Electronics Logic Gates: Universal NOR Gates
NOR (not-or) gates are universal logic gates for electronics applications. NOR gates can be combined in various and sundry ways to create NOT, AND, OR, and NAND gates.
The following paragraphs describe how the circuits work:
NOT: Creating a NOT gate from a NOR gate is the same as creating a NOT gate from a NAND gate: You simply tie the two inputs of the NOR gate together. If both inputs are LOW, the NOR gate will output a HIGH. Otherwise, the output is LOW.
OR: You need two NOR gates to create an OR gate. The first NOR gate returns LOW if either input is HIGH or both inputs are HIGH. Then the second NOR gate is configured as a NOT gate to invert the output of the first NOR gate.
AND: You need three NOR gates to create an AND gate. The first two are configured as NOT gates, so they invert the inputs. Then the third NOR gate produces a HIGH output if both of the original inputs are HIGH.
NAND: It takes four NOR gates to create a NAND gate. The first three NOR gates are configured just as they are for an AND gate. Then a fourth NOR gate configured as a NOT gate inverts output from the third NOR gate.