ABSTRACT
FBsprovideapathwaytointegrateestablishedautomationprogramminglanguages,suchasladder logic,instructionlist,orstructuredtext,intomoderncomponentarchitecture.However,theirapplicationextendspastsimplereplacementoflegacysystemsbecauseoftheinherentsupportfordistributed applicationsandabilitytoprovideaplatformformodelingandsimulatingwithwell-de¦nedinterfaces.IEC61499de¦nesthreeclassesofFBs-basicFBs,compositeFBs,andserviceinterfaceFBs-for
55.1 Introduction .................................................................................... 55-1 55.2Illustrative Example .......................................................................55-3 55.3Logic Encapsulated in Basic FB ....................................................55-7 55.4Extension ..........................................................................................55-7 55.5Distribution .....................................................................................55-9 55.6Communication FBs .................................................................... 55-10 55.7 Communication Using Services of Internet
Protocol Suite ........................................................................ 55-10 55.8Adding Distribution and Communication
to the Sample System ....................................................................55-13 55.9Internals of Communication FBs: Modbus ..............................55-15 55.10Communication via the CIP ....................................................... 55-17 55.11Impact of Communication Semantics on Application
Behavior.......................................................................................... 55-19 55.12Failures in Distributed Applications .........................................55-20 55.13Conclusion .....................................................................................55-20 References ..................................................................................................55-21
capturing and hiding platform-dependent functions of devices. Each FB has a set of input and output variables.¥einputvariablesarereadbytheinternalalgorithmwhenitisexecuted,whiletheresults from the algorithm are written to the outputs.
