How do you control the order of executing different blocks of ST code?

Question

I have a process recipe with 8 steps, each of which I have defined in ST. The user should be able to however, select the order in which these 8 steps are executed. I'm trying to come up with flags or variables which could be used for this but drawing a blank so far. Does anyone have any thoughts on how this could be implemented?

Answer 1

My proposal is to let the user fill an array with the step numbers in the order how it should be executed. Then put your different blocks of ST code in a CASE statement. For the CASE-variable use the array. This way the order of execution is fully flexible.

Here is an Sandwich Decorator as an example. The important part starts at E_SandwichDecoratorStep.RecipeExecution

Enumerations:

TYPE E_SandwichDecoratorStep :
(
    UserSelecting := 1,
    RecipeExecution,
    Finished
);
END_TYPE

---

TYPE E_SandwichDecoratorUserRecipe :
(
    Pepperoni := 1,
    Ham,
    Cheese,
    Tomato,
    Salad,
    Sauce,
    Salt,
    Pepper
);
END_TYPE

Program:

PROGRAM SANDWICHDECORATOR
VAR
    arrnStepOrder       : ARRAY[1..8] OF E_SandwichDecoratorStep;   (*User Recipe Configuration*)

    bRestart            : BOOL;
    bUserRecipeStart    : BOOL; (*Start the execution of the Recipe*)
    eCurStep            : E_SandwichDecoratorStep;
    nCurUserRecipeIndex : INT := 1;
END_VAR

---

CASE eCurStep OF
    E_SandwichDecoratorStep.UserSelecting:
        (*Example Order*)
        arrnStepOrder[1] := E_SandwichDecoratorUserRecipe.Ham;
        arrnStepOrder[2] := E_SandwichDecoratorUserRecipe.Tomato;
        arrnStepOrder[3] := E_SandwichDecoratorUserRecipe.Pepperoni;
        arrnStepOrder[4] := E_SandwichDecoratorUserRecipe.Cheese;
        arrnStepOrder[5] := E_SandwichDecoratorUserRecipe.Salt;
        arrnStepOrder[6] := E_SandwichDecoratorUserRecipe.Sauce;
        arrnStepOrder[7] := E_SandwichDecoratorUserRecipe.Pepper;
        arrnStepOrder[8] := E_SandwichDecoratorUserRecipe.Salad;

        IF bUserRecipeStart THEN
            bUserRecipeStart := FALSE;
            eCurStep := E_SandwichDecoratorStep.RecipeExecution;
        END_IF

    E_SandwichDecoratorStep.RecipeExecution:
        IF nCurUserRecipeIndex <= E_SandwichDecoratorUserRecipe.Pepper THEN
            CASE arrnStepOrder[nCurUserRecipeIndex] OF
                E_SandwichDecoratorUserRecipe.Pepperoni:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Ham:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Cheese:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Tomato:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Salad:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Sauce:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Salt:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;

                E_SandwichDecoratorUserRecipe.Pepper:
                    nCurUserRecipeIndex := nCurUserRecipeIndex + 1;
            END_CASE
        ELSE
            nCurUserRecipeIndex := 1;
            eCurStep := E_SandwichDecoratorStep.Finished;
        END_IF

    E_SandwichDecoratorStep.Finished:
        IF bRestart THEN
            bRestart := FALSE;
            eCurStep := E_SandwichDecoratorStep.UserSelecting;
        END_IF

END_CASE