Subject: RE: [IBIS-Users] [Pin Mapping] syntax
From: Todd Westerhoff (twesterh@cisco.com)
Date: Wed Mar 05 2003 - 15:46:52 PST
RE: [IBIS-Users] [Pin Mapping] syntaxThanks for the feedback. The original
model hadn't used the reserved keyword GND, I made the mistake when altering
the pin names for posting.
Thanks for pointing out that the
A11 GND VDDQ
syntax - though bizarre, is allowed.
Todd.
Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
============================================
"When did the choices get so hard, with so much more at stake?
Life gets mighty precious when there's less of it to waste"
- Bonnie Raitt, "Nick of Time"
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On Behalf
Of Mirmak, Michael
Sent: Wednesday, March 05, 2003 5:17 PM
To: Todd Westerhoff; ibis-users@eda.org
Subject: RE: [IBIS-Users] [Pin Mapping] syntax
An addendum to my own message: as "GND" is a reserved word, it's
preferable to use "GNDBUS" or something similar in the [Pin Mapping] signal
pin and supply pin declarations.
- Michael Mirmak, Intel Corp.
-----Original Message-----
From: Mirmak, Michael
Sent: Wednesday, March 05, 2003 2:04 PM
To: Todd Westerhoff; ibis-users@eda.org
Subject: RE: [IBIS-Users] [Pin Mapping] syntax
Todd,
From the definitions in the IBIS specification plus the latest BIRDs,
you have two options:
1) declare the signal pin as you have written it; the pulldown_ref and
pullup_ref "NC" entries will be overridden by the clamp column entries
2) declare the signal pin as follows:
[Pin Mapping] pulldown_ref pullup_ref gnd_clamp_ref power_clamp_ref
A11 GND VDDQ
Your way is, I think, much more clear and is preferable to the second
option, but both are allowed.
The spec is written assuming that tools will look first to the
pullup_ref and pulldown_ref columns, in the case of signal pins, for
information about the power rails of that device, *even if that device is an
input buffer.*
Under IBIS 3.2, you are allowed to have three or five columns of
information (three, five or six under 4.1 with BIRD 80). With only three
columns of data, the clamps on an input-only buffer would be connected to
the pulldown and pullup references. If connection information is given under
all the voltage columns, the clamp reference connections should override any
assumptions made by tools about the clamps and the pullup and pulldown
references.
I hope this helps!
- Michael Mirmak, Intel Corp.
-----Original Message-----
From: Todd Westerhoff [mailto:twesterh@cisco.com]
Sent: Wednesday, March 05, 2003 1:18 PM
To: ibis-users@eda.org
Subject: [IBIS-Users] [Pin Mapping] syntax
Hi all,
If I have a [Pin Mapping] section in an IBIS model, I expect to see the
mapping for an output or bidirectional buffer show something like:
[Pin Mapping] pulldown_ref pullup_ref gnd_clamp_ref
power_clamp_ref
A10 GND VDDQ GND VDDQ
... but what about an input pin? The input pin has no pullup/pulldown
device, so is "NC" the appropriate entry in the first two fields, as in:
[Pin Mapping] pulldown_ref pullup_ref gnd_clamp_ref
power_clamp_ref
A11 NC NC GND VDDQ
... or is some other syntax supposed to be used?
Todd.
Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
============================================
"When did the choices get so hard, with so much more at stake?
Life gets mighty precious when there's less of it to waste"
- Bonnie Raitt, "Nick of Time"
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