Reversible Adder and Subtractor Circuits
Hafiz Md. Hasan Babu · 2020
The design of reversible multi-operand n-digit decimal adder is composed of three components: carry skip adder (CSA); carry look-ahead adder (CLA) and carry generator unit; and adjust circuit and final CLA unit. This chapter describes the designs of full adder, CSA, and CLA by using an example of 3-operand n-digit decimal adder. It presents the designs for reversible binary coded decimal (BCD) and carry skip reversible BCD adders. For both designs, detailed algorithms with figures and examples are shown. The chapter discusses the mechanism and working procedures of reversible BCD subtractors. In the BCD subtraction, the nine's complement of the subtrahend is added to the minuend. To design reversible BCD subtractors, the whole reversible design must be divided into three sub-modules: design of the reversible nine's complement, design of the reversible BCD adder, and integration of the modules to design the reversible BCD subtractor.