Specifications

7.1.4 Frequency Converter Parameter
Settings for Modbus Communication
Define the RS-485 Communicaiton Set-up
Parameter Function
8-30 Protocol Select the application protocol to run on
the RS-485 interface
8-31 Address Set the node address.
NOTICE
The address range depends on the
protocol selected in 8-30 Protocol
8-32 Baud Rate Set the baud rate.
NOTICE
The default baud rate depends on the
protocol selected in 8-30 Protocol
8-33 Parity / Stop
Bits
Set the parity and number of stop bits.
NOTICE
The default selection depends on the
protocol selected in 8-30 Protocol
8-35 Minimum
Response Delay
Specify a minimum delay time between
receiving a request and transmitting a
response. This function is for overcoming
modem turnaround delays.
8-36 Maximum
Response Delay
Specify a maximum delay time between
transmitting a request and receiving a
response.
8-37 Maximum
Inter-char delay
If transmission is interrupted, specify a
maximum delay time between two received
bytes to ensure time-out.
Table 7.2 Modbus Communication Parameter Settings
7.1.5
EMC Precautions
To achieve interference-free operation of the RS-485
network, Danfoss recommends the following EMC
precautions.
NOTICE
Observe relevant national and local regulations, for
example regarding protective earth connection. To avoid
coupling of high-frequency noise between the cables,
the RS-485 communication cable must be kept away
from motor and brake resistor cables. Normally, a
distance of 200 mm (8 inches) is sufficient, but Danfoss
recommends keeping the greatest possible distance
between the cables. Especially where cables run in
parallel over long distances. When crossing is
unavoidable, the RS-485 cable must cross motor and
brake resistor cables at an angle of 90°.
7.2 FC Protocol Overview
The FC protocol, also referred to as FC bus or Standard
bus, is the Danfoss standard fieldbus. It defines an access
technique according to the master-follower principle for
communications via a serial bus.
One master and a maximum of 126 followers can be
connected to the bus. The master selects the individual
followers via an address character in the telegram. A
follower itself can never transmit without first being
requested to do so, and direct message transfer between
the individual followers is not possible. communications
occur in the half-duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS-485, thus utilising the RS-485 port
built into the frequency converter. The FC protocol
supports different telegram formats:
•
A short format of 8 bytes for process data.
•
A long format of 16 bytes that also includes a
parameter channel.
•
A format used for texts.
7.2.1
FC with Modbus RTU
The FC protocol provides access to the Control Word and
Bus Reference of the frequency converter.
The Control Word allows the Modbus master to control
several important functions of the frequency converter.
RS-485 Installation and Set...
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HVAC Basic Drive FC 101 Design Guide
MG18C502 - Rev. 2013-09-06 81
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