| 摘要 |
In multi-frequency push-button dialling systems, enquiry calls are made by means of loop interruptions of defined duration, e.g. 270 ms. The circuit for producing the interruption contains an arrangement for transmitting the multi-frequency push-button tone dialling signals (TD; R1-R2, C1, C2), an actual arrangement for producing the interruption (BC; NG2, NG3; SR) and an output switching arrangement (CC). A digital counter (BC) is controlled by an audio-frequency generator (TD). The duration of the loop interruption can be defined through the selection of the counter outputs (SD1-SD3) and of the audio frequency. <IMAGE>
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