PLC Structured Text Programming 語法整理

參考文獻: MELSEC-Q/L/F Structured Programming Manual (Fundamentals).pdf

• The ST language is a text language with a similar grammatical structure to the C language.
• Controls such as conditional judgement and repetition process written in syntax can be described.
• This language is suitable for programming complicated processes that cannot be easily described by a graphic language (structured ladder/FBD language).

Operators & Data Types

• Operators

• Data Types

Syntax

• Assignment
• 格式：<Left side> := <Right side>;
• 範例
• intV1 := 0;
• intV2 := 2;
• Array type labels
• The data type and the number of elements need to be the same for left side and right side.
• intAry1 := intAry2;
• Structure labels
• The data type (structured data type) needs to be the same for left side and right side.
• dutVar1 := dutVar2;

• IF THEN Conditional Syntax
• 格式：

  IF <Boolean expression> THEN     <Syntax ...>; END_IF;

• 範例

  IF bool1 THEN     intV1 := intV1 + 1; END_IF

• IF ...ELSE Conditional Syntax
• 格式：

  IF <Boolean expression> THEN     <Syntax 1 ...>; ELSE     <Syntax 2 ...>; END_IF;

• 範例

  IF bool1 THEN     intV3 := intV3 + 1; ELSE     intV4 := intV4 + 1; END_IF;

• IF ...ELSEIF Conditional Syntax
• 格式：

  IF <Boolean expression 1> THEN     <Syntax 1 ...>; ELSIF <Boolean expression 2> THEN     <Syntax 2 ...>; ELSIF <Boolean expression 3> THEN     <Syntax 3 ...>; END_IF;

• 範例

  IF bool1 THEN     intV1 := intV1 + 1; ELSIF bool2 THEN     intV2 := intV2 + 1; ELSIF bool3 THEN     intV3 := intV3 + 1; END_IF;

• CASE Conditional Syntax
• 格式：

  CASE <Integer expression> OF     <Integer selection 1> : <Syntax 1 ...>;     <Integer selection 2> : <Syntax 2 ...>;     ·     ·     ·     <Integer selection n> : <Syntax n ...>; ELSE     <Syntax n+1 ...>; END_CASE;

• 範例

  CASE intV1 OF     1: bool1 := TRUE;     2: bool2 := TRUE; ELSE     intv1 := intv1 + 1; END_CASE;

• FOR ...DO Syntax
• 格式：

  FOR <Repeat variable initialization>     TO <Last value>     BY <Incremental expression> DO         <Syntax ...>; END_FOR;

• 範例

  FOR intV1 := 0     TO 30     BY 1 DO         intV3 := intV1 + 1; END_FOR;

• WHILE...DO Syntax
• 格式：

  WHILE <Boolean expression> DO     <Syntax ...>; END_WHILE;

• 範例

  WHILE intV1 = 30 DO     intV1 := intV1 + 1; END_WHILE;

• REPEAT...UNTIL Syntax
• 格式：

  REPEAT         <Syntax ...>;     UNTIL <Boolean expression> END_REPEAT;

• 範例

  REPEAT         intV1 := intV1 + 1;     UNTIL intV1 = 30 END_REPEAT;

• RETURN Syntax
• 格式：

  RETRUN;

• 範例

  IF bool1 THEN     RETURN; END_IF;

• EXIT Syntax
• 格式：

  EXIT;

• 範例

  FOR intV1 := 0     TO 10     BY 1 DO         IF intV1 > 10 THEN             EXIT;         END_IF; END_FOR;

Calling Functions

• 格式

  function_name(Var1, Var2, ...);

• 範例

  Output1 := ABS(Input1); Output1 := MAX(Input1, Input2, Input3); boolENO := MOV(boolEN, Input1, Output1);

Calling Function Blocks

• 格式

  instance_name(Input var1 := Var1, ... Output var1 := Var2, ...);

• 範例

  FBADD1(IN1 := Input1); Output1 := FBADD1.OUT1; FBADD2(IN1 := Input1, IN2 := Input2, IN3 := Input3); Output1 := FBADD2.OUT1; Output2 := FBADD2.OUT2;