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 9600bps serial interface, compatible with most types of host µController. 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 µController 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.

Hardware support is provided for V.23 and Bell 202 Fast Turnaround and for rapid return to AT Command mode. A Fast Connect mode hasm been implemented to reduce modem connection time.
Flexible line driver and receive hybrid circuits are integrated on chip, requiring only passive external components to build a 2 or 4-wire line interface.
Complete examples of 2-wire line interfaces to an external host µC and to an RS232 interface, including the additional components required for Type 1 CLI, are provided.

The device features a Hook Switch relay drive output and a Ring Detector circuit that remain operational when the CMX866 is in ‘Zero-Power’ or Powersave mode, providing an interrupt which can be used to wake up an external host µC, as well as the CMX866, when line voltage reversal or ringing is detected.

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