ALU
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This document discusses the arithmetic logic unit (ALU) and its role in a central processing unit (CPU). It begins with an overview of the ALU and its functions, including that it performs arithmetic and logical operations. The document then shows a typical schematic symbol for an ALU and builds a sample 1-bit ALU circuit. It concludes by mentioning how ALUs can be expanded by connecting more 1-bit circuits in parallel.
ALU
- 1. By: Ahmad Yazdankhah CS 147 Fall 2008 Prof: Dr. Sin-Min Lee
- 2. 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. 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, …)
- 5. Registers (IR, PC, ACC) Control Unit (CU) Arithmetic Logic Unit (ALU)
- 6. Instruction Register (IR) Program Counter (PC) Control Unit (CU) ALU Accumulator (ACC) 0 1 2 3 4 5 . CPU RAM Status Register (FLAG)
- 7. 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. 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. 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. Adding a full adder to our ALU
- 11. By paralleling the one-bit ALUs and some other modification on the logical circuits, we can create bigger ALUs.
- 12. Virginia Tech online courses: http://courses.cs.vt.edu/~csonline/index.html Virginia Tech online Circuit Simulator http://courses.cs.vt.edu/~csonline/MachineArchitecture/L Virginia Tech Microprocessor Simulation: http://courses.cs.vt.edu/~csonline/MachineArchitect ure/Lessons/CPU/sumprogram.html
- 13. 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