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RE: PCI 2.1 spec



>1) Does the PCI 2.2 spec enforce the availability of 3.3V on the
>connector?
 
Yes.  An ECR was established prior to Revision 2.2, which made 3.3V power
mandatory on 5V PCI system board connectors too.

>My PCI product uses the 5V signaling environment but also taps the 3.3V
>for lower
>power/priced parts.
 
According to the Rev. 2.1 spec, you would have had to regulate your own 3.3V
on-card from one of the other supplies.

Even if you didn't, IN THEORY you would be covered because motherboards were
supposed to provide an upgrade to add 3.3V power if customers needed it.
But few may have ever done that.

> But, how then is
>anybody selling
>3.3V PCI cards to the general public?
 
If, by "3.3V PCI cards" you mean cards that are keyed for (only) 3.3V
signaling, (a) there were scant few of those cards or systems for them to go
into, but (b) they were OK because 3.3V connectors were always required to
have 3.3V power.  Only 5V connectors (which happened to be the ones everyone
used) were exempt.

All other cards (those keyed for 5V signaling but also having components on
board that needed 3.3V power; or "universal" cards keyed for both 3.3V and
5V connectors) were supposed to generate their own 3.3V, per the Rev. 2.1
spec.

It's not a very pretty situation.  Things would have been better if they
went differently.  I think there was an expectation that market forces would
have brought about an earlier introduction of 3.3V, without having to
require it against the wishes of PC makers (which didn't work back in the
early 90's when PCI 2.0 and 2.1 were hammered out).

Andy