Figure 2 shows a typical server-based design where the

root complex provides a PCI Express link that needs to

be expanded to a larger number of smaller ports for a

variety of I/O functions. In this example, the PEX 8548

would have a 16-lane upstream port, and as many as six

x8 or x4 downstream ports. The PEX 8548 will also

auto-negotiate down to x2 and x1 lane widths to support

endpoints requiring smaller links.

Peer-to-Peer & Backplane Usage

The PEX 8548 is also suitable for peer-to-peer

applications such as switch fabrics and backplanes.

Figure 3 represents a backplane where the device

provides peer-to-peer data exchange for a large number

of line cards where the CPU/Host plays the management

role.

x8

Power PC

Power PC

Power PC

Power PC

x8

PEX 8548

PEX 8548

PEX 8548

PEX 8548

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

x8

x8

x8

x8

x8

Figure 3. Peer-to-Peer/Backplane Usage

Graphics Fan-out Switch

The PEX 8548 offers three port configurations which are

optimal for High resolution 3D graphics applications.

Dual-graphics, high-resolution gaming, high resolution

scientific use, and image processing can benefit from its

performance features. Figure 4 illustrates usage of the

device in a dual graphics gaming application where two

GPUs drive a single monitor for the ultimate gaming

experience. The upstream x16 port links to the Root

Complex and the two downstream ports connect to the

graphics modules. The peer-to-peer support of the PEX

8548 allows the two GPU modules to communicate with

each other for maximum performance.

GPU

GPU

GPU

GPU

GPU

GPU

GPU

GPU

GPU

GPU

GPU

GPU

PEX 8548

PEX 8548

PEX 8548

PEX 8548

CPU

CPU

CPU

CPU

x16

x16

Root

Complex

Root

Complex

Root

Complex

Root

Complex

x16

Figure 4. Dual Graphics Fan-out

Blade Server Switch Fabric

The PEX 8548 can be cascaded to create an even greater

number of ports. For example, in a Blade Server

application, two PEX 8548 switches can be combined to

support up to sixteen blades (Figure 5). The switches can

be linked to available PCI Express ports. The PEX 8508

switch can isolate each CPU blade using its Non-

Transparent Bridging function.

PEX 8548

PEX 8548

PEX 8548

PEX 8548

14 CPU Blades

2 I/O Blades

CPU Blade

CPU Blade

CPU

CPU

CPU

CPU

CPU

CPU

Root

Complex

Root

Complex

PEX 8508

PEX 8508

NT

PEX 8548

PEX 8548

PEX 8548

PEX 8548

Figure 5. Blade Server

The number of ports and port widths can be configured

as needed. This example assumes a x4 link to each CPU

blade and a x8 link to the I/O blades. The link between

the two PEX 8548 devices is x8 lanes wide.