A digital logic circuit with multiple inputs outputs high only when none of the inputs are high represents which gate?

A digital logic circuit with multiple inputs outputs high only when none of the inputs are high represents which gate?

• A. NOR Gate
• B. AND Gate
• C. OR Gate
• D. NAND Gate

Answer: (A)

This tests the NOR gate, which is the inverted OR. It outputs a high signal only when all inputs are low, because it first ORs the inputs and then inverts the result. So with multiple inputs, the output is 1 exactly when every input is 0. For example, with two inputs, 0 0 produces 1, while any other combination (01, 10, 11) produces 0. The other gates don’t fit: OR would give a high if any input is high; AND would give a high only if all inputs are high; and NAND would be high in all cases except when all inputs are high.

This tests the NOR gate, which is the inverted OR. It outputs a high signal only when all inputs are low, because it first ORs the inputs and then inverts the result. So with multiple inputs, the output is 1 exactly when every input is 0. For example, with two inputs, 0 0 produces 1, while any other combination (01, 10, 11) produces 0. The other gates don’t fit: OR would give a high if any input is high; AND would give a high only if all inputs are high; and NAND would be high in all cases except when all inputs are high.