4 - Input & output

Abstract

The typical microcontroller unit (MCU)-based consumer product can be extremely complex, and contains a wide range of technologies around the main controller. A detailed understanding of these technologies requires a very high level of engineering skill. To help develop this skill, some simpler equivalent technologies such as how character-based information on a low-resolution monochrome alphanumeric liquid crystal display (LCD) is displayed should be studied. For designing microcontroller circuits, a range of input & output techniques are described here. The simplest input is a switch or push button. This can operate with just one additional support component, a pull-up resistor, but there are still some significant issues to consider, such as input loading and debouncing. When the contacts close in any mechanical switch or push button, they tend to bounce open before settling in closed position. This is called debouncing. In normal life, this is not noticeable or significant, but in microsystems it is liable to cause circuit misbehavior if ignored. Another input technique is keypad input. A keypad is simply an array of push buttons connected in rows and columns so that each can be tested for closure with the minimum number of connections.