The NOR gate is the same as an OR gate with the output inverted. The NOR gate logic symbol is an OR gate with a bubble on the output to indicate an inverted output. The NOR operation is shown with a plus sign (+) between the variables and an overbar covering them. Thus, the NOR operation is written as X = 
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The NOR gate truth table is the OR gate truth table with the output inverted. (The only time the output is high is when all the inputs are low.) The output of a NOR gate can be demonstrated with a timing diagram. The output is developed one segment at a time as the inputs change. The output again will follow the truth table.
Example Waveform:
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Date last modified: January 17, 2013.
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