PLX Technology PEX 8311RDK, Hardware Reference Manual

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PEX 8311RDK Hardware Reference Manual, Version 0.90
14 © 2005 PLX Technology, Inc. All rights reserved.
As the PEX 8311 is now the upstream device it may be necessary for the PEX 8311 RDK to source the
PCI Express clock. This can be achieved by populating the onboard PCI Express clock circuit – see sheet
7 of the schematics. To route the PCI Express clocks to the PEX 8311 remove R12
and R13 and insert
R1 and R2.
When operating in Endpoint mode the power for the PEX 8311RDK is normally provided by the PCI
Express edge connector. If power is unavailable from this connector other means must be used to
provide the +12V and +3.3V required by the board. It is possible to use the ATX connector (J4) to provide
+12V to the 3.3V regulator U4 by removing R21 and populating R22 with a 0 ohm jumper. The
PCIE3.3VCC can then be provided by U4 by populating R27 with a 0 ohm jumper. Extreme care must be
taken to ensure that the power sequencing requirements of the PEX 8311 are still met when using the
supplies in this manner. If there is any doubt with regards to power sequencing use one or more of J7, J8
and J9 to provide the supplies to the PEX 8311 from properly sequenced external sources.
The PCI Express edge connector is obviously designed for use in Endpoint mode as an adapter card. A
suitable converter will be required to allow other PCI Express devices/cards to be plugged into the RDK.
In addition, it may be necessary to provide a downstream PCI Express clock. The spare REFCLK2 may
be used for this function although care will be required with regards to the routing of this to the
downstream device.