Storage Of Data; Ind (Index); Text Blocks; Conversion Factor - Danfoss VLT Midi Drive FC 280 Design Manual

RS485 Installation and Set-...

5.9.2 Storage of Data

The coil 65 decimal determines whether data written to
the frequency converter is stored in EEPROM and RAM (coil
65=1), or only in RAM (coil 65=0).

5.9.3 IND (Index)

Some parameters in the frequency converter are array
parameters, for example parameter 3-10 Preset Reference.
Since the Modbus does not support arrays in the holding
registers, the frequency converter 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 parameters to be to the index 2.

5.9.4 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 space
filled.

5.9.5 Conversion Factor

A parameter value can only be transferred as a whole
number. To transfer decimals, use a conversion factor.

5.9.6 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 register (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 characters) up to 10 registers (20
characters).

5.10 Examples

The following examples show various Modbus RTU
commands.
MG07B102
Design Guide

5.10.1 Read Coil Status (01 hex)

Description
This function reads the ON/OFF status of discrete outputs
(coils) in the frequency converter. 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 slave device 01.
Field name
Slave address
Function
Starting address HI
Starting address LO
Number of points HI
Number of points LO
Error check (CRC)
Table 5.22 Query
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 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 are padded with
values 0 (toward the high-order end of the byte). The byte
count field specifies the number of complete bytes of data.
Field name
Slave address
Function
Byte count
Data (coils 40–33)
Data (coils 48–41)
Error check (CRC)
Table 5.23 Response
NOTICE
Coils and registers are addressed explicitly with an off-
set of -1 in Modbus.
For example, coil 33 is addressed as coil 32.
Danfoss A/S © 03/2016 All rights reserved.
Example (hex)
01 (frequency converter address)
01 (read coils)
00
20 (32 decimals) coil 33
00
10 (16 decimals)
–
Example (hex)
01 (frequency converter address)
01 (read coils)
02 (2 bytes of data)
07
06 (STW=0607hex)
–
5 5
65