Since this question comes up frequently I made a page with a list of interfaces. It's a first draft and more info could be added. If you want to edit the wiki create an account on wikidot and let me know you username/email address and I'll add you as an editor.

http://sats.wikidot.com/what-yaesu-g-5550-rotor-computer-interfaces-are-ther...

73, John Brier KG4AKV