结构式文件编程语言（）也称为ST语言，是为可程式逻辑控制器（PLC）设计的程式语言，是相关的IEC 61131-3标准中支援几种语言之一。结构式文件编程语言是支援块状结构（block structured）的高阶语言，以Pascal为基础，语法也类似Pascal。所有IEC 61131-3的语言都支援IEC61131通用元素（IEC61131 Common Elements）。其变数及函式呼叫是由IEC61131通用元素所定，因此同一个程式中可以使用IEC 61131-3中的不同语言。 结构式文件编程语言类似于PASCAL及C语言，因此可利用与微电脑及个人电脑相同的程式设计技术，进行阶梯图所难以执行的复杂计算，完成程式的建立。常用的程式及回路可透过FB（功能区块）的建立轻易地重复利用。 结构式文件编程语言支援复杂的叙述及巢状指令： 范例. 简单的程式. TxtState := STATES[StateMachine]; CASE StateMachine OF 1: ClosingValve(); ELSE ;; BadCase(); END_CASE; 另外一个结构式文件的程式范例. // 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 函式方块范例. // 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