Now coming to the operation of NAND gate, first we have to know about the basic operation of AND gate. We know that the basic AND gate gives the output as 1 when all the inputs are 1 and at all the other times the output is 0. Now as we have already discussed about the NOT gate and we clearly know that the operation of this gate is to invert the incoming data. So we can say that in case of NAND gate the NOT gate just inverts the output of the AND gate so the output of this gate is 1 at all the times except when both the inputs are 1, at that instant the output is zero. The symbol and truth table of the NAND gate are given below.
The above diagram is of a two input NAND gat. The first part of the diagram is similar to that of an AND gate and the dot after it represents the NOT gate. So it is clear from the picture that during the operation of NAND gate, the inputs are first go through AND gate and after that the output is reversed and we get the final output.
Now we will consider the truth table of the above NAND gate i.e. a two input gate. The two inputs are A and B.
The above table is the truth table for NAND gate. And from the operation of the gate we discussed earlier it is very easy to understand.
USE of NAND gate
NAND gate is one of the universal gates. It is called so because any of the three basic gates can be obtained by it. It is the main application of NAND gate. We will look at some of the making of other gates from NAND gate.
We can see two diagrams are here side by side, the picture on the left is of the basic NOT gate. The one on the right is NOT gate made by NAND gate.
The above diagram shows an AND gate made from NAND gates.