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 | |||||
|---|---|---|---|---|---|---|
| A1 | A0 | B1 | B0 | 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 |
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