Which of the following represents the borrow in a half subtractor?
2021
Which of the following represents the borrow in a half subtractor?
- A.
AB
- B.
AB̄
- C.
ĀB
- D.
ĀB̄
Attempted by 111 students.
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Correct answer: C
In a half subtractor computing A − B, a borrow is generated only when the minuend bit A is smaller than the subtrahend bit B, i.e. when A=0 and B=1. From the truth table, the borrow output is high only for the input combination A=0, B=1. Therefore Borrow = Ā·B (NOT A AND B), while the difference output is A ⊕ B.