27 TROUBLESHOOTING
27.1 Checking Module Status
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■C/N
C/N indicates 'Access status with the CPU module'.
■NAK
NAK indicates "Abnormal completion status".
■ACK.
ACK. indicates "Normal completion status".
■NEU.
NEU. indicates "Command message to be received/command message in processing".
NEU. is valid only when MC protocol (format 1 to 5) is set as the communication protocol.
This is in the OFF-status when the communication protocol is set to other than MC protocol.
Value Status Description
0001(ON) Error occurred • The target device issued a data write request to the CPU module when online change is set
to 'Disable' in the parameter settings with Engineering tool.
For functions that cannot be used when online change is set to 'Disable', refer to the
explanation section in each command list in the following manual.
( MELSEC Communication Protocol Reference Manual)
• An error occurred during the access between C24 and the CPU module.
Keeps the ON-status even after the communication returns to normal. Initialize the error
information as necessary.
Page 473 Error Code List
0000(OFF) Normal
Value Status Description
0001(ON) Abnormal completion transmission C24 that could not receive data normally sent a response message (NAK message) to the
target device to notice the abnormal completion.
0000(OFF) Normal completion transmission or before
data communication
• C24 that could receive data normally sent a response message (ACK message) to the
target device to notice the normal completion.
• Before data is communicated.
Value Status Description
0001(ON) Normal completion transmission C24 that could receive data normally sent a response message (ACK message) to the target
device to notice the normal completion.
0000(OFF) Abnormal completion transmission or
before data communication
• C24 that could not receive data normally sent a response message (NAK message) to the
target device to notice the abnormal completion.
• Before data is communicated.
Value Status Description
0001(ON) Neutral Waiting for command message to be received.
0000(OFF) Command reception Command message is in process.
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