• Interrupt is signals send by an external device to the processor, to request the processor to perform a particular task or work.

  • Mainly in the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor.

  • The processor will check the interrupts always at the 2nd T-state of last machine cycle.

  • If there is any interrupt it accept the interrupt and send the INTA (active low) signal to the peripheral.

  • The vectored address of particular interrupt is stored in program counter.

  • The processor executes an interrupt service routine (ISR) addressed in program counter.

  • It returned to main program by RET instruction.

Types of Interrupts:

It supports two types of interrupts.

  • Hardware        

  • Software

Software interrupts:

  • The software interrupts are program instructions. These instructions are inserted at desired locations in a program.

  • The 8085 has eight software interrupts from RST 0 to RST 7. The vector address for these interrupts can be calculated as follows.

  • Interrupt number * 8 = vector address
  • For RST 5,5 *  8 = 40 = 28H
  • Vector address for interrupt RST 5 is 0028H

The Table shows the vector addresses of all interrupts.
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