Patent GB-1224682-A (GB)
Title: Digitalized communication system with computation and control capabilities and employing transmission line loop for data transmission
IPC: H04L12/43
Filed: 1969-06-25
Abstract: 1,224,682. Electric signalling systems. COLLINS RADIO CO. 25 June, 1969 [2 July, 1968], No. 32180/69. Heading G4H. A system for computing, communicating and controlling comprises a data processor having a number of addressable storage locations, a transmission line with input and output means, a first interface means for accessing each of the storage locations in a predetermined sequence and for sequentially and serially supplying to the input means of the transmission line a plurality of data words, each derived from a data word stored in one of the storage locations and each of which occupies, in the transmission line, a time slot corresponding to the storage location, the interface means also receiving words serially from the output means of the transmission line and entering each into the storage location corresponding to its time slot, and a number of stations along the transmission line, each arranged to intercept certain ones of the data words, identifiable by their time slots to generate response words and insert these in predetermined time slots in the transmission line. The computer 100, Fig. 1, contains a table of words in its main core storage 99 consisting of 2<SP>n</SP> words, say 256, each in a storage location. The 256 words together constitute a "frame". Multiplex control unit 102 through transfer link 98 continuously reads out the words in the table in their stored sequence and applies them serially to loop 104. Loop 104 is coupled to Loop Coupler Units 105, 107 and returns to unit 102. Returning words are stored in the same location in store 99 as the corresponding command word was read. The transfer link 98 receives an address from the unit 102 and either loads data into or reads data from the addressed storage location. Words supplied to and from the store may be in parallel or serial mode. The words supplied by unit 102 to the loop 104 are in serial mode as shown in Fig. 2 or 3. In the form of Fig. 2, the signal in the loop is a sine wave, a "1" being represented by the absence of a phase change, and "0" by 180 degrees phase shift. The first four bits of each word constitute the supervisory field which together with the fifth bit (termed the dialogic control field) determines the status of a word. The remaining 31 bits comprise the data field and include a 5- or 7-bit address. The rest of the word (24 or 26 bits) comprises the "operator-operand field". Each Link Coupling Unit, e.g. 105, 107 counts each word as it passes through it, counting from the beginning of the frame. It responds only to words in the time slots allocated to that LCU. The word may be identified by grouping together the first four bits of successive pairs of words to give an eight-bit supervisory code. The start of the frame is identified by leaving the first four bit spaces of the word blank, i.e no signal is transmitted, the gap detected by the LCU's. This is shown in Fig. 3. The first pair of words, identified by the eight bits of the two supervisory fields, is pair No. 0, the second pair (words 3 and 4) is pair No. 1 and so on. The LCU store two words and assemble the two groups of 4 bits which identify the pair. If there are more than one frame the successive frames are identified by coding the four bit supervisory fields of the last two words in the frame. For example, the first word would carry the code 0000-0000 and the sixteenth, the code 0000-1111. Each LCU may be arranged to respond to 1, 2 or 4 words in each frame. If an LCU is to respond to 2 words they are spaced by a power of 2, e.g. 1 and 17, 2 and 18 and so on The LCU's identify their allocated time slots by recognizing the beginning of each frame and counting the successive words. Words in the allocated slots are diverted into the control bus 109, 120, Fig. 1. Each DCU 110, 119 examines the address of each word appearing on control bus 109 responding to its own unique address to pass the operator-operand field of the word having that address to the device control functional element 111. The device 112 controlled may be a machine tool, a process controller or a printer. The element 111 generates a response signal, either upon receipt of the instruction or when the control function is complete. The signal is returned via the DCU, which affixes the appropriate address recodes the supervisory field and sets the dialogic bit to "0". The resulting 32-bit word is passed from terminal 113 via the monitor bus 114 to the LCU 105, where it is stored until the corresponding time slot occurs. The word is then inserted into the loop 104 and entered by the MCU 102 in the proper address location. If the device to be controlled is at a remote distance the word intercepted by the LCU is converted to a form suitable for transmission over long distances in Bus Remote Unit 123 and Modem 125. The output is transmitted for example over telephone lines 126 to modem 127, Bus Remote Unit 129 and DCU 132. Reverse transmission is similar. The local and remote BRU's 123, 129 operate at the bit-rate of the system (i.e. 4800 bits per second) or at slower rates: 3600, 2400 or 1200 bits per second. When operating at 4800 bits per second, every word period passes from LCU to modem 125. At a lower speed, e.g. 2400 every other word period passes to the modem. The BRU 123 determines which word periods are to be passed by inspection of the seven-bit address field. At the remote end the data is reconstituted and passed to the bus at 4800 bits per second. Where the transmission distance is short two-level signals may be used instead of sine wave signals. In this case delimiter bus 116 carries a word-timing reference signal. The circuits and mode of operation are described in detail.