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CHAPTER 15 TROUBLESHOOTING
15
15.3 Checking for Functional Errors
15.3.6 MC protocol function
15.3.6 MC protocol function
If an error occurs during MC protocol communication, check the following items.
If an error occurs during MC protocol communication even after taking the above actions, the possible cause is a
hardware failure.
Please consult your local Mitsubishi representative.
*1 Two or more receive instructions may need to be executed to read the data sent by one send instruction since TCP does
not have architecture for specifying data boundaries.
For this reason, the received data size must be checked when receiving, and receive the remaining data if received data
size is insufficient.
For details, refer to the following.
QnUCPU User's Manual (Communication via Built-in Ethernet Port)
Check item Corrective action
The connected device does not send a command. Send a command to the CPU module.
No response is returned from the device to which the
command is sent.
Make sure the following:
• The communication protocol (TCP/IP) is consistent
between the CPU module and the target device.
• The command is sent to the port number specified in the
open setting of the CPU module.
• The sent command matches with the Communication data
code setting (binary/ASCII).
• The value of the sent sub-header is normal.
• Data of the request data length is sent.
• Requests from the multiple connected devices are
simultaneously sent to the single MC protocol port
specified in the open setting.
If no response is returned from the connected device even
though all items mentioned above are normal,
communication with the connected device is possibly failed.
Check the items described in
Page 290, Section
15.3.4 (3).
The end code of the response is not "0". According to the end code or error code, repair the error part.
The IP address specified in the command is not correct. Correct the IP address.
Command format specifications such as command type,
device, or address are not correct.
Correct the command format.
( MELSEC Communication Protocol Reference
Manual)
The length of the data to be received and the volume of
actually received data are not the same when using TCP.
Provide the processing for receiving remaining data when
the actual data is less than the response data length of the
receive message.
*1
When the operation above is already performed, the possible
cause is a hardware failure. Please consult your local
Mitsubishi representative.
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