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N - Bit Parallel Adder

A n-bit parallel adder can be constructed using a number of full adder circuits connected in parallel to add binary numbers with more than one bit. A parallel subtractor works by taking the 2's complement of the subtrahend and adding it to the minuend. A binary adder-subtractor circuit combines addition and subtraction into a single circuit by including an exclusive-OR gate with each full adder, and uses a mode input to select whether it performs addition or subtraction.

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530 views9 pages

N - Bit Parallel Adder

A n-bit parallel adder can be constructed using a number of full adder circuits connected in parallel to add binary numbers with more than one bit. A parallel subtractor works by taking the 2's complement of the subtrahend and adding it to the minuend. A binary adder-subtractor circuit combines addition and subtraction into a single circuit by including an exclusive-OR gate with each full adder, and uses a mode input to select whether it performs addition or subtraction.

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n –Bit Parallel Adder

A single full –adder is capable of adding two


one-bit numbers and an input carry . In order to
add binary numbers with more than one bit,
additional full adder must be employed. A n-bit
parallel adder can be constructed using number
of full adder circuits connected in parallel
Parallel Adder

B3 A3 B2 A2 B1 A1 BO AO

C out C in
F. A F. A F. A F. A

S3 S2 S1 S0
n-bit parallel subtractor
The subtractor of binary numbers can be done most
conveniently be means of complements.
The subtractor A-B can be done by taking the 2’s
complement of B and adding it to A .the
2’complement can be obtained by taking the
1’coplement and adding one to the least significant
pair of bits .
Parallel Subtractor

B3 B2 B1 BO
A3 A2 A1 AO

C out C in = VCC
F. A F. A F. A F. A

S3 S2 S1 S0
Binary Adder-Subtractor

The addition and subtractor operations can be


combined into one circuit with one common
binary adder. This is done by including an
exclusive –OR gate with each full adder, as
shown in fig. below
Adder Subtractor

B3 B2 B1 BO

A3 A2 A1 AO
VCC
C out
F. A F. A F. A F. A
C in

GND
S3 S2 S1 S0
Binary Adder-Subtractor

The mode input M controls the operation of the

circuit. When M= 0 (GND) the circuit is an adder

,and when M=1 the circuit becomes a

subtractor.
74 83

B3 B2 B1 BO A3 A2 A1 AO

C out C in
4-Bit Parallel Adder

S3 S2 S1 SO
inputs

outputs

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