Subject: RE: standard loads on 66 MHz PCI

From: "Muranyi, Arpad" <[email-masked]>
Date: Fri, 6 Nov 1998 16:09:00 -0800

Greg,

You can put the two Vref numbers into the IBIS model and comment one of them

out.  Unfortunately this means that you have to simulate things twice (with 
most IBIS based simulators), but fortunately the waveforms are not effected
by 
this, only the flight time measurements.  So one of the simulations could do

the falling edge measurements, and the other one the rising edge
measurements. 
If you need more detail send me another EMAIL, and I will give you an
example.

Arpad Muranyi
Intel Corporation
============================================================================

A question came up here at IBM today that I could not answer.  Has anyone
run 
into this?

The 66 MHz PCI bus spec has a different standard load for rising and falling

edges.  (10 pF and 25 Ohms to gnd for rising OR 10 pF and 25 Ohms to Vcc for

falling.)  As I read version 3.1 of IBIS, it only allows one value of Vref
per 
[Model] keyword.  This seems to make the 66 MHz PCI driver unable to be 
implemented in IBIS, at least if you want to do timing analysis.  I would
think 
someone else probably encountered this already.  How did you get around it?
Or 
am I missing something?

Much thanks in advance.

Greg Edlund
Advisory Engineer, AS/400 System Timing 
IBM
3650 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
[email-masked]

---

From: David Haedge <[email-masked]>
Date: Mon, 09 Nov 1998 09:36:11 -0600

We had a similar problem with a Motorola MPC750.  The L2 cache MAX timing
numbers are specified to a 20pF load and the MIN numbers to a 5pF load.
We were using ICX to analyze timing.  We looked at the output under no load,
then at 20pF and 5pF.  The delta was measured to be 477ps.  We then adjusted
the timing sheets in ICX so that the minimum allowed routing distance was
effectively increased by 477ps to compensate for the additional 'test' load.
This allowed us to use a single IBIS model with Cref set at 20pF.  You may
be able to apply a similar 'trick' with the PCI driver and Vref.

David Haedge
Raytheon Systems Company