The DE8661 Demonstration Board is a reference design for the CMX866 V.22 bis AT command modem IC. The main "socket modem" section contains the CMX866 and associated components in addition to the line interface components. Attached to the main section are two break-off sections which contain a 9pin D type socket for PC serial communications, RJ11 line connector, supply voltage connector and a hook-state LED. The CMX866 contains an on-chip Controller, which interprets AT Commands issued via a standard terminal emulator program running on a host PC or via an external Controller. Interfacing to the Demonstration Board can be via socket pins on the socket modem section, or via the connectors provided on the break-off sections. The board can be operated at 3V or 5V dc, which must be provided by an external, regulated power supply. The PCB has been laid out for both CTR21 and FCC68 compliant DAA designs. However the components fitted are for the simplified European/FCC68 design. Users wishing to convert to CTR21 should contact CML.