Section 3.5
NOR Operation

NOR and NAND gates are used extensively in digital circuitry. These gates combine the basic operations AND, OR and NOT, which make it relatively easy to describe then using Boolean Algebra.

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NOR is the same as the OR gate symbol except that it has a small circle on the output. This small circle represents the inversion operation. Therefore the output expression of the two input NOR gate is:

X = ( A + B )'

An example of three input OR gate can be constructed by a NOR gate plus a NOT gate: