A microcomputer-based engine control system has much greater flexibility than the early systems which were partly analog.

A suitably configured microcomputer can potentially perform any control or instrumentation task. For example, it will be shown in a later chapter that a microcomputer can be configured to control fuel metering and ignition for an engine. The microcomputer-based engine control system has much greater flexibility than the earliest electronic engine control systems, which, typically, used elementary logic circuits as well as analog circuits. For these early systems, changes in the performance of the control system required changes in the circuitry. With a microcomputer performing the logic functions, most changes can be made simply by reprogramming the computer. That is, the software (program) is changed rather than the hardware (logic circuits). This makes the microcomputer a very attractive building block in any digital system.

Microcomputers can also be used to replace analog circuitry. Special interface circuits can be used to enable a digital computer to input and output analog signals (this will be discussed later). The important point here is that microcomputers are excellent alternatives to hardwired (dedicated) logic and analog circuitry that is interconnected to satisfy a particular design.

In the subsequent portions of this chapter, both the computer hardware configuration and programs (software) are discussed. Because these two aspects of computers are so strongly interrelated, it is necessary for the following discussion to switch back and forth between the two.

In a modern personal computer, the...