Datasheet for the MT8870, a widely used DTMF receiver that decodes telephone keypad tones into a 4-bit code with a strobe output. This 260 KB PDF typically provides the pinout, guard-time network calculations, electrical characteristics and a reference circuit built around a 3.579545 MHz crystal. Repair technicians consult it when a dialler, door-entry system or remote-control module stops recognising tones, checking the StD output, crystal and input amplifier stage. Verify the exact chip marking against the document before probing.
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