Hardware Reference
In-Depth Information
Serial protocols like RS-232, USB, and IEEE 1394 (also
known as FireWire and i.Link) connect computers to
printers, hard drives, keyboards, mice, and other periph-
eral devices. Network protocols like Ethernet and TCP/
IP connect multiple computers through network hubs,
routers, and switches. A communications protocol usually
defines the rate at which messages are exchanged, the
arrangement of data in the messages, and the grammar of
the exchange. If it's a protocol for physical objects, it will
also specify the electrical characteristics, and sometimes
even the physical shape of the connectors. Protocols
don't specify what happens between objects, however.
The commands to make an object do something rely on
protocols in the same way that clear instructions rely on
good grammar—you can't give useful instructions if you
can't form a good sentence.
by sending timed pulses of energy across a shared con-
nection. The USB connection from your mouse to your
computer uses two wires for transmission and reception,
sending timed pulses of electrical energy across those
wires. Likewise, wired network connections are made up of
timed pulses of electrical energy sent down the wires. For
longer distances and higher bandwidth, the electrical wires
may be replaced with fiber optic cables , which carry timed
pulses of light. In cases where a physical connection is
inconvenient or impossible, the transmission can be sent
using pulses of radio energy between radio transceivers (a
transceiver
is two-way radio, capable of transmitting and
receiving). The meaning of data pulses is independent of
the medium that's carrying them. You can use the same
sequence of pulses whether you're sending them across
wires, fiber optic cables, or radios. If you keep in mind that
all of the communication you're dealing with starts with
a series of pulses—and that somewhere there's a guide
explaining the sequence of those pulses—you can work
with any communication system you come across.
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One thing that all communications protocols have in
common—from the simplest chip-to-chip message to the
most complex network architecture—is this: it's all about
pulses of energy. Digital devices exchange information
Computers of All Shapes and Sizes
You'll encounter at least four different types of computers in this topic, grouped
according to their physical interfaces. The most familiar of these is the personal
computer. Whether it's a desktop or a laptop, it's got a keyboard, screen, and mouse,
and you probably use it just about every working day. These three elements—the
keyboard, the screen, and the mouse—make up its physical interface.
The second type of computer you'll encounter in this topic,
the
microcontroller
, has no physical interface that humans
can interact with directly. It's just an electronic chip with
input and output pins that can send or receive electrical
pulses. Using a microcontroller is a three-step process:
In other words, the microcontroller's physical interface is
whatever you make of it.
The third type of computer in this topic, the
network
server
, is basically the same as a desktop computer—it
may even have a keyboard, screen, and mouse. Even
though it can do all the things you expect of a personal
computer, its primary function is to send and receive data
over a network. Most people don't think of servers as
physical things because they only interact with them over
a network, using their local computers as physical inter-
faces to the server. A server's most important interface for
most users' purposes is its software interface.
1. You connect sensors to the inputs to convert physical
energy like motion, heat, and sound into electrical energy.
2. You attach motors, speakers, and other devices to the
outputs to convert electrical energy into physical action.
3. Finally, you write a program to determine how the input
changes affect the outputs.
