Question

Design a 4-bit adder-subtractor circuit using the 4-bit binary Full adders (74LS83) 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 2’s 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 the2’s complement of B then add it to A. Hence, here the answer of theoperation A-B is expressed in 2’s 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 willnot generate overflow. So, you don’t have to worry aboutoverflow.

a. Draw the logic diagram that implements this circuit,and simulate the circuit on logisim program.

**please show details of your work

Answer 1