Implementation of Arithmetic Circuits for Arithmetic Micro-operation 

An arithmetic circuit can be implemented by a number of full adder circuits or parallel adder circuits. Figure below displays a logical implementation of a 4-bit arithmetic circuit. Circuit is created by employing 4 full adders and 4 multiplexers.

Figure: A Four-bit arithmetic circuit

The figure of a 4-bit arithmetic circuit has four 4×1 multiplexers as well as four full adders (FA). Please consider that FULL ADDER is a circuit which can add two input bits and a carry-in bit to generate one sum-bit and a carry-out-bit.  

Adder just adds three bits. And multiplexer controls one of the input bits. So such combination generates a series of micro-operations. 

Let's find out how multiplexer control lines will change one of the Inputs for Adder circuit. Please see following table. (Please consider the convention VALID ONLY FOR THE TABLE are that an uppercase alphabet denotes a Data Word while the lowercase alphabet signifies a bit.)

Figure: Multiplexer Inputs and Output of the Arithmetic Circuit of Figure 4