IBIS models due to this issue. They were made by 
IC vendors, SI Engineers and even model vendors/experts.

IBIS golden parser does not report this error either. BUG77 reports this 
ibischk3 bug.

Clarification is necessary for the documentation.

The changes were designated by |* lines

BIRD81.1 is issued with minor editorial corrections designated by |** lines.

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ANY OTHER BACKGROUND INFORMATION:   

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