8259 Microprocessor is architected in a unique style. It can program by means of some interrupts conditions by means of level or interrupt level often called edge triggered interrupt level. Masking is done to individual interrupt bits. As the number of 8259 increases interrupt pins up to 64 can be obtained. There are 3 registers 8259 contains along with one priority resolver(PR). They are as follows:
Interrupt Request Register(IIR) - It stores the bits who requests the interrupt.
Interrupt service register(ISR) - It stores the currently interrupt levels.
Interrupt Mask Register(IMR) -Stores the interrupt levels to be masked.
PriorityResolver(PR) - Set the priority of interrupts by examining all the three registers and set the interrupt level inISR having the highest priority.
SP/EN (low active pin) - When its value is 1 it works in master mode and when its value is 0 it works in slave mode.
Cascade Buffer - Used for cascading more Programmable Interrupt Controller.
Fig:8259 interfaced along with 8085 processor