Chapter 6. Service Request FunctionGFK-2950C February 2018 2776.1.2 Function Block DiagramThe SVC_REQ function requests the CPU to perform the special serviceidentified by the FNC operand.Parameters for SVC_REQ are located in the parameter block, which begins atthe reference identified by the PRM operand. The number of 16-bit referencesrequired depends on the type of special controller service being requested.The parameter block is used to store both the function's inputs and outputs.OperandsNote: Indirect referencing is available for all register references (%R, %P, %L, %W, %AI, and %AQ).Parameter Description Allowed Types Allowed Operands OptionalSolveOrderCalculated by the FBD editor. NA NA NoEN Enable input. When set to ON, theSVC_REQ executesBOOL data flow, I, Q, M, T, G, S, SA, SB, SC,discrete symbolic, I/O variableNoBit reference in anon-BOOLvariableI, Q, M, T, G, R, P, L, AI, AQ, W,non-discrete symbolic, I/O variableFNC Function number; Service Requestnumber. The constant or variable thatidentifies the requested service.INT, DINT, UINT,WORD, DWORDAll except %S - %SCYou can use data flow only if theparameter block requires only oneWORDIf you use a symbolic variable or anI/O variable, ensure that its ArrayDimension 1 property is set to avalue large enough to contain theentire parameter block.NoPRM The first word in the parameter blockfor the requested service. Successive16-bit locations store additionalparameters.INT, DINT, UINT,WORD, DWORDAll except flow, %S - %SC andconstantNoENO Set to ON unless an incorrectfunction number, incorrectparameters, or out-of-rangereferences are specified. SpecificSVC_REQ functions may haveadditional causes for failure.BOOL data flow, I, Q, M, T, G, non-discretesymbolic, I/O variableYesBit reference in anon-BOOLvariable.I, Q, M, T, G, R, P, L, AI, AQ, W,non-discrete symbolic, I/O variable
