Examples; Read Coil Status (01 Hex); Force/Write Single Coil (05 Hex) - Danfoss FC 101 Design Manual

RS-485 Installation and Set...
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 Registers." 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.

7.10.1 Read Coil Status (01 HEX)

Description
This function reads the ON/OFF status of discrete outputs
7 7
(coils) in the frequency converter. 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, that is, coil
33 is addressed as 32.
Example of a request to read coils 33-48 (Status Word)
from follower device 01.
Field Name
Follower Address
Function
Starting Address HI
Starting Address LO
No. of Points HI
No. of Points LO
Error Check (CRC)
Table 7.21 Query
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 8, the
remaining bits in the final data byte is padded with zeros
(toward the high order end of the byte). The Byte Count
field specifies the number of complete bytes of data.
92
®
VLT HVAC Basic Drive FC 101 Design Guide
Example (HEX)
01 (frequency converter address)
01 (read coils)
00
20 (32 decimals) Coil 33
00
10 (16 decimals)
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MG18C502 - Rev. 2013-09-06
Field Name Example (HEX)
Follower Address 01 (frequency converter 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) -
Table 7.22 Response
NOTICE
Coils and registers are addressed explicit
with an off-set of -1 in Modbus.
I.e. Coil 33 is addressed as Coil 32.

7.10.2 Force/Write Single Coil (05 HEX)

Description
This function forces the coil to either ON or OFF. When
broadcast the function forces the same coil references in
all attached followers.
Query
The query message specifies the coil 65 (parameter write
control) to be forced. Coil addresses start at zero, that is,
coil 65 is addressed as 64. Force Data=00 00HEX (OFF) or
FF 00HEX (ON).
Field Name Example (HEX)
Follower Address 01 (Frequency converter address)
Function 05 (write single coil)
Coil Address HI 00
Coil Address LO 40 (64 decimal) Coil 65
Force Data HI FF
Force Data LO 00 (FF 00=ON)
Error Check (CRC) -
Table 7.23 Query
Response
The normal response is an echo of the query, returned
after the coil state has been forced.
Field Name
Follower Address
Function
Force Data HI
Force Data LO
Quantity of Coils HI
Quantity of Coils LO
Error Check (CRC)
Table 7.24 Response
Example (HEX)
01
05
FF
00
00
01
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