[SI-LIST] Re: PCI
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 21 Jul 2004 08:08:42 -0400
The test points are a way of simplifying compliance with the driver
strengths.
First, PCI specifies minimum and maximum I-V curves that the output drivers
must have. The minimum curve (minimum current as a function of output
voltage) says what is the weakest driver that could be used. Weaker drivers
might result in long switching times that would violate timing requirements
at the normal clock speeds. The maximum curve (maximum current vs. voltage)
prevents very strong output drivers that would result in excessive
overshoot, ringing, and long settling times.
But because compliance to a curve over a range of voltages is not that easy
to measure and prove on a production basis, PCI also defines the test
points, which fall on those curves. If your driver is OK with respect to
the test points, it is probably OK with respect to the rest of the curves,
and therefore would meet PCI's output current-voltage requirements.
Regards,
Andy
> I am not clear with the definition of the Test point
> defined for the V/I Curves of the Output Buffer(With ac
> specifications)as given in the PCI SpecsRev2.1 . What is the criteria
> of
> chosing it value at 3.1 while we consider 5V signaling?
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