Full subtractor
Full subtractor is a decision making circuit that subtracts two binary numbers from each other.
A combinational logic circuit performs a subtraction between the two binary bits by considering borrow of the lower significant stage is called as the full subtractor. In this, subtraction of the two digits is performed by taking into consideration whether a 1 has already borrowed by the previous adjacent lower minuend bit or not.
It has three input terminals in which two terminals corresponds to the two bits to be subtracted (minuend A and subtrahend B), and a borrow bit Bi corresponds to the borrow operation. There are two outputs, one corresponds to the difference D output and other borrow output Bo as shown in figure along with truth table.
Full subtractor symbol
Full subtractor circuits
Full subtractor truth table
| A | B | B.in | B.out | diff |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 1 |
| 0 | 1 | 0 | 1 | 1 |
| 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 0 | 0 | 1 |
| 1 | 0 | 1 | 0 | 0 |
| 1 | 1 | 0 | 0 | 0 |
| 1 | 1 | 1 | 1 | 1 |