Access To Parameters - Danfoss VLT AQUA Drive FC 202 Design Manual

System Integration
3.8.10.9 How to Control the Adjustable
Frequency Drive
Codes available for use in the function and data fields of a
Modbus RTU message are listed in
chapter 3.8.10.10 Function Codes Supported by Modbus RTU
and chapter 3.8.10.11 Modbus Exception Codes.
3.8.10.10 Function Codes Supported by
Modbus RTU
Modbus RTU supports use of the function codes (see
Table 3.40) 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 communication event counter
Report slave ID
Table 3.40 Function Codes
Function Function Sub-
code function
code
Diagnostics 8 1
2
10
11
12
13
14
Table 3.41 Function Codes and Sub-function Codes
3.8.10.11 Modbus Exception Codes
For a full explanation of the structure of an exception code
response, refer to chapter 3.8.10.5 Function Field.
MG20N622
Design Guide
Function code (hex)
1
3
5
6
F
10
B
11
Sub-function
Restart communication
Return diagnostic register
Clear counters and
diagnostic register
Return bus message count
Return bus communi-
cation error count
Return slave error count
Return slave message
count
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Code Name Meaning
1 Illegal The function code received in the query is
function 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
because it is not configured and is being
asked to return register values.
2 Illegal data The data address received in the query is
address 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 request with offset 96 and length 4
would succeed, a request with offset 96
and length 5 generates exception 02.
3 Illegal data A value contained in the query data field
value 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 that the implied length is
incorrect. 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 An unrecoverable error occurred while the
failure server (or slave) was attempting to
perform the requested action.
Table 3.42 Modbus Exception Codes

3.8.11 Access to Parameters

3.8.11.1 Parameter Handling
The PNU (parameter number) is translated from the
register address contained in the Modbus read or write
message. The parameter number is translated to Modbus
as (10 x parameter number) decimal. Example: Reading
3-12 Catch up/slow-down Value (16 bit): The holding
register 3120 holds the parameters value. A value of 1352
(Decimal) means that the parameter is set to 12.52%
Reading 3-14 Preset Relative Reference (32 bit): The holding
registers 3410 and 3411 hold the parameter's value. A
value of 11300 (decimal), means that the parameter is set
to 1113.00.
For information on the parameters, size and converting
index, consult the Programming Guide.
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