1 Bit Full Adder Subtractor. It contains three inputs a b b in and produces two outputs d b out. A one bit full adder adds three one bit numbers often written as a b and c in.
A and b are the operands and c in is a bit carried in from the previous less significant stage. An adder subtractor is an arithmetic combinational logic circuit which can add subtract two n bit binary numbers and output their n bit binary sum difference a carry borrow status bit and if needed an overflow status bit. It is a combinational logic circuit designed to perform subtraction of three single bits.
A half subtractor subtracts two 1 bit binary numbers to give two outputs difference and borrow.
Truth table of full subtractor. This circuit has three inputs and two outputs the three inputs a b and bin denote the minuend subtrahend and previous borrow respectively. Such binary circuit can be designed by adding an ex or gate with each full adder as shown in below figure. Since it neglects any borrow inputs and essentially performs half the function of a subtractor it is known as the half subtractor.
