8.9.3 IND (Index)
Some parameters in the drive are array parameters, for example
parameter 3-10 Preset Reference
. Since the Modbus does not support
arrays in the holding registers, the drive has reserved the holding register 9 as pointer to the array. Before reading or writing an
array parameter, set the holding register 9. Setting holding register to the value of 2 causes all following read/write to array parame-
ters to be to the index 2.
8.9.4 Text Blocks
Parameters stored as text strings are accessed in the same way as the other parameters. The maximum text block size is 20 charac-
ters. 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 space filled.
8.9.5 Conversion Factor
A parameter value can only be transferred as a whole number. To transfer decimals, use a conversion factor.
8.9.6 Parameter Values
Standard data types
Standard data types are int 16, int 32, uint 8, uint 16, and uint 32. They are stored as 4x registers (40001–4FFFF). The parameters are
read using function 03 hex read holding registers. Parameters are written using the function 6 hex preset single register for 1 regis-
ter (16 bits), and the function 10 hex 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 and are stored as 4x registers (40001–4FFFF). The parameters are read using function 03
hex read holding registers and written using function 10 hex preset multiple registers. Readable sizes range from 1 register (2 char-
acters) up to 10 registers (20 characters).
8.10 Examples
8.10.1 Introduction
The following examples show various Modbus RTU commands.
8.10.2 Read Coil Status (01 hex)
Description
This function reads the ON/OFF status of discrete outputs (coils) in the drive. Broadcast is never supported for reads.
Query
The query telegram specifies the starting coil and quantity of coils to be read. Coil addresses start at 0, that is, coil 33 is addressed as
32. Example of a request to read coils 33–48 (status word) from follower device 01.
Table 70: Query
Field name
Example (hex)
Follower address
01 (drive address)
Function
01 (read coils)
Starting address HI
00
Starting address LO
20 (32 decimals) coil 33
Number of points HI
00
Number of points LO
10 (16 decimals)
Error check (CRC)
–
Response
The coil status in the response telegram is packed as 1 coil per bit of the data field. Status is indicated as: 1 = ON; 0 = OFF. The lsb of
the 1
st
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.
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RS485 Installation and Set-up
VLT® Flow Drive FC 111
Design Guide