PCI - decoupling of unused 3.3V connector pads

[tony@burched.com.au (burched - tony burch)]

Hi pci-sig members,

I am currently designing a PCI add-in card PCB,
and have been reading "PCI Hardware and
Software Architecture and Design, 4th edition".

Chapter 13 on Connector, Platform, and Add-In
Card Design, has useful info on layout and
decoupling issues.  However, the last dot
point of the chapter has me scratching my head.
It states:
"All unused 3.3 volt and 5 volt connector pads must
be individually attached to a 0.01 uF high speed
capacitor.... Several connector pads can share a
capacitor if trace requirements are met".

For this design, I am actually not using the 3.3 volt
from the PCI connector.  However, the above
implies that I should still decouple these pads.

Is that correct?  If so, what is the reasoning behind
needing to decouple those pads if I am not using
the 3.3 volt supply on this card?

Thanks for considering my question.

Best regards

Tony Burch

www.BurchED.com.au
Lowest cost, easiest-to-use
FPGA prototyping kits!