Logic NAND and NOR Function |
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The NAND Function
The NAND or Not AND function is a combination of two
separate functions, the AND function and the NOT function connected
together in series, and can be expressed by the Boolean expression of, A.B
Switch Representation of the 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 Function
and is denoted by a vertical bar or upwards arrow operator, for example, A NAND B = A|B
or A↑B.
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 NAND Gates. There is even a single chip 74LS30 8-input NAND Gate.
The NOR Function
Like the NAND Gate above, the NOR or
Not OR Gate is also a combination of two separate functions, the OR
function and the NOT function connected together in series and is expressed by the Boolean
expression as, A + B
Switch Representation of the NOR Function
Truth Table
| Switch A |
Switch B |
Output |
Description |
| 0 | 0 | 1 | Both A and B are open, lamp ON |
| 0 | 1 | 0 | A is open and B is closed, lamp OFF |
| 1 | 0 | 0 | A is closed and B is open, lamp OFF |
| 1 | 1 | 0 | A is closed and B is closed, lamp OFF |
| Boolean Expression (A OR B) |
A + B |
The NOR Function is sometimes known as the Pierce Function and is
denoted by a downwards arrow operator as shown, A NOR B = A↓B.
NOR Gates are available as standard i.c. packages such as the TTL 74LS02
Quadruple 2-input NOR Gate, the TTL 74LS27 Triple 3-input NOR Gate
or the 74LS260 Dual 5-input NOR Gate.
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