Serial Port Complete by Jan Axelson
he part of the book I liked most comes in the section that describes how to connect serial devices. Axelson covers not only RS-232 communications but also RS-485, a serial standard that allows for party-line or multi-drop connections. You would spend a lot of time looking for all the information that the book collects in one place. If you plan to use a serial port in any sort of application, buy this book. It should go on your bookshelf alongside Axelson's earlier book, Parallel Port Complete.

Visual Basic Programmer's Guide to Serial Communications by Richard Grier

Add serial communications to your Visual Basic applications using Custom Controls and the Windows API. Includes VB5! Here is the information you that you need to use modems and direct serial connections (including RS-232, RS-422 and RS-485) for almost any purpose. Richard Grier uses his many years of experience to guide you through the process, while providing the insight that you will need to extend and adapt the ideas that he presents to your own projects. Make your serial communications programs reliable. Learn how to debug communications problems.

INCLUDES .NET! Also includes VB5, VB6, and eVB for Windows CE.