Patent GB-1255068-A (GB)
Title: Electrical signalling arrangements in an automatic telephone or like switching system
Inventor: STIRLING HAROLD JAMES
IPC: H04Q3/545
Filed: 1969-03-28
Abstract: 1,255,068. Signalling in processor controlled exchange systems. PLESSEY TELECOMMUNICATIONS RESEARCH Ltd. 12 March, 1970 [28 March, 1969], No. 16281/69. Heading H4K.  Make/break conditions of relay contacts in exchange supervisory circuits are signalled to a common processor by detecting relay contact change of state to generate a demand for the services of an identifier common to a group of supervisory circuits, the identifier acting to find the demand, or one of a number of concurrent demands, so as to gate to the common processor the address of a supervisory circuit originating a demand and to add a signal giving the make/break condition of the associated relay contacts. The invention is applied to a reed-relay trunk transit switching centre, the supervisory circuits being the incoming and outgoing junction circuits. Data transmission between the peripheral circuits of the switching network and the processor complex is effected by seizure of one of a group of looped highways, switching to and from the highways being made at so-called highway stations, such a system being described in Specification 1,243,464. Each supervisory circuit, referred to as a line equipment, is one of a group of 96, the size of the group being extendable to 112 by the inclusion of tone or testing circuits, v.f. sender-receivers, or recorded announcement machines. Each supervisory circuit has four contacts the states of which need to be the subject of a message sent to a processor whenever a state changes; each circuit also has five relays any one or more of which can be switched on or off by an addressed instruction delivered by a processor the identifier of a circuit group acting as a distributer to select a circuit for receipt of such instructions. Each supervisory circuit is given an electronic section which by RC circuits produces positive or negative spikes to signal make-to-break or break-to-make transitions, interprets the transition to store the actual contact state, isolates itself from further input, and signals a demand for the identifier and a send-mode routine. Each such electronic section also has five bi-stables to control the supervisory circuit relays on instruction from the processors. Selection of a supervisory circuit by the identifier is effected by coincidence of 1-out-of-16 and 1-out-of-7 code wire markings, the identifier being cycled by a 7-stage counter in response to and in search of a change of state signal in the group, the 7-stage counter being set to mark out a particular circuit when instructions for relay operations are received. For each group of circuits there is a signal interface which has a ten stage stepping register acting as a sequence controller for send and receive-modes. Send-mode.-In response to a change of state notification the identifier, referred to as a scanner/distributer, starts up from the arbitrary position in which it was last discarded and cycles to an active circuit the electronic section of which routes the identifier's code marking back to the identifier as an equipment-found signal thereby halting the identifier on the active circuit. The signal interface, now presented with the circuit identity and a signal indicating the contact state, steps off its home sequence position to the first of six steps governing the send mode of operation. The first step in the signal interface comprises a request to the associated highway station for a free highway. Once signalled that a highway is available the second step obtains the address of a wanted processing unit; this address being set up as a strapping field to a 10-bit buffer register read out to the seized highway. On acknowledgement that the wanted processing unit is free the -third step is reached. If the wanted unit is busy the returned message to this effect reverts, the sequence to stage 1 to try again. If no such unit exists the highway station releases and a fault signal, referred to as Mayday, is generated. With a response from a free wanted processor unit the third step connects a second strapping field to send a so-called designation address which indicates the programme required for processing the forthcoming data. With suitable acknowledgement the fourth step sends the identity of the circuit involved and the fifth step sends the contact state that has changed in the circuit. The sixth state is reached when the highway station starts a release procedure and the sixth state effects resetting of the electronic section on behalf of which the transmission was effected so that further changes of state can be signalled. The interface then reverts to normal. Receive-mode.-If a processor wants access to a particular circuit served by a signalling interface the associated highway station applies an interrupt signal. If the interface is busy the interrupt signal is looped back to effect a delay. If free, the interface jumps from its normal sequence state to the seventh position of its stepping sequence register, a free signal being reverted. The highway then delivers a so-called designation signal which has no function but is looped back from the receiving buffer store to the highway station and is sent back to the processor for checking. This looping back of data is applied to all codes as a check. In response the processor sends the identity of the wanted circuit of the group served by the interface and this is held in a buffer store and the identifier is set to all-zero in readiness for its distributer function. At the eighth position of the sequence the circuit identity is gated back to the processor for checking and precipitates the sending of a code which indicates what pattern of relay operations and/or releases is required. Reception of this code ejects the circuit identity from the buffer store and transfers it to the identifier which gates the particular electronic section to the interface so that the relay operation code is set up on the electronic section bi-stables when the ninth sequence state is reached in response to a satisfactory check of the code on its reversion to the processor. The interface reverts to normal in response to an end-of-message code.  Fault routine.-If, in the receive-mode, the processor finds a mismatch between what it sent and what it has had in return in the above signalling process, the code is repeated and is registered in the interface by overwriting in the buffer. If the data returned as a result of this second attempt also results in a mismatch, it is judged to constitute evidence of a transmission fault and a so-called Mayday procedure is instituted by an "executive processor". In the send-mode the same procedure of checking is applied between the highway station and the processor involved in data exchange. Special case of v.f. digit signalling.-In place of a single state indication from the electronic section of a supervisory circuit, a six wire, six bit, channel common to the group is gated to the signal interface buffer register for parallel transfer.