External Interrupts — Maple v0.0.10beta Documentation

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# External Interrupts

External interrupts can be used to trigger routines to run in response to changes in voltage on a pin. Each GPIO pin can be used to detect transitions, such as when the voltage goes from LOW to HIGH, or from `HIGH` to `LOW`. This can be used to avoid checking for changes on a pin “manually” by waiting in a loop until the pin changes.

## Overview

External interrupts are often used to detect when events happen outside of the microcontroller. These can be used to tell Maple when events happen, such as when a sensor has data ready to be read, or when a button has been pushed. When such an event happens, an interrupt is raised, and the Maple can react to it with a preset interrupt handler, which is a function that gets called whenever the event occurs.

Every GPIO pin can generate an external interrupt, subject to certain constraints. There can be a maximum of 16 different external interrupts set up at a time. This is because the external interrupt lines on the STM32 are shared between GPIO ports. In effect, this means that every pin on the Maple connects to what is called an EXTI line, and within an EXTI line, only one of the pins that connects to it can be used to detect external interrupts at a time.

The EXTI Line Pin Map for your board lists which pins connect to which EXTI lines:

- Maple
- Maple RET6 Edition

Note

You should set the pin mode of your desired pin to an input mode (e.g `INPUT` or `INPUT_FLOATING`, `INPUT_PULLUP`, `INPUT_PULLDOWN`).

## Function Reference

- attachInterrupt()
- detachInterrupt()

## Recommended Reading

- ST manual RM0008 (PDF), Chapter 9, “General-purpose and alternate-function I/Os”, and Chapter 10, “Interrupts and Events”.

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