View pcd3316-04 datasheet:

PCD3316 Caller-ID on Call Waiting (CIDCW) receiver 11 March 1999 Product specification 1. General description The PCD3316 is a low power mixed signal CMOS integrated circuit for receiving physical layer signals like Bellcore’s ‘CPE1 Alerting Signal (CAS)’ and the signals used in similar services. The device is capable of a very high precision detection of the dual tone (2130 and 2750 Hz) by using a patented digital algorithm. The PCD3316 can be used for on-hook and off-hook Caller-ID (CID), Caller-ID on Call Waiting (CIDCW) and Caller-Name (CNAM) applications. For timing purposes the PCD3316 can be programmed to generate an interrupt signal to the microcontroller every second or every minute. These timings are derived from an on-chip 32.768 kHz oscillator. Also incorporated in