PURPOSE:To stably keep control function even if a trouble takes over in a communication line by providing a signal direct coupling section for a desired input processing section and an output processing section between desired data processing units in addition to the communication line between plural data processing units. CONSTITUTION:In connecting a digital signal transmission source 7a to an input processing section 1a, it is connected also to an input processing section 1b and the input processing section 1c through a direct signal line 10. Then the output of the output processing section 3 is connected to the input processing sections 1b, 1c via the signal direct coupling line 11. Moreover, the output of the section 3b is connected to the input processing section 1c via the signal direct coupling line 12. Thus, the control function is maintained locally even with communication trouble.
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