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
[编辑]簡單的程式
[编辑](* 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
[编辑]// 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
[编辑]//======================================================================= // 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