CONFIDENTIAL
Z3-DM8168-PCI-RPS V1.05.01c
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Z3 Technology, LLC
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100 N 8
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ST, STE 250
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Lincoln, NE 68508-1369 USA
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+1.402.323.0702
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10.
PCI Express
10.1 PCIe Lanes and Slots
The Z3-DM8168-APP-2x board is designed to be used as a PCI Express add-in card. The DM8168 chip
mounted on the module provides a PCI Express interface with 2 lanes. The PCI Express specification
standardizes on connectors for 1, 4, 8 and 16 lanes. The Z3-DM8168-APP-2x board is therefore designed to
mate with a 4-lane connector in order to allow the 2 lanes from the DM8168 processor to be active.
The PCI Express specification allows for plugging interface cards into any slot that provides at least as
many lanes as present in the interface card. Therefore, the PCIe spec allows you to plug the Z3-DM8168-
APP-2x board into any PCI Express slot that it will fit in – 4, 8 or 16 lanes.
The Z3-DM8168-PCI-RPS board set can also operate as 1 1-lane PCIe device. This means that if the
mechanical restrictions of inserting a big board into a small slot did not exist, it would also work. Since this
is a generic situation some motherboard vendors have included PCIe slots that have their backs open to
allow the insertion of a board with more lanes than the connector. Although this should work well (for all
devices including the Z3-DM8168-PCI-RPS system), there is no guarantee that it will in fact work in all
situations.
The “PCI Express Card Electromechanical Specification” document section on “Card Interoperability” is a
good reference. The document is available (for members) from the PCI Group at
http://www.pcisig.com/specifications/pciexpress/base.
10.2 PCIe BIOS on the PC
When the PC is first powered up, its BIOS performs some system tests and initialization, including PCI
Express initialization. The BIOS is required to assign resources to all peripherals on the system, including
those devices in PCI Express add-in cards, before it can proceed to boot the operating system. During this
initialization, the BIOS will determine allocation of memory addresses and interrupt lines, and use this
information to turn on each peripheral in a way that they don’t conflict with each other.
One of the functions of the BIOS is to determine if there is a display adapter card present in the system,
and if so the BIOS makes it the primary video monitor. Some BIOSes mistakenly think that any add-in card
present in its 16-lane PCIe slot must be a display controller, even if the PCIe card clearly tells the BIOS (via
configuration space) it isn’t. This BIOS behavior is most frequent on motherboards with only one PCIe slot
or one 16-lane and one 1-lane slot, where the most popular add-in card on the 16-lane slot would in fact
be a video controller. The problem is that these systems will effectively either not boot with the Z3-
DM8168-APP-2x card (or any other non-video card) plugged in, or boot without video. Usually there are no
configuration settings in the BIOS that will correct the behavior of the BIOS, making it effectively
impossible to use that motherboard.
