There often seems to be a division between the analog and digital worlds. Digital designers usually do not like to delve into analog, and analog designers tend to avoid the digital realm. The two groups often do not even use the same buzzwords. Even though microprocessors have become increasingly faster and more capable, the real world remains analog in nature. The digital designers who attempt to control or measure the real world must somehow connect this analog environment to their digital machines. There are books about analog design and books about microprocessor design. This book attempts to get at the problems encountered in connecting the two together. This book came about because of a comment made by someone about my first book (Embedded Microprocessor Systems: Real World Design): “it needs more analog interfacing information.” I felt that adding this material to that book would cause the book to lose focus. However, the more I thought about it, the more I thought that a book aimed at interfacing the real world to micro-processors could prove valuable. This book is the result. I hope it proves useful.