Re: 5V board in a 3.3V PCI slot

From: Steve Schefter (steve_schefter_at_hotmail.com)
Date: 06/23/04 

Date: 23 Jun 2004 07:23:43 -0700

Hi Marco.

> I installed that board in a Piv 1.6Ghz Mainboard D845WN and I can't do
> it starts. The board's power requirements are 22.5W @ 5V, and using PC
> Wizard I see that the PCI slot used by the Dialogic board has this
> description: "In Use (32-bit) 3.3v".
> Is this a problem?

When a PCI card or slot is defined as 3.3V or 5V, it is describing the
voltage used for signalling (what voltage is used to drive the address/
data and control lines). However, other voltages can be used as a
power source. In particular, the PCI spec says that 3.3V slots must
also provide power on the 5V power supply lines. This allows the
card to, for example, use 5V for the back end logic even though it talks
across the PCI bus at 3.3V.

The notch in the gold fingers only allow you to plug the correct type
of card (3.3V, 5V or universal) into the slot, so you don't have to
worry about that being wrong.

Having said that, I've seen at least one IBM server with 3.3V slots
which violated the PCI spec. It didn't provide the 5V supply to the
PCI cards. Checking the motherboard specs should resolve this though.

Regards,
       Steve
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Steve Schefter phone: +1 705 725 9999 x26
The Software Group Limited fax: +1 705 725 9666
642 Welham Road,
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