Simon Monk - Programming FPGAs: Getting Started with Verilog

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To my wife, Linda

About the Author

Dr. Simon Monk has a bachelors degree in cybernetics and computer science and a Ph.D. in software engineering. He is now a full-time writer and has authored numerous books, including Programming Arduino, Programming Raspberry Pi , Hacking Electronics , and is co-author of Practical Electronics for Inventors . Dr. Monk also runs the website .

Wouldnt it be great to be able to have your own chips made that do exactly what you want them to? Well, field-programmable gate arrays (FPGAs) let you get pretty close to this ideal. Rather than being a chip specifically designed for you, an FPGA is a general-purpose chip that can be configured to act any way you want.

What is more, the way you configure your FPGA is either by drawing schematics or using a hardware-definition language that could (if your design is successful) also be used to manufacture chips that are actually custom chips to your design. The language in question is called Verilog , and although this book shows you how to make designs using a schematic editor, the main focus is on learning the Verilog language.

The FPGA configuration can be changed as many times as you like, making it a great tool for prototyping your designs. If a problem rears its head, you can just reprogram the device until you get all the bugs out. The ultimate mind-bending flexibility comes when you realize that you could actually configure your FPGA to include a processor capable of running programs.

In this book you will learn both the general principals of using FPGAs and how to get the examples described in this book up and running on three of the most popular FPGA evaluation boards: the Mojo, the Papilio One, and the Elbert 2.

Although, logically, a microcontroller can do pretty much anything that a FPGA can, a FPGA generally will run faster, and some people find it easier to write a description of logic gates and hardware than they do a complex algorithm. You can use a FPGA to implement a microcontroller or other processor (and people do).

Perhaps the most compelling reasons to try out programming some Verilog on one of the many low-cost FPGA boards is simply to learn something new and have some fun!

As always, I thank Linda for her patience and support.

At TAB/McGraw-Hill and MPS Limited, my thanks go out to Michael McCabe, Patty Wallenburg, and their colleagues. As always, it was a pleasure working with such a great team.

Thanks also to Duncan Amos for his helpful and thorough technical review.

Field-programmable gate arrays (FPGAs) are digital devices that rely on digital logic. Computer hardware uses digital logic. Every calculation, every pixel rendered onto a screen, and every note of a music track is created using the building blocks of digital logic.

Although digital logic at times looks more like an abstract mathematical concept rather than physical electronics, the logic gates and other components of digital logic are constructed from transistors etched onto integrated circuits (ICs). In the case of FPGAs, a circuit can be designed by drawing logic gates that are then mapped onto general-purpose gates on the FPGA that are connected together so as to implement your logic design. Alternatively, the logic can be described using the Verilog (or another) hardware description language.

You can still buy chips that contain a small number of logic gates, such as the 7400, which has four two-input NAND gates. However, these are really only to maintain aged systems that use the chips or for educational use.

Logic gates have inputs and outputs. These digital inputs and outputs can be either high or low . A low digital input or output is indicated by a voltage close to 0 V (ground). A high digital input is usually something over half the supply voltage of the logic, and a high digital output is at the positive supply voltage. The supply voltage for a FPGA is usually one of 1.8, 3.3, or 5 V, and most FPGAs can operate over a range of voltages. Some allow multiple logic voltages to be used on one device.