There is a great variety of applications of microprocessors in automobiles. As will be explained in later chapters of this book, microprocessors find applications in engine and driveline control, instrumentation, ride control, antilock braking and other safety devices, entertainment, heating/air conditioning control, automatic seat position control, and many other systems. In each of these applications, the microprocessor serves as the functional core of what can properly be called a special-purpose microcomputer.

Although these applications are widely varied in operation, the essential configuration (or architecture) has much in common for all applications. Figure 4.21 is a simplified block diagram depicting the various components of each of the automotive systems having the applications listed previously. In this block diagram, the microprocessor is denoted MPU. It is connected to the other components by means of three buses: address bus (AB), data bus (DB), and control bus (CB). Each bus consists of a set of wires over which binary electrical signals are transmitted. By way of illustration, in early automotive application, the DB consists of 8 wires, the AB is typically 8 to 16 wires, and the control bus is a set of 3 or 4 wires.

Figure 4.21: Architecture for Typical Automotive Computer

The operation of each special-purpose microcomputer system is controlled by a program stored in ROM. As explained earlier in this chapter, the MPU generates addresses for the ROM in sequence to obtain each instruction in corresponding sequence. The operation of each microprocessorbased automotive subsystem...