How To Control The Frequency Converter; Function Codes Supported By Modbus Rtu; Modbus Exception Codes; How To Access Parameters - Danfoss FC 102 Design Manual

Installation and Set-up
8.8.9 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.
8.8.10 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
8 8
Report follower ID
Table 8.18 Function Codes
Function Function
Code
Diagnostics 8
Table 8.19 Function Codes

8.8.11 Modbus Exception Codes

For a full explanation of the structure of an exception code
response, refer to chapter 8.8.5 Function Field.
140
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 follower message
count
Danfoss A/S © Rev. 06/2014 All rights reserved.
Code Name Meaning
1 Illegal The function code received in the query is
function not an allowable action for the server (or
follower). 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 follower) 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.
2 Illegal data The data address received in the query is
address not an allowable address for the server
(or follower). 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.
3 Illegal data A value contained in the query data field
value is not an allowable value for server (or
follower). 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.
4 Follower An unrecoverable error occurred while the
device failure server (or follower) was attempting to
perform the requested action.
Table 8.20 Modbus Exception Codes

8.9 How to Access Parameters

8.9.1 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. Example: Reading
3-12 Catch up/slow Down Value (16bit): The holding register
3120 holds the parameters value. A value of 1352
(Decimal), means that the parameter is set to 12.52%
Reading 3-14 Preset Relative Reference (32bit): The holding
registers 3410 & 3411 holds the parameters value. A value
of 11300 (Decimal), means that the parameter is set to
1113.00 S.
For information on the parameters, size and converting
index, consult the product relevant programming guide.
MG11BC02