Parallel Input/Output and Interrupts
A microcomputer with no input/output (I/O) would be useless, because there would be no way of communicating with it. The two classes of communication used by microcomputers are parallel and serial. In parallel communication, which will be explored in this chapter, eight lines (for an 8-bit computer) are available to the outside. The voltage levels on these lines are either 0 or 5V, and the level of all lines is sensed simultaneously. Parallel I/O is thus conveying information to or from the world external to the microcomputer in the same manner as the data bus communicates within the microcomputer. In serial communication, on the other hand, only two lines participate in the process, and one of them is normally constant at ground potential. The voltage on the active line is high at one instant and low at another, so only one signal is transmitted at a time. Both parallel and serial communication are vital, and each has its place. Serial communication will be addressed in the next chapter.
KeywordsControl Register Memory Location Operating Program Serial Communication Interrupt Service Routine
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