Patent GB-1351631-A (GB)
Title: Multiprocessor computer arrangement
IPC: H04M9/00
Filed: 1971-06-03
Abstract: 1351631 Multiprocessor arrangement; key telephone systems WESTERN ELECTRIC CO Inc 3 June 1971 [5 June 1970 (3)] 18782/71 Heading H4K A plurality of station modules 4 to 6 in a key telephone system is controlled by programmed instructions sent on bus A0 to A6 from a system clock 7, each module having a processing capacity to perform combinatorial logic on serial selections of a number of circuit conditions presented to the module, said processing being in accordance with instructions from the system clock 7 and the result being used to establish an appropriate mode of operation suited to changing circuit conditions. Line modules 9 and 10 and service modules 11 to 14 also receive the programmed instructions on a duplicate bus B0 to B6 in order to be directed in matters of status and signalling. Connections between the key telephone stations 1, 2 and 3, served by the modules 4, 5 and 6, and the exchange lines and services accessed over the modules 9 to 14, as well as the control of lamp and ringing signals, is directed by the common cycle of program words sent out by system clock 7. As shown in Figs. 1A and 1B, the station modules 4 to 6 are linked to their associated stations by a pair of speech wires and a pair of wires for each direction to transmit data comprised of bipolar pulse trains. The modules 4 to 6 have as many outlets as there are line selection buttons at the associated key stations, each module outlet comprising a speech pair and a single wire for data. A cross-connection field 15, referred to as a service designation field, connects the key outlets singly or in groups to particular exchange line modules such as 9, 10, and to service feature modules, such as 11 to 13, providing privacy, which prevents breaking in by another station, providing hold, which allows an exchange line to be looped and supervised from the line module, and providing exclusion, which denies any particular station access to a line should this be desired. Only one of the modules 11 to 13 is necessary to provide the associated services. A message-waiting service is provided by modules such as 14 in respect of pairs of stations requiring the facility in which one station may answer for the other and direct the application of a call-waiting signal to the other's station. The cyclic clock program sequences may be produced by a magnetic drum and comprise 7-bit words sent in parallel over 7-wire buses A and B. Two bits of each word indicate mode or function, four bits indicate the specific action required, and one bit commands execution. Both buses carry precisely the same signals, the A bus serving station modules, the B bus serving the line and service modules. The buses are separate for security against fault. The system is designed so that in the event of power failure stations are left connected to exchange lines such connections through the station modules being referred to as prime line connections. Each station module decodes the received clock program words and conditions the circuit state of the module accordingly in respect to the function called for in the clock time and in relation to the sequence state existing in the module; Fig. 2, not shown. A station module converts bipolar signals from its station into two-level signals and records one bit in respect of each of the five station line buttons and in respect of the hook-switch contacts. These bits are received serially on a stepping register. As the current bit is being shifted on to the first stage of the register the corresponding last-look state of the bit is being shifted off the last stage of the register, an exlusive-OR gate being employed to compare the two bits and to signal a change of state, Fig. 3, not shown. The hookswitch and button states may be read out non- destructively by recirculation. A three-bit counter, Fig. 7, not shown, provides a code output step-by-step with the button state bits to identify the corresponding hook-switch and buttons and appropriately gate particular bits of six-bit incoming and six-bit outgoing registers which buffer signals between the station modules and the line and service modules. By this means the button and hook-switch states are communicated to the line and service modules and signals are sent back to the station module from the line and service modules to control ringing, lamp signals, and module switching. The threebit code is also employed to control the module switching which comprises a relay switching tree distributing the station line to one or more lines of services; Fig. 3, not shown. A station module also provides a timing function for the on-hook condition and provides a function calculator, Fig. 6, not shown, whereby in steps of the program the existing circuit conditions can be combined into logical functions involving directions to complement, to OR, to AND, or to produce a product, the result being presented over a single bit channel. By this means a sum of products calculation is made which enables program instructions to be rewritten in the module in dependence upon its interpretation of circuit variables. Line modules have a ringing circuit across the exchange line which is converted, in the hold condition, to a supervisory holding loop; Fig. 8, not shown. The data wire to the one or more associated station modules has three wiring options which provide lamp signals only, lamp and ringing signals, or provides delayed ringing in circumstances where an off-hook station will be automatically connected to a calling exchange line but, by virtue of delay in the ring- ing trip circuit, is given the opportunity of declining the connection by operating another button before the delay expires. A line module decodes the received clock program words to co-ordinate and time its functions and, over the data wire from each associated station module, receives off-hook, hold, and privacy signals. The off-hook and hold conditions are recorded in the line module to establish ring-trip or exchange line loop supervision, respectively. Detection of station off-hook by a line module causes the line module to signal all associated station modules to effect steady illumination of associated station lamps corresponding to the exchange line. During holding the station line lamp is supplied with wink signalling. Timing counters are provided in each line module to measure out maximum expected silent intervals of ringing to detect release before answer from the exchange end. Another counter delays ringing by 16 seconds when this option is in force, ringing being triggered in all available associated stations if no automatic ring trip occurs. A further counter times out release from the exchange during hold conditions, release being confirmed after 150 ms., the period being extended to 650 ms. when this option is required. Exchange line modules, when in receipt of a data signal indicating a request for privacy, direct the application of prohibition to all associated station module relay switching trees to prevent operation of these trees to make a connection to that exchange line, the existing connection in respect of which privacy is requested being unaffected.