| 摘要 |
PURPOSE:To prevent the successive effect of a fault by switching stepwise the transmission mode in response to the state of fault generation to cope respectively with intermittent and continuous abnormalities. CONSTITUTION:A sub system 3 such as a computer or a terminal device accesses a loop transmission line via plural transmission controllers 1. The controller is provided with means of error detection of a reception data, data storage and reception/transmission. The transmission by the through mode S1 where a reception data is sent directly is conducted normally. When an error is detected in the received data, the mode S1 is inhibited, all data frames are received, and after they are stored once in a RAM, they are sent newly according to the store and forward mode S2. When normal data are received continuously for the prescribed number of times during the operation in the mode S2, the mode is switched to the mode S1. When an abnormal state is consecutive for the prescribed number of times, since it is very probable that the error is a permanent error, the state is switched to a reception interruption (store and forward) inhibition mode S3. The reception state is checked in the mode S3 at a proper interval and when it is discriminated as the normal state, the mode is switchedinto the mode S2.
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