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Interrupts Of 8085

Published on Jun 18 2014 // Interrupts 8085


  • 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.

Hardware Interrupts – >>Page2