IC adds voice mail waiting to Caller ID chip range

8 November 2000 Telecoms, Datacoms, Wireless, IoT

The CMX612 has been added to the range of calling line identification (CLI) circuits from CML. The CMX612 adds VMWI (voice mail waiting indication or visual message waiting indicator) signal detection to the existing capability for Caller ID and Call Waiting ID. With the growth in use of voice mail systems customers are demanding adjunct boxes or feature phones with the ability to detect that messages are waiting on the voice mail server. The presence of a message is indicated by sending an FSK data burst to the subscriber's feature phone or adjunct box or by altering the dial tone; in some implementations both methods are used.

CMX612 provides the filtering and detection circuitry to meet both of the major standards for VMWI. A dual tone, 350 plus 440 Hz, detector used for stuttered dial tone (SDT)-based systems. For CLASS (custom local area signalling services) implementations of VMWI (An FSK based system.), the CMX612 has a 2130/2750 Hz tone alert detector and a 1200 baud FSK v.23/Bell202 compatible asynchronous data demodulator. The demodulator includes a data retiming circuit which eliminates the need for a UART in the controlling microprocessor.

The CMX612 also offers greater design flexibility for the Caller ID and Call Waiting ID functions through the introduction of a pair of adjustable gain differential input amplifiers which enable connection of the device to the tip/ring or across the telephone hybrid. By choosing the input source the designer can use the impedance of the hybrid to reduce the effects of near end voice and hence improve 'talk off' and 'talk down' performance in Caller ID Call Waiting (CIDCW) applications. Tip/ring detection will be needed to meet the proposed Bellcore MEI standard.

The CMX612 is packaged in either 20-pin TSSOP or 22-pin PDIP. An evaluation board is available.

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