The Logic NOT Function |
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The Logic NOT Function
The Logic NOT Function is simply a single input inverter that changes the input
of a logic level "1" to an output of logic level "0" and vice versa. It is generally denoted by a bar or overline
( ¯ ) over its input symbol which denotes the inversion operation. As
NOT gates perform the logic INVERT or COMPLEMENTATION function they are more
commonly known as Inverters. In logic circuits this negation can be represented by a
normally closed switch.
Switch Representation of the NOT Function
If A means that the switch is closed, then NOT A or
simply A says that the switch is NOT closed or in other words, it is open.
Truth Table
| Switch |
Output |
| 1 | 0 |
| 0 | 1 |
| Boolean Expression | A or A |
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NOT gates or Inverters can be used with standard
AND and OR gates to produce NAND and
NOR gates. Inverters can also be used to produce "Complementary" signals in more complex
decoder/logic circuits for example, the complement of logic A is A.
When designing logic circuits and you need only one or two inverters, but do not have the space or
the money for a dedicated Inverter chip such as the 74LS04, you can easily make inverter functions using any spare
NAND or NOR gates by simply connecting their inputs together
as shown below.
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