Learn BECKHOFF-TWINCAT with Real Code Examples

Updated Nov 27, 2025

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Code Sample Descriptions

Simple Output Toggle (Structured Text)

IF Input_Signal THEN
    DO_Toggle := NOT DO_Toggle
END_IF

Toggles a digital output whenever an input signal is TRUE.

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Motor Start Logic

IF Start_Button AND NOT Stop_Button THEN
    Motor_Running := TRUE
ELSE
    Motor_Running := FALSE
END_IF

Starts the motor when Start is pressed and Stop is not active.

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Analog Scaling Function

Scaled_Value := (AI_Raw - 0) * (100.0 - 0.0) / (27648 - 0)

Scales a raw analog input to engineering units.

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Timer Example (TON)

TON_1(IN := Enable_Signal, PT := T#5S)
IF TON_1.Q THEN
    Output_Signal := TRUE
END_IF

Runs a TON timer when input is true and sets an output.

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Rising Edge Detection

R_TRIG_1(CLK := Input_Flag)
IF R_TRIG_1.Q THEN
    Pulse_Output := TRUE
END_IF

Detects rising edges of a boolean input.

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Basic PID Control Assignment

PID_1.PV := Tank_Level
PID_1.SP := Level_Setpoint
Controller_Output := PID_1.CV

Assigns process variables into a PID block.

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Fault Latching Logic

IF Fault_Signal THEN
    Fault_Latched := TRUE
END_IF
IF Reset_Button THEN
    Fault_Latched := FALSE
END_IF

Latches a fault until reset is pressed.

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Counter Up Logic

CTU_1(CU := Pulse_In, R := Reset_Counter, PV := 100)
Pulse_Count := CTU_1.CV

Counts the number of pulses received.

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Mode Selection (Auto/Manual)

IF Mode_Select = 1 THEN
    Auto_Mode := TRUE
    Manual_Mode := FALSE
ELSE
    Auto_Mode := FALSE
    Manual_Mode := TRUE
END_IF

Switches control mode based on selector input.

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Emergency Stop Logic

IF EStop_Active THEN
    All_Outputs := FALSE
END_IF

Turns off all outputs when E-Stop is active.

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Code Sample Descriptions

Simple Output Toggle (Structured Text)

IF Input_Signal THEN
    DO_Toggle := NOT DO_Toggle
END_IF

Toggles a digital output whenever an input signal is TRUE.

Let’s Try →

Motor Start Logic

IF Start_Button AND NOT Stop_Button THEN
    Motor_Running := TRUE
ELSE
    Motor_Running := FALSE
END_IF

Starts the motor when Start is pressed and Stop is not active.

Let’s Try →

Analog Scaling Function

Scaled_Value := (AI_Raw - 0) * (100.0 - 0.0) / (27648 - 0)

Scales a raw analog input to engineering units.

Let’s Try →

Timer Example (TON)

TON_1(IN := Enable_Signal, PT := T#5S)
IF TON_1.Q THEN
    Output_Signal := TRUE
END_IF

Runs a TON timer when input is true and sets an output.

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Rising Edge Detection

R_TRIG_1(CLK := Input_Flag)
IF R_TRIG_1.Q THEN
    Pulse_Output := TRUE
END_IF

Detects rising edges of a boolean input.

Let’s Try →

Basic PID Control Assignment

PID_1.PV := Tank_Level
PID_1.SP := Level_Setpoint
Controller_Output := PID_1.CV

Assigns process variables into a PID block.

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Fault Latching Logic

IF Fault_Signal THEN
    Fault_Latched := TRUE
END_IF
IF Reset_Button THEN
    Fault_Latched := FALSE
END_IF

Latches a fault until reset is pressed.

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Counter Up Logic

CTU_1(CU := Pulse_In, R := Reset_Counter, PV := 100)
Pulse_Count := CTU_1.CV

Counts the number of pulses received.

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Mode Selection (Auto/Manual)

IF Mode_Select = 1 THEN
    Auto_Mode := TRUE
    Manual_Mode := FALSE
ELSE
    Auto_Mode := FALSE
    Manual_Mode := TRUE
END_IF

Switches control mode based on selector input.

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Emergency Stop Logic

IF EStop_Active THEN
    All_Outputs := FALSE
END_IF

Turns off all outputs when E-Stop is active.

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