RE: 3.3V power rail / M66EN

[jurry@csw.L-3com.com]

Section 4.3.4 of the 2.1 spec states that systems MUST supply 3.3V.  What is
optional is the 3.3Vaux power.  This 3.3Vaux is supplied on pin 14A and is
used for powering logic that needs to remain active when the rest of the
system is unpowered (see the PCI Bus Power Management Interface
Specification).  The reason you may find motherboards that do not provide
3.3V is simply that older versions of the PCI spec did not require the 3.3V.

John Urry

> -----Original Message-----
> From:	Austin Franklin [SMTP:austin@darkroom.com]
> Sent:	Tuesday, June 20, 2000 7:25 AM
> To:	'pci-sig@znyx.com'
> Subject:	RE: 3.3V power rail / M66EN
> 
> 1) Does really every motherboard have a 3.3V power supply connected to
> the PCI connectors?
> I understand section 4.3.4 of the spec that every motherboard must
> provide 3.3V to the connectors.
> 
> [Austin] My understanding is no, 4.3.4 of the 2.1 spec says it is
> 'basically' optional, but decoupling caps must be provided none the less.