Motor Jog Control Application Using a Siemens S7-1200 PLC with SCL Programming Language

Motor jog control is an industrial motor control technique that allows a motor to run for a short duration while a jog push button is pressed. When the button is released, the motor stops. It is commonly used for precise positioning, machine setup, conveyor alignment, and maintenance operations.

Functional schematic overview for the PLC application.

I/O and Internal Tags

Area	Tag	Type	Default	Description
INPUT	StartPB	Bool
INPUT	StopPB	Bool
INPUT	ResetPB	Bool
INPUT	AutoMode	Bool	TRUE
INPUT	EStopOK	Bool
INPUT	Permissive1	Bool
INPUT	Permissive2	Bool
INPUT	FeedbackOK	Bool
INPUT	FeedbackDelay	Time	T#3s
OUTPUT	RunCommand	Bool
OUTPUT	RunLamp	Bool
OUTPUT	ReadyLamp	Bool
OUTPUT	FaultLamp	Bool
OUTPUT	FaultCode	Int;		0 none, 1 estop, 2 permissive1, 3 permissive2, 4 feedback
VAR	StartPB	Bool
VAR	StopPB	Bool
VAR	ResetPB	Bool
VAR	AutoMode	Bool	TRUE
VAR	EStopOK	Bool
VAR	Permissive1	Bool
VAR	Permissive2	Bool
VAR	FeedbackOK	Bool
VAR	FeedbackDelay	Time	T#3s

SCL Program

// Application 002: Motor Jog Control

// Category: Motor and Drive Control

// PLC: Siemens S7-1200

// Language: SCL for TIA Portal

// Note: Training template. Validate all safety and machine behavior before commissioning.

 

FUNCTION_BLOCK "FB_002_MotorJogControl"

{ S7_Optimized_Access := 'TRUE' }

VERSION : 1.0

 

VAR_INPUT

    StartPB : Bool;

    StopPB : Bool;

    ResetPB : Bool;

    AutoMode : Bool := TRUE;

    EStopOK : Bool;

    Permissive1 : Bool;

    Permissive2 : Bool;

    FeedbackOK : Bool;

    FeedbackDelay : Time := T#3s;

END_VAR

 

VAR_OUTPUT

    RunCommand : Bool;

    RunLamp : Bool;

    ReadyLamp : Bool;

    FaultLamp : Bool;

    FaultCode : Int; // 0 none, 1 estop, 2 permissive1, 3 permissive2, 4 feedback

END_VAR

 

VAR

    RunLatch : Bool;

    FeedbackTimer : TON;

    FeedbackFault : Bool;

END_VAR

 

BEGIN

    IF ResetPB AND EStopOK AND Permissive1 AND Permissive2 THEN

        FeedbackFault := FALSE;

        FaultCode := 0;

    END_IF;

 

    IF NOT EStopOK THEN

        FaultCode := 1;

    ELSIF NOT Permissive1 THEN

        FaultCode := 2;

    ELSIF NOT Permissive2 THEN

        FaultCode := 3;

    ELSIF FeedbackFault THEN

        FaultCode := 4;

    END_IF;

 

    IF StopPB OR (FaultCode <> 0) OR NOT AutoMode THEN

        RunLatch := FALSE;

    ELSIF StartPB AND AutoMode AND EStopOK AND Permissive1 AND Permissive2 AND (FaultCode = 0) THEN

        RunLatch := TRUE;

    END_IF;

 

    RunCommand := RunLatch AND AutoMode AND EStopOK AND Permissive1 AND Permissive2 AND (FaultCode = 0);

 

    FeedbackTimer(IN := RunCommand AND NOT FeedbackOK, PT := FeedbackDelay);

    IF FeedbackTimer.Q THEN

        FeedbackFault := TRUE;

        RunLatch := FALSE;

        FaultCode := 4;

    END_IF;

 

    RunLamp := RunCommand AND FeedbackOK;

    ReadyLamp := AutoMode AND EStopOK AND Permissive1 AND Permissive2 AND (FaultCode = 0) AND NOT RunCommand;

    FaultLamp := FaultCode <> 0;

END_FUNCTION_BLOCK

Commissioning reminder: validate all I/O mapping, permissive behavior, feedback wiring, emergency-stop circuits, and local safety requirements before running real equipment.

Commissioning Checklist

·        Map every PLC tag to the correct physical input, output, HMI tag, or memory address.

·        Compile in TIA Portal and adjust tag names, timers, and setpoints for the real machine.

·        Test normal sequence, stop, reset, feedback failure, timeout, and alarm conditions in simulation first.

·        Use certified safety hardware or fail-safe logic for emergency stops, guards, and hazardous motion.