Patent GB-1258930-A (GB)
IPC: H04M9/00
Filed: 1969-02-25
Abstract: 1,258,930. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 25 Feb., 1969 [27 Feb., 1968], No. 9958/69. Heading H4K.  A key (push-button) telephone system including a switching network, a plurality of telephone lines on one side of the network, a plurality of key telephones, having keys each representative of an individual one of the lines, on the other side of the network, a data memory arranged to scan the keys in sequence and a means including a temporary memory arranged to send control signals to the key telephones, to receive and store status signals, e.g. switch-hook and key state signals and to control the switching network in accordance therewith. The telephone lines may be extension lines of a P.B.X. or may lead to a central office. The number of key telephones (or substations) is not related to the number of telephone lines and the substations need not all have the same number of keys. As detailed some substations have six line keys and are associated with six lines while others have thirty keys and are associated with thirty lines. More than one substation is associated with each line and in the event of an incoming call on a particular line any substation associated with that line may by lifting his receiver and pressing the appropriate key accept the call on that line, the incoming call being offered to such free substations in succession. Each station can by depressing more than one key connect to more than one line and has a hold key, operation of which causes a line to be connected to a hold bridge and held while an interim call is made. The type of switching network is not specified. Common control is effected by sequentially accessed read only twistor memory (the data memory) each word read out corresponding to one key of one of the substations thus offering or controlling a connection between that substation and the line corresponding to that key, and a temporary memory storing one word of each line which is active. The temporary memory is content-addressable parallel access memory and after a word is read out from the data memory is accessed for data relating to the corresponding line, any change in conditions, e.g. the detection of a new call being recorded in the temporary memory by modifying the data read out and writing it back in the temporary memory.  Substations.-The substations are connected to the switching network via separate speech wires such as the tip and ring conductors T2 and R2 of the station shown and to the central control over a common data bus formed by the conductors 110 to 114. Alternatively the speech paths may be a time division multiplex highway. All transmissions over the data bus are initiated by the common control. After each word specifying one key of one substation is read out of the data store the key and substation numbers are encoded and transmitted: over the data bus to all substations each substation being able to recognize its own identity number and to identify each of the key numbers. A station having only six line keys responds to only one identity number while in the 30 line key substation: shown the identity match circuit responds: to five different identities marking a corresponding one of five lines 591 to 595. The key match circuit marks one of six lines 551 to 556 and the marked lines enable one of thirty AND gates 901 to 930 corresponding oneto each of the thirty line keys effectively scanning that substation with respect to the line associated with that key. If for example gate 901 is enabled scanning key KK1 and the associated line a potential is applied to a line C1 enabling: (a) a gate KG1 which if key KK1 is depressed and the handset is off-hook enables at 569 a data transmission circuit 590 to send a "1" bit to the central control; (b) a gate H1 enabling the data transmission circuit 590 to send a "1" bit on a different line to the central control if the key KK1 and the hold key HKK are both depressed holding a call on that line; (c) the input gates of a lamp flip-flop 5L1 so that a "1' or "0" bit arriving from the central control over a line 112 can set or resetthe flip-flop illuminating or extinguishing a lamp LPP1 associated with the key KK1 to indicate at the substation the state of the associated line; and (d) gates 551 and 552 at the inputs of a ringer control flip-flop 5KG to allow theringer 520 to be similarly controlled by the central control.