Emc Precautions; Fc Protocol Overview; Network Configuration; Fc Protocol Message Framing Structure - Danfoss VLT Refrigeration Drive FC 103 Design Manual

System Integration

3.9.4 EMC Precautions

The following EMC precautions are recommended to
achieve interference-free operation of the RS485 network.
Observe relevant national and local regulations, for
example regarding protective earth connection. Keep the
RS485 communication cable away from motor and brake
resistor cables to avoid coupling of high frequency noise
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 RS485 cable must cross motor
cables at an angle of 90°.
Minimum 200 mm (8 in)
90° crossing
Illustration 3.44 Cable Routing

3.9.5 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/slave principle for
communications via a fieldbus.
1 master and a maximum of 126 slaves can be connected
to the bus. The master selects the individual slaves via an
address character in the telegram. A slave itself can never
transmit without first being requested to do so, and direct
message transfer between the individual slaves is not
possible. Communications occur in the half-duplex mode.
The master function cannot be transferred to another node
(single-master system).
MG16G202
Design Guide
The physical layer is RS485, thus utilising the RS485 port
built into the frequency converter. The FC protocol
supports different telegram formats:
•
•
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3.9.6 Network Configuration

To enable the FC protocol for the frequency converter, set
the following parameters:
Parameter number
Parameter 8-30 Protocol
Parameter 8-31 Address
Parameter 8-32 Baud Rate
Parameter 8-33 Parity / Stop Bits
Table 3.24 FC Protocol Parameters
3.9.7 FC Protocol Message Framing
Structure
3.9.7.1 Content of a Character (byte)
Each character transferred begins with a start bit. Then 8
data bits are transferred, corresponding to a byte. Each
character is secured via a parity bit. This bit is set at 1
when it reaches parity. Parity is when there is an equal
number of 1s in the 8 data bits and the parity bit in total.
A stop bit completes a character, thus consisting of 11 bits
in all.
Start
bit
Illustration 3.45 Content of a Character
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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.
Setting
FC
1–126
2400–115200
Even parity, 1 stop bit (default)
0 1 2 3 4 5
3
6 7 Even Stop
Parity bit
73
3