8259s are cascaded by connecting the INT line of one slave 8259 to the IRQ line of one master 8259.Įnd of interrupt (EOI) operations support specific EOI, non-specific EOI, and auto-EOI. Up to eight slave 8259s may be cascaded to a master 8259 to provide up to 64 IRQs. Other connections include CAS0 through CAS2 for cascading between 8259s. The main signal pins on an 8259 are as follows: eight interrupt request input lines named IRQ0 through IRQ7, an interrupt request output line named INTR, interrupt acknowledgment line named INTA, D0 through D7 for communicating the interrupt level or vector offset. However, while not anymore a separate chip, the 8259A interface is still provided by the Platform Controller Hub or southbridge on modern x86 motherboards. Modern PCs have begun to phase out the 8259A in favor of the Intel APIC Architecture. The 8259 has coexisted with the Intel APIC Architecture since its introduction in symmetric multiprocessor PCs. A second 8259A was added with the introduction of the PC/AT. The 8259A was included in the original PC introduced in 1981 and maintained by the PC/XT when introduced in 1983. The 8259 was introduced as part of Intel's MCS 85 family in 1976. The 8259A was the interrupt controller for the ISA bus in the original IBM PC and IBM PC AT. The 8259 combines multiple interrupt input sources into a single interrupt output to the host microprocessor, extending the interrupt levels available in a system beyond the one or two levels found on the processor chip. The initial part was 8259, a later A suffix version was upward compatible and usable with the 8086 or 8088 processor. The Intel 8259 is a programmable interrupt controller (PIC) designed for the Intel 8085 and Intel 8086 microprocessors. ( September 2013) ( Learn how and when to remove this template message)Ĭloseup of an Intel 8259A IRQ chip from a PC XT. Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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