GPIOs

GPIO stands for General-Purpose Input/Output. They are generic pins on many integrated circuits and microcontroller devices that can be configured by software to perform digital signaling tasks. A GPIO pin can be configured as an input to read a digital signal or as an output to drive a signal, often with options to enable an internal pull-up or pull-down resistor. In many devices, pins may also support multiple functions (alternate functions) beyond simple input or output.

Electrical characteristics vary by device but commonly use logic levels such as 3.3V or 5V. The pin may have a defined drive strength and a maximum current per pin and total for the package. When configured as input, a GPIO can be read by software; as output, it can drive high or low. Some pins support tri-state when not driven. Many GPIOs provide protective features like ESD protection and current-limiting, but improper use can damage the device.

GPIOs are widely used for interfacing with sensors, switches, LEDs, relays, and other digital devices. They can be used directly for simple tasks or in combination with level shifters, transistors, or driver ICs for higher voltages or currents. In some systems, multiple GPIOs can be accessed via libraries or memory-mapped registers. They may be grouped into ports and can be configured for special purposes such as interrupt input.

On single-board computers such as the Raspberry Pi, GPIO headers map to processor pins and may have software libraries to control them. In microcontroller-based systems, GPIO configuration is typically done in initialization code. For expanded I/O, GPIOs can be increased using I2C/SPI expander ICs or dedicated GPIO chips.

Design considerations include avoiding direct driving of inductive loads, using resistors and, where needed, transistors or driver ICs, ensuring voltage compatibility, and handling floating inputs and debouncing of switches.