E7A08

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 does an OR gate perform?

AIt produces a 1 at its output if any input is 1
BIt produces a 0 at its output if all inputs are 1
CIt produces a 0 at its output if some but not all inputs are 1
DIt produces a 1 at its output if all inputs are 0

Why An OR gate outputs a logical high whenever at least one of its inputs is high; it only outputs 0 when every input is 0. In Boolean terms the output is A + B, where the plus sign means logical OR, not addition. Its truth table for two inputs reads 0,1,1,1 going from both inputs low to both inputs high.

Watch out The choice about producing 0 when all inputs are 1 describes a NAND gate, and the one about producing 1 when all inputs are 0 describes a NOR gate.

OR = "any one will do." Only all-zeros in gives zero out.

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

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