Re: [SI-LIST] : PCI Bus propagation delay measurement

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Thu Nov 02 2000 - 09:27:57 PST


Marko,

I forgot the terminology of the PCI a bit - but the Tprop, is is a round
trip for the signal from the Transmitter to the closest end of the bus
and then back to the receiver?
If yes:
Still, your period at 33Mhz is 30ns. Now, the data are output by
transmitter on falling edge of the clock, with some delay. So you have
roughly 13ns before the next rising edge, unless you use protocol, where
you skip one clock. From these 13ns you have to deduct set-up time,
which is what...5ns worst case or so? Minus your clock skew (minus 2ns,
obviously, for the worst case)So you have about 6ns full trip time,
which will translate into 36 inches roundtrip.

If you have 24ns roundtrip time - this is too much.

Mike.

marko.pulli@nokia.com wrote:

> Hi SI people,
>
> When measuring a real PCI bus signal (not 25ohm test load);
> Would the starting point of Tprop be for a rising
> edge in this case at 0.285Vcc?
>
> Why Tprop isn't measured like in a TDR for example?
>
> Could this be possible in a 'known' system;
> I would know exactly which PCI devices are going to be
> connected to the bus.
> I would have for example;
> clock skew of 2ns
> setup time 2ns
> Tval 2ns
>
> Would Tprop of 24ns in this case be possible
> for a 33MHz system?
>
> Br,
> Marko
>
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