The CMX866 is a multi-standard modem for use in telephone based information and telemetry systems. Control of the device is via AT commands over a simple 9600b/s serial interface, compatible with most types of host Controller. An RS232 compatible interface can be created by the addition of a Level Converter. The data transmitted and received by the modem is also transferred over the same serial interface. The on-chip Controller interprets these AT commands and controls an internal DSP, which provides the modem and anciliary functions such as Ring Detection, Call Progress Detection, Hook Switch control and DTMF autodialling. User-specific DSP functions are also available via the AT command set.