Patent GB-1489285-A (GB)
Title: Electric signal exchange switching system
IPC: H04Q11/04
Filed: 1975-04-17
Abstract: 1489285 Automatic exchange systems; distributors INTERNATIONAL BUSINESS MACHINES CORP 17 April 1975 [3 June 1974] 15773/75 Headings H4K and H4M A TDM space switch comprises a plurality of node busses coupled by selectively controlled electronic gates to inlet terminals and to intermediate outlet terminals, said busses being arranged to be periodically discharged to a common source of reference potential between time slots, each outlet comprising a pair of simultaneously enabled gates coupled respectively to an intermediate outlet terminal and to the source of reference potential to provide pairs of signal and reference outputs which can be isolated between time slots. Fig. 3 shows two two wire speech terminals 10<SP>1</SP> and 28<SP>1</SP> (which may also be equipped for data sending) coupled via 2 to 4 wire (and vice versa) converters 121, 122 and 123, 124 respectively to the network which provides for each direction of transmission a single wire connection through the network (via one of the highways 0 to 15) with earth return (represented in the Figure by an earth G). Each outlet of the network comprises sample and hold circuits such as 148-0 and 148-00 connectable during each time slot to any one of the TDM highways 0 to 15 and to the common earth G respectively, the particular highway employed being that with which the require input 130-0 to 130-127 is associated. The additional output gates 152-0 to 152-1270 provide for complete isolation between the channels, the outputs being short circuited (via F.E.T.s 154-0 to 154-127) and the highways 0 to 15 being connected to earth (via F.E.T.s 160-0 to 160-15) between time slots. The network and control circuits therefor are fabricated from F.E.T. integrated circuit chips. Pulse amplitude modulation is employed. If a broader than normal bandwidth is required connections can be established at multiples of the frame frequency the necessary gates being opened by the distributor arrangement shown in Fig. 4. It comprises a common interface chip (via which instructions from the control processor 4211 are passed to other control chips) comprising a clock 180, a time slot register 170, a band width register, a register 174 for the address of the TDM highway to be employed, a register 176 for the instruction to be performed and a register 178 for the address of the input or output part to which it relates. Each of the other control chips comprises a clock 190, instruction and port decoders 186 and 184; and for each port a register 194 for the identity of the time slot during which the control must take place, a comparator 192 which determines when the clock 190 count goes through this valve and a bandwidth register 188 which limits the comparison to less than the full seven bits operate that port at corresponding multiple of the clock frequency. Output control chips also include a TDM highway address register 196 and decoder 198. The registers on the said other chips are loaded from their own clock 190 count its operation decoder 186 being enabled at 220 from the common chip at the appropriate moments.