You wrote... To me, by far the best book on this topic is "RS-232 made easy". It truely pains me to say that about a book with "made easy" in the title, but honestly, the book is extremely thorough and very detailed. They have large sections of how to build up a code library in C to talk directly to an 8250 UART. Sections on parity generation methodologies, etc. Also has lots of information to give you a clear understanding of exactly how to wire up your own custom cables, like when to cross what signals (DTE vs. DCE), several suggested methods for handling devices with disparate versions of hardware control signals, etc. Jay West --- [This E-mail scanned for viruses by Declude Virus]