Ard Interrupt Flags

In this tutorial, you'll learn about Arduino Interrupt Flag Not Clearing. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

The interrupt fires repeatedly without the expected trigger condition.

Quick Fix

Wrong

void myISR() {
  // No flag clearing — may re-trigger
  counter++;
}

counter increments multiple times per button press.

Right

volatile int counter = 0;
volatile unsigned long lastDebounce = 0;

void myISR() {
  unsigned long now = millis();
  if (now - lastDebounce > 50) {  // Debounce 50 ms
    counter++;
    lastDebounce = now;
  }
}

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(2), myISR, FALLING);
}

void loop() {
  Serial.println(counter);
  delay(100);
}

Counter increments exactly once per button press (debounced).

Prevention

Hardware interrupt flags are auto-cleared on AVR when the ISR exits. Repeated interrupts are caused by: bounce (10-20 ms), noise, or a floating pin. Debounce in the ISR with millis(). Use INPUT_PULLUP to avoid floating. The flag register (EIFR) can be manually cleared.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ