tel_4.pdf		FX631 Security and Telephone SPM Detector. This Application Note describes how two FX631 Low-Voltage (Subscriber Pulse Metering) SPM Detector microcircuits can be used, with additional external filter components, to detect both the 12kHz SPM and the 18kHz security tones employed in the French payphone/cardphone system.

tel_5.pdf			FX631 FX631xxX clocking information. Xtal/clock set-ups options.

631acalc.pdf			CMX631A/FX631 External Component Calculation. Worked calculations for selection of the component values for required 'must' and 'must-not' decode frequencies.