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Dale - Computer Science Illuminated 118

Dale - Computer Science Illuminated 118 - 4.2 Gates 91...

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4.2 Gates 91 Figure 4.1 Various representations of a NOT gate Logic Diagram Symbol Boolean Expression Truth Table A X 0 1 1 0 A X 1 0 –2 or 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 is 1, and if the input value is 1, the output is 0. A NOT gate is sometimes referred to as an inverter because it inverts the input value. In Boolean expressions, the NOT operation is represented by the 2 mark after the value being negated. Sometimes this operation is shown as a hori- zontal bar over the value being negated. In the Boolean expression in Figure 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 , in which the variable on the left of the equal sign takes on the value of the expression on the right-hand side. Assignment statements are discussed further in Chapter 8 on high-level programming languages.
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