A second edition of this book has given me the opportunity to respond to suggestions from both students and correspondents from around the world, fromdisparateregionsrangingfromScotlandtoHawaii. Sincethe time of the ?rst edition written in the late 1990s, the Microchip PIC range has become the largest volume selling 8-bit MCU. The mid-range f- ily used in the original edition has continued to expand vigorously, with some of the exemplars used becoming essentially obsolete. In addition, the enhanced-range 16-bit instruction line has been enlarged from vir- ally nothing to form a signi?cant proportion of the family. At the same time, new introductions to the original low- (or base-) end architecture continue apace. Because of the close relationship between the low-, mid-, high- and enhanced-range lines, the focus of the new edition has stayed with the mid-range line up. Virtually all diagrams have been modi?ed, many extensively, and - merous additional new ?gures have been added. Throughout the text, special attention has been paid to clarify the basic concepts. In Part I, Chapter 3 has been extensively rewritten with this in mind and to b- ter integrate with Chapters 4 and 5 in Part II, both of which bear only a super?cial relation to the original text. Chapter 7, covering interrupt handling, has also been largely rewritten to elucidate a di?cult topic.