Operating instructions

VLT
®
2800, VLT
®
6000 HVAC and VLT
®
8000 AQUA Modbus RTU
■ Supported Modbus RTU Function Codes
This section describes the following functions
supported by the Modbus RTU.
Read Coil Status (01
HEX
) Read Holding Registers (03
HEX
)
Force Single Coil (05
HEX
) Preset Single Register (06
HEX
)
Force Multiple Coils (0F
HEX
) Preset Multiple Registers (10
HEX
)
■ Read Coil Statu
s(01
HEX
)
Description
Reads the ON/OFF status of discrete outputs
(0X reference
s, 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 33-48 (Status
Word) from slave device 01.
Field Name Example (HEX)
Slave Address 01
Functi
on
01
Starting Address HI 00
Starting Address LO 20
No. of Poin
ts 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
thehighorderendofthebyte). TheByteCountfield
specifies the quantity of complete bytes of data.
Field Name Example (HEX)
Slave Address 01
Function 01
Byte Count 02
Data (Coils 40-33) 55
Data (Coils 48-41) AA
Error Check (CRC) -
■ ForceSingleCoil(05
HEX
)
Description
Forces a single co
il (0X reference) to either ON or
OFF. When broadcast, the function forces the same
coil references in all attached slaves.
Query
The query me
ssage specifies the coil reference
to be forced. Coils are addressed starting at
zero.Coil1isaddressedas0.ForceData=00
00HEX (O
FF) or FF 00HEX (ON).
See exa
mple 1 Start Motor, Run Speed 40%.
Field
Name
Examp
le (HEX)
Slave Address 01
Function 05
Coil Addr
ess HI
00
Coil Address LO 00
ForceDataHI FF
Force Data
LO
00
Error Check (CRC) -
Response
The normal response is an echo of the query, returned
after the coil state has been forced.
Field Name Example (HEX)
Slave Address 01
Function 05
ForceDataHI FF
Force Data LO 00
Quantity of Coils HI 00
Quantity of Coils LO 0A
Error Check (CRC) -
■ Force Multiple Coils (0F
HEX
)
Description
Forces each coil (0X reference) in a sequence of coils to
either ON or OFF. When broadcast, the function forces
the same coil references in all attached slaves.
MG.10.S2.02 - VLT is a registered Danfoss trademark
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