| 摘要 |
An automatic electronic call-reply unit. It has interface circuits made up of transmitters, receivers and associated circuitry, as well as a processing unit, consisting of a microprocessor, the programme memory, the non-volatile memory and input-output circuit, a multifrequency generator and generator of the call tone, interface circuits with the telephone line consisting of an oscillating transformer, the line retention circuit, the line current detection circuit and the call detector. Finally the said unit has a call tones generator, consisting of a sinusoidal synthesizer followed by a bandpass filter, and the said unit also has a switchboard tones detector and therefore the detector of tones and reply. <IMAGE>
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