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Re: 3.3V supply

> Dear Monish,
> the 2.2 SPEC has changed the power supply rules: all PCI connectors
> four power rails: +5V, +3.3V, +12V and -12V. Systems providing PCI
> connectors are required to provide all four rails.
> In my opinion you don't need to put a LD Voltage Regulator on your PCI
> if it's full compliant with PCI 2.2 systems. Do you agree with what I'm
> saying?

I agree that it it is plugged into a fully compliant 2.2 system, I don't
need a regulator.  But, here are the problems:.

1.  Just because my card is 2.2 compliant doesn't mean the slot it is
plugging into is also 2.2 compliant.  Backwards compatibility is a major
objective in PCI.  (2.2 cards should work with 2.1 slots and vice versa.)

2.  If some idiot forgets to connect 3.3V power to his PCI slot and still
claims it to be PCI 2.2 compliant, and my card is the only one that doesn't
work in that system because everyone else is conservative enough to just use
5V, the customer will blame my card.

But, there are special circumstances in my case.  I don't plan to sell this
card retail.  It will only be bundled by OEMs.  So, this issue is more
manageable in my case.  Still, I want to know how likely it is that I would
run into problems with some OEMs.


> Regards,
> Marco Serafini - QR s.r.l.
> "Any views or opinions presented
> are solely those of the author and do not necessarily represent those
> of QR."
> ----- Original Message -----
> From: "Monish Shah" <monish.shah@indranetworks.com>
> To: "PCI SIG" <pci-sig@znyx.com>
> Sent: 03 November, 2001 2:50 PM
> Subject: 3.3V supply
> > Hello everyone,
> >
> > I just wanted to check to see if all PCI slots in *new* systems supply
> 3.3V
> > power these days.
> >
> > Background:  PCI 2.1 said that 3.3V supply was optional for 5V signaling
> > slots.  Indeed, in the old days, many systems did not supply 3.3V.  I
> > remember lots of people complaining about this fact on this list about 4
> > years ago.
> >
> > Meanwhile, PCI 2.2 came along and required 3.3V supply for all slots.
> > Technically, any system claiming PCI 2.2 compliance would supply it.
> > there is no compliance police to throw people in jail if they violate
> this,
> > so there's still no guarantee.
> >
> > I've tried a few PCs around the office and they all have 3.3V power.
> These
> > are all new systems.  They are not particularly advanced or high-end
> > systems.  This gives me hope that 3.3V power must be universal in new
> > slots these days.
> >
> > Can anyone confirm or deny this observation?
> >
> > The bottom line is, I'm building a card that needs 3.3V power.  Do I
> to
> > put in a regulator to go from 5V to 3.3V?  Note that I don't expect to
> sell
> > to people with 4 year old PCs.  I expect the card to be bundled with new
> > systems.
> >
> > Monish
> > ----
> > Monish Shah
> > Indra Networks
> >