Question

Design a 4-bit ALU to perform five of the following operations:

• A + B
• A + B + 1
• A + B – 1
• A - B
• A - B + 1

Answer 1

To design a 4-bit ALU to perform the given operations, we can use adder and subtractor circuits to perform addition and subtraction. The carry-out and borrow-out bits can be used to chain the operations together.

Step-by-step explanation:

To design a 4-bit ALU to perform the given operations, we will need to implement a circuit that can add, subtract, and perform bitwise operations on two 4-bit inputs, A and B. Here's how we can implement each operation:

1. To perform A + B, we can use a 4-bit adder circuit. The output of this circuit will be the sum of A and B.
2. To perform A + B + 1, we can add 1 to the sum obtained from the previous operation. This can be done by connecting the carry-out bit of the adder circuit to the carry-in of another adder circuit, with the other input set to 1.
3. To perform A + B - 1, we can subtract 1 from the sum obtained from the first operation. This can be done by connecting the carry-out bit of the adder circuit to the carry-in of a subtractor circuit, with the other input set to 1.
4. To perform A - B, we can use a 4-bit subtractor circuit. The output of this circuit will be the difference between A and B.
5. To perform A - B + 1, we can add 1 to the difference obtained from the previous operation. This can be done by connecting the borrow-out bit of the subtractor circuit to the carry-in of an adder circuit, with the other input set to 1.