General-purpose input/output

Last updated

A general-purpose input/output (GPIO) is an uncommitted digital signal pin on an integrated circuit or electronic circuit (e.g. MCUs/MPUs) board which may be used as an input or output, or both, and is controllable by software.

Contents

GPIOs have no predefined purpose and are unused by default. [1] [2] If used, the purpose and behavior of a GPIO is defined and implemented by the designer of higher assembly-level circuitry: the circuit board designer in the case of integrated circuit GPIOs, or system integrator in the case of board-level GPIOs.

Integrated circuit GPIOs

Integrated circuit (IC) GPIOs are implemented in a variety of ways. Some ICs provide GPIOs as a primary function whereas others include GPIOs as a convenient "accessory" to some other primary function. Examples of the former include the Intel 8255, which interfaces 24 GPIOs to a parallel communication bus, and various GPIO expander ICs, which interface GPIOs to serial communication buses such as I²C and SMBus. An example of the latter is the Realtek ALC260 IC, which provides eight GPIOs along with its main function of audio codec.

Microcontroller ICs usually include GPIOs. Depending on the application, a microcontroller's GPIOs may comprise its primary interface to external circuitry or they may be just one type of I/O used among several, such as analog signal I/O, counter/timer, and serial communication.

In some ICs, particularly microcontrollers, a GPIO pin may be capable of other functions than GPIO. Often in such cases it is necessary to configure the pin to operate as a GPIO (vis-á-vis its other functions) in addition to configuring the GPIO's behavior. Some microcontroller devices (e.g., Microchip dsPIC33 family) incorporate internal signal routing circuitry that allows GPIOs to be programmatically mapped to device pins. Field-programmable gate arrays (FPGA) extend this ability by allowing GPIO pin mapping, instantiation and architecture to be programmatically controlled.

Board-level GPIOs

Many circuit boards expose board-level GPIOs to external circuitry through integrated electrical connectors. Usually, each such GPIO is accessible via a dedicated connector pin.

Like IC-based GPIOs, some boards merely include GPIOs as a convenient, auxiliary resource that augments the board's primary function, whereas in other boards the GPIOs are the central, primary function of the board. Some boards, which are classified usually as multi-function I/O boards, are a combination of both; such boards provide GPIOs along with other types of general-purpose I/O. GPIOs are also found on embedded controller boards and Single board computers such as Arduino, BeagleBone, and Raspberry Pi. [3]

Board-level GPIOs are often given abilities which IC-based GPIOs usually lack. For example, Schmitt-trigger inputs, high-current output drivers, optical isolators, or combinations of these, may be used to buffer and condition the GPIO signals and to protect board circuitry. Also, higher-level functions are sometimes implemented, such as input debounce, input signal edge detection, and pulse-width modulation (PWM) output.

Usage

GPIOs are used in a diverse variety of applications, limited only by the electrical and timing specifications of the GPIO interface and the ability of software to interact with GPIOs in a sufficiently timely manner.

GPIOs usually employ standard logic levels and cannot supply significant current to output loads. When followed by an appropriate high-current output buffer (or mechanical or solid-state relay), a GPIO may be used to control high-power devices such as lights, solenoids, heaters, and motors (e.g., fans and blowers). Similarly, an input buffer, relay or opto-isolator is often used to translate an otherwise incompatible signal (e.g., high voltage) to the logic levels required by a GPIO.

Integrated circuit GPIOs are commonly used to control or monitor other circuitry (including other ICs) on a board. Examples of this include enabling and disabling the operation of (or power to) other circuitry, reading the states of on-board switches and configuration shunts, and driving light-emitting diode (LED) status indicators. In the latter case, a GPIO can, in many cases, supply enough output current to directly power an LED without using an intermediate buffer.

Multiple GPIOs are sometimes used together as a bit banging communication interface. For example, two GPIOs may be used to implement a serial communication bus such as Inter-Integrated Circuit (I²C), and four GPIOs can be used to implement a Serial Peripheral Interface (SPI) bus; these are usually used to facilitate serial communication with ICs and other devices which have compatible serial interfaces, such as sensors (e.g., temperature sensors, pressure sensors, accelerometers) and motor controllers. Taken to the extreme, this method may be used to implement an entire parallel bus, thus allowing communication with bus-oriented ICs or circuit boards.

Although GPIOs are fundamentally digital in nature, they are often used to control linear processes. For example, a GPIO may be used to control motor speed, light intensity, or temperature. Usually, this is done via PWM, in which the duty cycle of the GPIO output signal determines the effective magnitude of the process control signal. For example, when controlling light intensity, the light may be dimmed by reducing the GPIO duty cycle. Some linear processes require a linear control voltage. In such cases, it may be feasible to connect a GPIO, which is operated as a PWM output, to an RC filter to create a simple, low cost digital-to-analog converter.

Implementation

GPIO interfaces vary widely. In some cases, they are simple—a group of pins that can switch as a group to either input or output. In others, each pin can be set up to accept or source different logic voltages, with configurable drive strengths and pull ups/downs. Input and output voltages are usually, but not always, limited to the supply voltage of the device with the GPIOs, and may be damaged by greater voltages.

A GPIO pin's state may be exposed to the software developer through one of a number of different interfaces, such as a memory-mapped I/O peripheral, or through dedicated IO port instructions. Some GPIOs have 5 V tolerant inputs: even when the device has a low supply voltage (such as 2 V), the device can accept 5 V without damage.

A GPIO port is a group of GPIO pins (often 8 pins, but it may be less) arranged in a group and controlled as a group.

GPIO abilities may include: [2]

See also

Related Research Articles

<span class="mw-page-title-main">Microcontroller</span> Small computer on a single integrated circuit

A microcontroller or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of ferroelectric RAM, NOR flash or OTP ROM is also often included on chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips.

<span class="mw-page-title-main">Embedded system</span> Computer system with a dedicated function

An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.

<span class="mw-page-title-main">Universal asynchronous receiver-transmitter</span> Computer hardware device

A universal asynchronous receiver-transmitter is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Common signal levels are RS-232, RS-485, and raw TTL for short debugging links. Early teletypewriters used current loops.

<span class="mw-page-title-main">AVR microcontrollers</span> Family of microcontrollers

AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. These are modified Harvard architecture 8-bit RISC single-chip microcontrollers. AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to one-time programmable ROM, EPROM, or EEPROM used by other microcontrollers at the time.

<span class="mw-page-title-main">Single-board computer</span> Computer whose components are on a single printed circuit board

A single-board computer (SBC) is a complete computer built on a single circuit board, with microprocessor(s), memory, input/output (I/O) and other features required of a functional computer. Single-board computers are commonly made as demonstration or development systems, for educational systems, or for use as embedded computer controllers. Many types of home computers or portable computers integrate all their functions onto a single printed circuit board.

<span class="mw-page-title-main">TI MSP430</span>

The MSP430 is a mixed-signal microcontroller family from Texas Instruments, first introduced on 14 February 1992. Built around a 16-bit CPU, the MSP430 was designed for use with low power consumption embedded applications and for low cost.

Serial Peripheral Interface (SPI) is a de facto standard for synchronous serial communication, used primarily in embedded systems for short-distance wired communication between integrated circuits.

JTAG is an industry standard for verifying designs and testing printed circuit boards after manufacture.

<span class="mw-page-title-main">In-system programming</span> Embedded system programming technique

In-system programming (ISP), or also called in-circuit serial programming (ICSP), is the ability of some programmable logic devices, microcontrollers, chipsets and other embedded devices to be programmed while installed in a complete system, rather than requiring the chip to be programmed prior to installing it into the system. It also allows firmware updates to be delivered to the on-chip memory of microcontrollers and related processors without requiring specialist programming circuitry on the circuit board, and simplifies design work.

<span class="mw-page-title-main">Intel MCS-96</span> Family of microcontrollers (MCU) commonly used in embedded systems

The Intel MCS-96 is a family of microcontrollers (MCU) commonly used in embedded systems. The family is often referred to as the 8xC196 family, or 80196, the most popular MCU in the family. These MCUs are commonly used in hard disk drives, modems, printers, pattern recognition and motor control. In 2007, Intel announced the discontinuance of the entire MCS-96 family of microcontrollers. Intel noted that "There are no direct replacements for these components and a redesign will most likely be necessary."

<span class="mw-page-title-main">Chip select</span>

Chip select (CS) or slave select (SS) is the name of a control line in digital electronics used to select one of integrated circuits out of several connected to the same computer bus, usually utilizing the three-state logic.

Universal EXTension (UEXT) is a connector layout which includes power and three serial buses: Asynchronous, I2C, and SPI separately over 10 pins in a 2x5 layout. The connector layout was specified by Olimex Ltd and declared an open-project that is royalty-free in 2011, and was used in all their boards after 2004.

<span class="mw-page-title-main">Single-board microcontroller</span> Microcontroller built onto a single printed circuit board

A single-board microcontroller is a microcontroller built onto a single printed circuit board. This board provides all of the circuitry necessary for a useful control task: a microprocessor, I/O circuits, a clock generator, RAM, stored program memory and any necessary support ICs. The intention is that the board is immediately useful to an application developer, without requiring them to spend time and effort to develop controller hardware.

<span class="mw-page-title-main">XC800 family</span>

The Infineon XC800 family is an 8-bit microcontroller family, first introduced in 2005, with a dual cycle optimized 8051 "E-Warp" core. The XC800 family is divided into two categories, the A-Family for Automotive and the I-Family for Industrial and multi-market applications.

A gate driver is a power amplifier that accepts a low-power input from a controller IC and produces a high-current drive input for the gate of a high-power transistor such as an IGBT or power MOSFET. Gate drivers can be provided either on-chip or as a discrete module. In essence, a gate driver consists of a level shifter in combination with an amplifier. A gate driver IC serves as the interface between control signals and power switches. An integrated gate-driver solution reduces design complexity, development time, bill of materials (BOM), and board space while improving reliability over discretely-implemented gate-drive solutions.

<span class="mw-page-title-main">Arduino Uno</span> Microcontroller board

The Arduino Uno is an open-source microcontroller board based on the Microchip ATmega328P microcontroller (MCU) and developed by Arduino.cc and initially released in 2010. The microcontroller board is equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields) and other circuits. The board has 14 digital I/O pins, 6 analog I/O pins, and is programmable with the Arduino IDE, via a type B USB cable. It can be powered by a USB cable or a barrel connector that accepts voltages between 7 and 20 volts, such as a rectangular 9-volt battery. It has the same microcontroller as the Arduino Nano board, and the same headers as the Leonardo board. The hardware reference design is distributed under a Creative Commons Attribution Share-Alike 2.5 license and is available on the Arduino website. Layout and production files for some versions of the hardware are also available.

The MSP432 is a mixed-signal microcontroller family from Texas Instruments. It is based on a 32-bit ARM Cortex-M4F CPU, and extends their 16-bit MSP430 line, with a larger address space for code and data, and faster integer and floating point calculation than the MSP430. Like the MSP430, it has a number of built-in peripheral devices, and is designed for low power requirements. In 2021, TI confirmed that the MSP432 has been discontinued and "there will be no new MSP432 products".

<span class="mw-page-title-main">Arduino Nano</span> Single-board microcontroller

The Arduino Nano is an open-source breadboard-friendly microcontroller board based on the Microchip ATmega328P microcontroller (MCU) and developed by Arduino.cc and initially released in 2008. It offers the same connectivity and specs of the Arduino Uno board in a smaller form factor.

In digital electronics, a level shifter, also called level converter or logic level shifter, or voltage level translator, is a circuit used to translate signals from one logic level or voltage domain to another, allowing compatibility between integrated circuits with different voltage requirements, such as TTL and CMOS. Modern systems use level shifters to bridge domains between processors, logic, sensors, and other circuits. In recent years, the three most common logic levels have been 1.8V, 3.3V, and 5V, though levels above and below these voltages are also used.

<span class="mw-page-title-main">RP2040</span> ARM-architecture microcontroller by the Raspberry Pi Foundation

RP2040 is a 32-bit dual ARM Cortex-M0+ microcontroller integrated circuit by Raspberry Pi Ltd. In January 2021, it was released as part of the Raspberry Pi Pico board.

References

  1. ↑ White, Jon, ed. (2016). Raspberry Pi - The Complete Manual (7th ed.). Bournemouth, England, United Kingdom: Imagine Publishing. p. 36. ISBN   978-1785463709.
  2. 1 2 "General Purpose Input/Output". Oracle Java ME Embedded Developer's Guide (8 ed.). Oracle Corporation. 2014.
  3. ↑ "GPIO - Raspberry Pi Documentation". Raspberry Pi Foundation. Retrieved 3 November 2016.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.