Page 147 - Understanding Automotive Electronics

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4 MICROCOMPUTER INSTRUMENTATION AND CONTROL

Figure 4.21
Architecture for
Typical Automotive
Computer

FPO

The hardware in the The operation of each special-purpose microcomputer system is
microcomputer remains controlled by a program stored in ROM. As explained earlier in this chapter,
fixed, while the pro- the MPU generates addresses for the ROM in sequence to obtain each
grams stored in ROM instruction in corresponding sequence. The operation of each microprocessor-
can be changed as based automotive subsystem has a specific program that is permanently stored
desired to perform dif- (electronically) in the ROM. Changes in the system operation can be achieved
ferent applications. by replacing the ROM chip(s) with new chip(s) that contain the appropriate
program for the desired operation. This feature is advantageous during the
engineering development phase for any microprocessor-based system. While
the hardware remains fixed, the system modifications and improvements are
achieved by substituting ROM chips.
A typical automotive microprocessor-based system also incorporates some
amount of RAM. This memory is used for a variety of purposes, including
storing temporary results, storing the stack, and storing all of the variables, not
to mention all of the other activities discussed earlier in this chapter.
The input/output (I/O) device for any given automotive microcomputer
system serves as the interface connection of the microcomputer with the

134 UNDERSTANDING AUTOMOTIVE ELECTRONICS