Two's compliment as we have seen can be used to represent negative numbers in binary.
The easiest way to work out the denary value of a two's compliment binary number is simply to add all the column headings where the column contains a 1 just like with normal numbers.
-128 + 32 + 8 + 4 = -84
| -128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Total |
|---|---|---|---|---|---|---|---|---|
| 1 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | -84 |
Click the button below to generate a number to convert to two's compliment binary.
| -128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Total |
|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
You should also be aware of this other method. This involves flipping the bits, adding one and converting the number to its denary equivalent.
| Action | -128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Total |
|---|---|---|---|---|---|---|---|---|---|
| two's comp | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | -46 |
| flip | 0 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | |
| add 1 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 46 |