7.9.3 IND
The array index is set in Holding Register 9 and used when
accessing array parameters.
7.9.4 Text Blocks
Parameters stored as text strings are accessed in the same
way as the other parameters. The maximum text block size
is 20 characters. If a read request for a parameter is for
more characters than the parameter stores, the response is
truncated. If the read request for a parameter is for fewer
characters than the parameter stores, the response is
padded with spaces.
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.
7.9.6 Parameter Values
Standard Data Types
Standard data types are int16, int32, uint8, uint16 and
uint32. They are stored as 4x registers (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).
Non standard Data Types
Non standard data types are text strings 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. 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 discrete outputs
(coils) in the Adjustable frequency drive. 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 (Status Word)
from slave device 01.
Field Name
Example (HEX)
Slave Address
01 (Adjustable frequency drive
address)
Function
01 (read coils)
Starting Address HI
00
Starting Address LO
20 (32 decimals) Coil 33
No. of Points HI
00
No. of Points LO
10 (16 decimals)
Error Check (CRC)
-
Table 7.21
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 number of complete bytes of
data.
Field Name
Example (HEX)
Slave Address
01 (Adjustable frequency drive
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
RS-485 Installation and Set...
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HVAC Drive Design Guide
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