The CMX673 is a general purpose call progress tone detector for use in Public Switched Telephone System (PSTN) applications. Call progress detection allows equipment which dials into the PSTN network to monitor the progress of the resulting call. Ringing, Busy, Not available and Answer states can be determined. The CMX673 uses advanced digital signal processing techniques to detect tones in the frequency band 315Hz to 650Hz. The use of DSP techniques allows the CMX673 to distinguish between valid call progress tone signals and line noise or voice, low false detection rates result. This is in contrast to other call progress detection devices which are based on simple filtering techniques. The detection timing of the CMX673 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 digital processing and small geometry CMOS design techniques allows the CMX673 to offer a complete call progress detector which analyses both frequency and amplitude in a single 8 pin package. This, coupled with industry leading performance and substantially lower power supply requirements than comparable devices, demonstrates CML's unique capability in this area. A single 3.58MHz crystal ensures accurate and repeatable performance. With supply requirements between 2.7V and 5.5V the CMX673 can be easily integrated into a wide range of telecom equipments. The CMX673 is pin to pin compatible with the M980 and TSC 75T980 and SSI980. It is available in DIP, TSSOP and SOIC packages. The CMX673 integrated circuit coupled with cadence measurement of the signals detected can identify virtually all call progress tones used worldwide.