alu
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By: Ahmad YazdankhahCS 147
Fall 2008Prof: Dr. Sin-Min Lee
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Assumptions Review: Bus Concept Review: CPU Building Block The Simplest Computer Building Blocks What’s ALU? Typical Schematic Symbol of an ALU Let’s Build a 1-Bit ALU Useful Links References
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You are familiar with:1. Number representations (1s complement,
2s comp.)2. Arithmetic operations (Add, Sub, . . .)3. Floating Point concept4. Registers in CPU (Accumulator, Program
Counter, Instruction Register, …)
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Registers (IR, PC, ACC)
Control Unit(CU)
Arithmetic Logic Unit (ALU)
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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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1. ALU stands for: Arithmetic Logic Unit2. 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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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
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By paralleling the one-bit ALUs and some other modification on the logical circuits, we can create bigger ALUs.
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Virginia Tech online courses:http://courses.cs.vt.edu/~csonline/index.html
Virginia Tech online Circuit Simulatorhttp://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/Circuits/simcir_frame.html
Virginia Tech Microprocessor Simulation:http://courses.cs.vt.edu/~csonline/MachineArchitecture/Lessons/CPU/sumprogram.html
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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)
Professor’s Lecture Notes. Virginia Tech online courses:
http://courses.cs.vt.edu/~csonline/index.html