PCI 66MHz 5V Signaling environment?

Hello!

I have to design a PCI motherboard with the Intel21154BE PCI bridge on it. The primary PCI bus has to work at 66MHz (64bits) and the secondary PCI bus at 33MHz (32bits).

My problem is that our customer requires for the primary PCI bus a signaling environment of 5V (VI/O = +5V, PCI connectors 64bit, 5V). This would be against the PCI Local Bus Specification, which says that a PCI 66MHz bus uses a +3.3V signaling environment. Do you have any idea how the PCI-Bridge chip will behave? Are there any chances for a correct behavior of the system?

I saw that Intel recommends to connect always the P_VIO pin to +5V (to avoid some performance problems). In the document “21154 PCI-to-PCI Bridge Specification Update March 2002”, page 19, it is written: “P_VIO and S_VIO set the value of the voltage clamp only and has no effect on the signaling levels of the bus”.

Thank you!

Laurentiu