8259 Programmable Interrupt Controller The Intel 8259A programmable Interrupt Controller (PIC) is one of the most common interrupt controller used in IBM PCs. It can handle eight vectored priority interrupts for the CPU. It is a 28 pin DIP package and requires a single +5V DC supply for its operation. It is designed to minimize the software and real time overhead in handling multi-level priority interrupts. It has several modes, permitting optimization for a variety of system requirements. The pin diagram of 8259A is shown in figure-1 below. PIN Number Pin Name Description 1 CS’ Chip Select Input 2 WR’ Write control signal 3 RD’ Read control signal 4-11 D7-D0 Data Bus 12-13, 15 CAS0, CAS1 Cascade control 14 GND Ground 16 SP’/EN’ 17 INT Interrupt output for processor 18-25 IRQ0 – IRQ7 Interrupt request inputs 26 INTA Interrupt Acknowledge input 27 A0 Address input 28 VCC +5V supply   8259 interrupt Overview If the 8086 interrupt flag is set and INTR