Examples; Modbus Rtu Overview; Prerequisite Knowledge; What The User Should Already Know - Danfoss VLT Micro Drive FC 51 Design Manual

RS485 Installation and Set-...

8.5 Examples

8.5.1 Writing a Parameter Value
Change parameter 4-14 Motor Speed High Limit [Hz] to 100
Hz.
Write the data in EEPROM.
PKE = E19E hex - Write single word in
parameter 4-14 Motor Speed High Limit [Hz]:
•
IND = 0000 hex.
•
PWEHIGH = 0000 hex.
•
PWELOW = 03E8 hex.
Data value 1000, corresponding to 100 Hz, see
chapter 8.4.12 Conversion.
The telegram looks like Illustration 8.10.
E19E H 0000 H 0000
PKE IND PWE
Illustration 8.10 Telegram
NOTICE
Parameter 4-14 Motor Speed High Limit [Hz] is a single
word, and the parameter command for write in EEPROM
is E. Parameter 4-14 Motor Speed High Limit [Hz] is 19E in
hexadecimal.
The response from the slave to the master is shown in
Illustration 8.11.
119E H 0000 H 0000
PWE
PKE IND
Illustration 8.11 Response from Master
8.5.2 Reading a Parameter Value
Read the value in parameter 3-41 Ramp 1 Ramp Up Time.
PKE = 1155 hex - Read parameter value in
parameter 3-41 Ramp 1 Ramp Up Time:
•
IND = 0000 hex.
•
PWE = 0000 hex.
HIGH
•
PWE = 0000 hex.
LOW
MG02K402
Design Guide
H 03E8 H
PWE
high low
H 03E8 H
PWE
low
high
Danfoss A/S © 01/2016 All rights reserved.
1155 H 0000 H 0000
PKE IND
Illustration 8.12 Telegram
If the value in parameter 3-41 Ramp 1 Ramp Up Time is 10
s, the response from the slave to the master is shown in
Illustration 8.13.
1155 H 0000 H 0000
PKE
IND
Illustration 8.13 Response
3E8 hex corresponds to 1000 decimal. The conversion
index for parameter 3-41 Ramp 1 Ramp Up Time is -2, that
is, 0.01.
Parameter 3-41 Ramp 1 Ramp Up Time is of the type
Unsigned 32.

8.6 Modbus RTU Overview

8.6.1 Prerequisite Knowledge

Danfoss assumes that the installed controller supports the
interfaces in this manual, and strictly observes all
requirements and limitations stipulated in the controller
and frequency converter.
The built-in Modbus RTU (remote terminal unit) is
designed to communicate with any controller that
supports the interfaces defined in this manual. It is
assumed that the user has full knowledge of the
capabilities and limitations of the controller.

8.6.2 What the User Should Already Know

The built-in Modbus RTU is designed to communicate with
any controller that supports the interfaces defined in this
manual. It is assumed that the user has full knowledge of
the capabilities and limitations of the controller.

8.6.3 Overview

Regardless of the type of physical communication
networks, this section describes the process a controller
uses to request access to another device. This process
includes how the Modbus RTU responds to requests from
another device, and how errors are detected and reported.
It also establishes a common format for the layout and
contents of telegram fields.
H 0000 H
PWE PWE
high low
H 03E8 H
PWE PWE
high low
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