Mitsubishi Electric MELSEC iQ-RJ71C24-R2 - Whether the Communication Error Is Caused on C24 or Target Device Is Unclear; Communication Is Not Established Via Modem

27 TROUBLESHOOTING
27.3 Troubleshooting by Symptom
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27
Whether the communication error is caused on C24 or target
device is unclear
Communication is not established via modem
Symptom Cause Corrective action MC Non Bi Pd
Whether the communications
error is caused on the C24
side or the target device side
is unclear.
 Perform the following tests on the C24 side to investigate
where the cause is.
• Check the hardware.
C24 is mounted correctly.
The pins of C24 has no abnormalities such as bent.
• Perform the individual station test on C24. (Page 449
Individual station test)
No errors occur by the hardware test.
No errors occur by the self-loopback test.
• Check the CPU module condition.
No errors that stop the CPU module operation occur.
■Remarks
The following methods are available for testing if normal
communications are possible with C24 alone.
• For single C24, set CH1 and CH2 to the nonprocedural
protocol with self-loopback wiring.
When data transmitted from one channel and data received
at the other channel match, the transmission/reception
processing is performed normally.
• When two C24s are used, set one C24 to the nonprocedural
protocol and the other C24 to the MC protocol, and transmit
an MC protocol message from the station which is set to the
nonprocedural protocol. If the station which is set to the MC
protocol returns the transmission message normally,
transmission/reception processing is performed normally.

Symptom Cause Corrective action MC Non Bi Pd
Auto modem initialization
cannot be performed.
A modem initialization error
occurs.
• Check the error code and take corrective actions. 
Modem connection CH
specification is not performed.
• Set the modem connection CH specification. 
The parameter settings are
incorrect.
• Set the parameters to match the host station modem/TA. 
Review the parameter settings below with Engineering tool.
Then, write the parameter settings to the CPU module, and
reset it.
• Communication speed setting
• Transmission setting
• Communication protocol setting
• Station number setting