Publication 1766-RM001A-EN-P - October 2008
Protocol Configuration
621
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
(2)
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.
(1)
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) See on page 617 for valid Modbus memory mapping.
(2) If Modbus Command is sent with a valid Broadcast address, then no exception reply will be sent for Error Codes 2…11.
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
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