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MICROCOMPUTER INSTRUMENTATION AND CONTROL 4

Microcomputer

Instrumentation and Control

This chapter explains microcomputers and how they are used in
instrumentation and control systems. Topics include microcomputer
fundamentals, microcomputer equipment, microcomputer inputs and
outputs, computerized instrumentation, and computerized control systems.
The specific automotive applications of microcomputers are explained in later
chapters.

MICROCOMPUTER FUNDAMENTALS
Digital versus Analog Computers
A digital computer rep- In digital computer-based systems, physical variables are represented by a
resents each variable in numerical equivalent using a form of the binary (base 2) number system. In the
terms of binary num- previous chapter it was shown that transistor circuits can be constructed to have
bers. one of two stable states: saturation and cutoff. These two states can be used to
represent a 0 (zero) or a 1 (one) in a binary number system. To be practically
useful, there must be groups of such circuits that are arranged in the form of a
place position, binary number system.
By contrast, an analog system has a single lead with a voltage (relative to
ground) that is proportional to the relevant physical variable. A digital system
will have a group of leads, each one of which can have only two voltage levels
representing 0 or 1 (as discussed in Chapter 3). It is common practice for a
digital computer to have the number of voltages representing the binary digits
(bits) be a multiple of 8. For example, early automotive engine control
8
computers used 8 bits to represent data, which means that 256 (2 ) possible
levels can be represented. In any application, including automotive, a
computer performs various operations on the data. To explain the operation of
a digital computer, it is helpful to first explain the operation of its various
components.
Parts of a Computer

The parts of a digital computer are shown in Figure 4.1. The central
processing unit (CPU) is the processor that is the heart of the system. When
made in an integrated circuit, it is called a microprocessor. This is where all of

UNDERSTANDING AUTOMOTIVE ELECTRONICS 99