It is the AppMod connector. Parallax sells a few boards that plug into it. Of course you can use the connections if they are more convient than the female header by the breadboard.
It has all the IO pins available, along with regulated 5v and ground. You can use it to connect two BS2s together by simply plugging in a servo extension cable on the part with ground and an IO pin or two.
Comments
John Abshier
http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/28850-BOE-USB-v1.4.pdf
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
To make something work one must build, test, and verify bfore proceding.· -- myself