INTERRUPT STRUCTURE
- 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.
