Reading
3-14 Preset Relative Reference
(32bit): The holding
registers 3410 & 3411 hold the parameters values. A value
of 11300 (
decimal
), means that the parameter is set to
1113.00.
For information on the parameters, size, and converting
index, consult the programming guide.
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 e.g.
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. Use a conversion factor to transfer decimals.
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 illustrate various Modbus RTU
commands.
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 message 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
Example (hex)
Slave address
01 (frequency converter 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)
–
Table 5.22 Query
Response
The coil status in the response message 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-
orderin subsequent bytes.
If the returned coil quantity is not a multiple of 8, the
remaining bits in the final data byte are padded with 0s
(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 (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 5.23 Response
RS485 Installation and Set-...
Design Guide
MG06B402
Danfoss A/S © 09/2014 All rights reserved.
71
5
5
