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Illustration 66: Minimum Distance between Communication and Power Cables
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Fieldbus cable
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Minimum 200 mm (8 in) distance
8.2 FC Protocol
8.2.1 Overview
The FC protocol, also referred to as FC bus or standard bus, is the Danfoss standard fieldbus. It defines an access technique accord-
ing to the master/follower principle for communications via a fieldbus.
One master and a maximum of 126 followers can be connected to the bus. The master selects the individual followers via an ad-
dress character in the telegram. A follower itself can never transmit without first being requested to do so, and direct telegram
transfer between the individual followers is not possible. Communications occur in the halfduplex mode.
The master function cannot be transferred to another node (single-master system).
The physical layer is RS485, thus utilizing the RS485 port built into the drive. 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.
8.2.2 FC with Modbus RTU
The FC protocol provides access to the control word and bus reference of the drive.
The control word allows the Modbus master to control several important functions of the drive:
Start.
Stop of the drive in various ways:
Coast stop.
Quick stop.
DC brake stop.
Normal (ramp) stop.
Reset after a fault trip.
AJ363928382091en-000101 / 130R0983
104 | Danfoss A/S © 2021.04
RS485 Installation and Set-up
VLT® Flow Drive FC 111
Design Guide