Date: 8 Feb 2002 20:03:52 -0400

 Do you want actual code, or do you want books that explain what's going
 on?

 1) Source code

 First, check your compiler's run-time library. Many compilers offer
 functions similar to Microsoft C's _bios_serialcom() or Borland's
 bioscom(), which may meet your needs.

 Second, check for downloadable resources at SimTel and Garbo. At SimTel,
 <http://www.simtel.net/pub/pd/41750.html> (March 1993) is described as
 "Asynchronous communications library for C"; Garbo has a whole
 <ftp://garbo.uwasa.fi/pc/> directory. Also, an extended example is
 in Borland's TechFax TI445, downloadable as part of:
 <http://www.simtel.net/pub/pd/50843.html>
 <ftp://garbo.uwasa.fi/pc/c-lang/bchelp10.zip>

 Though written by Borland, much of it is applicable to other forms of C,
 and it should give you ideas for other programming languages.

 Third, SNIPPETS (see <Q:02.08> [What and where is SNIPPETS?]) contains a
 sample interrupt-driven serial communications library.

 2) Reference books

 Highly recommended: Joe Campbell's {C Programmer's Guide to Serial
 Communications}, ISBN 0-672-22584-0. He gives complete details on how
 serial ports work, along with complete programs for doing polled or
 interrupt-driver I/O. The book is quite thick, and none of it looks like
 filler.

 If Campbell's book is overkill for you, you'll find a good short
 description of serial I/O in {DOS 5: A Developer's Guide}, ISBN
 1-55851-177-6, by Al Williams.

 Finally, a reader has recommended {Serial Communications Programming in
 C/C++} by Mark Goodwin (ISBN 1-55828-198-3), with source code in the
 book and on disk. Topics include the basics, various methods of serial
 communications on the PC (with consideration of high-speed modems), ANSI
 screen interface, file transfer protocols (Xmodem and Ymodem), etc.
 There is code in C, and that code is extended into a C++ class for those
 who use C++. There are also subroutines in Assembly.

 3) Downloadable information files

 A "Serial Port FAQ" is occasionally posted to this newsgroup, and is
 downloadable as multiple files:

 <ftp://ftp.phil.uni-sb.de/pub/people/chris/>

 This directory contains a series of files beginning with Serial_Port.