EE 107reference materials for adder/subtractor/ALU circuits design

Instructor: Dr. Qun (Vincent) Zhang

qun.zhang@mnsu.edu

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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