4-4
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Technical Reference Guide
System Support
Link Layer
The link layer provides data integrity by adding a sequence information prefix and a CRC suffix
to the packet created by the transaction layer. Flow-control methods ensure that a packet will
only be transferred if the receiving device is ready to accomodate it. A corrupted packet will be
automatically re-sent.
Physical Layer
The PCI Express bus uses a point-to-point, high-speed TX/RX serial lane topology. One or more
full-duplex lanes transfer data serially, and the design allows for scalability depending on
end-point capabilities. Each lane consists of two differential pairs of signal paths; one for
transmit, one for receive (Figure 4-1).
Figure 4-1. PCI Express Bus Lane
Each byte is transferred using 8b/10b encoding. which embeds the clock signal with the data.
Operating at a 2.5 Gigabit transfer rate, a single lane can provide a data flow of 200 MBps. The
bandwidth is increased if additional lanes are available for use. During the initialization process,
two PCI Express devices will negotiate for the number of lanes available and the speed the link
can operate at. In a x1 (single lane) interface, all data bytes are transferred serially over the lane.
In a multi-lane interface, data bytes are distributed across the lanes using a multiplex scheme.
4.2.3 Option ROM Mapping
During POST, the PCI bus is scanned for devices that contain their own specific firmware in
ROM. Such option ROM data, if detected, is loaded into system memory's DOS compatibility
area (refer to the system memory map shown in chapter 3).
4.2.4 PCI Interrupts
Eight interrupt signals (INTA- thru INTH-) are available for use by PCI devices. These signals
may be generated by on-board PCI devices or by devices installed in the PCI slots. For more
information on interrupts including PCI interrupt mapping refer to the “System Resources”
section 4.3.
4.2.5 PCI Power Management Support
This system complies with the PCI Power Management Interface Specification (rev 1.0). The
PCI Power Management Enable (PME-) signal is supported by the chipset and allows compliant
PCI peripherals to initiate the power management routine.
Device A
Device B
TX
System Board
PCI Express Card
RX
Summary of Contents for Compaq dc7800 MT
Page 8: ...1 2 www hp com Technical Reference Guide Introduction ...
Page 32: ...2 16 www hp com Technical Reference Guide System Overview ...
Page 80: ...6 8 www hp com Technical Reference Guide Integrated Graphics Subsystem ...
Page 92: ...7 12 www hp com Technical Reference Guide Power and Signal Distribution ...
