[IBIS] RE: [IBIS-Users] Bush Hold and Enable node

Xuefeng,

You are raising an excellent question.  The IBIS
spec may not be totally clear on this, but the
enable signal should have no effect on the operation
of the bus hold portion of a model.

The bus-hold buffer's purpose in life is to keep
the bus from floating and/or to terminate it to
reduce reflections.  You can think of it as a
buffer that drives the pad based on a signal level
that is sees on the pad (instead of a stimulus
coming from an internal logic output).  You can
also think of it as an active terminator which
changes states as the signal is changing on the pad.
Based on this description it would not make sense to
disable such a buffer.

Of course, I could imagine cases when the bus hold
is turned off while the driver is driving, or when
special conditions require that, but those cases
could be taken care of with making separate models
and using the [Model Selector] keyword.

I hope this answered your question.

Arpad Muranyi
Intel Corporation
------------------------------------------------------



-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Xuefeng Chen
Sent: Tuesday, February 28, 2006 12:48 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS-Users] Bush Hold and Enable node

Hi expert,

  Is there any relation between the transition of Bush Hold submodel and
the shift of enable->disable of top model? I failed to find the relation
in IBIS4.1.

  I think the transition of Bush Hold is only related to Vdie,
disregarding whether or not top buffer is disable. Is it right?
  
Many thanks
Xuefeng
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