Patent GB-1290442-A (GB)
IPC: H04Q11/04
Filed: 1970-01-29
Abstract: 1290442 Automatic exchange systems MARCONI CO Ltd 17 Dec 1970 [29 Jan 1970] 4258/70 Heading H4K  In a T.D.M. system the speech switches are cross-bar switches with individual control units and connections are set up through a plurality of switches in step by step fashion. The P.C.M. system shown includes two cross-bar switching stages A and B connected between an input distribution frame 1 and a junctor distribution frame. To connect say a calling line to a register, units 7 and 9 referred to as interrogators, common to a group of lines and a group of registers respectively transmit calling and called codes respectively each to a plurality of adjacent cross-bar switches in stage A. The codes are propagated through the stages to the junctor distribution frame in a manner detailed below. During three successive time intervals zero delay junctors, fixed delay junctors and variable delay junctors determine whether they are able to connect between the calling and called appearances on the junctor distribution frame. The first junctors able to effect such a connection each signal to a junction selector (Fig. 4, not shown) which selects one such junctor. This junctor code marks the B stage cross-bar switch over which a calling code was received and this cross-bar switch and its associated control equipment effects a connection to an A stage cross-bar switch over which a calling code was received. The A stage switch similarly effects a connection to the input distribution frame appearance, connecting a calling line to a junctor. When this half of the connection has been established the junctor marks a B stage cross-bar switch over which a called code was received and the second half of the connection is set up in similar fashion. A counter incremented each time a path establishment signal is returned to the input distribution frame side steps to the count of three then transmits test patterns and their inverses in both directions over the path (now assumed to be set up) before it is used for the call. Cross-bar switch control.-Each cross-bar switch has sixteen rows and fifteen columns the sixteenth row being split to provide individual column outputs. Corresponding recirculating stores associated with each cross-bar switch column have fifteen storage locations (one for each time slot of a connection cycle) in which are stored the address of the crosspoints to be operated. Idle time slots store a zero code which causes the crosspoint in the sixteenth row of that column to operate. Associated with each cross-bar switch is a corresponding encoder and selector 4 which if it receives a calling or called code at one or more inputs propagates this code via an OR gate 3 and the sixteenth row of the cross-bar switch to each column outlet which is associated with a stored zero code during the time slot in which that code is found. The encoder is also arranged during the call establishment mode to respond to a code mark received from a selected junctor over a column of the cross-bar and the sixteenth row crosspoint to scan the row inputs for a calling or called code and to connect the first found input of the required code to the column over which the code mark was received inserting the relevant crosspoint address in a storage location.