How To Control The Frequency Converter; Function Codes Supported By Modbus Rtu; Modbus Exception Codes - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS485 Installation and Set-...
Write
Master Frequency Converter
Controlled by
Holding
Parameter
Register
2810 8-42 [0]
CTW
8-42 [1]
2811
REF
PCD 2
8-42 [2]
2812
write
PCD 3
8-42 [3]
2813
write
PCD 4
2814 8-42 [4]
write
PCD 5
2815 8-42 [5]
write
...
... ...
write
PCD 63
2873 8-42 [63]
write
Illustration 7.14 Accessing via PCD write/read
NOTICE
The boxes marked in grey are not changeable, they are
default values.
NOTICE
The 32 bit parameters must be mapped inside the 32 bit
boundaries (PCD2 & PCD3 or PCD4 & PCD5, and so on.),
where the parameter number is mapped twice to
parameter 8-42 PCD Write Configuration or
parameter 8-43 PCD Read Configuration.
7.8.10 How to Control the Frequency
Converter
This section describes codes which can be used in the
function and data fields of a Modbus RTU telegram.
7.8.11 Function Codes Supported by
Modbus RTU
Modbus RTU supports use of the following function codes
in the function field of a telegram.
MG18C702
Design Guide
Read
Frequency
Converter Master
Controlled by
Holding
Parameter
Register
2910 8-43 [0]
STW
8-43 [1]
2911
MAV
PCD 2
8-43 [2]
2912
read
PCD 3
8-43 [3]
2913
read
PCD 4
2914 8-43 [4]
read
PCD 5
2915 8-43 [5]
read
...
... ...
read
PCD 63
2919 8-43 [63]
read
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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
Read write multiple registers
Table 7.19 Function Codes
Function Subfunction
Function
code code
1
2
10
Diagnostics 8 11
12
13
14
Table 7.20 Function Codes

7.8.12 Modbus Exception Codes

For a full explanation of the structure of an exception code
response, refer to chapter 7.8.5 Function Field.
Code Name
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
Illegal and was not implemented in the unit
1
function 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
Illegal data of reference number and transfer length is
2
address 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.
Function code (hex)
1
3
5
6
F
10
B
11
17
Subfunction
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.
Meaning
91
7 7