PLC 5 and ControlLogix Subroutine Parameters
Input Parameters Simple Example Three variable frequency drives heat sink temperatures input to PLC Temperatures input in degrees Celsius Convert to degrees Fahrenheit and display on operator interface
Option #1 Ladder Conversion Each time temperature input could add a rung to do calculations. This would make ladder file longer. More rungs Slower scan
Option #2 Subroutine Conversion Put conversion instructions in a subroutine Access subroutine each time conversion necessary Less rungs in ladder JSR input parameters used to move temperature data to subroutine
JSR Instructions with Parameters
Heat Sink Temperature from Three Different Sources Drive node 21 temperature to F8:0 Drive node 22 temperature to F8:1 Drive node 23 temperature to F8:2
JSR Sends Information to SBR JSR sends temperature information to SBR instruction input parameter address F8:10. Node 21, F8:0 temperature Node 22, F8:1 temperature Node 23, F8:2 temperature
Subroutine Shares Data - F8:10 is where temperature is stored. - F8:10 data used in calculation
CPT Destination Stores Result
Result, F8:11 to RET Output Parameter
Data Returned to JSR Data from RET instruction return parameter to JSR return parameter F8:12
Data Flow Ladder 2 A D E Ladder 3 C B
No Return Parameter Faults Processor