The CMX683 is a general purpose Call Progress tone detector for use in monitoring the progress of calls in Public Switched Telephone System (PSTN) applications. Dial Tone, Ringing, Busy and Not Available states can be distinguished by using the host C to qualify the cadence of the CP DETECT output. The CMX683 uses advanced digital techniques to characterise valid Call Progress tones, unwanted tones, line noise and voice or music signals. In contrast to Call Progress detection devices based on simple filtering techniques, the CMX683 offers excellent sensitivity coupled with low false detection rates. The response time of the CMX683 allows it to operate with almost any Call Progress system. In particular the `stuttered dial tone' of voice mail messaging systems is supported. The use of statistical processing techniques, which analyse signal frequency, duration and amplitude, enable the CMX683 to distinguish voice or music activity from DTMF or Call Progress signals. Separate outputs integrate the "voice" activity over both shorter and longer periods, enabling payphone and other billing systems to commence charging when a line connection has been established. A single 3.58MHz crystal ensures accurate and repeatable performance. With supply requirements between 2.7V and 5.5V and a low current consumption, the CMX683 can be easily integrated into a wide range of telecom equipments. The CMX683 has a similar pinout to all commonly used Call Progress detectors and is available in DIP, TSSOP or SOIC packages.