science

Instruction list

Instruction list is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Instruction list rather than just read about it. In short: Instruction list (IL) is one of the 5 languages supported by the initial versions of IEC 61131-3 standard, and subsequently deprecated in the third edition. It is designed for programmable logic controllers (PLCs).

Key takeaways

Instruction list belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Instruction list to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Instruction list from memory before moving on to harder problems.

Reference excerpt

Instruction list (IL) is one of the 5 languages supported by the initial versions of IEC 61131-3 standard, and subsequently deprecated in the third edition. It is designed for programmable logic controllers (PLCs). It is a low level language and resembles assembly. All of the languages share IEC61131 Common Elements. The variables and function call are defined by the common elements so different languages can be used in the same program. Program control (control flow) is achieved by jump instructions and function calls (subroutines with optional parameters). The file format has now been standardized to XML by PLCopen.

Example

Variations from IEC 61131 Many vendors whilst incorporating the full IEC 61131-3 requirements have additional vendor specific calls/function blocks to suit their hardware such as reading or writing to I/O. Siemens PLC instruction list language is known as "Statement List" or "STL" in English, and "Anweisungs-Liste" or "AWL" in German, Italian and Spanish. The user of a Simatic development package may choose between German and International mnemonics to represent instructions. For example, "A" for "AND" or "U" for "UND", "I" for "Input" or "E" for "Eingang".

Worked examples

Example 1 — a first encounter with Instruction list

Start with the simplest possible case. Write down what Instruction list claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Instruction list before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Instruction list ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Instruction list

In research: Instruction list appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Instruction list in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Instruction list is common in secondary-school and first-year university syllabi. It links to neighbouring topics IEC 61131-3, Programmable logic controllers, Programming language topic stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Instruction list outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Instruction list in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Instruction list means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Instruction list out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Instruction list in simple terms?

Why does Instruction list matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Instruction list?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Instruction list.