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5.3 How to Control the frequency converter
This section describes codes which can be used in the function and data fields of a Modbus RTU message. For a complete description of all the message fields
please refer to the section Modbus RTU Message Framing Structure.
5.3.1 Function Codes Supported by Modbus RTU
Modbus RTU supports use of the following function codes in the function field of a message:
Function
Read coils
Read holding registers
Write single coil
Write single register
Write multiple coils
Write multiple registers
Get comm. event counter
Report slave ID
Function
Diagnostics
5.3.2 Exception and Error Codes
In the event of an error, the following exception codes may appear in the data field of a response message. For a full explanation of the structure of an exception
(i.e. error) response, please refer to Function Field in section Modbus RTU Message Framing Structure.
Code Name
Meaning
1
Illegal function
The function code received in the query is not an allowable action for the server (or slave). 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
slave) is in the wrong state to process a request of this type, for example it is not configured and is being asked to return register
values.
2
Illegal data address The data address received in the query is not an allowable address for the server (or slave). More specifically, the combination
of reference number and transfer length is invalid. For a controller with 100 registers, a register with offset 96 and length 4 would
succeed, a request with offset 96 and length 5 will generate exception 02.
3
Illegal data value
A value contained in the query data field is not an allowable value for server (or slave). This indicates a fault in the structure of
the remainder of a complex request, such as an incorrect implied length. It specifically 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 particular value of any particular register.
4
Slave device failure An unrecoverable error occurred while the server (or slave) was attempting to perform the requested action
In case of an exception code 4 while accessing parameter values in the drive, detailed information about the latest exception can be read from the drives Holding
Register 0007. This register may contain one of the following, detailed error codes regarding the latest occurring MODBUS Exception.
Function Code
1 hex
3 hex
5 hex
6 hex
F hex
10 hex
B hex
11 hex
Function code
Sub-function code
8
MODBUS Exception Codes
DET-579A
AF-60 LP™ Micro Drive Operating Instructions
Sub-function
1
Restart communication
2
Return diagnostic register
10
Clear counters and diagnostic register
11
Return bus message count
12
Return bus communication error count
13
Return bus exception error count
14
Return slave message count
5
31
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