Subject: Comments about IBIS (EIA-656) specification

From: [email-masked] (Dileep Divekar)
Date: Mon, 7 Aug 1995 15:07:18 +0800

Comment about keyword [Model] (Page 12):

If I look at the explanation of model types Open_drain and Open_source
from the point of view of the output stage being a cmos inverter, then
I can understand it. But if I look at the type Open_sink from the
point of view of the output stage sourcing or sinking current, then
the explanation seems backwards. Generally, the top device (pullup)
sources current and the bottom device (pulldown) sinks current.
Therefore, I would have thought that Open_sink model type will
not have the Pulldown table, but the explanation says not to use
Pullup table.
One possible solution is instead of introducing the new keyword
Open_sink, it may be more intuitive if new keywords Open_pullup
and Open_pulldown are introduced,

Other:
Are blank lines allowed in ibis files?
For nonblank lines, is it necessary to have a non white space
character as the first character?

------------------------------------------------------------
Dileep Divekar
Contec CAE, Ltd.
2188 Bering Drive
San Jose, CA 95131

Phone - (408)-434-6767 x 126
Fax   - (408)-434-6884
Email - [email-masked]
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From: [email-masked] ( Bob Ross)
Date: Tue, 8 Aug 95 12:55 PDT

Dileep:

The way the names "Open_sink" and "Open_source" should be viewed is

  open AND sink     (top side is open and the device sinks current)

  open AND source   (bottom side is open and device sources current)

Your are correct that there could be confusion, but we adopted the
above convention after much discussion (E-mail and direct) and considered
many alternatives including your suggestion.  Here are some of the 
points.

(1) We wanted terminology that was technology independent. We wanted
to avoid requiring Open_drain for TTL devices and also to avoid enumerating
technology dependent alternatives (e.g., Open_collector).

(2) With CMOS, some ASIC data books have used Open_drain and Open_source
pair.

(3) The terminology "sink" and "source" have been used in products and 
have appeared in at least one data book.

(4) While "pullup" and "pulldown" match the IBIS terminology, they could
be confused within the context of an ASIC model when you consider the option
of an internal "pullup resistor" or "pulldown resistor".

After much discussion, "Open_sink" and "Open_source" emerged as the consensus
choice.

Regarding your other questions, blank lines are allowed (they are not
prohibited).  Except for keywords, the white space characters (tab, space)
are allowed as the first character of any line.  For example, columns of
numbers can be indented and aligned at the decimal point.

Bob Ross,
Interconnectix, Inc.