972,337. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. July 20, 1962 [July 27, 1961], No. 28065/62. Heading H4K. In a time-division multiplex communication system in which a plurality of primary highways have access to a plurality of secondary highways via a co-ordinate array of static electrical gate circuits, each highway has associated therewith a store in which information relating to the time division channels on that highway is stored, there being a common control circuit which utilizes the information in said stores for setting up a connection via said switch. The invention is particularly applicable to a system in which it is necessary to connect a channel in one time position on a primary highway to a channel in a second time position on a secondary highway, the information relating to these channels, which is contained in the stores, being interchanged via the switch during a third time position. Each 4- wire primary highway, i.e. JA2 is connected to a row R1 . . . Rn1 of the co-ordinate switch 100 and each 4-wire secondary highway such as JAS3 is connected to a column C1 . . . Cn2 of the switch. The speech signals are transmitted, in the form of P.C.M. signals. Each highway such as JA2, has two stores 101, 102 and during each time slot incoming speech signals are written into, and outgoing speech signals are read out of, corresponding eight bit words in 101, 102 respectively. Similar stores 121, 122 are provided for highway JAS3. The signals are passed from store 101 to 122 and from 121 to 102 via the switch during a " connectiontime-slot " different in general from either of those used on the highways. The number of connection-time-slots is in general equal to the number of channel time slots, i.e. 25, one of these being used to carry signals by which various operations performed by the control circuit can be initiated. The eight bits in each word of the stores are interchanged in successive portions of a single connection-time-slot, each portion being subdivided for transmission in alternate directions over the 2-wire trunks used in the switch. These stores are more fully described in Specification 960,511. A " timepath " store 108 (or 129) is associated with each highway and this store is scanned cyclically " by " the connection-time-slots (leads HC). This store contains the identity of the channel which is using any particular connection-timeslot, i.e. the address of this channel in stores 101, 102 (or 121, 122). A " space-path " store 109 is associated with each row trunk and this is similarly scanned. This store contains the identity of the column trunk to which the row trunk is to be connected during any particular connection-time-slot. Once a call is in progress, the information, in the form of a 5-digit binary code, obtained from stores 108, 109, 129 during each time slot is decoded in units 107, 106, 103, 127, 126 in order to address the stores 101, 102, 121, 122 and enable the relevant gate Rn Cn of the switch. The reference letters a b c d adjacent the AND gates 111, 112, 123, 124 indicate the above-mentioned subdivided portions of a connection-time-slot during which transmission from JAE2 to JAS3 (ab) and from JAS3 to JAE2 (cd) occurs. Setting up a call.-Assuming that there is a " calling " channel Vs on highway JAS3, then the control circuit (Fig. 10, not shown) is connected through a marker 300 (and Figs. 5-9, not shown) to this highway and ((successively) to the highways, i.e. JA2, which lead in the wanted direction, this connection being initiated by circuits not described. The marker gains access successively to the highways JA via a decoder 487 which opens a set of AND gates 481-484 individual to each of these highways. Store 108, say, is scanned during one scanning period and the code numbers of the channels in use in hghway JA2 are thereby passed via gate 482 to the marker where they are compared with a particular channel number stored therein. This last number is changed during successive scanning periods until during one such period none of the channel numbers incoming to the marker from store 108 coincides therewith. This channel number Ve, which represents a free channel on highway JA2, and. the highway number JR (representing JA2, say) are then stored in the control circuit together with the channel code number Vs and the trunk number JC giving rise to the calling condition. If there, are no available channels Ve on highway JA2, testing of the next highway occurs. A free connection-time-slot is then found by scanning stores 108, 129 and comparing their outputs via gates 482, 486, a free time slot being indicated by a coincidence of " no-signals " on both outputs (this means that during this time slot neither store contains a channel code number). The number of the time slot, say, tz, so found is stored in the marker. Finally, the control circuit passes the code numbers Ve, Vs, JC, JR to the marker so that during the time slot tz thes codes may be passed via gates 481, 485, 483 respectively to the corresponding stores 108, 129, 109. (Code number JR is only used to open the gates 481-484 and is not stored since it is of no further use in maintaining the connection.) The control circuit and marker are released. Release.-In order to break-down a connection it is necessary to place the code numbers Ve, Vs, JC, JR and tz in the marker and during the time slot tz to replace these codes in stores 108, 129, 109 by the code number zero so that the connection cannot be maintained during the successive time slot tz. Furthermore, it is possible that the control circuit can only provide certain of these codes, i.e. Vs and JC, so that it is necessary for the remainder to be identified before the connection can be broken down. Thisis done by scanning store 129 (or 108) of the known highway and comparing the output of this store via gate 486 (or 482) with the marked channel Vs (or Ve), the time slot tz during which coincidence occurs being the required connection-time-slot. Then the marker connects itself in turn to the highways JAE (decoder 487) and the output of the stores 109 via gate 484 during the time slot tz is compared with the input to decoder 488 (JC is known) until coincidence occurs, whereby the highway JR to which JC is connected at this time is identified. Alternatively, if JR is known, the store 109 of highway JR is scanned in order to discover the number of the highway JC to which JR is connected during the time slot tz. Next, store 108 (or 129) is scanned and the code number Ve (or Vs) therein at time tz is passed to the marker. Finally, the marker converts all these codes into zero codes (Figs. 4 and 7, not shown) and passes them into stores 108, 109, 129 during the relevant time slot in order to break-down the connection.