However, high-priority interrupts cannot be stopped by low-priority interrupts. A high-priority interrupt can stop a low-priority interrupt that is in progress and gain access to the CPU. Applications that require more attention can be placed in the higher priority group. Interrupts in the PIC18F family can be divided into two groups: high priority and low priority. There are ten registers in the PIC18F452 microcontroller that control interrupt operations:
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Like most PIC18F series PIC Microcontrollers, the PIC18F452 has the following interrupts: Figure 1 below shows the diagram of the PIC18F452. Always check your device datasheet to find out more about the interrupts. To check if a certain tasks have been completed: Some applications may need to know when a task, such as an A/D conversion, is completed, or instead of keep on listening (polling) for an incoming data from an UART or USB port for example, an interrupt could be raise immediately when an A/D conversion is done or when there is an incoming data instead of keeping the microcontroller doing nothing but waiting for this to happen.ĭifferent PIC Microcontrollers have different interrupts, but most have both the core and peripheral interrupt sources.A timer interrupt scheduled with the required timing can divert the microcontroller from normal program execution to accomplish the task at the precise time required. Performing routine tasks: If an application requires the microcontroller to perform routine tasks at precise times, such as blinking a status LED, reading inputs of sensors connected to the microcontroller exactly every few millisecond.In such applications an external interrupt can force the microcontroller to stop whatever it is doing and take immediate action. For example, in an emergency such as a power failure in an hazardous environment where a the microcontroller has to take some precise coordinated actions like switching off the system immediately in an orderly manner. Fail safe applications:Applications which require the immediate attention of the microcontroller when there is a fault in the system can use interrupts.Interrupts can be very useful in many applications such as: The processes of continuous monitoring is known as POLLING. This can save power and much needed processor power especially if the application if battery powered. The best way is to leave the microcontroller do its normal main program, and if there is nothing to do, let the microcontroller go into sleep mode and be awaken only to respond to an interrupt that occurs. As you can see, this is not an efficient way of programming as it consumes all its processing time for monitoring and they can be a possibility of missing a short process that can require immediate attention. If there were no interrupt, while playing the game, the microcontroller would time to time pause the game and monitor if there is no one trying to call you.
This initiates your mobile phone conversation which is similar to executing Interrupt Service Routine (ISR). You can think the main service routine in this case as playing the game and the ringing of the mobile phone as causing an interrupt.
This process is similar to ISR execution. Only once you are done with the call, then the phone will jump back to the game. Your phone will immediately leave the game and start ringing. Here is a simple example to understand interrupts, let say you are playing a game with your phone and Suddenly your mobile phone rings somebody is calling you.
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The interrupt code is called Interrupt Service Routine (ISR) or Interrupt Handler. An interrupt requires immediate attention, only once the microcontroller will finish executing the interrupt code, then it can go back to continue with the main program. An interrupt is basically an event that requires the microcontroller to stop normal program execution and then to jump to execute a program code related to the event causing the interrupt. Interrupts are one of the most powerful features of PIC Microcontrollers, interrupts make it possible to create applications that can respond to external stimulus in real time.
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