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4 MICROCOMPUTER INSTRUMENTATION AND CONTROL

Figure 4.12
Buffer

FPO

unconnected. The computer will gate in and read the state of those lines, but
the program will be written to purposely ignore them. With the logic signals
interfaced to the microcomputer, a program can be written that will perform
the required logic function.
However, before writing a program, one must know the code or language
in which the program is to be written. Computer languages come in various
levels, including high-level language such as BASIC, assembly language that is
designed for a specific microprocessor, and machine language, which is the
actual language in which a program is stored in memory. For the present
example, we choose the intermediate-level language (assembly language) to
illustrate specific CPU operations.

Assembly Language
Microcomputer instruc- Assembly language is a special type of abbreviated language, each
tions are written in symbol of which pertains to a specific microprocessor operation. Some
assembly language, a type assembly language instructions, such as branch, jump, jump-to-
of shorthand that uses subroutine, and return-from-subroutine, have already been discussed.
initials or shortened Others will be discussed as they are needed to execute an example
words to represent micro- program. Assembly language instructions have the form of initials or
computer instructions. shortened words that represent microcomputer functions. These

118 UNDERSTANDING AUTOMOTIVE ELECTRONICS