Page 57 - Digital Electronics by harish
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Figure : Block diagram of full subtractor using two half subtractors
The logic diagram and logic equations for DIFFERENCE and BORROW are given in figure.
Figure : Logic diagram of full subtractor
DIFFERENCE = A ⊕ B ⊕ C
BORROW = B + ( ⊕ ) C
The first Halfsubtractor HS1 is used for (A - B). Then C is subtracted from (A-B) using the
second Half subtractor HS 2. The DIFFERENCE output of HA2 is the final DIFFERENCE.
The BORROW outputs of HS1 and HS2 are ORed to get the final BORROW output.
2.6Parallel Adder
Parallel adders are digital circuits that add „n‟ bits in parallel. The symbol and logic diagram
of parallel adder are shown in Figure.
Figure : Symbol of Parallel adder
Figure : Logic diagram of Parallel adder
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