Nor Gate
A NoR gate is a combination of an inverter and an OR gate. Its name derives from its NOT-OR function. Like the NAND gate, the NOR gate can also be used to construct an AND gate, an OR gate, and an inverter.
The logic symbol for the NOR gate is shown in Figure 42-10. Also shown is its equivalency to an OR gate and an inverter. The bubble on the output of the symbol means to invert the OR function.
Figure 42-11 shows the truth table for a two-input NOR gate. Notice that the output is the complement of the OR-function output. A 1 occurs only when 0 is applied to both inputs. A 1 input produces a 0 output.
The algebraic expression for NOR-gate output is Y 5 A 1 B, where Y is the output, and A and B are the inputs. NOR gates are available with two, three, four, and eight inputs.
Questions
1. What is a NOR gate?
2. Why is the NOR gate useful in designing digital circuits?
3. Draw the symbol used to represent a NOR gate.
4. What is the algebraic expression for a NOR gate?
Develop a truth table for a three-input NOR gate.