computer science

Keyboard controller (computing)

Keyboard controller (computing) is a computer 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 Keyboard controller (computing) rather than just read about it. In short: In computing, a keyboard controller is a device that interfaces a keyboard to a computer. Its main function is to inform the computer when a key is pressed or released.

Key takeaways

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

Reference excerpt

In computing, a keyboard controller is a device that interfaces a keyboard to a computer. Its main function is to inform the computer when a key is pressed or released. When data from the keyboard arrives, the controller raises an interrupt (a keyboard interrupt) to allow the CPU to handle the input. If a keyboard is a separate peripheral system unit (such as in most modern desktop computers), the keyboard controller is not directly attached to the keys, but receives scancodes from a microcontroller embedded in the keyboard via some kind of serial interface. In this case, the controller usually also controls the keyboard's LEDs by sending data back to keyboard through the wire. The IBM PC AT used an Intel 8042 chip to interface to the keyboard. This chip had two additional functions: it controlled access to the Intel 80286 CPU's A20 line in order to implement a workaround for a chip bug, and it was used to initiate a software CPU reset in order to allow the CPU to transition from protected mode to real mode because the 286 did not allow the CPU to go from protected mode to real mode unless the CPU is reset. The latter was a problem because the BIOS and services provided by real mode operating systems such as MS-DOS and similar operating systems could only be called by programs in real mode. These behaviors have been used by plenty of software that expects this behavior, and therefore keyboard controllers have continued controlling the A20 line and performing software CPU resets even when the need for a reset via the keyboard controller was obviated by the Intel 80386's ability to switch to real mode from protected mode without a CPU reset. The keyboard controller also handles PS/2 mouse input if a PS/2 mouse port is present.

Modern interface Today the keyboard controller is either a unit inside a Super I/O device or is missing, having its keyboard and mouse functions handled by a USB controller and its role in controlling the A20 line becoming integrated into the chipset's northbridge and then later into the CPU's built-in integrated memory controller.

See also Keyboard buffer AT keyboard KVM extender Embedded controller: The Intel 8042 and other keyboard controllers used in computers based on the IBM PC/AT design can be considered embedded controllers.

References

External links KBD43W13 Keyboard and PS/2 Mouse Controller

Illustrations

Worked examples

Example 1 — a first encounter with Keyboard controller (computing)

Start with the simplest possible case. Write down what Keyboard controller (computing) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer 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 Keyboard controller (computing) 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 Keyboard controller (computing) 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 Keyboard controller (computing)

In research: Keyboard controller (computing) appears in computer 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 Keyboard controller (computing) 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: Keyboard controller (computing) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer hardware stubs, Computer keyboards, Microcontrollers, so understanding it makes those chapters shorter.
In everyday life: Look for Keyboard controller (computing) 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 Keyboard controller (computing) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Keyboard controller (computing) 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 Keyboard controller (computing) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Keyboard controller (computing) in simple terms?

In computing, a keyboard controller is a device that interfaces a keyboard to a computer. Its main function is to inform the computer when a key is pressed or released.

Why does Keyboard controller (computing) matter?

Because it connects several computer 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 Keyboard controller (computing)?

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 Keyboard controller (computing).