GE PACSystems RXi User Manual

Chapter 6. Program Organization106 PACSystems* RXi Distributed IO Controller User Manual GFK-2816FUsing Parameters with UDFBsUDFBs support up to 63 inputs and up to 64 outputs.Each UDFB has a predefined Boolean output parameter, Y0, which the CPU sets to trueupon each invocation of the block. Y0 can be controlled by logic within the block and providesthe output status of the block.The following table lists the TYPEs, LENGTHs, and parameter-passing mechanisms allowedfor UDFB parameters. For additional information on parameter passing, refer to Section6.1.7, Parameter Passing Mechanisms.Type Length Parameter Passing Mechanism Retentiveness of InstanceData for ParametersBOOL 1 to 256 INPUTS: by reference, constant reference,value, or value result. (Default: value)Not Applicable if passed byreference, since not stored ininstance data.Can be retentive (default) ornon-retentive for value or valueresult.OUTPUTS: by result; except Y0, which is byinitial-value resultRetentive (default) orNon-retentive.BYTE 1 to 1024 INPUTS: by reference, constant reference,value, or value result. (Default: value)Retentive for value or valueresult.Not applicable for referenceOUTPUTS: by resultINT, UINT, and WORD 1 to 512 INPUTS: by reference, constant reference,value, or value result. (Default: value)Retentive for value or valueresult.Not applicable for referenceOUTPUTS: by resultDINT, REAL, andDWORD1 to 256 INPUTS: by reference, constant reference,value, or value result. (Default: value)Retentive for value or valueresult.Not applicable for referenceOUTPUTS: by resultLREAL 1 to 128 INPUTS: by reference, constant reference,value, or value result. (Default: value)Retentive for value or valueresult.Not applicable for referenceOUTPUTS: by resultFunction block 1 INPUTS: by reference, constant reference,(Default: reference)Not applicable since passed byreferenceOUTPUTS: by resultUDFB4 1 INPUTS: by reference, constant reference,friendNot applicable since passed byreferenceOUTPUTS: not allowedUDT 1 to 1024 INPUTS: by reference, constant reference Not applicable since passed byreferenceOUTPUTS: not allowedIf an input parameter is passed by reference or by value result, it requires an argument. Allother parameters of a UDFB are optional. That is, they do not have to be given arguments oneach instance of the UDFB. If no argument is given for an optional parameter, the variableelement associated with the parameter retains the value it previously had.UDFB outputs cannot be passed as arguments to input parameters that are passed byreference or passed by value result. This restriction prevents modification of a UDFB output.4 A maximum of 16 input parameters can be of type UDFB.