Hitachi, Ltd.

Hitachi Process Computer Engineering, Inc.

Masakazu Okada

Takuji Hamada

Seiichi Yasumoto

Hitoshi Fushimi

Jushi Ide

Masahiro Takahashi

Syoji Yamaguchi

Hiroshi Tomizawa

Keiichi Nakane

Hirokazu Kasashima

Sadao Mizokawa

Norihiko Sugimoto

Hiroaki Nakanishi

Hiromasa Yamaoka

Katsumi Tadamura

Shuji Ohno

Shunji Inada

Takayuki Morioka

Hideyuki Hara

Ken Onuki

Yoshinori Okura

Kunio Suzuki

Tetsuya Kawahara

Katsuhiko Yoneda

Yoshimi Fujimata

Ryoichi Takamatsu

Mitsuro Takakura

Toshifumi Yamamoto

Yasushi Mutoh

Shozi Yamaguchi

Toshihisa Oka

The main storage, the communication interface portion and the circuit control module hold transmission data in the buffers until completion of the transmission has been confirmed. When a fault has occurred in the current operating system of the duplexed portions in the configuration elements of the host computer and the multi-circuit control unit, the duplexed portions are changed over from the current operating system to the stand-by system. In this case, information for reproducing data that has been lost due to the change-over is transmitted from the main storage and the circuit control module to the communication interface portion which has become the new current operating system. The communication interface portion which has become the new current operating system restarts the processing based on this information. Data integrity is guaranteed for the data of both directions of transmission and receiving between the host computer and the terminal without mutually confirming the state of data communications before the occurrence of the fault between the terminal and the host computer after the occurrence of the fault. Information exchanges of layer 3 or above are not carried out between the host computer and the terminal. Therefore, overhead of data communications can be minimized.

Data integrity guarantee system

A network system includes a transmission line including a plurality of transmission channels, a plurality of transmission equipment connected to the transmission line to effect the transmission and reception of information between each other, and a plurality of devices connected to each of the transmission equipment, thereby effecting the transmission of information between the devices connected to the plurality of transmission equipment. Each of the transmission equipment includes a demultiplexing unit for separating an input signal from the transmission line into a plurality of receiving transmission channels, a channel switch unit for receiving the plurality of receiving transmission channels, outputting designated one of the transmission channels to one of the devices connected to the transmission equipment in question, and receiving transmitting information to form an information transmitting channel and combining it with other channels to be passed to form a plurality of sending transmission channels, and a multiplexing unit for receiving the plurality of sending transmission channels from the channel switch unit to multiplex and output the plurality of sending transmission channels.

Network system

In an information communication system for performing both point-to-point communication and point-to-multipoint communication between a host computer and terminals by using same lines while distributing loads of data communication, data communication report tables are provided on a main storage unit of the host computer for each type of communication. The data communication process is executed distributively at each CPU unit and communication interface unit of the host computer and at each control module of a communication control unit. A plurality of destination pattern tables indicating data destinations are provided for point-to-multipoint communication. For the point-to-multipoint communication, CPU unit designates a particular destination pattern table for each interface unit, and data transmission is requested to each control module in accordance with the destination pattern table.

Information communication system for point-to-point communication and

In a method of controlling a buffer device, data are received from a communication transmission line, and the received data are written in a buffer device at a predetermined write rate. The data written from the buffer device are started to be read at a predetermined read rate. The quantity of data written and accumulated in the buffer device is compared with a predetermined threshold for a predetermined period from the read start point of time. When it is found as the result of comparison that the quantity of accumulated data is the same as or less than the threshold, the buffer device performs only write of data from the communication transmission line and, when the quantity of accumulated data is larger than the threshold, the buffer device performs both write of data from the communication transmission line and read of data out of the buffer device at the same time during a predetermined period.

Data communication system

A circuit device (e.g. mounted on a printed circuit board) is connected to a data network, to which network are also connected a plurality of other circuit devices under power. On removal of such a circuit device, the output driver connecting the circuit components of the output device to the communications bus of the bus network is first disconnected from power, and only when its disconnection is stable is the device withdrawn. A control device of the circuit device is connected to the control bus of the data network, and before power is disconnected from the output driver, the control device signals to the network so as to prevent other circuit devices connected to the network from signalling on the network. Effectively, the circuit device to be removed 'occupies' the bus. This occupation is maintained until the disconnection of the output driver is stable, and then the circuit device can be removed from the network. Similarly, on insertion, the network is first occupied before power is connected to the output driver. In this way, it becomes possible to prevent faults due to missignalling between the other circuit devices connected to the network when one circuit device is inserted or removed.

Insertion and removal of a circuit device into a bus network

A method and apparatus for transmission of data among computers or peripherals along a loop transmission line includes a master system which provides signals along the transmission line for establishing a series of data frames of equivalent length. Each data frame is assigned a frame number, and is allotted a preselected amount of available space for placement of data. Subsequent computers or peripherals are preprogramed with a series of frame numbers which identify those data frames into which they may write data, or from which data is to be read. The allotment of preselected frame numbers for placement and reception of data by the respective devices provides for equivalent sharing of the available data transmission capability of the loop transmission system.

Data communication method and apparatus

In an annular transmitting system including a ring-like transmission path realized by interconnecting serially a plurality of transmission stations in an annular form, at least one of the transmissions stations generating repetitively a transmitting frame constituted by a plurality of transmission units referred to as time slots, the frame being circulated along the transmission path, wherein transmission of information among transmission stations is performed in such a manner in which each of the transmission stations having a request to send information inserts the information in the slots by dividing the information, which information is ultimately fetched by the transmission station destined to receive that information, a multi-slot access system in which each of the time slots is provided with an area indicating whether the associated time slot is 'free' or 'busy', wherein the transmission station having a request to send information determines that the sending of the information is enabled when it is detected that one time slot located at a particular position within the transmitting frame is 'free' or when it is detected that the time slot succeeding immediately to the 'busy' slot is 'free', to thereby set successively those usable time slots which succeed to the detected 'free' time slot to the 'busy' state and insert the information in these usable time slots.

Multi-slot access system

A looped data transmission system has a pair of looped transmission lines forming two transmission systems having different transmission directions, and a plurality of stations including at least one control station connected to said transmission lines of the two transmission systems. If a fault occurs in the two transmission lines of the two transmission systems in the same section, a loopback configuration is established such that stations adjacent to the faulty section send signals from one system back to the other system. With the loopback configuration being established, the stations which have received supervisory signals sent from a loopback end station send them back to the transmission line of the other system. When one of the loopback end stations has received a supervisory signal from the direction of the faulty section, it is judged that a portion of the faulty section is recovered, and the result of the judgement is communicated to the control station.

Method of detecting recovery from fault in a data transmission system

A multi-computer system includes a plurality of data processors and at least one I/O device which is commonly accessible by the data processors. A plurality of serial bus loops are configurated in hierarchy with interbus linkage devices disposed between adjacent layers of the hierarchy. The data processors are connected to a plurality of first layer serial bus loops and the I/O device which is commonly accessible by the data processors is connected to a second layer of serial bus loop. The interbus linkage devices control linkage among the plurality of serial bus loops and carry out routing control for a start command from the data processor to the I/O device, routing control for an interruption to report the end of I/O device operation, routing control for data transfer, routing control for a request interruption and exclusive use control of the shared I/O device.

Multi-computer system with plural serial bus loops

A duplex transmission control system having active and inactive systems for totally controlling a looped transmission line on which computers and terminal devices are connected through respective stations. Each transmission control unit is operable to transmit and receive specific data related to the priority level specified for each unit. Each transmission control unit suspends the transmission of the clock for a certain period in response to the detection of the clock suspension, then transmits the specific priority data. When a transmission control unit detects its own transmitted signal, it is designated as the active system when another transmission control unit receives the signal defining the active system, it is designated as the inactive system.

Loop data transmission control method and system

A central station and a plurality of transmission stations are connected in cascade by a serial transmission line, and constitute a looped data highway system. The central station controls the whole system. The system allows the transmission station having a data signal transmission request to send out a data signal by means of a normal polling signal, but only the station having sent out the data signal by means of the preceding normal polling signal is allowed to send out the data signal again in response to a retry polling signal.

Data transmission system and method

A loop type data highway system in which a plurality of data transmission control stations (abbreviated hereinafter as stations) are connected to a single loop transmission line for data transmission and reception between any desired ones. A transmit station transmitting data makes a compare check to compare successive predetermined unit lengths of the transmitted data with the corresponding ones of the data returning after travelling round the loop, thereby detecting an error occurring during the data transmission when non-coincidence exists therebetween. A receive station receiving the data monitors the number of data words to be received, thereby detecting an error occurring during the data transmission when a data transmission end signal is detected prior to arrival of all the data words. Upon detection of the error occurring during the data transmission, the transmit station transmits the data transmission end signal to the receive station to inform the receive station of occurrence of the error.

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Katsuta, Japan

Masakazu Okada