Mitsubishi Electric MELSEC iQ-R Series Reference Manual page 53

Exception code list
This section lists the exception codes that are stored in the lower byte of the response message format.
Exception code Error name
01H Function code error
02H Device address error
03H Data error
04H Processing failure
06H Slave busy
Error definition and cause
The slave received an unsupported function
code.
The specified MODBUS device address is
incorrect.
The content of the protocol data unit of the
request message is abnormal.
Processing was not possible because of an error
that occurred during request message
processing on the slave.
The slave cannot execute the processing of the
request message because it is executing other
processing.
Action
Check the function codes that are supported by the
slave, and then check the request message sent from
the master.
Check the types and sizes of the MODBUS devices
that are supported by the slave, and then check the
address specification of the request message sent
from the master.
Revise the data unit of the request message sent
from the master.
Eliminate the error factor that has occurred on the
slave.
If a module is issuing this code, use the module
diagnostics or a similar method to identify the
problem from the error that is occurring, and then
perform the appropriate actions.
Retry at a later time.
If a module is issuing this code, revise the settings so
that the number of request messages that can be
received at the same time is 64 or less.
4 EXCEPTION CODES
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