External Interrupt

Definition of External Interrupt

An external interrupt is a signal generated by a hardware device outside the processor, prompting an immediate response from the system or program. It temporarily stops the execution of the current operation, forcing the system to address the interrupting event. Upon completion, the system resumes normal operation from where it left off.


The phonetic pronunciation for “External Interrupt” is:Ex-tur-nuhl In-tuhr-ruhpt

Key Takeaways

  1. External Interrupts are signals generated by external devices, such as sensors or buttons, to request the attention of a microcontroller or processor. They allow the system to react to real-time changes or events.
  2. They can be configured to trigger on specific conditions, such as a rising or falling edge of a signal, or on a change in the signal level. This provides a flexible way to handle a variety of external inputs without continuous polling.
  3. External Interrupts can simplify and improve the performance of a system by allowing the processor to perform tasks in parallel and make optimal use of its resources. However, proper interrupt handling and prioritization are essential for maintaining system stability and avoid potential conflicts or errors.

Importance of External Interrupt

External interrupt is an important technology term because it allows a processor within a system to respond to external events or peripheral devices efficiently.

This functionality enhances the overall performance and versatility of a computing system.

Instead of constantly polling the status of peripheral devices, which can be resource-consuming, the processor can allocate resources to other tasks and processes while the system remains in a standby mode.

When an external interrupt is triggered, it informs the processor to pause its current operation and switch its attention to handling the interrupt service routine (ISR) related to the event.

This enables a smooth and efficient multitasking environment, resulting in better responsiveness and optimized usage of processing power.


External Interrupts play a vital role in enhancing the efficiency and versatility of microcontroller-based systems. They are built to respond to external events or signal changes promptly, thereby serving as a key component in real-time systems and applications.

These versatile interrupts are primarily used to increase a system’s responsiveness, ensuring that the processor can quickly react to external events such as incoming data or peripheral device signals. This capacity to rapidly intervene enables microcontrollers to manage numerous peripherals and operations effectively, without wasting computational resources on constantly polling or waiting for events to transpire.

As a key feature of microcontroller systems, external interrupts streamline communication with various devices and peripherals, enhancing the overall performance of the application. For example, the system can leverage these interrupts to optimize power consumption by only responding when an event requires attention.

Similarly, they can be employed to manage time-sensitive tasks, including data collection for monitoring sensors and critical safety systems. Additionally, programming interrupt-based routines enables microcontrollers to attend to multiple tasks simultaneously, ensuring all processes remain balanced and resulting in the seamless functioning of the entire system.

Examples of External Interrupt

External interrupts are essential technological elements in microcontroller systems, allowing the system to respond to external events or conditions. Three real-world examples of external interrupt technology are:

Door Security System: In a door access security system, an external interrupt can be triggered by a magnetic switch or a push button at the door. When the door opens or a button is pressed, the interrupt prompts the microcontroller to respond, for example, by sounding an alarm, enabling or disabling access, or logging the event.

Vehicle Speed Sensor: In automotive applications, a speed sensor sends signals to the engine control unit (ECU) to monitor and manage the vehicle’s speed, fuel efficiency, and overall performance. The sensor can generate external interrupts based on wheel rotation, and the ECU uses these interrupts to monitor vehicle speed, adjust transmission gear changes, and optimize fuel efficiency.

Weather Monitoring Station: For a weather monitoring system, an anemometer measures wind speed, and a tipping-bucket rain gauge detects precipitation amounts. These devices send external interrupts to the monitoring system when wind speeds reach preset thresholds or when each tipping-bucket tips. The system then processes these interrupts to record weather data, issue alerts, or trigger automated actions, such as closing a roof skylight when it starts raining.

FAQ: External Interrupt

What is an external interrupt?

An external interrupt is a signal that originates outside the microcontroller or processor and triggers an interrupt subroutine to be executed. This allows the processor to stop its current operation and shift its attention to the function specified by the interrupt.

How can external interrupts be generated?

External interrupts can be generated by various sources such as external push-buttons, sensors or communication devices. The specific method for generating interrupts depends on the microcontroller being used and the type of device connected to it. In most cases, interrupts occur when the input signal changes from a LOW state to a HIGH state or vice versa.

What is the purpose of using external interrupts?

Using external interrupts allows your program to efficiently respond to changes in external signals, making it possible for the microcontroller to perform other tasks in between these occurrences. This results in a more efficient and responsive system, especially when dealing with time-critical events and monitoring real-time systems.

How do you configure external interrupts?

To configure external interrupts, you need to perform three main steps: define the interrupt source, set the type of triggering event (rising or falling edge), and specify the interrupt service routine (ISR) to be executed when the interrupt occurs. This process can vary based on the microcontroller or platform you are working with, so refer to your specific platform’s documentation for detailed information.

Can multiple external interrupts be used simultaneously?

Yes, multiple external interrupts can be used simultaneously, provided that the microcontroller or processor has enough interrupt pins and resources to handle the desired number of interrupts. However, it is important to ensure that your program is capable of efficiently dealing with multiple interrupt sources, and proper coordination is needed when handling simultaneous interrupts to avoid conflicts and overlapping code execution.

Related Technology Terms

  • Interrupt Request Line (IRQ)
  • Interrupt Service Routine (ISR)
  • Interrupt Vector Table (IVT)
  • Programmable Interrupt Controller (PIC)
  • Edge-triggered Interrupt

Sources for More Information


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