11.6.13 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
PCD 2
Control (master
⇒
slave Control word)
Reference-value
Control (slave
⇒
master) Status word
Present output
frequency
11.7 Examples
11.7.1 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 Conversion.
The telegram will look like this:
E19E H
PKE
IND
PWE
high
PWE
low
0000 H 0000 H 03E8 H
130BA092.10
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 will be:
119E H
PKE
IND
PWE
high
PWE
low
0000 H 0000 H 03E8 H
130BA093.10
11.7.2 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
PKE
IND
PWE
high
PWE
low
0000 H 0000 H 0000 H
130BA094.10
If the value in
3-41 Ramp 1 Ramp Up Time
is 10 s, the
response from the slave to the master will be:
130BA267.10
1155 H
PKE
IND
0000 H 0000 H 03E8 H
PWE
high
PWE
low
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
.
11.8 Modbus RTU Overview
11.8.1 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.
11.8.2 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.
11.8.3 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
requests from another device, and how errors are detected
and reported. It also establishes a common format for the
layout and contents of message fields.
During communications over a Modbus RTU network, the
protocol determines:
How each controller learns its device address
Recognizes a message addressed to it
Determines which actions to take
Extracts any data or other information contained
in the message
If a reply is required, the controller constructs the reply
message and sends it.
Controllers communicate using a master-slave technique in
which only one device (the master) can initiate
RS-485 Installation and Set...
FC 300 Design Guide
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