What is interrupt in microcontroller?

 

An interrupt in a microcontroller is a signal or event that temporarily halts the normal execution flow of your program so the microcontroller can respond to an urgent task or event immediately.

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Simple Definition:

An interrupt is like someone tapping your shoulder while you're working — you pause what you're doing, handle the urgent matter, then go back to your original task.

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How It Works:

1. The MCU is running your main program (called the main loop).

2. An interrupt event occurs (e.g., a button press, timer overflow, data received).

3. The MCU pauses the main program.

4. It jumps to a special function called an Interrupt Service Routine (ISR) or interrupt handler.

5. Once the ISR is done, it returns to where it left off in the main program.

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Types of Interrupts:

1. External Interrupts – Triggered by changes on input pins (e.g. button press).

2. Timer Interrupts – Triggered by internal timers reaching a value.

3. Peripheral Interrupts – Triggered by events in peripherals (UART, ADC, SPI, etc.).

4. Software Interrupts – Triggered manually in code.

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Key Concepts:

Concept	Description
ISR (Interrupt Service Routine)	The function that handles the interrupt
Interrupt Vector Table	A lookup table that tells the MCU which ISR to call
Masking/Disabling	Temporarily turning off specific interrupts
Priority	Some interrupts are more urgent and can interrupt other ISRs

Why Use Interrupts?

• React immediately to real-world events (e.g. sensor input, communication).

• Improve efficiency (no need to poll constantly).

• Enable multitasking behavior in real-time systems.

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Example (Pseudocode):

c

void main() {
  setup_button_interrupt();  // Configure external interrupt
  while(1) {
    // Main loop doing other stuff
  }
}

void EXTI0_IRQHandler() {
  // This runs when the button is pressed
  toggle_LED();
}

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 Without interrupts:

You’d need to keep checking inputs in a loop (polling), which wastes CPU time and may miss fast events.