DDC controllers not only execute the algorithms that form the basis of DDC (control loops), but they also perform the entirety of the BAS sequences of operation. They are literally the brains behind BAS operation. DDC controllers vary in processing power, point capacity, point types, the sequences that can be executed, the programming language used, use of BACnet/IP and/or MS/TP communications, and the BACnet services supported. Other capabilities may include alarming, trending, scheduling, and even the ability to serve up graphic screens. These variations depend on the controller’s purpose/cost, BTL listing, and how it fits into a manufacturer’s BAS architecture.