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
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 3-14 Preset Relative Reference (32 bit): The holding
registers 3410 and 3411 hold 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.
7.9.2
Storage of Data
The Coil 65 decimal determines whether data written to
the adjustable frequency drive are stored in EEPROM and
RAM (coil 65=1) or only in RAM (coil 65=0).
7.9.3
IND
Some parameters in the adjustable frequency drive are
array parameters, e.g., 3-10 Preset Reference. Since the
Modbus does not support arrays in the Holding registers,
the adjustable frequency drive 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.
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
padded with spaces.
7.9.5
Conversion Factor
The different attributes for each parameter can be seen in
the section on factory settings. Since a parameter value
can only be transferred as a whole number, a conversion
factor must be used to transfer decimals.
7.9.6 Parameter Values
Standard data types
Standard data types are int16, int32, uint8, uint16 and
uint32. They are stored as 4x registers (40001–4FFFF). The
parameters are read using function 03HEX "Read Holding
Registers." Parameters are written using the function 6HEX
"Preset Single Register" for one register (16 bits), and the
function 10 HEX "Preset Multiple Registers" for two
registers (32 bits). Readable sizes range from one register
(16 bits) up to ten 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 03HEX "Read Holding Registers" and written using
function 10HEX "Preset Multiple Registers." Readable sizes
range from one register (two characters) up to ten
registers (20 characters).
7.10
Examples
The following examples illustrate 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 adjustable frequency drive. Broadcast is never
supported for reads.
Query
The query message specifies the starting coil and quantity
of coils to be read. Coil addresses start at zero, that is, coil
33 is addressed as 32.
RS-485 Installation and Set... Design Guide
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