This is what I found when looking for info on the Feature Port
The Gemini Feature Port allows hardware designers to add additional functionality to Gemini that can be controlled via the serial connection.
In order to focus using the Gemini, you must have an adapter board accessory connected to the feature port.
(f) PC Control
Gemini can be controlled by a remote computer via an RS232C serial cable. Such control is most often accomplished with planetarium software using the LX200 protocol, the ASCOM standard or with the Gemini Control Center program available online from Daniel Görlich at
http://www.DocGoerlich.com/GCC. The serial command set description allows the development of custom software. In addition, Gemini's Feature and Encoder Ports can be used to control user-designed hardware.
Don't know if you've read all that and if its any help