Examples - Danfoss VLT Series Design Manual

7. RS-485 Installation and Set-up
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
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).
7

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:
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
140
Parameters section
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).
Field Name
Slave Address
Function
Starting Address HI 00
Starting Address LO 20 (32 decimals)
No. of Points HI
No. of Points LO
Error Check (CRC)
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)
®
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VLT HVAC Drive Design Guide
.
Example (HEX)
01 (frequency con-
verter address)
01 (read coils)
00
10 (16 decimals)
-
Example (HEX)
01 (frequency con-
verter address)
01 (read coils)
02 (2 bytes of data)
07
06 (STW=0607hex)
-