computer science

Programmable input/output

Programmable input/output 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 Programmable input/output rather than just read about it. In short: In embedded systems and other computers, a programmable input/output (programmable IO, PIO) is a piece of hardware that manages input/output pins (such as GPIO) without requiring the constant attention of the CPU – essentially one that performs bit-banging in place of the CPU. Its behavior is determined by a program uploaded to the PIO chip by the CPU.

Key takeaways

Programmable input/output 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 Programmable input/output to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Programmable input/output from memory before moving on to harder problems.

Reference excerpt

In embedded systems and other computers, a programmable input/output (programmable IO, PIO) is a piece of hardware that manages input/output pins (such as GPIO) without requiring the constant attention of the CPU – essentially one that performs bit-banging in place of the CPU. Its behavior is determined by a program uploaded to the PIO chip by the CPU. It communicates with the CPU using interrupts.

Embedded systems Some microcontrollers include a PIO module to improve I/O performance. Two classic examples of embedded PIO include the PIO of Raspberry Pi Pico (RP2040; 2021) and the FlexIO from NXP (KL43; 2010s). Much has been written about the PIO module of the RP2040 because of its low cost and educational focus. The RP2040 has two PIO modules, each of which has four hardware state machines, a RX FIFO, a TX FIFO, and a pair of shift registers. These state machines are programmed using a special assembly language (or equivalently, a syntactical transliteration from MicroPython). The PIO modules can access GPIO pins (only digitally), set/unset IRQ, and perform direct memory access. PIO can be used for UART serial communication, MIDI, and even send-only 10BASE-T and 100BASE-T Ethernet. The FlexIO from NXP predates the RP2040 PIO. It consists of 4 32-bit shifters, 4 16-bit timers, 8 bidirectional digital I/O pins, a number of configuration registers for each shifter and timer, and multiplexers for the input, timer, and output. It is programmed by setting the configuration registers so that the components chain together into the desired behavior. Official documentation is available for emulating UART, SPI, I2C, and I2S.

Industrial systems Industrial programmable I/O controllers are available, but they generally represent more complex systems than an embedded PIO. They commonly capable of analog I/O, RS-232, and RS-485. For example:

A EN 50155 PIO designed for railcar use contains its own CPU, an NXP Vybrid VF50N. An industrial "remote IO module" contains an Atmel SAM4E16E (Cortex-M4). It provides Ethernet access. A IEC 61131-3 PIO is described as functioning as a "local microcontroller".

FPGA There are dedicated PIO modules to be used with FPGA chips. These modules contain their own FPGA chip so they can perform the task in place of the main module.

See also Freescale 683XX, which has a Timing Processor Unit (TPU)

References

External links RP2040 PIO Emulator

Worked examples

Example 1 — a first encounter with Programmable input/output

Start with the simplest possible case. Write down what Programmable input/output 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 Programmable input/output 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 Programmable input/output 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 Programmable input/output

In research: Programmable input/output 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 Programmable input/output 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: Programmable input/output is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer buses, Computer engineering, Industrial computing, so understanding it makes those chapters shorter.
In everyday life: Look for Programmable input/output 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 Programmable input/output in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Programmable input/output 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 Programmable input/output out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Programmable input/output in simple terms?

Why does Programmable input/output 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 Programmable input/output?

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 Programmable input/output.