Digital comparator

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A digital comparator is a hardware electronic device that compares two numbers in binary form and generates a one or a zero at its output depending on whether they are the same or not.

Comparators can be used in a central processing unit (CPU) or microcontroller in branching software. A comparator can be simulated by subtracting the two values (A & B) in question and checking if the result is zero. This works because if A = B then A - B = 0.

The analog equivalent is the comparator. Many microcontrollers have analog comparators on some of their inputs that can be read or trigger an interrupt.

The operation of a single bit digital comparator can be expressed as a truth table:

Inputs		Outputs
$A$	$B$	$A < B$	$A = B$	$A > B$
0	0	0	1	0
0	1	1	0	0
1	0	0	0	1
1	1	0	1	0

The operation of a two bit digital comparator can be expressed as a truth table:

Inputs				Outputs
$A 1$	$A 0$	$B 1$	$B 0$	$A < B$	$A = B$	$A > B$
0	0	0	0	0	1	0
0	0	0	1	1	0	0
0	0	1	0	1	0	0
0	0	1	1	1	0	0
0	1	0	0	0	0	1
0	1	0	1	0	1	0
0	1	1	0	1	0	0
0	1	1	1	1	0	0
1	0	0	0	0	0	1
1	0	0	1	0	0	1
1	0	1	0	0	1	0
1	0	1	1	1	0	0
1	1	0	0	0	0	1
1	1	0	1	0	0	1
1	1	1	0	0	0	1
1	1	1	1	0	1	0