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Appendix C: Exception Codes
If an exception occurs during Modbus communication, the slave device will return an Exception
Code in the response message. The following is an explanation of the Exception Codes:
Exception Codes:
Code
Name and Description
0x01
ILLEGALFUNCTION
Indicates that the function code received in the query is not an allowable action for the slave. If not an
allowable action for the slave. If a Poll Program Complete command was issued, this code indicates that
no program function preceded it.
0x02
ILLEGALDATAADDRESS
Indicates that the data address received in the query is not an allowable address for the slave.
0x03
ILLEGALDATAVALUE
Indicates that a value contained in the query data field is not an allowable value for the slave.
0x04
SLAVEDEVICEFAILURE
Indicates that an unrecoverable error occurred while the slave was attempting to perform the requested
action.
0x05
ACKNOWLEDGE
Indicates that the slave has accepted the request and is processing it, but it will take an extended period
of time to do so. This response is returned to prevent a timeout error from occurring in the master. The
master can issue a Poll Program Complete message later to determine whether the processing is
complete.
0x06
SLAVEDEVICEBUSY
Indicates that the slave is engaged in processing a long–duration program command. The master should
retransmit the message later when the slave is free.
0x07
NEGATIVEACKNOWLEDGE
Indicates that the extended file area failed to pass a consistency check, and the slave cannot perform the
program function received in the query. This code is returned when a programming request using function
code 13 or 14 decimal was unsuccessful. The master should request diagnostic or error information from
the slave.
0x08
MEMORYPARITYERROR
Indicates that the slave attempted to read extended memory, but detected a parity error in the memory.
The master can retransmit the request, but maintenance may be required on the slave device.
