#529 ATtiny Pin Change Interrupts

How to use pin change interrupts with the ATtiny85

Build

Here’s a quick demo..

Notes

The ATtiny only has one hardware interrupt pin (PB0) but since this is often used for other purposes (like I²C), handling interrupts on other pins needs to be done using the pinc change interrupt (see 9.2 External Interrupts in the datasheet).

This example demonstrates pin change interrupts being used to detect and debounce a pushbutton. On every change, and LED is toggled.

Setting up Pin Change Interrupts

Two steps required:

The relevant bits of the Pin Change Mask Register (PCMSK) register are set to enable interrupts for pins PCINT0 to PCINT5
Enable Pin Change Interrupt by setting bit PCIE in the General Interrupt Mask Register (GIMSK) register

The ATtiny hardware support for the Arduino IDE includes a number of macros to help generalise the register control, including:

digitalPinToPCMSKbit for setting PCMSK register
digitalPinToPCICRbit for setting GIMSK register

Pin definitions, with specific reference to the 8-pin PDIP8 ATtiny85:

Interrupt pin	Port bit	PDIP8 Pin
PCINT0	PB0	5
PCINT1	PB1	6
PCINT2	PB2	7
PCINT3	PB3	2
PCINT4	PB4	3
PCINT5	PB5	1

Example Sketch

The PinChangeInterrupts.ino sketch is a simple demonstration of pin change interrupts. It uses the ATtiny register macros to setup the registers accordingly.

The ATtiny85 is programmed using the Arduino ISP sketch running on an Arduino Uno. See LEAP#070 ProgrammingWithArduinoISP for more info.

Construction

Breadboard

Schematic