Arithmetic Logic Unit Design

for the Simple RISC Computer

Group: E=MJ2

Arithmetic Logic Unit Design

• Objective• Introduction• Design• Implementation• Components• Timing Diagrams• Conclusion• References

Objective

• Learn and experience the benefits of VHDL

• Design the components of an ALU that perform the predefined functions specified for the SRC.

• Implement them in VHDL to simulate the operations of the ALU.

Introduction

• ALU (“Arithmetic and Logic Unit”)– Responsible for certain arithmetic and logic

functions. (Ex:addition,substaction,and, xor etc).

• The Control Unit (“CU”)– Keep all elements of the ALU working in a

harmonic way.

• Different Components can be added as modules to help perform certain operations– Adder, Shifter, Delatch, etc…

Design

Components

• AdderArithmetic functions are perform in this circuits.

1-bit adder

8-bit adder

Components

• ASIReceive the operand of add, subtract and increment

1-bit adder

8-bit ASI pkg

8-bit ASI

Components

• NegatorArithmetic functions are perform in this circuits.

8-bit negator

8-bit negator pkg

Components

• RegisterIts is use for the ADC function. The rest of the functions done via the 2 buses.

8-bit register

8-bit register pkg

Components

• LogicThis circuit performs the logic functions and, or and all of the shifting operations.

It is copied 8 times to work as an 8 bit circuit.

1-bit logic/shifter

1-bit logic/shifter pkg

Timing Diagram

Conclusion

• In our design we were able to create an ALU capable of completing all of the logic and arithmetic functions specified in our simulator.

• The design can be used for further continuation of a project, in which it can be used as the ALU of a microcontroller or CPU.

• Our ALU might not have the fastest performance, but it has one of the simplest hardware designs.

References

• Computer System Design Architecture, second ed, Vincent P. Heuring and Harry F. Jordan.

• A 32-Bit ALU Design Example, http://lgjohn.ecen.ceat.okstate.edu/5253/lectures/

aludesver.pdf

Questions