1. Objectives The objective of this lab is to design and build combinational logic circuits that perform basic arithmetic operations. II. Preparations 1. Part 1: Design a 4-bit adder-subtractor circuit using the 4-bit binary adders and any necessary additional logic gates. The circuit has a mode input bit, M, that controls its operation. 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 2s complement of B. Where A and B are two 4-bits binary numbers. That is, When M=0, we perform A+B, and we assume that both numbers are unsigned numbers. So the maximum sum value will be 15 (since we are assuming A and B are 4-bit numbers). When M=1, we perform A+ (B)2's Complement. That is, we find first the 2's complement of B then add it to A. Hence, here the answer of the operation A-B is expressed in 2s complement representation. In both cases above, assume that overflow will not happen. That is, you may assume that your inputs are chosen in a way that will not generate overflow. So, you don't have to worry about overflow. a. Draw the logic diagram that implements this circuit