National Instruments NI-DNET User Manual

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National Instruments NI-DNET User Manual Manual pdf 58 page image

Appendix A DeviceNet Overview© National Instruments Corporation A-11 NI-DNET User ManualFigure A-5 shows an example of four COS/cyclic I/O connections.Figure A-5. COS/Cyclic I/O ExampleAssembly ObjectsOne of the more important objects in the DeviceNet Specification is theAssembly Object. There are two types of Assembly Object: inputassemblies and output assemblies. Assembly objects act like a switchboard,routing incoming and outgoing data to its proper location within the device.Output assemblies receive an output message from an I/O connection anddistribute its contents to multiple attributes within the slave. Inputassemblies gather multiple attributes within the slave for transmission onan I/O connection.Figure A-6 shows the operation of input and output assemblies.MasterMAC ID = 1SlaveMAC ID = 9SlaveMAC ID = 11SlaveMAC ID = 12SlaveMAC ID = 13COS ACK to Slave6 Byte COSto SlaveEPR = 400 ms,no ACK4 Byte COS to MasterEPR = 200 ms2 Byte Cyclic to MasterEPR = 500 ms, no ACKCyclic ACKto Master12 Byte Cyclicto SlaveEPR = 100 msOutput dataInput data