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

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Tue Jan 04 2000 - 13:45:46 PST


"Peterson, James F (FL51)" wrote:
>
> Differential interfaces on a PCI-like bus....I think my I/O just got doubled
> (from around 50 to 100). The old single-ended ttl-like PCI Bus still has
> some punch : the 66MHZ/64bit version bursts at 528MB/s - let's see, that's
> about 4Gbits/sec - certainly a nontrivial speed...

Pincount hardly changes, since the reference voltage is common to many
signals. (see DDR for a similar application.)

> -----Original Message-----
> From: D. C. Sessions [mailto:dc.sessions@vlsi.com]
> Sent: Monday, January 03, 2000 11:40 AM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Input switching threshold & CPCI
>
> 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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-- 
D. C. Sessions
dc.sessions@vlsi.com

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