Interrupt function

In Arduino, the interrupt function allows the microcontroller to pause its normal program execution and immediately run a special function (called an Interrupt Service Routine or ISR) in response to a specific event, like a change in a pin's state or the expiration of a timer.

How Interrupts Work:

• Interrupts are like alarms that tell the processor to stop what it's doing and pay attention to something important.
  
  
• When an interrupt occurs, the processor stops the current task, saves its state, and executes the ISR.
• Once the ISR completes, the processor resumes its normal tasks.

Key Points About Arduino Interrupts:

1. Pin-based Interrupts:

   • Arduino supports hardware interrupts on specific pins. For example:
     • On an Arduino Uno, hardware interrupts are available on pins 2 and 3.
     • Other boards may support interrupts on additional or all pins.
   • These pins are associated with specific interrupt numbers.

2. Function to Attach an Interrupt:

   • Use the attachInterrupt() function to define an interrupt and associate it with a pin and ISR:

     attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);
     

     • pin: The pin you want to monitor for an interrupt.
     • ISR: The name of the Interrupt Service Routine to execute.
     • mode: Defines the event that triggers the interrupt:
       • LOW: Triggers when the pin is LOW.
       • CHANGE: Triggers when the pin changes state (HIGH to LOW or LOW to HIGH).
       • RISING: Triggers when the pin changes from LOW to HIGH.
       • FALLING: Triggers when the pin changes from HIGH to LOW.

3. Disabling and Re-enabling Interrupts:

   • Use detachInterrupt(interruptNumber) to disable the interrupt.

4. Characteristics of an ISR:

• Keep it Short: The ISR should execute quickly to avoid delaying other interrupts.
• No delay() or Serial Communication: These functions depend on interrupts themselves and will not work inside an ISR.
• Variables in ISRs: Use the volatile keyword for variables shared between the ISR and the main program.