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

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 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

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

Using A Less-Than Comparator

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 Compare Unit into a logic NOT gate by comparing the input x to b, i.e.

y = (x < b)

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

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 Compare Unit into a logic NOT gate by comparing the input x to 0, i.e.

y = (x = 0)

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

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.

y = (m - x)

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

Circuit setup

unit	unit type	connector/setting	source/value
math 1	Math Unit	Input 1	x (input)
		Input 2	m (constant, see above)
		Operation	Subtract
		Output	y (output)