Datasheet
Identifying Characteristics of Ports and Cables
69
Type B plugs connect in the direction of the component. Therefore, you see a Type B
interface on the hub as well as on the end devices to allow them to cable back to the system
or another hub. Although they exist, USB cables with both ends of the same type, a sort
of extension cable, are in violation of the USB specification. Collectively, these rules make
cabling your USB subsystem quite straightforward.
Although the system receptacle, the Type A, remains somewhat of a constant, the compo-
nent receptacle often differs, usually based on the size of the USB device. For example, a USB-
attached printer is large enough for a Type B connector, but a compact digital camera might
only be large enough to accommodate a Mini-B receptacle of some sort. While the standard
calls for one Mini-B connector, others have been developed, some common, others a bit rarer.
The four connectors shown in Figure 1.50 are the most common. You might also run across
older, rare Mini-A connectors or newer small-form factor interfaces, called Micro-A and
Micro-B, none of which are discussed further in this book.
USB connectors are keyed and will go into a USB port only one way. If the
connector will not go into the port properly, try rotating it.
For more information on USB, check out
HTTPWWWUSBORG.
IEEE 1394 (FireWire)
The IEEE 1394 interface is about one thing: speed. Its first iteration, now known as
FireWire 400, has a maximum data throughput of 400Mbps in half duplex. The next
iteration, FireWire 800 (specified under IEEE 1394b), has a maximum data throughput
of 800Mbps and works in full duplex. FireWire 400 carries data over a maximum cable
length of 4.5 meters with a maximum of 63 devices connected to each interface on the
computer. Using new beta connectors and associated cabling, including a fiber-optic solu-
tion, FireWire 800 extends to 100 meters. IEEE 1394c proposes to run FireWire over
the same Category 5e infrastructure that supports Ethernet, including the use of RJ-45
connectors.
FireWire (also known as i.LINK in Sony’s parlance) uses a very special type of cable, as
shown in Figure 1.52 for FireWire 400. Notice the difference in the system end on the left
and the component end on the right. It is difficult to mistake this cable for anything but a
FireWire cable. The beta connector of a FireWire 800 cable is equally distinctive.
Although most people think of FireWire as a tool for connecting their digital camcord-
ers to their computers, it’s much more than that. Because of its high data transfer rate, it
is being used more and more as a universal, high-speed data interface for things like hard
drives, optical drives, and digital video editing equipment.
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