How To Control The Frequency Converter; Function Codes Supported By Modbus Rtu; Modbus Exception Codes; How To Access Parameters - Danfoss VLT FC 360 Design Manual

RS-485 Installation and Set...
3.8.9 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.
3 3
3.8.10 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
Table 3.18 Function Codes
Function Function
Code
Diagnostics 8
Table 3.19 Function Codes
52
®
VLT AutomationDrive FC 360 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 communi-
cation error count
13 Return bus exception error
count
14 Return slave message
count
MG06B202 - VLT

3.8.11 Modbus Exception Codes

For a full explanation of the structure of an exception code
response, refer to 3.8.5 Function Field.
Code Name
1 Illegal
function
2 Illegal data
address
3 Illegal data
value
4 Slave device
failure
Table 3.20 Modbus Exception Codes

3.9 How to Access Parameters

3.9.1 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.
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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.
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 request with offset
96 and length 4 would succeed, a request
with offset 96 and length 5 generates
exception 02.
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 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.
An unrecoverable error occurred while the
server (or slave) was attempting to
perform the requested action.