Two other types of gates that are commonly used are the NAND and the NOR gate. The NAND gate is like an AND gate with a NOT gate on its output, while a NOR gate is like an OR gate with a NOT on its output. NAND and NOR gates are quite common, because they are usually easier to build than AND and OR gates. Click on the button below to see the NAND gate.
The symbols for NAND and NOR are exactly the same as those for AND and OR, except for the little circle at the output. We have hidden the ports in these diagrams to make these circles more evident. The little circle is used in various ways to indicate inversions. Note that the little circle appears at the output of a NOT gate. A NOT gate without the little circle is called a BUFFER gate. The output of a BUFFER gate is always equal to its input.
As the simulation shows, the output of the NAND gate is equal to 1 if any input is equal to 0, and equal to 0 otherwise. Similarly the output of the NOR gate is equal to 0 if any input is equal to 1, and is equal to 1 otherwise. Try all circuits with all inputs.. When you are finished with this, click here to go to the next lesson.