How To Access Parameters; Parameter Handling; Storage Of Data; Ind - Danfoss VLT AQUA Drive FC 202 Design Manual

RS-485 Installation and Set...

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 (10xparameter number) DECIMAL.

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

The array index is set in holding register 9 and used when
accessing array parameters.

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

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 1 register (16 bits), and the
function 10HEX "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 03HEX "Read Holding Registers" and written using
function 10HEX "Preset Multiple Registers." Readable sizes
range from 1 register (2 characters) up to 10 registers (20
characters).
®
VLT AQUA Drive FC 202 Design Guide

7.10 Examples

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 message specifies the starting coil and quantity
of coils to read. Coil addresses start at zero.
Example of a request to read coils 33–48 (Status Word)
from slave device 01.
Field Name
Slave Address
Function
Starting Address HI
Starting Address LO
No. of Points HI
No. of Points LO
Error Check (CRC)
Table 7.19 Query
Response
The coil status in the response message is packed as one
coil per bit of the data field. Status is indicated as: 1 = ON;
0 = OFF. The LSB of the first data byte contains the coil
addressed in the query. The other coils follow toward the
high-order end of this byte, and from 'low order to high
order' in subsequent bytes.
If the returned coil quantity is not a multiple of eight, the
remaining bits in the final data byte are padded with zeros
(toward the high-order end of the byte). The Byte Count
field specifies the number of complete bytes of data.
Field Name
Slave Address
Function
Byte Count
Data (Coils 40–33)
Data (Coils 48–41)
Error Check (CRC)
Table 7.20 Response
NOTE
Coils and registers are addressed explicit with an off-set of
-1 in Modbus.
Coil 33 is addressed as Coil 32, for example.
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MG20Z102 - VLT is a registered Danfoss trademark
Example (HEX)
01 (frequency converter address)
01 (read coils)
00
20 (32 decimals) Coil 33
00
10 (16 decimals)
-
Example (HEX)
01 (frequency converter address)
01 (read coils)
02 (2 bytes of data)
07
06 (STW=0607hex)
-
7 7
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