AUTOMATIC TELEPHONE SYSTEM PROVIDED WITH MEANS OF PROTECTION AGAINST IN INTERNATIONAL INTERRUPTION DURING REGISTER SIGNALLING

摘要

1531296 Tone code receivers TELEFONAKTIEBOLAGET LM ERICSSON 29 July 1976 [1 Aug 1975 (2)] 31740/76 Heading H4K A tone code receiver which returns an acknowledgement signal after each tone code received includes three delay means activated by each acknowledgement signal and arranged respectively to inhibit a further acknowledgement during a first time period (equal to the transit time delay over the return signalling path), to prepare for setting a storage element if a break in reception of the tone code is detected after a second time period, and to reset the storage element after a third time period, the storage element being arranged when set also to inhibit a further acknowledgement.As shown tone codes are detected at 1 and each detection enables via gates 18 and 23 a pulse generator 16 feeding a tone code acknowledgement unit 17. Due to the length of the transmission path the received tone code may continue for over 500 ms this being the transit time delay over the return path plus the switching delay. A monostable 12 triggered by the end of the pulse from generator 16 inhibits via gate 23 the pulse generator and a receiving register 6. If a termination in the received tone code is received within the permitted limits related to the expected transit time and switching delays and defined by monostables 13 and 14 a bistable 15 is set when the termination is detected and reset when monostable 14 times out or is itself reset via gates 12 and 22 when a further end of the received code is detected. The end of each tone code detected sets a bistable 19 which steps a counter 21 which addresses successively the locations in receiver store 6 to be used for successive digits. Monostables 12 and 14 are of the retriggering type and include a bipolar transistor the base of which is connected to the trigger input and the emitter collector path arranged to short circuit a capacitor the charge time of which determines the delay.