Hitachi, Ltd.

Hiroshi Tomizawa

Takuji Hamada

Sadao Mizokawa

Masakazu Okada

Hitoshi Fushimi

Seiichi Yasumoto

Shinichiro Yamaguchi

Masahiro Takahashi

Yoshinori Ohkura

Shunji Inada

Ken Onuki

A data communication system carries out transmission and reception of periodic data between a plurality of computers, and especially an improved data communication system which aims at more effective utilization of a system bus in each computer and which also aims at more effective utilization of a data transmission channel transmitting periodic data, so that the load imposed on the system bus during transfer of periodic data in each computer can be minimized, and the rate of occupation of the data transmission channel during transmission and reception of periodic data can also be minimized.

Cyclic data communication 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

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 loop type data highway system in which a plurality of data transmission control stations (abbreviated herein as stations) are connected in cascade to a loop transmission line. Each of the stations responds to a polling frame inquiring of request for reservation of the transmission line. The polling frame is composed of a first field for inquiring of the line reservation request and a second field indicative of whether the line is reserved or not. Each station receives signals inputted from the upstream side along the line and sequentially repeats them to the downstream side along the line without delay. In the station having the line reservation requests, a pattern representative of the line reservation is written in the second field after reception of the first field and sends out the polling frame to the downstream. When the second field as received indicates the non-reserved state of the transmission line, transmission of data is initiated in succession to the second field.

Loop type data highway system

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Hitachi, Japan

Hiroshi Tomizawa