What is the difference between interrupt and polling?

What is the difference between interrupt and polling?

What is the difference between interrupt and polling? A solitary microcontroller can serve a few gadgets. There are two techniques by which devices get administration from the microcontroller: interrupt and polling. In the interfere with strategy, at whatever point any gadget needs the microcontroller’s administration the gadget tells it by conveying an intrude on message the microcontroller stops whatever it is doing and serves the gadget. The sign after getting in (ISR) program related with the hinder is known as the intrude on help routine or interfere with overseer.

In surveying, the microcontroller constantly screens the situation with a given gadget; when the status condition is met, it plays out the help. From that point forward, it proceeds onward to screen the following gadget until every one is adjusted. Despite the fact that surveying can screen the situation with a few gadgets and serve every one of them as specific conditions are met, it’s anything but a productive utilization of the microcontroller. What is the difference between interrupt and polling?

The benefit of hinders is that the microcontroller can serve numerous gadgets (not all simultaneously, obviously); every gadget can stand out enough to be noticed of the microcontroller dependent on the need doled out to it.

The surveying strategy can’t allot need since it checks all gadgets in a cooperative style. All the more critically, in the intrude on technique the microcontroller can likewise disregard (veil) a gadget demand for administration. This additionally is preposterous with the surveying technique.

The main explanation that the intrude on strategy is ideal is that the surveying technique burns through a large part of the microcontroller’s time by surveying gadgets that needn’t bother with administration. So hinders are utilized to keep away from secures the microcontroller. For instance, in examining clocks in Chapter 9 we utilized the piece test guidance “BTFSS TMROIF” and held up until the clock turned over, and keeping in mind that we were holding up we were unable to do whatever else.

That is a misuse of microcontroller time that might have been utilized to perform sonic helpful errands. On account of the clock on the off chance that we utilize the intrude on strategy, the microcontroller can approach doing different errands, and when the TMROIF banner is raised, the clock will interfere with the microcontroller in whatever it is doing.


Interfere with administration routine for each intrude, there should be an interfere with administration routine (ISR), or intrude on controller. At the point when a hinder is summoned, the microcontroller runs the interfere with administration schedule..By and large, in many microchips for each interfere with there is a fixed area in memory that holds the location of its ISR. The gathering of me memory area is saved to hold the location of ISRs is known as the hinder.


Steps.in executing an endless supply of an interfere with, the microcontroller goes through the accompanying advances:

  • It completions the guidance it is executing and saves the location of the following guidance (program counter) on the stack.
  • It leaps to a fixed area in memory called the intrude on vector table. The intrude on vector table coordinates the microcontroller to the location of the interfere with administration routine (ISR).
  • The microcontroller gets the location of the ISR from the interfere with vector table and leaps to it. It begins to execute the interfere with administration subroutine until it arrives at the last guidance of the subroutine which is RTFIE


  • After executing the RETFIE guidance, the microcontroller gets back to where it was interfered. To start with, it gets the program counter (PC) address from the stack by popping the top bytes of the stack into the PC. At that point it begins to execute from that location.

Notice from Step 4 the basic job of the stack. Thus, we should be cautious in controlling the stack substance in the ISR. In particular, in the ISR, similarly as in any CALL subroutine, the quantity of pushes and pops should be equivalent.


There are numerous wellsprings of hinders in the PIC18, contingent upon which fringe is consolidated into the chip. Coming up next are probably the most generally utilized wellsprings of hinders in the PIC18:

  • There is an intrude on saved for every one of the clocks, Timers 0, 1, 2, etc.
  • Three hinders are saved for outside equipment intrudes. Pins RBO (PORTB.0), RB1 (PORTB. I), and RB2 (PORTB.2) are for the outer hard-product hinders INTO, INT1, and INT2, separately.
  • Sequential correspondence’s USART has two intrudes on, one for get and another for send.
  • The PORTB-Change interfere.
  • The ADC (simple to-computerized converter)
  • The CCP (think about catch beat width tweak)


To empower any of the intrudes on, we make the accompanying strides:

  • Touch D7 (GIE) of the INTCON register should be set to HIGH to permit the hinders to occur. This is finished with the “BSF INTCON, GIE” guidance.
  • In the event that GIE = 1, each hinder is empowered by setting to HIGH the hinder empower (1E) banner piece for that intrude. Since there are an enormous number of hinders in the PIC18, we have numerous registers holding the hinder empower bit. Figure 11-2 shows that the INTCON has interfered with empower bits for Timer () (TMROIE) and outside intrude on 0 (INTOIE). As we concentrate every one of peripherals all through the book we will inspect the registers holding the hinder empower bits. It should be noticed that if GIE = 0, no hinder will be reacted to, regardless of whether the comparing hinder empower bit is high. To comprehend this significant point look
  • For a portion of the fringe hinders like TMR1IF, TMR2IF, and TXIF, we need to empower the PEIE banner notwithstanding the GIE bit.

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Interrupt priority of PIC18 microcontroller

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