Page 138 - Understanding Automotive Electronics

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MICROCOMPUTER INSTRUMENTATION AND CONTROL 4

such a lag, there may be applications where variables change more rapidly than
the sampling time. Special compromises must be made in such cases, or a new
technique must be found to solve the problem.

MICROCOMPUTER HARDWARE
The microcomputer system electronic components are known as
computer hardware. (The programs that the computer runs are called
software.) The basic microcomputer parts are the CPU, memory, and I/O
(input and output peripherals). We next expand upon this discussion of
important components and their associated operations.
Central Processing Unit
The central processing unit is a microprocessor. It is an integrated circuit
similar to the one shown in Figure 4.16a. It contains thousands of transistors
and diodes on a chip of silicon small enough to fit on the tip of a finger. It
includes some form of arithmetic logic unit (ALU), as well as registers for data
and instruction storage and a control section. The chip is housed in a
rectangular, flat package similar to the one shown in Figure 4.16b. It is less
than three inches long and has two rows of small pins that make connections
to external circuits. The CPU gets program instructions from a memory
device.

Memory: ROM
Permanent memory, There are several types of memory devices available, and each has its
called ROM, maintains own special features. Systems such as those found in the automobile that
its contents even when must permanently store their programs use a type of permanent memory
power is turned off. called read-only memory (ROM). This type of memory can be programmed
ROM is used for CPU only one time and the program is stored permanently, even when the
instructions requiring microcomputer power is turned off. The programs stored in ROM are
permanent storage. sometimes called firmware rather than software since they are unchangeable.
This type of memory enables the microcomputer to immediately begin
running its program as soon as it is turned on.
Memory: RAM
A form of memory that Another type of memory, one that can be written to as well as read from,
can be written to and is required for the program stack, data storage, and program variables. This type
changed, as well as read of memory is called random access memory (RAM). This is really not a good
from, is commonly name to distinguish this type of memory from ROM because ROM is also a
referred to as RAM. random access type of memory. Random access means the memory locations
can be accessed in any order rather than in a particular sequence. A better
name for the data storage memory would be read/write memory (RWM).
However, the term RAM is commonly used to indicate a read/write memory, so
that is what will be used here. A typical microcomputer contains both ROM
and RAM type memory.

UNDERSTANDING AUTOMOTIVE ELECTRONICS 125