4.2Gates91Figure 4.1Various representations of a NOT gateLogic Diagram SymbolBoolean ExpressionTruth TableAX0110AX1 0 –2or 1. The variable X represents the output signal, whose value (also 0 or 1)is determined by the value of A.By definition, if the input value for a NOT gate is 0, the output value is1, and if the input value is 1, the output is 0. A NOT gate is sometimesreferred to as an inverterbecause it inverts the input value.In Boolean expressions, the NOT operation is represented by the 2markafter the value being negated. Sometimes this operation is shown as a hori-zontal bar over the value being negated. In the Boolean expression inFigure 4.1, X is assigned the value determined by applying the NOT opera-tion to input value A. This is an example of an assignment statement, inwhich the variable on the left of the equal sign takes on the value of theexpression on the right-hand side. Assignment statements are discussedfurther in Chapter 8 on high-level programming languages.
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