Page 115 - Understanding Automotive Electronics

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4 MICROCOMPUTER INSTRUMENTATION AND CONTROL

numbers with a definite number of bits and stored in a memory location. Each
memory location has an address number associated with it like a post office
box. In fact, one could think of the computer memory bank as a large bank of
post office boxes. The computer reads the binary number (instruction or data)
stored in each memory location by going to the address (box number) of the
information it wants to read. When the address for a particular memory
location is generated, a copy of its information is transferred to the computer.
(Note that the original information stays in its location in memory while the
memory is being read.)
All modern electronic Storing a computer program inside the computer’s memory is what
computers have the abil- separates a real computer from a fancy calculator. The computer can use some
ity to store a program in of its memory for storing programs (instructions) and other memory for
internal memory and use storing data. The program or data can be easily changed simply by loading in a
it over and over to different program or different data. The stored program concept is
accomplish tasks. fundamental to all modern electronic computers.

MICROCOMPUTER TASKS
A microcomputer-based A suitably configured microcomputer can potentially perform any
engine control system control or instrumentation task. For example, it will be shown in a later
has much greater flexi- chapter that a microcomputer can be configured to control fuel metering and
bility than the early sys- ignition for an engine. The microcomputer-based engine control system has
tems which were partly much greater flexibility than the earliest electronic engine control systems,
analog. which, typically, used elementary logic circuits as well as analog circuits. For
these early systems, changes in the performance of the control system required
changes in the circuitry. With a microcomputer performing the logic
functions, most changes can be made simply by reprogramming the computer.
That is, the software (program) is changed rather than the hardware (logic
circuits). This makes the microcomputer a very attractive building block in
any digital system.
Microcomputers can also be used to replace analog circuitry. Special
interface circuits can be used to enable a digital computer to input and
output analog signals (this will be discussed later). The important point here
is that microcomputers are excellent alternatives to hardwired (dedicated)
logic and analog circuitry that is interconnected to satisfy a particular
design.
In the subsequent portions of this chapter, both the computer hardware
configuration and programs (software) are discussed. Because these two aspects
of computers are so strongly interrelated, it is necessary for the following
discussion to switch back and forth between the two.

102 UNDERSTANDING AUTOMOTIVE ELECTRONICS