FreeLists / si-list / [SI-LIST] Re: PCI-X Specification!

[Tariq Abou-Jeyab <aboujeyab@xxxxxxxxx>]

Thanks Andrew,

The second question is pretty much answered.
For the first one, I was interested in knowing if
there is an overshoot value (+ or -) specified for
PCI-X. They specify Vil (min) = 0.5V and Vih (max) =
Vcc+0.5. But I beleive these are the DC level values
not the transient (AC) ones.

If you notice in PCI 2.2 specification section
4.2.2.3,
it shows in the AC waveform that Vp-p = 7.1V. So I was
trying to find something like that in PCI-X but
nothing was specified!

Thanks,

Tariq Abou-Jeyab


--- "Ingraham, Andrew" <Andrew.Ingraham@xxxxxxxxxx>
wrote:
> 
> Inmyung Song wrote:
> 
> > +overshoot =3D overshoot
> > I think -overshoot =3D undershoot? right?
> 
> There has been some discussion on this list about
> this before.  There is
> much disagreement out there.  The answer to your
> question is not
> necessarily.
> 
> One accepted definition ... and this might be the
> IEEE definition, but I
> don't have it in black-and-white ... is that
> overshoot is when there is
> "too much" transient signal, i.e., it goes beyond
> normal levels in
> either direction.  Thus, for most logic families,
> "-overshoot," or
> negative overshoot, or falling-edge overshoot, would
> mean overshooting
> below 0 volts.  You are literally overshooting the
> desired voltage by
> going too far in a negative direction.  Undershoot
> is entirely
> different, and would mean a signal that falls short,
> i.e., is too much
> positive on a falling edge to reach a normal low
> level.
> 
> But other people, most notably Intel, have used
> "undershoot" to mean
> what others (and IEEE?) would call overshoot on
> falling edges.
> 
> And then there are some of us, who occasionally use
> either definition,
> depending on context.  (I've gotta get out of that
> habit!)
> 
> As for the PCI-X definition of "Cin", I don't see
> anything that would
> clarify, so I would assume that it means the total
> input capacitance,
> both package and die.  It has been fairly common for
> years to call this
> the "input pin" capacitance, even though it applies
> to the entire input,
> not just the package pin portion of it.
> 
> If you are making a generic IBIS model, you get to
> decide how much of it
> to allocate to Cpin and how much is Ccomp.
> 
> Tariq Abou-Jeyab also asked:
> 
> > 2) What is the +overshoot and -overshoot number?
> I'm
> > asking about the transient numbers not the dc
> level.
> 
> I am not sure what you are looking for.  Do you want
> an absolute maximum
> overshoot voltage that a PCI-X device must tolerate?
>  As with
> conventional PCI, I don't think there is such a
> limit.  The conventional
> PCI Spec had a "maximum AC waveform" requirement,
> which was expressed in
> the form of tolerance to a certain Thevenin
> equivalent stimulus, but not
> an absolute voltage level.  (Many people
> misinterpret that part of the
> PCI Spec.)
> 
> Regards,
> Andy
> 
> 
>
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