HDL （hardware description language） and FPGA （field-programmable gate array） devices allow designers to quickly develop and simulate a sophisticated digital circuit， realize it on a prototyping device， and verify operation of the physical implementation. As these technologies mature， they have become mainstream practice. We can now use a PC and an inexpensive FPGA prototyping board to construct a complex and sophisticated digital system. This book uses a “learning by doing” approach and illustrates the FPGA and HDL development and design process by a series of examples. A wide range of examples is included， from a simple gate-level circuit to an embedded system with an 8-bit soft-core microcontroller and customized 110 peripherals. All examples can be synthesized and physically tested on a prototyping board. Focus and audience FOCUS The main focus of this book is on the effective derivation of hardware， not the syntax of HDL. Instead of explaining every language construct， the book focuses on a small synthesizable subset and uses about a dozen code templates to provide the skeletons of various types of circuits. These templates are general and can easily be integrated to construct a large， complex system. Although this approach limits the “freedom” of syntactic expression， it will not prevent us from developing innovative hardware architecture. Because of the generality and flexibility of HDL， the same circuit can usually be described by a wide variety of language constructs and coding styles. Many of these codes are intended for modeling. They may lead to unnecessarily complex hardware implementation and sometimes cannot be synthesized at all. The template approach actually forces us to think more about hardware and develop a good coding practice for synthesis. Since we are