Guide to VHDL for embedded software developers: Part 3 - ALU logic & FSMs

Peter Wilson
EETimes (7/25/2011 1:17 AM EDT)

Editor’s Note: In this series of articles based on his book – Design Recipes for FPGAs – Peter Wilson provides a basic quick overview of VHDL (VHSIC hardware description language) followed by examples of its use in describing - in HDL code form - functions familiar to most embedded software developers such as arithmetic logic units (ALUs) and finite state machines (FSMs). It is not intended as a comprehensive VHDL reference. For that, he recommends “Digital System Design with VHDL,” by Mark Zwolinski; ”VHDL: Analysis and modeling of digital systems,” by Zainalabedin Navabi or “Designer’s Guide to VHDL” by Peter Ashenden. This third part in a series describes how low-level logic and arithmetic functions can be implemented in VHDL to build simple arithmetic logic units and finite state machines.

A central part of microprocessors is the ALU (Arithmetic Logic Unit). This block in a processor takes a number of inputs from registers and as its name suggests carries out either logic functions (such as NOT, AND, OR and XOR) on the inputs,or arithmetic functions (addition or subtraction as a minimum).

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