Re: Serious s2ibis problem?

<snip>
> Why does s2ibis not subtract the ***Tri-state (un-enabled)*** data
> from the entire range of both pull-down and pull-up data to derive the
> corresponding [Pulldown] and [Pullup] tables? Instead, it appears that it
> takes EXTRA steps to produce seemingly innacurate tables... Is this a
> serious mistake with s2ibis, or are am I missunderstanding something.
> Thanks ahead for all feedback.
<snip>

Scott:

While I didn't write the version of s2ibis that you refer to, I think I
can answer your question.

The answer lies in the voltage ranges of the pullup (or pulldown) and
power clamp (or ground clamp) curves, and the assumption that a tool
will add the pullup and power clamp curves of a tristate device together
to get the correct total behavior.

If you look at the voltage points in the pullup curve, you'll see that
they vary from -Vcc to 2*Vcc, while those in the power clamp curve only
vary from Vcc to 2*Vcc. When the simulator adds these two curves
together, then, it only adds values to the pullup curve in the range Vcc
to 2*Vcc, not the whole range of the curve.

If one were to subtract the tristated pullup curve from the active
pullup curve over the entire -Vcc to 2*Vcc range, the IBIS tool would be
unable to reconstruct the correct behavior of the model, as the required
data (i.e. the tristated data from -Vcc to Vcc) would not be present in
the IBIS file.

Hope that clears things up.

Regards,

-- 
Alan Glaser                         "It's not a competition,
ECE Dept.                            it's just a mint..." - K
North Carolina State University