4. Binary Subtractor

A. We define as a 1-bit binary half subtractor to be a subtractor with 2 inputs: X X , Y Y ; and two output D D , B B . The idea is that D D is the difference between X X and Y Y , while B B is the borrow bit. Draw the truth table for this unit.

B. Write down the boolean expressions for a 1-bit half subtractor. (0.5pt)

C. Draw the circuit diagram of a 1-bit full subtractor with an extra input Z Z for previous borrow using 2 1-bit half subtractor (1pt). No