Installation manual

Publication 1747-RM001G-EN-P - November 2008

SLC Communication Channels 13-97

Modbus Error Codes

Upon receiving a Modbus command that is not supported or improperly

formatted, the controller configured for Modbus RTU Master will respond

with one of the exception codes listed in the following table:

Table 13.30 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.

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.

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.

84 Slave Device Failure An unrecoverable error occurred while the slave was attempting to

perform the requested action.

85 Acknowledge The slave has accepted the request, but a long duration of time will

be required to process the request.

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.

88 Memory Parity Error The slave attempted to read extended memory, but detected a

parity error in the memory.

89 Non-standard Error Code An error code greater than 8 was returned by the slave. >8