Re: Purpose of VIO Lines ???

["Andy Ingraham" <ingraham@wrksys.ENET.dec.com>]

> What is the purpose of the VIO pins, and what is a PCI-target-board's
> responsibility with respect to these pins ?

The Vio pins are power pins.

They will have +5V power on them when plugged into a 5V PCI bus, and
+3.3V power in a 3.3V PCI bus.

If your PCI adapter card is a 5V card, you should treat them identically
to the other 5V pins.  If your PCI card is a 3.3V card, treat them
identically to the other 3.3V pins.

If your PCI card is an UNIVERSAL card, these pins must be kept separate
from the 5V pins and 3.3V pins, and should be used to power something in
the PCI interface chip.  This may mean providing power to its I/O cells,
or its output drivers, or maybe just the clamps.  It depends on the PCI
chip's requirements.

Like all the power pins, you should bypass them on the card near the
connector (as they provide part of the signal return path for the rest
of the bus).

Regards,
Andy Ingraham


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