This article provides the differences between the 2216 and the 2218 touch controllers

The 2216 and 2218 controllers are functionally equivalent.  They both use the Elo SmartSet data packet.  They both support either seral or USB interface. The 2218, which replaces the 2216, converts data packets in about half the time and in general uses less power, particulary when idle (see attached spec comparisons).  If an old application works with a 2216 but not with a 2218, then it's probably due to an old end-user driver that does something like querry the controller's ID string to determine the controller type.  The controllers do have small differences in their ID strings.