28farithmetic logic unit

8/2/2019 28FArithmetic Logic Unit

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Arithmetic Logic UnitALU

By: Ahmad Yazdankhah

CS 147

Fall 2008Prof: Dr. Sin-Min Lee


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Table of Contents

Assumptions

Review: Bus Concept

Review: CPU Building Block

The Simplest Computer Building Blocks Whats ALU?

Typical Schematic Symbol of an ALU

Lets Build a 1-Bit ALU

Useful Links

References


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Assumptions

You are familiar with:

1. Number representations (1s complement, 2s

comp.)

2. Arithmetic operations (Add, Sub, . . .)

3. Floating Point concept

4. Registers in CPU (Accumulator, ProgramCounter, Instruction Register, )


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Review: Bus Concept


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Review: CPU Building Blocks

Registers

(IR, PC, ACC)

Control Unit

(CU)

Arithmetic

Logic Unit

(ALU)


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The Simplest Computer Building Blocks

Instruction Register (IR) Program Counter (PC)

Control Unit (CU)

ALU

Accumulator (ACC)

0

1

2

3

4

5

.

CPU RAM

Status Register (FLAG)


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Whats ALU?

1. ALU stands for: Arithmetic Logic Unit

2. ALU is a digital circuit that performs

Arithmetic (Add, Sub, . . .) and Logical

(AND, OR, NOT) operations.

3. John Von Neumann proposed the ALU in

1945 when he was working on EDVAC.


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Typical Schematic Symbol of an ALU

A and B: the inputs to the ALU

(aka operands)

R: Output or Result

F: Code or Instruction from the

Control Unit (aka as op-code)

D: Output status; it indicates cases

such as:

carry-in

carry-out,overflow,

division-by-zero

And . . .


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Lets Build a 1-Bit ALU

This is an one-bit ALU which can do Logical AND and Logical OR operation.

Result = a AND b when operation = 0

Result = a OR b when operation = 1

The operation line is the input of a MUX.


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Adding a full adder to our ALU

Building a 1-Bit ALU (contd)


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A 32-Bit ALU

By paralleling the one-bit ALUs and some other modification on the

logical circuits, we can create bigger ALUs.


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Useful Links

Virginia Tech online courses:http://courses.cs.vt.edu/~csonline/index.html

Virginia Tech online Circuit Simulator

http://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.html

Virginia Tech Microprocessor Simulation:http://courses.cs.vt.edu/~csonline/MachineArchitecture/Less

ons/CPU/sumprogram.html
http://courses.cs.vt.edu/~csonline/index.htmlhttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://courses.cs.vt.edu/~csonline/index.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/CPU/sumprogram.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/CPU/sumprogram.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/CPU/sumprogram.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/CPU/sumprogram.htmlhttp://courses.cs.vt.edu/~csonline/index.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.htmlhttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://courses.cs.vt.edu/~csonline/index.html


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References:

Text book: Computer System Architecture(By: Rob Williams, 2nd Edition, Prentice Hall, 2006)

Site Wikipedia:

http://en.wikipedia.org/wiki/Arithmetic_logic_unit

Previous Student Lectures:(By: Anna Kurek, Spring 2008)

Professors Lecture Notes.

Virginia Tech online courses:http://courses.cs.vt.edu/~csonline/index.html
http://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://courses.cs.vt.edu/~csonline/index.htmlhttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://courses.cs.vt.edu/~csonline/index.htmlhttp://en.wikipedia.org/wiki/Arithmetic_logic_unit

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