The CMX869B is a multi-standard modem for use in EPOS terminals and telephone based information and telemetry systems. This highly integrated single-chip modem IC provides the functions needed to construct a ITU V.32 bis automode modem or a V.22 bis, V.22, V.21 and Bell 202, Bell 103 compatible modem operating under the control of external host timing for EPOS and other proprietary protocols.

The V.32 bis automode-modem provides operation from 14400 bps with automatic fallback through to 4800 bps, retrain, rate re-negotiation and automatic detection of V.22 and V.22 bis modems.

A high-quality DTMF decoder with excellent immunity to falsing on voice and a standard DTMF encoder are included. Alternatively, the device can transmit and detect user-programmed single and dual-tone signals, call progress signals or modem calling and answering tones.

The CMX869B features a software controlled output to drive a hook switch relay and a ring detector block that continues to function when the device is in Powersave mode.
When a line voltage reversal or ringing signal is detected, the ring detector circuit provides an interrupt that can wake up the host µController.

Line input and line outputs can be single-ended or differential and the line-output amplifier is capable of directly driving into a low-impedance transformer or opto-isolated DAA. The hybrid and gain control circuits are integrated on chip, requiring only passive external components to build a 2- or 4-wire line interface.

Host control and data transfer is via a simple, high-speed serial bus that operates in normal and Powersave modes and which is compatible with popular µC serial interfaces. An embedded USART accepts multi-format asynchronous data with V.14 support, or allows unformatted synchronous data or HDLC framed data to be received or transmitted. Data transfer can be in either an 8- or 16-bit format.

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