Programmable Logic Controller (PLC) Practice Test

Which of the following best describes when an OR operation outputs a high in digital logic?

Only when both inputs are high When any input is high When neither input is high When the inputs are equal

Correct Answer:

When any input is high

Explanation:

In digital logic, an OR gate outputs a high whenever any of its inputs is high. For two inputs, the output is low only when both inputs are low; if one input is high (or if both are high), the output goes high. This shows the inclusive nature of OR: the presence of at least one high signal is enough to produce a high output. In practical terms, if any one of several signals indicates a condition, the OR gate can trigger the next stage. This differs from AND, which needs all inputs high to produce a high, and from equality-based ideas, which look at whether inputs match rather than whether any one input is high.

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