Chapter04

# Chapter04 - Chapter 4 Gates and Circuits Computers and...

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Chapter 4 Gates and Circuits

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2 Computers and Electricity Gate: A device that performs a basic operation on electrical signals. Circuits: Gates combined to perform more complicated tasks.
3 Computers and Electricity There are three different, but equally powerful, notational methods for describing the behavior of gates and circuits: Boolean expressions logic diagrams truth tables

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4 Computers and Electricity Boolean expressions: Expressions in Boolean algebra, a mathematical notation for expressing two-valued logic. This algebraic notation is an elegant and powerful way to demonstrate the activity of electrical circuits.
5 Computers and Electricity Logic diagram: a graphical representation of a circuit Each type of gate is represented by a specific graphical symbol. Truth table: A table showing all possible input values and the associated output values.

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6 Gates Let’s examine the processing of the following six types of gates: NOT AND OR XOR NAND NOR Typically, logic diagrams are black and white, and the gates are distinguished only by their shape.
7 NOT Gate A NOT gate accepts one input value and produces one output value. Figure 4.1 Various representations of a NOT gate

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8 NOT Gate 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.
9 AND Gate An AND gate accepts two input signals. If the input values for an AND gate are both 1, the output is 1; otherwise, the output is 0. Figure 4.2 Various representations of an AND gate

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10 OR Gate If the two input values are both 0, the output value is 0; otherwise, the output is 1. Figure 4.3 Various representations of a OR gate
11 XOR Gate XOR gate ( eXclusive OR) An XOR gate produces 0 if its two inputs are the same, and a 1 otherwise. Note the difference between the XOR gate and the OR gate; they differ only in one input situation: When both input signals are 1, the OR gate produces a 1 but the XOR produces a 0.

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12 XOR Gate Figure 4.4 Various representations of an XOR gate
NAND and NOR Gates The NAND and NOR gates are essentially the opposite of the AND and OR gates, respectively. Figure 4.5 Various representations of a NAND gate Figure 4.6 Various representations of a NOR gate 4–15

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Review of Gate Processing A NOT gate inverts its single input value. An AND gate produces 1 if both input values
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## This note was uploaded on 07/16/2010 for the course CSE CSE 1520 taught by Professor Paul during the Spring '09 term at York University.

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Chapter04 - Chapter 4 Gates and Circuits Computers and...

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