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

7. RS-485 Installation and Set-up
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
Diagnostics
7
7.8.11. Modbus Exception Codes
For a full explanation of the structure of an exception code response, please refer to the section
Code Name
1 Illegal function
2 Illegal data address
3 Illegal data value
4 Slave device failure

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.
140
Function Code
1 hex
3 hex
5 hex
6 hex
F hex
10 hex
B hex
11 hex
Function Code Sub-function code
8 1
2
10
11
12
13
14
Modbus Exception Codes
MG.11.B7.02 - VLT
Sub-function
Restart communication
Return diagnostic register
Clear counters and diagnostic register
Return bus message count
Return bus communication error count
Return bus exception error count
Return slave message count
Modbus RTU Message Framing Structure, Function Field.
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 refer-
ence 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.
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 at-
tempting to perform the requested action.
® is a registered Danfoss trademark
®
VLT HVAC Drive Design Guide