Patent GB-938685-A (GB)
Title: Automatic telecommunication exchanges
IPC: H03K17/62
Filed: 1960-08-26
Abstract: 938,685. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Aug. 26, 1960 [Sept. 1, 1959], No. 29585/60. Class 40 (4). The line circuits of an exchange are scanned cyclically and a calling or a called line is connected to an allotted link circuit by the operation of a crosspoint of a finder or a connector matrix by signals in the time position of the line concerned. Allotter operation. Seizure of the link circuit preceding that shown in Fig. 1 marks lead S1 to operate the trigger circuit 11; thus marking the ALLOT conductor shown, to assign the link shown for use, and lead R1, to cancel the assignment of the preceding link. Operation of a finder crosspoint in the matrix 7 marks the finder hold conductor 261, whereupon AND gate 12 conducts to mark lead S2 and so allot the next link. Initiation of a call.-When a subscriber takes down his handset seize tone is received by tone detector 30 which marks AND gate 31. When the line is next scanned by the marking of the relevant tens and units scan lines 1, 2 the AND gate 32 in the line circuit conducts, thus enabling AND gate 31 to mark conductor P1. This marking, in conjunction with that on the ALLOT conductor, actuates the relevant crosspoint in the matrix 7 to extend the calling line to the allotted link circuit. The resulting marking on hold conductor 261 enables tone gate 407 whereby dial tone is reverted to the caller, and marks conductor 261A (Fig. 2) to prepare the signal receiver 231. It also starts the timer 246 which initiates release of the link if no dial signals are received during a three minute period. The trigger circuit 211 provides a steering potential on 211A to ensure that the first digit dialled is routed to the tens register 53. The two-out-of-five tone signal from the subscriber's dial is applied to filters U to Z (Z being used for release and recall signals only). Each of the five AND gates 221, 223, 225, 227 229 is enabled by the coincidence of the steering potential, the output of the filter corresponding to its frequency U to Y, and the output of any other of the filters U to Y via one of the OR gates 232 to 236. The reception of a digit thus results in operation of two of the five trigger circuits 220, 222, 224, 226, 228. The OR gate 200 thus conducts, but with 232 or 233 conducting, 214 is enabled and a signal is passed via 212 and 213 to inhibit operation of trigger circuit 210. When the caller releases the digit key, cessation of the digit frequencies causes OR gates 232 and 233 to cease conduction and the inhibition is removed from 210, which operates to the output of OR gate 200. The trigger circuit 211 is thus operated and a steering potential is applied to the units register AND gates. The second digit is received in like manner and two AND gates 0-90 of comparator 300 (Fig. 3) corresponding to the two digits are marked. On release of the digit key the inhibition applied by 214 to the amplifier 320 is removed and when, next the tens and units scan lines of the line concerned are marked, these two gates are enabled, whereupon one of the OR gates 301, 302, 303 and one of the OR gates 305, 306, 308 conduct and AND gate 321 is enabled. Busy test.-If a line is busy, a marking is present on one of the sleeve conductors P1 or P2 (Fig. 1) and is extended via OR gate 35, so that when the line is scanned AND gate 34 conducts and marks the busy bus 4, which is connected to the control terminal of a "1-2 switch " 322 (Fig. 3). Such a switch normally passes a signal from its input via the radial line in the switch symbol to its normal output conductor, but when the control conductor is marked, an input signal passes instead to the switched output conductor. If the called line is busy the output of AND gate 321 will therefore be applied to trigger circuit 325, thus opening tone gate 411 (Fig. 4) to revert busy tone to the caller. The output of 325 also starts the timer 246 which initiates forced release after three minutes if the caller has not previously hung up. Called line idle.-The output of AND gate 321 is applied to the seize bus 5 and the connector closure bus 91 via switch 322 normal. The AND gate 33 (Fig. 1) thus conducts and marks the P2 conductor to effect operation of the matrix crosspoint at its intersection with conductor 91. Closure of this crosspoint marks conductor 421 to reset the tens and units registers and inhibit trigger circuit 210, whereupon trigger circuit 211 restores to normal. The marking also passes via amplifier 441 and switch 442 normal to open tone gates 444 and 440 for the supply of ringing current and ringing tone. On the reply of the called party the momentary transmission of a tone S energizes receiver 430 and the S filter 435 so that trigger circuit 449 is set and OR gate 450 opened, the latter inhibiting amplifier 451. The output of 449 opens OR gate 445 to inhibit amplifier 441, whereupon tone gates 440 and 444 are closed. On cessation of the S tone, the output of amplifier 451 operates switch 452 to switch through the talking circuit. Release.-Arrangements for first party release are shown but the system may be modified to give release under control of either or both parties. When the calling subscriber hangs up, his hookswitch causes the transmission of frequencies Y and Z over conductors 422 and 426 to receiver 231, and the filter outputs enable AND gate 242 thus passing a signal via OR gate 243 to the timer 245 which after a fixed interval marks conductors 260 and 420 to release the operated crosspoints. The output from timer 245 also resets the tens and units registers, via OR gates 251 and 404, and trigger circuits 449, 325 and 326, via amplifier 263, as well as opening gates 431 and 432 momentarily to allow release tone to pass from generator 433 over the talking conductors to effect release of any trunk equipment included in the connection. If the called party clears first the Y and Z frequencies energize receiver 430 whereupon AND gate 460 is opened and a signal passes via gate 447 to OR gate 243, whereafter the release is effected as described above. PBX final selector (Fig. 6).-An incoming call over an idle trunk 1 (say) of the group of PBX trunks 662 is effective in opening OR gate 602 and marking AND gate 606 so that when this trunk group is scanned over lines 661 during the time allotted to it, AND gate 606 is opened to mark lead P1 and thus cause the operation of the associated cross-point as explained above. In addition gate 605 is enabled so as to, mark the tone detector 601 busy, open OR gate 602 and inhibit gate 609. For an outgoing call (assuming at least one of the trunks 662 is free) a signal on the seize bus opens gate 608 when the PBX lines are scanned and if gate 609 is not inhibited a cross-point operating signal is extended on lead P2. However, if line circuit 600 is busy i.e. gate 609 inhibited, then the opening of AND gate 603 when the PBK lines are scanned enables gate 632 and hence AND gate 628 whereby the second line of the trunk group is seized. This sequential testing of the line circuits continues, in the same time frame, until a free one is found. If all the line circuits are busy, AND gate 660 is effective to signal this condition to the busy bus. A night service key K1-K3 is actuated if the PBX facility is to be dispensed with for a period, the operation of the individual line circuits then being as described with reference to Fig. 1. Special services.-In the case of a call to an embryo exchange, an operator or a toll line, in which the first dialled digit is immediately indicative of such a call, gates 201-205 (Fig. 2) are responsive to the appearance of such a digit in the tens register 53. The embryo exchange case viz. a digit absorbing facility, is discussed, but specific circuits are not shown. A call to an operator is signified by the digit " 0 " to which gate 201 responds, a signal thus being passed over conductor 471 (Fig. 4) to the operator and to a ring-back tone generator RBT. When the operator replies RBT is cut-off by a signal over conductor 476, this signal also resetting the register via OR gate 404. For a digit indicative of a toll call, gate 205 is enabled thereby inhibiting gate 212 and allowing the same digit to be immediately stored in the units register 55, whereafter the call is set up as previously described. The cross-point switches comprise matrices of double-base diodes or bi-stable germanium transistors, the control and operation of which are described in Specification 938,684.