Patent GB-1063993-A (GB)
Title: Improvements relating to automatic telephone exchange systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1963-07-02
Abstract: 1,063,993. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. May 26, 1964 [July 2, 1963], No. 26268/63. Heading H4K. In an exchange system employing registers for storing called lines' identities, at least one additional register is provided and seized when all normal registers are engaged to store the identity of the calling junction and initiate connection of busy tone thereto. As described, the exchange system of Specification 1,063,991 is provided with an extra dummy register, Figs. 2b-2d (not shown), similar to the normal registers described in Specification 1,063,991. Seizing and marking dummy register.-The dummy register has a busy/free transistor bistable circuit BS14, Fig. 2a, whose free signal is normally blocked by gate GA19 so that the dummy register tests busy to a register allotter over lead ta. Busy/free leads bf1 . . . bf50 from the normal registers are connected to AND gates GA5 . . . GA17, and when all are busy AND gate GA18 is primed to open on receipt of a pulse over ci from an electronic incoming junction scanner. Bi-stable circuit BS13 is switched over and GA19 opened. When the electronic scanner finds a calling junction not already allotted to a register it seizes the dummy register over lead ca, changing over BS14 to close GA19 and signify busy to the allotter. The seize signal is applied to the store of the dummy register to set the bi-stable circuits therein, Figs. 2b, 2c (not shown), in accordance with the calling lines' identity. BS14 sends a signal over tr to prepare the translator to receive the junction identity stored in the dummy register, together with a marking indicative of the group of lines served by this group of registers on leads ui1 . . . ui5. Resetting dummy register. - Multivibrator MVX is started when BS14 changes to busy and the pulses produced are fed to a counter comprising bi-stable circuits BS15; BS16 the outputs of which open gates GA21 and GA22 in sequence producing " S " and " K " pulses respectively. If during the S pulse busy tone has been connected to the incoming junction, the scanner detects " junction disconnect" and the K pulse will be applied to lead m to reset BS14. If no " junction disconnect " is detected gate GA24 is opened to feed the K pulse to an alarm circuit. BS14 is reset by a pulse over lead m. Connection of busy tone.-A tone circuit, Fig. 3, is seized by a pulse on C from the translator which energizes relay S. Closure of contacts s1 connects negative potential from the +ve line wires of the calling junction to energize self-holding relay ET which applies busy tone to the centre of relay L. Relays CB and E are also energized, the latter locking up with the result that pulses are applied over leads p1, p2 to count-of-eight binary counter BS20, BS21, BS22. When the seize pulse is removed s3 opens and relay SA picks up. Earth is connected to the P and C wires to initiate the operation of the cross-point switches connecting the tone circuit to the calling junction circuit. When the " B " section of BS22 conducts GT26 is opened to energize relay GA. Closure of contacts ga2 energize relay HA thus connecting busy tone received over relay L to the calling junction and D.C. energizing L. A ¢ min. pulse supply is connected to p3 over ha4. If the calling subscriber clears, L drops out and an earth pulse is applied to BS22 making the A sections of all of BS20, BS21 and BS22 conducting. Contacts l1 energize relay RL and when the B section of BS22 next conducts relay TB is operated followed by relay TC which instigates the return of the whole circuit to its ready state. If the caller does not clear, a pulse on p3 energizes relay TA. When the next ¢ min. pulse is received on the lead p3 relay RS is operated over tb2. Relay RL is operated by the output of GT27 and thereafter the circuit returns to ready state in the same way as if the caller had cleared. N.U. tone.-If N.U. tone is required instead of busy, positive instead of negative potential is applied to the +ve wire and relay NT picks up in place of ET. Parking incoming junctions.-When the last free tone circuit is taken up by the translator, neither positive nor negative potential is applied to the +ve wire. ET and NT are not operated, and in consequence L remains deenergized and the release sequence of operations starts as soon as the "A" sections of BS20, BS21 and BS22 are conducting. The calling junction circuit is thus parked on lead P and the tone circuit freed to ensure that there is always one free tone circuit to deal with calling junctions that fail to find a normal register.