A logic gate is an electronic circuit in which the logic level of the output signal depends on the logic state of one or several input signals. It is the basic building block of most digital electronic circuits. The fig 15.1 below shows a general block diagram of a logic gate.
The alphabets A, B and C represent the input signals while F is for the output signals. They represent logic variables which can either be logic 1 or logic 0, “true” or “false”, “high” or “low” positive” or “negative’. Below is the summary of the equivalent logic conditions.
1 = True = Positive high
0 = False Negative = low