How To Access Parameters In Modbus Rtu - Danfoss VLT AAF006 Operating Instructions Manual

RS485 Installation and Set-...
Conversion index
100
75
74
67
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
7 7
-6
-7
Table 7.8 Conversion Table
7.3.13 Process Words (PCD)
The block of process words is divided into 2 blocks of 16
bits, which always occur in the defined sequence.
PCD 1
Control telegram (master⇒slave control
word)
Control telegram (slave⇒master) status word Present output
Table 7.9 Process Words (PCD)
7.4 How to Access Parameters in Modbus
RTU
7.4.1 Parameter Handling
The PNU (Parameter Number) is translated from the
register address contained in the Modbus read or write
message. The parameter number is translated to Modbus
as (10 x parameter number) DECIMAL.
7.4.2 Data Storage
The coil 65 decimal determines whether data written to
the unit are stored in EEPROM and RAM (coil 65=1) or only
in RAM (coil 65=0).
74
Operating Instructions
Conversion factor
1000000
100000
10000
1000
100
10
1
0.1
0.01
0.001
0.0001
0.00001
0.000001
0.0000001
PCD 2
Reference value
frequency
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7.4.3 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.
7.4.4 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.
7.4.5 Conversion Factor
A parameter value can only be transferred as a whole
number. Use a conversion factor to transfer decimals.
7.4.6 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).
MG90V302