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3 TROUBLESHOOTING
3.5 List of Error Codes
C842H The routing setting is not set to reach to the destination
network number.
• Execute the link dedicated instruction again after
correcting the target network number and station
number.
• When the dynamic routing is used, check that
communication path to the destination network number
is set.
• When the dynamic routing is not used, or a module of
the series other than MELSEC iQ-R is included, retry
the operation after correcting the settings in "Routing
Setting" of "CPU Parameter".
C843H Link dedicated instruction that cannot be executed on the
network type were executed.
Check the network type of the Ethernet-equipped
module.
C844H Incorrect frame is received.
• Unsupported pre-conversion protocol
• Unsupported frame type
• Application header variable part
• Application header HDS
• Application header RTP
• Read command not requiring response
Correct the request data at the transient request source,
and retry the operation.
C860H The CPU response monitoring timer issued a timeout
during MODBUS/TCP communications.
When the CPU module has an error, eliminate it.
C861H During MODBUS/TCP communications, a request
message containing an unsupported function code was
received.
Check the supported function code, and correct the
request message issued on the master side.
C862H During MODBUS/TCP communications, a request
message containing an unsupported sub-code was
received.
Check the supported sub-code and correct the request
message issued on the master side.
C863H In MODBUS/TCP communications, the MODBUS device
assignment parameters have not been set for the
MODBUS device specified in the received request
message.
Set the MODBUS device assignment parameters for the
MODBUS device specified in the request message.
C864H In MODBUS/TCP communications, the range of the
MODBUS devices specified in the received request
message exceeded the setting range of the MODBUS
device assignment parameters.
Set the MODBUS device assignment parameters so that
they include the range of the MODBUS devices specified
in the request message.
C865H In MODBUS/TCP communications, the range of the
MODBUS devices specified in the received request
message exceeded the upper limit (*) for the MODBUS
devices.
* The upper limit for the extended file register is 10000
and the upper limit for other MODBUS devices is 65536.
Check the MODBUS devices specified on the master
side that sent the request message.
C866H In MODBUS/TCP communications, the start address and
the number of access points of the MODBUS devices
specified in the received request message are incorrect.
• Check if the specified value exceeds the maximum
number of access points for the function.
• Ensure that the number of access points is not 0.
• When accessing a MODBUS device to which a long
device is assigned in the MODBUS device assignment
parameters, check that the start address and the
number of access points are specified in units of two
points.
• When accessing a MODBUS device to which LTN or
LSTN is assigned in the MODBUS device assignment
parameters, check that the start address and the
number of access points are specified in units of four
points.
C867H In MODBUS/TCP communications, the number of write
points specified for the received request message does
not match with the specified number of bytes.
Check the number of write points and the number of
bytes specified on the master side that issued the
request message.
C868H In MODBUS/TCP communications, the received write
data size does not match with the specified number of
bytes.
Check the write data size and the number of bytes
specified on the master side that issued the request
message.
C869H In MODBUS/TCP communications, the value of the
reference type specified in the received request message
(FC20, FC21) is incorrect.
Check the reference type specified on the master side
that issued the request message.
Error
code
Error details and causes Action Detailed information
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