GPIO Foundations

~10 min slides

What is GPIO?

General Purpose Input/Output

Standard digital interface to the outer world. The most basic peripheral: making pins go high or low, and reading whether they're high or low.

Configurations: Direction

• Output — you drive the pin (e.g., turn on an LED)
• Input — you read the pin (e.g., detect a button press)

Configurations: Output

Modes

• Push-pull (typically default) — actively drives the pin high and low
• Open-drain — actively drives low, but floats when "high" (needs external pull-up)

Drive Strength

How much current the pin can source or sink. Higher drive strength = brighter LED, but more power consumption.

Configurations: Input

Internal Pull Resistor

• Pull-up — pin reads high when nothing is connected; button pulls it low
• Pull-down — pin reads low when nothing is connected; button pulls it high
• Floating — no pull resistor; pin state is undefined when nothing is connected