Basic Computer Architecture
Microprocessors are central components of almost all digital systems, because
combinations of hardware and software are used to solve design problems.
A computer is formed by combining a mi- croprocessor with a mix of certain
basic elements and customized logic. Software runs on a microprocessor and
provides a ?exible framework that orchestrates the behavior of hardware that
has been customized to ?t the application. When many people think about
computers, images of desktop PCs and laptops come to their minds.
Computers are much more diverse than the stereotypical image and permeate
everyday life in increasing numbers. Small computers control microwave ovens,
telephones, and CD players.
Computer architecture is fundamental to the design of digital systems.
Understanding how a basic computer is designed enables a digital system to take
shape by using a microprocessor as a central control element. The microprocessor
becomes a programmable platform upon which the major components of an
algorithm can be implemented. Digital logic can then be designed to surround the
microprocessor and assist the software in carrying out a speci?c set of tasks.
The ?rst portion of this chapter explains the basic elements of a computer,
including the micro- processor, memory, and input/output devices. Basic
microprocessor operation is presented from a hardware perspective to show
how instructions are executed and how interaction with other system components
is handled. Interrupts, registers, and stacks are introduced as well to provide
an overall picture of how computers function. Following this basic introduction
is a complete example of how an actual eight-bit computer might be designed,
with detailed descriptions of bus operation and address decoding.
Once basic computer architecture has been discussed, common techniques for
improving and augmenting microprocessor capabilities are covered, including
direct memory access and bus expan- sion. These techniques are not relegated to
high-end computing but are found in many smaller digital systems in which it is
more economical to add a little extra hardware to achieve feature and
performance goals instead of having to use a microprocessor that may be
too complex and more expensive than desired.
The chapter closes with an introduction to assembly language and
microprocessor addressing modes. Writing software is not a primary topic of this
book, but basic software design is an insepara- ble part of digital systems
design. Without software, a computer performs no useful function. As-sembly
language basics are presented in a general manner, because each microprocessor
has its own instruction set and assembly language, requiring speci?c reading
focused on that particular device. Basic concepts, however, are universal
across different microprocessor implementations and serve to further explain
how microprocessors actually function.
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