RS-232 Diagnosis Tech Bulletin From Mike Sandman  
   RS-232 Serial Communications is not that hard.
   http://www.sandman.com/rs232.html

Quick Reference  
   For RS485, RS422, RS232 and RS423.
   http://www.rs485.com/rs485spec.html

Computer Tips  
   RS-232 was created for one purpose, to interface between data terminal equipment and data communications equipment employing serial binary data interchange.
   http://www.ctips.com/rs232.html

RS-232  
   Protocols and computer networks, by Dr. D. Koren of Tel-Aviv University.
   http://www.rad.com/networks/1995/rs232/rs232.htm

Keith's RS-232 Library  
   Documentation with download.
   http://www.ent.ohiou.edu/~welker/rs232/

Serial/Rs-232 Interfacing  
   Detailed explanations on interfacing the serial port.
   http://www.beyondlogic.org/serial/serial.htm

The RS232 Standard  
   A tutorial with signal names and definitions.
   http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html

HW Server  
   Overview of the RS-232 standard and cabling.
   http://www.hw-server.com/rs232