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Flip to reveal answersDefine a logic gate.
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All 4 Flashcards — Digital signals
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Question
Define a logic gate.
Answer
A circuit whose single output is decided entirely by the combination of its inputs, where every signal is 1 or 0. Its truth table lists every input combination and the output for each.
Question
Give the rule for AND, OR, NOT and XOR.
Answer
AND: on only when both inputs are on. OR: on when either or both are on. NOT: the opposite of the input. XOR: on when the inputs are different.
Question
How many rows does a two-input truth table have, and why?
Answer
Four. Each input has two possible states, so two inputs give 2 × 2 = 4 combinations. Three inputs give eight.
Question
Why build a safety interlock from gates rather than software?
Answer
A gate responds in nanoseconds, has no program to crash or hang, cannot be broken by an update, and its behaviour is fixed by the wiring — so it works when the software does not.
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