Danfoss vlt aqua Design Manual

Also see for vlt aqua: Instructions Instruction manual Operating instructions Design guide Operating instructions

Contents

Danfoss vlt aqua Design Manual Manual pdf 190 page image

7.2 FC Protocol OverviewThe adjustable frequency protocol, also referred to as adjustable frequency bus or standard bus, is the Danfoss standard serial communication bus. Itdefines 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 individual slaves are selected by the master via an address character in themessage. 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 utilizing the RS-485 port built into the adjustable frequency drive. The adjustable frequency protocol supports differentmessage formats; a short format of 8 bytes for process data, and a long format of 16 bytes that also includes a parameter channel. A third messageformat is used for texts.7.2.1 VLT AQUA with Modbus RTUThe 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 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 adjustable frequency driveThe bus reference is commonly used for speed control. It is also possible to access the parameters, read their values, and where possible, write valuesto them. This permits a range of control options, including controlling the setpoint of the adjustable frequency drive when its internal PID controller isused.7 RS-485 Installation and Set-up VLT® AQUA Drive Design Guide7-4 MG.20.N5.22 - VLT® is a registered Danfoss trademark7