25
VLT is a registered Danfoss trade mark MG.10.P2.22
Supported
Modbus
Function
Codes
Appendix A describes the following functions
supported by the Modbus RTU option card.
Read Coil Status (01
HEX
)
Force Single Coil (05
HEX
)
Force Multiple Coils (0F
HEX
)
Read Coil
Status
(01
HEX
)
Description
Reads the ON/OFF status of discrete outputs
(0X references, coils) in the slave. Broadcast
is never supported for reads.
Query
The query message specifies the starting coil
and quantity of coils to be read. Coils are
addressed starting at zero. Coils 1-16 are
addressed as 0-15.
Example of a request to read coils 1-16 from slave device 01.
Field Name Example (HEX)
Slave Address 01
Function 01
Starting Address HI 00
Starting Address LO 00
No. of Points HI 00
No. of Points LO 10
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 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 quantity of complete bytes of
data.
Field Name Example (HEX)
Slave Address 01
Function 01
Byte Count 02
Data (Coils 8-1) 55
Data (Coils 16-9) AA
Error Check (CRC) –
Read Holding Registers (03
HEX
)
Preset Single Register (06
HEX
)
Preset Multiple Registers (10
HEX
)
APPENDIX A
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