3.3V power rail / M66EN

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

Correction: The statement below applies to revision 2.2 of the spec and not
2.1.  In revision 2.1 the 3.3V is considered optional, but "encouraged".

John Urry

> -----Original Message-----
> From:	Urry, John @ CSW-SLC 
> Sent:	Tuesday, June 20, 2000 8:54 AM
> To:	'pci-sig@znyx.com'
> Subject:	RE: 3.3V power rail / M66EN
> 
> 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.