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

D. C. Sessions (dc.sessions@tempe.vlsi.com)
Tue, 21 Apr 1998 13:54:43 -0700

Andrew Ingraham wrote:
> D. C. Sessions wrote:

> > the PCI pullup spec for 5v has a *minimum* short-circuit Ioh of 44mA!
> > Pumping that much current out of a 3.3v pullup without 3.3v clamping
> > is fer-sher begging for disaster. OTOH, staying within the 12-24mA
> > range for 3.3v (no, PCI doesn't have a max but 2:1 is achievable and
> > weak is better) keeps ringback within reason.
>
> Where do you get this (implied) 12mA minimum short-current Ioh for 3.3v
> PCI ?
>
> Last I looked, the minimum Ioh curves for 3.3v and 5v were almost on top
> of one another. The big difference is in the pulldown curves.

Apologies to all. The minimum is 3Vcc (separate grumble wrt dimensions)
which gives 36mA min. I have an old copy where Intel had misprinted the
axis labels framed and never replaced it; every time I get away from
PCI for a while I forget the convention and do something stupid.

> Just out of curiosity, how do you folks deal with drivers that are
> technically, no, blatantly non-compliant, even if it makes them work
> better? If someone asks if your drivers comply with the PCI spec rev
> 2.1, do you admit that they don't? Do you advertise them as meeting the
> spec?

The only ones that don't strictly comply are the 5v tolerant ones, and
there we take refuge in the fact that Intel never defined 5vT clearly
enough to say whether *anything* complies. The gory details are all
in our cell data anyway, and the product designer is ultimately
repsonsible for deciding whether to comply or to make it work. One
of the little benefits of being an ASIC company, perhaps.

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