CSCI 150, Spring 2003

Digital Electronics.

Introduction
Welcome to the fascinating world of digital electronics. The field of digital electronics is exciting, fast moving, and constantly changing. Advances are being made daily making it possible to do things never imagined possible only a few years ago. Digital electronics are a key element of many products which we take for granted such as personal computers, sophisticated sewing machines, microwave ovens, compact disc players, and video cassette players. The brains of all of these products and many more are composed of digital electronics. Without digital electronics the world would be very different than it is today.

What is Digital Electronics?
The first step we need to take is to gain an understanding of what is meant by digital electronics. A digital system can be defined as one in which all communication within the system is carried out in a digital manner. Typically, this digital communication means that all signals within the system can have only two possible conditions or states. A signal can be on or off. Digital electronics is the branch of electronics concerned with electronic systems which are composed of elements that exhibit this digital behavior. Because a digital system can only exhibit one of two possible states, they are usually easier to understand than analog systems which can have an infinite number of states. The light in the living room of your home is probably a digital system. It is either on or off and by flipping the switch you control this simple digital system.

In this tutorial you will learn the language used to describe and talk about these circuits. One barrier which must be overcome first is the language or jargon barrier. Digital electronics has a language all its own and it is necessary for you to understand this language in order to successfully understand and construct the circuits.

Presented on the next few pages is a short list of the most important terms which you will see used and the meaning of each. Please study this list before beginning any of the experiments.

Frequently Used Terms

clock pulse: A cycle within a circuit from a logic 0 to a logic 1 and back to a logic 0 or vice versa. Clock pulses are commonly used as control signals within a circuit.

clock generator: A device which produces a clock pulse(s). Clock generators are available as a single integrated circuit and are commonly used as the clock source for microprocessors and other integrated circuits which require a clock in order to function. A clock generator called a ³pulser² is provided in CircuitMaker and the pulser is completely programmable from within CircuitMaker.

complement: The opposite state. The complement of a logic 0 is a logic 1 and the complement of a logic 1 is a logic 0. Inverters are commonly used to invert or complement signals within a circuit.

component: The smallest subsystem of a circuit. The integrated circuits and LED's are components of a circuit.

connection: The joint or attachment between two components in a circuit. In order to make any circuit work it is necessary to connect the components together in the correct way.

device: See component.

DIP: See dual in-line package.

dual in-line package: A type of container or housing for integrated circuits. The dual in-line package or DIP has pins extending from it to which wires can be connected in order to wire a circuit.

frequency: The number of times that a logic level changes states each second. The unit of frequency is the hertz. If a level changes from 0 to 1 to 0 100 times each second in some circuit that signal is said to have a frequency of 100 hertz.

ground: The reference point for all voltage measurements within a circuit. It is called ground because often times this point is actually connected to the earth through a conductor.

IC: Integrated circuit. A small device which is composed of many tiny transistors and other components connected together to perform some useful function. Integrated circuits are packaged in a manner which makes them easy to use in designing circuits. IC's can be compared to tiny black boxes which can he wired together to form the heart of everything from computers to digital clocks.

LED: Light emitting diode. A device which resembles a tiny light bulb and can be turned on Or off. LED's are available in several colors such as red, green, and yellow and are commonly used as power indicators and such on computers and other electronic devices.

logic 0: One of the possible voltage levels within a digital circuit. In many circuits a logic 0 is 0 volts.

logic 1: The opposite or complement of a logic 0. In many circuits a logic 1 is about 5 volts.

logic diagram: A special type of diagram used to show the logic elements and the way they are interconnected in a digital circuit.

node: Any point along a wire or wires that are connected between two points in a circuit. Any point along a wire connected between two integrated circuits would he called a node.

power supply: The source of electrical power for a circuit. The power supply provides the voltage and current necessary to operate a circuit. In CircuitMaker you are not required to connect a power supply to the devices to make them function. It is very important that you realize that in the real world a circuit will not function unless every IC is connected to a power supply of the correct voltage, usually 5 volts.

pulse: A change from a logic 0 to logic 1 and back to logic 0 or visa versa.

schematic diagram: A special type of drawing which shows the interconnections of all devices which form a circuit.

seven segment LED: A special type of LED in which seven individual LED's are formed into the shape of an 8. All segments are individually controllable and can be turned on in various combinations to form the numbers 0 through 9.

state: The logic level at some point in a circuit.

truth table: A tabular table used to show the behavior of a circuit for all possible logic states presented at the inputs of thc circuit.

voltage: Potential difference between two points in a circuit. Voltage represents the pressure that causes electrons to move within a circuit. Thc symbol for voltage is "V".