Communications Using Modbus/Tcp Cannot Be Performed; Communication Fails At Modbus/Tcp Connection; A Response Message Cannot Be Sent To The Modbus/Tcp Master Device - Mitsubishi Electric MELSEC iQ-RJ71EN71 User Manual

Communications using MODBUS/TCP cannot be performed.

■Communication fails at MODBUS/TCP connection.

When communication is not possible at MODBUS/TCP connection, check the following items and take action.
Check item
Does the external device support MODBUS/TCP?
Is the external device a MODBUS/TCP master device?
Was a new connection attempted when 64 external devices have already
been connected?
Is the Ethernet-equipped module supporting the MODBUS/TCP function
used?
■Messages sent from the MODBUS/TCP master device cannot be received.
When messages sent from the MODBUS/TCP master device cannot be received completely or frequently, check the following
items and take action.
Check item
Are there times when 'State of receive buffer' (Un\G1900030) becomes 1
(Receive buffer full)?

■A response message cannot be sent to the MODBUS/TCP master device.

When a response message to the request message sent from the MODBUS/TCP master device or a supposed response
message cannot be sent, check the following items and take action.
Check item
Is the registration of the MODBUS device assignment parameters correct?
Was an abnormal response code sent?
Is there any error code stored in 'Error log area for MODBUS/TCP function'
(Un\G720896 to Un\G721153)?
Is the request message received from the MODBUS/TCP master device
correct?
Is the message length of the application data area of the Ethernet frame six
bytes or longer (from communication ID to message length of the MBAP
header)?
Does the message length of the MBAP header + 6 bytes match with the
message length of the application data area of the Ethernet frame?
3 TROUBLESHOOTING
302
3.4 Troubleshooting by Symptom
Action
If the device does not support MODBUS/TCP, replace it with the one
supporting the MODBUS/TCP standard.
The external device must be a MODBUS/TCP master device.
Reduce the number of external devices connected to the Ethernet-equipped
module.
If the number of connections with external devices exceeds 64, the connection
is disconnected automatically from the device for which the longest time has
elapsed from the last communication.
Check the firmware version of the Ethernet-equipped module and ensure that
the module supports the MODBUS/TCP function.
When the Ethernet-equipped module being used does not support the
MODBUS/TCP function, replace it with the module that supports the function.
Action
The load on the Ethernet line may high due to the data communication
between the nodes. Take the following actions.
• Reduce the load on the Ethernet line by separating networks, decreasing
the number of data sending, or other method.
• Consult with the network manager and reduce the load on the Ethernet line.
Action
Check the settings of the MODBUS device assignment parameters.
Check the abnormal response code and correct any possible problems.
Take an appropriate action in accordance with the stored error code.
(Page 310 List of Error Codes)
Correct the request message that the MODBUS/TCP master device sends.