How To Access Parameters - Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

RS-485 Installation and Set...
7.8.10 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 Function
7 7
Code
Diagnostic 8
s
7.8.11 Modbus Exception Codes
For a full explanation of the structure of an exception code
response, please refer to 7.7 Modbus RTU Message Framing
Structure , Function Field.
Co Name
de
1 Illegal
function
74
VLT HVAC Basic Drive Design Guide
Function Code
1 hex
3 hex
5 hex
6 hex
F hex
10 hex
B hex
11 hex
Sub- Sub-function
function
code
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
Modbus Exception Codes
Meaning
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
because it is not configured and is being
asked to return register values.
MG.18.C2.02 - VLT
Modbus Exception Codes
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 will generate exception 02.
3 Illegal data A value contained in the query data field is
value 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 specif-
ically 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.

7.9 How to Access Parameters

7.9.1 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.
7.9.2 Storage of Data
The Coil 65 decimal determines whether data written to
the frequency converter are stored in EEPROM and RAM
(coil 65 = 1) or only in RAM (coil 65 = 0).
7.9.3 IND
The array index is set in Holding Register 9 and used when
accessing array parameters.
7.9.4 Text Blocks
Parameters stored as text strings are accessed in the same
way as the other parameters. The maximum text block size
is 20 characters. If a read request for a parameter is for
more characters than the parameter stores, the response is
truncated. If the read request for a parameter is for fewer
characters than the parameter stores, the response is space
filled.
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