981,335. Automatic exchange systems. SIEMENS & HALSKE A.G. June 9, 1961 [June 10, 1960; March 8, 1961], No. 20932/61. Heading H4K. In a time division multiplex exchange in 2 which communication channels are represented by pulse positions in a recurring cycle of such positions, a control system may, when effecting a control operation, take a period comprising two of such cycles, the first cycle being used to collect relevant information from the relevant subscribers and other equipment, and if such information indicates that a control operation is necessary the operation is carried out during the second of said cycles. Allocation of pulse position to newly calling subscriber.-As shown, connections are established between subscribers Tn1 ... Tnx by synchronous closure of gates S1, Sx leading to the speech pulse multiplex highway SM the gates being opened by pulses inserted in combinations of delay lines Ua for the calling subscriber and Ub for the called subscriber. The outputs from the delay line combinations operate via decoders Da, Db to give pulse output on individual leads one for each subscriber. Between the end of each multiplex cycle and the beginning of the next a sequence of six control pulses lp, 2p . . . 5p, 6po occur. A register G is stepped cyclically once per multiplex cycle to emit the coded identities of all the subscribers. These pass gate Sd, opened at time 6po, to pass a pulse to the decoder Da which thereupon opens the gate Ts1 of the subscriber in question. If the subscriber is off-hook a pulse will be sent to the lead YM during this period and gated in at gate Wo at this time. If no control is being issued at this moment W15 will be opened to allow W1 to pass the off-hook signal to set the trigger K1. If the subscriber already has a pulse it will be present in the appropriate combinations of delay lines in either Ua or Ub. The outputs of these sets of delay lines are fed to comparators Va, Vb respectively which are fed with the identities of the scanned subscriber present in register G, and a pulse present in the appropriate combinations is fed to either terminals va or vb. Fig. 2, to set K 2 or K 3 . In either of these cases W5 remains closed. If however the subscriber is newly calling with K1 set and K2, K3 not set W5 emits a signal which at time 3p of the next cycle opens W9 to set K5. At the same time W9 sets K7. W15 which had been closed by K8 at time lp is now held closed for the remainder of the cycle by K7, to prevent any more signals from being accepted by E1 during the control cycle. The decoders associated with stores Ua, Ub and any other relevant stores provide pulses to leads ua, ub . . . indicative of free phases in these stores. Gate W7 therefore emits pulses free in all these stores and these are delayed in t 1 by an amount equal to the duration of one cycle and the first of these passes via gate W11, opened by K5 to lead sa and also resets K5. The pulse on lead sa passes via gates So opened by the code registered in G to the appropriate combination of stores Ua. Disconnection of ringing current on called subscriber answering.-Sending of ringing current is effected by the presence of the pulse in question in store Ud. The pulse is also present in the called subscriber's combination of stores in Ub. In these circumstances when the called party answers then in an information cycle, when register G contains the called subscriber's identity, K1 is operated by the 6po pulse received over ym and vb receives an input from comparator Vb to operate K3. The pulse in Ud is also gated in at W8 to operate K4. Consequently W6 opens to set K6 and during the next cycle the pulse from vb, delayed for the period of one cycle by t2, is emitted by W13 to erase the pulse from store Ud. If certain operations require more than one control cycle trigger K7 may be replaced by a counter which counts the cycles and prevents W15 from opening until the count is complete. Statistical metering.-Each control operation causes the disappearance of the output from W15. These are used to operate a meter indicating the number of control operations which take place during a given time. Specifications 981,336, 981,337, 981,338 and 981,339 are referred to.