1. Arithmetic Logic Unit ALU By: Ahmad Yazdankhah CS 147 Fall 2008 Prof: Dr. Sin-Min Lee

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. 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. Review: Bus Concept

5. Review: CPU Building Blocks  Registers (IR, PC, ACC)  Control Unit (CU)  Arithmetic Logic Unit (ALU)

6. The Simplest Computer Building Blocks Instruction Register (IR)Program Counter (PC) Control Unit (CU) ALU Accumulator (ACC) 0 1 2 3 4 5. CPURAM Status Register (FLAG)

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. 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. 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. Adding a full adder to our ALU Building a 1-Bit ALU (cont’d)

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. Useful Links Virginia Tech online courses: http://courses.cs.vt.edu/~csonline/index.html http://courses.cs.vt.edu/~csonline/index.html Virginia Tech online Circuit Simulator http://courses.cs.vt.edu/~csonline/MachineArchitecture/Less ons/Circuits/simcir_frame.html http://courses.cs.vt.edu/~csonline/MachineArchitecture/Less ons/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/MachineArchitecture/Less ons/CPU/sumprogram.html

13. References: Text book: Computer System Architecture (By: Rob Williams, 2 nd Edition, Prentice Hall, 2006) Site Wikipedia: http://en.wikipedia.org/wiki/Arithmetic_logic_unit 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 http://courses.cs.vt.edu/~csonline/index.html