Fc Protocol Overview - Danfoss VLT AQUA Drive FC 202 Design Manual

RS-485 Installation and Set...
unavoidable, the RS-485 cable must cross motor and brake
resistor cables at an angle of 90°.
Min.200mm
90° crossing
Illustration 7.2 EMC Precautions

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-slave principle for
communications via a serial bus.
One 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).
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.
MG20Z202
Design Guide
7.2.1 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:
•
•
•
•
•
•
•
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, permitting a
range of control options, including controlling the setpoint
of the frequency converter when its internal PID controller
is used.
Danfoss A/S © Rev. 06/2014 All rights reserved.
Start
Stop of the frequency converter 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 frequency
converter
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