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# ALU

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### ALU

1. 1. By: Ahmad Yazdankhah CS 147 Fall 2008 Prof: Dr. Sin-Min Lee
2. 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. 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, …)
4. 4.  Registers (IR, PC, ACC)  Control Unit (CU)  Arithmetic Logic Unit (ALU)
5. 5. Instruction Register (IR) Program Counter (PC) Control Unit (CU) ALU Accumulator (ACC) 0 1 2 3 4 5 . CPU RAM Status Register (FLAG)
6. 6. 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.
7. 7. 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 . . .
8. 8. 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.