INTERRUPT STRUCTURE -Free 8085 Microprocessor notes

INTERRUPT STRUCTURE

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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