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