Electronics Engineering (ELEX) Board Practice Exam

Which logic gate outputs HIGH or "1" when any of its inputs are HIGH?

1. NAND gate

2. OR gate

3. XOR gate

4. NOR gate

The correct answer is: OR gate

The OR gate operates based on the principle that it will output a HIGH signal, or "1," when at least one of its inputs is HIGH. This characteristic makes the OR gate a fundamental building block in digital electronics, as it can be used to create circuits that need to respond positively when any input condition is met. For instance, in a scenario where there are two inputs to the OR gate, if either input A or input B (or both) is HIGH, the output will also be HIGH. This is due to the logical behavior defined in the truth table for the OR gate, which clearly shows that the output is only LOW (or "0") when both inputs are LOW. In contrast, the other types of gates have different output conditions. The NAND gate outputs LOW only when all its inputs are HIGH, the XOR gate outputs HIGH only when the inputs are different from one another, and the NOR gate outputs HIGH only when all its inputs are LOW. Understanding these distinctions is crucial for designing circuits that perform specific logical functions effectively.