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TT1 sequence dial tone decoder and digits

2017-08-15 09:10  
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A dial tone decoder is also a standard feature of touch tone telephones, and makes the phone capable of converting the numerical and symbolic information that is entered using the phone's keypad into a signal that can complete the transmission.A decoder can also detect a busy signal.The circuit takes active low inputs from a Touch Tone decoder and reacts to a proper sequence of digits.The proper sequence is determined by which Touch Tone digits the user connects to the sequence decoder inputsTT1 , TT2, TT3, and TT4.Another method is to subject tone decoding to a time constraint. In the case of Quik Call I or a string of DTMF digits, the falsing would have to occur in the exact order required to actuate the decoder. This is much more improbable than falsing in a single tone decoder. In two-tone sequential, tone and voice radio paging, decoders are actuated by decoding one tone and then a second in the proper sequence. Falsing could only occur if the two decoders falsed in a valid sequence within the decoder's time constraints.
 

Tone dial sequence decoder