Intel Xeon Processor and Intel E7500/E7501Chipset Compatible Platform Design Guide

Intel
®
82870P2 (P64H2)
140 Intel
®
Xeon™ Processor and Intel
®
E7500/E7501 Chipset Compatible Platform Design Guide
M66EN Isolation Switch Solution
One possible solution to the issue described in the previous paragraphs is to place a single
5
kΩ ± 5% pull-up on the P64H2 side of the isolation logic and a 5 kΩ ± 5% pull-up on the slot side
after the isolation logic, but with its own isolation switch, which uses an inverted version of the bus
enable control signal. This way, when the isolation logic has the bus disconnected, the slot side will
be pulled up with a 5
kΩ ± 5% resistor. When the isolation logic has the bus connected, the slot side
resistor will be isolated, and the M66EN line will be pulled up by the 5
kΩ ± 5% pull-up on the
P64H2 side of the isolation logic. Using this method, the P64H2 would only be sinking through a
single 5
kΩ resistor at any time and would always be meeting the PCI Local Bus Specification,
Revision 2.2 on the M66EN pull-up (PCI Local Bus Specification, Revision 2.2, Section 7.7.7). See
Figure 8-22.
Figure 8-22. M66EN Isolation Switch Solution
PCI SLOT
M66EN
+3.3 V
+3.3 V
5 k
Ω
5 kΩ
PCI Bus
Isolation Switch
M66EN
Isolation
Switch
HxM66EN
PxM66EN
Intel
®
P64H2
HxBUSEN#