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Re: 3.3V Decoupling
- To: Mailing List Recipients <pci-sig-request@znyx.com>
- Subject: Re: 3.3V Decoupling
- From: "John R Pierce" <pierce@scruznet.com>
- Date: Thu, 21 Nov 1996 17:56:23 +0000
- Comments: Authenticated sender is <pierce@mail.scruznet.com>
- Organization: Graphics Control
- Priority: normal
- Reply-To: pierce@scruznet.com
- Resent-Date: Thu, 21 Nov 1996 17:56:23 +0000
- Resent-From: pci-sig-request@znyx.com
- Resent-Message-Id: <"7CLn12.0.3w4.RaGbo"@dart>
- Resent-Sender: pci-sig-request@znyx.com
> Date: Thu, 21 Nov 1996 15:50:35 -0500
> From: Jerry Sabath <sabath@atla3.agfa.com>
> Subject: 3.3V Decoupling
> To: Mailing List Recipients <pci-sig-request@znyx.com>
> Section 4.4.2.1 of the PCI Spec Revision 2.1 states:
>
> Additionally, all +3.3V pins (even if they are not actually
> delivering power) . . . on the PCI edge connector provide
> an AC return path, and must have plated edge fingers and be
> coupled to the ground plane on the add-in board . . . to
> ensure that they continue to function as efficient AC
> reference points . . ."
>
> Can someone explain why the specification does not allow
> unplated fingers? Would a board with unplated +3.3V fingers
> have significantly different characteristics than an
> unpopulated PCI slot?
The decoupling of the 3.3V pins is so that they act as an AC ground
for YOUR board... There aren't enough ground pins on the PCI bus
alone to provide this function...
-jrp
7 ö