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New Arduino interrupt library, designed for Arduino Uno/Mega 2560/Leonardo/Due
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New Arduino interrupt library, designed for all versions of the Arduino.


enableInterrupt- Enables interrupt on a selected Arduino pin. disableInterrupt - Disables interrupt on the selected Arduino pin.

*What's New?

  • Fri Jun 22 06:49:57 CDT 2018
    • Version 1.0.0 of the library has been released. Alex Reinert contributed Bobuino support. Thanks, Alex! And at this point, I think it's long past due that we stick a non-beta sticker on this thing. Congratulations, EnableInterrupt- you are all grown up. Version 1.0.0 it is.

The EnableInterrupt library is an Arduino interrupt library, designed for all versions of the Arduino- at this writing, the Uno (and other ATmega328p-based boards, like the mini), Due, Zero, Leonardo (and other ATmega32u4-based boards, like the Micro), the Mega2560 (and other ATmega2560-based boards, like the MegaADK), and for non-Arduino chips: the 644/1284p (Mighty1284, Sodaq Mbili and EnviroDIY Mayfly) ATtiny 44/84, and ATtiny 45/85 (using DA Mellis' support files). The library enables you to assign an interrupt to pins on your chip that support them, and presents a common interface to all supported chips. This means that on the Arduino Uno and Mega you don't give it an interrupt number, as per Rather, your first argument is a pin number of a pin that's supported on that chip (see ).


See the page to download the library.

More Information

See the Wiki at . For detailed usage information see .

See the examples subdirectory in the distribution or in this Git site for code examples.

See the extras subdirectory in the distribution or in this Git site for License and Release Notes.

For a tutorial on interrupts, see The posting gets into low-level details on interrupts.

IMPORTANT NOTE: In 0.9.2 I discovered a rather pernicious bug, wherein the library was setting the global interrupt enable bit. This could cause a serious and difficult-to-debug race condition, as it is not the job of the library to manage that bit. The chips come with interrupts enabled so existing code should not be affected, but if you were relying on that behavior note that it has changed. My thanks to (the 'How are interrupts queued?' section).

ATmega Processor Interrupt Types

Note that the ATmega processor at the heart of the Arduino Uno/Mega2560/Leonardo/ATmega1284 has two different kinds of interrupts: “external”, and “pin change”. For the list of available interrupt pins and their interrupt types, see the PORT / PIN BESTIARY, below.

External Interrupts

There are a varying number of external interrupt pins on the different processors. The Uno supports only 2 and they are mapped to Arduino pins 2 and 3. The 2560 supports 6 usable, the Leonardo supports 5, and the ATmega1284p supports 3. These interrupts can be set to trigger on RISING, or FALLING, or both ("CHANGE") signal levels, or on LOW level. The triggers are interpreted by hardware, so by the time your user function is running, you know exactly which pin interrupted at the time of the event, and how it changed. On the other hand, as mentioned there are a limited number of these pins.

Pin Change Interrupts

On the Arduino Uno (and again, all 328p-based boards) and 644/1284-based boards, the pin change interrupts can be enabled on any or all of the pins. The two pins 2 and 3 on 328p-based boards, or three pins (2, 10, and 11) on the 1284-based boards support either pin change or external interrupts. On 2560-based Arduinos, there are 18 pin change interrupt pins in addition to the 6 external interrupt pins. On the Leonardo there are 7 pin change interrupt pins in addition to the 5 external interrupt pins. See PIN BESTIARY below for the pin numbers and other details.

Pin Change interrupts trigger on all RISING and FALLING (ie, "CHANGE") signal edges. Furthermore, the processor's pins, and pin change interrupts, are grouped into “port”s, so for example on the Arduino Uno there are three ports and therefore only 3 interrupt vectors (subroutines) available for the entire body of 20 pin change interrupt pins.

The Library and Pin Change Interrupts

The foregoing means that not only do pin change interrupts trigger on all pin transitions, but a number of pins share a single interrupt subroutine. It's the library's function to make pin change interrupts appear that each pin can support RISING, FALLING, or CHANGE, and each pin can support its own user-defined interrupt subroutine.

When an event triggers an interrupt on any interrupt-enabled pin on a port, a library subroutine ("interrupt handler", "interrupt service routine", or "ISR") attached to that pin's port is triggered. It is up to the EnableInterrupt library to set the proper port to receive interrupts for a pin, to determine what happened when an interrupt is triggered (which pin? ...did the signal rise, or fall?), to handle it properly (Did we care if the signal fell? Did we care if it rose?), then to call the programmer's chosen subroutine (ISR). This makes the job of resolving the action on a single pin somewhat complicated. There is a definitive slowdown in the interrupt routine because of this complication. So there is a significant* time between when the interrupt triggers and when the pins are read to determine what actually happened (rising or falling) and which pin changed. So the signal could have changed by the time the pin's status is read, returning a false reading back to your sketch. Therefore, these pins are not suitable for fast changing signals, and under the right conditions such events as a bouncing switch may actually be missed. Caveat Programmer. If you're concerned about this, continue to read the following information and make sure to read the wiki pages; especially see . For a further review of this issue see


Basic Usage

enableInterrupt- Enables interrupt on a selected Arduino pin.

enableInterrupt(uint8_t pinNumber, void (*userFunction)(void), uint8_t mode);
enableInterrupt(uint8_t interruptDesignator, void (*userFunction)(void), uint8_t mode);

The arguments are:
* pinNumber - The number of the Arduino pin, such as 3, or A0, or SCK. Note that
these are *not* strings, so when you use A0 for example, do not use quotes.
* interruptDesignator- very much like a pin. See below.
* userFunction - The name of the function you want the interrupt to run. Do not
use a pointer here, just give it the name of your function. See the example code
in the Examples directory.
* mode - What you want the interrupt to interrupt on. For Pin Change Interrupt
pins, the modes supported are RISING, FALLING, or CHANGE.
** RISING - The signal went from "0", or zero volts, to "1", or 5 volts.
** FALLING - The signal went from "1" to "0".
** CHANGE - The signal either rose or fell.

For External Interrupts, the same modes are supported plus the additional mode
of LOW signal level.
** LOW - The signal is at a low level for some time.

Each pin supports only 1 function and 1 mode at a time.

disableInterrupt- Disables interrupt on a selected Arduino pin.

disableInterrupt(uint8_t pinNumber);
disableInterrupt(uint8_t interruptDesignator);
  • interruptDesignator: Essentially this is an Arduino pin, and if that's all you want to give the function, it will work just fine. Why is it called an "interruptDesignator", then? Because there's a twist: You can perform a bitwise "and" with the pin number and PINCHANGEINTERRUPT to specify that you want to use a Pin Change Interrupt type of interrupt on those pins that support both Pin Change and External Interrupts. Otherwise, the library will choose whatever interrupt type (External, or Pin Change) normally applies to that pin, with priority to External Interrupt.

  • The complexity is because of pins 2 and 3 on the ATmega328-based Arduinos, and pins 2, 10, and 11 on 1284-based boards. Those are the only pins on the processors supported by this library that can share External or Pin Change Interrupt types. Otherwise, each pin only supports a single type of interrupt and the PINCHANGEINTERRUPT scheme changes nothing. This means you can ignore this whole discussion for ATmega2560, ATmega32U4, or SAM3X8E (Due)-based Arduinos.

It is possible to change the user function assigned to an interrupt after enabling it (if you want). Later in your code simply disable the interrupt and enable it with a different function.

Determine the Pin That Was Interrupted

There is a facility in the library to identify the most recent pin that triggered an interrupt. Set the following definition '''before''' including the EnableInterrupt.h file in your sketch:


Then, the ATmega chip will set a variable with every interrupt, and you can query it to find which pin interrupted your sketch. The variable is arduinoInterruptedPin and it is of type uint8_t.

See the wiki page for more information.


Theoretically pins 0 and 1 (RX and TX) are supported but as these pins have a special purpose on the Arduino, their use in this library has not been tested.


Arduino Uno/Duemilanove/etc.

Interrupt Type Pins
External 2 3
Pin Change 2-13 and A0-A5

Arduino Mega2560

Interrupt Type Pins
External 2 3 and 18-21
Pin Change 10-15 and A8-A15 and SS, SCK, MOSI, MISO

Arduino Leonardo

Interrupt Type Pins
External 0-3 and 7
Pin Change 8-11 and SCK, MOSI, MISO

Mighty 1284, Sodaq Mbili, EnviroDIY Mayfly

Interrupt Type Pins
External 2 10 11
Pin Change 0-31 (aka: 0-23 and A0-A7)


Arduino Uno

Interrupt Pins:
Arduino	External                Arduino Pin Change      Arduino Pin Change
Pin     Interrupt               Pin     Interrupt       Pin     Interrupt
                Port                           Port                     Port
2       INT0    PD2             2       PCINT18 PD2     A0      PCINT8  PC0
3       INT1    PD3             3       PCINT19 PD3     A1      PCINT9  PC1
                                4       PCINT20 PD4     A2      PCINT10 PC2
                                5       PCINT21 PD5     A3      PCINT11 PC3
                                6       PCINT22 PD6     A4      PCINT12 PC4
                                7       PCINT23 PD7     A5      PCINT13 PC5
                                8       PCINT0  PB0
                                9       PCINT1  PB1
                                10      PCINT2  PB2
                                11      PCINT3  PB3
                                12      PCINT4  PB4
                                13      PCINT5  PB5

Leonardo Pins LEONARDO

Interrupt pins:
Arduino                         Arduino
Pin     External                Pin     Pin Change
        Interrupt                       Interrupt
               Port                               Port
 3      INT0   PD0              8       PCINT4    PB4
 2      INT1   PD1              9       PCINT5    PB5
 0      INT2   PD2              10      PCINT6    PB6
 1      INT3   PD3              11      PCINT7    PB7
 7      INT6   PE6              SCK/15  PCINT1    PB1
                                MOSI/16 PCINT2    PB2
                                MISO/14 PCINT3    PB3

                                on ICSP:
                                SCK/15:  PCINT1 (PB1)
                                MOSI/16: PCINT2 (PB2)
                                MISO/14: PCINT3 (PB3)

// Map SPI port to 'new' pins D14..D17
static const uint8_t SS   = 17;
static const uint8_t MOSI = 16;
static const uint8_t MISO = 14;
static const uint8_t SCK  = 15;
// A0 starts at 18

ATmega2560 Support

External Interrupts ------------------------------------------------------------
The following External Interrupts are available on the Arduino:
  Pin  PORT INT  ATmega2560 pin
  21     PD0  0     43
  20     PD1  1     44
  19     PD2  2     45
  18     PD3  3     46
   2     PE4  4      6
   3     PE5  5      7
 n/c     PE6  6      8  (fake pin 75) **
 n/c     PE7  7      9  (fake pin 76)

Pin Change Interrupts ----------------------------------------------------------

ATMEGA2560 Pin Change Interrupts
Arduino              Arduino              Arduino
  A8     PK0  16       10     PB4   4       SS     PB0   0
  A9     PK1  17       11     PB5   5       SCK    PB1   1
 A10     PK2  18       12     PB6   6       MOSI   PB2   2
 A11     PK3  19       13     PB7   7       MISO   PB3   3
 A12     PK4  20       14     PJ1  10
 A13     PK5  21       15     PJ0   9
 A14     PK6  22        0     PE0   8 - this one is a little odd. *
 A15     PK7  23

The library supports all interrupt pins, even though not all pins to the ATmega-2560 processor are exposed on the Arduino board. These pins are supported as "fake pins", and begin with pin 70 (there are 70 pins on the ATmega 2560 board). The fake pins are as follows:

pin: fake70 PJ2 this is Pin Change Interrupt PCINT11
pin: fake71 PJ3 this is Pin Change Interrupt PCINT12
pin: fake72 PJ4 this is Pin Change Interrupt PCINT13
pin: fake73 PJ5 this is Pin Change Interrupt PCINT14
pin: fake74 PJ6 this is Pin Change Interrupt PCINT15
pin: fake75 PE6 this is External Interrupt INT6
pin: fake76 PE7 this is External Interrupt INT7
  • Note: Arduino Pin 0 is PE0 (PCINT8), which is RX0. Also, it is the only other pin on another port on PCI1. This would make it very costly to integrate with the library's code and thus is not supported by this library. It is the same pin the Arduino uses to upload sketches, and it is connected to the FT232RL USB-to-Serial chip (ATmega16U2 on the R3).

Mighty 1284, Bobuino, EnviroDIY Mayfly, Sodaq Mbili Support

The ATmega 1284p shares pinout with the 644; the only difference is in memory size. We use the "Mighty 1284" platform as our model, because the needed files are mature and complete.

Interrupt Pins:
Mighty  External                Mighty                                 Mighty           
Pin     Interrupt               Pin*  PORT PCINT ATmega644/1284 pin    Pin*  PORT PCINT ATmega644/1284 pin
                Port            0     PB0   8         1                15    PD7  31        21
2       INT2    PB2             1     PB1   9         2                16    PC0  16        22
10      INT1    PD2             2     PB2   2         3                17    PC1  17        23
11      INT0    PD3             3     PB3  11         4                18    PC2  18        24
                                4     PB4  12         5                19    PC3  19        25
                                5     PB5  13         6                20    PC4  20        26
                                6     PB6  14         7                21    PC5  21        27
                                7     PB7  15         8                22    PC6  22        28
                                8     PD0  24        14                23    PC7  23        29
                                9     PD1  25        15             31/A7    PA7   7        33
                               10     PD2  26        16             30/A6    PA6   6        34
                               11     PD3  27        17             29/A5    PA5   5        35
                               12     PD4  28        18             28/A4    PA4   4        36
                               13     PD5  29        19             27/A3    PA3   3        37
                               14     PD6  30        20             26/A2    PA2   2        38
                                                                    25/A1    PA1   1        39
                                                                    24/A0    PA0   0        40

Bobuino External                Bobuino                                Bobuino           
Pin     Interrupt               Pin*  PORT PCINT ATmega644/1284 pin    Pin*  PORT PCINT ATmega644/1284 pin
                Port            4     PB0   8         1                31    PD7  31        21
2       INT2    PB2             5     PB1   9         2                22    PC0  16        22
10      INT1    PD2             6     PB2   2         3                23    PC1  17        23
11      INT0    PD3             7     PB3  11         4                24    PC2  18        24
                               10     PB4  12         5                25    PC3  19        25
                               11     PB5  13         6                26    PC4  20        26
                               12     PB6  14         7                27    PC5  21        27
                               13     PB7  15         8                28    PC6  22        28
                                0     PD0  24        14                29    PC7  23        29
                                1     PD1  25        15             14/A0    PA7   7        33
                                2     PD2  26        16             15/A1    PA6   6        34
                                3     PD3  27        17             16/A2    PA5   5        35
                               30     PD4  28        18             17/A3    PA4   4        36
                                8     PD5  29        19             18/A4    PA3   3        37
                                9     PD6  30        20             19/A5    PA2   2        38
                                                                    20/A6    PA1   1        39
                                                                    21/A7    PA0   0        40

Mayfly                          Mayfly                                 Mayfly
Mbili   External                Mbili                                  Mbili           
Pin     Interrupt               Pin*  PORT PCINT ATmega644/1284 pin    Pin*  PORT PCINT ATmega644/1284 pin
                Port            8     PB0   8         1                 7    PD7  31        21
2       INT2    PB2             9     PB1   9         2                16    PC0  16        22
10      INT1    PD2            10     PB2   2         3                17    PC1  17        23
11      INT0    PD3            11     PB3  11         4                18    PC2  18        24
                               12     PB4  12         5                19    PC3  19        25
                               13     PB5  13         6                20    PC4  20        26
                               14     PB6  14         7                21    PC5  21        27
                               15     PB7  15         8                22    PC6  22        28
                                0     PD0  24        14                23    PC7  23        29
                                1     PD1  25        15             31/A7    PA7   7        33
                                2     PD2  26        16             30/A6    PA6   6        34
                                3     PD3  27        17             29/A5    PA5   5        35
                                4     PD4  28        18             28/A4    PA4   4        36
                                5     PD5  29        19             27/A3    PA3   3        37
                                6     PD6  30        20             26/A2    PA2   2        38
                                                                    25/A1    PA1   1        39
                                                                    24/A0    PA0   0        40
# Thanks! Thank you for downloading and enjoying the EnableInterrupt library. I hope you find it useful. Heck, I wrote it for you- yeah, that's right- you. The Maker and/or Geek sitting before your project and trying to make little computers do fun stuff. It's not easy, and my hat goes off to you. I hope I've made stuff a little easier for you.

This software would not be nearly as useful as it is without the help of the following people:

Thanks to Loranzo Cafaro for his switch debounce example, to Jevon Wild for his changes to make the library more functional with PlatformIO (, Ricardo JL Rufino for some PlatformIO fixes to the library.json file, and Sara Damiano for adding support for the Sodaq Mbili and EnviroDIY Mayfly.

And, from the past, this library's predecessor was the PinChangeInt library. I have done a complete rewrite and not used any of its code, but I learned a lot by doing the previous one and I feel like I still owe a debt of gratitude to all the geeks who created/contributed/helped/debugged. So without further ado, I present the "ACKNOWLEDGEMENTS" section from the previous library. Note that "this" library in the following refers to PinChangeInt:

This library was originally written by Chris J. Kiick, Robot builder and all around geek, who said of it, "Hi, Yeah, I wrote the original PCint library. It was a bit of a hack and the new one has better features. I intended the code to be freely usable. Didn't really think about a license. Feel free to use it in your code: I hereby grant you permission." Thanks, Chris! A hack? I dare say not, if I have taken this any further it's merely by standing on the shoulders of giants. This library was the best "tutorial" I found on Arduino Pin Change Interrupts and because of that I decided to continue to maintain and (hopefully) improve it. We, the Arduino community of robot builders and geeks, owe you a great debt of gratitude for your hack- a hack in the finest sense.

The library was then picked up by Lex Talionis, who created the Google Code website. We all owe a debt of thanks to Lex, too, for all his hard work! He is currently the other official maintainer of this code.

Many thanks to all the contributors who have contributed bug fixes, code, and suggestions to this project:

John Boiles and Baziki (who added fixes to PcInt), Maurice Beelen, nms277, Akesson Karlpetter, and Orly Andico for various fixes to this code, Rob Tillaart for some excellent code reviews and nice optimizations, Andre' Franken for a good bug report that kept me thinking, cserveny.tamas a special shout out for providing the MEGA code to PinChangeInt, and Pat O'Brien for testing and reporting on the Arduino Yun.- Thanks!

A HUGE thanks to JRHelbert for fixing the PJ0 and PJ1 interrupt PCMSK1 issue on the Mega... 06/2014

A HUGE thanks to Jan Baeyens ("jantje"), who has graciously DONATED an Arduino Mega ADK to the PinChangeInt project!!! Wow, thanks Jan! This makes the 2560-based Arduino Mega a first class supported platform- I will be able to test it and verify that it works.

Finally, a shout out to Leonard Bernstein. I was inspired by him ( from a Ted talk by Itay Talgam. None of the contributors, myself included, has any interest in making money from this library and so I decided to free up the code as much as possible for any purpose. ...But! You must give credit where credit is due (it's not only a nice idea, it's the law- as in, the license terms)!

"If you love something, give it away."

I apologize if I have forgotten anyone here. Please let me know if so.

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