the RS485 communication cable away from motor andbrake resistor cables to avoid coupling of high frequencynoise from one cable to another. Normally a distance of200 mm (8 in) is sufficient, but keeping the greatestpossible distance between the cables is recommended,especially where cables run in parallel over long distances.When crossing is unavoidable, the RS485 cable must crossmotor and brake resistor cables at an angle of 90°.Fieldbus cableMin. 200 mm90° crossingBrake resistor130BD507.11Figure 3.44 Cable Routing3.8.5 FC Protocol OverviewThe FC protocol, also referred to as FC bus or standard bus,is the Danfoss standard serial communication bus. Itdefines an access technique according to the master-slaveprinciple for communications via a serial bus.One master and a maximum of 126 slaves can beconnected to the bus. The master selects the individualslaves via an address character in the message. A slaveitself can never transmit without first being requested todo so, and direct message transfer between the individualslaves 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 RS485, thus utilizing the RS485 portbuilt into the adjustable frequency drive. The FC protocolsupports different message formats:• A short format of 8 bytes for process data.• A long format of 16 bytes that also includes aparameter channel.• A format used for texts.3.8.6 Network ConfigurationSet the following parameters to enable the FC protocol forthe adjustable frequency drive:Parameter number Setting8-30 Protocol FC8-31 Address 1–1268-32 FC Port Baud Rate 2400–1152008-33 Parity / Stop Bits Even parity, 1 stop bit (default)Table 3.26 FC Protocol Parameters3.8.7 FC Protocol Message FramingStructure3.8.7.1 Content of a Character (byte)Each character transferred begins with a start bit. Then 8data bits are transferred, corresponding to a byte. Eachcharacter is secured via a parity bit. This bit is set at 1when it reaches parity. Parity is when there is an equalnumber of 1s in the 8 data bits and the parity bit in total.A stop bit completes a character, thus consisting of 11 bitsin all.Figure 3.45 Content of a Character3.8.7.2 Message StructureEach message has the following structure:• Start character (STX)=02 hex.• A byte denoting the message length (LGE).• A byte denoting the adjustable frequency driveaddress (ADR).A number of data bytes (variable, depending on the typeof message) follows.System Integration VLT® AQUA Drive FC 20282 Danfoss A/S © 09/2014 All rights reserved. MG20N62233