720,484. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Jan. 27, 1953 [Feb. 8, 1952], No. 3335/52. Class 40 (4). In an automatic exchange a marking circuit, which receives a plurality of digits designating a wanted line and controls the operation of selector switches in a plurality of stages to complete a connection to that line by way of any trunk in one of a plurality of groups of trunks accessible to the first of the stages, the groups of trunks having no rigid numerical association with the digits, is arranged to effect translation of the digits into markings which define the wanted line and the particular group of trunks giving access to that line by the provision of switching devices, each responsive to the plurality of digits to select a single contact, together with a cross-connecting field between the contacts of the switching devices and marking wires. As described, the switching devices are cross-bar switches, each of which in response to three digits selects one of one thousand contacts. General arrangement: Fig. 1. Ten incoming trunks 1IT to 10IT from a selector such as the first group selector described in Specification 720,485 ultimately give access to 1000 subscribers' lines. The trunks terminate in battery-feeding relay sets 1BFS to 10BFS, any one of which may take into use the common control equipment CCE of the penultimate selector P,S. This receives the final three digits of the wanted number from the register (which is then released), and stores them in relay groups SHD, STD, SUD. A marker MKR is then associated with CCE, and all the digits are transferred to set each of three cross-bar switches H, D and U, in each of which a single one of 1000 contacts is operated to mark in each case one of 1000 points in a cross-connecting field CCF. These points are jumpered to the relevant HM, DM and UM marking leads wired to the common control circuits of three line finder/final selector units, thus marking the particular line circuit associated with the stored digits. The LF/FS (viz. line finder/final selector) concerned then indicates to the penultimate selector via the marker whether or not any link-busy conditions exist, so that unnecessary testing of trunks which are thereby made inaccessible is avoided. Testing for an idle trunk to the final stage is carried out over test leads T extending directly to the LF/FS common control circuit, and eventually switches P,S complete the connection. Trunking in penultimate selector: Fig. 2. This selector comprises two 10x10 cross-bar switches with the select magnets SM1 to SM4 of S giving access to LF/FS1; SM5 to SM8 to LF/FS2; and SM9, SM10 to LF/FS3. As the marker deals only with 1000 lines, only 200 of the 400 lines of LF/FS3 are included, the other 200 being part of another 1000-line group. Detailed description: Seizure of penultimate selector, Figs. 4-9. Relay sat 1BFS (Fig. 4) is seized by 1IT and ground on the P wire brings up ATS, which removes the idle battery from wire T, connects up the code relays W,X,Y,Z to wires + and -, and operates E. This relay disconnects the busy tone lead BTL, and grounds the start lead ST of the control equipment. The digits are sent from the register as combinations of full ground and/or resistance ground on the + and/or - wires. Relays W and Y operate to full ground only, and X and Z to both. Each digit is sent by first transmitting a " seize " signal (full ground on both wires) to operate W,X,Y and Z, followed by the digital signal. The five digital signals represent 1 or 6, 2 or 7, 3 or 8, 4 or 9, and 5 or 0 respectively, and for digits greater than 5 they are preceded by an " over 5 " signal which holds X, Y and Z. Digits signalled. The seize signal brings up W,X,Y,Z followed by PU (Fig. 7) and ST. On receipt of the first digit " 5," relay Y relapses, ATB operates slowly, and PU releases bringing up CH. Relays AW, AX and AZ thus record the first digit and mark leads CW, CX and CZ to the marker MKR. Relay TRA pulls up, and disconnects the code relays to signal to the register that the hundreds digit is stored. Relays ATB and TRA fall away and the code relays are re-connected. The second seize signal again operates W,X,Y,Z and PU, and OA follows, connecting up BW to BZ. The second digit being " 8," the " over 5 " signal, which follows, releases W, so that OFA operates and prepares a circuit for BY; PU falls away followed by CH. The " 3 or 8 " signal then holds X and Z operated and ATB re-operates. Relays BX, BY and BZ mark leads DX, DY and DZ, and TRA comes up as before. The re-operation of W,X,Y,Z and PU to the third seize signal brings up OB which connects up CW to CZ, and grounds the marker start lead MST (Fig. 8). The third digit being " O," leads UW, UX, UY and UZ are marked, TRA holding with OB to the lead ST and grounding the lead CN individual to the control equipment. Marker: Figs. 10-14. This includes three 10x10 cross-bar switches H, D and U concerned with hundreds, tens, and units digit marking to three LF/FS units of the type described in Specification 718,394. The marker serves 10 penultimate selectors and a chain of ten relays CA to CK (Fig. 12) is arranged for cyclic operation. Assuming the selector of Figs. 4 to 9 to be selector A (the other nine- B to K-not being shown), its lead CN (Fig. 8) terminates on lead CNA (Fig. 12). In the rest condition one of the relays CA to CK will be operated, say CJ, and the next prepared. The ground applied over start lead MST (Fig. 11) brings up that relay (CK), and the chain operates cyclically, connecting the leads CNACNK in turn to relay FT (Fig. 12) and at the same time preparing circuits to AP-KP. As soon as the three digits are stored, ground is applied to lead CNA, and when CA is next operated, FT pulls up to stop the cyclic operation and bring up AP. This connects the digit storage relays AWM-CZM to leads CWA-UZA whereupon AWM, AXM, AZM; BXM, BYM, BZM; and CWM, CXM, CYM, CZM all operate. As a result select magnet 5SM is operated in all three cross-bar switches, followed in each case by bridge magnet 8BM, so that crosspoint CP5/8 is operated in each switch, and ground is extended to all the tenth bridge commons of the switch H so that contact 580 (Fig. 11) is grounded. Each such contact of each of the switches is wired to the corresponding one of 1000 terminals on the directory number side of the cross-connecting field CCF (Figs. 11, 12, 13), which is jumpered to the relevant hundreds, tens and units terminals 1H-0H, 1D-0D, 1U-0U corresponding to the position of the line in the LF/FS units. The line number in the LF/FS is in this case assumed to be 219. The ground extended to terminal 2H (Fig. 11) operates TA, which connects the test relay SWA (Fig. 13) to the lead TIC of LF/FS1. SWA operates to idle battery connected to lead TIC in LF/FS1, grounds lead SIC (Fig. 11) of LF/FS1 to condition it for the incoming call, connects lead 20 (Fig. 14) and its ten contacts AP13-KP13 (of which only AP13 is shown) to lead ST of LF/FS1, and operates MA (Fig. 10) which extends ground to the operated contacts 580 of switches D and U, and switches through leads HM1-HM4 to LF/FS1. The markings on leads 2HM, 1DM and 9UM are thus extended to LF/FS1, and when they are accepted, ground is returned on lead ST (Fig. 14) and is extended to the relevant penultimate selector over leads 1GA and 1G (Fig. 9) to bring up TAA and TD. The test relays 1TR-4TR are thus connected respectively to the four groups of ten test leads T(LF/FS1) (Fig. 6) of the trunks leading to LF/FS1, and ground is extended from lead ST (Fig. 4) to the upper winding of 1A (Fig. 5). The pairs of relays 1A,AR-1K,KR then operate cyclically so that the test relays 1TR-4TR test the trunks four at a time, each four being associated with a single bridge magnet of switch S. If these tests are unsuccessful, relay EC (Fig. 8) pulls up, restores the relay pairs, and then relapses to initiate a new cycle. Link-busy conditions. If a link in the penultimate selector is in use, the bridge magnet is operated and all the outlets from that link are therefore inaccessible. For links 1L-8L (Fig. 2) the relevant relays 1GC-8GC (Figs. 8-9) will thus be up and will ensure that the corresponding pairs of 1A,AR-1K,KR are by-passed in the testing cycle. For links 9L and 10L the bridge magnet contacts 9BM1(S) and 10BM1(S) are directly effective in the chain of relay pairs. The non-accessibility of any of the eight incoming trunk groups A-H in the LF/FS is indicated by ground on leads GCA-GCH (Fig. 14) extended to 1GL-8GL (Figs. 8-9) to operate 1GC-8GC. Idle trunk found. Assuming trunk 2H to be the first idle trunk tested, then when HR (Fig. 8) operates, idle battery on its lead T (Fig. 6) will bring up 2TR which stops the testing cycle and operates TO. Select magnet 2SM(S) (Fig. 6) is thus operated, followed by 8BM(S) (Fig. 5) over 2SM1(S). Relay TO also operates 8SM(P) and relay AB (Fig. 4), and grounds the relevant lead of PSA-PSH (Fig. 9) to initiate, via the marker, the operation of the primary switch bridge magnet in the LF/FS. The closure of 8SM1(P) (Fig. 5) operates the primary switch bridge magnet appropriate to 1BFS, i.e. 1BM(P). Contacts 1BM1(P) (Fig. 4) release ATS. Crosspoints CP2/8(S) and CP8/1(P) are now actuated and the ground on the H wire holds 8BM(S) (Fig. 5) and is also extended forward to operate the appropriate secondary switch bridge magnet in LF/FS1. The operation of AB (Fig. 4) connects up AA which pulls up to the calling loop, whereas the relapse of ATS places AB under control of AA and disconnects E. During the release time of E, HH tests the called line. Called line busy. Relay HH remains down and when E releases it connects up busy tone and initiates release of the common equipment. Called line idle. Relay HH operates, connects up ringing tone from lead RTL, and disconnects start lead ST to release ST,TRA,OA,OB, the operated pair of 1A,AR-1K,KR, TO, and the operated TR relay.