The CMX228 is an ISDN data and telephony protocol engine which implements the lower level ISDN interface and communicates with the CMX605 and other standard devices to form a fully integrated ISDN chipset for both voice and data communications. The CMX228 puts all the main data processing elements in a single device. No ISDN software has to be written and simple `Plug and Play' design results. This reduces development time and provides a highly cost-effective hardware solution. By using proven circuit designs, the designer can move quickly from initial concept through design in to manufacture. The CMX228 supports one voice port over the ISDN Line, which can be used to provide ISDN telephony services or a POTS line interface, and a single data channel, capable of operation at 115,200bps. The CMX228 features a full set of `Hayes' compatible AT command codes on its asynchronous data interface, in addition to providing keypad-configurable voice telephony services. The CMX228's feature set and architecture allow most analog systems to be converted to an ISDN equivalent with enhanced features. The CMX228 is designed to work with the AMD 79C30 S/T bus interface, the Siemens PSB-21525 HDLC formatter and the MX-COM CMX605 POTS interface circuit, and also comes complete with embedded applications software. In addition, the CMX228 offers data transfer (up to 16kb/s) over the D-channel by using the X.25 protocol. To support the CMX228, MX-COM can also provide licensed reference designs on user request. A flexible Applications Program Interface (API) allows users to customize the features and operation of their own design. The CMX228 is available in an 80-pin QFP (CMX228S1) package. 1 The CMX228 is a data processor integrated circuit that supports the protocol layers 1, 2 and 3 of the ISDN protocol stack in accordance with the specifications of CCITT (now ITU). These specifications, which are widely used around the world, might not be supported within the U.S.