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 23, F8:2 temperature

Node 22, F8:1 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

A

B C

E

Ladder 2

Ladder 3

D

No Return Parameter Faults Processor