Examples; Modbus Rtu Overview - Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

RS-485 Installation and Set...
Conversion index
74
2
1
0
-1
-2
-3
-4
-5
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.
PCD 1
Control (master⇒ slave Control word)
Control (slave ⇒ master) Status word

7.5 Examples

7.5.1 Writing a Parameter Value
Change 4-14 Motor Speed High Limit [Hz] to 100Hz.
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 100Hz, see
7.3.12 Conversion.
The telegram looks like this:
E19E H 0000 H 0000
PKE IND PWE
Note: 4-14 Motor Speed High Limit [Hz] is a single word, and
the parameter command for write in EEPROM is "E".
Parameter number 4-14 is 19E in hexadecimal.
The response from the slave to the master is:
VLT HVAC Basic Drive Design Guide
Conversion factor
0.1
100
10
1
0.1
0.01
0.001
0.0001
0.00001
PCD 2
Reference-value
Present output
frequency
H 03E8 H
PWE
high low
®
MG.18.C2.02 - VLT is a registered Danfoss trademark
119E H 0000 H 0000
PWE
IND
PKE
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
Ramp up Time
IND = 0000 Hex
PWEHIGH = 0000 Hex
PWELOW = 0000 Hex
1155 H 0000 H 0000
PKE IND
If the value in 3-41 Ramp 1 Ramp up Time is 10 s, the
response from the slave to the master is:
1155 H 0000 H 0000
PKE
IND
3E8 Hex corresponds to 1000 decimal. The conversion
index for 3-41 Ramp 1 Ramp up Time is -2, i.e. 0.01.
3-41 Ramp 1 Ramp up Time is of the type Unsigned 32.

7.6 Modbus RTU Overview

7.6.1 Assumptions
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.
7.6.2 What the User Should Already Know
The Modbus RTU (Remote Terminal Unit) is designed to
communicate with any controller that supports the
interfaces defined in this document. It is assumed that the
user has full knowledge of the capabilities and limitations
of the controller.
7.6.3 Modbus RTU Overview
Regardless of the type of physical communication
networks, the Modbus RTU Overview describes the process
a controller uses to request access to another device. This
process includes how the Modbus RTU responds to
H 03E8 H
PWE
high low
H 0000 H
PWE PWE
high low
H 03E8 H
PWE PWE
high low
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