1,027,315. Automatic exchange systems. SIEMENS & HALSKE A.G. Dec. 31, 1962 [Dec. 29, 1961 (2)], No. 48992/62. Heading H4K. In a T.D.M. exchange in which equipment numbers are stored in different phases in combinations indicative of the subscribers they serve, the stores are also used to store directory numbers. When a called subscriber's directory number is inserted in a store Ub tests are made to see if the subscriber is free and if so the equipment number is substituted for the directory number and is then used to pulse a gate such as SN2 to connect the called subscriber to the T.D.M. speech highway SM. For this purpose a counter AZ emitting equipment numbers over A2 is stepped once per cycle and feeds a converter UM which emits (inter alia) directory numbers. These are compared in RB with the outputs from Ub and when coincidence is obtained an output is provided over r/vb. During the cycle the AZ output is compared in AA, AB with all equipment numbers in Ua and Ub. If the number occurs in Ua or Ub outputs are provided on a/va or a/vb to show that the subscriber is busy. In the absence of such outputs the control circuit ST then effects the above-mentioned substitution by pulsing DS<SP>1</SP> in the phase allotted to the call. In the time cycle of 100 positions P 0 . . . P 99 , P 0 is used for off-hook scanning P 1 . . . P 95 are speech phases and P 96 . . . P 99 are used by ST for processing information received from the comparators &c. In the event that ST has to perform an operation of the above character AZ is prevented from stepping to enable the subsequent cycle to be used for these operations. Call finder action.-Pulse position P 0 is used as a scanning pulse and is applied successively to subscriber's or exchange line circuits under control of AZ which emits equipment numbers in succession, normally for a duration equal to the whole of the multiplex cycle. When a subscriber, say N1, is off-hook a P 0 pulse is fed over lead smn to the control circuit ST to set a trigger therein. During the pulse positions P 1 . . . P 95 which are used for speech and with A2 applying the calling subscriber's equipment number to comparators AA, AB, the latter indicate if the equipment number already has a pulse in which case appropriate triggers are brought up in ST over leads a/va, a/vb. In the absence of such marks a further trigger is brought up at P97 to open a gate during the succeeding cycle. The reception of a P 0 pulse in ST also causes a store carrying free pulses to emit one of these pulses, say P 1 , through the open gate to leads da, vbl. The pulse over da is stored in Uda, and the pulse over vb1 opens gate DS<SP>11</SP> to admit the code present in AZ (which has been inhibited from stepping by means not shown) to the store Ua in that pulse position. The pulse in Uda subsequently enables the decoder Da to pulse the gate SN1 to connect the subscriber N1 to the speech highway SM. A free register is then connected to the speech highway SM in manner not shown, and incoming digits in the form of V.F. signals are received and registered. Called subscriber free.-By means not shown, the directory number is written into Ub at phase P1. When the counter AZ reaches the equipment number of the called subscriber, the converter UM issues the corresponding directory number, and a successful comparison takes place at P1 in RB so that pulse P1 is emitted over lead r/vb, and provided the line is not marked busy by a P1 pulse in Ubz this sets a trigger in ST. During the remainder of the cycle the called subscriber's equipment number is tested in comparators RA, RB to see if it is already in use in Ua or Ub in which case outputs at some phase are provided over a/va, or a/vb to set triggers in ST. If the subscriber tests free a " free " trigger is operated at P97 to enable during the subsequent cycle, a gate feeding lead vb<SP>1</SP>. The P 1 pulse on r/vb has meanwhile been stored in a delay line and this is applied to the last mentioned gate. This pulse on vb<SP>1</SP> is stored in Udb and also opens gate DS<SP>1</SP> to admit the equipment number from AZ (whose stepping has again been arrested) to Ub. Insertion of the new (equipment) number automatically deletes the old (directory) number from Ub. The called subscriber is thereby connected to the speech highway SM. The pulse over vb<SP>1</SP> is also inserted in Urz, Ufz to cause ringing signals to be sent. This latter operation and switch-through on called subscriber answer are not described in detail. Called subscriber busy.-Operations occur as before but with a busy marking on a/va or a/vb operating the appropriate trigger in ST a " busy " trigger is operated to enable an output gate for lead bs<SP>1</SP>. The P 1 pulse, stored as before, is therefore emitted on bs<SP>1</SP> and stored in Ubz to connect up busy tone in that phase to the speech highway SM. Transfer when called subscriber busy.-When a call can be transferred the converter UM emits the directory number of a second choice subscriber over leads to gate D together with a special marking on a lead wb (not shown) to the control circuit ST. This inhibits the gate leading to bs<SP>1</SP> and instead opens a gate leading to lead rw over which the stored P 1 pulse is emitted. This causes the substitution of the second choice directory number into store Ub and operations proceed afresh for calling the second choice subscriber. This process may be repeated until absence of a marking on lead wb permits busy tone to be reverted. Alternatively, the call may be caused to revert to the original subscriber if the second choice subscriber is also busy. Transfer when called subscriber fails to answer within a given time.-For this to be possible the converter UM emits a signal over a lead wf (not shown), which provided the " free " trigger is operated opens a gate to emit the stored P 1 pulse to lead rwm<SP>1</SP>. This is stored in RWZ for 30 sees. after which it emits a pulse train in this phase over lead rws. When AZ next arrives at the called equipment number comparator A/VA emits a P1 pulse over a/va which is gated into ST by the rws pulse to operate a transfer trigger. This P1 pulse is also stored. Towards the end of the cycle (P96) this operates a further trigger to emit the stored P1 pulse over lead rw. This as described above, causes the storage of the second choice directory number in Ub and operations are recommenced in respect of this number. If the second number is engaged either busy tone may be given or the call transferred back to the previous subscriber. Exchange line or PBX hunting.-A special control circuit is taken into use when exchange equipment numbers are fed from the address generator. This operates in a similar manner with the exception that no action is taken if the exchange line is busy except in the case where all the exchange lines are busy, an appropriate signal then being received by the control circuit to allow busy tone to be reverted in the manner described above. In the case where one-way and both-way junctions are provided arrangements are provided to inhibit the testing of both-way junctions until all the one-way (outgoing) junctions are all busy. PBX hunting arrangements are similar to those for interexchange lines.