Overview

A microcontroller interacts in many ways with the system in which it is embedded. It may receive inputs from a human user through switches, for example. These are digital in the sense that they are either on or off, high or low. Similar signals arise from some sensors, such as detectors for the water level or door lock in a washing machine. Going in the opposite direction, the microcontroller turns external devices on or off. These might be indicators, such as simple light-emitting diodes (LEDs) or more complicated seven-segment displays. The MSP430 can supply these directly if they work from the same voltage and draw a sufficiently small current. Heavier loads require transistors or integrated circuits to drive them.

The early sections of this chapter concern digital inputs and outputs like these. Although they are digital in the sense that they should take only two levels, it is not possible even here to ignore the uncomfortable feature that the real world is analog. For example, you might think that a push button gives the simplest input of all. Unfortunately its signal is spoiled by bounce caused by the mechanical motion of the contacts as they are brought together and released. This can make it appear that the button was pressed several times when the user operated it only once. The effects of bounce must be removed by hardware or software so that the user sees the expected result.

Liquid crystal displays (LCDs) are the second major topic of...