Question

Design a BCD Adder/Subtractor similar to a normal one; in which the circuit will add the two 4-bit BCD digits (A and B) when the selector has the value M = 0, and subtract B from A when the selector has the value M = 1.

However, the key difference between this circuit and the normal one is that 9’s Complement should be used on the Addend (B) to accomplish the subtraction.

The following assumptions can be made:

• When the subtraction operation is selected A will always be greater than or equal to B.

• Only BCD values will be entered as inputs, 0 ≤ A ≤ 9 and 0 ≤ B ≤ 9.

Please be sure to include all truth tables, k maps, circuit realizations.

Answer 1