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9 Troubleshooting and Maintenance
9-48
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
Event name Overrun Error Event code 8469 0000 hex
Meaning An overrun occurred.
Source PLC Function Module Source details CJ-series Unit Detection
timing After serial com-
munications start
Error attributes Level Observation Recovery --- Log category System
Effects User program Continues. Operation Not affected.
System-defined
variables Variable Data type Name
None --- ---
Cause and
correction Assumed cause Correction Prevention
In Serial Gateway Mode or Protocol
Macro Mode:
• The reception circuits in the Serial
Communications Unit are faulty.
• A transmission error occurred due
to noise or other factors.
• Perform a loopback test in the serial
communications mode and check
the transmission lines. If an error
occurs during testing, replace the
Serial Communications Unit.
• Implement noise countermeasures.
Increase the setting for the number
of resends in the device that sent
the command. If required, perform
retry processing for communica-
tions.
Perform countermeasures in
advance.
No-protocol Mode:
• The reception buffer received more
than 259 bytes of data before the
SerialRcv/SerialRcvNoClear
instruction was executed.
Cycle the power supply, reset the
Controller, or restart the Unit and
clear the receive buffer.
During Loopback Test
• Loopback test jig failure.
• Noise
• The communications circuits in the
Serial Communications Unit are
faulty.
• Correct any mistakes in wiring the
loopback test jig.
• Implement noise countermeasures.
• Replace the Unit.
• Check the wiring of the loopback
test jig.
• Use the Unit away from sources of
noise. Implement noise counter-
measures.
Attached
information Attached information 1: Port number where error was detected
Precautions/
Remarks After an overrun error occurs, you can return the Overrun Error Flag for the Serial Communications Unit to FALSE by
cycling the power supply, resetting the Controller, restarting the Serial Communications Unit, or restarting the port.