Publication 1763-RM001C-EN-P - October 2009
Protocol Configuration 533
Modbus Error Codes
Upon receiving a Modbus command that is not supported or improperly
formatted, the controller configured for Modbus RTU Slave will respond
with one of the exception codes listed in below:
Modbus Error Codes Returned by Modbus RTU Slave
Error
Code
Error Description Transmitted
Exception Code
(1)
0 No error. none
1 Function Code cannot Broadcast. The function does not support Broadcast. nothing transmitted
2 Function Code not supported. The controller does not support this Modbus function or
subfunction.
1
3 Bad Command Length. The Modbus Command is the wrong size. 3
4 Bad Length. The function attempted to read/write past the end of a data file. 3
5 Bad parameter The function cannot be executed with these parameters. 1
6 Bad File Type The file number being referenced is not the proper file type. 2
7 Bad File Number The file number does not exist 2
8 Bad Modbus Address
The function attempted to access an invalid Modbus address.
(2)
3
9 Table Write protected The function attempted to write to a read-only file. 3
10 File Access Denied Access to this file is not granted. 2
11 File Already Owned Data file is already owned by another process. 2
(1) If Modbus Command is sent with a valid Broadcast address, then no exception reply will be sent for Error Codes 2 through 11.
(2) See on page 530 for valid Modbus memory mapping.
Modbus Error Codes in Modbus RTU Master MSG Instruction
Error
Code
Error Description Received Exception
Code
81 Illegal Function The function code sent by the Master is not supported by the slave
or has an incorrect parameter.
1
82 Illegal Data Address The data address referenced in the Master command does not exist
in the slave, or access to that address is not allowed.
2
83 Illegal Data Value The data value being written is not allowed, either because it is out
of range, or it is being written to a read-only address.
3
84 Slave Device Failure An unrecoverable error occurred while the slave was attempting to
perform the requested action.
4
85 Acknowledge The slave has accepted the request, but a long duration of time will
be required to process the request.
5
86 Slave Device Busy The slave is currently processing a long-duration command. 6
87 Negative Acknowledge The slave cannot perform the program function received in the
command.
7
88 Memory Parity Error The slave attempted to read extended memory, but detected a
parity error in the memory.
8
89 Non-standard Error Code An error code greater than 8 was returned by the slave. >8
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