The NOR gate
The NOR gate is an OR gate followed by a NOT: “not or”. It gives 1 only when all of its inputs are 0. As soon as any input is 1, the output drops to 0.
Formula Y = (A + B)‾
Truth table
| A | B | Y |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
Try it Click the inputs to change them.
Y1
Where it is used
Like NAND, NOR is a universal gate: every other gate can be built from NOR gates alone. The computer that guided the Apollo missions to the Moon was built almost entirely from NOR gates.
Two NOR gates connected in a loop make the simplest memory there is, the SR latch.