Table 59: Modbus Exception Codes
Code Name Meaning
1 Illegal function The function code received in the query is not an allowable action for the server (or follower). This may
be because the function code is only applicable to newer devices and was not implemented in the
unit selected. It could also indicate that the server (or follower) is in the wrong state to process a re-
quest of this type, for example, because it is not configured and is being asked to return register val-
ues.
2 Illegal data ad-
dress
The data address received in the query is not an allowable address for the server (or follower). More
specifically, the combination of reference number and transfer length is invalid. For a controller with
100 registers, a request with offset 96 and length 4 succeeds, while a request with offset 96 and length
5 generates exception 02.
3 Illegal data value A value contained in the query data field is not an allowable value for server (or follower). This indi-
cates a fault in the structure of the remainder of a complex request, such as that the implied length is
incorrect. It does NOT mean that a data item submitted for storage in a register has a value outside the
expectation of the application program, since the Modbus protocol is unaware of the significance of
any value of any register.
4 Follower device
failure
An unrecoverable error occurred while the server (or follower) was attempting to perform the re-
quested action.
104 | Danfoss A/S © 2024.03 AB413939445838en-000301 / 130R1254
Application Guide | iC2-Micro Frequency Converters
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