If you have ever tried to port an Arduino project that uses interrupts from one board type to another, you have probably experienced frustration, this includes the sample code throughout RCArduino.
The following post examines the differences in interrupts between the popular boards, the Arduino UNO, Micro, Mega, Mini and Leonardo. Based on this information we can modify sketches to run on the full range of 8-bit Arduinos.
The 8-bitArduino boards are based on one of three related chips -
ATMega328 - UNO and Mini
ATMega32u4 - Leonardo and Micro
ATMega2560 - Mega
Each of these chips supports two types of interrupts -
1) External Interrupts
These are flexible easy to use interrupts which can be triggered by rising, falling or changing signals. The disadvantage is that there are a limited number available on each chip type.
If we want to access more interrupts we need to look at the next type -
2) Pin Change Interrupts
The underlying chip in your Arduino supports a second type of interrupt however these interrupts are not directly supported by Arduino and need to be accessed through an additional library.
Differences In External Interrupts
The external interrupts are associated with specific digital pins on each chip type, the following table taken from the attachInterrupt reference page lists the available external interrupts and the associated Arduino pin on each chip -
The Arduino team have hidden some of the differences between the ATMega328 and ATM2560 so that attaching INT0 using the attachInterrupt function will attach an interrupt to digital pin 2 on both chips even though on the Mega digital pin2 is actually INT4.
The same logic has not been carried across to the ATMega32u4 Based leonardo. Notice how int0 and int1 are actually reversed on the Leonardo, this will be a major trap for people who are porting code from the UNO.
Does the Leonardo have four external interrupts ?
While the Leonardo appears to have 4 external interrupts, int2 and int3 are attached to digital pins 0 and 1 which are almost always reserved for serial input/output. So yes there are four interrupts, but two of them are only available by disabling serial functionality.
Differences In Pin Change Interrupts
On the Arduino UNO, pin change interrupts can be used to enable interrupts on any of the Arduino PINs to give access to a total of 19 interrupts (13 digital pins and 6 Analog pins).
I initially assumed that this was also possible on the Mega, Micro and Leonardo as well. It isn't.
Pin change interrupts are supported on the following Leonardo/Micro pins - 8,9,10 and 11.
Pin change interrupts are supported on Arduino Mega pins 10,11,12,13,14,15 and analog pins 6 to 15
Interrupts and RCArduino
These differences between the Arduino platforms will have been responsible for some of the difficulty that users have had in porting RCArduino code to Minis, Micros, Leonardos and Megas.
The good news is that now we have a full understanding of the inconsistencies between the different devices there should be no problem in modifying the sample sketches to run on them.
If your having trouble with a sample sketch, get in touch, in the meantime I will be updating some of the sketches to work across multiple boards.
Stay tuned
Duane B
The following post examines the differences in interrupts between the popular boards, the Arduino UNO, Micro, Mega, Mini and Leonardo. Based on this information we can modify sketches to run on the full range of 8-bit Arduinos.
The 8-bitArduino boards are based on one of three related chips -
ATMega328 - UNO and Mini
ATMega32u4 - Leonardo and Micro
ATMega2560 - Mega
Each of these chips supports two types of interrupts -
1) External Interrupts
These are flexible easy to use interrupts which can be triggered by rising, falling or changing signals. The disadvantage is that there are a limited number available on each chip type.
If we want to access more interrupts we need to look at the next type -
2) Pin Change Interrupts
The underlying chip in your Arduino supports a second type of interrupt however these interrupts are not directly supported by Arduino and need to be accessed through an additional library.
Differences In External Interrupts
The external interrupts are associated with specific digital pins on each chip type, the following table taken from the attachInterrupt reference page lists the available external interrupts and the associated Arduino pin on each chip -
| Board | int.0 | int.1 | int.2 | int.3 | int.4 | int.5 |
| Uno, Ethernet, Mini | 2 | 3 | ||||
| Mega2560 | 2 | 3 | 21 | 20 | 19 | 18 |
| Leonardo, Micro | 3 | 2 | 0 | 1 |
The Arduino team have hidden some of the differences between the ATMega328 and ATM2560 so that attaching INT0 using the attachInterrupt function will attach an interrupt to digital pin 2 on both chips even though on the Mega digital pin2 is actually INT4.
The same logic has not been carried across to the ATMega32u4 Based leonardo. Notice how int0 and int1 are actually reversed on the Leonardo, this will be a major trap for people who are porting code from the UNO.
Does the Leonardo have four external interrupts ?
While the Leonardo appears to have 4 external interrupts, int2 and int3 are attached to digital pins 0 and 1 which are almost always reserved for serial input/output. So yes there are four interrupts, but two of them are only available by disabling serial functionality.
Differences In Pin Change Interrupts
On the Arduino UNO, pin change interrupts can be used to enable interrupts on any of the Arduino PINs to give access to a total of 19 interrupts (13 digital pins and 6 Analog pins).
I initially assumed that this was also possible on the Mega, Micro and Leonardo as well. It isn't.
Pin change interrupts are supported on the following Leonardo/Micro pins - 8,9,10 and 11.
Pin change interrupts are supported on Arduino Mega pins 10,11,12,13,14,15 and analog pins 6 to 15
Interrupts and RCArduino
These differences between the Arduino platforms will have been responsible for some of the difficulty that users have had in porting RCArduino code to Minis, Micros, Leonardos and Megas.
The good news is that now we have a full understanding of the inconsistencies between the different devices there should be no problem in modifying the sample sketches to run on them.
If your having trouble with a sample sketch, get in touch, in the meantime I will be updating some of the sketches to work across multiple boards.
Stay tuned
Duane B
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