How To Access Parameters; Parameter Handling; Storage Of Data; Ind (Index) - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS485 Installation and Set-...
Code Name
Illegal data
3
value
Slave device
4
failure
Table 7.21 Modbus Exception Codes
7 7

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. Example: Reading
parameter 3-12 Catch up/slow Down Value (16 bit): The
holding register 3120 holds the parameters value. A value
of 1352 (decimal) means that the parameter is set to
12.52%.
Reading parameter 3-14 Preset Relative Reference (32 bit):
The holding registers 3410 and 3411 hold the parameters
values. A value of 11300 (decimal), means that the
parameter is set to 1113.00.
For information on the parameters, size, and conversion
index, see chapter 6 Programming.

7.9.2 Storage of Data

The coil 65 decimal determines whether data written to
the frequency converter is stored in EEPROM and RAM (coil
65 = 1), or only in RAM (coil 65 = 0).

7.9.3 IND (Index)

Some parameters in the frequency converter are array
parameters, for example parameter 3-10 Preset Reference.
Since the Modbus does not support arrays in the holding
registers, the frequency converter has reserved the holding
register 9 as pointer to the array. Before reading or writing
an array parameter, set the holding register 9. Setting
holding register to the value of 2 causes all following read/
write to array parameters to be to the index 2.
92
®
VLT HVAC Basic Drive FC 101
Meaning
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 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 value of any register.
An unrecoverable error occurred while the
server (or slave) was attempting to
perform the requested action.
Danfoss A/S © 04/2016 All rights reserved.

7.9.4 Text Blocks

Parameters stored as text strings are accessed in the same
way as the other parameters. The maximum text block size
is 20 characters. If a read request for a parameter is for
more characters than the parameter stores, the response is
truncated. If the read request for a parameter is for fewer
characters than the parameter stores, the response is space
filled.

7.9.5 Conversion Factor

A parameter value can only be transferred as a whole
number. To transfer decimals, use a conversion factor.

7.9.6 Parameter Values

Standard data types
Standard data types are int 16, int 32, uint 8, uint 16, and
uint 32. They are stored as 4x registers (40001–4FFFF). The
parameters are read using function 03 hex read holding
registers. Parameters are written using the function 6 hex
preset single register for 1 register (16 bits), and the
function 10 hex preset multiple registers for 2 registers (32
bits). Readable sizes range from 1 register (16 bits) up to
10 registers (20 characters).
Non-standard data types
Non-standard data types are text strings and are stored as
4x registers (40001–4FFFF). The parameters are read using
function 03 hex read holding registers and written using
function 10 hex preset multiple registers. Readable sizes
range from 1 register (2 characters) up to 10 registers (20
characters).

7.10 Examples

The following examples show various Modbus RTU
commands.

7.10.1 Read Coil Status (01 hex)

Description
This function reads the ON/OFF status of discrete outputs
(coils) in the frequency converter. Broadcast is never
supported for reads.
Query
The query telegram specifies the starting coil and quantity
of coils to be read. Coil addresses start at 0, that is, coil 33
is addressed as 32.
Example of a request to read coils 33–48 (status word)
from slave device 01.
MG18C702