Re: [SI-LIST] : Input switching threshold & CPCI

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Mon Jan 03 2000 - 08:39:30 PST


Jon Keeble wrote:
>
> I hear that the cpi/cpci guys are looking at a new termination technique for
> backplanes that supports more devices on the bus with the existing
> controllers.
>
> I guess this involves parallel termination at both ends in Zo to Vt with Vt
> close to the threshold region (?).
>
> How much variation in Vt exists across the range of controllers, and across
> the range of fpgas and cplds that people use for pci?

PCI does the old (idiotic) 0.8-2.0 input thresholds that were first
documented on cave walls. In contrast, anyone trying to do serious
signaling at nontrivial speeds uses very tight thresholds, usually
scaled to the driver supply and usually with differential receivers.

The implications of this difference are left to the reader to infer.

-- 
D. C. Sessions
dc.sessions@vlsi.com

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