ABB DCS 系统 培训课程 系列讲座 Code sorting.docx

ABB DCS 系统 培训课程 系列讲座 Code sorting.docx

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ABBDCS系统培训课程系列讲座Codesorting

Chapter18Codesorting

18.1GeneralInformation

18.1.1Description

Thischapterdescribesthedifferentmethodsofcodesortingandhowtohandleloops.

18.1.2Objectives

Oncompletionofthischapteryouwillbeableto:

∙Describethedifferencesbetweendifferentmethodsofcodesorting

∙Describetheadvantagesofeachmethod

∙Analyzeandsolveloopsintheprogramcode.

18.1.3ReferenceDocumentation

Usetheonlinehelp:

Contentstab,ControlModuleDiagramEditor>WorkingwithControlModules

18.2

Lesson1-Codesorting

18.2.1Description

Thischapterdescribesthedifferentmethodsofcodesortingandhowtohandleloops.

18.2.2Objectives

Oncompletionofthislessonyouwillbeableto:

∙Describethedifferencesbetweendifferentmethodsofcodesorting

∙Describetheadvantagesofeachmethod

∙Analyzeandsolveloopsintheprogramcode.

18.2.3AccordingtoIEC61131-3

Theexecutionorderoffunctionblocksfollowstheprogramflowasimplementedbytheprogrammer.

18.2.4ControlModuleCodeSorting-introduction

ForControlModules,thecompileranalyzeseachcodeblock（ST,IL,FBD,andLD-SFCistreatedsomewhatdifferently,seeremarkbelow）separatelywithrespecttowhichvariablesthatarereadandwritten,respectively,byeachblock.Thecompilerthendeterminestheoptimalexecutionorder.Acodeblockthatassignsavaluetoavariablehastobeexecutedbeforetheblockthatreadsthevariablevalue（comparefigurebelowinwhichthecodeblockincontrolmodule1mustbeexecutedbeforethecodeblockincontrolmodule2）.

Thetechniqueiscalledcodesortingandmeansthattheoptimalexecutionorderwillbebasedondataflowinsteadofprogramflow（asisthecaseforfunctionblocks）.Codesortingguaranteesthatthecodewillbeexecutedincorrectorder.Codesortingsuppressestime-delaysandresultsinthatanewcontrolmoduleautomaticallybecomescorrectlyplacedintheprocess.

ForanyfromcontrolmodulescalledFunctionBlocks,itisonlytheparameterinterface（In,Out,orIn_out）thataffectsthecode-blocksorting.Thatis,noanalysisismadeonhowtheFunctionBlocksactuallyusetheparameters.Inaddition,FunctionBlockreferencestoexternalvariablesdonotaffecttheexecutionorderofcontrolmodulecodeblocks.

Codesortinghasnoeffectoncontrolmodulesconnectedtodifferenttasks.

WithinaSFCcodeblockonlytheNactionparts（notP1orP2actions）aresorted.

18.2.5Loophandling

However,incaseboththecontrolmodulesusethesamevariableforbothreadingandwriting,thecompilergivesawarningmessagethataloopexists,meaningthattheexecutionordercannotberesolved:

Thiscaseyieldsthefollowingerrorinformation:

Intheexampleabove,theRequestvaluedeterminestheDelivervalue,which,inturn,determinestheRequestvalue.Thisconditionisshownintheautomaticallygeneratedtextfile,wherethefigureswithinparenthesesrefertowhichcodeblocktherespectiveparameterdependson.Providedthatcirculardependenceactuallyexists（andisnotmerelyaresultofaprogrammingerror）,theproblemcanbesolvedbyassigningaState-qualifiertotheDeliveredvariableandintroducinganewcodeblockinControlModule1,Code_Block_12:

Theloopdependencyisnoweliminated;Delivered:

oldstoresthevaluefromthepreviousscanandDelivered:

newcontainstheupdatedvaluefromthecurrentscan.Hence,theexecutionorderbecomesCode_Block_11-Code_Block_21-Code_Block_12.Theapproachisparticularlyvaluableforcomplexapplications,whicharedifficulttomonitormanually.

18.2.5.1RemarksonState

Statecanonlybespecifiedforlocalvariablesoftypebool,int,uint,dint,andreal.IfyouforsomereasonwanttooverridethesortingandtherebyavoidtheStateimplications,youcanassignthenosortattributetothevariable.

18.2.5.2RemarksonNoSort

Incorrectlyused,thenosortattributemaycauseimproperexecutionandapplicationfailure.Nosortshouldtypicallybeusedonlywhenthecodeblockconnectionsthemselvesunambiguouslydeterminetheexecutionorder

Usenosortonlyifyouknowthedataflowcharacteristicsindetail.

18.2.6

CodeSortingAdvantages

Theadvantagesofcodesortingarebestillustratedwithacoupleofexamples:

FirstconsideraPIDcascadeloop（usedforupdatingthePIDintegratorsincaseofmanualoperation）,inwhichdataflowinbothdirectionsbetweenthemasterandtheslave.Thisishandledbythe"Back"codeblocksattheendofthescan.Thisisnotpossibletodowithfunctionblocksifyouwanttoworkinanobject-orientedwayandavoidtimedelays.

Second,nowconsideranapplicationaccordingtotheillustrationbelow.Let'ssaythatsometimeaftertheapplicationwassetup,theneedforathirdconveyerarises.Becauseofthecodesorting,aControlModulerepresentingthefunctionalityofthenewconveyerbecomesaddedandconnectedintherightplaceintheapplicationlogic（providedthattheapplicationhasbeenproperlydesignedinthespecificationphase）.

18.3Exercise18.1–Codesorting

Pleasedoexercise18.1

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TABLEOFCONTENTS

Chapter18Codesorting1

18.1GeneralInformation1

18.1.1Description1

18.1.2Objectives1

18.1.3ReferenceDocumentation1

18.2Lesson1-Codesorting2

18.2.1Description2

18.2.2Objectives2

18.2.3AccordingtoIEC61131-32

18.2.4ControlModuleCodeSorting-introduction2

18.2.5Loophandling3

18.2.5.1RemarksonState4

18.2.5.2RemarksonNoSort4

18.2.6CodeSortingAdvantages5

18.3Exercise18.1–Codesorting6

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