Danfoss VLT Series Design Manual page 154

7. RS-485 Installation and Set-up
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 (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)
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
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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
Slave Address
Function
Byte Count
Data (Coils 40-33)
Data (Coils 48-41)
Error Check (CRC)
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Example (HEX)
01 (adjustable frequency drive address)
01 (read coils)
00
20 (32 decimals)
00
10 (16 decimals)
-
Example (HEX)
01 (adjustable frequency drive address)
01 (read coils)
02 (2 bytes of data)
07
06 (STW=0607hex)
-
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
VLT ® HVAC Drive Design Guide