Danfoss VLT Series Design Manual

Also see for VLT series: Service manual Installation guide Operating instructions Operating instructions Service manual

Contents

Danfoss VLT Series Design Manual Manual pdf 124 page image

7.2. FC Protocol OverviewThe FC protocol, also referred to as FC bus or Standard bus, is the Danfoss Drives standard field-bus. It defines an access technique according to the master-slave principle for communicationsvia a serial bus.One master and a maximum of 126 slaves can be connected to the bus. The individual slaves areselected by the master via an address character in the telegram. A slave itself can never transmitwithout first being requested to do so, and direct message transfer between the individual slavesis 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 utilizing the RS-485 port built into the frequency converter. TheFC protocol supports different telegram formats; a short format of 8 bytes for process data, anda long format of 16 bytes that also includes a parameter channel. A third telegram format is usedfor texts.7.2.1. VLT HVAC with Modbus RTUThe FC protocol provides access to the Control Word and Bus Reference of the frequency con-verter.The Control Word allows the Modbus master to control several important functions of the fre-quency converter:• Start• Stop of the frequency converter in various ways:Coast stopQuick stopDC Brake stopNormal (ramp) stop• Reset after a fault trip• Run at a variety of preset speeds• Run in reverse• Change of the active set-up• Control of the two relays built into the frequency converterThe Bus Reference is commonly used for speed control. It is also possible to access the parame-ters, read their values, and where possible, write values to them. This permits a range of controloptions, including controlling the setpoint of the frequency converter when its internal PID con-troller is used.7.3. Network Configuration7.3.1. VLT HVAC Frequency Converter Set-upSet the following parameters to enable the FCprotocol for the VLT HVAC.7. RS-485 Installation and Set-up VLT® HVAC Drive Design Guide124 MG.11.B2.02 - VLT® is a registered Danfoss trademark7