RE: [IBIS-Users] I/O model with dynamically changing pullup

Gaurav,
 
You can model this type of behavior using the
[Driver Schedule] keyword.  Make the pullup
a single shot with a 1 us timeout.
 
Arpad
==============================================
 
________________________________

From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of gaurav Singh
Sent: Tuesday, December 16, 2008 9:35 PM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] I/O model with dynamically changing pullup



Dear all,

 

I have a special case where the pullup of an I/O pin changes
dynamically. This is how it works:

 

1.       The I/O has a 100kOhm resistor pullup in parallel with the
clamp 

2.       While the pin is HIGH, it can be pulled LOW externally -
behaving like a open-drain I/O with a 100K pullup

3.       When the pin is pulled LOW by the device - it is a strong
pull-down

4.       Here is the problem:

When this pin is pulled HIGH from a LOW state - a strong internal pullup
acts on it for (~)1us - after this time, the strong pullup is disabled
and it acts like the point 2 above.

 

Sequence:

Pin is LOW -> Pulled high with a strong pullup (20Ohm) for 1us -> Strong
pullup is disabled and pin acts as an open-drain I/O with an weak
internal pullup

 

Any ideas on how this pin needs to be modeled?

I understand that the resistive pullup should be accounted for in the
Clamp currents. However, how do I account for the fact that the pull-up
table changes dynamically.

 

Your help would be greatly appreciated.

 

Thanks,

Gaurav


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