Celestron's Auxiliary Port Accessory Kit is designed to expand your Advanced GT telescope's ability to interface with multiple devices---including personal computers and the CN-16 GPS Module.
The Auxiliary Port Accessory Kit has a PC port which allows you to update motor control firmware downloaded from the internet, and two auxiliary ports (one for the NexStar Hand Control & one for CN-16 GPS Module).
The Auxiliary Port Accessory Kit can also be used on the NexStar "i" series telescopes for upgrading motor control firmware.