The NAND or “Not AND” function is a combination of the two separate logical functions, the AND function and the NOT function connected together in series.
The logic NAND function can be expressed by the Boolean expression of, A.B
The Logic NAND Function only produces an output when “ANY” of its inputs are not present and in Boolean Algebra terms the output will be TRUE only when any of its inputs are FALSE.
Switch Representation of the NAND Function
The truth table for the NAND function is the opposite of that for the previous AND function because the NAND gate performs the reverse operation of the AND gate. In other words, the NAND gate is the complement of the basic AND gate.
NAND Function Truth Table
|Switch A||Switch B||Output||Description|
|0||0||1||A and B are both open, lamp ON|
|0||1||1||A is open and B is closed, lamp ON|
|1||0||1||A is closed and B is open, lamp ON|
|1||1||0||A is closed and B is closed, lamp OFF|
|Boolean Expression (A AND B)||A . B|
The NAND Function is sometimes known as the Sheffer Stroke Functionand is denoted by a vertical bar or upwards arrow operator, for example, A NAND B = A|B or A↑B.
Logic NAND gates are used as the basic “building blocks” to construct other logic gate functions and are available in standard i.c. packages such as the very common TTL 74LS00 Quadruple 2-input NAND Gates, the TTL 74LS10 Triple 3-input NAND Gates or the 74LS20 Dual 4-input NANDGates. There is even a single chip 74LS30 8-input NAND Gate.