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Interrupts in 8051

There are five interrupt sources for the 8051 microcontroller. The prioritywise five different interrupts of 8051 microcontroller are given below:

  • External Interrupt 0
  • Timer 0
  • External Interrupt 1
  • Timer 1
  • Serial Port

These interrupts can recognize 5 different events that can interrupt regular program execution.

  • Each interrupt can be enabled separately.
  • Each interrupt type has a separate vector address.
  • Each interrupt type can be programmed to one of two priority levels.
  • External interrupts can be programmed for edge or level sensitivity.
  • Each interrupt can be enabled or disabled by setting bits of the IE (interrupt enable) register. Likewise, the whole interrupt system can be disabled by clearing the EA bit of the same register as shown in the figure.

Interrupts of 8051


Table: Interrupt vector addresses

Interrupt Control Register


The priority of interrupts is given below:

  • IE0 (External Interrupt 0)
  • TF0 (Timer Flag 0)
  • IE1 (External Interrupt 1)
  • TF1 (Timer Flag 1)
  • RI/TI (Serial Port)

Execution of Interrupt

The sequence of interrupt operation

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