Chapter 33 Basic Logic Gates

2 Objectives –After completing this chapter, the student should be able to: Identify and explain the function of the basic logic gates. Draw the symbols for the basic logic gates. Develop truth tables for the basic logic gates.

3 AND gates –A logic circuit that has two or more inputs and a single output. –Produce an output of 1, only when all its inputs are 1. –Perform the basic operation of multiplication.

4 OR gates –Produce a 1 output if any of its inputs are 1’s. –The output is a 0 if all the inputs are 0’s. –Performs the basic operation of addition.

5 NOT gates –Simplest logic circuit. –Performs the function called inversion, commonly referred to as an inverter. –Makes the output the opposite of the input state.

6 NAND gates –Combine an inverter and an AND gate. –Most commonly used logic gate. –Can be used to construct an AND gate, an OR gate, an inverter, or any combination of these functions. –The availability and flexibility allow them to be used for other types of gates.

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8 NOR gates –Combine an inverter and an OR gate. –Can be used to construct an AND gate or an OR gate and an inverter.

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10 Exclusive OR gates (XOR) –Has only two inputs. –Generates a 1 output if either input is a 1. –When both inputs are 1’s or 0’s, the output is 0.

11 Exclusive NOR gates (XNOR) –The complement of the XOR gate. –Produces a 1 output only when both inputs are different.

12 BUFFER gate –A logic circuit that isolates conventional gates from other circuitry and –Provides a high-driving current for heavy circuit loads or fan-out. –Provides noninverting input and output.

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14 3-STATE BUFFER gate –Another type of buffer that has the usual 1 and 0 output states, but it also has third state. –Third state is referred to as a high impedance state.

15 –This state provides an open circuit between the input circuitry and the output and is controlled by the EN line. –The EN line represents an enable/disable control input.

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17 In Summary –An AND gate: Produces a 1 output when all of its inputs are 1’s. Performs the basic operation of multiplication. –An OR gate: Produces a 1 output if any of its inputs are 1’s. Performs the basic operation of addition. –A NOT gate: Performs the function called inversion or complementation.

18 Converts the input state to an opposite output state. –A NAND gate: Is a combination of an AND gate and an inverter. Produces 1 output when any of the inputs are 0’s. –A NOR gate: Is a combination of an OR gate and an inverter. Produces a 1 output only when both inputs are 0’s.

19 –An exclusive OR (XOR) gate: Produces a 1 output only if both inputs are different. Produces a 1 output only when both inputs are the same.