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Chapter 4

# ITM207 Chapter 4.docx

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Ryerson University

Information Technology Management

ITM 207

Youcef Derbal

Winter

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Chapter4GatesandCircuitsThis chapter is all about how computers use electrical signals to represent and manipulate binary values and the basic hardware elements in a computer41Computers and ElectricityAs mentioned previously we distinguish between 2 values of interest binary 0 and 1 by the voltage level of a signaloVoltage in the range of 0 and 2 is considered low or 0 in binaryoVoltage in the range of 2 to 5 volts is considered high or 1 in binaryA gate is a device that performs a basic operation on electrical signals It accepts one or more input signals and produces a single output signal There are several types of gatesGates are combined into circuits to perform more complicated tasks Circuits can be designed to perform arithmetic and to store valuesoIn a circuit the output of one gate often serves as an input value for one or more other gates The flow of electricity through a circuit is controlled by the carefully designed logic of the interacting gatesThere are 3 different but equally powerful notational methods that describe the behavior of gates and circuitsoBoolean expressionsA mathematician George Boole invented a form of algebra in which variables and functions take on only one of two values 0 and 1 This algebra is called Boolean AlgebraoLogic diagramsA logic diagram is a graphical representation of a circuit Each type of gate is represented by a specific graphical symbol We can visually represent the logic of an entire circuitoTruth tablesA truth table defines the function of a gate by listing all possible input combinations that the gate could encounter and the corresponding output We can make more complex tables to show how entire circuits perform for any set of inputs

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