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. Please refer to the
Parameters section
.
7.9.6. Parameter Values
Standard Data Types
Standard data types are int16, int32, uint8,
uint16 and uint32. They are stored as 4x reg-
isters (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 Regis-
ters." Readable sizes range from 1 register (2
characters) up to 10 registers (20 characters).
7.10. Examples
The following examples illustrate various Modbus RTU commands. If an error occurs, please refer
to the Exception Codes section.
7.10.1. Read Coil Status (01 HEX)
Description
This function reads the ON/OFF status of dis-
crete outputs (coils) in the frequency convert-
er. 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, i.e. coil 33 is addressed as 32.
Example of a request to read coils 33-48 (Sta-
tus Word) from slave device 01:
Field Name
Example (HEX)
Slave Address
01 (frequency con-
verter address)
Function
01 (read coils)
Starting Address HI 00
Starting Address LO 20 (32 decimals)
No. of Points HI
00
No. of Points LO
10 (16 decimals)
Error Check (CRC)
-
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 ad-
dressed 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 will be 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
Example (HEX)
Slave Address
01 (frequency con-
verter address)
Function
01 (read coils)
Byte Count
02 (2 bytes of data)
Data (Coils 40-33)
07
Data (Coils 48-41)
06 (STW=0607hex)
Error Check (CRC)
-
7. RS-485 Installation and Set-up
VLT
®
HVAC Drive Design Guide
140
MG.11.B2.02 - VLT
®
is a registered Danfoss trademark
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