Structured Text (ST) is a list of statements that are run in order.
Structured Text is one of the five programming languages defined the IEC 61131-3 standard.
You can build structured text code using these statement types:
| Statement Type | Examples |
|---|---|
| Assignment Statement |
Assigns a value to a variable. For example:
Running := TRUE; Setpoints[0] := 12.5; Setpoints[1] := Setpoints[0] + 2.5; |
| Function Call Statement |
Call a function discarding the return value. For example:
StartPump(); IncreaseTargetSetpoint( Increment:=5.5 ); |
| IF Statement |
Choose different statements to run depending on a condition.
For example:
IF Level < 2.5 THEN
State := 'Normal';
ELSE
State := 'High';
END_IF; |
| CASE Statement |
Run a block of statements based on a selector value.
For example:
CASE PumpState OF
0:
StateDescription := "Stopped";
1:
StateDescription := "Running";
2:
StateDescription := "Failed";
ELSE
StateDescription := "Invalid";
END_CASE; |
| FOR Statement |
Run statements a defined number of times.
For example:
Sum := 0;
FOR Index:=0 TO 3 DO
Sum := Sum + Values[ Index ];
END_FOR; |
| FOR EACH Statement |
Run statements for each item in a collection.
For example:
FOR EACH Item IN Collection DO
...
END_FOR; |
| WHILE Statement |
Run statements while a condition is true.
For example:
Index := 0;
Sum := 0;
WHILE Index < 10 DO
Sum := Sum + Values[ Index ];
Index := Index + 1;
END_WHILE; |
| REPEAT Statement |
Run statements until a condition is true.
For example:
Index := 0;
Sum := 0;
REPEAT
Sum := Sum + Values[ Index ];
Index := Index + 1;
UNTIL Index >= 10 END_REPEAT; |
| EXIT Statement |
Exit a loop statement early.
For example:
FOR Idx:=0 TO 9 DO
IF Flags[ Idx ] THEN
EXIT;
END_IF;
END_FOR; |
| RETURN Statement |
Return from a Program Unit early.
For example:
IF ProcessedFinished THEN
RETURN;
END_IF; |
In Fernhill SCADA you can use Structured Text code in:
To learn about IEC 61131-3 Common Elements you can use in ST programs and functions.
For the meaning of terms used in Fernhill SCADA.