| 摘要 |
<p>Each of the host transmitting/receiving blocks (11) of a plurality of I/O units (A1,A2,A3,A4,A5) connected to a CNC (1) reads the destination specification data and a diagnostic result bit each time the host transmitting/receiving block receives a signal packet from the CNC. When the diagnostic result bit indicates the execution of a diagnosis, the signal packet contains diagnostic DO data (b1), and the relevant DO signal output terminal is short-circuited to the relevant DI signal input terminal to form a diagnostic loop. The diagnostic packet signal passes through the diagnostic loop, the external signal transmitting/receiving block (12), and the host transmitting/receiving block (11) and returns to the CNC through the host transmitting/receiving block of an adjacent I/O unit closer to the CNC. The CNC analyzes the packet signal to determine whether each of the I/O units is operating normally or not.
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