Patent GB-1247110-A (GB)
Title: Scanning circuit
IPC: H04Q3/52
Filed: 1969-07-23
Abstract: 1,247,110. Automatic exchange apparatus. INTERNATIONAL STANDARD ELECTRIC CORP. 23 July, 1969 [1 Aug., 1968], No. 36998/69. Addition to 1,203,526. Heading H4K. An m x n matrix the cross-points of which are MOS transistors is employed to connect a consecutive set of m matrix inlets to the m outlets, the first member at the head of a set being disconnected and a new member being added to the tail of the set repetitively in order to scan the inlets. The matrices are constructed as large scale integrated circuits, as suggested in Specifications 1,203,526 and 1,199,119 and in their employment as scanners only diagonally disposed cross-points are switched. As seen in Fig. 2 the cross-points X, having associated bi-stable circuits and access gates, have gates G<SP>1</SP> common to the rows to produce signals on leads e, so as to inhibit the cross-points of a row when any one of them is operated, and to produce signals on leads e<SP>1</SP> to act as row select signals for the immediately succeeding rows Column select signals are produced by a genera tor 4 for application cyclically to column selectleads cl to cm. Column select pulses first clear accessible operated cross-points and then, over delay circuits L and select leads c1, effect operation of a cross-point in coincidence with a row select signal. The first column select pulse c1 along with a start signal S T  opens a gate 5 to set bi-stable 3 to establish a row select signal on row select lead 81 and at the same time pulse column select leads cl, c<SP>1</SP>1. Cross-point XII operates in consequence and gate G<SP>1</SP> puts a row select signal on lead s2 of the second row. The second column select pulse c2 therefore operates cross-point X22 and, similarly, select pulse c3 operates X33, and so on. When the mth crosspoint Xmm is operated by select pulse cm a complete set of m inlets is connected to the m outlets. The cycle of select pulses returns to c1 which disconnects X11 and operates Xw+1,1, the following select pulse c2 disconnecting X22 and operating Xm+2,2, and so on. When the last row is reached the operated cross-points of preceding rows are successively cleared and no additional cross-points are operated unless the last row is coupled back as a means of selecting the first row, in which case the set of m inlets is rebuilt from the top of the matrix step by step with its contraction at the bottom. If a group of 256 inlets is to be scanned by connecting a running set of four outlets, parasitic capacitances make it impractical to employ select leads over a column of 256 cross-points. The two stage arrangement of Fig. 4 is employed, the inlets being distributed over eight 4 x 32 matrices M1 to M8 the outlets of which are inlets to a second stage 4 x 32 matrix M<SP>1</SP>. The column select leads c to c4 of M<SP>1</SP> are pulsed cyclically from generator 8, each appearance of c1 stepping a counter/decoder Cp2, D2, to mark leads B1 to B8 in succession. Lead B1 for instance, provides a row select signal for the first row of M<SP>1</SP> so that the pulses cl to c4 operate the diagonally disposed cross-points of the first four rows, the operated cross-point of the first row enabling the second row and so on to the fourth row. The operated cross-points provide column select signals in succession to the matrix M1 the first row of which is marked by a select signal on lead Al of a counter/ decoder Cpl, D1 driven by pulse K1 produced by every eighth pulse cl. As a result the diagonally disposed cross-points of the first four rows of matrix M1 are operated in succession, the first row enabling the second and so on up to the fourth. At this point the set of four inlets H1 to H4 of M1 is connected through to the four outlets V1 to V4 of M<SP>1</SP>. Decoder D2 advances to its output B2 with the next cl pulse and provides a select signal to the fifth row of matrix M<SP>1</SP>, the pulses cl to c4 operating the diagonally disposed cross-points across rows 5 to 8. This provides column select signals for matrix M2 the first row of which is marked by a select signal on lead Al. As a result the diagonally disposed cross-points of the first four rows of matrix M are operated to connect inlets H33 to H36 to the outlets V1 to V4 of M<SP>1</SP>. As each inlet H33 to H36 is connected a corresponding one of the inlets H1 to H4 is disconnected. Similarly, as leads B1 to B8 are marked in succession the top sets of four inlets to each matrix M1 to M8 are connected through. When the eighth set is connected the decoder D1 advances to mark lead A2 and the same cycle of operations is applied to the second sets of four inlets of each matrix M1 to M8, and so on through to the eighth set.