Page 106 - Understanding Automotive Electronics

2735 | CH 3 Page 93 Tuesday, March 10, 1998 11:03 AM

ELECTRONICS FUNDAMENTALS 3

arithmetic operations on two 4-bit inputs, A and B. Table 3.4 summarizes these
various operations using the logical notation explained earlier in this chapter.
The Microprocessor
Perhaps the single most important digital IC to evolve has been the
microprocessor (MPU). This important device, incorporating more than
250,000 gates in an area of about / -inch square, has truly revolutionized
1
4
digital electronic system development. A microprocessor is the operational core
of a microcomputer and has broad application in automotive electronic
systems.
The MPU incorporates a relatively complicated combination of digital
circuits including an ALU, registers, and decoding logic. A typical MPU block
diagram is shown in Figure 3.12. The double lines labeled “bus’’ are actually
sets of conductors for carrying digital data throughout the MPU. Common IC
MPUs use 8, 16, or 32 conductor buses.
The microprocessor in A microprocessor by itself can accomplish nothing. It requires additional,
combination with mem- external digital circuitry as explained in the next chapter. One of the tasks
ory and other circuits performed by the external circuitry is to provide instructions in the form of
under program control digitally encoded electrical signals. For example, an 8-bit microprocessor
can accomplish very operates with 8-bit instructions. There are 28 (or 256) possible logical
complex tasks. combinations of 8 bits, corresponding to 256 possible MPU instructions, each

Figure 3.12
MPU Block Diagram

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 93