One will signify the difference bit, and another will signify the borrow bit. The output of half subtractor is described in two columns. The resultant of all the 4 inputs will be described as outputs. Thus the number of possible combinations will be 4. In case of half subtractor there are two inputs. The truth table is nothing but the possible combination of inputs and their resultant output. The truth table is a key tool to understand the working of any digital circuit.
Similarly, the borrow generated by half subtractor can be easily obtained by using the combination of NOT gate and AND gate. Thus, we can easily utilize the EX-OR gate for generating difference bit. If we observe carefully, it is quite evident that the difference operation performed by half subtractor is exactly similar to the operation of EX-OR gate. Secondly, the borrow generated by half subtractor will also be in accordance with the particular operation which will resemble operation of any logic gate. First is the difference operation of half subtractor resembles operation of which logic circuit. In order to design logic circuit, we should understand two concepts. The logic circuit of Half subtractor involves usage of logic gates. Let’s take an example of subtraction of two multi-bit number with the help of above-defined rules. The above image clearly elaborates the subtraction rule of binary numbers.
To understand the internal operation of the half subtractor, we must first understand the subtraction rules of binary numbers. We are very familiar with the addition procedure it is quite easy to add two binary numbers rather than subtracting them. The logic symbol of half subtractor is represented in the diagram below. The word “HALF” before the subtractor signifies that it deals with only two 1-bit numbers, it has nothing to do with the borrow from the previous stage.