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 ground 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 8 inches [200 mm] 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 Adjustable Frequency Protocol
Overview
The FC protocol, also referred to as FC bus or Standard
bus, is the Danfoss standard serial communication bus. 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 message. 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 half-duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS-485, thus utilizing the RS-485 port
built into the adjustable frequency drive. The FC protocol
supports different message 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 adjustable frequency drive.
The Control Word allows the Modbus master to control
several important functions of the adjustable frequency
drive.
•
Start
•
Stop of the adjustable frequency drive in various
ways:
•
Coast stop
•
Quick stop
•
DC Brake stop
•
Normal (ramp) stop
•
Reset after a fault trip
•
Run at various preset speeds
•
Run in reverse
•
Change of the active set-up
•
Control of the two relays built into the adjustable
frequency drive
The bus reference is commonly used for speed control. It is
also possible to access the parameters, read their values,
and where possible, write values to them. This permits a
range of control options, including controlling the setpoint
of the adjustable frequency drive when its internal PI
controller is used.
7.3
Network Configuration
7.3.1 Adjustable Frequency Drive Set-up
Set the following parameters to enable the FC protocol for
the adjustable frequency drive.
Parameter Setting
8-30 Protocol FC
8-31 Address 1-126
8-32 Baud Rate 2,400-115,200
8-33 Parity / Stop Bits Even parity, 1 stop bit (default)
Table 7.3
RS-485 Installation and Set...
Design Guide
88 Danfoss A/S © Rev. 2014-01-14 All rights reserved. MG18C522
77
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