42 Program features Control of a supply unit (LSU)GeneralWith drives that consist of a supply unit and one inverter unit, the supply unit can becontrolled through the inverter unit. (In drive systems consisting of multiple inverterunits, this feature is not typically used.) For example, the inverter unit can send acontrol word and references to the supply unit, enabling the control of both units fromthe interfaces of one control program.Note: This function is only supported by inverter units with a BCU control unit.For more information, refer to the firmware manual of the other converter.TopologyThe control units of the supply unit and the inverter unit are connected by fiber opticcables. With BCU-x2 control units equipped with RDCO modules, CH1 of the inverteris connected to CH0 of the supply unit.An example connection with a BCU-based drive system is shown below.The fiber optic link specifications stated under Specifications of the fiber opticmaster/follower link (page 39) apply.CommunicationThe communication between the converters and the drive consists of data sets ofthree 16-bit words each. The inverter unit sends a data set to the supply unit, whichreturns the next data set to the inverter unit.The communication uses data sets 10 and 11, updated at 2 ms intervals. Data sets10 is sent by the inverter unit to the supply unit, while data set 11 is sent by the supplyunit to the inverter unit. The contents of the data sets are freely configurable, but dataset 10 typically contains the control word, while data set 11 returns the status word.With ACS880 single drives with a separate supply unit, the basic communication isinitialized by parameter 95.20 HW options word 1. If the supply unit is regenerative, itT = Transmitter; R = ReceiverInverter unit (INU)(BCU) Control unitRDCOCH1Supply unit (LSU)(BCU) Control unitRDCOCH0RT RT
