case_of
Use case_of to select what to do based on a numerical value.
Operands
case
numeric_expression of
selector1: statement;
selectorN: statement;
else
Structured Text
Operand | Type | Format | Enter |
|---|---|---|---|
Numeric_ expression | SINT INT DINT REAL | Tag expression | Tag or expression that evaluates to a number (numeric expression) |
Selector | SINT INT DINT REAL | Immediate | Same type as numeric_expression |
IMPORTANT:
If using REAL values, use a range of values for a selector because a
REAL value is more likely to be within a range of values than an exact match of one,
specific value.
Description
The syntax is described in the table.
These are the syntax for entering the selector values.
When selector is | Enter |
One value | value: statement |
Multiple, distinct values | value1, value2, valueN : <statement> Use a comma (,) to separate each value. |
A range of values | value1..valueN : <statement> Use two periods (..) to identify the range. |
Distinct values plus a range of values | valuea, valueb, value1..valueN : <statement> |
The
case
construct is similar to a switch statement in the C or C++ programming
languages. With the case
construct, the controller executes only the statements that
associated with the first matching selector value. Execution always breaks after the
statements of that selector and goes to the end_case
statement.Affects Math Status Flags
No
Major/Minor Faults
None
Example
If you want this | Enter this structured text |
If recipe number = 1 then Ingredient A outlet 1 = open (1) Ingredient B outlet 4 = open (1) | case recipe_number of |
1: Ingredient_A.Outlet_1 :=1; Ingredient_B.Outlet_4 :=1; | |
If recipe number = 2 or 3 then Ingredient A outlet 4 = open (1) Ingredient B outlet 2 = open (1) | 2,3: Ingredient_A.Outlet_4 :=1; Ingredient_B.Outlet_2 :=1; |
If recipe number = 4, 5, 6, or 7 then Ingredient A outlet 4 = open (1) Ingredient B outlet 2 = open (1) | 4..7: Ingredient_A.Outlet_4 :=1; Ingredient_B.Outlet_2 :=1; |
If recipe number = 8, 11, 12, or 13 then Ingredient A outlet 1 = open (1) Ingredient B outlet 4 = open (1) | 8,11..13 Ingredient_A.Outlet_1 :=1; Ingredient_B.Outlet_4 :=1; |
Otherwise all outlets = closed (0) | else |
Ingredient_A.Outlet_1 [:=]0; Ingredient_A.Outlet_4 [:=]0; Ingredient_B.Outlet_2 [:=]0; Ingredient_B.Outlet_4 [:=]0; | |
end_case ; |
The [:=] tells the controller to also clear the outlet tags whenever the controller does the following:
Enters the RUN mode.
Leaves the step of an SFC if configuring the SFC for Automatic reset. This applies only embedding the assignment in the action of the step or using the action to call a structured text routine via a JSR instruction.
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