The NAND Gate
The term NAND is a combination of the NOT-AND gate and indicates an AND function with an inverted output. A standard logic symbol for a two input NAND gate is shown in Figure 10-246. Notice that an equivalent AND gate with an inverter is also shown.
The logical operation of the NAND gate is such that a low output occurs only if all inputs are high. If any of the inputs are low, the output will be high. An example of a two input NAND gate and its corresponding truth table are shown in Figure 10-247.
The NOR Gate
The term NOR is a combination of the NOT and OR and indicates an OR function with an inverted output. The standard logic symbol for a two-inputs NOR gate is shown in Figure 10-248. Notice that an equivalent AND gate with an inverter is also shown. The logical
operation of the NOR gate is such that a low output happens when any of its inputs are high. Only when all of its inputs are low is the output high. The logic of this gate produces resultant outputs that are the opposite of the OR gate. In the NOR gate, the low output is the active output level. Figure 10-249 illustrates the logical operation of a two-input NOR gate for all of its possible combinations and the truth table.
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