Patent GB-1175944-A (GB)
Title: Improvements to Electronic Scanners
IPC: H04Q3/545
Filed: 1968-07-18
Abstract: 1,175,944. Line scanning arrangements. INTERNATIONAL STANDARD ELECTRIC CORP. 18 July, 1968 [21 July, 1967], No. 34325/68. Heading H4K. Subscribers' line circuits are scanned in a matrix each cross-point of which includes a saturable magnetic core and a contact of a line circuit, interrogation of the core and the contact in each scan allowing off-hook for a call origination and off-hook after a connection has been released to be distinguished. The scanner includes a logic circuit which determines significant loop changes for the instruction of a processor which is in consequence not burdened with complete scanning cycles. A line circuit is shown in Fig. 2 for the line lg, contacts ct1, ct2 connecting battery to the loop in the idle condition and contacts ct3 being open. A saturable core TFA has windings en1, en2, in the loop, an interrogation winding en3, and a readout winding en4. In the idle condition interrogation produces output in en4. If the loop is closed with an off-hook condition, the core TFA saturates and interrogation produces no output in en4. When a connection is released but the loop remains off-hook, contact ct3 is closed by means not disclosed. The scanning matrix ME, Fig. 3, comprises an array of 2,560 cross-points in 32 columns and 80 rows, each cross-point serving four line circuits scanned in parallel to give a capacity of 10,240 lines. Row units ER1 to ER10 serve groups of eight rows, reading units EL1 to EL4 serving pairs of rows in each group. Column select is effected by circuit CC, the matrix being accessed by a logic circuit LC which acts on instruction from a processor. A row pair and associated reading unit is shown in Fig. 4. Each column is defined by a single column wire cl. Each row has a main wire rg1 and four interrogation wires rg11 to rg14 for each of the contacts ct3 in each of the four line circuits at each cross-point. A closed contact ct3 couples an interrogation wire to the column wire so that current in the wire produces output in a corresponding one of the transformers TD1 to TD4, the interrogation result being set up on a respective one of bi-stables al1 to al4 in the read circuit EL1. The interrogation windings en3 of the four line circuits at a crosspoint are connected in series between the main row wire rg1 and the column wire. The read-out windings en4 are connected to respective wires lt1 to lt4 for registration of the interrogation results on bi-stables al5 to al8 in the read circuit EL1. Corresponding secondary windings of current sensing transformers TD1-TD4 in EL1 for both rows of the pair served by EL1 are connected in series as the rows are always interrogated separately and share the same bi-stables al1-al4. Corresponding read-out windings en4 of both rows are similarly in series. Scanning is started on instructions from the processor which indicates a row number (oneout-of-eight for each group), a row unit number, and a column number. A scanning cycle by running through the row unit numbers from 1 to 10 for a given column number examines the scanning results for each cross-point in the ten rows indicated by the row number. For each cycle through the row unit numbers the column number is incremented by one up to a count of 16 which is half the columns. The processor, therefore, instructs scanning of line circuits in blocks of 640. When a significant change of state is encountered, the scanner locks on to the row unit involved while row unit cycling continues without effect to its end, the processor then being called up to collect the change of state data identified by the locked-up state of the scanner. Fresh start instructions are then provided by the processor in the way of row, row unit, and column numbers. The processor may direct interrogation of one particularly identified cross-point of the scanning matrix.