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EE 107 reference materials for adder/subtractor/ALU circuits design Instructor: Dr. Qun (Vincent) Zhang [email protected] ECET Dept., 02/13/2019
EE 107reference materials for adder/subtractor/ALU circuits design
Instructor: Dr. Qun (Vincent) Zhang
ECET Dept., 02/13/2019
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Part 1. Adders & Subtractors
Addition of two 4-bit binary numbers:
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The circuit for
the addition of
a signal slice is
known as a full
adder (FA):
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We connect four FAs together in series, resulting in a
ripple-carry adder for adding two 4-bit operands.
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Carry-Lookahead Adder • Ripple-carry adder is slow (why?)
• Solution: Carry-lookahead adder
• Let’s see how Carry-lookahead adder removes the dependency on the previous carry-out signal
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Subtractor
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There is a
better way!
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Recall: 2’s complement Binary Numbers
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Part 2. Arithmetic Logic Unit (ALU)
• ALU is one of the main components inside a microprocessor
• Responsible for performing arithmetic + logic operations
• Use ideas in constructing the adder-subtractor combination circuit
• Implement arithmetic + logic functions by inserting some combinational circuitry in front of the input operands.
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