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Preface
A major revolution in digital design has taken place over the past decade.
Field programmable gate arrays (FPGAs) can now contain over a million equivalent
logic gates and tens of thousands of flip-flops. This means that it is not possible to
use traditional methods of logic design involving the drawing of logic diagrams
when the digital circuit may contain thousands of gates. The reality is that today
digital systems are designed by writing software in the form of hardware
description languages (HDLs). The most common HDLs used today are VHDL and
Verilog. Both are in widespread use. When using these hardware description
languages the designer typically describes the behavior of the logic circuit rather
than writing traditional Boolean logic equations. Computer-aided design tools are
used to both simulate the Verilog or VHDL design and to synthesize the design to
actual hardware.
This book assumes no previous knowledge of digital design. We use 30
examples to show you how to get started designing digital circuits that you can
implement on a Xilinx Spartan3E FPGA using either the Digilent BASYS™ system
board that can be purchased from www.digilentinc.com for $59 or the Digilent
Nexys-2 board that costs $99. We will use Active-HDL from Aldec to design,
simulate, synthesize, and implement our digital designs. A free student edition of
Active-HDL is available from Aldec, Inc. (www.aldec.com). To synthesize your
designs to a Spartan3E FPGA you will need to download the free ISE WebPACK
from Xilinx, Inc. (www.xilinx.com). The Xilinx synthesis tools are called from
within the Aldec Active-HDL integrated GUI. We will use the ExPort utility to
download your synthesized design to the Spartan3E FPGA. ExPort is part of the
Adept software suite that you can download free from Digilent, Inc.
(www.digilentinc.com). A more complete book called Digital Design Using
Digilent FPGA Boards – Verilog / Active-HDL Edition is also available from
Digilent or LBE Books (www.lbebooks.com). This more comprehensive book
contains over 75 examples including examples of using the VGA and PS/2 ports.
Similar books that use VHDL are also available from Digilent or LBE Books.
Many colleagues and students have influenced the development of this
book. Their stimulating discussions, probing questions, and critical comments are
greatly appreciated.
Richard E. Haskell
Darrin M. Hanna
