The CMX661 is a low power, Dual Subscriber Pulse Metering (SPM) Detector two detectors on a single chip to indicate the presence on a telephone line of either 12kHz or 16kHz telephone call charge frequencies. The detection frequency and bandwidth are common to both detectors and may be externally selected. The detection sensitivity is set independently for each channel by external components and the detector outputs can be set to a high impedance state for device multiplexing requirements in PBX and PABX line card applications. Flexibility of decode bandwidth settings allows the CMX661 to operate in systems where the SPM generation is not necessarily perfectly accurate or stable. External hardwired selection of functionality economises on the number of host C I/O control lines required, whilst the rapid response and deresponse times of the CMX661 permit flexible tone length qualification by the host C. The CMX661 offers low (3.0V) operating voltage and power, consuming 750A at 3V. It is available in low-cost 16-pin plastic DIL and SOIC packages.