The circuit has a mode input bit m that controls its operation.
Design a combinational circuit for 4 bit binary subtractor.
It has two inputs the minuend and subtrahend and two outputs the difference and borrow out the borrow out signal is set when the subtractor needs to borrow from the next digit in a multi digit subtraction.
Specifically when m 0 the circuit becomes a 4 bit adder and when m 1 the circuit becomes a 4 bit subtractor that performs the operation a plus the 2 s complement.
The control input is controls the addition or subtraction operation.
From the figure it can be seen that the bits of the binary numbers are given to full adder through the xor gates.
Figure above the realization of 4 bit adder subtractor.
Lets consider two 4 bit binary numbers a and b as inputs to the digital circuit for the operation with digits.
The result with the proper sign is to be displayed in un complemented binary form.
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.
Half subtractor is the most essential combinational logic circuit which is used in digital electronics basically this is an electronic device or in other terms we can say it as a logic circuit.
A0 a1 a2 a3 for a b0 b1 b2 b3 for b.
However to add more than one bit of data in length a parallel adder is used.
Half subtractor is used to perform two binary digits subtraction.
A parallel adder is an arithmetic combinational logic circuit that is used to add more than one bit of data simultaneously.
When the subtraction input is logic 0 the b3 b2 b1 b0 are passed to the full adders.
A parallel adder adds corresponding bits simultaneously using full adders.
A full adder adds two 1 bits and a carry to give an output.
The half subtractor is a combinational circuit which is used to perform subtraction of two bits.
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.
Given two 4 bit positive binary numbers a and b you are to design an adder subtractor circuit to compute a b or a b depending upon a mode input which controls the operation.
You may use one s or two s compliment of b to perform subtraction.