Patent GB-1462150-A (GB)
Title: Stored programme controlled telecommunication system
IPC: H04Q3/54
Filed: 1975-05-29
Abstract: 1462150 Automatic exchange systems TELEFONAKTIEBOLAGET L M ERICSSON 29 May 1975 [6 June 1974] 23514/75 Heading H4K In an SPC exchange, operation of and condition-testing of telecommunications components is effected with a microprocessor type interface which steps through a programme sequence in a manner dependent on a start instruction, each step comprising three time phases during which only prescribed actions may take place and a phase being lengthened so as to prolong the step until a certain result is achieved. An exchange EX (Fig. 1) has a plurality of addressable operating points OP, e.g. bi-stable circuits that serve as relay drivers, a plurality of test points TP, e.g. flip-flops that have a "0" or "1" state in dependence upon an open or closed line loop condition, and a plurality of registers Rl, R2 containing, for example, a binary word indicative of the condition of a set of crosspoints. All the above components are linked by a data bus DB to the interface which comprises instruction registers IR, an addressing arrangement ASG and a three-phase clock pulse generator PG. In operation, an initial address register IAR is filled with a code indicative of where a programme sequence should begin. This code is effective to start the generator PG whereby during the first phase #1 of a processing cycle, the code is decoded by the addressing arrangement ASG (logic L1) in order to access a particular register (usually an instruction register IR). During phase #2, an address a is read out of the accessed IR register, decoded in ASG and used over line as to address a particular operating or test point or to read-out a particular data register R1, R2. During subsequent cycles, in phases #2, #3, data may be transferred from one register to another (logic L3). In the cases where an operate (or test) function is required, the successful completion of the function will be denoted by a change of state of a test point associated with the operating point, such successful conclusion being indicated through logic L4 during the final phase #3 of a cycle. Many functions require a plurality of steps to achieve satisfactory completion. This is achieved by incrementing the initial address in IAR by one during each processing cycle (logic L2 or L4) so that a further instruction register IR may be accessed in the following cycle. When the function is complete, the phase generator PG is turned off and the system is zeroized. In a path finding arrangement (Fig. 2), registers R4, R5 contain the free/busy conditions at the inlet and outlet stages of a network. Useable paths are denoted by coincidence of "1" marks in these two registers (AND gate G3). A demand for path finding is inserted by a marker into register SR. This mark is used via gates G6, G7 to start the phase generator PG and via logic L3 is written into the initial address register IAR. The instruction registers, in this case, are formed as a read-only memory ROM which is first accessed during phase #1 (gate G2) of the first processing cycle by the mark in IAR. The steps of the process are then run-through during successive cycles by incrementing the mark in IAR thereby accessing different cells in ROM. The cells contain relevant address and operate instructions for the seven different steps of the process. (An eighth step permits branching to another instruction in the event that no free path is available.) These consist essentially in gaining access to particular register R4, R5; transferring their ANDed contents to SHR; checking that SHR has at least one "1" bit; stepping SHR to find the first "1" bit (this entails holding the same phase in a same cycle, gate L5); and then conveying the addresses of the inlet and outlet crosspoints corresponding to the selected path to the buffers. A next, but different function, would be to use these addresses to set-up the path.