[SI-LIST] : Worst case VI curve for PCI spec a reality?

McCormick, Robert (robertm@seussnt.stratus.com)
Mon, 20 Apr 1998 09:59:47 -0400

The worst case high state vi curve in the PCI spec shows Voh=2.4v for
I=0 to 2mA (Figure 4-3, VI curve for 5V signaling). Section 4.1.2 of
the PCI spec says that "PCI is a CMOS bus", which would mean that Voh
should be close to the rail (note that Ioh &IiL ~ 70uA per the PCI
spec.) Granted, 3.3v devices are allowed to drive in a 5V environment,
and specs for 3.3v parts do say that Voh_min=2.4v but isn't this a
holdover from the TTL / Bipolar days?

The difficulty arises in meeting the PCI spec of Tpd_max = 10nsec (due
to ringback).
Does anyone know of PCI devices that actually put out 2.4v at I=0 amps
(high temperature, low supply voltage) or is the spec just too worst
case?Note that I also question Vol=0.55v at I=0amps for the low state vi
curve as well.

Thanks,

Bob McCormick
Stratus Computer
Marlboro, MA
TEL: 508-460-2485
robert_mccormick@stratus.com