General-purpose input/output

General Purpose Input/Output (GPIO) is a generic pin on a chip whose behavior (including whether it is an input or output pin) can be controlled (programmed) through software.

GPIO pins have no special purpose defined, and go unused by default. The idea is that sometimes the system integrator building a full system that uses the chip might find useful to have a handful of additional digital control lines, and having these available from the chip can save the hassle of having to arrange additional circuitry to provide them. For example, the Realtek ALC260 chips (audio codec) have 8 GPIO pins, which go unused by default. Some system integrators (Acer laptops) employing the ALC260 use the first GPIO (GPIO0) to turn on the amplifier used for the laptop's internal speakers and external headphone jack.

Usage

GPIOs are used in:

• chips with pin scarcity: IC, SoC, embedded and custom hardware, programmable logic devices (e.g., FPGAs)
• multifunction chips: power managers, audio codecs, video cards
• embedded applications (i.e., Arduino) make heavy use of GPIO for reading from various environmental sensors (IR, video, temperature, 3-axis orientation, acceleration), and for writing output to dc motors (via PWM), audio, LCD displays, or LEDs for status.

Capabilities

GPIO capabilities may include:

• direction: GPIO pins can be configured to be input or output
• enable mask (aka GPIO mask): GPIO pins can be enabled/disabled
• input values are readable (typically high=1, low=0)
• output values are writable/readable
• input values can often be used as IRQs (typically for wakeup events)
• can use DMA to move large quantities of data efficiently into or out of the device

GPIO peripherals vary quite widely. In some cases, they are very simple, a group of pins that can be switched as a group to either input or output. In others, each pin can be set up flexibly to accept or source different logic voltages, with configurable drive strengths and pull ups/downs. The input and output voltages are typically, though not universally limited to the supply voltage of the device with the GPIOs on, and may be damaged by greater voltages.

Some GPIOs have 5 V tolerant inputs: even on low supply voltages (2 V), the device can accept 5 V without damage.

Ports

A GPIO port is a group of GPIO pins (typically 8 GPIO pins) arranged in a group, and treated as a single port.

See also

• Programmed input/output
• SGPIO
• I²C
• Serial Peripheral Interface Bus
• Special Input/Output

References

• ALSA Development List
• Linux Kernel Doc on GPIO
• LinuxTV GPIO Pins Info