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ALU arithmetic logic unit

Computer parts

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ALU arithmetic logic unit

  1. 1. Arithmetic Logic Unit ALU By: Ahmad Yazdankhah CS 147 Fall 2008 Prof: Dr. Sin-Min Lee
  2. 2. Table of Contents • 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
  3. 3. 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, Program Counter, Instruction Register, …)
  4. 4. Review: Bus Concept
  5. 5. Review: CPU Building Blocks  Registers (IR, PC, ACC)  Control Unit (CU)  Arithmetic Logic Unit (ALU)
  6. 6. 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)
  7. 7. What’s 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.
  8. 8. 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 . . .
  9. 9. Let’s 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.
  10. 10. Adding a full adder to our ALU Building a 1-Bit ALU (cont’d)
  11. 11. A 32-Bit ALU By paralleling the one-bit ALUs and some other modification on the logical circuits, we can create bigger ALUs.
  12. 12. Useful Links • Virginia Tech online courses: • Virginia Tech online Circuit Simulator • Virginia Tech Microprocessor Simulation: ons/CPU/sumprogram.html
  13. 13. References: • Text book: Computer System Architecture (By: Rob Williams, 2nd Edition, Prentice Hall, 2006) • Site Wikipedia: • Previous Student Lectures: (By: Anna Kurek, Spring 2008) • Professor’s Lecture Notes. • Virginia Tech online courses: