What's New? March 20, 2012: Version 1.72 has been released! It contains no code changes since 1.71beta. The beta has been complete for a couple of weeks so it's time to stick a fork in it and call it done! Also uploaded a new version of the speed test document.

See the Wiki pages for Installation instructions.

The PinChangeInt library implements Pin Change interrupts for the Arduino environment. This library was designed for the Arduino Uno/Duemilanove. It will likely work with other ATmega328- or ATmega168-based Arduinos; it has been reported to work just fine on the Nano. It will probably not work on the Arduino Mega without some serious updating.

What are Pin Change interrupts? The ATmega328p processor at the heart of the Arduino has two different kinds of interrupts: “external”, and “pin change”. There are only two external interrupt pins, INT0 and INT1, and they are mapped to Arduino pins 2 and 3. These interrupts can be set to trigger on RISING or FALLING signal edges, or on low level. The triggers are interpreted by hardware, and the interrupt is very fast. On the other hand there are only 2 such pins on the ATmega328p in the Arduino Uno and Duemilanove.

On the other hand the pin change interrupts can be enabled on any or all of the Arduino's signal pins. They are triggered equally on RISING or FALLING signal edges, so it is up to the interrupt code to set the proper pins to receive interrupts, to determine what happened (which pin? ...did the signal rise, or fall?), and to handle it properly. Furthermore, the pin change interrupts are grouped into 3 “port”s on the MCU, so there are only 3 interrupt vectors (subroutines) for the entire body of 20 pins. This makes the job of resolving the action on a single interrupt even more complicated. The interrupt routine should be fast, but complication is the enemy of speed. The PinChangeInt library is designed to handle the Arduino's pin change interrupts as quickly and reasonably as possible.

Version 1.4 (and later) puts all the code in the .h file, to allow the programmer to configure it through their sketch for minimum ram usage. In earlier versions, it must be configured through the PinChangeIntConfig header file instead.

See the Wiki pages for more information.