E7A09

PRACTICAL CIRCUITS · Digital circuits: digital circuit principles and logic circuits; classes of logic elements; positive and negative logic; frequency dividers; truth tables

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What logical operation is performed by a two-input exclusive NOR gate?

AIt produces a 0 at its output only if all inputs are 0
BIt produces a 1 at its output only if all inputs are 1
CIt produces a 0 at its output if one and only one of its inputs is 1
DIt produces a 1 at its output if one and only one input is 1

Why An exclusive NOR is an exclusive OR followed by an inverter, so it is an equality detector: the output is 1 when the two inputs match (0,0 or 1,1) and 0 when they differ. With two inputs, "they differ" means exactly one input is 1, so that condition drives the output low.

Watch out The choice saying a 1 appears when one and only one input is 1 describes the plain exclusive OR, which is the XNOR's complement. The choices about all inputs 0 or all inputs 1 describe NOR and AND behavior.

XNOR = "same" detector: match gives 1, mismatch gives 0. The NOR in the name means invert the XOR answer.

HamSandwich explanation, first draft. The question and answers are the NCVEC text.

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