View source for User:Carsten Milkau/NOT Gate

= NOT Gate =

A NOT gate, sometimes also called ''inverter'', is a circuit that outputs the value that was not input. It has a single input and output, and each can only take one of two pre-defined values (typically 0 and 1). Whatever the input value is selected, the output value will be the other of the two.

== Definition ==

{| class="wikitable"
|+ value table
|-
!'''inputs''' || '''outputs'''
|-
!x || y
|-
|0||1
|-
|1||0
|}

=== Connectors ===

* Input x: one of two values (0 or 1)
* Output y: the other of the two values

== Implementation ==

NOT gates can often be avoided by modifying the circuit. For instance, an [[User:Carsten Milkau/OR Gate|OR Gate]] with two NOT gates connected to its inputs and outputs can always be replaced by an AND gate with just one NOT gate connected.

=== Single Block ===

[[File:CompareUnit.png|thumb]]

Use the Gate Unit, set it to Nor and both inputs to the same Logic Reader.

=== Using A Less-Than Comparator ===

[[File:CompareUnit.png|thumb]]

If you have a circuit available (e.g. a constant memory) that has a value ''b'' known to stay between 0 and 1 (but not 0), you can turn a [[Kit (Logic Processor)#Compare Unit|Compare Unit]] into a logic NOT gate by comparing the input ''x'' to ''b'', i.e.

<pre>y = (x < b)</pre>

{| class="wikitable"
|+ circuit setup
|-
! unit || unit type || connector/setting || source / value
|-
|compare 1 || Compare Unit || Input 1 || x '''(input)'''
|-
| || || Input 2 || ''b'' (constant or bounded value)
|-
| || || Operation Selector || Lesser
|-
| || || Output || y '''(output)'''
|}

=== Using An Equality Comparator ===

[[File:CompareUnit.png|thumb]]

If you have a circuit output available that is known to be zero when the NOT gate is used (e.g. a constant memory), you can turn a [[Kit (Logic Processor)#Compare Unit|Compare Unit]] into a logic NOT gate by comparing the input ''x'' to ''0'', i.e.

<pre>y = (x = 0)</pre>

{| class="wikitable"
|+ circuit setup
|-
! unit || unit type || connector/setting || source / value
|-
|compare 1 || Compare Unit || Input 1 || x '''(input)'''
|-
| || || Input 2 || 0 (constant)
|-
| || || Operation Selector || Equals
|-
| || || Output || y '''(output)'''
|}

=== Using Subtraction ===

[[File:MathUnit.png|thumb]]

If you do not use 0 and 1 as the two possible input values of the inverter, you can use subtraction for implementation. In this case, you need a constant that is exactly the mean of the two input values, i.e.

<pre>y = (m - x)</pre>

where m = (a + b)/2 is the mean of the two allowed input values, (called ''a'' and ''b'' here).

{| class="wikitable"
|+ Circuit setup
|-
! unit || unit type  || connector/setting || source/value
|-
| math 1 || [[Kit (Logic Processor)#Math Unit|Math Unit]] || Input 1 || x '''(input)'''
|-
| || || Input 2 || m (constant, see above)
|-
| || || Operation || Subtract
|-
| || || Output || y '''(output)'''
|}