Arithmetic Logic Unit Design for the Simple RISC Computer Group: E=MJ 2

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 Adder Arithmetic functions are perform in this circuits. 1-bit adder 8-bit adder

Components ASI Receive the operand of add, subtract and increment 1-bit adder 8-bit ASI pkg 8-bit ASI

Components Negator Arithmetic functions are perform in this circuits. 8-bit negator 8-bit negator pkg

Components Register Its is use for the ADC function. The rest of the functions done via the 2 buses. 8-bit register 8-bit register pkg

Components Logic This 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, aludesver.pdf

Questions