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Generate Structured Text Code with VAR_IN_OUT Variables

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This example shows how to model and generate structured text code that has VAR_IN_OUT variables. A VAR_IN_OUT variable is an input and output variable that is a part of the function block interface. Use VAR_IN_OUT variables to pass values to the function block by using the pass by reference method.

Open the Model

open_system('GenerateVarInOutVariables.slx')

The model consists of a subsystem TriangleAreaCalculator at the top level that accepts three inputs a, b, and c. The subsystem contains :

  • A subsystem block CalculateTriangleSemiPerimeter that accepts a, b, and c as an input and generates an output s.

  • A MATLAB® Function block CalculateTriangleArea that accepts TriangleArea and s as inputs and generates TriangleArea as the output.

Model to Generate VAR_IN_OUT Variables

Generate VAR_IN_OUT variables by using a MATLAB Function block and declaring a function of type:

function x = function_name(x)
% body of function

Simulink® PLC Coder supports VAR_IN_OUT generation only from MATLAB Function blocks. This is the structure of the MATLAB Function Block:

function TriangleArea = fcn(s,TriangleArea)
intermediate_area = (s-TriangleArea.a)*(s-TriangleArea.b)*(s-TriangleArea.c); 
TriangleArea.area = sqrt(s*intermediate_area);

Generate Structured Text Code

To generate structured text code,

  1. In the Apps tab, click PLC Coder.

  2. In the PLC Coder tab, clock Settings > PLC Code Generation Settings. Change the Target IDE to 3S CodeSys 2.3. Click OK.

  3. Select the subsystem block. In the PLC Code tab, click Generate PLC Code.

Alternatively, to generate structured text code from the MATLAB command line, use the plcgeneratecode function.

generatedfiles = plcgeneratecode('GenerateVarInOutVariables/TriangleAreaCalculator');
### Generating PLC code for 'GenerateVarInOutVariables/TriangleAreaCalculator'.
### Using model settings from 'GenerateVarInOutVariables' for PLC code generation parameters.
### Begin code generation for IDE codesys23.
### Emit PLC code to file.
### Creating PLC code generation report GenerateVarInOutVariables_codegen_rpt.html.
### PLC code generation successful for 'GenerateVarInOutVariables/TriangleAreaCalculator'.
### Generated files:
plcsrc/GenerateVarInOutVariables.exp

The generated structured text code contains VAR_IN_OUT variable declarations. The MATLAB Function block takes the variable TriangleArea as an input and generates the same variable as the output.

FUNCTION_BLOCK TriangleAreaCalculator
VAR_INPUT
    a: LREAL;
    b: LREAL;
    c: LREAL;
END_VAR
VAR_OUTPUT
    TriangleArea_e: TriangleArea;
END_VAR
VAR
    i0_CalculateTriangleArea: CalculateTriangleArea;
END_VAR
(* Outputs for Atomic SubSystem: '<Root>/TriangleAreaCalculator' *)
(* BusCreator: '<S1>/Bus Creator' incorporates:
 *  MATLAB Function: '<S1>/CalculateTriangleArea'
 *  Outport: '<Root>/TriangleArea' *)
TriangleArea_e.area := 0.0;
TriangleArea_e.a := a;
TriangleArea_e.b := b;
TriangleArea_e.c := c;
(* Product: '<S3>/Divide' incorporates:
 *  Constant: '<S3>/Constant'
 *  Outport: '<Root>/TriangleArea'
 *  Sum: '<S3>/Add' *)
i0_CalculateTriangleArea(b_s := ((a + b) + c) / 2.0, TriangleArea_i := TriangleArea_e);
(* End of Outputs for SubSystem: '<Root>/TriangleAreaCalculator' *)
END_FUNCTION_BLOCK
FUNCTION_BLOCK CalculateTriangleArea
VAR_INPUT
    b_s: LREAL;
END_VAR
VAR_IN_OUT
    TriangleArea_i: TriangleArea;
END_VAR
(* MATLAB Function 'TriangleAreaCalculator/CalculateTriangleArea': '<S2>:1' *)
(* '<S2>:1:2' intermediate_area = (s-TriangleArea.a)*(s-TriangleArea.b)*(s-TriangleArea.c); *)
(* '<S2>:1:3' TriangleArea.area = sqrt(s*intermediate_area); *)
TriangleArea_i.area := SQRT((((b_s - TriangleArea_i.a)
 * (b_s - TriangleArea_i.b)) * (b_s - TriangleArea_i.c)) * b_s);
END_FUNCTION_BLOCK
TYPE TriangleArea:
    STRUCT
        area: LREAL;
        b: LREAL;
        c: LREAL;
        a: LREAL;
    END_STRUCT
END_TYPE

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