1. HALF SUBTRACTOR
III PHYSICS – 10.03.2022
Dr.R.Hepzi Pramila Devamani,
Assistant Professor of Physics,
V.V.Vanniaperumal College for Women,
Virudhunagar.
2. Half Subtractor
• The half subtractor is a combinational circuit which is used to
perform subtraction of two bits.
• It has two inputs X (minuend) and Y (subtrahend) and two
outputs D(difference) and Bout (borrow out).
• The symbol and truth table for half subtractor is shown in
figure.
• The difference output is 0 if X = Y and 1 if X ≠ Y.
• The borrow output Bout is 1 whenever X is less than Y, then
subtraction is done by borrowing 1 from the next higher order
bit.
4. Half Subtractor
• The Boolean expression for difference (D) and
borrow out (Bout) can be written as
5. Full Subtractor
• The full subtractor is a combinational circuit
which is used to perform subtraction involving
three bits.
• It has two inputs X (minuend) and Y (subtrahend)
and the borrow from the previous stage and two
outputs D(difference) and Bout (borrow out).
• The symbol and truth table for half subtractor is
shown in figure. The full subtractor can be
implemented using two subtractors and an OR
gate shown in figure.