RE: 3.3V power rail / M66EN

[maarten.ghijsen@philips.com]

Hello,

In version 2.1 of the PCI spec. 3.3V is optional (in 5V I/O environments), which means that most (all) manufactures didn't implement 3.3V on the motherboard. In version 2.2 of the specification it is stated that 3.3V is required, so all motherboard that 
comply to version 2.2 should supply 3.3V on the 3.3V power rails.

So if you want to be sure that there is 3.3V on the 3.3V power rails make sure you have a motherboard that is versions 2.2 compatible. Or alternatively make your own on-board 3.3V power supply from the 5V power rails (always there in both version 2.1 & 
2.2).

Regards from Maarten




austin@darkroom.com on 06/20/2000 05:03:22 PM
To:	pci-sig@znyx.com@SMTP
cc:	 
Subject:	RE: 3.3V power rail / M66EN
Classification:	Restricted
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.