Installation Guide, Third Edition - Server Expansion Unit

Chapter 1
Introduction
Detailed Server Expansion Unit Description
10
System Backplane
The Server Expansion Unit system backplane provides inter-connection between the PCI-X backplane and
the core I/O backplane. The Server Expansion Unit backplane also provides a connection point for the SBA
link cables and routes the SBA link cable signals to and from the PCI-X backplane. The backplane receives
primary (48V) and standby (12V) power from the bulk power supplies and distributes this power to loads on
the Server Expansion Unit backplane and to the other boards connected to it. Besides providing interconnect,
the Server Expansion Unit backplane contains clock generation circuits.
Figure 1-5 System Backplane (Side View in Chassis)
The backplane includes the connections for the PCI-X backplane and power. It also has manageability circuits
for monitoring and running the Server Expansion Unit chassis. PCI-X clock distribution is done on this board.
The voltage regulator modules (VRMs) that provide 3.3V and 3.3V standby are located on this backplane. The
backplane also has the connectors to provide a hardware interface to the Server Expansion Unit chassis.
Clocks and Reset
The system backplane contains reset and clock circuitry that propagates through the whole system. The
system backplane central clocks drive all major chip set clocks.
I/O Subsystem
The cell board to the PCI-X board path runs from the cell controller (CC) to the SBA, from the SBA to the
ropes, from the ropes to the LBA, and from the LBA to the PCI slots as seen in Figure 1-6 on page 11. The CC
on cell board 2 and cell board 3 communicates with each SBA over the SBA link. The SBA link consists of both
an inbound and an outbound link with an effective bandwidth of approximately 1 GB/sec. The SBA converts
the SBA link protocol into “ropes.” A rope is defined as a high-speed, point-to-point data bus. The SBA can
support up to 16 of these high-speed bi-directional rope links for a total aggregate bandwidth of
approximately 4 GB/sec. Each LBA acts as a bus bridge, supporting either one or two ropes and capable of
driving 33 MHz or 66 MHz for PCI cards. The LBAs can also drive at 66 MHz or 133 MHz for PCI-X cards.
System Backplane