Subject: BIRD11.1 COMMENTS

From: [email-masked] ( Bob Ross)
Date: Fri, 8 Apr 94 18:59:14 PDT

Kellee and IBIS Committee:

I am in basic agreement with BIRD11.1 and plan to support it.  There are some 
"nitpick" technical points that could be a problem and cause ambiguity.  They
relate to the fundamental question: Will tables composed of only 0 mA entries
or of only constant current entries be flagged as an error in Version 2.0?
They are acceptable in Version 1.1, and could be useful to get around some
Model_type omissions and do some (beyond IBIS) constant current source
modeling or biasing of tables modeling. 

I prefer to retain the capability of having table with only 0 mA or of 
constant current.  However, because Version 2.0 will contain all of the
Model_types I need, I can accept an explicit restriction that no table 
may consist of only 0 mA or constant current entries.  What is the
intention of BIRD11.1 is in this regard?

Here are some "editorial" changes which relate exactly to this question.

I.  In BIRD11.1, Change 2 states,

"For each of the following V/I tables: Pullup, Pulldown, POWER_clamp, GND_clamp

1) Find the minimum and maximum voltage points (Vmin, Vmax) in the table.

2) IF:The current in the TYPICAL column corresponding to Vmax is less than
      the current in the TYPICAL column corresponding to Vmin than the table is
      assumed to have decreasing current.
   ELSE: The table is assumed to have increasing current."

>From this wording, "increasing" includes both EQUAL and INCREASING.  I
believe you really mean:

"2) IF:The current in the TYPICAL column corresponding to Vmax is less than
      the current in the TYPICAL column corresponding to Vmin than the table is
      assumed to have decreasing current.

   ELSE IF:The current in the TYPICAL column corresponding to Vmax is greater 
      than the current in the TYPICAL column corresponding to Vmin than the
      table is assumed to have increasing current.

   ELSE: The table is assumed to have equal current."

The last "ELSE" condition may be omitted if it is not used based on how 
case II is handled. 

II.  Here is the change I really want, but do not need as long as we are
all in agreement with our expectations.  The test in Change 2 states:

"3)  If the model is any of the following types:(Input_ECL, Output_ECL, I/O_ECL)

    {
    Verify that:
    - Pullup      V/I table has decreasing current
    - POWER_clamp V/I table has decreasing current
    - Pulldown    V/I table has decreasing current
    - GND_clamp   V/I table has increasing current
    }
  ELSE
    {
    Verify that:
    - Pullup      V/I table has decreasing current
    - POWER_clamp V/I table has decreasing current
    - Pulldown    V/I table has increasing current
    - GND_clamp   V/I table has increasing current
    }"

I would prefer the valid cases be enlarged:

3)  If the model is any of the following types:(Input_ECL, Output_ECL, I/O_ECL)

    {
    Verify that:
    - Pullup      V/I table has decreasing current
    - POWER_clamp V/I table has equal or decreasing current
    - Pulldown    V/I table has decreasing current
    - GND_clamp   V/I table has equal or increasing current
    }
  ELSE
    {
    Verify that:
    - Pullup      V/I table has equal or decreasing current
    - POWER_clamp V/I table has equal or decreasing current
    - Pulldown    V/I table has equal or increasing current
    - GND_clamp   V/I table has equal or increasing current
    }

III.  Finally Change 2, section 4) states:

"4) If any table moves in the wrong direction report the following error message:
'Error found in xxx V/I table at line number nnn!'.  Where xxx is one of the
following: Pullup, Pulldown, POWER_clamp, GND_clamp.   Where nnn is the line
number.

Note: It is acceptable to stop the parser after the first line found with this
error."

I could technically be very happy with the wording as is, and yet we
may have entirely different expectations.  To me "If any table MOVES in the
wrong direction ..." means an error is NOT reported if there is NO table
movement - e.g., NO error is reported if the tests reveal EQUAL currents.
I believe you really intended "If any table verification fails ...".

I would prefer that the IBIS_CHK parser not stop, but continue to check the
file for all errors (including other occurances of this error).  So I would
delete the "Note" entirely.

Bob Ross,
Interconnectix, Inc.