Amazon.com: DTech DB9 RS232 Serial Cable Male to Male Null Modem Cord Full Handshaking 7 Wire Crossover for Data Communication (1.5 Feet, Black) : Electronics
Null modem Serial cable Pinout RS-232 Serial port, Serial Cable, angle, text, rectangle png | PNGWing
Null Modem cable wiring - THUNDERDOME – the ATARI site
All you have to learn about serial connector pinouts