Process Words (Pcd); Examples; Modbus Rtu Overview; Assumptions - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS-485 Installation and Set...
Conversion index
74
2
1
0
-1
-2
-3
-4
-5
Table 7.9

7.4.13 Process Words (PCD)

The block of process words is divided into two blocks of
16 bits, which always occur in the defined sequence.
7 7
Control telegram (master⇒slave Control
word)
Control telegram (slave⇒master) Status word Present output
Table 7.10

7.5 Examples

7.5.1 Writing a Parameter Value
Change 4-14 Motor Speed High Limit [Hz] to 100 Hz.
Write the data in EEPROM.
PKE=E19E Hex - Write single word in 4-14 Motor Speed High
Limit [Hz]:
IND=0000 Hex
PWEHIGH=0000 Hex
PWELOW=03E8 Hex
Data value 1000, corresponding to 100 Hz, see
7.4.12 Conversion.
The telegram looks like this:
E19E H 0000
PKE
Illustration 7.9
82
VLT
Conversion factor
0.1
100
10
1
0.1
0.01
0.001
0.0001
0.00001
PCD 1
Reference-value
frequency
H 0000 H 03E8
IND PWE PWE
high low
MG18C402 - VLT
®
HVAC Basic Drive Design Guide
NOTE
4-14 Motor Speed High Limit [Hz] is a single word, and the
parameter command for write in EEPROM is "E". Parameter
4-14 is 19E in hexadecimal.
The response from the slave to the master is:
119E
PKE
Illustration 7.10
7.5.2 Reading a Parameter Value
Read the value in 3-41 Ramp 1 Ramp Up Time
PKE=1155 Hex - Read parameter value in 3-41 Ramp 1
PCD 2
Ramp Up Time
IND=0000 Hex
PWE =0000 Hex
HIGH
PWE =0000 Hex
LOW
1155
PKE
Illustration 7.11
If the value in 3-41 Ramp 1 Ramp Up Time is 10 s, the
response from the slave to the master is:
1155
PKE
Illustration 7.12
3E8 Hex corresponds to 1000 decimal. The conversion
index for 3-41 Ramp 1 Ramp Up Time is -2, that is, 0.01.
3-41 Ramp 1 Ramp Up Time is of the type Unsigned 32.

7.6 Modbus RTU Overview

7.6.1 Assumptions

H
Danfoss assumes that the installed controller supports the
interfaces in this document, and strictly observe all
requirements and limitations stipulated in the controller
and frequency converter.
®
is a registered Danfoss trademark
H 0000 H 0000 H 03E8
PWE
IND
high
H 0000 H 0000 H 0000
IND PWE
high
H 0000 H 0000 H 03E8
PWE
IND
high
H
PWE
low
H
PWE
low
H
PWE
low