Subject: Vmeas

From: "Amir Shavit (r56010)" <[email-masked]>
Date: Tue, 05 Oct 1999 17:02:57 +0200

Hi,
I'm cuurrently working on an ibis model. I'v encountered some problem
with this parameter since it is different for rising and falling time. I
don't know what it should be equal to, since there are 2 different
values.
Thanks for your answers
Amir Shavit
Motorola Semiconductors Israel

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From: "D. C. Sessions" <[email-masked]>
Date: Tue, 05 Oct 1999 10:24:25 -0700

> Motorola Semiconductors Israel

Shalom Amir.

I'm a bit puzzled about the "different rising and falling" cases.
Are the defined timing points for the device you're working with
actually specified differently for the two directions?  The reason
I ask is because it's very hard to have a setup time, for instance,
which is different for rising and falling edges.

Vmeas _should_ be the point at which the characterized ("data sheet")
timing is defined.  This is usually 1.5v for LVCMOS, but is sometimes
50% of supply (a better way), 40% of supply (PCI and AGP), or an
external threshold (SSTL, HSTL, GTL, Rambus, etc.)

-- 
D. C. Sessions
[email-masked]

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From: "Amir Shavit" <[email-masked]>
Date: Wed, 06 Oct 1999 08:22:17 +0200

Hi,
Thanks for your answer. 
The data sheet takes the worst case between rising and falling, or
specifies falling (for strobes). The measurments were done from
clock=2.0v (active gigh) to either signal=2.0v (rising) or signal = 0.8v
(falling). These measurments are done so that the signal is active
(wither high or low), and not just mid way through the device voltage.
Thanks