結構式文件編程語言

結構式文件編程語言（英語：Structured text）也稱為ST語言，是為可程式邏輯控制器（PLC）設計的程式語言，是相關的IEC 61131-3標準中支援幾種語言之一^[1]。結構式文件編程語言是支援塊狀結構（block structured）的高階語言，以Pascal為基礎，語法也類似Pascal。所有IEC 61131-3的語言都支援IEC61131通用元素（IEC61131 Common Elements）。其變數及函式呼叫是由IEC61131通用元素所定，因此同一個程式中可以使用IEC 61131-3中的不同語言。

結構式文件編程語言類似於PASCAL及C語言，因此可利用與微電腦及個人電腦相同的程式設計技術，進行階梯圖所難以執行的複雜計算，完成程式的建立。常用的程式及迴路可透過FB（功能區塊）的建立輕易地重複利用。

結構式文件編程語言支援複雜的敘述及巢狀指令：

• 迴圈（REPEAT-UNTIL; WHILE-DO）
• 條件式執行（IF-THEN-ELSE; CASE）
• 函數（SQRT(), SIN()）

範例

簡單的程式

(* simple state machine *) TxtState := STATES[StateMachine]; CASE StateMachine OF  1: ClosingValve(); ELSE  ;; BadCase(); END_CASE; 

另外一個結構式文件的程式範例

// PLC configuration CONFIGURATION DefaultCfg  VAR_GLOBAL  b_Start_Stop : BOOL; // Global variable to represent a boolean.  b_ON_OFF : BOOL; // Global variable to represent a boolean.  Start_Stop AT %IX0.0:BOOL; // Digital input of the PLC (Address 0.0)  ON_OFF AT %QX0.0:BOOL; // Digital output of the PLC (Address 0.0). (Coil)  END_VAR  // Schedule the main program to be executed every 20 ms  TASK Tick(INTERVAL := t#20ms);  PROGRAM Main WITH Tick : Monitor_Start_Stop; END_CONFIGURATION PROGRAM Monitor_Start_Stop // Actual Program  VAR_EXTERNAL  Start_Stop : BOOL;  ON_OFF : BOOL;  END_VAR  VAR // Temporary variables for logic handling  ONS_Trig : BOOL;  Rising_ONS : BOOL;  END_VAR  // Start of Logic  // Catch the Rising Edge One Shot of the Start_Stop input  ONS_Trig := Start_Stop AND NOT Rising_ONS;    // Main Logic for Run_Contact -- Toggle ON / Toggle OFF ---  ON_OFF := (ONS_Trig AND NOT ON_OFF) OR (ON_OFF AND NOT ONS_Trig);   // Rising One Shot logic   Rising_ONS := Start_Stop; END_PROGRAM 

函式方塊範例

//======================================================================= // Function Block Timed Counter : Incremental count of the timed interval //======================================================================= FUNCTION_BLOCK FB_Timed_Counter  VAR_INPUT  Execute : BOOL := FALSE; // Trigger signal to begin Timed Counting  Time_Increment : REAL := 1.25; // Enter Cycle Time (Seconds) between counts  Count_Cycles : INT := 20; // Number of Desired Count Cycles  END_VAR    VAR_OUTPUT  Timer_Done_Bit : BOOL := FALSE; // One Shot Bit indicating Timer Cycle Done  Count_Complete : BOOL := FALSE; // Output Bit indicating the Count is complete   Current_Count : INT := 0; // Accumulating Value of Counter  END_VAR    VAR  CycleTimer : TON; // Timer FB from Command Library  CycleCounter : CTU; // Counter FB from Command Library  TimerPreset : TIME; // Converted Time_Increment in Seconds to MS  END_VAR    // Start of Function Block programming  TimerPreset := REAL_TO_TIME(in := Time_Increment) * 1000;   CycleTimer(  in := Execute AND NOT CycleTimer.Q,  pt := TimerPreset);  Timer_Done_Bit := CycleTimer.Q;    CycleCounter(  cu := CycleTimer.Qa,  r := NOT Execute,  pv := Count_Cycles);   Current_Count := CycleCounter.cv;  Count_Complete := CycleCounter.q;   END_FUNCTION_BLOCK 

参考文献

1. . [2015-03-19]. （原始内容存档于2015-04-02）.