Datasheet

Identifying Characteristics of Ports and Cables 67
TABLE 1.4 Common Serial Cable Configurations
1st Connector 2nd Connector Description
DE-9 female DB-25 male Standard modem cable
DE-9 female DE-9 male Standard serial extension cable
DE-9 female DE-9 female Null modem cable
DB-25 female DB-25 female Null modem cable
DB-25 female DB-25 male Standard serial cable or standard serial
extension cable
Universal Serial Bus (USB)
USB cables are used to connect a wide variety of peripherals to computers, including key-
boards, mice, digital cameras, printers, and scanners. The latest version of USB, version 2.0,
requires a cable with better shielding than did earlier versions. Not all USB cables work with
USB 2.0 ports. The connectors are identical, so perhaps look for cables that are transparent
with a view to the silver metallic shielding within.
USB’s simplicity of use and ease of expansion make it an excellent interface for just about
any kind of peripheral. This fact alone makes the USB interface one of the most popular on
the modern computer, perhaps behind only the video, input, and network connectors.
The USB interface is fairly straightforward. Essentially, it was designed to be Plug and
Play—just plug in the peripheral, and it should work (providing the software is installed to
support it). The USB cable varies based on the USB male connector on each end. Because
there can be quite a number of daisy-chained USB devices on a single system, it helps to
have a scheme to clarify their connectivity. The USB standard specifies two broad types
of connectors. They are designated Type A and Type B connectors. A standard USB cable
has some form of Type A connector on one end and some form of Type B connector on the
other end. Figure 1.50 shows four USB cable connectors. From left to right, they are:
Type A
ßN
Standard Mini-B
ßN
Type B
ßN
Alternate Mini-B
ßN
One part of the USB interface specification that makes it so appealing is the fact that if
your computer runs out of USB ports, you can simply plug a device known as a USB hub
into one of your computer’s USB ports, which will give you several more USB ports from
one USB port. Figure 1.51 shows an example of a USB hub.
86498book.indb 67 7/22/09 5:37:54 AM