| 摘要 |
PURPOSE:To release unefficiency that other data transmission is hindered because of a communication line having no data transmission/reception by opening automatically an invalid communication line having no data transmission/ reception for a prescribed time. CONSTITUTION:A supervisory circuit 14, a counter circuit 15 and a clear signal line for the counter circuit 15 and provided. When the supervisory circuit 14 uses a central processing unit 6 to detect the forming of a communication line by a data highway 13 through a control bus 12, the circuit 14 starts supervising operation representing the presence of a transmission/reception data at the communication line of the channel. When the transmission/reception of the data is started between DTE1A and 1B, and count of the channel in the counter circuit 15 is cleared to zero via a clear signal line 16. The zero clearing is executed at every presence of transmission/reception data. When the count reaches a prescribed value, that is, the time without transmission/reception data reaches a prescribed time, the counter circuit 15 sets the timeout signal of the channel.
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