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MICROOPERATION
elementary operation performed on data stored in registers
TYPES OF MICROOPERATIONS
Register Transfer
Arithmetic
Logic
Shift
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ARITHMETIC MICROOPERATIONS
Add, Subtract, Increment, Decrement and Shift
Add :- R3 R1 + R2
Subtract :- R3 R1 + R2 + 1
Increment :- R1 R1 + 1
Decrement :- R1 R1 - 1
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Full Adder - Digital circuit that performs sum of 2 bits
and a previous carry
Binary Adder - Digital circuit that generates the arit-
hmetic sum of 2 binary numbers of a
any length
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Constructed with full-adders connected in cascade
Output carry from one full-adder connected to the input
carry of the next full-adder
The S outputs of the full-adders generate the required
sumbits
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Mode input M controls the operation
M = 0 => Acts as adder circuit
M = 1 => Acts as subtractor circuit
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Each EX-OR gate receives input M and one of the inputs of
B
When M = 0 , B ex-or 0 = B,
Full adders receive value of B, input carry is 0,
hence circuit performs A + B
When M = 1, B ex-or 1 = B',Full adder receive complement of B,
input carry is 1,
hence circuit performs A - B
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The increment microoperation adds one to the number in
the register
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One of the inputs to the least significant half-adder is
conn-
ected to logic-1
The other input is connected to the least significant bit ofthe
number to be incremented
The output carry from one half-adder is connected to one of
the inputs of the next higher-order half-adder
The incremented output of the bits A0 through A3 is obtained
from S0 through S3
The output carry C4 will be 1 only after incrementing binary
1111
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ARIHTMETIC CIRCUIT FUNCTION TABLE
