Fc Protocol Overview - Danfoss FC 102 Design Manual

Installation and Set-up
ON
1
Illustration 8.3 Terminator Switch Factory Setting
The factory setting for the dip switch is OFF.
8.1.3 Frequency Converter Parameter
Settings for Modbus Communication
The following parameters apply to the RS-485 interface
(FC-port):
Parameter Function
8-30 Protocol Select the application protocol to run on
the RS-485 interface
8-31 Address Set the node address. Note: The address
range depends on the protocol selected in
8-30 Protocol
8-32 Baud Rate Set the baud rate. Note: The default baud
rate depends on the protocol selected in
8-30 Protocol
8-33 Parity / Stop Set the parity and number of stop bits.
Bits Note: The default selection depends on the
protocol selected in 8-30 Protocol
8-35 Minimum Specify a minimum delay time between
Response Delay receiving a request and transmitting a
response. This can be used for overcoming
modem turnaround delays.
8-36 Maximum Specify a maximum delay time between
Response Delay transmitting a request and receiving a
response.
8-37 Maximum Specify a maximum delay time between
Inter-Char Delay two received bytes to ensure time-out if
transmission is interrupted.
Table 8.2 Parameters Apply to the RS-485 Interface (FC-port)
8.1.4 EMC Precautions
The following EMC precautions are recommended to
achieve interference-free operation of the RS-485 network.
Observe relevant national and local regulations, for
example regarding protective earth connection. Keep the
RS-485 communication cable away from motor and brake
resistor cables to avoid coupling of high frequency noise
MG11BC02
Design Guide
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Danfoss A/S © Rev. 06/2014 All rights reserved.
from one cable to another. Normally, a distance of 200 mm
(8 inches) is sufficient, but keeping the greatest possible
distance between the cables is recommended, 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°.
Min. 200 mm
90° crossing
Illustration 8.4 Cable Routing

8.2 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
Brake resistor
131
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