Hardware Reference
In-Depth Information
An embedded system is a special-purpose computer system designed to perform a dedicated
function. Unlike a general-purpose computer, such as a personal computer, an embedded sys-
tem performs one or a few predefined tasks, usually with very specific requirements, and often
includes task-specific hardware and mechanical parts not usually found in a general-purpose
computer. Since the system is dedicated to specific tasks, design engineers can optimize it, re-
ducing the size and cost of the product. Embedded systems are often mass produced, benefiting
from economy of scale.
Physically, embedded systems range from portable devices such as digital watches and MP3
players, to large stationary installations like traffic lights, factory controllers, or the systems
that control power plants. In terms of complexity, embedded systems run from simple, with
a single microcontroller chip, to very complex with multiple units, peripherals, and networks
mounted inside a large chassis or enclosure.
Mobile phones or handheld computers share some elements with embedded systems, such
as the operating systems and microprocessors that power them, but are not truly embedded sys-
tems themselves because they tend to be more general purpose, allowing different applications
to be loaded and peripherals to be connected.
C
HARACTERISTICS
OF
E
MBEDDED
S
YSTEMS
Embedded systems have the following characteristics:
•
Embedded systems are designed to perform some specific task, rather than being a
general-purpose computer for multiple tasks. Some also have real-time performance
constraints that must be met, for reasons such as safety and usability; others may
have low or no performance requirements, allowing the system hardware to be
simplified to reduce costs.
•
An embedded system is not always a separate block; very often it is physically built
into the device it is controlling.
•
The software written for embedded systems is often called firmware and is stored
in read-only memory or flash memory chips rather than a disk drive. It often runs
with limited computer hardware resources: small or no keyboard or screen and
little memory.
U
SER
I
NTERFACES
Embedded systems range from having no interface at all—dedicated to only one task—to
full user interfaces similar to desktop operating systems in devices such as personal digital
assistants (PDAs).
A simple embedded system may use buttons for input and use
LEDs
or small character-
only display for output. A simple
menu system
may be provided for users to interface with.
A more complex system may use a full graphical screen that has
touch
sensing or screen-
edge buttons to provide flexibility while at the same time minimize space. The meaning of the
buttons can change with the screen.
Handheld systems often have a screen with a “joystick button” for a pointing device. The
rise of the World Wide Web has given embedded designers another quite different option: pro-
viding a webpage interface over a network connection. This avoids the cost of a sophisticated
display, yet provides complex input and display capabilities when needed, on another computer.
This is successful for remote, permanently installed equipment. In particular, routers take
advantage of this ability.
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