Danfoss FC 101 - How to Control the Frequency Converter; Function Codes Supported by Modbus RTU

Bus adress
Bus register
1
PLC Register Content Access Description
0 1 40001 Reserved Reserved for Legacy Drives VLT 5000 and VLT 2800
1 2 40002 Reserved Reserved for Legacy Drives VLT 5000 and VLT 2800
2 3 40003 Reserved Reserved for Legacy Drives VLT 5000 and VLT 2800
3 4 40004 Free
4 5 40005 Free
5 6 40006 Modbus conf Read/Write TCP only. Reserved for Modbus TCP (p12-28 and 12-29 -
store in Eeprom etc.)
6 7 40007 Last error code Read only Error code recieved from parameter database, refer to
WHAT 38295 for details
7 8 40008 Last error register Read only Address of register with which last error occurred, refer
to WHAT 38296 for details
8 9 40009 Index pointer Read/Write Sub index of parameter to be accessed. Refer to WHAT
38297 for details
9 10 40010 FC par. 0-01 Dependent on
parameter access
Parameter 0-01 (Modbus Register=10 parameter number
20 bytes space reserved pr parameter in Modbus Map
19 20 40020 FC par. 0-02 Dependent on
parameter access
Parameter 0-02
20 bytes space reserved pr parameter in Modbus Map
29 30 40030 FC par. xx-xx Dependent on
parameter access
Parameter 0-03
20 bytes space reserved pr parameter in Modbus Map
Table 7.17 Adress/Registers
1)
Value written in Modbus RTU telegram must be one or less than register number. E.g. Read Modbus Register 1 by writing value 0 in telegram.
7.8.9
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.
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 Function Code
Read coils 1 hex
Read holding registers 3 hex
Write single coil 5 hex
Write single register 6 hex
Write multiple coils F hex
Write multiple registers 10 hex
Get comm. event counter B hex
Report follower ID 11 hex
Table 7.18 Function Codes
Function Function
Code
Sub-
function
code
Sub-function
Diagnostics 8 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 follower message
count
Table 7.19 Function Codes
RS-485 Installation and Set...
VLT
®
HVAC Basic Drive FC 101 Design Guide
90 MG18C502 - Rev. 2013-09-06
77