Why Do We Use MW40, MW42, MW44… Instead of MW40, MW41, MW42 in Siemens PLC Programming?

There is a small concept in Siemens PLC programming that often creates confusion for beginners:

Why do we use MW40, MW42, MW44, MW46… instead of MW40, MW41, MW42, MW43…?

At first, it may look like a simple numbering convention.

But it is actually related to how the PLC memory is organized.

Understanding this concept is important because incorrect memory addressing can create overlapping data, unexpected values, and difficult-to-troubleshoot PLC programs.

Let's understand it with a simple practical example.

 

First, Understand MB, MW and MD

Before understanding why MW addresses normally increase by 2, we need to understand three common Siemens memory formats.

MB – Memory Byte

MB represents one byte.

One byte contains:

8 bits

For example:

MB40

represents the byte located at memory address 40.

 

MW – Memory Word

MW represents a word.

A word contains:

2 bytes = 16 bits

Therefore:

MW40 = MB40 + MB41

This is the most important point to remember.

 

MD – Memory Double Word

MD represents a double word.

A double word contains:

4 bytes = 32 bits

Therefore:

MD40 = MB40 + MB41 + MB42 + MB43

This memory structure explains why address planning is important.

 

Why MW40, MW42, MW44?

Let's take a practical example.

Suppose we want to store four integer values:

Value 1 → MW40 = 30

Value 2 → MW42 = 50

Result → MW44 = 80

Final Output → MW46 = 80

Why did we select 40, 42, 44 and 46?

Because an MW occupies 2 bytes.

Therefore:

MW40 → MB40 + MB41

MW42 → MB42 + MB43

MW44 → MB44 + MB45

MW46 → MB46 + MB47

Notice something important.

Each word has its own two-byte area.

There is no overlap.

This makes the memory structure clear and predictable.

 

What Happens If We Use MW40 and MW41?

Now let's consider another example.

Suppose someone writes:

MW40

and then:

MW41

At first glance, it may look like two different words.

But let's look at the actual byte allocation.

MW40 → MB40 + MB41

While:

MW41 → MB41 + MB42

Now we have a problem.

MB41 is being used by both memory words.

This means the two MW areas overlap.

That can create unexpected behavior if both values are being written or used independently.

For beginners, this is one of the most important memory-addressing concepts to understand.

 

Visualizing the Memory

Think of PLC memory as a row of boxes.

For example:

MB40 | MB41 | MB42 | MB43 | MB44 | MB45 | MB46 | MB47

If we create:

MW40

it occupies:

MB40 + MB41

Then the next available two-byte word starts at:

MB42

So:

MW42 = MB42 + MB43

Then:

MW44 = MB44 + MB45

And:

MW46 = MB46 + MB47

This is why you commonly see even-numbered MW addresses.

The important principle is not that Siemens requires every MW address to be even.

The important principle is:

A Word occupies two consecutive bytes, so adjacent non-overlapping word storage is naturally allocated at 2-byte boundaries.

 

Practical TIA Portal Example

Let's take a simple addition program.

Suppose:

Value 1 = 30

stored in:

%MW40

and:

Value 2 = 50

stored in:

%MW42

We want the result to be stored in:

%MW44

The logic is:

%MW40 + %MW42 → %MW44

Therefore:

30 + 50 = 80

So:

%MW44 = 80

Now suppose we want to transfer the result to another memory location.

We can use a MOVE instruction:

%MW44 → %MW46

The final result becomes:

%MW46 = 80

The memory allocation looks like this:

%MW40 → Value 1 → 30

%MW42 → Value 2 → 50

%MW44 → Result → 80

%MW46 → Final Output → 80

This is a very simple example, but it teaches an important PLC programming principle:

Plan your memory addresses properly.

 

Why Does This Matter in Real Industrial Projects?

A beginner may think:

"If the PLC accepts the address, why should I worry about it?"

Because industrial PLC programs can become very large.

A machine may have:

• Hundreds of signals
• Hundreds of calculations
• Multiple motors
• Multiple drives
• Analog values
• Production counters
• Setpoints
• Alarm values
• Recipe parameters
• Communication data

If memory addresses are not planned properly, troubleshooting can become difficult.

Imagine a technician is troubleshooting a machine.

The engineer expects:

MW40 = Motor Speed

But because of overlapping memory usage, another program operation changes a byte that is part of MW40.

Suddenly, the motor-speed value may change unexpectedly.

The technician may initially suspect:

• Sensor problem
• Communication problem
• PLC hardware problem
• Analog input problem
• Scaling problem

when the real problem is simply incorrect memory addressing.

 

Understanding Byte-Level Memory Helps Troubleshooting

This is why PLC programmers should not only learn Ladder Logic.

They should also understand how the PLC stores data.

For example, if you know:

MW40 = MB40 + MB41

you can investigate the memory at the byte level.

If a value is unexpected, you can check:

• Which byte is being modified?
• Which instruction is writing to the memory?
• Is another word using the same byte?
• Is a byte instruction affecting a word?
• Is a double-word instruction overlapping the same area?

This type of thinking makes troubleshooting much more systematic.

 

What About MD Addressing?

The same principle becomes even more important with Double Words.

An MD occupies four bytes.

For example:

MD40 → MB40 + MB41 + MB42 + MB43

If you then use:

MD44

it occupies:

MB44 + MB45 + MB46 + MB47

There is no overlap.

But if you use another double word beginning at a nearby address, you need to carefully check the byte ranges.

This becomes especially important when working with:

• DINT values
• REAL values
• Floating-point calculations
• Large counters
• Data communication
• Process values

 

What About SCL Programming?

The same memory concepts apply even when you move from Ladder Logic to SCL.

For example:

"Result" := "Value 1" + "Value 2";

"Final Output" := "Result";

Here, the programmer may work with symbolic tag names rather than directly writing addresses such as MW40 or MW42.

This is one reason symbolic programming is useful.

Instead of remembering:

MW40 = Value 1

you can use a meaningful name such as:

"Value_1"

Similarly:

MW42 → "Value_2"

MW44 → "Result"

MW46 → "Final_Output"

This can make programs much easier to understand.

However, even when using symbolic addressing, understanding the underlying memory structure remains valuable.

A good PLC programmer should know both:

What the variable means

and

How the PLC stores the data.

 

Direct Addressing vs Symbolic Addressing

In older PLC programs, you may frequently see addresses such as:

MW40

MW42

MW44

In newer TIA Portal projects, symbolic tags are often preferred because they improve readability.

For example:

Instead of:

MW40

we can have:

Motor_Speed

Instead of:

MW42

we can have:

Speed_Setpoint

Instead of:

MW44

we can have:

Speed_Error

This makes troubleshooting and program maintenance easier.

But when you work with existing machines, legacy programs, or direct memory addressing, understanding MB/MW/MD is extremely important.

 

A Simple Rule for Beginners

When working with Word data, remember:

WORD = 2 bytes

Therefore, if you want consecutive non-overlapping word locations, think:

MW40 → MW42 → MW44 → MW46 → MW48

For Double Word data:

DWORD = 4 bytes

So consecutive non-overlapping double-word locations would follow the byte boundaries accordingly.

The exact address you choose depends on the memory layout and the application, but always check the number of bytes occupied by the data type.

 

The Bigger Lesson

This small addressing concept teaches something much bigger.

PLC programming is not only about writing logic.

You also need to understand:

How data is stored.

How memory is organized.

How different data types occupy memory.

How instructions access that memory.

How overlapping addresses can create unexpected behavior.

When these fundamentals are clear, troubleshooting becomes much easier.

 

Final Thought

For beginners, MW40, MW42, MW44 may initially look like a simple numbering pattern.

But behind this pattern is an important concept:

A Memory Word occupies 2 bytes.

Therefore:

MW40 → MB40 + MB41

MW42 → MB42 + MB43

MW44 → MB44 + MB45

MW46 → MB46 + MB47

Whereas:

MW40 → MB40 + MB41

MW41 → MB41 + MB42

creates an overlapping byte area.

The goal is not simply to memorize:

"Always use even MW addresses."

The real lesson is:

Understand the memory structure and allocate addresses according to the size of the data.

And whenever possible, use meaningful symbolic tags in your TIA Portal projects for better readability and maintainability.

Small PLC concepts may look simple.

But these small concepts build strong PLC fundamentals.

And strong fundamentals lead to:

Better programming.

Faster troubleshooting.

Cleaner machine control.

More reliable automation systems.

Small PLC concepts → Strong PLC fundamentals → Better troubleshooting skills.

 

Are We Facing a Job Challenge or a Skill Challenge?

Every day, we hear two very different perspectives about employment.

Students say:
"We are facing challenges in getting jobs."

Industries say:
"We are facing challenges in finding skilled professionals."

Both statements can be true.

So, what is the real challenge?

Is it a job shortage?

Or is it a skill gap?

In many technical fields, the challenge is not simply the availability of jobs. A major challenge is ensuring that graduates and job seekers have the practical, technical, and behavioural skills that industries actually require.

This gap between education and employment has become an important issue that needs attention from students, educational institutions, trainers, industries, and policymakers.

 

 

The Gap Between Qualification and Employability

Today, thousands of students graduate every year with technical qualifications.

They have certificates.

They have degrees or diplomas.

They have studied theoretical concepts.

They have completed examinations.

But when they enter an industrial environment, they may face a very different reality.

Industry may expect them to:

• Read electrical drawings
• Understand industrial sensors
• Troubleshoot machines
• Program PLCs
• Understand pneumatics and hydraulics
• Work with HMIs and SCADA
• Understand industrial communication
• Follow safety procedures
• Diagnose machine faults
• Work in a production environment
• Communicate effectively with technicians and engineers

This creates a critical question:

Are we preparing students to pass examinations, or are we preparing them to solve real industrial problems?

The answer needs to be both.

Education provides the foundation.

Industry exposure converts that foundation into practical capability.

 

Let's Take a Simple Example

Suppose a manufacturing company announces:

20 openings for Automation Technicians.

Around 300 candidates apply.

On paper, many candidates may have relevant qualifications.

But after a practical assessment, the company discovers that only around 30 candidates are comfortable with practical areas such as:

• PLC programming
• Sensors
• Motor control
• Pneumatics
• Electrical troubleshooting
• Industrial automation
• Machine fault finding

After technical interviews, behavioral assessment, and other selection criteria, perhaps only 15 candidates are finally selected.

Now look at the situation from both sides.

From the student's perspective:

"There were 20 vacancies, but I could not get the job."

The student may feel that opportunities are limited.

From the industry's perspective:

"We had 20 vacancies, but finding 20 candidates with the required practical skills was difficult."

The company may feel that skilled manpower is limited.

Both perspectives are understandable.

This is where the skill gap becomes visible.

 

The Problem Is Not Only Technical Knowledge

When we talk about employability, we often focus only on technical skills.

But industrial employability is a combination of several capabilities.

A technically strong candidate should also develop:

Problem-Solving Skills

Machines do not always fail according to textbook examples.

A sensor may work intermittently.

A motor may trip after several hours.

A communication network may fail randomly.

A pneumatic cylinder may move slowly.

The engineer or technician must investigate the actual problem.

Troubleshooting Ability

Knowing PLC instructions is different from troubleshooting a real PLC-controlled machine.

A candidate should learn to ask:

What is the input condition?

What should happen?

What is actually happening?

Where is the signal lost?

This troubleshooting mindset is extremely valuable.

Communication Skills

Technical professionals work with operators, maintenance teams, production managers, engineers, vendors, and customers.

A person may have excellent technical knowledge but still struggle if they cannot communicate the problem and solution clearly.

 

Safety Awareness

Industrial work involves electrical systems, rotating equipment, pneumatic systems, hydraulic systems, robots, machines, and high-energy equipment.

Safety cannot be treated as an optional topic.

A skilled professional must understand that:

Productivity without safety is not sustainable productivity.

Education and Industry Need to Work Together

One of the strongest ways to reduce the skill gap is to create a closer connection between educational institutions and industries.

Educational institutions understand:

How to teach.

Industries understand:

What the workplace requires.

The combination of both can create much stronger workforce development.

For example, an automation training program can include:

PLC Programming

Students should not only learn instructions. They should develop actual machine-control programs.

Industrial Automation

Students should understand how sensors, actuators, controllers, drives, and machines work together.

Mechatronics

Students should integrate mechanical, electrical, electronics, and control concepts.

Pneumatics and Hydraulics

Students should understand real circuits, components, troubleshooting, and applications.

Robotics

Students should understand robot operation, programming, safety, and industrial applications.

Smart Manufacturing

Students should understand machine connectivity, data collection, monitoring, and digital manufacturing concepts.

Industry 4.0 and AI Applications

Students should understand where technologies such as IIoT, analytics, AI, and predictive maintenance can create practical value.

But there is another important element:

Hands-on practice.

 

Practical Training Changes the Learning Experience

There is a major difference between:

"I have studied PLC."

and

"I can troubleshoot a PLC-controlled machine."

There is a difference between:

"I have studied pneumatics."

and

"I can identify and troubleshoot a pneumatic circuit."

There is a difference between:

"I know Industry 4.0."

and

"I can connect machine data, visualize it, and use that information to improve a manufacturing process."

This is why practical training matters.

Students need opportunities to:

• Build circuits
• Program PLCs
• Operate machines
• Create HMI screens
• Troubleshoot faults
• Perform measurements
• Analyze machine problems
• Work on projects
• Visit industries
• Interact with industry professionals

The objective should be to transform knowledge into capability.

 

Industry Exposure Should Start Earlier

Industry exposure should not begin only after students graduate.

Students should interact with industry while they are still learning.

Industry visits, guest lectures, live projects, internships, apprenticeships, demonstrations, industrial case studies, and practical assessments can help students understand workplace expectations.

For example, a student may learn about a conveyor system in a classroom.

But seeing an actual production conveyor can answer many practical questions:

How are sensors positioned?

How are safety interlocks implemented?

How does the PLC control the sequence?

What happens when a sensor fails?

How does the maintenance team troubleshoot the problem?

What happens when production stops?

These experiences create a connection between theory and reality.

 

What Can Students Do?

Students also have an important responsibility.

Do not depend only on your certificate.

Build your skills.

If you are studying automation, don't just learn PLC theory.

Program a PLC.

If you are studying electrical engineering, don't just study circuit diagrams.

Understand real panels and troubleshooting.

If you are learning robotics, don't just learn terminology.

Work with a robot or simulation environment.

If you are learning Industry 4.0, don't just memorize definitions.

Build a small connected manufacturing project.

Create a portfolio.

Show what you can actually do.

In today's competitive environment, a candidate who can demonstrate practical capability can create a stronger impression than someone who can only present theoretical knowledge.

 

What Can Educational Institutions Do?

Educational institutions can strengthen employability by focusing on:

Industry-aligned curriculum

What skills are actually required in today's factories?

Hands-on laboratories

Students should spend significant time performing practical activities.

Real-world projects

Projects should solve realistic industrial problems.

Industry interaction

Bring industry professionals into the learning process.

Practical assessments

Don't assess only whether students remember concepts. Assess whether they can apply them.

Trainer development

Trainers also need continuous exposure to emerging industrial technologies.

Education itself must continuously evolve.

 

What Can Industry Do?

Industry also has a role.

Companies can support workforce development through:

• Apprenticeships
• Internships
• Industrial visits
• Guest lectures
• Curriculum feedback
• Live projects
• Skill assessments
• Industry-sponsored laboratories
• Trainer development programs
• Structured entry-level training

Instead of expecting every graduate to be completely job-ready from day one, industry and education can work together to build a stronger talent pipeline.

 

From Job Seekers to Problem Solvers

Perhaps the biggest change we need is a mindset change.

Students should not think only:

"How can I get a job?"

They should also think:

"What problems can I solve?"

Industry needs people who can contribute.

Someone who can troubleshoot a machine.

Someone who can reduce downtime.

Someone who can improve productivity.

Someone who can identify a process problem.

Someone who can implement automation.

Someone who can improve quality.

Someone who can learn new technology.

That is the difference between simply being a job seeker and becoming a problem solver.

 

The Future Requires Continuous Learning

Technology is changing rapidly.

PLC systems are becoming more connected.

Robotics is expanding.

AI is entering manufacturing.

Digital twins are becoming more practical.

Industrial data is becoming increasingly important.

Smart factories are evolving.

This means learning cannot stop after graduation.

A certificate may open the door, but continuous learning helps you stay relevant.

Professionals need to keep upgrading their skills throughout their careers.

 

So, Is It a Job Challenge or a Skill Challenge?

The answer is:

It can be both.

Some sectors and regions may genuinely have limited opportunities.

But at the same time, industries can struggle to find candidates with the right combination of technical knowledge, practical skills, problem-solving ability, communication, and workplace readiness.

The real opportunity is to reduce the gap between:

What education provides

and

What industry requires.

This is not the responsibility of students alone.

It is a shared responsibility.

Students must learn.

Institutions must adapt.

Trainers must upgrade.

Industries must engage.

And all stakeholders must work together.

 

Final Thought

The future workforce will not be defined only by degrees, diplomas, or certificates.

It will be defined by capability.

Can you understand the problem?

Can you apply your knowledge?

Can you operate the technology?

Can you troubleshoot the system?

Can you work safely?

Can you communicate?

Can you continuously learn?

If the answer is yes, you are moving toward true employability.

The goal should not simply be:

"Create more graduates."

The goal should be:

"Create more capable professionals."

Because when education and industry work together, the question changes from:

"Where are the jobs?"

to:

"How can we prepare more people to successfully take the opportunities that exist?"

The real challenge is not only creating jobs.

It is creating job-ready talent.

And closing that gap will require collaboration, practical training, industry exposure, continuous learning, and a strong commitment from everyone involved.

 

How to Start Learning SCL Programming in Siemens TIA Portal

Many PLC beginners start their programming journey with Ladder Logic (LAD) because it looks like traditional electrical control circuits.

And that's exactly where you should begin.

When a beginner sees contacts, coils, timers, counters, and interlocks in Ladder Logic, the relationship with conventional control panels is easy to understand.

Ladder Logic helps you visualize how a machine works.

It helps you understand:

• Inputs and outputs
• Start and stop commands
• Interlocks
• Permissive conditions
• Motor control
• Timers and counters
• Sequence control
• Alarm conditions

Once these fundamentals are clear, however, the next important step is to learn SCL – Structured Control Language in Siemens TIA Portal.

SCL does not replace Ladder Logic.

It complements it.

A good PLC programmer should understand both and, more importantly, know when to use each one.

 

Why Learn SCL?

As PLC programs become more complex, the amount of logic and data that needs to be processed also increases.

Consider a simple machine.

You may need to calculate:

• Production quantity
• Speed
• Temperature
• Pressure
• Flow
• Energy consumption
• Cycle time
• Production efficiency

You may also need to perform comparisons, mathematical calculations, data processing, and repetitive operations.

Ladder Logic can certainly perform many of these tasks.

But for calculation-heavy or data-processing applications, SCL can provide a much more compact and structured approach.

Instead of creating several graphical blocks, you can often express the same operation in a few lines of text.

This is one of the major advantages of SCL.

 

Start With a Very Simple Example

Suppose we have two INT variables:

Value_1

and

Value_2

We want to add them and store the result in another variable:

Result

In SCL, the basic concept can be represented as:

Result := Value_1 + Value_2;

This looks very simple.

But this single line introduces several important programming concepts.

And this is exactly where a beginner should start.

Don't begin SCL learning with complex machine sequences, arrays, loops, or advanced Function Blocks.

Start with simple operations.

Understand what each line means.

Then gradually increase the complexity.

 

Concept 1: Variables

The first important concept is variables.

A variable is used to store information that the PLC program needs to use.

For example:

Start_Command

Motor_Speed

Temperature

Production_Count

Pressure

Result

Different variables can have different data types.

For example:

BOOL can be used for TRUE/FALSE conditions.

INT can be used for integer values.

DINT can be used when a larger integer range is required.

REAL can be used for decimal or floating-point values.

WORD and DWORD can be used for bit-oriented or numerical data depending on the application.

Understanding variables is one of the foundations of SCL programming.

 

Concept 2: The Assignment Operator

One of the most important symbols in SCL is:

:=

This is called the assignment operator.

For example:

Result := Value_1 + Value_2;

It means:

Calculate Value_1 + Value_2 and assign the result to Result.

Another example:

Motor_Run := TRUE;

This means that TRUE is assigned to the variable Motor_Run.

Similarly:

Motor_Run := FALSE;

assigns FALSE to Motor_Run.

Once you understand the assignment operator, many SCL statements become easier to read.

 

Concept 3: Arithmetic Operations

SCL allows you to perform arithmetic operations directly in the program.

The basic operations include:

Addition (+)

Subtraction (-)

Multiplication (*)

Division (/)

For example:

Total := Quantity * Price;

or:

Average := Total / Count;

This is especially useful in industrial applications involving measurements and calculations.

For example, a PLC may receive a raw analog value and convert it into an engineering value.

You may need to calculate:

Temperature

Pressure

Flow

Speed

Level

Percentage

SCL can make these calculations easier to read and maintain.

 

Concept 4: Program Readability

One of the biggest advantages of SCL is readability.

Imagine a calculation that requires several mathematical operations.

In Ladder Logic, you may need several graphical blocks connected together.

In SCL, the same calculation may be expressed in a few lines.

For example:

Output := (Input_1 + Input_2) * Factor;

An experienced programmer can immediately understand the data flow.

This does not mean Ladder Logic is difficult or inferior.

LAD has a major advantage: visual understanding.

The point is that different programming languages provide different ways of representing the same control logic.

 

Concept 5: Understanding Data Flow

SCL also teaches an important programming concept:

Data flow.

Consider:

Sum := Value_1 + Value_2;

Average := Sum / Count;

First, the PLC calculates the sum.

Then that result is used to calculate the average.

This creates a clear flow:

Input → Calculation → Intermediate Result → Final Result

Understanding this type of data flow becomes increasingly important as PLC programs become larger.

 

Don't Jump Directly Into Advanced SCL

A common mistake beginners make is trying to learn everything at once.

They start with:

• Arrays
• Loops
• Structures
• Complex Function Blocks
• Advanced data types
• Large machine sequences

without first understanding basic Boolean logic and variables.

This often creates confusion.

A better approach is:

Start simple → Practice → Apply → Increase complexity

SCL is a programming language.

Like any language, you need to learn the basic vocabulary and grammar before writing complex programs.

 

Step 1: Convert Simple LAD Into SCL

One of the best methods for learning SCL is to take an existing Ladder Logic program and convert it into SCL.

Start with simple examples.

For example:

LAD: Start command → Motor ON

Then write the equivalent SCL logic.

Next:

LAD: Start + Stop + Interlock → Motor ON

Convert it into SCL.

Then move to:

LAD: Two sensors → Conveyor control

Convert it into SCL.

This approach is extremely effective because you already understand what the Ladder program is doing.

Now your objective is simply to express the same logic using SCL.

 

Step 2: Learn Boolean Logic

Before writing complex SCL programs, become comfortable with:

AND

OR

NOT

For example:

IF Safety_OK AND Start_Command THEN

    Motor_Run := TRUE;

END_IF;

Or:

IF Field_Start OR SCADA_Start THEN

    Start_Command := TRUE;

END_IF;

Parentheses are also important when combining multiple conditions.

The key is not to memorize syntax.

Understand the logic first.

 

Step 3: Learn IF...THEN...ELSE

Once Boolean logic is comfortable, move to decision-making statements.

For example:

IF Temperature > 80.0 THEN

    High_Temperature_Alarm := TRUE;

ELSE

    High_Temperature_Alarm := FALSE;

END_IF;

This is useful for:

• Alarms
• Interlocks
• Process conditions
• Equipment control
• Quality decisions
• Machine sequences

Again, start with small examples.

 

Step 4: Learn Timers, Counters and Comparisons

After IF statements, gradually introduce industrial functions.

Practice:

Timers

Counters

Greater than

Less than

Equal to

Not equal to

For example:

IF Pressure > Pressure_Limit THEN

    High_Pressure_Alarm := TRUE;

END_IF;

Then build a small machine application around it.

This is much more effective than learning individual instructions without understanding their purpose.

 

Step 5: Understand Data Types

As you progress, spend time understanding data types.

Start with:

• BOOL
• INT
• DINT
• REAL
• WORD
• DWORD

Then understand how different data types behave during calculations and assignments.

For example, if you are working with temperature values containing decimals, REAL may be appropriate.

If you are counting production parts, an integer-based data type may be more suitable.

Correct data-type selection is an important part of reliable PLC programming.

 

Step 6: Move to Advanced SCL

Once your fundamentals are strong, gradually move toward:

• CASE statements
• FOR loops
• WHILE loops
• Arrays
• Structures
• User-defined data types
• Functions
• Function Blocks
• Data Blocks
• Recipe management
• Data processing
• Sequence programming

At this stage, SCL becomes much more powerful.

But remember:

Advanced SCL is built on simple programming concepts.

 

SCL and Function Blocks

SCL becomes particularly powerful when combined with Function Blocks (FBs).

For example, you can develop a standard motor-control FB using SCL.

The FB could include:

• Start/stop logic
• Interlocks
• Permissives
• Trip handling
• Feedback monitoring
• Alarm generation
• Operating modes
• Status information

The same FB can then be reused for multiple motors with appropriate instance data.

This approach can make large automation programs more structured, reusable, and maintainable.

 

Should You Stop Using Ladder Logic?

Absolutely not.

Ladder Logic remains extremely valuable.

For many machine-control applications, LAD is excellent for:

• Motor control
• Interlocks
• Start/stop circuits
• Troubleshooting
• Maintenance
• Simple sequence logic

SCL becomes particularly useful when you have:

• Complex calculations
• Data processing
• Arrays
• Repetitive operations
• Complex conditions
• Structured algorithms
• Large data sets

Therefore, don't think:

LAD vs SCL

Think:

LAD + SCL

Use the right programming language for the right application.

 

A Practical SCL Learning Roadmap

For a beginner, I would recommend the following learning sequence:

Level 1 – PLC Fundamentals

Inputs → Logic → Outputs

↓

Level 2 – Ladder Logic

Contacts → Coils → Timers → Counters → Interlocks

↓

Level 3 – SCL Fundamentals

Variables → Assignment → Arithmetic

↓

Level 4 – Boolean Logic

AND → OR → NOT → Parentheses

↓

Level 5 – Decision Making

IF → THEN → ELSE → END_IF

↓

Level 6 – Data

BOOL → INT → DINT → REAL → WORD → DWORD

↓

Level 7 – Industrial Applications

Motor → Pump → Conveyor → Valve → Heating → Alarms

↓

Level 8 – Advanced SCL

CASE → Loops → Arrays → Structures → FBs

This gradual approach can make SCL much easier to learn.

 

Final Thought

SCL programming should not be treated as something completely different from Ladder Logic.

The control philosophy remains the same.

The programming representation changes.

Ladder Logic teaches you how the machine works visually.

SCL teaches you how to express that logic in a structured and scalable way.

A strong PLC programmer should be able to look at a problem and decide:

Should I use LAD?

Should I use SCL?

Should I use an FC?

Should I use an FB?

How should I structure the data?

That is the real programming skill.

Don't try to become an SCL expert in one day.

Start with one simple calculation.

Then one Boolean condition.

Then one IF statement.

Then one machine function.

Practice converting LAD into SCL.

Learn the logic first.

Learn the syntax second.

Apply it to real industrial problems third.

Because programming languages will continue to evolve, but the ability to understand logic, processes, machines, and problems will always remain the foundation of a good automation engineer.

LAD for visualization.

SCL for structure.

Logic for engineering.