How to Successfully Trigger External Interrupts on Arduino Nano using AVR Assembly

Discover the ultimate guide to triggering external interrupts on an Arduino Nano (ATMega328p) using AVR Assembly code. Uncover common pitfalls and learn the correct approach to making your LED blink!
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Mastering External Interrupts on Arduino Nano with AVR Assembly

Using external interrupts effectively is crucial for responsive electronic projects. If you're working with the Arduino Nano (ATMega328p) and are trying to change the state of the LED on pin 13 (PB5) via external interrupts on pin INT0 (PD2) using AVR assembly, you've come to the right place!

The Problem at Hand

A common scenario occurs when developers run into issues where external interrupts don't trigger as expected. This can lead to frustrating debugging sessions and confusing results, especially for those newer to assembly programming. In this case, there's a specific issue with the code used to enable the external interrupt that needs addressing.

A Glance at the Original Code

The code provided aims to configure the Arduino Nano to toggle the LED on pin 13 every time INT0 receives a signal. Here’s a breakdown of the problematic code:

[[See Video to Reveal this Text or Code Snippet]]

Identifying the Error

Upon examining the code, the main issue lies in how the external interrupt mask is being set. The line:

[[See Video to Reveal this Text or Code Snippet]]

is incorrect because EIMSK (External Interrupt Mask Register) is not memory-mapped like regular RAM. Instead, it is an I/O register. Therefore, we need to use the out instruction to write to it.

The Correct Instruction

To resolve the issue, replace the faulty line with the following:

[[See Video to Reveal this Text or Code Snippet]]

Summary of the Corrected Code

After making this adjustment, the initialization of the external interrupt mask will properly activate the interrupt feature you're trying to implement. For clarity, here’s how the corrected section looks now:

[[See Video to Reveal this Text or Code Snippet]]

With this fix implemented, your code should work as expected, allowing external interrupts to trigger and successfully change the state of the LED on pin 13.

Conclusion

Successfully utilizing external interrupts on the Arduino Nano using AVR assembly can be tricky. However, even small adjustments—like changing the instruction to write to an I/O register—can make a significant difference in functionality. Now that you've corrected the mistake, you can enjoy seamless interrupt handling in your projects.

Whether you're developing on a simulator or directly with the microcontroller, pay close attention to how you interact with hardware registers. Happy coding!